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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/licenses/publicdomain |
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*/ |
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|
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package jsr166y; |
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|
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import java.util.concurrent.*; |
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|
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import java.util.ArrayList; |
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import java.util.Arrays; |
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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.concurrent.locks.LockSupport; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.CountDownLatch; |
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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 subtasks created by other active tasks (eventually blocking |
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* waiting for work if none exist). This enables efficient processing |
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* when most tasks spawn other subtasks (as do most {@code |
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* ForkJoinTask}s). When setting <em>asyncMode</em> to true in |
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* constructors, {@code ForkJoinPool}s may also be appropriate for use |
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* with event-style tasks that are never joined. |
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* |
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* <p>A {@code ForkJoinPool} is constructed with a given target |
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* parallelism level; by default, equal to the number of available |
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* processors. The pool attempts to maintain enough active (or |
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* available) threads by dynamically adding, suspending, or resuming |
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* internal worker threads, even if some tasks are stalled waiting to |
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* join others. However, no such adjustments are guaranteed in the |
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* face of blocked IO or other unmanaged synchronization. The nested |
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* {@link ManagedBlocker} interface enables extension of the kinds of |
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* synchronization accommodated. |
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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 |
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* table. These are designed to be used by clients not already engaged |
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* in fork/join computations in the current pool. The main forms of |
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* these methods accept instances of {@code ForkJoinTask}, but |
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* 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 |
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* <em>NOT</em> use these pool execution methods, but instead use the |
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* within-computation forms listed in the table. |
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* |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <tr> |
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* <td></td> |
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* <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
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* <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
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* </tr> |
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* <tr> |
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* <td> <b>Arange async execution</td> |
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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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* <td> <b>Await and obtain result</td> |
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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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* <td> <b>Arrange exec and obtain Future</td> |
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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><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is |
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* used for all parallel task execution in a program or subsystem. |
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* Otherwise, use would not usually outweigh the construction and |
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* bookkeeping overhead of creating a large set of threads. For |
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* example, a common pool could be used for the {@code SortTasks} |
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* illustrated in {@link RecursiveAction}. Because {@code |
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* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon |
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* daemon} mode, there is typically no need to explicitly {@link |
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* #shutdown} such a pool upon program exit. |
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* |
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* <pre> |
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* static final ForkJoinPool mainPool = new ForkJoinPool(); |
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* ... |
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* public void sort(long[] array) { |
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* mainPool.invoke(new SortTask(array, 0, array.length)); |
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* } |
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* </pre> |
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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 exhuasted. |
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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 provides the central bookkeeping and control for a |
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* set of worker threads: Submissions from non-FJ threads enter |
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* into a submission queue. Workers take these tasks and typically |
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* split them into subtasks that may be stolen by other workers. |
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* The main work-stealing mechanics implemented in class |
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* ForkJoinWorkerThread give first priority to processing tasks |
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* from their own queues (LIFO or FIFO, depending on mode), then |
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* to randomized FIFO steals of tasks in other worker queues, and |
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* lastly to new submissions. These mechanics do not consider |
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* affinities, loads, cache localities, etc, so rarely provide the |
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* best possible performance on a given machine, but portably |
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* provide good throughput by averaging over these factors. |
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* (Further, even if we did try to use such information, we do not |
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* usually have a basis for exploiting it. For example, some sets |
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* of tasks profit from cache affinities, but others are harmed by |
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* cache pollution effects.) |
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* |
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* Beyond work-stealing support and essential bookkeeping, the |
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* main responsibility of this framework is to take actions when |
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* one worker is waiting to join a task stolen (or always held by) |
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* another. Becauae we are multiplexing many tasks on to a pool |
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* of workers, we can't just let them block (as in Thread.join). |
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* We also cannot just reassign the joiner's run-time stack with |
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* another and replace it later, which would be a form of |
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* "continuation", that even if possible is not necessarily a good |
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* idea. Given that the creation costs of most threads on most |
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* systems mainly surrounds setting up runtime stacks, thread |
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* creation and switching is usually not much more expensive than |
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* stack creation and switching, and is more flexible). Instead we |
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* combine two tactics: |
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* |
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* Helping: Arranging for the joiner to execute some task that it |
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* would be running if the steal had not occurred. Method |
