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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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|
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import java.lang.Thread.UncaughtExceptionHandler; |
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import java.lang.invoke.MethodHandles; |
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import java.lang.invoke.VarHandle; |
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import java.security.AccessController; |
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import java.security.AccessControlContext; |
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import java.security.Permission; |
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import java.security.Permissions; |
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import java.security.PrivilegedAction; |
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import java.security.ProtectionDomain; |
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import java.util.ArrayList; |
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import java.util.Collection; |
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import java.util.Collections; |
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import java.util.List; |
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import java.util.function.Predicate; |
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import java.util.concurrent.locks.LockSupport; |
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|
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
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* A {@code ForkJoinPool} provides the entry point for submissions |
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* from non-{@code ForkJoinTask} clients, as well as management and |
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* monitoring operations. |
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* |
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* <p>A {@code ForkJoinPool} differs from other kinds of {@link |
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* ExecutorService} mainly by virtue of employing |
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* <em>work-stealing</em>: all threads in the pool attempt to find and |
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* execute tasks submitted to the pool and/or created by other active |
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* tasks (eventually blocking waiting for work if none exist). This |
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* enables efficient processing when most tasks spawn other subtasks |
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* (as do most {@code ForkJoinTask}s), as well as when many small |
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* tasks are submitted to the pool from external clients. Especially |
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* when setting <em>asyncMode</em> to true in constructors, {@code |
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* ForkJoinPool}s may also be appropriate for use with event-style |
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* tasks that are never joined. All worker threads are initialized |
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* with {@link Thread#isDaemon} set {@code true}. |
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* |
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* <p>A static {@link #commonPool()} is available and appropriate for |
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* most applications. The common pool is used by any ForkJoinTask that |
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* is not explicitly submitted to a specified pool. Using the common |
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* pool normally reduces resource usage (its threads are slowly |
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* reclaimed during periods of non-use, and reinstated upon subsequent |
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* use). |
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* |
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* <p>For applications that require separate or custom pools, a {@code |
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* ForkJoinPool} may be constructed with a given target parallelism |
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* level; by default, equal to the number of available processors. |
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* The pool attempts to maintain enough active (or available) threads |
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* by dynamically adding, suspending, or resuming internal worker |
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* threads, even if some tasks are stalled waiting to join others. |
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* However, no such adjustments are guaranteed in the face of blocked |
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* I/O or other unmanaged synchronization. The nested {@link |
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* ManagedBlocker} interface enables extension of the kinds of |
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* synchronization accommodated. The default policies may be |
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* overridden using a constructor with parameters corresponding to |
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* those documented in class {@link ThreadPoolExecutor}. |
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* |
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* <p>In addition to execution and lifecycle control methods, this |
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* class provides status check methods (for example |
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* {@link #getStealCount}) that are intended to aid in developing, |
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* tuning, and monitoring fork/join applications. Also, method |
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* {@link #toString} returns indications of pool state in a |
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* convenient form for informal monitoring. |
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* |
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* <p>As is the case with other ExecutorServices, there are three |
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* main task execution methods summarized in the following table. |
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* These are designed to be used primarily by clients not already |
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* engaged in fork/join computations in the current pool. The main |
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* forms of these methods accept instances of {@code ForkJoinTask}, |
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* but overloaded forms also allow mixed execution of plain {@code |
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* Runnable}- or {@code Callable}- based activities as well. However, |
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* tasks that are already executing in a pool should normally instead |
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* use the within-computation forms listed in the table unless using |
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* async event-style tasks that are not usually joined, in which case |
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* there is little difference among choice of methods. |
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* |
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* <table class="plain"> |
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* <caption>Summary of task execution methods</caption> |
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* <tr> |
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* <td></td> |
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* <th scope="col"> Call from non-fork/join clients</th> |
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* <th scope="col"> Call from within fork/join computations</th> |
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* </tr> |
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* <tr> |
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* <th scope="row" style="text-align:left"> Arrange async execution</th> |
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* <td> {@link #execute(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row" style="text-align:left"> Await and obtain result</th> |
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* <td> {@link #invoke(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#invoke}</td> |
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* </tr> |
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* <tr> |
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* <th scope="row" style="text-align:left"> Arrange exec and obtain Future</th> |
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* <td> {@link #submit(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
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* </tr> |
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* </table> |
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* |
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* <p>The parameters used to construct the common pool may be controlled by |
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* setting the following {@linkplain System#getProperty system properties}: |
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* <ul> |
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* <li>{@code java.util.concurrent.ForkJoinPool.common.parallelism} |
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* - the parallelism level, a non-negative integer |
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* <li>{@code java.util.concurrent.ForkJoinPool.common.threadFactory} |
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* - the class name of a {@link ForkJoinWorkerThreadFactory}. |
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* The {@linkplain ClassLoader#getSystemClassLoader() system class loader} |
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* is used to load this class. |
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* <li>{@code java.util.concurrent.ForkJoinPool.common.exceptionHandler} |
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* - the class name of a {@link UncaughtExceptionHandler}. |
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* The {@linkplain ClassLoader#getSystemClassLoader() system class loader} |
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* is used to load this class. |
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* <li>{@code java.util.concurrent.ForkJoinPool.common.maximumSpares} |
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* - the maximum number of allowed extra threads to maintain target |
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* parallelism (default 256). |
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* </ul> |
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* If no thread factory is supplied via a system property, then the |
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* common pool uses a factory that uses the system class loader as the |
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* {@linkplain Thread#getContextClassLoader() thread context class loader}. |
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* In addition, if a {@link SecurityManager} is present, then |
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* the common pool uses a factory supplying threads that have no |
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* {@link Permissions} enabled. |
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* |
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* Upon any error in establishing these settings, default parameters |
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* are used. It is possible to disable or limit the use of threads in |
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* the common pool by setting the parallelism property to zero, and/or |
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* using a factory that may return {@code null}. However doing so may |
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* cause unjoined tasks to never be executed. |
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* |
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* <p><b>Implementation notes</b>: This implementation restricts the |
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* maximum number of running threads to 32767. Attempts to create |
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* pools with greater than the maximum number result in |
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* {@code IllegalArgumentException}. |
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* |
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* <p>This implementation rejects submitted tasks (that is, by throwing |
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* {@link RejectedExecutionException}) only when the pool is shut down |
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* or internal resources have been exhausted. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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*/ |
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public class ForkJoinPool extends AbstractExecutorService { |
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|
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/* |
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* Implementation Overview |
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* |
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* This class and its nested classes provide the main |
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* functionality and control for a set of worker threads: |
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* Submissions from non-FJ threads enter into submission queues. |
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* Workers take these tasks and typically split them into subtasks |
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* that may be stolen by other workers. Work-stealing based on |
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* randomized scans generally leads to better throughput than |
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* "work dealing" in which producers assign tasks to idle threads, |
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* in part because threads that have finished other tasks before |
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* the signalled thread wakes up (which can be a long time) can |
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* take the task instead. Preference rules give first priority to |
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* processing tasks from their own queues (LIFO or FIFO, depending |
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* on mode), then to randomized FIFO steals of tasks in other |
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* queues. This framework began as vehicle for supporting |
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* tree-structured parallelism using work-stealing. Over time, |
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* its scalability advantages led to extensions and changes to |
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* better support more diverse usage contexts. Because most |
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* internal methods and nested classes are interrelated, their |
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* main rationale and descriptions are presented here; individual |
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* methods and nested classes contain only brief comments about |
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* details. |
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* |
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* WorkQueues |
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* ========== |
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* |
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* Most operations occur within work-stealing queues (in nested |
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* class WorkQueue). These are special forms of Deques that |
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* support only three of the four possible end-operations -- push, |
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* pop, and poll (aka steal), under the further constraints that |
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* push and pop are called only from the owning thread (or, as |
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* extended here, under a lock), while poll may be called from |
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* other threads. (If you are unfamiliar with them, you probably |
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* want to read Herlihy and Shavit's book "The Art of |
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* Multiprocessor programming", chapter 16 describing these in |
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* more detail before proceeding.) The main work-stealing queue |
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* design is roughly similar to those in the papers "Dynamic |
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* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005 |
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* (http://research.sun.com/scalable/pubs/index.html) and |
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* "Idempotent work stealing" by Michael, Saraswat, and Vechev, |
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* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186). |
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* The main differences ultimately stem from GC requirements that |
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* we null out taken slots as soon as we can, to maintain as small |
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* a footprint as possible even in programs generating huge |
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* numbers of tasks. To accomplish this, we shift the CAS |
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* arbitrating pop vs poll (steal) from being on the indices |
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* ("base" and "top") to the slots themselves. |
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* |
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* Adding tasks then takes the form of a classic array push(task) |
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* in a circular buffer: |