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* ForkJoinWorkerThread.helpJoinTask tracks joining->stealing |
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* links to try to find such a task. |
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* |
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* Compensating: Unless there are already enough live threads, |
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* method helpMaintainParallelism() may create or or |
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* re-activate a spare thread to compensate for blocked |
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* joiners until they unblock. |
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* |
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* Because the determining existence of conservatively safe |
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* helping targets, the availability of already-created spares, |
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* and the apparent need to create new spares are all racy and |
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* require heuristic guidance, we rely on multiple retries of |
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* each. Further, because it is impossible to keep exactly the |
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* target (parallelism) number of threads running at any given |
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* time, we allow compensation during joins to fail, and enlist |
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* all other threads to help out whenever they are not otherwise |
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* occupied (i.e., mainly in method preStep). |
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* |
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* The ManagedBlocker extension API can't use helping so relies |
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* only on compensation in method awaitBlocker. |
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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 steal tasks from each |
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* other. We do not want to negate this by creating bottlenecks |
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* implementing other management responsibilities. So we use a |
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* collection of techniques that avoid, reduce, or cope well with |
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* contention. These entail several instances of bit-packing into |
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* CASable fields to maintain only the minimally required |
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* atomicity. To enable such packing, we restrict maximum |
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* parallelism to (1<<15)-1 (enabling twice this (to accommodate |
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* unbalanced increments and decrements) to fit into a 16 bit |
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* field, which is far in excess of normal operating range. Even |
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* though updates to some of these bookkeeping fields do sometimes |
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* contend with each other, they don't normally cache-contend with |
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* updates to others enough to warrant memory padding or |
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* isolation. So they are all held as fields of ForkJoinPool |
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* objects. The main capabilities are as follows: |
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* |
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* 1. Creating and removing workers. Workers are recorded in the |
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* "workers" array. This is an array as opposed to some other data |
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* structure to support index-based random steals by workers. |
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* Updates to the array recording new workers and unrecording |
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* terminated ones are protected from each other by a lock |
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* (workerLock) but the array is otherwise concurrently readable, |
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* and accessed directly by workers. 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. Currently, all worker thread |
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* creation is on-demand, triggered by task submissions, |
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* replacement of terminated workers, and/or compensation for |
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* blocked workers. However, all other support code is set up to |
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* work with other policies. |
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* |
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* To ensure that we do not hold on to worker references that |
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* would prevent GC, ALL accesses to workers are via indices into |
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* the workers array (which is one source of some of the unusual |
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* code constructions here). In essence, the workers array serves |
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* as a WeakReference mechanism. Thus for example the event queue |
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* stores worker indices, not worker references. Access to the |
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* workers in associated methods (for example releaseEventWaiters) |
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* must both index-check and null-check the IDs. All such accesses |
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* ignore bad IDs by returning out early from what they are doing, |
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* since this can only be associated with shutdown, in which case |
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* it is OK to give up. On termination, we just clobber these |
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* data structures without trying to use them. |
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* |
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* 2. Bookkeeping for dynamically adding and removing workers. We |
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* aim to approximately maintain the given level of parallelism. |
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* When some workers are known to be blocked (on joins or via |
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* ManagedBlocker), we may create or resume others to take their |
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* place until they unblock (see below). Implementing this |
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* requires counts of the number of "running" threads (i.e., those |
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* that are neither blocked nor artifically suspended) as well as |
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* the total number. These two values are packed into one field, |
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* "workerCounts" because we need accurate snapshots when deciding |
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* to create, resume or suspend. Note however that the |
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* correspondance of these counts to reality is not guaranteed. In |
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* particular updates for unblocked threads may lag until they |
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* actually wake up. |
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* |
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* 3. Maintaining global run state. The run state of the pool |
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* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to |
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* those in other Executor implementations, as well as a count of |
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* "active" workers -- those that are, or soon will be, or |
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* recently were executing tasks. The runLevel and active count |
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* are packed together in order to correctly trigger shutdown and |
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* termination. Without care, active counts can be subject to very |
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* high contention. We substantially reduce this contention by |
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* relaxing update rules. A worker must claim active status |
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* prospectively, by activating if it sees that a submitted or |
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* stealable task exists (it may find after activating that the |
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* task no longer exists). It stays active while processing this |
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* task (if it exists) and any other local subtasks it produces, |
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* until it cannot find any other tasks. It then tries |
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* inactivating (see method preStep), but upon update contention |
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* instead scans for more tasks, later retrying inactivation if it |
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* doesn't find any. |
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* |
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* 4. Managing idle workers waiting for tasks. We cannot let |
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* workers spin indefinitely scanning for tasks when none are |
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* available. On the other hand, we must quickly prod them into |
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* action when new tasks are submitted or generated. We |
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* park/unpark these idle workers using an event-count scheme. |
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* Field eventCount is incremented upon events that may enable |
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* workers that previously could not find a task to now find one: |
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* Submission of a new task to the pool, or another worker pushing |
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* a task onto a previously empty queue. (We also use this |
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* mechanism for termination actions that require wakeups of idle |
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* workers). Each worker maintains its last known event count, |
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* and blocks when a scan for work did not find a task AND its |
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* lastEventCount matches the current eventCount. Waiting idle |
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* workers are recorded in a variant of Treiber stack headed by |
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* field eventWaiters which, when nonzero, encodes the thread |
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* index and count awaited for by the worker thread most recently |
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* calling eventSync. This thread in turn has a record (field |
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* nextEventWaiter) for the next waiting worker. In addition to |
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* allowing simpler decisions about need for wakeup, the event |
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* count bits in eventWaiters serve the role of tags to avoid ABA |
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* errors in Treiber stacks. To reduce delays in task diffusion, |
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* workers not otherwise occupied may invoke method |
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* releaseEventWaiters, that removes and signals (unparks) workers |
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* not waiting on current count. To reduce stalls, To minimize |
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* task production stalls associate with signalling, any worker |
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* pushing a task on an empty queue invokes the weaker method |
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* signalWork, that only releases idle workers until it detects |
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* interference by other threads trying to release, and lets them |
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* take over. The net effect is a tree-like diffusion of signals, |
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* where released threads (and possibly others) help with unparks. |
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* To further reduce contention effects a bit, failed CASes to |
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* increment field eventCount are tolerated without retries. |
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* Conceptually they are merged into the same event, which is OK |
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* when their only purpose is to enable workers to scan for work. |
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* |
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* 5. Managing suspension of extra workers. When a worker is about |
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* to block waiting for a join (or via ManagedBlockers), we may |
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* create a new thread to maintain parallelism level, or at least |
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* avoid starvation. Usually, extra threads are needed for only |
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* very short periods, yet join dependencies are such that we |
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* sometimes need them in bursts. Rather than create new threads |
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* each time this happens, we suspend no-longer-needed extra ones |
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* as "spares". For most purposes, we don't distinguish "extra" |
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* spare threads from normal "core" threads: On each call to |
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* preStep (the only point at which we can do this) a worker |
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* checks to see if there are now too many running workers, and if |
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* so, suspends itself. Method helpMaintainParallelism looks for |
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* suspended threads to resume before considering creating a new |
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* replacement. The spares themselves are encoded on another |
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* variant of a Treiber Stack, headed at field "spareWaiters". |
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* Note that the use of spares is intrinsically racy. One thread |
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* may become a spare at about the same time as another is |
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* needlessly being created. We counteract this and related slop |
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* in part by requiring resumed spares to immediately recheck (in |
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* preStep) to see whether they they should re-suspend. To avoid |
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* long-term build-up of spares, the oldest spare (see |
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* ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if |
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* not signalled and calls tryTrimSpare, which uses two different |
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* thresholds: Always killing if the number of spares is greater |
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* that 25% of total, and killing others only at a slower rate |
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* (UNUSED_SPARE_TRIM_RATE_NANOS). |
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* |
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* 6. Deciding when to create new workers. The main dynamic |
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* control in this class is deciding when to create extra threads |
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* in method helpMaintainParallelism. We would like to keep |
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* exactly #parallelism threads running, which is an impossble |
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* task. We always need to create one when the number of running |
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* threads would become zero and all workers are busy. Beyond |
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* this, we must rely on heuristics that work well in the the |
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* presence of transients phenomena such as GC stalls, dynamic |
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* compilation, and wake-up lags. These transients are extremely |
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* common -- we are normally trying to fully saturate the CPUs on |
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* a machine, so almost any activity other than running tasks |
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* impedes accuracy. Our main defense is to allow some slack in |
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* creation thresholds, using rules that reflect the fact that the |
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* more threads we have running, the more likely that we are |
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* underestimating the number running threads. The rules also |
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* better cope with the fact that some of the methods in this |
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* class tend to never become compiled (but are interpreted), so |
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* some components of the entire set of controls might execute 100 |
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* times faster than others. And similarly for cases where the |
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* apparent lack of work is just due to GC stalls and other |
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* transient system activity. |
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* |
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* Beware that there is a lot of representation-level coupling |
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* among classes ForkJoinPool, ForkJoinWorkerThread, and |
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* ForkJoinTask. For example, direct access to "workers" array by |
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* workers, and direct access to ForkJoinTask.status by both |