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* q.array[q.top++ % length] = task; |
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* |
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* (The actual code needs to null-check and size-check the array, |
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* uses masking, not mod, for indexing a power-of-two-sized array, |
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* adds a release fence for publication, and possibly signals |
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* waiting workers to start scanning -- see below.) Both a |
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* successful pop and poll mainly entail a CAS of a slot from |
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* non-null to null. |
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* |
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* The pop operation (always performed by owner) is: |
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* if ((the task at top slot is not null) and |
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* (CAS slot to null)) |
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* decrement top and return task; |
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* |
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* And the poll operation (usually by a stealer) is |
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* if ((the task at base slot is not null) and |
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* (CAS slot to null)) |
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* increment base and return task; |
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* |
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* There are several variants of each of these. Most uses occur |
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* within operations that also interleave contention or emptiness |
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* tracking or inspection of elements before extracting them, so |
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* must interleave these with the above code. When performed by |
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* owner, getAndSet is used instead of CAS (see for example method |
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* nextLocalTask) which is usually more efficient, and possible |
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* because the top index cannot independently change during the |
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* operation. |
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* |
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* Memory ordering. See "Correct and Efficient Work-Stealing for |
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* Weak Memory Models" by Le, Pop, Cohen, and Nardelli, PPoPP 2013 |
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* (http://www.di.ens.fr/~zappa/readings/ppopp13.pdf) for an |
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* analysis of memory ordering requirements in work-stealing |
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* algorithms similar to (but different than) the one used here. |
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* Extracting tasks in array slots via (fully fenced) CAS provides |
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* primary synchronization. The base and top indices imprecisely |
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* guide where to extract from. We do not usually require strict |
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* orderings of array and index updates. Many index accesses use |
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* plain mode, with ordering constrained by surrounding context |
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* (usually with respect to element CASes or the two WorkQueue |
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* volatile fields source and phase). When not otherwise already |
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* constrained, reads of "base" by queue owners use acquire-mode, |
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* and some externally callable methods preface accesses with |
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* acquire fences. Additionally, to ensure that index update |
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* writes are not coalesced or postponed in loops etc, "opaque" |
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* mode is used in a few cases where timely writes are not |
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* otherwise ensured. The "locked" versions of push- and pop- |
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* based methods for shared queues differ from owned versions |
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* because locking already forces some of the ordering. |
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* |
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* Because indices and slot contents cannot always be consistent, |
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* a check that base == top indicates (momentary) emptiness, but |
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* otherwise may err on the side of possibly making the queue |
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* appear nonempty when a push, pop, or poll have not fully |
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* committed, or making it appear empty when an update of top has |
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* not yet been visibly written. (Method isEmpty() checks the |
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* case of a partially completed removal of the last element.) |
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* Because of this, the poll operation, considered individually, |
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* is not wait-free. One thief cannot successfully continue until |
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* another in-progress one (or, if previously empty, a push) |
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* visibly completes. This can stall threads when required to |
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* consume from a given queue (see method poll()). However, in |
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* the aggregate, we ensure at least probabilistic |
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* non-blockingness. If an attempted steal fails, a scanning |
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* thief chooses a different random victim target to try next. So, |
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* in order for one thief to progress, it suffices for any |
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* in-progress poll or new push on any empty queue to complete. |
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* |
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* This approach also enables support of a user mode in which |
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* local task processing is in FIFO, not LIFO order, simply by |
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* using poll rather than pop. This can be useful in |
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* message-passing frameworks in which tasks are never joined. |
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* |
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* WorkQueues are also used in a similar way for tasks submitted |
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* to the pool. We cannot mix these tasks in the same queues used |
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* by workers. Instead, we randomly associate submission queues |
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* with submitting threads, using a form of hashing. The |
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* ThreadLocalRandom probe value serves as a hash code for |
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* choosing existing queues, and may be randomly repositioned upon |
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* contention with other submitters. In essence, submitters act |
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* like workers except that they are restricted to executing local |
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* tasks that they submitted. Insertion of tasks in shared mode |
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* requires a lock but we use only a simple spinlock (using field |
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* phase), because submitters encountering a busy queue move to a |
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* different position to use or create other queues -- they block |
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* only when creating and registering new queues. Because it is |
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* used only as a spinlock, unlocking requires only a "releasing" |
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* store (using setRelease) unless otherwise signalling. |
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* |
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* Management |
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* ========== |
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* |
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* The main throughput advantages of work-stealing stem from |
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* decentralized control -- workers mostly take tasks from |
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* themselves or each other, at rates that can exceed a billion |
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* per second. The pool itself creates, activates (enables |
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* scanning for and running tasks), deactivates, blocks, and |
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* terminates threads, all with minimal central information. |
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* There are only a few properties that we can globally track or |
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* maintain, so we pack them into a small number of variables, |
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* often maintaining atomicity without blocking or locking. |
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* Nearly all essentially atomic control state is held in a few |
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* volatile variables that are by far most often read (not |
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* written) as status and consistency checks. We pack as much |
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* information into them as we can. |
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* |
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* Field "ctl" contains 64 bits holding information needed to |
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* atomically decide to add, enqueue (on an event queue), and |
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* dequeue and release workers. To enable this packing, we |
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* restrict maximum parallelism to (1<<15)-1 (which is far in |
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* excess of normal operating range) to allow ids, counts, and |
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* their negations (used for thresholding) to fit into 16bit |
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* subfields. |
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* |
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* Field "mode" holds configuration parameters as well as lifetime |
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* status, atomically and monotonically setting SHUTDOWN, STOP, |
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* and finally TERMINATED bits. |
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* |
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* Field "workQueues" holds references to WorkQueues. It is |
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* updated (only during worker creation and termination) under |
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* lock (using field workerNamePrefix as lock), but is otherwise |
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* concurrently readable, and accessed directly. We also ensure |
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* that uses of the array reference itself never become too stale |
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* in case of resizing, by arranging that (re-)reads are separated |
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* by at least one acquiring read access. To simplify index-based |
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* operations, the array size is always a power of two, and all |
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* readers must tolerate null slots. Worker queues are at odd |
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* indices. Shared (submission) queues are at even indices, up to |
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* a maximum of 64 slots, to limit growth even if array needs to |
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* expand to add more workers. Grouping them together in this way |
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* simplifies and speeds up task scanning. |
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* |
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* All worker thread creation is on-demand, triggered by task |
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* submissions, replacement of terminated workers, and/or |
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* compensation for blocked workers. However, all other support |
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* code is set up to work with other policies. To ensure that we |
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* do not hold on to worker references that would prevent GC, all |
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* accesses to workQueues are via indices into the workQueues |
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* array (which is one source of some of the messy code |
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* constructions here). In essence, the workQueues array serves as |
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* a weak reference mechanism. Thus for example the stack top |
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* subfield of ctl stores indices, not references. |
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* |
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* Queuing Idle Workers. Unlike HPC work-stealing frameworks, we |
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* cannot let workers spin indefinitely scanning for tasks when |
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* none can be found immediately, and we cannot start/resume |
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* workers unless there appear to be tasks available. On the |
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* other hand, we must quickly prod them into action when new |
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* tasks are submitted or generated. In many usages, ramp-up time |
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* is the main limiting factor in overall performance, which is |
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* compounded at program start-up by JIT compilation and |
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* allocation. So we streamline this as much as possible. |
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* |
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* The "ctl" field atomically maintains total worker and |
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* "released" worker counts, plus the head of the available worker |
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* queue (actually stack, represented by the lower 32bit subfield |
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* of ctl). Released workers are those known to be scanning for |
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* and/or running tasks. Unreleased ("available") workers are |
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* recorded in the ctl stack. These workers are made available for |
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* signalling by enqueuing in ctl (see method runWorker). The |
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* "queue" is a form of Treiber stack. This is ideal for |
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* activating threads in most-recently used order, and improves |
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* performance and locality, outweighing the disadvantages of |
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* being prone to contention and inability to release a worker |
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* unless it is topmost on stack. To avoid missed signal problems |
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* inherent in any wait/signal design, available workers rescan |
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* for (and if found run) tasks after enqueuing. Normally their |
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* release status will be updated while doing so, but the released |
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* worker ctl count may underestimate the number of active |
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* threads. (However, it is still possible to determine quiescence |
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* via a validation traversal -- see isQuiescent). After an |
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* unsuccessful rescan, available workers are blocked until |
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* signalled (see signalWork). The top stack state holds the |
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* value of the "phase" field of the worker: its index and status, |
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* plus a version counter that, in addition to the count subfields |
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* (also serving as version stamps) provide protection against |
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* Treiber stack ABA effects. |
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* |
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* Creating workers. To create a worker, we pre-increment counts |
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* (serving as a reservation), and attempt to construct a |
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* ForkJoinWorkerThread via its factory. Upon construction, the |
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* new thread invokes registerWorker, where it constructs a |
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* WorkQueue and is assigned an index in the workQueues array |
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* (expanding the array if necessary). The thread is then started. |
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* Upon any exception across these steps, or null return from |
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* factory, deregisterWorker adjusts counts and records |
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* accordingly. If a null return, the pool continues running with |
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* fewer than the target number workers. If exceptional, the |
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* exception is propagated, generally to some external caller. |
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* Worker index assignment avoids the bias in scanning that would |
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* occur if entries were sequentially packed starting at the front |
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* of the workQueues array. We treat the array as a simple |
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* power-of-two hash table, expanding as needed. The seedIndex |
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* increment ensures no collisions until a resize is needed or a |
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* worker is deregistered and replaced, and thereafter keeps |
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* probability of collision low. We cannot use |
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* ThreadLocalRandom.getProbe() for similar purposes here because |
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* the thread has not started yet, but do so for creating |
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* submission queues for existing external threads (see |
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* externalPush). |
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* |
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* WorkQueue field "phase" is used by both workers and the pool to |
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* manage and track whether a worker is UNSIGNALLED (possibly |
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* blocked waiting for a signal). When a worker is enqueued its |
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* phase field is set. Note that phase field updates lag queue CAS |
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* releases so usage requires care -- seeing a negative phase does |
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* not guarantee that the worker is available. When queued, the |
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* lower 16 bits of scanState must hold its pool index. So we |
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* place the index there upon initialization and otherwise keep it |
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* there or restore it when necessary. |
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* |
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* The ctl field also serves as the basis for memory |
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* synchronization surrounding activation. This uses a more |
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* efficient version of a Dekker-like rule that task producers and |
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* consumers sync with each other by both writing/CASing ctl (even |
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* if to its current value). This would be extremely costly. So |
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* we relax it in several ways: (1) Producers only signal when |
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* their queue is possibly empty at some point during a push |
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* operation (which requires conservatively checking size zero or |
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* one to cover races). (2) Other workers propagate this signal |
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* when they find tasks in a queue with size greater than one. (3) |
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* Workers only enqueue after scanning (see below) and not finding |
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* any tasks. (4) Rather than CASing ctl to its current value in |
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* the common case where no action is required, we reduce write |
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* contention by equivalently prefacing signalWork when called by |
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* an external task producer using a memory access with |
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* full-volatile semantics or a "fullFence". |
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* |
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* Almost always, too many signals are issued, in part because a |
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* task producer cannot tell if some existing worker is in the |
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* midst of finishing one task (or already scanning) and ready to |
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* take another without being signalled. So the producer might |
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* instead activate a different worker that does not find any |
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* work, and then inactivates. This scarcely matters in |
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* steady-state computations involving all workers, but can create |
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* contention and bookkeeping bottlenecks during ramp-up, |
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* ramp-down, and small computations involving only a few workers. |
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* |
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* Scanning. Method scan (from runWorker) performs top-level |
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* scanning for tasks. (Similar scans appear in helpQuiesce and |
441 |
* pollScan.) Each scan traverses and tries to poll from each |
442 |
* queue starting at a random index. Scans are not performed in |
443 |
* ideal random permutation order, to reduce cacheline |
444 |
* contention. The pseudorandom generator need not have |
445 |
* high-quality statistical properties in the long term, but just |
446 |
* within computations; We use Marsaglia XorShifts (often via |
447 |
* ThreadLocalRandom.nextSecondarySeed), which are cheap and |
448 |
* suffice. Scanning also includes contention reduction: When |
449 |
* scanning workers fail to extract an apparently existing task, |
450 |
* they soon restart at a different pseudorandom index. This form |
451 |
* of backoff improves throughput when many threads are trying to |
452 |
* take tasks from few queues, which can be common in some usages. |
453 |
* Scans do not otherwise explicitly take into account core |
454 |
* affinities, loads, cache localities, etc, However, they do |
455 |
* exploit temporal locality (which usually approximates these) by |
456 |
* preferring to re-poll from the same queue after a successful |
457 |
* poll before trying others (see method topLevelExec). However |
458 |
* this preference is bounded (see TOP_BOUND_SHIFT) as a safeguard |
459 |
* against infinitely unfair looping under unbounded user task |
460 |
* recursion, and also to reduce long-term contention when many |
461 |
* threads poll few queues holding many small tasks. The bound is |
462 |
* high enough to avoid much impact on locality and scheduling |
463 |
* overhead. |
464 |
* |
465 |
* Trimming workers. To release resources after periods of lack of |
466 |
* use, a worker starting to wait when the pool is quiescent will |
467 |
* time out and terminate (see method runWorker) if the pool has |
468 |
* remained quiescent for period given by field keepAlive. |
469 |
* |
470 |
* Shutdown and Termination. A call to shutdownNow invokes |
471 |
* tryTerminate to atomically set a runState bit. The calling |
472 |
* thread, as well as every other worker thereafter terminating, |
473 |
* helps terminate others by cancelling their unprocessed tasks, |
474 |
* and waking them up, doing so repeatedly until stable. Calls to |
475 |
* non-abrupt shutdown() preface this by checking whether |
476 |
* termination should commence by sweeping through queues (until |
477 |
* stable) to ensure lack of in-flight submissions and workers |
478 |
* about to process them before triggering the "STOP" phase of |
479 |
* termination. |
480 |
* |
481 |
* Joining Tasks |
482 |
* ============= |
483 |
* |
484 |
* Any of several actions may be taken when one worker is waiting |
485 |
* to join a task stolen (or always held) by another. Because we |
486 |
* are multiplexing many tasks on to a pool of workers, we can't |
487 |
* always just let them block (as in Thread.join). We also cannot |
488 |
* just reassign the joiner's run-time stack with another and |
489 |
* replace it later, which would be a form of "continuation", that |
490 |
* even if possible is not necessarily a good idea since we may |
491 |
* need both an unblocked task and its continuation to progress. |
492 |
* Instead we combine two tactics: |
493 |
* |
494 |
* Helping: Arranging for the joiner to execute some task that it |
495 |
* would be running if the steal had not occurred. |
496 |
* |
497 |
* Compensating: Unless there are already enough live threads, |
498 |
* method tryCompensate() may create or re-activate a spare |
499 |
* thread to compensate for blocked joiners until they unblock. |
500 |
* |
501 |
* A third form (implemented in tryRemoveAndExec) amounts to |
502 |
* helping a hypothetical compensator: If we can readily tell that |
503 |
* a possible action of a compensator is to steal and execute the |
504 |
* task being joined, the joining thread can do so directly, |
505 |
* without the need for a compensation thread. |
506 |
* |
507 |
* The ManagedBlocker extension API can't use helping so relies |
508 |
* only on compensation in method awaitBlocker. |
509 |
* |
510 |
* The algorithm in awaitJoin entails a form of "linear helping". |
511 |
* Each worker records (in field source) the id of the queue from |
512 |
* which it last stole a task. The scan in method awaitJoin uses |
513 |
* these markers to try to find a worker to help (i.e., steal back |
514 |
* a task from and execute it) that could hasten completion of the |
515 |
* actively joined task. Thus, the joiner executes a task that |
516 |
* would be on its own local deque if the to-be-joined task had |
517 |
* not been stolen. This is a conservative variant of the approach |
518 |
* described in Wagner & Calder "Leapfrogging: a portable |
519 |
* technique for implementing efficient futures" SIGPLAN Notices, |
520 |
* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs |
521 |
* mainly in that we only record queue ids, not full dependency |
522 |
* links. This requires a linear scan of the workQueues array to |
523 |
* locate stealers, but isolates cost to when it is needed, rather |
524 |
* than adding to per-task overhead. Searches can fail to locate |
525 |
* stealers GC stalls and the like delay recording sources. |
526 |
* Further, even when accurately identified, stealers might not |
527 |
* ever produce a task that the joiner can in turn help with. So, |
528 |
* compensation is tried upon failure to find tasks to run. |
529 |
* |
530 |
* Compensation does not by default aim to keep exactly the target |
531 |
* parallelism number of unblocked threads running at any given |
532 |
* time. Some previous versions of this class employed immediate |
533 |
* compensations for any blocked join. However, in practice, the |
534 |
* vast majority of blockages are transient byproducts of GC and |
535 |
* other JVM or OS activities that are made worse by replacement |
536 |
* when they cause longer-term oversubscription. Rather than |
537 |
* impose arbitrary policies, we allow users to override the |
538 |
* default of only adding threads upon apparent starvation. The |
539 |
* compensation mechanism may also be bounded. Bounds for the |
540 |
* commonPool (see COMMON_MAX_SPARES) better enable JVMs to cope |
541 |
* with programming errors and abuse before running out of |
542 |
* resources to do so. |
543 |
* |
544 |
* Common Pool |
545 |
* =========== |
546 |
* |
547 |
* The static common pool always exists after static |
548 |
* initialization. Since it (or any other created pool) need |
549 |
* never be used, we minimize initial construction overhead and |
550 |
* footprint to the setup of about a dozen fields. |
551 |
* |
552 |
* When external threads submit to the common pool, they can |
553 |
* perform subtask processing (see externalHelpComplete and |
554 |
* related methods) upon joins. This caller-helps policy makes it |
555 |
* sensible to set common pool parallelism level to one (or more) |
556 |
* less than the total number of available cores, or even zero for |
557 |
* pure caller-runs. We do not need to record whether external |
558 |
* submissions are to the common pool -- if not, external help |
559 |
* methods return quickly. These submitters would otherwise be |
560 |
* blocked waiting for completion, so the extra effort (with |
561 |
* liberally sprinkled task status checks) in inapplicable cases |
562 |
* amounts to an odd form of limited spin-wait before blocking in |
563 |
* ForkJoinTask.join. |
564 |
* |
565 |
* As a more appropriate default in managed environments, unless |
566 |
* overridden by system properties, we use workers of subclass |
567 |
* InnocuousForkJoinWorkerThread when there is a SecurityManager |
568 |
* present. These workers have no permissions set, do not belong |
569 |
* to any user-defined ThreadGroup, and erase all ThreadLocals |
570 |
* after executing any top-level task (see |
571 |
* WorkQueue.afterTopLevelExec). The associated mechanics (mainly |
572 |
* in ForkJoinWorkerThread) may be JVM-dependent and must access |
573 |
* particular Thread class fields to achieve this effect. |
574 |
* |
575 |
* Memory placement |
576 |
* ================ |
577 |
* |
578 |
* Performance can be very sensitive to placement of instances of |
579 |
* ForkJoinPool and WorkQueues and their queue arrays. To reduce |
580 |
* false-sharing impact, the @Contended annotation isolates |
581 |
* adjacent WorkQueue instances, as well as the ForkJoinPool.ctl |
582 |
* field. WorkQueue arrays are allocated (by their threads) with |
583 |
* larger initial sizes than most ever need, mostly to reduce |
584 |
* false sharing with current garbage collectors that use cardmark |
585 |
* tables. |
586 |
* |
587 |
* Style notes |
588 |
* =========== |
589 |
* |
590 |
* Memory ordering relies mainly on VarHandles. This can be |
591 |
* awkward and ugly, but also reflects the need to control |
592 |
* outcomes across the unusual cases that arise in very racy code |
593 |
* with very few invariants. All fields are read into locals |
594 |
* before use, and null-checked if they are references. Array |
595 |
* accesses using masked indices include checks (that are always |
596 |
* true) that the array length is non-zero to avoid compilers |
597 |
* inserting more expensive traps. This is usually done in a |
598 |
* "C"-like style of listing declarations at the heads of methods |
599 |
* or blocks, and using inline assignments on first encounter. |
600 |
* Nearly all explicit checks lead to bypass/return, not exception |
601 |
* throws, because they may legitimately arise due to |
602 |
* cancellation/revocation during shutdown. |
603 |
* |
604 |
* There is a lot of representation-level coupling among classes |
605 |
* ForkJoinPool, ForkJoinWorkerThread, and ForkJoinTask. The |
606 |
* fields of WorkQueue maintain data structures managed by |
607 |
* ForkJoinPool, so are directly accessed. There is little point |
608 |
* trying to reduce this, since any associated future changes in |
609 |
* representations will need to be accompanied by algorithmic |
610 |
* changes anyway. Several methods intrinsically sprawl because |
611 |
* they must accumulate sets of consistent reads of fields held in |
612 |
* local variables. Some others are artificially broken up to |
613 |
* reduce producer/consumer imbalances due to dynamic compilation. |
614 |
* There are also other coding oddities (including several |
615 |
* unnecessary-looking hoisted null checks) that help some methods |
616 |
* perform reasonably even when interpreted (not compiled). |
617 |
* |
618 |
* The order of declarations in this file is (with a few exceptions): |
619 |
* (1) Static utility functions |
620 |
* (2) Nested (static) classes |
621 |
* (3) Static fields |
622 |
* (4) Fields, along with constants used when unpacking some of them |
623 |
* (5) Internal control methods |
624 |
* (6) Callbacks and other support for ForkJoinTask methods |
625 |
* (7) Exported methods |
626 |
* (8) Static block initializing statics in minimally dependent order |
627 |
*/ |
628 |
|
629 |
// Static utilities |
630 |
|
631 |
/** |
632 |
* If there is a security manager, makes sure caller has |
633 |
* permission to modify threads. |
634 |
*/ |
635 |
private static void checkPermission() { |
636 |
SecurityManager security = System.getSecurityManager(); |
637 |
if (security != null) |
638 |
security.checkPermission(modifyThreadPermission); |
639 |
} |
640 |
|
641 |
// Nested classes |
642 |
|
643 |
/** |
644 |
* Factory for creating new {@link ForkJoinWorkerThread}s. |
645 |
* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
646 |
* for {@code ForkJoinWorkerThread} subclasses that extend base |
647 |
* functionality or initialize threads with different contexts. |
648 |
*/ |
649 |
public static interface ForkJoinWorkerThreadFactory { |
650 |
/** |
651 |
* Returns a new worker thread operating in the given pool. |
652 |
* Returning null or throwing an exception may result in tasks |
653 |
* never being executed. If this method throws an exception, |
654 |
* it is relayed to the caller of the method (for example |
655 |
* {@code execute}) causing attempted thread creation. If this |
656 |
* method returns null or throws an exception, it is not |
657 |
* retried until the next attempted creation (for example |
658 |
* another call to {@code execute}). |
659 |
* |
660 |
* @param pool the pool this thread works in |
661 |
* @return the new worker thread, or {@code null} if the request |
662 |
* to create a thread is rejected |
663 |
* @throws NullPointerException if the pool is null |
664 |
*/ |
665 |