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* ForkJoinPool and ForkJoinWorkerThread. There is little point |
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* trying to reduce this, since any associated future changes in |
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* representations will need to be accompanied by algorithmic |
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* changes anyway. |
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* |
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* Style notes: There are lots of inline assignments (of form |
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* "while ((local = field) != 0)") which are usually the simplest |
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* way to ensure the required read orderings (which are sometimes |
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* critical). Also several occurrences of the unusual "do {} |
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* while(!cas...)" which is the simplest way to force an update of |
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* a CAS'ed variable. There are also other coding oddities that |
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* help some methods perform reasonably even when interpreted (not |
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* compiled), at the expense of some messy constructions that |
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* reduce byte code counts. |
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* |
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* The order of declarations in this file is: (1) statics (2) |
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* fields (along with constants used when unpacking some of them) |
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* (3) internal control methods (4) callbacks and other support |
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* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported |
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* methods (plus a few little helpers). |
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*/ |
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|
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/** |
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* Factory for creating new {@link ForkJoinWorkerThread}s. |
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* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
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* for {@code ForkJoinWorkerThread} subclasses that extend base |
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* functionality or initialize threads with different contexts. |
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*/ |
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public static interface ForkJoinWorkerThreadFactory { |
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/** |
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* Returns a new worker thread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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* @throws NullPointerException if the pool is null |
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*/ |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
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} |
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|
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/** |
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* Default ForkJoinWorkerThreadFactory implementation; creates a |
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* new ForkJoinWorkerThread. |
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*/ |
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static class DefaultForkJoinWorkerThreadFactory |
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implements ForkJoinWorkerThreadFactory { |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
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return new ForkJoinWorkerThread(pool); |
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} |
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} |
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|
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/** |
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* Creates a new ForkJoinWorkerThread. This factory is used unless |
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* overridden in ForkJoinPool constructors. |
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*/ |
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public static final ForkJoinWorkerThreadFactory |
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defaultForkJoinWorkerThreadFactory = |
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new DefaultForkJoinWorkerThreadFactory(); |
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|
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/** |
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* Permission required for callers of methods that may start or |
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* kill threads. |
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*/ |
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private static final RuntimePermission modifyThreadPermission = |
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new RuntimePermission("modifyThread"); |
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|
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/** |
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* If there is a security manager, makes sure caller has |
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* permission to modify threads. |
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*/ |
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private static void checkPermission() { |
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SecurityManager security = System.getSecurityManager(); |
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if (security != null) |
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security.checkPermission(modifyThreadPermission); |
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} |
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|
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/** |
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* Generator for assigning sequence numbers as pool names. |
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*/ |
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private static final AtomicInteger poolNumberGenerator = |
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new AtomicInteger(); |
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|
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/** |
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* Absolute bound for parallelism level. Twice this number plus |
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* one (i.e., 0xfff) must fit into a 16bit field to enable |
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* word-packing for some counts and indices. |
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*/ |
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private static final int MAX_WORKERS = 0x7fff; |
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|
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/** |
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* Array holding all worker threads in the pool. Array size must |
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* be a power of two. Updates and replacements are protected by |
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* workerLock, but the array is always kept in a consistent enough |
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* state to be randomly accessed without locking by workers |
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* performing work-stealing, as well as other traversal-based |
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* methods in this class. All readers must tolerate that some |
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* array slots may be null. |
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*/ |
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volatile ForkJoinWorkerThread[] workers; |
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|
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/** |
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* Queue for external submissions. |
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*/ |
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private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
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|
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/** |
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* Lock protecting updates to workers array. |
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*/ |
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private final ReentrantLock workerLock; |
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|
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/** |
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* Latch released upon termination. |
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*/ |
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private final Phaser termination; |
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|
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/** |
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* Creation factory for worker threads. |
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*/ |
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private final ForkJoinWorkerThreadFactory factory; |
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|
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/** |
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* Sum of per-thread steal counts, updated only when threads are |
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* idle or terminating. |
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*/ |
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private volatile long stealCount; |
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|
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/** |
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* The last nanoTime that a spare thread was trimmed |
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*/ |
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private volatile long trimTime; |
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|
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/** |
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* The rate at which to trim unused spares |
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*/ |
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static final long UNUSED_SPARE_TRIM_RATE_NANOS = |
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1000L * 1000L * 1000L; // 1 sec |
475 |
|
476 |
/** |
477 |
* Encoded record of top of treiber stack of threads waiting for |
478 |
* events. The top 32 bits contain the count being waited for. The |
479 |
* bottom 16 bits contains one plus the pool index of waiting |
480 |
* worker thread. (Bits 16-31 are unused.) |
481 |
*/ |
482 |
private volatile long eventWaiters; |
483 |
|
484 |
private static final int EVENT_COUNT_SHIFT = 32; |
485 |
private static final long WAITER_ID_MASK = (1L << 16) - 1L; |
486 |
|
487 |
/** |
488 |
* A counter for events that may wake up worker threads: |
489 |
* - Submission of a new task to the pool |
490 |
* - A worker pushing a task on an empty queue |
491 |
* - termination |
492 |
*/ |
493 |
private volatile int eventCount; |
494 |
|
495 |
/** |
496 |
* Encoded record of top of treiber stack of spare threads waiting |
497 |
* for resumption. The top 16 bits contain an arbitrary count to |
498 |
* avoid ABA effects. The bottom 16bits contains one plus the pool |
499 |
* index of waiting worker thread. |
500 |
*/ |
501 |
private volatile int spareWaiters; |
502 |
|
503 |
private static final int SPARE_COUNT_SHIFT = 16; |
504 |
private static final int SPARE_ID_MASK = (1 << 16) - 1; |
505 |
|
506 |
/** |
507 |
* Lifecycle control. The low word contains the number of workers |
508 |
* that are (probably) executing tasks. This value is atomically |
509 |
* incremented before a worker gets a task to run, and decremented |
510 |
* when worker has no tasks and cannot find any. Bits 16-18 |
511 |
* contain runLevel value. When all are zero, the pool is |
512 |
* running. Level transitions are monotonic (running -> shutdown |
513 |
* -> terminating -> terminated) so each transition adds a bit. |
514 |
* These are bundled together to ensure consistent read for |
515 |
* termination checks (i.e., that runLevel is at least SHUTDOWN |
516 |
* and active threads is zero). |
517 |
*/ |
518 |
private volatile int runState; |
519 |
|
520 |
// Note: The order among run level values matters. |
521 |
private static final int RUNLEVEL_SHIFT = 16; |
522 |
private static final int SHUTDOWN = 1 << RUNLEVEL_SHIFT; |
523 |
private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1); |
524 |
private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2); |
525 |
private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1; |
526 |
private static final int ONE_ACTIVE = 1; // active update delta |
527 |
|
528 |
/** |
529 |
* Holds number of total (i.e., created and not yet terminated) |
530 |
* and running (i.e., not blocked on joins or other managed sync) |
531 |
* threads, packed together to ensure consistent snapshot when |
532 |
* making decisions about creating and suspending spare |
533 |
* threads. Updated only by CAS. Note that adding a new worker |
534 |
* requires incrementing both counts, since workers start off in |
535 |
* running state. |
536 |
*/ |
537 |
private volatile int workerCounts; |
538 |
|
539 |
private static final int TOTAL_COUNT_SHIFT = 16; |
540 |
private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1; |
541 |
private static final int ONE_RUNNING = 1; |
542 |
private static final int ONE_TOTAL = 1 << TOTAL_COUNT_SHIFT; |
543 |
|
544 |
/** |
545 |
* The target parallelism level. |
546 |
* Accessed directly by ForkJoinWorkerThreads. |
547 |
*/ |
548 |
final int parallelism; |
549 |
|
550 |
/** |
551 |
* True if use local fifo, not default lifo, for local polling |
552 |
* Read by, and replicated by ForkJoinWorkerThreads |
553 |
*/ |
554 |
final boolean locallyFifo; |
555 |
|
556 |
/** |
557 |
* The uncaught exception handler used when any worker abruptly |
558 |
* terminates. |
559 |
*/ |
560 |
private final Thread.UncaughtExceptionHandler ueh; |
561 |
|
562 |
/** |
563 |
* Pool number, just for assigning useful names to worker threads |
564 |
*/ |
565 |
private final int poolNumber; |
566 |
|
567 |
|
568 |
// Utilities for CASing fields. Note that several of these |
569 |
// are manually inlined by callers |
570 |
|
571 |
/** |
572 |
* Increments running count part of workerCounts |
573 |
*/ |
574 |
final void incrementRunningCount() { |
575 |
int c; |
576 |
do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
577 |
c = workerCounts, |
578 |
c + ONE_RUNNING)); |
579 |
} |
580 |
|
581 |
/** |
582 |
* Tries to decrement running count unless already zero |
583 |
*/ |
584 |
final boolean tryDecrementRunningCount() { |
585 |
int wc = workerCounts; |
586 |
if ((wc & RUNNING_COUNT_MASK) == 0) |
587 |
return false; |
588 |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
589 |
wc, wc - ONE_RUNNING); |
590 |
} |
591 |
|
592 |
/** |
593 |
* Forces decrement of encoded workerCounts, awaiting nonzero if |
594 |
* (rarely) necessary when other count updates lag. |
595 |
* |
596 |
* @param dr -- either zero or ONE_RUNNING |
597 |
* @param dt == either zero or ONE_TOTAL |
598 |
*/ |
599 |
private void decrementWorkerCounts(int dr, int dt) { |
600 |
for (;;) { |
601 |
int wc = workerCounts; |
602 |
if (wc == 0 && (runState & TERMINATED) != 0) |
603 |
return; // lagging termination on a backout |
604 |
if ((wc & RUNNING_COUNT_MASK) - dr < 0 || |
605 |
(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) |
606 |
Thread.yield(); |
607 |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
608 |
wc, wc - (dr + dt))) |
609 |
return; |
610 |
} |
611 |
} |
612 |
|
613 |
/** |
614 |
* Increments event count |
615 |
*/ |
616 |
private void advanceEventCount() { |
617 |
int c; |
618 |
do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset, |
619 |
c = eventCount, c+1)); |
620 |
} |
621 |
|
622 |
/** |
623 |
* Tries incrementing active count; fails on contention. |
624 |
* Called by workers before executing tasks. |
625 |
* |
626 |
* @return true on success |
627 |
*/ |
628 |
final boolean tryIncrementActiveCount() { |
629 |
int c; |
630 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
631 |
c = runState, c + ONE_ACTIVE); |
632 |
} |
633 |
|
634 |
/** |
635 |
* Tries decrementing active count; fails on contention. |
636 |
* Called when workers cannot find tasks to run. |
637 |
*/ |
638 |
final boolean tryDecrementActiveCount() { |
639 |
int c; |
640 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
641 |
c = runState, c - ONE_ACTIVE); |
642 |
} |
643 |
|
644 |
/** |
645 |
* Advances to at least the given level. Returns true if not |
646 |
* already in at least the given level. |
647 |
*/ |
648 |
private boolean advanceRunLevel(int level) { |
649 |
for (;;) { |
650 |
int s = runState; |
651 |
if ((s & level) != 0) |
652 |
return false; |
653 |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level)) |
654 |
return true; |
655 |
} |
656 |
} |
657 |
|
658 |
// workers array maintenance |
659 |
|
660 |
/** |
661 |
* Records and returns a workers array index for new worker. |
662 |
*/ |
663 |
private int recordWorker(ForkJoinWorkerThread w) { |
664 |
// Try using slot totalCount-1. If not available, scan and/or resize |
665 |
int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1; |
666 |
final ReentrantLock lock = this.workerLock; |
667 |
lock.lock(); |
668 |
try { |
669 |
ForkJoinWorkerThread[] ws = workers; |
670 |
int n = ws.length; |
671 |
if (k < 0 || k >= n || ws[k] != null) { |
672 |
for (k = 0; k < n && ws[k] != null; ++k) |
673 |
; |
674 |
if (k == n) |
675 |
ws = Arrays.copyOf(ws, n << 1); |
676 |
} |
677 |
ws[k] = w; |
678 |
workers = ws; // volatile array write ensures slot visibility |
679 |
} finally { |
680 |
lock.unlock(); |
681 |
} |
682 |
return k; |
683 |
} |
684 |
|
685 |
/** |
686 |
* Nulls out record of worker in workers array |
687 |
*/ |
688 |
private void forgetWorker(ForkJoinWorkerThread w) { |
689 |
int idx = w.poolIndex; |
690 |
// Locking helps method recordWorker avoid unecessary expansion |
691 |
final ReentrantLock lock = this.workerLock; |
692 |
lock.lock(); |
693 |
try { |
694 |
ForkJoinWorkerThread[] ws = workers; |
695 |
if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify |
696 |
ws[idx] = null; |
697 |
} finally { |
698 |
lock.unlock(); |
699 |
} |
700 |
} |
701 |
|
702 |
// adding and removing workers |
703 |
|
704 |
/** |
705 |
* Tries to create and add new worker. Assumes that worker counts |
706 |
* are already updated to accommodate the worker, so adjusts on |
707 |
* failure. |
708 |
*/ |
709 |
private void addWorker() { |
710 |
ForkJoinWorkerThread w = null; |
711 |
try { |
712 |
w = factory.newThread(this); |
713 |
} finally { // Adjust on either null or exceptional factory return |
714 |
if (w == null) { |
715 |
decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL); |
716 |
tryTerminate(false); // in case of failure during shutdown |
717 |
} |
718 |
} |
719 |
if (w != null) |
720 |
w.start(recordWorker(w), ueh); |
721 |
} |
722 |
|
723 |
/** |
724 |
* Final callback from terminating worker. Removes record of |
725 |
* worker from array, and adjusts counts. If pool is shutting |
726 |
* down, tries to complete terminatation. |
727 |
* |
728 |
* @param w the worker |
729 |
*/ |
730 |
final void workerTerminated(ForkJoinWorkerThread w) { |
731 |
forgetWorker(w); |
732 |
decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL); |
733 |