public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
666 |
} |
667 |
|
668 |
static AccessControlContext contextWithPermissions(Permission ... perms) { |
669 |
Permissions permissions = new Permissions(); |
670 |
for (Permission perm : perms) |
671 |
permissions.add(perm); |
672 |
return new AccessControlContext( |
673 |
new ProtectionDomain[] { new ProtectionDomain(null, permissions) }); |
674 |
} |
675 |
|
676 |
/** |
677 |
* Default ForkJoinWorkerThreadFactory implementation; creates a |
678 |
* new ForkJoinWorkerThread using the system class loader as the |
679 |
* thread context class loader. |
680 |
*/ |
681 |
private static final class DefaultForkJoinWorkerThreadFactory |
682 |
implements ForkJoinWorkerThreadFactory { |
683 |
private static final AccessControlContext ACC = contextWithPermissions( |
684 |
new RuntimePermission("getClassLoader"), |
685 |
new RuntimePermission("setContextClassLoader")); |
686 |
|
687 |
public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
688 |
return AccessController.doPrivileged( |
689 |
new PrivilegedAction<>() { |
690 |
public ForkJoinWorkerThread run() { |
691 |
return new ForkJoinWorkerThread( |
692 |
pool, ClassLoader.getSystemClassLoader()); }}, |
693 |
ACC); |
694 |
} |
695 |
} |
696 |
|
697 |
// Constants shared across ForkJoinPool and WorkQueue |
698 |
|
699 |
// Bounds |
700 |
static final int SWIDTH = 16; // width of short |
701 |
static final int SMASK = 0xffff; // short bits == max index |
702 |
static final int MAX_CAP = 0x7fff; // max #workers - 1 |
703 |
static final int SQMASK = 0x007e; // max 64 (even) slots |
704 |
|
705 |
// Masks and units for WorkQueue.phase and ctl sp subfield |
706 |
static final int UNSIGNALLED = 1 << 31; // must be negative |
707 |
static final int SS_SEQ = 1 << 16; // version count |
708 |
static final int QLOCK = 1; // must be 1 |
709 |
|
710 |
// Mode bits and sentinels, some also used in WorkQueue id and.source fields |
711 |
static final int OWNED = 1; // queue has owner thread |
712 |
static final int FIFO = 1 << 16; // fifo queue or access mode |
713 |
static final int SHUTDOWN = 1 << 18; |
714 |
static final int TERMINATED = 1 << 19; |
715 |
static final int STOP = 1 << 31; // must be negative |
716 |
static final int QUIET = 1 << 30; // not scanning or working |
717 |
static final int DORMANT = QUIET | UNSIGNALLED; |
718 |
|
719 |
/** |
720 |
* Initial capacity of work-stealing queue array. |
721 |
* Must be a power of two, at least 2. |
722 |
*/ |
723 |
static final int INITIAL_QUEUE_CAPACITY = 1 << 13; |
724 |
|
725 |
/** |
726 |
* Maximum capacity for queue arrays. Must be a power of two less |
727 |
* than or equal to 1 << (31 - width of array entry) to ensure |
728 |
* lack of wraparound of index calculations, but defined to a |
729 |
* value a bit less than this to help users trap runaway programs |
730 |
* before saturating systems. |
731 |
*/ |
732 |
static final int MAXIMUM_QUEUE_CAPACITY = 1 << 26; // 64M |
733 |
|
734 |
/** |
735 |
* The maximum number of top-level polls per worker before |
736 |
* checking other queues, expressed as a bit shift to, in effect, |
737 |
* multiply by pool size, and then use as random value mask, so |
738 |
* average bound is about poolSize*(1<<TOP_BOUND_SHIFT). See |
739 |
* above for rationale. |
740 |
*/ |
741 |
static final int TOP_BOUND_SHIFT = 10; |
742 |
|
743 |
/** |
744 |
* Queues supporting work-stealing as well as external task |
745 |
* submission. See above for descriptions and algorithms. |
746 |
*/ |
747 |
@jdk.internal.vm.annotation.Contended |
748 |
static final class WorkQueue { |
749 |
volatile int source; // source queue id, or sentinel |
750 |
int id; // pool index, mode, tag |
751 |
int base; // index of next slot for poll |
752 |
int top; // index of next slot for push |
753 |
volatile int phase; // versioned, negative: queued, 1: locked |
754 |
int stackPred; // pool stack (ctl) predecessor link |
755 |
int nsteals; // number of steals |
756 |
ForkJoinTask<?>[] array; // the queued tasks; power of 2 size |
757 |
final ForkJoinPool pool; // the containing pool (may be null) |
758 |
final ForkJoinWorkerThread owner; // owning thread or null if shared |
759 |
|
760 |
WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner) { |
761 |
this.pool = pool; |
762 |
this.owner = owner; |
763 |
// Place indices in the center of array (that is not yet allocated) |
764 |
base = top = INITIAL_QUEUE_CAPACITY >>> 1; |
765 |
} |
766 |
|
767 |
/** |
768 |
* Tries to lock shared queue by CASing phase field. |
769 |
*/ |
770 |
final boolean tryLockPhase() { |
771 |
return PHASE.compareAndSet(this, 0, 1); |
772 |
} |
773 |
|
774 |
final void releasePhaseLock() { |
775 |
PHASE.setRelease(this, 0); |
776 |
} |
777 |
|
778 |
/** |
779 |
* Returns an exportable index (used by ForkJoinWorkerThread). |
780 |
*/ |
781 |
final int getPoolIndex() { |
782 |
return (id & 0xffff) >>> 1; // ignore odd/even tag bit |
783 |
} |
784 |
|
785 |
/** |
786 |
* Returns the approximate number of tasks in the queue. |
787 |
*/ |
788 |
final int queueSize() { |
789 |
int n = (int)BASE.getAcquire(this) - top; |
790 |
return (n >= 0) ? 0 : -n; // ignore transient negative |
791 |
} |
792 |
|
793 |
/** |
794 |
* Provides a more accurate estimate of whether this queue has |
795 |
* any tasks than does queueSize, by checking whether a |
796 |
* near-empty queue has at least one unclaimed task. |
797 |
*/ |
798 |
final boolean isEmpty() { |
799 |
ForkJoinTask<?>[] a; int n, cap, b; |
800 |
VarHandle.acquireFence(); // needed by external callers |
801 |
return ((n = (b = base) - top) >= 0 || // possibly one task |
802 |
(n == -1 && ((a = array) == null || |
803 |
(cap = a.length) == 0 || |
804 |
a[(cap - 1) & b] == null))); |
805 |
} |
806 |
|
807 |
/** |
808 |
* Pushes a task. Call only by owner in unshared queues. |
809 |
* |
810 |
* @param task the task. Caller must ensure non-null. |
811 |
* @throws RejectedExecutionException if array cannot be resized |
812 |
*/ |
813 |
final void push(ForkJoinTask<?> task) { |
814 |
ForkJoinTask<?>[] a; |
815 |
int s = top, d, cap, m; |
816 |
ForkJoinPool p = pool; |
817 |
if ((a = array) != null && (cap = a.length) > 0) { |
818 |
QA.setRelease(a, (m = cap - 1) & s, task); |
819 |
top = s + 1; |
820 |
if (((d = s - (int)BASE.getAcquire(this)) & ~1) == 0 && |
821 |
p != null) { // size 0 or 1 |
822 |
VarHandle.fullFence(); |
823 |
p.signalWork(); |
824 |
} |
825 |
else if (d == m) |
826 |
growArray(false); |
827 |
} |
828 |
} |
829 |
|
830 |
/** |
831 |
* Version of push for shared queues. Call only with phase lock held. |
832 |
* @return true if should signal work |
833 |
*/ |
834 |
final boolean lockedPush(ForkJoinTask<?> task) { |
835 |
ForkJoinTask<?>[] a; |
836 |
boolean signal = false; |
837 |
int s = top, b = base, cap, d; |
838 |
if ((a = array) != null && (cap = a.length) > 0) { |
839 |
a[(cap - 1) & s] = task; |
840 |
top = s + 1; |
841 |
if (b - s + cap - 1 == 0) |
842 |
growArray(true); |
843 |
else { |
844 |
phase = 0; // full volatile unlock |
845 |
if (((s - base) & ~1) == 0) // size 0 or 1 |
846 |
signal = true; |
847 |
} |
848 |
} |
849 |
return signal; |
850 |
} |
851 |
|
852 |
/** |
853 |
* Doubles the capacity of array. Call either by owner or with |
854 |
* lock held -- it is OK for base, but not top, to move while |
855 |
* resizings are in progress. |
856 |
*/ |
857 |
final void growArray(boolean locked) { |
858 |
ForkJoinTask<?>[] newA = null; |
859 |
try { |
860 |
ForkJoinTask<?>[] oldA; int oldSize, newSize; |
861 |
if ((oldA = array) != null && (oldSize = oldA.length) > 0 && |
862 |
(newSize = oldSize << 1) <= MAXIMUM_QUEUE_CAPACITY && |
863 |
newSize > 0) { |
864 |
try { |
865 |
newA = new ForkJoinTask<?>[newSize]; |
866 |
} catch (OutOfMemoryError ex) { |
867 |
} |
868 |
if (newA != null) { // poll from old array, push to new |
869 |
int oldMask = oldSize - 1, newMask = newSize - 1; |
870 |
for (int s = top - 1, k = oldMask; k >= 0; --k) { |
871 |
ForkJoinTask<?> x = (ForkJoinTask<?>) |
872 |
QA.getAndSet(oldA, s & oldMask, null); |
873 |
if (x != null) |
874 |
newA[s-- & newMask] = x; |
875 |
else |
876 |
break; |
877 |
} |
878 |
array = newA; |
879 |
VarHandle.releaseFence(); |
880 |
} |
881 |
} |
882 |
} finally { |
883 |
if (locked) |
884 |
phase = 0; |
885 |
} |
886 |
if (newA == null) |
887 |
throw new RejectedExecutionException("Queue capacity exceeded"); |
888 |
} |
889 |
|
890 |
/** |
891 |
* Takes next task, if one exists, in FIFO order. |
892 |
*/ |
893 |
final ForkJoinTask<?> poll() { |
894 |
int b, k, cap; ForkJoinTask<?>[] a; |
895 |
while ((a = array) != null && (cap = a.length) > 0 && |
896 |
top - (b = base) > 0) { |
897 |
ForkJoinTask<?> t = (ForkJoinTask<?>) |
898 |
QA.getAcquire(a, k = (cap - 1) & b); |
899 |
if (base == b++) { |
900 |
if (t == null) |
901 |
Thread.yield(); // await index advance |
902 |
else if (QA.compareAndSet(a, k, t, null)) { |
903 |
BASE.setOpaque(this, b); |
904 |
return t; |
905 |
} |
906 |
} |
907 |
} |
908 |
return null; |
909 |
} |
910 |
|
911 |
/** |
912 |
* Takes next task, if one exists, in order specified by mode. |
913 |
*/ |
914 |
final ForkJoinTask<?> nextLocalTask() { |
915 |
ForkJoinTask<?> t = null; |
916 |
int md = id, b, s, d, cap; ForkJoinTask<?>[] a; |
917 |
if ((a = array) != null && (cap = a.length) > 0 && |
918 |
(d = (s = top) - (b = base)) > 0) { |
919 |
if ((md & FIFO) == 0 || d == 1) { |
920 |
if ((t = (ForkJoinTask<?>) |
921 |
QA.getAndSet(a, (cap - 1) & --s, null)) != null) |
922 |
TOP.setOpaque(this, s); |
923 |
} |
924 |
else if ((t = (ForkJoinTask<?>) |
925 |
QA.getAndSet(a, (cap - 1) & b++, null)) != null) { |
926 |
BASE.setOpaque(this, b); |
927 |
} |
928 |
else // on contention in FIFO mode, use regular poll |
929 |
t = poll(); |
930 |
} |
931 |
return t; |
932 |
} |
933 |
|
934 |
/** |
935 |
* Returns next task, if one exists, in order specified by mode. |
936 |
*/ |
937 |
final ForkJoinTask<?> peek() { |
938 |
int cap; ForkJoinTask<?>[] a; |
939 |
return ((a = array) != null && (cap = a.length) > 0) ? |
940 |
a[(cap - 1) & ((id & FIFO) != 0 ? base : top - 1)] : null; |
941 |
} |
942 |
|
943 |
/** |
944 |
* Pops the given task only if it is at the current top. |
945 |
*/ |
946 |
final boolean tryUnpush(ForkJoinTask<?> task) { |
947 |
boolean popped = false; |
948 |
int s, cap; ForkJoinTask<?>[] a; |
949 |
if ((a = array) != null && (cap = a.length) > 0 && |
950 |
(s = top) != base && |
951 |
(popped = QA.compareAndSet(a, (cap - 1) & --s, task, null))) |
952 |
TOP.setOpaque(this, s); |
953 |
return popped; |
954 |
} |
955 |
|
956 |
/** |
957 |
* Shared version of tryUnpush. |
958 |
*/ |
959 |
final boolean tryLockedUnpush(ForkJoinTask<?> task) { |
960 |
boolean popped = false; |
961 |
int s = top - 1, k, cap; ForkJoinTask<?>[] a; |
962 |
if ((a = array) != null && (cap = a.length) > 0 && |
963 |
a[k = (cap - 1) & s] == task && tryLockPhase()) { |
964 |
if (top == s + 1 && array == a && |
965 |
(popped = QA.compareAndSet(a, k, task, null))) |
966 |
top = s; |
967 |
releasePhaseLock(); |
968 |
} |
969 |
return popped; |
970 |
} |
971 |
|
972 |
/** |
973 |
* Removes and cancels all known tasks, ignoring any exceptions. |
974 |
*/ |
975 |
final void cancelAll() { |
976 |
for (ForkJoinTask<?> t; (t = poll()) != null; ) |
977 |
ForkJoinTask.cancelIgnoringExceptions(t); |
978 |
} |
979 |
|
980 |
// Specialized execution methods |
981 |
|
982 |
/** |
983 |
* Runs the given (stolen) task if nonnull, as well as |
984 |
* remaining local tasks and others available from the given |
985 |
* queue, up to bound n (to avoid infinite unfairness). |
986 |
*/ |
987 |
final void topLevelExec(ForkJoinTask<?> t, WorkQueue q, int n) { |
988 |
if (t != null && q != null) { // hoist checks |
989 |
int nstolen = 1; |
990 |
for (;;) { |
991 |
t.doExec(); |
992 |
if (n-- < 0) |
993 |
break; |
994 |
else if ((t = nextLocalTask()) == null) { |
995 |
if ((t = q.poll()) == null) |
996 |
break; |
997 |
else |
998 |
++nstolen; |
999 |
} |
1000 |
} |
1001 |
ForkJoinWorkerThread thread = owner; |
1002 |
nsteals += nstolen; |
1003 |
source = 0; |
1004 |
if (thread != null) |
1005 |
thread.afterTopLevelExec(); |
1006 |
} |
1007 |
} |
1008 |
|
1009 |
/** |
1010 |
* If present, removes task from queue and executes it. |
1011 |
*/ |
1012 |
final void tryRemoveAndExec(ForkJoinTask<?> task) { |
1013 |
ForkJoinTask<?>[] a; int s, cap; |
1014 |
if ((a = array) != null && (cap = a.length) > 0 && |
1015 |
(s = top) - base > 0) { // traverse from top |
1016 |
for (int m = cap - 1, ns = s - 1, i = ns; ; --i) { |
1017 |
int index = i & m; |
1018 |
ForkJoinTask<?> t = (ForkJoinTask<?>)QA.get(a, index); |
1019 |
if (t == null) |
1020 |
break; |
1021 |
else if (t == task) { |
1022 |
if (QA.compareAndSet(a, index, t, null)) { |
1023 |
top = ns; // safely shift down |
1024 |
for (int j = i; j != ns; ++j) { |
1025 |
ForkJoinTask<?> f; |
1026 |
int pindex = (j + 1) & m; |
1027 |
f = (ForkJoinTask<?>)QA.get(a, pindex); |
1028 |
QA.setVolatile(a, pindex, null); |
1029 |
int jindex = j & m; |
1030 |
QA.setRelease(a, jindex, f); |
1031 |
} |
1032 |
VarHandle.releaseFence(); |
1033 |
t.doExec(); |
1034 |
} |
1035 |
break; |
1036 |
} |
1037 |
} |
1038 |
} |
1039 |
} |
1040 |
|
1041 |
/** |
1042 |
* Tries to pop and run tasks within the target's computation |
1043 |
* until done, not found, or limit exceeded. |
1044 |
* |
1045 |
* @param task root of CountedCompleter computation |
1046 |
* @param limit max runs, or zero for no limit |
1047 |
* @param shared true if must lock to extract task |
1048 |
* @return task status on exit |
1049 |
*/ |
1050 |
final int helpCC(CountedCompleter<?> task, int limit, boolean shared) { |
1051 |
int status = 0; |
1052 |
if (task != null && (status = task.status) >= 0) { |
1053 |
int s, k, cap; ForkJoinTask<?>[] a; |
1054 |
while ((a = array) != null && (cap = a.length) > 0 && |
1055 |
(s = top) - base > 0) { |
1056 |
CountedCompleter<?> v = null; |
1057 |
ForkJoinTask<?> o = a[k = (cap - 1) & (s - 1)]; |
1058 |
if (o instanceof CountedCompleter) { |
1059 |
CountedCompleter<?> t = (CountedCompleter<?>)o; |
1060 |
for (CountedCompleter<?> f = t;;) { |
1061 |
if (f != task) { |
1062 |
if ((f = f.completer) == null) |
1063 |
break; |
1064 |
} |
1065 |
else if (shared) { |
1066 |
if (tryLockPhase()) { |
1067 |
if (top == s && array == a && |
1068 |
QA.compareAndSet(a, k, t, null)) { |
1069 |
top = s - 1; |
1070 |
v = t; |
1071 |
} |
1072 |
releasePhaseLock(); |
1073 |
} |
1074 |
break; |
1075 |
} |
1076 |
else { |
1077 |
if (QA.compareAndSet(a, k, t, null)) { |
1078 |
top = s - 1; |
1079 |
v = t; |
1080 |
} |
1081 |
break; |
1082 |
} |
1083 |
} |
1084 |
} |
1085 |
if (v != null) |
1086 |
v.doExec(); |
1087 |
if ((status = task.status) < 0 || v == null || |
1088 |
(limit != 0 && --limit == 0)) |
1089 |
break; |
1090 |
} |
1091 |
} |
1092 |
return status; |
1093 |
} |
1094 |
|
1095 |
/** |
1096 |
* Tries to poll and run AsynchronousCompletionTasks until |
1097 |
* none found or blocker is released |
1098 |
* |
1099 |
* @param blocker the blocker |
1100 |
*/ |
1101 |
final void helpAsyncBlocker(ManagedBlocker blocker) { |
1102 |
if (blocker != null) { |
1103 |
int b, k, cap; ForkJoinTask<?>[] a; ForkJoinTask<?> t; |
1104 |
while ((a = array) != null && (cap = a.length) > 0 && |
1105 |
top - (b = base) > 0) { |
1106 |
t = (ForkJoinTask<?>)QA.getAcquire(a, k = (cap - 1) & b); |
1107 |
if (blocker.isReleasable()) |
1108 |
break; |
1109 |
else if (base == b++ && t != null) { |
1110 |
if (!(t instanceof CompletableFuture. |
1111 |
AsynchronousCompletionTask)) |
1112 |
break; |
1113 |
else if (QA.compareAndSet(a, k, t, null)) { |
1114 |
BASE.setOpaque(this, b); |
1115 |
t.doExec(); |
1116 |
} |
1117 |
} |
1118 |
} |
1119 |
} |
1120 |
} |
1121 |
|
1122 |
/** |
1123 |
* Returns true if owned and not known to be blocked. |
1124 |
*/ |
1125 |
final boolean isApparentlyUnblocked() { |
1126 |
Thread wt; Thread.State s; |
1127 |
return ((wt = owner) != null && |
1128 |
(s = wt.getState()) != Thread.State.BLOCKED && |
1129 |
s != Thread.State.WAITING && |
1130 |
s != Thread.State.TIMED_WAITING); |
1131 |
} |
1132 |
|
1133 |
// VarHandle mechanics. |
1134 |
static final VarHandle PHASE; |
1135 |
static final VarHandle BASE; |
1136 |
static final VarHandle TOP; |
1137 |
static { |
1138 |
try { |
1139 |
MethodHandles.Lookup l = MethodHandles.lookup(); |
1140 |
PHASE = l.findVarHandle(WorkQueue.class, "phase", int.class); |
1141 |
BASE = l.findVarHandle(WorkQueue.class, "base", int.class); |
1142 |
TOP = l.findVarHandle(WorkQueue.class, "top", int.class); |
1143 |
} catch (ReflectiveOperationException e) { |
1144 |
throw new Error(e); |
1145 |
} |
1146 |
} |
1147 |
} |
1148 |
|
1149 |
// static fields (initialized in static initializer below) |
1150 |
|
1151 |
/** |
1152 |
* Creates a new ForkJoinWorkerThread. This factory is used unless |
1153 |
* overridden in ForkJoinPool constructors. |
1154 |
*/ |
1155 |
public static final ForkJoinWorkerThreadFactory |
1156 |
defaultForkJoinWorkerThreadFactory; |
1157 |
|
1158 |
/** |
1159 |
* Permission required for callers of methods that may start or |
1160 |
* kill threads. |
1161 |
*/ |
1162 |
static final RuntimePermission modifyThreadPermission; |
1163 |
|
1164 |
/** |
1165 |
* Common (static) pool. Non-null for public use unless a static |
1166 |
* construction exception, but internal usages null-check on use |
1167 |
* to paranoically avoid potential initialization circularities |
1168 |
* as well as to simplify generated code. |
1169 |
*/ |
1170 |
static final ForkJoinPool common; |
1171 |
|
1172 |
/** |
1173 |
* Common pool parallelism. To allow simpler use and management |
1174 |
* when common pool threads are disabled, we allow the underlying |
1175 |
* common.parallelism field to be zero, but in that case still report |
1176 |
* parallelism as 1 to reflect resulting caller-runs mechanics. |
1177 |
*/ |
1178 |
static final int COMMON_PARALLELISM; |
1179 |
|
1180 |
/** |
1181 |
* Limit on spare thread construction in tryCompensate. |
1182 |
*/ |
1183 |
private static final int COMMON_MAX_SPARES; |
1184 |
|
1185 |
/** |
1186 |
* Sequence number for creating workerNamePrefix. |
1187 |
*/ |
1188 |
private static int poolNumberSequence; |
1189 |
|
1190 |
/** |
1191 |
* Returns the next sequence number. We don't expect this to |
1192 |
* ever contend, so use simple builtin sync. |
1193 |
*/ |
1194 |
private static final synchronized int nextPoolId() { |
1195 |
return ++poolNumberSequence; |
1196 |
} |
1197 |
|
1198 |
// static configuration constants |
1199 |
|
1200 |
/** |
1201 |
* Default idle timeout value (in milliseconds) for the thread |
1202 |
* triggering quiescence to park waiting for new work |
1203 |
*/ |
1204 |
private static final long DEFAULT_KEEPALIVE = 60_000L; |
1205 |
|
1206 |
/** |
1207 |
* Undershoot tolerance for idle timeouts |
1208 |
*/ |
1209 |
private static final long TIMEOUT_SLOP = 20L; |
1210 |
|
1211 |
/** |
1212 |
* The default value for COMMON_MAX_SPARES. Overridable using the |
1213 |
* "java.util.concurrent.ForkJoinPool.common.maximumSpares" system |
1214 |
* property. The default value is far in excess of normal |
1215 |
* requirements, but also far short of MAX_CAP and typical OS |
1216 |
* thread limits, so allows JVMs to catch misuse/abuse before |
1217 |