while (w.stealCount != 0) // collect final count |
734 |
tryAccumulateStealCount(w); |
735 |
tryTerminate(false); |
736 |
} |
737 |
|
738 |
// Waiting for and signalling events |
739 |
|
740 |
/** |
741 |
* Releases workers blocked on a count not equal to current count. |
742 |
* Normally called after precheck that eventWaiters isn't zero to |
743 |
* avoid wasted array checks. |
744 |
* |
745 |
* @param signalling true if caller is a signalling worker so can |
746 |
* exit upon (conservatively) detected contention by other threads |
747 |
* who will continue to release |
748 |
*/ |
749 |
private void releaseEventWaiters(boolean signalling) { |
750 |
ForkJoinWorkerThread[] ws = workers; |
751 |
int n = ws.length; |
752 |
long h; // head of stack |
753 |
ForkJoinWorkerThread w; int id, ec; |
754 |
while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 && |
755 |
(int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) && |
756 |
id < n && (w = ws[id]) != null) { |
757 |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
758 |
h, h = w.nextWaiter)) |
759 |
LockSupport.unpark(w); |
760 |
if (signalling && (eventCount != ec || eventWaiters != h)) |
761 |
break; |
762 |
} |
763 |
} |
764 |
|
765 |
/** |
766 |
* Tries to advance eventCount and releases waiters. Called only |
767 |
* from workers. |
768 |
*/ |
769 |
final void signalWork() { |
770 |
int c; // try to increment event count -- CAS failure OK |
771 |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1); |
772 |
if (eventWaiters != 0L) |
773 |
releaseEventWaiters(true); |
774 |
} |
775 |
|
776 |
/** |
777 |
* Blocks worker until terminating or event count |
778 |
* advances from last value held by worker |
779 |
* |
780 |
* @param w the calling worker thread |
781 |
*/ |
782 |
private void eventSync(ForkJoinWorkerThread w) { |
783 |
int wec = w.lastEventCount; |
784 |
long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1)); |
785 |
long h; |
786 |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
787 |
((h = eventWaiters) == 0L || |
788 |
(int)(h >>> EVENT_COUNT_SHIFT) == wec) && |
789 |
eventCount == wec) { |
790 |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
791 |
w.nextWaiter = h, nh)) { |
792 |
while (runState < TERMINATING && eventCount == wec) { |
793 |
if (!tryAccumulateStealCount(w)) // transfer while idle |
794 |
continue; |
795 |
Thread.interrupted(); // clear/ignore interrupt |
796 |
if (eventCount != wec) |
797 |
break; |
798 |
LockSupport.park(w); |
799 |
} |
800 |
break; |
801 |
} |
802 |
} |
803 |
w.lastEventCount = eventCount; |
804 |
} |
805 |
|
806 |
// Maintaining spares |
807 |
|
808 |
/** |
809 |
* Pushes worker onto the spare stack |
810 |
*/ |
811 |
final void pushSpare(ForkJoinWorkerThread w) { |
812 |
int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1); |
813 |
do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
814 |
w.nextSpare = spareWaiters,ns)); |
815 |
} |
816 |
|
817 |
/** |
818 |
* Tries (once) to resume a spare if running count is less than |
819 |
* target parallelism. Fails on contention or stale workers. |
820 |
*/ |
821 |
private void tryResumeSpare() { |
822 |
int sw, id; |
823 |
ForkJoinWorkerThread w; |
824 |
ForkJoinWorkerThread[] ws; |
825 |
if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
826 |
id < (ws = workers).length && (w = ws[id]) != null && |
827 |
(workerCounts & RUNNING_COUNT_MASK) < parallelism && |
828 |
eventWaiters == 0L && |
829 |
spareWaiters == sw && |
830 |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
831 |
sw, w.nextSpare) && |
832 |
w.tryUnsuspend()) { |
833 |
int c; // try increment; if contended, finish after unpark |
834 |
boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
835 |
c = workerCounts, |
836 |
c + ONE_RUNNING); |
837 |
LockSupport.unpark(w); |
838 |
if (!inc) { |
839 |
do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
840 |
c = workerCounts, |
841 |
c + ONE_RUNNING)); |
842 |
} |
843 |
} |
844 |
} |
845 |
|
846 |
/** |
847 |
* Callback from oldest spare occasionally waking up. Tries |
848 |
* (once) to shutdown a spare if more than 25% spare overage, or |
849 |
* if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at |
850 |
* least #parallelism running threads. Note that we don't need CAS |
851 |
* or locks here because the method is called only from the oldest |
852 |
* suspended spare occasionally waking (and even misfires are OK). |
853 |
* |
854 |
* @param now the wake up nanoTime of caller |
855 |
*/ |
856 |
final void tryTrimSpare(long now) { |
857 |
long lastTrim = trimTime; |
858 |
trimTime = now; |
859 |
helpMaintainParallelism(); // first, help wake up any needed spares |
860 |
int sw, id; |
861 |
ForkJoinWorkerThread w; |
862 |
ForkJoinWorkerThread[] ws; |
863 |
int pc = parallelism; |
864 |
int wc = workerCounts; |
865 |
if ((wc & RUNNING_COUNT_MASK) >= pc && |
866 |
(((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25% |
867 |
now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) && |
868 |
(id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
869 |
id < (ws = workers).length && (w = ws[id]) != null && |
870 |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
871 |
sw, w.nextSpare)) |
872 |
w.shutdown(false); |
873 |
} |
874 |
|
875 |
/** |
876 |
* Does at most one of: |
877 |
* |
878 |
* 1. Help wake up existing workers waiting for work via |
879 |
* releaseEventWaiters. (If any exist, then it probably doesn't |
880 |
* matter right now if under target parallelism level.) |
881 |
* |
882 |
* 2. If below parallelism level and a spare exists, try (once) |
883 |
* to resume it via tryResumeSpare. |
884 |
* |
885 |
* 3. If neither of the above, tries (once) to add a new |
886 |
* worker if either there are not enough total, or if all |
887 |
* existing workers are busy, there are either no running |
888 |
* workers or the deficit is at least twice the surplus. |
889 |
*/ |
890 |
private void helpMaintainParallelism() { |
891 |
// uglified to work better when not compiled |
892 |
int pc, wc, rc, tc, rs; long h; |
893 |
if ((h = eventWaiters) != 0L) { |
894 |
if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount) |
895 |
releaseEventWaiters(false); // avoid useless call |
896 |
} |
897 |
else if ((pc = parallelism) > |
898 |
(rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) { |
899 |
if (spareWaiters != 0) |
900 |
tryResumeSpare(); |
901 |
else if ((rs = runState) < TERMINATING && |
902 |
((tc = wc >>> TOTAL_COUNT_SHIFT) < pc || |
903 |
(tc == (rs & ACTIVE_COUNT_MASK) && // all busy |
904 |
(rc == 0 || // must add |
905 |
rc < pc - ((tc - pc) << 1)) && // within slack |
906 |
tc < MAX_WORKERS && runState == rs)) && // recheck busy |
907 |
workerCounts == wc && |
908 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
909 |
wc + (ONE_RUNNING|ONE_TOTAL))) |
910 |
addWorker(); |
911 |
} |
912 |
} |
913 |
|
914 |
/** |
915 |
* Callback from workers invoked upon each top-level action (i.e., |
916 |
* stealing a task or taking a submission and running |
917 |
* it). Performs one or more of the following: |
918 |
* |
919 |
* 1. If the worker cannot find work (misses > 0), updates its |
920 |
* active status to inactive and updates activeCount unless |
921 |
* this is the first miss and there is contention, in which |
922 |
* case it may try again (either in this or a subsequent |
923 |
* call). |
924 |
* |
925 |
* 2. If there are at least 2 misses, awaits the next task event |
926 |
* via eventSync |
927 |
* |
928 |
* 3. If there are too many running threads, suspends this worker |
929 |
* (first forcing inactivation if necessary). If it is not |
930 |
* needed, it may be killed while suspended via |
931 |
* tryTrimSpare. Otherwise, upon resume it rechecks to make |
932 |
* sure that it is still needed. |
933 |
* |
934 |
* 4. Helps release and/or reactivate other workers via |
935 |
* helpMaintainParallelism |
936 |
* |
937 |
* @param w the worker |
938 |
* @param misses the number of scans by caller failing to find work |
939 |
* (saturating at 2 just to avoid wraparound) |
940 |
*/ |
941 |
final void preStep(ForkJoinWorkerThread w, int misses) { |
942 |
boolean active = w.active; |
943 |
int pc = parallelism; |
944 |
for (;;) { |
945 |
int wc = workerCounts; |
946 |
int rc = wc & RUNNING_COUNT_MASK; |
947 |
if (active && (misses > 0 || rc > pc)) { |
948 |
int rs; // try inactivate |
949 |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, |
950 |
rs = runState, rs - ONE_ACTIVE)) |
951 |
active = w.active = false; |
952 |
else if (misses > 1 || rc > pc || |
953 |
(rs & ACTIVE_COUNT_MASK) >= pc) |
954 |
continue; // force inactivate |
955 |
} |
956 |
if (misses > 1) { |
957 |
misses = 0; // don't re-sync |
958 |
eventSync(w); // continue loop to recheck rc |
959 |
} |
960 |
else if (rc > pc) { |
961 |
if (workerCounts == wc && // try to suspend as spare |
962 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
963 |
wc, wc - ONE_RUNNING) && |
964 |
!w.suspendAsSpare()) // false if killed |
965 |
break; |
966 |
} |
967 |
else { |
968 |
if (rc < pc || eventWaiters != 0L) |
969 |
helpMaintainParallelism(); |
970 |
break; |
971 |
} |
972 |
} |
973 |
} |
974 |
|
975 |
/** |
976 |
* Helps and/or blocks awaiting join of the given task. |
977 |
* Alternates between helpJoinTask() and helpMaintainParallelism() |
978 |
* as many times as there is a deficit in running count (or longer |
979 |
* if running count would become zero), then blocks if task still |
980 |
* not done. |
981 |
* |
982 |
* @param joinMe the task to join |
983 |
*/ |
984 |
final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) { |
985 |
int threshold = parallelism; // descend blocking thresholds |
986 |
while (joinMe.status >= 0) { |
987 |
boolean block; int wc; |
988 |
worker.helpJoinTask(joinMe); |
989 |
if (joinMe.status < 0) |
990 |
break; |
991 |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
992 |
if (threshold > 0) |
993 |
--threshold; |
994 |
else |
995 |
advanceEventCount(); // force release |
996 |
block = false; |
997 |
} |
998 |
else |
999 |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1000 |
wc, wc - ONE_RUNNING); |
1001 |
helpMaintainParallelism(); |
1002 |
if (block) { |
1003 |
int c; |
1004 |
joinMe.internalAwaitDone(); |
1005 |
do {} while (!UNSAFE.compareAndSwapInt |
1006 |
(this, workerCountsOffset, |
1007 |
c = workerCounts, c + ONE_RUNNING)); |
1008 |
break; |
1009 |
} |
1010 |
} |
1011 |
} |
1012 |
|
1013 |
/** |
1014 |
* Same idea as awaitJoin, but no helping |
1015 |
*/ |
1016 |
final void awaitBlocker(ManagedBlocker blocker) |
1017 |
throws InterruptedException { |
1018 |
int threshold = parallelism; |
1019 |
while (!blocker.isReleasable()) { |
1020 |
boolean block; int wc; |
1021 |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
1022 |
if (threshold > 0) |
1023 |
--threshold; |
1024 |
else |
1025 |
advanceEventCount(); |
1026 |
block = false; |
1027 |
} |
1028 |
else |
1029 |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1030 |
wc, wc - ONE_RUNNING); |
1031 |
helpMaintainParallelism(); |
1032 |
if (block) { |
1033 |
try { |
1034 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1035 |
} finally { |
1036 |
int c; |
1037 |
do {} while (!UNSAFE.compareAndSwapInt |
1038 |
(this, workerCountsOffset, |
1039 |
c = workerCounts, c + ONE_RUNNING)); |
1040 |
} |
1041 |
break; |
1042 |
} |
1043 |
} |
1044 |
} |
1045 |
|
1046 |
/** |
1047 |
* Possibly initiates and/or completes termination. |
1048 |
* |
1049 |
* @param now if true, unconditionally terminate, else only |
1050 |
* if shutdown and empty queue and no active workers |
1051 |
* @return true if now terminating or terminated |
1052 |
*/ |
1053 |
private boolean tryTerminate(boolean now) { |
1054 |
if (now) |
1055 |
advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN |
1056 |
else if (runState < SHUTDOWN || |
1057 |
!submissionQueue.isEmpty() || |
1058 |
(runState & ACTIVE_COUNT_MASK) != 0) |
1059 |
return false; |
1060 |
|
1061 |
if (advanceRunLevel(TERMINATING)) |
1062 |
startTerminating(); |
1063 |
|
1064 |
// Finish now if all threads terminated; else in some subsequent call |
1065 |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) { |
1066 |
advanceRunLevel(TERMINATED); |
1067 |
termination.arrive(); |
1068 |
} |
1069 |
return true; |
1070 |
} |
1071 |
|
1072 |
/** |
1073 |
* Actions on transition to TERMINATING |
1074 |
* |
1075 |
* Runs up to four passes through workers: (0) shutting down each |
1076 |
* quietly (without waking up if parked) to quickly spread |
1077 |
* notifications without unnecessary bouncing around event queues |
1078 |
* etc (1) wake up and help cancel tasks (2) interrupt (3) mop up |
1079 |
* races with interrupted workers |
1080 |
*/ |
1081 |
private void startTerminating() { |
1082 |
cancelSubmissions(); |
1083 |
for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) { |
1084 |
advanceEventCount(); |
1085 |
eventWaiters = 0L; // clobber lists |
1086 |
spareWaiters = 0; |
1087 |
ForkJoinWorkerThread[] ws = workers; |
1088 |
int n = ws.length; |
1089 |
for (int i = 0; i < n; ++i) { |
1090 |
ForkJoinWorkerThread w = ws[i]; |
1091 |
if (w != null) { |
1092 |
w.shutdown(true); |
1093 |
if (passes > 0 && !w.isTerminated()) { |
1094 |
w.cancelTasks(); |
1095 |
LockSupport.unpark(w); |
1096 |
if (passes > 1) { |
1097 |
try { |
1098 |
w.interrupt(); |
1099 |
} catch (SecurityException ignore) { |
1100 |
} |
1101 |
} |
1102 |
} |
1103 |
} |
1104 |
} |
1105 |
} |
1106 |
} |
1107 |
|
1108 |
/** |
1109 |
* Clear out and cancel submissions, ignoring exceptions |
1110 |
*/ |
1111 |
private void cancelSubmissions() { |
1112 |
ForkJoinTask<?> task; |
1113 |
while ((task = submissionQueue.poll()) != null) { |
1114 |
try { |
1115 |
task.cancel(false); |
1116 |
} catch (Throwable ignore) { |
1117 |
} |
1118 |
} |
1119 |
} |
1120 |
|
1121 |
// misc support for ForkJoinWorkerThread |
1122 |
|
1123 |
/** |
1124 |
* Returns pool number |
1125 |
*/ |
1126 |
final int getPoolNumber() { |
1127 |
return poolNumber; |
1128 |
} |
1129 |
|
1130 |
/** |
1131 |
* Tries to accumulates steal count from a worker, clearing |
1132 |
* the worker's value. |
1133 |
* |
1134 |
* @return true if worker steal count now zero |
1135 |
*/ |
1136 |
final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) { |
1137 |
int sc = w.stealCount; |
1138 |
long c = stealCount; |
1139 |
// CAS even if zero, for fence effects |
1140 |
if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) { |
1141 |
if (sc != 0) |
1142 |
w.stealCount = 0; |
1143 |
return true; |
1144 |
} |
1145 |
return sc == 0; |
1146 |
} |
1147 |
|
1148 |
/** |
1149 |
* Returns the approximate (non-atomic) number of idle threads per |
1150 |
* active thread. |
1151 |
*/ |
1152 |
final int idlePerActive() { |
1153 |
int pc = parallelism; // use parallelism, not rc |
1154 |
int ac = runState; // no mask -- artifically boosts during shutdown |
1155 |
// Use exact results for small values, saturate past 4 |
1156 |
return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3; |
1157 |
} |
1158 |
|
1159 |
// Public and protected methods |
1160 |
|
1161 |
// Constructors |
1162 |
|
1163 |
/** |
1164 |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
1165 |
* java.lang.Runtime#availableProcessors}, using the {@linkplain |
1166 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1167 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1168 |
* |
1169 |
* @throws SecurityException if a security manager exists and |
1170 |
* the caller is not permitted to modify threads |
1171 |
* because it does not hold {@link |
1172 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1173 |
*/ |
1174 |
public ForkJoinPool() { |
1175 |
this(Runtime.getRuntime().availableProcessors(), |
1176 |
defaultForkJoinWorkerThreadFactory, null, false); |
1177 |
} |
1178 |
|
1179 |
/** |
1180 |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
1181 |
* level, the {@linkplain |
1182 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1183 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1184 |
* |
1185 |
* @param parallelism the parallelism level |
1186 |
* @throws IllegalArgumentException if parallelism less than or |
1187 |
* equal to zero, or greater than implementation limit |
1188 |
* @throws SecurityException if a security manager exists and |
1189 |
* the caller is not permitted to modify threads |
1190 |
* because it does not hold {@link |
1191 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1192 |
*/ |
1193 |
public ForkJoinPool(int parallelism) { |
1194 |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
1195 |
} |
1196 |
|
1197 |
/** |
1198 |
* Creates a {@code ForkJoinPool} with the given parameters. |
1199 |
* |
1200 |
* @param parallelism the parallelism level. For default value, |
1201 |
* use {@link java.lang.Runtime#availableProcessors}. |
1202 |
* @param factory the factory for creating new threads. For default value, |
1203 |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
1204 |
* @param handler the handler for internal worker threads that |
1205 |
* terminate due to unrecoverable errors encountered while executing |
1206 |
* tasks. For default value, use <code>null</code>. |
1207 |
* @param asyncMode if true, |
1208 |
* establishes local first-in-first-out scheduling mode for forked |
1209 |
* tasks that are never joined. This mode may be more appropriate |
1210 |
* than default locally stack-based mode in applications in which |
1211 |
* worker threads only process event-style asynchronous tasks. |
1212 |
* For default value, use <code>false</code>. |
1213 |
* @throws IllegalArgumentException if parallelism less than or |
1214 |
* equal to zero, or greater than implementation limit |
1215 |
* @throws NullPointerException if the factory is null |
1216 |
* @throws SecurityException if a security manager exists and |
1217 |
* the caller is not permitted to modify threads |
1218 |
* because it does not hold {@link |
1219 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1220 |
*/ |
1221 |
public ForkJoinPool(int parallelism, |
1222 |
ForkJoinWorkerThreadFactory factory, |
1223 |
Thread.UncaughtExceptionHandler handler, |
1224 |
boolean asyncMode) { |
1225 |
checkPermission(); |
1226 |
if (factory == null) |
1227 |
throw new NullPointerException(); |
1228 |
if (parallelism <= 0 || parallelism > MAX_WORKERS) |
1229 |
throw new IllegalArgumentException(); |
1230 |
this.parallelism = parallelism; |
1231 |
this.factory = factory; |
1232 |
this.ueh = handler; |
1233 |
this.locallyFifo = asyncMode; |
1234 |
int arraySize = initialArraySizeFor(parallelism); |
1235 |
this.workers = new ForkJoinWorkerThread[arraySize]; |
1236 |
this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
1237 |
this.workerLock = new ReentrantLock(); |
1238 |
this.termination = new Phaser(1); |
1239 |
this.poolNumber = poolNumberGenerator.incrementAndGet(); |
1240 |
this.trimTime = System.nanoTime(); |
1241 |
} |
1242 |
|
1243 |
/** |
1244 |
* Returns initial power of two size for workers array. |
1245 |
* @param pc the initial parallelism level |
1246 |
*/ |
1247 |
private static int initialArraySizeFor(int pc) { |
1248 |
// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16) |
1249 |
int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS; |
1250 |
size |= size >>> 1; |
1251 |
size |= size >>> 2; |
1252 |
size |= size >>> 4; |
1253 |
size |= size >>> 8; |
1254 |
return size + 1; |
1255 |
} |
1256 |
|
1257 |
// Execution methods |
1258 |
|
1259 |
/** |
1260 |
* Common code for execute, invoke and submit |
1261 |
*/ |
1262 |
private <T> void doSubmit(ForkJoinTask<T> task) { |
1263 |
if (task == null) |
1264 |
throw new NullPointerException(); |
1265 |
if (runState >= SHUTDOWN) |
1266 |
throw new RejectedExecutionException(); |
1267 |
submissionQueue.offer(task); |
1268 |
advanceEventCount(); |
1269 |
helpMaintainParallelism(); // start or wake up workers |
1270 |
} |
1271 |
|
1272 |
/** |
1273 |
* Performs the given task, returning its result upon completion. |
1274 |
* If the caller is already engaged in a fork/join computation in |
1275 |
* the current pool, this method is equivalent in effect to |
1276 |
* {@link ForkJoinTask#invoke}. |
1277 |
* |
1278 |
* @param task the task |
1279 |
* @return the task's result |
1280 |
* @throws NullPointerException if the task is null |
1281 |
* @throws RejectedExecutionException if the task cannot be |