* running out of resources needed to do so. |
1218 |
*/ |
1219 |
private static final int DEFAULT_COMMON_MAX_SPARES = 256; |
1220 |
|
1221 |
/** |
1222 |
* Increment for seed generators. See class ThreadLocal for |
1223 |
* explanation. |
1224 |
*/ |
1225 |
private static final int SEED_INCREMENT = 0x9e3779b9; |
1226 |
|
1227 |
/* |
1228 |
* Bits and masks for field ctl, packed with 4 16 bit subfields: |
1229 |
* RC: Number of released (unqueued) workers minus target parallelism |
1230 |
* TC: Number of total workers minus target parallelism |
1231 |
* SS: version count and status of top waiting thread |
1232 |
* ID: poolIndex of top of Treiber stack of waiters |
1233 |
* |
1234 |
* When convenient, we can extract the lower 32 stack top bits |
1235 |
* (including version bits) as sp=(int)ctl. The offsets of counts |
1236 |
* by the target parallelism and the positionings of fields makes |
1237 |
* it possible to perform the most common checks via sign tests of |
1238 |
* fields: When ac is negative, there are not enough unqueued |
1239 |
* workers, when tc is negative, there are not enough total |
1240 |
* workers. When sp is non-zero, there are waiting workers. To |
1241 |
* deal with possibly negative fields, we use casts in and out of |
1242 |
* "short" and/or signed shifts to maintain signedness. |
1243 |
* |
1244 |
* Because it occupies uppermost bits, we can add one release count |
1245 |
* using getAndAddLong of RC_UNIT, rather than CAS, when returning |
1246 |
* from a blocked join. Other updates entail multiple subfields |
1247 |
* and masking, requiring CAS. |
1248 |
* |
1249 |
* The limits packed in field "bounds" are also offset by the |
1250 |
* parallelism level to make them comparable to the ctl rc and tc |
1251 |
* fields. |
1252 |
*/ |
1253 |
|
1254 |
// Lower and upper word masks |
1255 |
private static final long SP_MASK = 0xffffffffL; |
1256 |
private static final long UC_MASK = ~SP_MASK; |
1257 |
|
1258 |
// Release counts |
1259 |
private static final int RC_SHIFT = 48; |
1260 |
private static final long RC_UNIT = 0x0001L << RC_SHIFT; |
1261 |
private static final long RC_MASK = 0xffffL << RC_SHIFT; |
1262 |
|
1263 |
// Total counts |
1264 |
private static final int TC_SHIFT = 32; |
1265 |
private static final long TC_UNIT = 0x0001L << TC_SHIFT; |
1266 |
private static final long TC_MASK = 0xffffL << TC_SHIFT; |
1267 |
private static final long ADD_WORKER = 0x0001L << (TC_SHIFT + 15); // sign |
1268 |
|
1269 |
// Instance fields |
1270 |
|
1271 |
volatile long stealCount; // collects worker nsteals |
1272 |
final long keepAlive; // milliseconds before dropping if idle |
1273 |
int indexSeed; // next worker index |
1274 |
final int bounds; // min, max threads packed as shorts |
1275 |
volatile int mode; // parallelism, runstate, queue mode |
1276 |
WorkQueue[] workQueues; // main registry |
1277 |
final String workerNamePrefix; // for worker thread string; sync lock |
1278 |
final ForkJoinWorkerThreadFactory factory; |
1279 |
final UncaughtExceptionHandler ueh; // per-worker UEH |
1280 |
final Predicate<? super ForkJoinPool> saturate; |
1281 |
|
1282 |
@jdk.internal.vm.annotation.Contended("fjpctl") // segregate |
1283 |
volatile long ctl; // main pool control |
1284 |
|
1285 |
// Creating, registering and deregistering workers |
1286 |
|
1287 |
/** |
1288 |
* Tries to construct and start one worker. Assumes that total |
1289 |
* count has already been incremented as a reservation. Invokes |
1290 |
* deregisterWorker on any failure. |
1291 |
* |
1292 |
* @return true if successful |
1293 |
*/ |
1294 |
private boolean createWorker() { |
1295 |
ForkJoinWorkerThreadFactory fac = factory; |
1296 |
Throwable ex = null; |
1297 |
ForkJoinWorkerThread wt = null; |
1298 |
try { |
1299 |
if (fac != null && (wt = fac.newThread(this)) != null) { |
1300 |
wt.start(); |
1301 |
return true; |
1302 |
} |
1303 |
} catch (Throwable rex) { |
1304 |
ex = rex; |
1305 |
} |
1306 |
deregisterWorker(wt, ex); |
1307 |
return false; |
1308 |
} |
1309 |
|
1310 |
/** |
1311 |
* Tries to add one worker, incrementing ctl counts before doing |
1312 |
* so, relying on createWorker to back out on failure. |
1313 |
* |
1314 |
* @param c incoming ctl value, with total count negative and no |
1315 |
* idle workers. On CAS failure, c is refreshed and retried if |
1316 |
* this holds (otherwise, a new worker is not needed). |
1317 |
*/ |
1318 |
private void tryAddWorker(long c) { |
1319 |
do { |
1320 |
long nc = ((RC_MASK & (c + RC_UNIT)) | |
1321 |
(TC_MASK & (c + TC_UNIT))); |
1322 |
if (ctl == c && CTL.compareAndSet(this, c, nc)) { |
1323 |
createWorker(); |
1324 |
break; |
1325 |
} |
1326 |
} while (((c = ctl) & ADD_WORKER) != 0L && (int)c == 0); |
1327 |
} |
1328 |
|
1329 |
/** |
1330 |
* Callback from ForkJoinWorkerThread constructor to establish and |
1331 |
* record its WorkQueue. |
1332 |
* |
1333 |
* @param wt the worker thread |
1334 |
* @return the worker's queue |
1335 |
*/ |
1336 |
final WorkQueue registerWorker(ForkJoinWorkerThread wt) { |
1337 |
UncaughtExceptionHandler handler; |
1338 |
wt.setDaemon(true); // configure thread |
1339 |
if ((handler = ueh) != null) |
1340 |
wt.setUncaughtExceptionHandler(handler); |
1341 |
int tid = 0; // for thread name |
1342 |
int idbits = mode & FIFO; |
1343 |
String prefix = workerNamePrefix; |
1344 |
WorkQueue w = new WorkQueue(this, wt); |
1345 |
if (prefix != null) { |
1346 |
synchronized (prefix) { |
1347 |
WorkQueue[] ws = workQueues; int n; |
1348 |
int s = indexSeed += SEED_INCREMENT; |
1349 |
idbits |= (s & ~(SMASK | FIFO | DORMANT)); |
1350 |
if (ws != null && (n = ws.length) > 1) { |
1351 |
int m = n - 1; |
1352 |
tid = m & ((s << 1) | 1); // odd-numbered indices |
1353 |
for (int probes = n >>> 1;;) { // find empty slot |
1354 |
WorkQueue q; |
1355 |
if ((q = ws[tid]) == null || q.phase == QUIET) |
1356 |
break; |
1357 |
else if (--probes == 0) { |
1358 |
tid = n | 1; // resize below |
1359 |
break; |
1360 |
} |
1361 |
else |
1362 |
tid = (tid + 2) & m; |
1363 |
} |
1364 |
w.phase = w.id = tid | idbits; // now publishable |
1365 |
|
1366 |
if (tid < n) |
1367 |
ws[tid] = w; |
1368 |
else { // expand array |
1369 |
int an = n << 1; |
1370 |
WorkQueue[] as = new WorkQueue[an]; |
1371 |
as[tid] = w; |
1372 |
int am = an - 1; |
1373 |
for (int j = 0; j < n; ++j) { |
1374 |
WorkQueue v; // copy external queue |
1375 |
if ((v = ws[j]) != null) // position may change |
1376 |
as[v.id & am & SQMASK] = v; |
1377 |
if (++j >= n) |
1378 |
break; |
1379 |
as[j] = ws[j]; // copy worker |
1380 |
} |
1381 |
workQueues = as; |
1382 |
} |
1383 |
} |
1384 |
} |
1385 |
wt.setName(prefix.concat(Integer.toString(tid))); |
1386 |
} |
1387 |
return w; |
1388 |
} |
1389 |
|
1390 |
/** |
1391 |
* Final callback from terminating worker, as well as upon failure |
1392 |
* to construct or start a worker. Removes record of worker from |
1393 |
* array, and adjusts counts. If pool is shutting down, tries to |
1394 |
* complete termination. |
1395 |
* |
1396 |
* @param wt the worker thread, or null if construction failed |
1397 |
* @param ex the exception causing failure, or null if none |
1398 |
*/ |
1399 |
final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) { |
1400 |
WorkQueue w = null; |
1401 |
int phase = 0; |
1402 |
if (wt != null && (w = wt.workQueue) != null) { |
1403 |
Object lock = workerNamePrefix; |
1404 |
int wid = w.id; |
1405 |
long ns = (long)w.nsteals & 0xffffffffL; |
1406 |
if (lock != null) { |
1407 |
synchronized (lock) { |
1408 |
WorkQueue[] ws; int n, i; // remove index from array |
1409 |
if ((ws = workQueues) != null && (n = ws.length) > 0 && |
1410 |
ws[i = wid & (n - 1)] == w) |
1411 |
ws[i] = null; |
1412 |
stealCount += ns; |
1413 |
} |
1414 |
} |
1415 |
phase = w.phase; |
1416 |
} |
1417 |
if (phase != QUIET) { // else pre-adjusted |
1418 |
long c; // decrement counts |
1419 |
do {} while (!CTL.weakCompareAndSet |
1420 |
(this, c = ctl, ((RC_MASK & (c - RC_UNIT)) | |
1421 |
(TC_MASK & (c - TC_UNIT)) | |
1422 |
(SP_MASK & c)))); |
1423 |
} |
1424 |
if (w != null) |
1425 |
w.cancelAll(); // cancel remaining tasks |
1426 |
|
1427 |
if (!tryTerminate(false, false) && // possibly replace worker |
1428 |
w != null && w.array != null) // avoid repeated failures |
1429 |
signalWork(); |
1430 |
|
1431 |
if (ex == null) // help clean on way out |
1432 |
ForkJoinTask.helpExpungeStaleExceptions(); |
1433 |
else // rethrow |
1434 |
ForkJoinTask.rethrow(ex); |
1435 |
} |
1436 |
|
1437 |
/** |
1438 |
* Tries to create or release a worker if too few are running. |
1439 |
*/ |
1440 |
final void signalWork() { |
1441 |
for (;;) { |
1442 |
long c; int sp; WorkQueue[] ws; int i; WorkQueue v; |
1443 |
if ((c = ctl) >= 0L) // enough workers |
1444 |
break; |
1445 |
else if ((sp = (int)c) == 0) { // no idle workers |
1446 |
if ((c & ADD_WORKER) != 0L) // too few workers |
1447 |
tryAddWorker(c); |
1448 |
break; |
1449 |
} |
1450 |
else if ((ws = workQueues) == null) |
1451 |
break; // unstarted/terminated |
1452 |
else if (ws.length <= (i = sp & SMASK)) |
1453 |
break; // terminated |
1454 |
else if ((v = ws[i]) == null) |
1455 |
break; // terminating |
1456 |
else { |
1457 |
int np = sp & ~UNSIGNALLED; |
1458 |
int vp = v.phase; |
1459 |
long nc = (v.stackPred & SP_MASK) | (UC_MASK & (c + RC_UNIT)); |
1460 |
Thread vt = v.owner; |
1461 |
if (sp == vp && CTL.compareAndSet(this, c, nc)) { |
1462 |
v.phase = np; |
1463 |
if (vt != null && v.source < 0) |
1464 |
LockSupport.unpark(vt); |
1465 |
break; |
1466 |
} |
1467 |
} |
1468 |
} |
1469 |
} |
1470 |
|
1471 |
/** |
1472 |
* Tries to decrement counts (sometimes implicitly) and possibly |
1473 |
* arrange for a compensating worker in preparation for blocking: |
1474 |
* If not all core workers yet exist, creates one, else if any are |
1475 |
* unreleased (possibly including caller) releases one, else if |
1476 |
* fewer than the minimum allowed number of workers running, |
1477 |
* checks to see that they are all active, and if so creates an |
1478 |
* extra worker unless over maximum limit and policy is to |
1479 |
* saturate. Most of these steps can fail due to interference, in |
1480 |
* which case 0 is returned so caller will retry. A negative |
1481 |
* return value indicates that the caller doesn't need to |
1482 |
* re-adjust counts when later unblocked. |
1483 |
* |
1484 |
* @return 1: block then adjust, -1: block without adjust, 0 : retry |
1485 |
*/ |
1486 |
private int tryCompensate(WorkQueue w) { |
1487 |
int t, n, sp; |
1488 |
long c = ctl; |
1489 |
WorkQueue[] ws = workQueues; |
1490 |
if ((t = (short)(c >>> TC_SHIFT)) >= 0) { |
1491 |
if (ws == null || (n = ws.length) <= 0 || w == null) |
1492 |
return 0; // disabled |
1493 |
else if ((sp = (int)c) != 0) { // replace or release |
1494 |
WorkQueue v = ws[sp & (n - 1)]; |
1495 |
int wp = w.phase; |
1496 |
long uc = UC_MASK & ((wp < 0) ? c + RC_UNIT : c); |
1497 |
int np = sp & ~UNSIGNALLED; |
1498 |
if (v != null) { |
1499 |
int vp = v.phase; |
1500 |
Thread vt = v.owner; |
1501 |
long nc = ((long)v.stackPred & SP_MASK) | uc; |
1502 |
if (vp == sp && CTL.compareAndSet(this, c, nc)) { |
1503 |
v.phase = np; |
1504 |
if (vt != null && v.source < 0) |
1505 |
LockSupport.unpark(vt); |
1506 |
return (wp < 0) ? -1 : 1; |
1507 |
} |
1508 |
} |
1509 |
return 0; |
1510 |
} |
1511 |
else if ((int)(c >> RC_SHIFT) - // reduce parallelism |
1512 |
(short)(bounds & SMASK) > 0) { |
1513 |
long nc = ((RC_MASK & (c - RC_UNIT)) | (~RC_MASK & c)); |
1514 |
return CTL.compareAndSet(this, c, nc) ? 1 : 0; |
1515 |
} |
1516 |
else { // validate |
1517 |
int md = mode, pc = md & SMASK, tc = pc + t, bc = 0; |
1518 |
boolean unstable = false; |
1519 |
for (int i = 1; i < n; i += 2) { |
1520 |
WorkQueue q; Thread wt; Thread.State ts; |
1521 |
if ((q = ws[i]) != null) { |
1522 |
if (q.source == 0) { |
1523 |
unstable = true; |
1524 |
break; |
1525 |
} |
1526 |
else { |
1527 |
--tc; |
1528 |
if ((wt = q.owner) != null && |
1529 |
((ts = wt.getState()) == Thread.State.BLOCKED || |
1530 |
ts == Thread.State.WAITING)) |
1531 |
++bc; // worker is blocking |
1532 |
} |
1533 |
} |
1534 |
} |
1535 |
if (unstable || tc != 0 || ctl != c) |
1536 |
return 0; // inconsistent |
1537 |
else if (t + pc >= MAX_CAP || t >= (bounds >>> SWIDTH)) { |
1538 |
Predicate<? super ForkJoinPool> sat; |
1539 |
if ((sat = saturate) != null && sat.test(this)) |
1540 |
return -1; |
1541 |
else if (bc < pc) { // lagging |
1542 |
Thread.yield(); // for retry spins |
1543 |
return 0; |
1544 |
} |
1545 |
else |
1546 |
throw new RejectedExecutionException( |
1547 |
"Thread limit exceeded replacing blocked worker"); |
1548 |
} |
1549 |
} |
1550 |
} |
1551 |
|
1552 |
long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); // expand pool |
1553 |
return CTL.compareAndSet(this, c, nc) && createWorker() ? 1 : 0; |
1554 |
} |
1555 |
|
1556 |
/** |
1557 |
* Top-level runloop for workers, called by ForkJoinWorkerThread.run. |
1558 |
* See above for explanation. |
1559 |
*/ |
1560 |
final void runWorker(WorkQueue w) { |
1561 |
int r = (w.id ^ ThreadLocalRandom.nextSecondarySeed()) | FIFO; // rng |
1562 |
w.array = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; // initialize |
1563 |
for (;;) { |
1564 |
int phase; |
1565 |
if (scan(w, r)) { // scan until apparently empty |
1566 |
r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // move (xorshift) |
1567 |
} |
1568 |
else if ((phase = w.phase) >= 0) { // enqueue, then rescan |
1569 |
long np = (w.phase = (phase + SS_SEQ) | UNSIGNALLED) & SP_MASK; |
1570 |
long c, nc; |
1571 |
do { |
1572 |
w.stackPred = (int)(c = ctl); |
1573 |
nc = ((c - RC_UNIT) & UC_MASK) | np; |
1574 |
} while (!CTL.weakCompareAndSet(this, c, nc)); |
1575 |
} |
1576 |
else { // already queued |
1577 |
int pred = w.stackPred; |
1578 |
Thread.interrupted(); // clear before park |
1579 |
w.source = DORMANT; // enable signal |
1580 |
long c = ctl; |
1581 |
int md = mode, rc = (md & SMASK) + (int)(c >> RC_SHIFT); |
1582 |
if (md < 0) // terminating |
1583 |
break; |
1584 |
else if (rc <= 0 && (md & SHUTDOWN) != 0 && |
1585 |
tryTerminate(false, false)) |
1586 |
break; // quiescent shutdown |
1587 |
else if (rc <= 0 && pred != 0 && phase == (int)c) { |
1588 |
long nc = (UC_MASK & (c - TC_UNIT)) | (SP_MASK & pred); |
1589 |
long d = keepAlive + System.currentTimeMillis(); |
1590 |
LockSupport.parkUntil(this, d); |
1591 |
if (ctl == c && // drop on timeout if all idle |
1592 |
d - System.currentTimeMillis() <= TIMEOUT_SLOP && |
1593 |
CTL.compareAndSet(this, c, nc)) { |
1594 |
w.phase = QUIET; |
1595 |
break; |
1596 |
} |
1597 |
} |
1598 |
else if (w.phase < 0) |
1599 |
LockSupport.park(this); // OK if spuriously woken |
1600 |
w.source = 0; // disable signal |
1601 |
} |
1602 |
} |
1603 |
} |
1604 |
|
1605 |
/** |
1606 |
* Scans for and if found executes one or more top-level tasks from a queue. |
1607 |
* |
1608 |
* @return true if found an apparently non-empty queue, and |
1609 |
* possibly ran task(s). |
1610 |
*/ |
1611 |
private boolean scan(WorkQueue w, int r) { |
1612 |
WorkQueue[] ws; int n; |
1613 |
if ((ws = workQueues) != null && (n = ws.length) > 0 && w != null) { |
1614 |
for (int m = n - 1, j = r & m;;) { |
1615 |
WorkQueue q; int b; |
1616 |
if ((q = ws[j]) != null && q.top != (b = q.base)) { |
1617 |
int qid = q.id; |
1618 |
ForkJoinTask<?>[] a; int cap, k; ForkJoinTask<?> t; |
1619 |
if ((a = q.array) != null && (cap = a.length) > 0) { |
1620 |
t = (ForkJoinTask<?>)QA.getAcquire(a, k = (cap - 1) & b); |
1621 |
if (q.base == b++ && t != null && |
1622 |
QA.compareAndSet(a, k, t, null)) { |
1623 |
q.base = b; |
1624 |
w.source = qid; |
1625 |
if (q.top - b > 0) |
1626 |
signalWork(); |
1627 |
w.topLevelExec(t, q, // random fairness bound |
1628 |
r & ((n << TOP_BOUND_SHIFT) - 1)); |
1629 |
} |
1630 |
} |
1631 |
return true; |
1632 |
} |
1633 |
else if (--n > 0) |
1634 |
j = (j + 1) & m; |
1635 |
else |
1636 |
break; |
1637 |
} |
1638 |
} |
1639 |
return false; |
1640 |
} |
1641 |
|
1642 |
/** |
1643 |
* Helps and/or blocks until the given task is done or timeout. |
1644 |
* First tries locally helping, then scans other queues for a task |
1645 |
* produced by one of w's stealers; compensating and blocking if |
1646 |
* none are found (rescanning if tryCompensate fails). |
1647 |
* |
1648 |
* @param w caller |
1649 |
* @param task the task |
1650 |
* @param deadline for timed waits, if nonzero |
1651 |
* @return task status on exit |
1652 |
*/ |
1653 |
final int awaitJoin(WorkQueue w, ForkJoinTask<?> task, long deadline) { |
1654 |
int s = 0; |
1655 |
int seed = ThreadLocalRandom.nextSecondarySeed(); |
1656 |
if (w != null && task != null && |
1657 |
(!(task instanceof CountedCompleter) || |
1658 |
(s = w.helpCC((CountedCompleter<?>)task, 0, false)) >= 0)) { |
1659 |
w.tryRemoveAndExec(task); |
1660 |
int src = w.source, id = w.id; |
1661 |
int r = (seed >>> 16) | 1, step = (seed & ~1) | 2; |
1662 |
s = task.status; |
1663 |
while (s >= 0) { |
1664 |
WorkQueue[] ws; |
1665 |
int n = (ws = workQueues) == null ? 0 : ws.length, m = n - 1; |
1666 |
while (n > 0) { |
1667 |
WorkQueue q; int b; |
1668 |
if ((q = ws[r & m]) != null && q.source == id && |
1669 |
q.top != (b = q.base)) { |
1670 |
ForkJoinTask<?>[] a; int cap, k; |
1671 |
int qid = q.id; |
1672 |
if ((a = q.array) != null && (cap = a.length) > 0) { |
1673 |
ForkJoinTask<?> t = (ForkJoinTask<?>) |
1674 |
QA.getAcquire(a, k = (cap - 1) & b); |
1675 |
if (q.source == id && q.base == b++ && |
1676 |
t != null && QA.compareAndSet(a, k, t, null)) { |
1677 |
q.base = b; |
1678 |
w.source = qid; |
1679 |
t.doExec(); |
1680 |
w.source = src; |
1681 |
} |
1682 |
} |
1683 |
break; |
1684 |
} |
1685 |
else { |
1686 |
r += step; |
1687 |
--n; |
1688 |
} |
1689 |
} |
1690 |
if ((s = task.status) < 0) |
1691 |
break; |
1692 |
else if (n == 0) { // empty scan |
1693 |
long ms, ns; int block; |
1694 |
if (deadline == 0L) |
1695 |
ms = 0L; // untimed |
1696 |
else if ((ns = deadline - System.nanoTime()) <= 0L) |
1697 |
break; // timeout |
1698 |
else if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) <= 0L) |
1699 |
ms = 1L; // avoid 0 for timed wait |
1700 |
if ((block = tryCompensate(w)) != 0) { |
1701 |
task.internalWait(ms); |
1702 |
CTL.getAndAdd(this, (block > 0) ? RC_UNIT : 0L); |
1703 |
} |
1704 |
s = task.status; |
1705 |
} |
1706 |
} |
1707 |
} |
1708 |
return s; |
1709 |
} |
1710 |
|
1711 |
/** |
1712 |
* Runs tasks until {@code isQuiescent()}. Rather than blocking |
1713 |
* when tasks cannot be found, rescans until all others cannot |
1714 |
* find tasks either. |
1715 |
*/ |
1716 |
final void helpQuiescePool(WorkQueue w) { |
1717 |
int prevSrc = w.source; |
1718 |
int seed = ThreadLocalRandom.nextSecondarySeed(); |
1719 |
int r = seed >>> 16, step = r | 1; |
1720 |
for (int source = prevSrc, released = -1;;) { // -1 until known |
1721 |
ForkJoinTask<?> localTask; WorkQueue[] ws; |
1722 |
while ((localTask = w.nextLocalTask()) != null) |
1723 |
localTask.doExec(); |
1724 |
if (w.phase >= 0 && released == -1) |
1725 |
released = 1; |
1726 |
boolean quiet = true, empty = true; |
1727 |
int n = (ws = workQueues) == null ? 0 : ws.length; |
1728 |
for (int m = n - 1; n > 0; r += step, --n) { |
1729 |
WorkQueue q; int b; |
1730 |
if ((q = ws[r & m]) != null) { |
1731 |
int qs = q.source; |
1732 |
if (q.top != (b = q.base)) { |
1733 |
quiet = empty = false; |
1734 |
ForkJoinTask<?>[] a; int cap, k; |
1735 |
int qid = q.id; |
1736 |
if ((a = q.array) != null && (cap = a.length) > 0) { |
1737 |
if (released == 0) { // increment |
1738 |
released = 1; |
1739 |
CTL.getAndAdd(this, RC_UNIT); |
1740 |
} |
1741 |
ForkJoinTask<?> t = (ForkJoinTask<?>) |
1742 |
QA.getAcquire(a, k = (cap - 1) & b); |
1743 |
if (q.base == b++ && t != null && |
1744 |
QA.compareAndSet(a, k, t, null)) { |
1745 |
q.base = b; |
1746 |
w.source = qid; |
1747 |
t.doExec(); |
1748 |
w.source = source = prevSrc; |
1749 |
} |
1750 |
} |
1751 |
break; |
1752 |
} |
1753 |
else if ((qs & QUIET) == 0) |
1754 |
quiet = false; |
1755 |
} |
1756 |
} |
1757 |
if (quiet) { |
1758 |
if (released == 0) |
1759 |
CTL.getAndAdd(this, RC_UNIT); |
1760 |
w.source = prevSrc; |
1761 |
break; |
1762 |
} |
1763 |
else if (empty) { |
1764 |
if (source != QUIET) |
1765 |
w.source = source = QUIET; |
1766 |
if (released == 1) { // decrement |
1767 |
released = 0; |
1768 |
CTL.getAndAdd(this, RC_MASK & -RC_UNIT); |
1769 |
} |
1770 |
} |
1771 |
} |
1772 |
} |
1773 |
|
1774 |
/** |
1775 |
* Scans for and returns a polled task, if available. |
1776 |
* Used only for untracked polls. |
1777 |
* |
1778 |
* @param submissionsOnly if true, only scan submission queues |
1779 |
*/ |
1780 |
private ForkJoinTask<?> pollScan(boolean submissionsOnly) { |
1781 |
WorkQueue[] ws; int n; |
1782 |
rescan: while ((mode & STOP) == 0 && (ws = workQueues) != null && |
1783 |
(n = ws.length) > 0) { |
1784 |
int m = n - 1; |
1785 |
int r = ThreadLocalRandom.nextSecondarySeed(); |
1786 |
int h = r >>> 16; |
1787 |
int origin, step; |
1788 |
if (submissionsOnly) { |
1789 |
origin = (r & ~1) & m; // even indices and steps |
1790 |
step = (h & ~1) | 2; |
1791 |
} |
1792 |
else { |
1793 |
origin = r & m; |
1794 |
step = h | 1; |
1795 |
} |
1796 |
boolean nonempty = false; |
1797 |
for (int i = origin, oldSum = 0, checkSum = 0;;) { |
1798 |
WorkQueue q; |
1799 |
if ((q = ws[i]) != null) { |
1800 |
int b; ForkJoinTask<?> t; |
1801 |
if (q.top - (b = q.base) > 0) { |
1802 |
nonempty = true; |
1803 |
if ((t = q.poll()) != null) |
1804 |
return t; |
1805 |
} |
1806 |
else |
1807 |
checkSum += b + q.id; |
1808 |
} |
1809 |
if ((i = (i + step) & m) == origin) { |
1810 |
if (!nonempty && oldSum == (oldSum = checkSum)) |
1811 |
break rescan; |
1812 |
checkSum = 0; |
1813 |
nonempty = false; |
1814 |
} |
1815 |
} |
1816 |
} |
1817 |
return null; |
1818 |
} |
1819 |
|
1820 |
/** |
1821 |
* Gets and removes a local or stolen task for the given worker. |
1822 |
* |
1823 |
* @return a task, if available |
1824 |
*/ |
1825 |
final ForkJoinTask<?> nextTaskFor(WorkQueue w) { |
1826 |
ForkJoinTask<?> t; |
1827 |
if (w == null || (t = w.nextLocalTask()) == null) |
1828 |
t = pollScan(false); |
1829 |
return t; |
1830 |
} |
1831 |
|
1832 |
// External operations |
1833 |
|
1834 |
/** |
1835 |
* Adds the given task to a submission queue at submitter's |
1836 |
* current queue, creating one if null or contended. |
1837 |
* |
1838 |
* @param task the task. Caller must ensure non-null. |
1839 |
*/ |
1840 |
final void externalPush(ForkJoinTask<?> task) { |
1841 |
int r; // initialize caller's probe |
1842 |
if ((r = ThreadLocalRandom.getProbe()) == 0) { |
1843 |
ThreadLocalRandom.localInit(); |
1844 |
r = ThreadLocalRandom.getProbe(); |
1845 |
} |
1846 |
for (;;) { |
1847 |
WorkQueue q; |
1848 |
int md = mode, n; |
1849 |
WorkQueue[] ws = workQueues; |
1850 |
if ((md & SHUTDOWN) != 0 || ws == null || (n = ws.length) <= 0) |
1851 |
throw new RejectedExecutionException(); |
1852 |
else if ((q = ws[(n - 1) & r & SQMASK]) == null) { // add queue |
1853 |
int qid = (r | QUIET) & ~(FIFO | OWNED); |
1854 |
Object lock = workerNamePrefix; |
1855 |
ForkJoinTask<?>[] qa = |
1856 |
new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
1857 |
q = new WorkQueue(this, null); |
1858 |
q.array = qa; |
1859 |
q.id = qid; |
1860 |
q.source = QUIET; |
1861 |
if (lock != null) { // unless disabled, lock pool to install |
1862 |
synchronized (lock) { |
1863 |
WorkQueue[] vs; int i, vn; |
1864 |
if ((vs = workQueues) != null && (vn = vs.length) > 0 && |
1865 |
vs[i = qid & (vn - 1) & SQMASK] == null) |
1866 |
vs[i] = q; // else another thread already installed |
1867 |
} |
1868 |
} |
1869 |
} |
1870 |
else if (!q.tryLockPhase()) // move if busy |
1871 |
r = ThreadLocalRandom.advanceProbe(r); |
1872 |
else { |
1873 |
if (q.lockedPush(task)) |
1874 |
signalWork(); |
1875 |
return; |
1876 |
} |
1877 |
} |
1878 |
} |
1879 |
|
1880 |
/** |
1881 |
* Pushes a possibly-external submission. |
1882 |
*/ |
1883 |
private <T> ForkJoinTask<T> externalSubmit(ForkJoinTask<T> task) { |
1884 |
Thread t; ForkJoinWorkerThread w; WorkQueue q; |
1885 |
if (task == null) |
1886 |
throw new NullPointerException(); |
1887 |
if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && |
1888 |
(w = (ForkJoinWorkerThread)t).pool == this && |
1889 |
(q = w.workQueue) != null) |
1890 |
q.push(task); |
1891 |
else |
1892 |
externalPush(task); |
1893 |
return task; |
1894 |
} |
1895 |
|
1896 |
/** |
1897 |
* Returns common pool queue for an external thread. |
1898 |
*/ |
1899 |
static WorkQueue commonSubmitterQueue() { |
1900 |
ForkJoinPool p = common; |
1901 |
int r = ThreadLocalRandom.getProbe(); |
1902 |
WorkQueue[] ws; int n; |
1903 |
return (p != null && (ws = p.workQueues) != null && |
1904 |
(n = ws.length) > 0) ? |
1905 |
ws[(n - 1) & r & SQMASK] : null; |
1906 |
} |
1907 |
|
1908 |
/** |
1909 |
* Performs tryUnpush for an external submitter. |
1910 |
*/ |
1911 |
final boolean tryExternalUnpush(ForkJoinTask<?> task) { |
1912 |
int r = ThreadLocalRandom.getProbe(); |
1913 |
WorkQueue[] ws; WorkQueue w; int n; |
1914 |
return ((ws = workQueues) != null && |
1915 |
(n = ws.length) > 0 && |
1916 |
(w = ws[(n - 1) & r & SQMASK]) != null && |
1917 |
w.tryLockedUnpush(task)); |
1918 |
} |
1919 |
|
1920 |
/** |
1921 |
* Performs helpComplete for an external submitter. |
1922 |
*/ |
1923 |
final int externalHelpComplete(CountedCompleter<?> task, int maxTasks) { |
1924 |
int r = ThreadLocalRandom.getProbe(); |
1925 |
WorkQueue[] ws; WorkQueue w; int n; |
1926 |
return ((ws = workQueues) != null && (n = ws.length) > 0 && |
1927 |
(w = ws[(n - 1) & r & SQMASK]) != null) ? |
1928 |
w.helpCC(task, maxTasks, true) : 0; |
1929 |
} |
1930 |
|
1931 |
/** |
1932 |
* Tries to steal and run tasks within the target's computation. |
1933 |
* The maxTasks argument supports external usages; internal calls |
1934 |
* use zero, allowing unbounded steps (external calls trap |
1935 |
* non-positive values). |
1936 |
* |
1937 |
* @param w caller |
1938 |
* @param maxTasks if non-zero, the maximum number of other tasks to run |
1939 |
* @return task status on exit |
1940 |
*/ |
1941 |
final int helpComplete(WorkQueue w, CountedCompleter<?> task, |
1942 |
int maxTasks) { |
1943 |
return (w == null) ? 0 : w.helpCC(task, maxTasks, false); |
1944 |
} |
1945 |
|
1946 |
/** |
1947 |
* Returns a cheap heuristic guide for task partitioning when |
1948 |
* programmers, frameworks, tools, or languages have little or no |
1949 |
* idea about task granularity. In essence, by offering this |
1950 |
* method, we ask users only about tradeoffs in overhead vs |
1951 |
* expected throughput and its variance, rather than how finely to |
1952 |
* partition tasks. |
1953 |
* |
1954 |
* In a steady state strict (tree-structured) computation, each |
1955 |
* thread makes available for stealing enough tasks for other |
1956 |
* threads to remain active. Inductively, if all threads play by |
1957 |
* the same rules, each thread should make available only a |
1958 |
* constant number of tasks. |
1959 |
* |
1960 |
* The minimum useful constant is just 1. But using a value of 1 |
1961 |
* would require immediate replenishment upon each steal to |
1962 |
* maintain enough tasks, which is infeasible. Further, |
1963 |
* partitionings/granularities of offered tasks should minimize |
1964 |
* steal rates, which in general means that threads nearer the top |
1965 |
* of computation tree should generate more than those nearer the |
1966 |
* bottom. In perfect steady state, each thread is at |
1967 |
* approximately the same level of computation tree. However, |
1968 |
* producing extra tasks amortizes the uncertainty of progress and |
1969 |
* diffusion assumptions. |
1970 |
* |
1971 |
* So, users will want to use values larger (but not much larger) |
1972 |
* than 1 to both smooth over transient shortages and hedge |
1973 |
* against uneven progress; as traded off against the cost of |
1974 |
* extra task overhead. We leave the user to pick a threshold |
1975 |
* value to compare with the results of this call to guide |
1976 |
* decisions, but recommend values such as 3. |
1977 |
* |
1978 |
* When all threads are active, it is on average OK to estimate |
1979 |
* surplus strictly locally. In steady-state, if one thread is |
1980 |
* maintaining say 2 surplus tasks, then so are others. So we can |
1981 |
* just use estimated queue length. However, this strategy alone |
1982 |
* leads to serious mis-estimates in some non-steady-state |
1983 |
* conditions (ramp-up, ramp-down, other stalls). We can detect |
1984 |
* many of these by further considering the number of "idle" |
1985 |
* threads, that are known to have zero queued tasks, so |
1986 |
* compensate by a factor of (#idle/#active) threads. |
1987 |
*/ |
1988 |
static int getSurplusQueuedTaskCount() { |
1989 |
Thread t; ForkJoinWorkerThread wt; ForkJoinPool pool; WorkQueue q; |
1990 |
if (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) && |
1991 |
(pool = (wt = (ForkJoinWorkerThread)t).pool) != null && |
1992 |
(q = wt.workQueue) != null) { |
1993 |
int p = pool.mode & SMASK; |
1994 |
int a = p + (int)(pool.ctl >> RC_SHIFT); |
1995 |
int n = q.top - q.base; |
1996 |
return n - (a > (p >>>= 1) ? 0 : |
1997 |
a > (p >>>= 1) ? 1 : |
1998 |
a > (p >>>= 1) ? 2 : |
1999 |
a > (p >>>= 1) ? 4 : |
2000 |
8); |
2001 |
} |
2002 |
return 0; |
2003 |
} |
2004 |
|
2005 |
// Termination |
2006 |
|
2007 |
/** |
2008 |
* Possibly initiates and/or completes termination. |
2009 |
* |
2010 |
* @param now if true, unconditionally terminate, else only |
2011 |
* if no work and no active workers |
2012 |
* @param enable if true, terminate when next possible |
2013 |
* @return true if terminating or terminated |
2014 |
*/ |
2015 |
private boolean tryTerminate(boolean now, boolean enable) { |
2016 |
int md; // 3 phases: try to set SHUTDOWN, then STOP, then TERMINATED |
2017 |
|
2018 |
while (((md = mode) & SHUTDOWN) == 0) { |
2019 |
if (!enable || this == common) // cannot shutdown |
2020 |
return false; |
2021 |
else |
2022 |
MODE.compareAndSet(this, md, md | SHUTDOWN); |
2023 |
} |
2024 |
|
2025 |
while (((md = mode) & STOP) == 0) { // try to initiate termination |
2026 |
if (!now) { // check if quiescent & empty |
2027 |
for (long oldSum = 0L;;) { // repeat until stable |
2028 |
boolean running = false; |
2029 |
long checkSum = ctl; |
2030 |
WorkQueue[] ws = workQueues; |
2031 |
if ((md & SMASK) + (int)(checkSum >> RC_SHIFT) > 0) |
2032 |
running = true; |
2033 |
else if (ws != null) { |
2034 |
WorkQueue w; int b; |
2035 |
for (int i = 0; i < ws.length; ++i) { |
2036 |
if ((w = ws[i]) != null) { |
2037 |
checkSum += (b = w.base) + w.id; |
2038 |
if (b != w.top || |
2039 |
((i & 1) == 1 && w.source >= 0)) { |
2040 |
running = true; |
2041 |
break; |
2042 |
} |
2043 |
} |
2044 |
} |
2045 |
} |
2046 |
if (((md = mode) & STOP) != 0) |
2047 |
break; // already triggered |
2048 |
else if (running) |
2049 |
return false; |
2050 |
else if (workQueues == ws && oldSum == (oldSum = checkSum)) |
2051 |
break; |
2052 |
} |
2053 |
} |
2054 |
if ((md & STOP) == 0) |
2055 |
MODE.compareAndSet(this, md, md | STOP); |
2056 |
} |
2057 |
|
2058 |
while (((md = mode) & TERMINATED) == 0) { // help terminate others |
2059 |
for (long oldSum = 0L;;) { // repeat until stable |
2060 |
WorkQueue[] ws; WorkQueue w; |
2061 |
long checkSum = ctl; |
2062 |
if ((ws = workQueues) != null) { |
2063 |
for (int i = 0; i < ws.length; ++i) { |
2064 |
if ((w = ws[i]) != null) { |
2065 |
ForkJoinWorkerThread wt = w.owner; |
2066 |
w.cancelAll(); // clear queues |
2067 |
if (wt != null) { |
2068 |
try { // unblock join or park |
2069 |
wt.interrupt(); |
2070 |
} catch (Throwable ignore) { |
2071 |
} |
2072 |
} |
2073 |
checkSum += w.base + w.phase; |
2074 |
} |
2075 |
} |
2076 |
} |
2077 |
if (((md = mode) & TERMINATED) != 0 || |
2078 |
(workQueues == ws && oldSum == (oldSum = checkSum))) |
2079 |
break; |
2080 |
} |
2081 |
if ((md & TERMINATED) != 0) |
2082 |
break; |
2083 |
else if ((md & SMASK) + (short)(ctl >>> TC_SHIFT) > 0) |
2084 |
break; |
2085 |
else if (MODE.compareAndSet(this, md, md | TERMINATED)) { |
2086 |
synchronized (this) { |
2087 |
notifyAll(); // for awaitTermination |
2088 |
} |
2089 |
break; |
2090 |
} |
2091 |
} |
2092 |
return true; |
2093 |
} |
2094 |
|
2095 |
// Exported methods |
2096 |
|
2097 |
// Constructors |
2098 |
|
2099 |
/** |
2100 |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
2101 |
* java.lang.Runtime#availableProcessors}, using defaults for all |
2102 |
* other parameters (see {@link #ForkJoinPool(int, |
2103 |
* ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, |
2104 |
* int, int, int, Predicate, long, TimeUnit)}). |
2105 |
* |
2106 |
* @throws SecurityException if a security manager exists and |
2107 |
* the caller is not permitted to modify threads |
2108 |
* because it does not hold {@link |
2109 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2110 |
*/ |
2111 |
public ForkJoinPool() { |
2112 |
this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()), |
2113 |
defaultForkJoinWorkerThreadFactory, null, false, |
2114 |
0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
2115 |
} |
2116 |
|
2117 |
/** |
2118 |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
2119 |
* level, using defaults for all other parameters (see {@link |
2120 |
* #ForkJoinPool(int, ForkJoinWorkerThreadFactory, |
2121 |
* UncaughtExceptionHandler, boolean, int, int, int, Predicate, |
2122 |
* long, TimeUnit)}). |
2123 |
* |
2124 |
* @param parallelism the parallelism level |
2125 |
* @throws IllegalArgumentException if parallelism less than or |
2126 |
* equal to zero, or greater than implementation limit |
2127 |
* @throws SecurityException if a security manager exists and |
2128 |
* the caller is not permitted to modify threads |
2129 |
* because it does not hold {@link |
2130 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2131 |
*/ |
2132 |
public ForkJoinPool(int parallelism) { |
2133 |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false, |
2134 |
0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
2135 |
} |
2136 |
|
2137 |
/** |
2138 |
* Creates a {@code ForkJoinPool} with the given parameters (using |
2139 |
* defaults for others -- see {@link #ForkJoinPool(int, |
2140 |
* ForkJoinWorkerThreadFactory, UncaughtExceptionHandler, boolean, |
2141 |
* int, int, int, Predicate, long, TimeUnit)}). |
2142 |
* |
2143 |
* @param parallelism the parallelism level. For default value, |
2144 |
* use {@link java.lang.Runtime#availableProcessors}. |
2145 |
* @param factory the factory for creating new threads. For default value, |
2146 |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
2147 |
* @param handler the handler for internal worker threads that |
2148 |
* terminate due to unrecoverable errors encountered while executing |
2149 |
* tasks. For default value, use {@code null}. |
2150 |
* @param asyncMode if true, |
2151 |
* establishes local first-in-first-out scheduling mode for forked |
2152 |
* tasks that are never joined. This mode may be more appropriate |
2153 |
* than default locally stack-based mode in applications in which |
2154 |
* worker threads only process event-style asynchronous tasks. |
2155 |
* For default value, use {@code false}. |
2156 |
* @throws IllegalArgumentException if parallelism less than or |
2157 |
* equal to zero, or greater than implementation limit |
2158 |
* @throws NullPointerException if the factory is null |
2159 |
* @throws SecurityException if a security manager exists and |
2160 |
* the caller is not permitted to modify threads |
2161 |
* because it does not hold {@link |
2162 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2163 |
*/ |
2164 |
public ForkJoinPool(int parallelism, |
2165 |
ForkJoinWorkerThreadFactory factory, |
2166 |
UncaughtExceptionHandler handler, |
2167 |
boolean asyncMode) { |
2168 |
this(parallelism, factory, handler, asyncMode, |
2169 |
0, MAX_CAP, 1, null, DEFAULT_KEEPALIVE, TimeUnit.MILLISECONDS); |
2170 |
} |
2171 |
|
2172 |
/** |
2173 |
* Creates a {@code ForkJoinPool} with the given parameters. |
2174 |
* |
2175 |
* @param parallelism the parallelism level. For default value, |
2176 |
* use {@link java.lang.Runtime#availableProcessors}. |
2177 |
* |
2178 |
* @param factory the factory for creating new threads. For |
2179 |
* default value, use {@link #defaultForkJoinWorkerThreadFactory}. |
2180 |
* |
2181 |
* @param handler the handler for internal worker threads that |
2182 |
* terminate due to unrecoverable errors encountered while |
2183 |
* executing tasks. For default value, use {@code null}. |
2184 |
* |
2185 |
* @param asyncMode if true, establishes local first-in-first-out |
2186 |
* scheduling mode for forked tasks that are never joined. This |
2187 |
* mode may be more appropriate than default locally stack-based |
2188 |
* mode in applications in which worker threads only process |
2189 |
* event-style asynchronous tasks. For default value, use {@code |
2190 |
* false}. |
2191 |
* |
2192 |
* @param corePoolSize the number of threads to keep in the pool |
2193 |
* (unless timed out after an elapsed keep-alive). Normally (and |
2194 |
* by default) this is the same value as the parallelism level, |
2195 |
* but may be set to a larger value to reduce dynamic overhead if |
2196 |
* tasks regularly block. Using a smaller value (for example |
2197 |
* {@code 0}) has the same effect as the default. |
2198 |
* |
2199 |
* @param maximumPoolSize the maximum number of threads allowed. |
2200 |
* When the maximum is reached, attempts to replace blocked |
2201 |
* threads fail. (However, because creation and termination of |
2202 |
* different threads may overlap, and may be managed by the given |
2203 |
* thread factory, this value may be transiently exceeded.) To |
2204 |
* arrange the same value as is used by default for the common |
2205 |
* pool, use {@code 256} plus the {@code parallelism} level. (By |
2206 |
* default, the common pool allows a maximum of 256 spare |
2207 |
* threads.) Using a value (for example {@code |
2208 |
* Integer.MAX_VALUE}) larger than the implementation's total |
2209 |
* thread limit has the same effect as using this limit (which is |
2210 |
* the default). |
2211 |
* |
2212 |
* @param minimumRunnable the minimum allowed number of core |
2213 |
* threads not blocked by a join or {@link ManagedBlocker}. To |
2214 |
* ensure progress, when too few unblocked threads exist and |
2215 |
* unexecuted tasks may exist, new threads are constructed, up to |
2216 |
* the given maximumPoolSize. For the default value, use {@code |
2217 |
* 1}, that ensures liveness. A larger value might improve |
2218 |
* throughput in the presence of blocked activities, but might |
2219 |
* not, due to increased overhead. A value of zero may be |
2220 |
* acceptable when submitted tasks cannot have dependencies |
2221 |
* requiring additional threads. |
2222 |
* |
2223 |
* @param saturate if non-null, a predicate invoked upon attempts |
2224 |
* to create more than the maximum total allowed threads. By |
2225 |
* default, when a thread is about to block on a join or {@link |
2226 |
* ManagedBlocker}, but cannot be replaced because the |
2227 |
* maximumPoolSize would be exceeded, a {@link |
2228 |
* RejectedExecutionException} is thrown. But if this predicate |
2229 |
* returns {@code true}, then no exception is thrown, so the pool |
2230 |
* continues to operate with fewer than the target number of |
2231 |
* runnable threads, which might not ensure progress. |
2232 |
* |
2233 |
* @param keepAliveTime the elapsed time since last use before |
2234 |
* a thread is terminated (and then later replaced if needed). |
2235 |
* For the default value, use {@code 60, TimeUnit.SECONDS}. |
2236 |
* |
2237 |
* @param unit the time unit for the {@code keepAliveTime} argument |
2238 |
* |
2239 |
* @throws IllegalArgumentException if parallelism is less than or |
2240 |
* equal to zero, or is greater than implementation limit, |
2241 |
* or if maximumPoolSize is less than parallelism, |
2242 |
* of if the keepAliveTime is less than or equal to zero. |
2243 |
* @throws NullPointerException if the factory is null |
2244 |
* @throws SecurityException if a security manager exists and |
2245 |
* the caller is not permitted to modify threads |
2246 |
* because it does not hold {@link |
2247 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2248 |
* @since 9 |
2249 |
*/ |
2250 |
public ForkJoinPool(int parallelism, |
2251 |
ForkJoinWorkerThreadFactory factory, |
2252 |
UncaughtExceptionHandler handler, |
2253 |
boolean asyncMode, |
2254 |
int corePoolSize, |
2255 |
int maximumPoolSize, |
2256 |
int minimumRunnable, |
2257 |
Predicate<? super ForkJoinPool> saturate, |
2258 |
long keepAliveTime, |
2259 |
TimeUnit unit) { |
2260 |
// check, encode, pack parameters |
2261 |
if (parallelism <= 0 || parallelism > MAX_CAP || |
2262 |
maximumPoolSize < parallelism || keepAliveTime <= 0L) |
2263 |
throw new IllegalArgumentException(); |
2264 |
if (factory == null) |
2265 |
throw new NullPointerException(); |
2266 |
long ms = Math.max(unit.toMillis(keepAliveTime), TIMEOUT_SLOP); |
2267 |
|
2268 |
int corep = Math.min(Math.max(corePoolSize, parallelism), MAX_CAP); |
2269 |
long c = ((((long)(-corep) << TC_SHIFT) & TC_MASK) | |
2270 |
(((long)(-parallelism) << RC_SHIFT) & RC_MASK)); |
2271 |
int m = parallelism | (asyncMode ? FIFO : 0); |
2272 |
int maxSpares = Math.min(maximumPoolSize, MAX_CAP) - parallelism; |
2273 |
int minAvail = Math.min(Math.max(minimumRunnable, 0), MAX_CAP); |
2274 |
int b = ((minAvail - parallelism) & SMASK) | (maxSpares << SWIDTH); |
2275 |
int n = (parallelism > 1) ? parallelism - 1 : 1; // at least 2 slots |
2276 |
n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16; |
2277 |
n = (n + 1) << 1; // power of two, including space for submission queues |
2278 |
|
2279 |
this.workerNamePrefix = "ForkJoinPool-" + nextPoolId() + "-worker-"; |
2280 |
this.workQueues = new WorkQueue[n]; |
2281 |
this.factory = factory; |
2282 |
this.ueh = handler; |
2283 |
this.saturate = saturate; |
2284 |
this.keepAlive = ms; |
2285 |
this.bounds = b; |
2286 |
this.mode = m; |
2287 |
this.ctl = c; |
2288 |
checkPermission(); |
2289 |
} |
2290 |
|
2291 |
private static Object newInstanceFromSystemProperty(String property) |
2292 |
throws ReflectiveOperationException { |
2293 |
String className = System.getProperty(property); |
2294 |
return (className == null) |
2295 |
? null |
2296 |
: ClassLoader.getSystemClassLoader().loadClass(className) |
2297 |
.getConstructor().newInstance(); |
2298 |
} |
2299 |
|
2300 |
/** |
2301 |
* Constructor for common pool using parameters possibly |
2302 |
* overridden by system properties |
2303 |
*/ |
2304 |
private ForkJoinPool(byte forCommonPoolOnly) { |
2305 |
int parallelism = -1; |
2306 |
ForkJoinWorkerThreadFactory fac = null; |
2307 |
UncaughtExceptionHandler handler = null; |
2308 |
try { // ignore exceptions in accessing/parsing properties |
2309 |
String pp = System.getProperty |
2310 |
("java.util.concurrent.ForkJoinPool.common.parallelism"); |
2311 |
if (pp != null) |
2312 |
parallelism = Integer.parseInt(pp); |
2313 |
fac = (ForkJoinWorkerThreadFactory) newInstanceFromSystemProperty( |
2314 |
"java.util.concurrent.ForkJoinPool.common.threadFactory"); |
2315 |
handler = (UncaughtExceptionHandler) newInstanceFromSystemProperty( |
2316 |
"java.util.concurrent.ForkJoinPool.common.exceptionHandler"); |
2317 |
} catch (Exception ignore) { |
2318 |
} |
2319 |
|
2320 |
if (fac == null) { |
2321 |
if (System.getSecurityManager() == null) |
2322 |
fac = defaultForkJoinWorkerThreadFactory; |
2323 |
else // use security-managed default |
2324 |
fac = new InnocuousForkJoinWorkerThreadFactory(); |
2325 |
} |
2326 |
if (parallelism < 0 && // default 1 less than #cores |
2327 |
(parallelism = Runtime.getRuntime().availableProcessors() - 1) <= 0) |
2328 |
parallelism = 1; |
2329 |
if (parallelism > MAX_CAP) |
2330 |
parallelism = MAX_CAP; |
2331 |
|
2332 |
long c = ((((long)(-parallelism) << TC_SHIFT) & TC_MASK) | |
2333 |
(((long)(-parallelism) << RC_SHIFT) & RC_MASK)); |
2334 |
int b = ((1 - parallelism) & SMASK) | (COMMON_MAX_SPARES << SWIDTH); |
2335 |
int n = (parallelism > 1) ? parallelism - 1 : 1; |
2336 |
n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16; |
2337 |
n = (n + 1) << 1; |
2338 |
|
2339 |
this.workerNamePrefix = "ForkJoinPool.commonPool-worker-"; |
2340 |
this.workQueues = new WorkQueue[n]; |
2341 |
this.factory = fac; |
2342 |
this.ueh = handler; |
2343 |
this.saturate = null; |
2344 |
this.keepAlive = DEFAULT_KEEPALIVE; |
2345 |
this.bounds = b; |
2346 |
this.mode = parallelism; |
2347 |
this.ctl = c; |
2348 |
} |
2349 |
|
2350 |
/** |
2351 |
* Returns the common pool instance. This pool is statically |
2352 |
* constructed; its run state is unaffected by attempts to {@link |
2353 |
* #shutdown} or {@link #shutdownNow}. However this pool and any |
2354 |
* ongoing processing are automatically terminated upon program |
2355 |
* {@link System#exit}. Any program that relies on asynchronous |
2356 |
* task processing to complete before program termination should |
2357 |
* invoke {@code commonPool().}{@link #awaitQuiescence awaitQuiescence}, |
2358 |
* before exit. |
2359 |
* |
2360 |
* @return the common pool instance |
2361 |
* @since 1.8 |
2362 |
*/ |
2363 |
public static ForkJoinPool commonPool() { |
2364 |
// assert common != null : "static init error"; |
2365 |
return common; |
2366 |
} |
2367 |
|
2368 |
// Execution methods |
2369 |
|
2370 |
/** |
2371 |
* Performs the given task, returning its result upon completion. |
2372 |
* If the computation encounters an unchecked Exception or Error, |
2373 |
* it is rethrown as the outcome of this invocation. Rethrown |
2374 |
* exceptions behave in the same way as regular exceptions, but, |
2375 |
* when possible, contain stack traces (as displayed for example |
2376 |
* using {@code ex.printStackTrace()}) of both the current thread |
2377 |
* as well as the thread actually encountering the exception; |
2378 |
* minimally only the latter. |
2379 |
* |
2380 |
* @param task the task |
2381 |
* @param <T> the type of the task's result |
2382 |
* @return the task's result |
2383 |
* @throws NullPointerException if the task is null |
2384 |
* @throws RejectedExecutionException if the task cannot be |
2385 |
* scheduled for execution |
2386 |
*/ |
2387 |
public <T> T invoke(ForkJoinTask<T> task) { |
2388 |
if (task == null) |
2389 |
throw new NullPointerException(); |
2390 |
externalSubmit(task); |
2391 |
return task.join(); |
2392 |
} |
2393 |
|
2394 |
/** |
2395 |
* Arranges for (asynchronous) execution of the given task. |
2396 |
* |
2397 |
* @param task the task |
2398 |
* @throws NullPointerException if the task is null |
2399 |
* @throws RejectedExecutionException if the task cannot be |
2400 |
* scheduled for execution |
2401 |
*/ |
2402 |
public void execute(ForkJoinTask<?> task) { |
2403 |
externalSubmit(task); |
2404 |
} |
2405 |
|
2406 |
// AbstractExecutorService methods |
2407 |
|
2408 |
/** |
2409 |
* @throws NullPointerException if the task is null |
2410 |
* @throws RejectedExecutionException if the task cannot be |
2411 |
* scheduled for execution |
2412 |
*/ |
2413 |
public void execute(Runnable task) { |
2414 |
if (task == null) |
2415 |
throw new NullPointerException(); |
2416 |
ForkJoinTask<?> job; |
2417 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
2418 |
job = (ForkJoinTask<?>) task; |
2419 |
else |
2420 |
job = new ForkJoinTask.RunnableExecuteAction(task); |
2421 |
externalSubmit(job); |
2422 |
} |
2423 |
|
2424 |
/** |
2425 |
* Submits a ForkJoinTask for execution. |
2426 |
* |
2427 |
* @param task the task to submit |
2428 |
* @param <T> the type of the task's result |
2429 |
* @return the task |
2430 |
* @throws NullPointerException if the task is null |
2431 |
* @throws RejectedExecutionException if the task cannot be |
2432 |
* scheduled for execution |
2433 |
*/ |
2434 |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
2435 |
return externalSubmit(task); |
2436 |
} |
2437 |
|
2438 |
/** |
2439 |
* @throws NullPointerException if the task is null |
2440 |
* @throws RejectedExecutionException if the task cannot be |
2441 |
* scheduled for execution |
2442 |
*/ |
2443 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
2444 |
return externalSubmit(new ForkJoinTask.AdaptedCallable<T>(task)); |
2445 |
} |
2446 |
|
2447 |
/** |
2448 |
* @throws NullPointerException if the task is null |
2449 |
* @throws RejectedExecutionException if the task cannot be |
2450 |
* scheduled for execution |
2451 |
*/ |
2452 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
2453 |
return externalSubmit(new ForkJoinTask.AdaptedRunnable<T>(task, result)); |
2454 |
} |
2455 |
|
2456 |
/** |
2457 |
* @throws NullPointerException if the task is null |
2458 |
* @throws RejectedExecutionException if the task cannot be |
2459 |
* scheduled for execution |
2460 |
*/ |
2461 |
@SuppressWarnings("unchecked") |
2462 |
public ForkJoinTask<?> submit(Runnable task) { |
2463 |
if (task == null) |
2464 |
throw new NullPointerException(); |
2465 |
return externalSubmit((task instanceof ForkJoinTask<?>) |
2466 |
? (ForkJoinTask<Void>) task // avoid re-wrap |
2467 |
: new ForkJoinTask.AdaptedRunnableAction(task)); |
2468 |
} |
2469 |
|
2470 |
/** |
2471 |
* @throws NullPointerException {@inheritDoc} |
2472 |
* @throws RejectedExecutionException {@inheritDoc} |
2473 |
*/ |
2474 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
2475 |
// In previous versions of this class, this method constructed |
2476 |
// a task to run ForkJoinTask.invokeAll, but now external |
2477 |
// invocation of multiple tasks is at least as efficient. |
2478 |
ArrayList<Future<T>> futures = new ArrayList<>(tasks.size()); |
2479 |
|
2480 |
try { |
2481 |
for (Callable<T> t : tasks) { |
2482 |
ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t); |
2483 |
futures.add(f); |
2484 |
externalSubmit(f); |
2485 |
} |
2486 |
for (int i = 0, size = futures.size(); i < size; i++) |
2487 |
((ForkJoinTask<?>)futures.get(i)).quietlyJoin(); |
2488 |
return futures; |
2489 |
} catch (Throwable t) { |
2490 |
for (int i = 0, size = futures.size(); i < size; i++) |
2491 |
futures.get(i).cancel(false); |
2492 |
throw t; |
2493 |
} |
2494 |
} |
2495 |
|
2496 |
/** |
2497 |
* Returns the factory used for constructing new workers. |
2498 |
* |
2499 |
* @return the factory used for constructing new workers |
2500 |
*/ |
2501 |
public ForkJoinWorkerThreadFactory getFactory() { |
2502 |
return factory; |
2503 |
} |
2504 |
|
2505 |
/** |
2506 |
* Returns the handler for internal worker threads that terminate |
2507 |
* due to unrecoverable errors encountered while executing tasks. |
2508 |
* |
2509 |
* @return the handler, or {@code null} if none |
2510 |
*/ |
2511 |
public UncaughtExceptionHandler getUncaughtExceptionHandler() { |
2512 |
return ueh; |
2513 |
} |
2514 |
|
2515 |
/** |
2516 |
* Returns the targeted parallelism level of this pool. |
2517 |
* |
2518 |
* @return the targeted parallelism level of this pool |
2519 |
*/ |
2520 |
public int getParallelism() { |
2521 |
int par = mode & SMASK; |
2522 |
return (par > 0) ? par : 1; |
2523 |
} |
2524 |
|
2525 |
/** |
2526 |
* Returns the targeted parallelism level of the common pool. |
2527 |
* |
2528 |
* @return the targeted parallelism level of the common pool |
2529 |
* @since 1.8 |
2530 |
*/ |
2531 |
public static int getCommonPoolParallelism() { |
2532 |
return COMMON_PARALLELISM; |
2533 |
} |
2534 |
|
2535 |
/** |
2536 |
* Returns the number of worker threads that have started but not |
2537 |
* yet terminated. The result returned by this method may differ |
2538 |
* from {@link #getParallelism} when threads are created to |
2539 |
* maintain parallelism when others are cooperatively blocked. |
2540 |
* |
2541 |
* @return the number of worker threads |
2542 |
*/ |
2543 |
public int getPoolSize() { |
2544 |
return ((mode & SMASK) + (short)(ctl >>> TC_SHIFT)); |
2545 |
} |
2546 |
|
2547 |
/** |
2548 |
* Returns {@code true} if this pool uses local first-in-first-out |
2549 |
* scheduling mode for forked tasks that are never joined. |
2550 |
* |
2551 |
* @return {@code true} if this pool uses async mode |
2552 |
*/ |
2553 |
public boolean getAsyncMode() { |
2554 |
return (mode & FIFO) != 0; |
2555 |
} |
2556 |
|
2557 |
/** |
2558 |
* Returns an estimate of the number of worker threads that are |
2559 |
* not blocked waiting to join tasks or for other managed |
2560 |
* synchronization. This method may overestimate the |
2561 |
* number of running threads. |
2562 |
* |
2563 |
* @return the number of worker threads |
2564 |
*/ |
2565 |
public int getRunningThreadCount() { |
2566 |
WorkQueue[] ws; WorkQueue w; |
2567 |
VarHandle.acquireFence(); |
2568 |
int rc = 0; |
2569 |
if ((ws = workQueues) != null) { |
2570 |
for (int i = 1; i < ws.length; i += 2) { |
2571 |
if ((w = ws[i]) != null && w.isApparentlyUnblocked()) |
2572 |
++rc; |
2573 |
} |
2574 |
} |
2575 |
return rc; |
2576 |
} |
2577 |
|
2578 |
/** |
2579 |
* Returns an estimate of the number of threads that are currently |
2580 |
* stealing or executing tasks. This method may overestimate the |
2581 |
* number of active threads. |
2582 |
* |
2583 |
* @return the number of active threads |
2584 |
*/ |
2585 |
public int getActiveThreadCount() { |
2586 |
int r = (mode & SMASK) + (int)(ctl >> RC_SHIFT); |
2587 |
return (r <= 0) ? 0 : r; // suppress momentarily negative values |
2588 |
} |
2589 |
|
2590 |
/** |
2591 |
* Returns {@code true} if all worker threads are currently idle. |
2592 |
* An idle worker is one that cannot obtain a task to execute |
2593 |
* because none are available to steal from other threads, and |
2594 |
* there are no pending submissions to the pool. This method is |
2595 |
* conservative; it might not return {@code true} immediately upon |
2596 |
* idleness of all threads, but will eventually become true if |
2597 |
* threads remain inactive. |
2598 |
* |
2599 |
* @return {@code true} if all threads are currently idle |
2600 |
*/ |
2601 |
public boolean isQuiescent() { |
2602 |
for (;;) { |
2603 |
long c = ctl; |
2604 |
int md = mode, pc = md & SMASK; |
2605 |
int tc = pc + (short)(c >>> TC_SHIFT); |
2606 |
int rc = pc + (int)(c >> RC_SHIFT); |
2607 |
if ((md & (STOP | TERMINATED)) != 0) |
2608 |
return true; |
2609 |
else if (rc > 0) |
2610 |
return false; |
2611 |
else { |
2612 |
WorkQueue[] ws; WorkQueue v; |
2613 |
if ((ws = workQueues) != null) { |
2614 |
for (int i = 1; i < ws.length; i += 2) { |
2615 |
if ((v = ws[i]) != null) { |
2616 |
if (v.source > 0) |
2617 |
return false; |
2618 |
--tc; |
2619 |
} |
2620 |
} |
2621 |
} |
2622 |
if (tc == 0 && ctl == c) |
2623 |
return true; |
2624 |
} |
2625 |
} |
2626 |
} |
2627 |
|
2628 |
/** |
2629 |
* Returns an estimate of the total number of tasks stolen from |
2630 |
* one thread's work queue by another. The reported value |
2631 |
* underestimates the actual total number of steals when the pool |
2632 |
* is not quiescent. This value may be useful for monitoring and |
2633 |
* tuning fork/join programs: in general, steal counts should be |
2634 |
* high enough to keep threads busy, but low enough to avoid |
2635 |
* overhead and contention across threads. |
2636 |
* |
2637 |
* @return the number of steals |
2638 |
*/ |
2639 |
public long getStealCount() { |
2640 |
long count = stealCount; |
2641 |
WorkQueue[] ws; WorkQueue w; |
2642 |
if ((ws = workQueues) != null) { |
2643 |
for (int i = 1; i < ws.length; i += 2) { |
2644 |
if ((w = ws[i]) != null) |
2645 |
count += (long)w.nsteals & 0xffffffffL; |
2646 |
} |
2647 |
} |
2648 |
return count; |
2649 |
} |
2650 |
|
2651 |
/** |
2652 |
* Returns an estimate of the total number of tasks currently held |
2653 |
* in queues by worker threads (but not including tasks submitted |
2654 |
* to the pool that have not begun executing). This value is only |
2655 |
* an approximation, obtained by iterating across all threads in |
2656 |
* the pool. This method may be useful for tuning task |
2657 |
* granularities. |
2658 |
* |
2659 |
* @return the number of queued tasks |
2660 |
*/ |
2661 |
public long getQueuedTaskCount() { |
2662 |
WorkQueue[] ws; WorkQueue w; |
2663 |
VarHandle.acquireFence(); |
2664 |
int count = 0; |
2665 |
if ((ws = workQueues) != null) { |
2666 |
for (int i = 1; i < ws.length; i += 2) { |
2667 |
if ((w = ws[i]) != null) |
2668 |
count += w.queueSize(); |
2669 |
} |
2670 |
} |
2671 |
return count; |
2672 |
} |
2673 |
|
2674 |
/** |
2675 |
* Returns an estimate of the number of tasks submitted to this |
2676 |
* pool that have not yet begun executing. This method may take |
2677 |
* time proportional to the number of submissions. |
2678 |
* |
2679 |
* @return the number of queued submissions |
2680 |
*/ |
2681 |
public int getQueuedSubmissionCount() { |
2682 |
WorkQueue[] ws; WorkQueue w; |
2683 |
VarHandle.acquireFence(); |
2684 |
int count = 0; |
2685 |
if ((ws = workQueues) != null) { |
2686 |
for (int i = 0; i < ws.length; i += 2) { |
2687 |
if ((w = ws[i]) != null) |
2688 |
count += w.queueSize(); |
2689 |
} |
2690 |
} |
2691 |
return count; |
2692 |
} |
2693 |
|
2694 |
/** |
2695 |
* Returns {@code true} if there are any tasks submitted to this |
2696 |
* pool that have not yet begun executing. |
2697 |
* |
2698 |
* @return {@code true} if there are any queued submissions |
2699 |
*/ |
2700 |
public boolean hasQueuedSubmissions() { |
2701 |
WorkQueue[] ws; WorkQueue w; |
2702 |
VarHandle.acquireFence(); |
2703 |
if ((ws = workQueues) != null) { |
2704 |
for (int i = 0; i < ws.length; i += 2) { |
2705 |
if ((w = ws[i]) != null && !w.isEmpty()) |
2706 |
return true; |
2707 |
} |
2708 |
} |
2709 |
return false; |
2710 |
} |
2711 |
|
2712 |
/** |
2713 |
* Removes and returns the next unexecuted submission if one is |
2714 |
* available. This method may be useful in extensions to this |
2715 |
* class that re-assign work in systems with multiple pools. |
2716 |
* |
2717 |
* @return the next submission, or {@code null} if none |
2718 |
*/ |
2719 |
protected ForkJoinTask<?> pollSubmission() { |
2720 |
return pollScan(true); |
2721 |
} |
2722 |
|
2723 |
/** |
2724 |
* Removes all available unexecuted submitted and forked tasks |
2725 |
* from scheduling queues and adds them to the given collection, |
2726 |
* without altering their execution status. These may include |
2727 |
* artificially generated or wrapped tasks. This method is |
2728 |
* designed to be invoked only when the pool is known to be |
2729 |
* quiescent. Invocations at other times may not remove all |
2730 |
* tasks. A failure encountered while attempting to add elements |
2731 |
* to collection {@code c} may result in elements being in |
2732 |
* neither, either or both collections when the associated |
2733 |
* exception is thrown. The behavior of this operation is |
2734 |
* undefined if the specified collection is modified while the |
2735 |
* operation is in progress. |
2736 |
* |
2737 |
* @param c the collection to transfer elements into |
2738 |
* @return the number of elements transferred |
2739 |
*/ |
2740 |
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
2741 |
WorkQueue[] ws; WorkQueue w; ForkJoinTask<?> t; |
2742 |
VarHandle.acquireFence(); |
2743 |
int count = 0; |
2744 |
if ((ws = workQueues) != null) { |
2745 |
for (int i = 0; i < ws.length; ++i) { |
2746 |
if ((w = ws[i]) != null) { |
2747 |
while ((t = w.poll()) != null) { |
2748 |
c.add(t); |
2749 |
++count; |
2750 |
} |
2751 |
} |
2752 |
} |
2753 |
} |
2754 |
return count; |
2755 |
} |
2756 |
|
2757 |
/** |
2758 |
* Returns a string identifying this pool, as well as its state, |
2759 |
* including indications of run state, parallelism level, and |
2760 |
* worker and task counts. |
2761 |
* |
2762 |
* @return a string identifying this pool, as well as its state |
2763 |
*/ |
2764 |
public String toString() { |
2765 |
// Use a single pass through workQueues to collect counts |
2766 |
int md = mode; // read volatile fields first |
2767 |
long c = ctl; |
2768 |
long st = stealCount; |
2769 |
long qt = 0L, qs = 0L; int rc = 0; |
2770 |
WorkQueue[] ws; WorkQueue w; |
2771 |
if ((ws = workQueues) != null) { |
2772 |
for (int i = 0; i < ws.length; ++i) { |
2773 |
if ((w = ws[i]) != null) { |
2774 |
int size = w.queueSize(); |
2775 |
if ((i & 1) == 0) |
2776 |
qs += size; |
2777 |
else { |
2778 |
qt += size; |
2779 |
st += (long)w.nsteals & 0xffffffffL; |
2780 |
if (w.isApparentlyUnblocked()) |
2781 |
++rc; |
2782 |
} |
2783 |
} |
2784 |
} |
2785 |
} |
2786 |
|
2787 |
int pc = (md & SMASK); |
2788 |
int tc = pc + (short)(c >>> TC_SHIFT); |
2789 |
int ac = pc + (int)(c >> RC_SHIFT); |
2790 |
if (ac < 0) // ignore transient negative |
2791 |
ac = 0; |
2792 |
String level = ((md & TERMINATED) != 0 ? "Terminated" : |
2793 |
(md & STOP) != 0 ? "Terminating" : |
2794 |
(md & SHUTDOWN) != 0 ? "Shutting down" : |
2795 |
"Running"); |
2796 |
return super.toString() + |
2797 |
"[" + level + |
2798 |
", parallelism = " + pc + |
2799 |
", size = " + tc + |
2800 |
", active = " + ac + |
2801 |
", running = " + rc + |
2802 |
", steals = " + st + |
2803 |
", tasks = " + qt + |
2804 |
", submissions = " + qs + |
2805 |
"]"; |
2806 |
} |
2807 |
|
2808 |
/** |
2809 |
* Possibly initiates an orderly shutdown in which previously |
2810 |
* submitted tasks are executed, but no new tasks will be |
2811 |
* accepted. Invocation has no effect on execution state if this |
2812 |
* is the {@link #commonPool()}, and no additional effect if |
2813 |
* already shut down. Tasks that are in the process of being |
2814 |
* submitted concurrently during the course of this method may or |
2815 |
* may not be rejected. |
2816 |
* |
2817 |
* @throws SecurityException if a security manager exists and |
2818 |
* the caller is not permitted to modify threads |
2819 |
* because it does not hold {@link |
2820 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2821 |
*/ |
2822 |
public void shutdown() { |
2823 |
checkPermission(); |
2824 |
tryTerminate(false, true); |
2825 |
} |
2826 |
|
2827 |
/** |
2828 |
* Possibly attempts to cancel and/or stop all tasks, and reject |
2829 |
* all subsequently submitted tasks. Invocation has no effect on |
2830 |
* execution state if this is the {@link #commonPool()}, and no |
2831 |
* additional effect if already shut down. Otherwise, tasks that |
2832 |
* are in the process of being submitted or executed concurrently |
2833 |
* during the course of this method may or may not be |
2834 |
* rejected. This method cancels both existing and unexecuted |
2835 |
* tasks, in order to permit termination in the presence of task |
2836 |
* dependencies. So the method always returns an empty list |
2837 |
* (unlike the case for some other Executors). |
2838 |
* |
2839 |
* @return an empty list |
2840 |
* @throws SecurityException if a security manager exists and |
2841 |
* the caller is not permitted to modify threads |
2842 |
* because it does not hold {@link |
2843 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
2844 |
*/ |
2845 |
public List<Runnable> shutdownNow() { |
2846 |
checkPermission(); |
2847 |
tryTerminate(true, true); |
2848 |
return Collections.emptyList(); |
2849 |
} |
2850 |
|
2851 |
/** |
2852 |
* Returns {@code true} if all tasks have completed following shut down. |
2853 |
* |
2854 |
* @return {@code true} if all tasks have completed following shut down |
2855 |
*/ |
2856 |
public boolean isTerminated() { |
2857 |
return (mode & TERMINATED) != 0; |
2858 |
} |
2859 |
|
2860 |
/** |
2861 |
* Returns {@code true} if the process of termination has |
2862 |
* commenced but not yet completed. This method may be useful for |
2863 |
* debugging. A return of {@code true} reported a sufficient |
2864 |
* period after shutdown may indicate that submitted tasks have |
2865 |
* ignored or suppressed interruption, or are waiting for I/O, |
2866 |
* causing this executor not to properly terminate. (See the |
2867 |
* advisory notes for class {@link ForkJoinTask} stating that |
2868 |
* tasks should not normally entail blocking operations. But if |
2869 |
* they do, they must abort them on interrupt.) |
2870 |
* |
2871 |
* @return {@code true} if terminating but not yet terminated |
2872 |
*/ |
2873 |
public boolean isTerminating() { |
2874 |
int md = mode; |
2875 |
return (md & STOP) != 0 && (md & TERMINATED) == 0; |
2876 |
} |
2877 |
|
2878 |
/** |
2879 |
* Returns {@code true} if this pool has been shut down. |
2880 |
* |
2881 |
* @return {@code true} if this pool has been shut down |
2882 |
*/ |
2883 |
public boolean isShutdown() { |
2884 |
return (mode & SHUTDOWN) != 0; |
2885 |
} |
2886 |
|
2887 |
/** |
2888 |
* Blocks until all tasks have completed execution after a |
2889 |
* shutdown request, or the timeout occurs, or the current thread |
2890 |
* is interrupted, whichever happens first. Because the {@link |
2891 |
* #commonPool()} never terminates until program shutdown, when |
2892 |
* applied to the common pool, this method is equivalent to {@link |
2893 |
* #awaitQuiescence(long, TimeUnit)} but always returns {@code false}. |
2894 |
* |
2895 |
* @param timeout the maximum time to wait |
2896 |
* @param unit the time unit of the timeout argument |
2897 |
* @return {@code true} if this executor terminated and |
2898 |
* {@code false} if the timeout elapsed before termination |
2899 |
* @throws InterruptedException if interrupted while waiting |
2900 |
*/ |
2901 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
2902 |
throws InterruptedException { |
2903 |
if (Thread.interrupted()) |
2904 |
throw new InterruptedException(); |
2905 |
if (this == common) { |
2906 |
awaitQuiescence(timeout, unit); |
2907 |
return false; |
2908 |
} |
2909 |
long nanos = unit.toNanos(timeout); |
2910 |
if (isTerminated()) |
2911 |
return true; |
2912 |
if (nanos <= 0L) |
2913 |
return false; |
2914 |
long deadline = System.nanoTime() + nanos; |
2915 |
synchronized (this) { |
2916 |
for (;;) { |
2917 |
if (isTerminated()) |
2918 |
return true; |
2919 |
if (nanos <= 0L) |
2920 |
return false; |
2921 |
long millis = TimeUnit.NANOSECONDS.toMillis(nanos); |
2922 |
wait(millis > 0L ? millis : 1L); |
2923 |
nanos = deadline - System.nanoTime(); |
2924 |
} |
2925 |
} |
2926 |
} |
2927 |
|
2928 |
/** |
2929 |
* If called by a ForkJoinTask operating in this pool, equivalent |
2930 |
* in effect to {@link ForkJoinTask#helpQuiesce}. Otherwise, |
2931 |
* waits and/or attempts to assist performing tasks until this |
2932 |
* pool {@link #isQuiescent} or the indicated timeout elapses. |
2933 |
* |
2934 |
* @param timeout the maximum time to wait |
2935 |
* @param unit the time unit of the timeout argument |
2936 |
* @return {@code true} if quiescent; {@code false} if the |
2937 |
* timeout elapsed. |
2938 |
*/ |
2939 |
public boolean awaitQuiescence(long timeout, TimeUnit unit) { |
2940 |
long nanos = unit.toNanos(timeout); |
2941 |
ForkJoinWorkerThread wt; |
2942 |
Thread thread = Thread.currentThread(); |
2943 |
if ((thread instanceof ForkJoinWorkerThread) && |
2944 |
(wt = (ForkJoinWorkerThread)thread).pool == this) { |
2945 |
helpQuiescePool(wt.workQueue); |
2946 |
return true; |
2947 |
} |
2948 |
else { |
2949 |
for (long startTime = System.nanoTime();;) { |
2950 |
ForkJoinTask<?> t; |
2951 |
if ((t = pollScan(false)) != null) |
2952 |
t.doExec(); |
2953 |
else if (isQuiescent()) |
2954 |
return true; |
2955 |
else if ((System.nanoTime() - startTime) > nanos) |
2956 |
return false; |
2957 |
else |
2958 |
Thread.yield(); // cannot block |
2959 |
} |
2960 |
} |
2961 |
} |
2962 |
|
2963 |
/** |
2964 |
* Waits and/or attempts to assist performing tasks indefinitely |
2965 |
* until the {@link #commonPool()} {@link #isQuiescent}. |
2966 |
*/ |
2967 |
static void quiesceCommonPool() { |
2968 |
common.awaitQuiescence(Long.MAX_VALUE, TimeUnit.NANOSECONDS); |
2969 |
} |
2970 |
|
2971 |
/** |
2972 |
* Interface for extending managed parallelism for tasks running |
2973 |
* in {@link ForkJoinPool}s. |
2974 |
* |
2975 |
* <p>A {@code ManagedBlocker} provides two methods. Method |
2976 |
* {@link #isReleasable} must return {@code true} if blocking is |
2977 |
* not necessary. Method {@link #block} blocks the current thread |
2978 |
* if necessary (perhaps internally invoking {@code isReleasable} |
2979 |
* before actually blocking). These actions are performed by any |
2980 |
* thread invoking {@link ForkJoinPool#managedBlock(ManagedBlocker)}. |
2981 |
* The unusual methods in this API accommodate synchronizers that |
2982 |
* may, but don't usually, block for long periods. Similarly, they |
2983 |
* allow more efficient internal handling of cases in which |
2984 |
* additional workers may be, but usually are not, needed to |
2985 |
* ensure sufficient parallelism. Toward this end, |
2986 |
* implementations of method {@code isReleasable} must be amenable |
2987 |
* to repeated invocation. |
2988 |
* |
2989 |
* <p>For example, here is a ManagedBlocker based on a |
2990 |
* ReentrantLock: |
2991 |
* <pre> {@code |
2992 |
* class ManagedLocker implements ManagedBlocker { |
2993 |
* final ReentrantLock lock; |
2994 |
* boolean hasLock = false; |
2995 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
2996 |
* public boolean block() { |
2997 |
* if (!hasLock) |
2998 |
* lock.lock(); |
2999 |
* return true; |
3000 |
* } |
3001 |
* public boolean isReleasable() { |
3002 |
* return hasLock || (hasLock = lock.tryLock()); |
3003 |
* } |
3004 |
* }}</pre> |
3005 |
* |
3006 |
* <p>Here is a class that possibly blocks waiting for an |
3007 |
* item on a given queue: |
3008 |
* <pre> {@code |
3009 |
* class QueueTaker<E> implements ManagedBlocker { |
3010 |
* final BlockingQueue<E> queue; |
3011 |
* volatile E item = null; |
3012 |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
3013 |
* public boolean block() throws InterruptedException { |
3014 |
* if (item == null) |
3015 |
* item = queue.take(); |
3016 |
* return true; |
3017 |
* } |
3018 |
* public boolean isReleasable() { |
3019 |
* return item != null || (item = queue.poll()) != null; |
3020 |
* } |
3021 |
* public E getItem() { // call after pool.managedBlock completes |
3022 |
* return item; |
3023 |
* } |
3024 |
* }}</pre> |
3025 |
*/ |
3026 |
public static interface ManagedBlocker { |
3027 |
/** |
3028 |
* Possibly blocks the current thread, for example waiting for |
3029 |
* a lock or condition. |
3030 |
* |
3031 |
* @return {@code true} if no additional blocking is necessary |
3032 |
* (i.e., if isReleasable would return true) |
3033 |
* @throws InterruptedException if interrupted while waiting |
3034 |
* (the method is not required to do so, but is allowed to) |
3035 |
*/ |
3036 |
boolean block() throws InterruptedException; |
3037 |
|
3038 |
/** |
3039 |
* Returns {@code true} if blocking is unnecessary. |
3040 |
* @return {@code true} if blocking is unnecessary |
3041 |
*/ |
3042 |
boolean isReleasable(); |
3043 |
} |
3044 |
|
3045 |
/** |
3046 |
* Runs the given possibly blocking task. When {@linkplain |
3047 |
* ForkJoinTask#inForkJoinPool() running in a ForkJoinPool}, this |
3048 |
* method possibly arranges for a spare thread to be activated if |
3049 |
* necessary to ensure sufficient parallelism while the current |
3050 |
* thread is blocked in {@link ManagedBlocker#block blocker.block()}. |
3051 |
* |
3052 |
* <p>This method repeatedly calls {@code blocker.isReleasable()} and |
3053 |
* {@code blocker.block()} until either method returns {@code true}. |
3054 |
* Every call to {@code blocker.block()} is preceded by a call to |
3055 |
* {@code blocker.isReleasable()} that returned {@code false}. |
3056 |
* |
3057 |
* <p>If not running in a ForkJoinPool, this method is |
3058 |
* behaviorally equivalent to |
3059 |
* <pre> {@code |
3060 |
* while (!blocker.isReleasable()) |
3061 |
* if (blocker.block()) |
3062 |
* break;}</pre> |
3063 |
* |
3064 |
* If running in a ForkJoinPool, the pool may first be expanded to |
3065 |
* ensure sufficient parallelism available during the call to |
3066 |
* {@code blocker.block()}. |
3067 |
* |
3068 |
* @param blocker the blocker task |
3069 |
* @throws InterruptedException if {@code blocker.block()} did so |
3070 |
*/ |
3071 |
public static void managedBlock(ManagedBlocker blocker) |
3072 |
throws InterruptedException { |
3073 |
if (blocker == null) throw new NullPointerException(); |
3074 |
ForkJoinPool p; |
3075 |
ForkJoinWorkerThread wt; |
3076 |
WorkQueue w; |
3077 |
Thread t = Thread.currentThread(); |
3078 |
if ((t instanceof ForkJoinWorkerThread) && |
3079 |
(p = (wt = (ForkJoinWorkerThread)t).pool) != null && |
3080 |
(w = wt.workQueue) != null) { |
3081 |
int block; |
3082 |
while (!blocker.isReleasable()) { |
3083 |
if ((block = p.tryCompensate(w)) != 0) { |
3084 |
try { |
3085 |
do {} while (!blocker.isReleasable() && |
3086 |
!blocker.block()); |
3087 |
} finally { |
3088 |
CTL.getAndAdd(p, (block > 0) ? RC_UNIT : 0L); |
3089 |
} |
3090 |
break; |
3091 |
} |
3092 |
} |
3093 |
} |
3094 |
else { |
3095 |
do {} while (!blocker.isReleasable() && |
3096 |
!blocker.block()); |
3097 |
} |
3098 |
} |
3099 |
|
3100 |
/** |
3101 |
* If the given executor is a ForkJoinPool, poll and execute |
3102 |
* AsynchronousCompletionTasks from worker's queue until none are |
3103 |
* available or blocker is released. |
3104 |
*/ |
3105 |
static void helpAsyncBlocker(Executor e, ManagedBlocker blocker) { |
3106 |
if (e instanceof ForkJoinPool) { |
3107 |
WorkQueue w; ForkJoinWorkerThread wt; WorkQueue[] ws; int r, n; |
3108 |
ForkJoinPool p = (ForkJoinPool)e; |
3109 |
Thread thread = Thread.currentThread(); |
3110 |
if (thread instanceof ForkJoinWorkerThread && |
3111 |
(wt = (ForkJoinWorkerThread)thread).pool == p) |
3112 |
w = wt.workQueue; |
3113 |
else if ((r = ThreadLocalRandom.getProbe()) != 0 && |
3114 |
(ws = p.workQueues) != null && (n = ws.length) > 0) |
3115 |
w = ws[(n - 1) & r & SQMASK]; |
3116 |
else |
3117 |
w = null; |
3118 |
if (w != null) |
3119 |
w.helpAsyncBlocker(blocker); |
3120 |
} |
3121 |
} |
3122 |
|
3123 |
// AbstractExecutorService overrides. These rely on undocumented |
3124 |
// fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
3125 |
// implement RunnableFuture. |
3126 |
|
3127 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
3128 |
return new ForkJoinTask.AdaptedRunnable<T>(runnable, value); |
3129 |
} |
3130 |
|
3131 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
3132 |
return new ForkJoinTask.AdaptedCallable<T>(callable); |
3133 |
} |
3134 |
|
3135 |
// VarHandle mechanics |
3136 |
private static final VarHandle CTL; |
3137 |
private static final VarHandle MODE; |
3138 |
static final VarHandle QA; |
3139 |
|
3140 |
static { |
3141 |
try { |
3142 |
MethodHandles.Lookup l = MethodHandles.lookup(); |
3143 |
CTL = l.findVarHandle(ForkJoinPool.class, "ctl", long.class); |
3144 |
MODE = l.findVarHandle(ForkJoinPool.class, "mode", int.class); |
3145 |
QA = MethodHandles.arrayElementVarHandle(ForkJoinTask[].class); |
3146 |
} catch (ReflectiveOperationException e) { |
3147 |
throw new Error(e); |
3148 |
} |
3149 |
|
3150 |
// Reduce the risk of rare disastrous classloading in first call to |
3151 |
// LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773 |
3152 |
Class<?> ensureLoaded = LockSupport.class; |
3153 |
|
3154 |
int commonMaxSpares = DEFAULT_COMMON_MAX_SPARES; |
3155 |
try { |
3156 |
String p = System.getProperty |
3157 |
("java.util.concurrent.ForkJoinPool.common.maximumSpares"); |
3158 |
if (p != null) |
3159 |
commonMaxSpares = Integer.parseInt(p); |
3160 |
} catch (Exception ignore) {} |
3161 |
COMMON_MAX_SPARES = commonMaxSpares; |
3162 |
|
3163 |
defaultForkJoinWorkerThreadFactory = |
3164 |
new DefaultForkJoinWorkerThreadFactory(); |
3165 |
modifyThreadPermission = new RuntimePermission("modifyThread"); |
3166 |
|
3167 |
common = AccessController.doPrivileged(new PrivilegedAction<>() { |
3168 |
public ForkJoinPool run() { |
3169 |
return new ForkJoinPool((byte)0); }}); |
3170 |
|
3171 |
COMMON_PARALLELISM = Math.max(common.mode & SMASK, 1); |
3172 |
} |
3173 |
|
3174 |
/** |
3175 |
* Factory for innocuous worker threads. |
3176 |
*/ |
3177 |
private static final class InnocuousForkJoinWorkerThreadFactory |
3178 |
implements ForkJoinWorkerThreadFactory { |
3179 |
|
3180 |
/** |
3181 |
* An ACC to restrict permissions for the factory itself. |
3182 |
* The constructed workers have no permissions set. |
3183 |
*/ |
3184 |
private static final AccessControlContext ACC = contextWithPermissions( |
3185 |
modifyThreadPermission, |
3186 |
new RuntimePermission("enableContextClassLoaderOverride"), |
3187 |
new RuntimePermission("modifyThreadGroup"), |
3188 |
new RuntimePermission("getClassLoader"), |
3189 |
new RuntimePermission("setContextClassLoader")); |
3190 |
|
3191 |
public final ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
3192 |
return AccessController.doPrivileged( |
3193 |
new PrivilegedAction<>() { |
3194 |
public ForkJoinWorkerThread run() { |
3195 |
return new ForkJoinWorkerThread. |
3196 |
InnocuousForkJoinWorkerThread(pool); }}, |
3197 |
ACC); |
3198 |
} |
3199 |
} |
3200 |
} |