1282 |
* scheduled for execution |
1283 |
*/ |
1284 |
public <T> T invoke(ForkJoinTask<T> task) { |
1285 |
doSubmit(task); |
1286 |
return task.join(); |
1287 |
} |
1288 |
|
1289 |
/** |
1290 |
* Arranges for (asynchronous) execution of the given task. |
1291 |
* If the caller is already engaged in a fork/join computation in |
1292 |
* the current pool, this method is equivalent in effect to |
1293 |
* {@link ForkJoinTask#fork}. |
1294 |
* |
1295 |
* @param task the task |
1296 |
* @throws NullPointerException if the task is null |
1297 |
* @throws RejectedExecutionException if the task cannot be |
1298 |
* scheduled for execution |
1299 |
*/ |
1300 |
public void execute(ForkJoinTask<?> task) { |
1301 |
doSubmit(task); |
1302 |
} |
1303 |
|
1304 |
// AbstractExecutorService methods |
1305 |
|
1306 |
/** |
1307 |
* @throws NullPointerException if the task is null |
1308 |
* @throws RejectedExecutionException if the task cannot be |
1309 |
* scheduled for execution |
1310 |
*/ |
1311 |
public void execute(Runnable task) { |
1312 |
ForkJoinTask<?> job; |
1313 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1314 |
job = (ForkJoinTask<?>) task; |
1315 |
else |
1316 |
job = ForkJoinTask.adapt(task, null); |
1317 |
doSubmit(job); |
1318 |
} |
1319 |
|
1320 |
/** |
1321 |
* Submits a ForkJoinTask for execution. |
1322 |
* If the caller is already engaged in a fork/join computation in |
1323 |
* the current pool, this method is equivalent in effect to |
1324 |
* {@link ForkJoinTask#fork}. |
1325 |
* |
1326 |
* @param task the task to submit |
1327 |
* @return the task |
1328 |
* @throws NullPointerException if the task is null |
1329 |
* @throws RejectedExecutionException if the task cannot be |
1330 |
* scheduled for execution |
1331 |
*/ |
1332 |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
1333 |
doSubmit(task); |
1334 |
return task; |
1335 |
} |
1336 |
|
1337 |
/** |
1338 |
* @throws NullPointerException if the task is null |
1339 |
* @throws RejectedExecutionException if the task cannot be |
1340 |
* scheduled for execution |
1341 |
*/ |
1342 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
1343 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task); |
1344 |
doSubmit(job); |
1345 |
return job; |
1346 |
} |
1347 |
|
1348 |
/** |
1349 |
* @throws NullPointerException if the task is null |
1350 |
* @throws RejectedExecutionException if the task cannot be |
1351 |
* scheduled for execution |
1352 |
*/ |
1353 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
1354 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); |
1355 |
doSubmit(job); |
1356 |
return job; |
1357 |
} |
1358 |
|
1359 |
/** |
1360 |
* @throws NullPointerException if the task is null |
1361 |
* @throws RejectedExecutionException if the task cannot be |
1362 |
* scheduled for execution |
1363 |
*/ |
1364 |
public ForkJoinTask<?> submit(Runnable task) { |
1365 |
ForkJoinTask<?> job; |
1366 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1367 |
job = (ForkJoinTask<?>) task; |
1368 |
else |
1369 |
job = ForkJoinTask.adapt(task, null); |
1370 |
doSubmit(job); |
1371 |
return job; |
1372 |
} |
1373 |
|
1374 |
/** |
1375 |
* @throws NullPointerException {@inheritDoc} |
1376 |
* @throws RejectedExecutionException {@inheritDoc} |
1377 |
*/ |
1378 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
1379 |
ArrayList<ForkJoinTask<T>> forkJoinTasks = |
1380 |
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
1381 |
for (Callable<T> task : tasks) |
1382 |
forkJoinTasks.add(ForkJoinTask.adapt(task)); |
1383 |
invoke(new InvokeAll<T>(forkJoinTasks)); |
1384 |
|
1385 |
@SuppressWarnings({"unchecked", "rawtypes"}) |
1386 |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1387 |
return futures; |
1388 |
} |
1389 |
|
1390 |
static final class InvokeAll<T> extends RecursiveAction { |
1391 |
final ArrayList<ForkJoinTask<T>> tasks; |
1392 |
InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } |
1393 |
public void compute() { |
1394 |
try { invokeAll(tasks); } |
1395 |
catch (Exception ignore) {} |
1396 |
} |
1397 |
private static final long serialVersionUID = -7914297376763021607L; |
1398 |
} |
1399 |
|
1400 |
/** |
1401 |
* Returns the factory used for constructing new workers. |
1402 |
* |
1403 |
* @return the factory used for constructing new workers |
1404 |
*/ |
1405 |
public ForkJoinWorkerThreadFactory getFactory() { |
1406 |
return factory; |
1407 |
} |
1408 |
|
1409 |
/** |
1410 |
* Returns the handler for internal worker threads that terminate |
1411 |
* due to unrecoverable errors encountered while executing tasks. |
1412 |
* |
1413 |
* @return the handler, or {@code null} if none |
1414 |
*/ |
1415 |
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
1416 |
return ueh; |
1417 |
} |
1418 |
|
1419 |
/** |
1420 |
* Returns the targeted parallelism level of this pool. |
1421 |
* |
1422 |
* @return the targeted parallelism level of this pool |
1423 |
*/ |
1424 |
public int getParallelism() { |
1425 |
return parallelism; |
1426 |
} |
1427 |
|
1428 |
/** |
1429 |
* Returns the number of worker threads that have started but not |
1430 |
* yet terminated. This result returned by this method may differ |
1431 |
* from {@link #getParallelism} when threads are created to |
1432 |
* maintain parallelism when others are cooperatively blocked. |
1433 |
* |
1434 |
* @return the number of worker threads |
1435 |
*/ |
1436 |
public int getPoolSize() { |
1437 |
return workerCounts >>> TOTAL_COUNT_SHIFT; |
1438 |
} |
1439 |
|
1440 |
/** |
1441 |
* Returns {@code true} if this pool uses local first-in-first-out |
1442 |
* scheduling mode for forked tasks that are never joined. |
1443 |
* |
1444 |
* @return {@code true} if this pool uses async mode |
1445 |
*/ |
1446 |
public boolean getAsyncMode() { |
1447 |
return locallyFifo; |
1448 |
} |
1449 |
|
1450 |
/** |
1451 |
* Returns an estimate of the number of worker threads that are |
1452 |
* not blocked waiting to join tasks or for other managed |
1453 |
* synchronization. This method may overestimate the |
1454 |
* number of running threads. |
1455 |
* |
1456 |
* @return the number of worker threads |
1457 |
*/ |
1458 |
public int getRunningThreadCount() { |
1459 |
return workerCounts & RUNNING_COUNT_MASK; |
1460 |
} |
1461 |
|
1462 |
/** |
1463 |
* Returns an estimate of the number of threads that are currently |
1464 |
* stealing or executing tasks. This method may overestimate the |
1465 |
* number of active threads. |
1466 |
* |
1467 |
* @return the number of active threads |
1468 |
*/ |
1469 |
public int getActiveThreadCount() { |
1470 |
return runState & ACTIVE_COUNT_MASK; |
1471 |
} |
1472 |
|
1473 |
/** |
1474 |
* Returns {@code true} if all worker threads are currently idle. |
1475 |
* An idle worker is one that cannot obtain a task to execute |
1476 |
* because none are available to steal from other threads, and |
1477 |
* there are no pending submissions to the pool. This method is |
1478 |
* conservative; it might not return {@code true} immediately upon |
1479 |
* idleness of all threads, but will eventually become true if |
1480 |
* threads remain inactive. |
1481 |
* |
1482 |
* @return {@code true} if all threads are currently idle |
1483 |
*/ |
1484 |
public boolean isQuiescent() { |
1485 |
return (runState & ACTIVE_COUNT_MASK) == 0; |
1486 |
} |
1487 |
|
1488 |
/** |
1489 |
* Returns an estimate of the total number of tasks stolen from |
1490 |
* one thread's work queue by another. The reported value |
1491 |
* underestimates the actual total number of steals when the pool |
1492 |
* is not quiescent. This value may be useful for monitoring and |
1493 |
* tuning fork/join programs: in general, steal counts should be |
1494 |
* high enough to keep threads busy, but low enough to avoid |
1495 |
* overhead and contention across threads. |
1496 |
* |
1497 |
* @return the number of steals |
1498 |
*/ |
1499 |
public long getStealCount() { |
1500 |
return stealCount; |
1501 |
} |
1502 |
|
1503 |
/** |
1504 |
* Returns an estimate of the total number of tasks currently held |
1505 |
* in queues by worker threads (but not including tasks submitted |
1506 |
* to the pool that have not begun executing). This value is only |
1507 |
* an approximation, obtained by iterating across all threads in |
1508 |
* the pool. This method may be useful for tuning task |
1509 |
* granularities. |
1510 |
* |
1511 |
* @return the number of queued tasks |
1512 |
*/ |
1513 |
public long getQueuedTaskCount() { |
1514 |
long count = 0; |
1515 |
ForkJoinWorkerThread[] ws = workers; |
1516 |
int n = ws.length; |
1517 |
for (int i = 0; i < n; ++i) { |
1518 |
ForkJoinWorkerThread w = ws[i]; |
1519 |
if (w != null) |
1520 |
count += w.getQueueSize(); |
1521 |
} |
1522 |
return count; |
1523 |
} |
1524 |
|
1525 |
/** |
1526 |
* Returns an estimate of the number of tasks submitted to this |
1527 |
* pool that have not yet begun executing. This method takes time |
1528 |
* proportional to the number of submissions. |
1529 |
* |
1530 |
* @return the number of queued submissions |
1531 |
*/ |
1532 |
public int getQueuedSubmissionCount() { |
1533 |
return submissionQueue.size(); |
1534 |
} |
1535 |
|
1536 |
/** |
1537 |
* Returns {@code true} if there are any tasks submitted to this |
1538 |
* pool that have not yet begun executing. |
1539 |
* |
1540 |
* @return {@code true} if there are any queued submissions |
1541 |
*/ |
1542 |
public boolean hasQueuedSubmissions() { |
1543 |
return !submissionQueue.isEmpty(); |
1544 |
} |
1545 |
|
1546 |
/** |
1547 |
* Removes and returns the next unexecuted submission if one is |
1548 |
* available. This method may be useful in extensions to this |
1549 |
* class that re-assign work in systems with multiple pools. |
1550 |
* |
1551 |
* @return the next submission, or {@code null} if none |
1552 |
*/ |
1553 |
protected ForkJoinTask<?> pollSubmission() { |
1554 |
return submissionQueue.poll(); |
1555 |
} |
1556 |
|
1557 |
/** |
1558 |
* Removes all available unexecuted submitted and forked tasks |
1559 |
* from scheduling queues and adds them to the given collection, |
1560 |
* without altering their execution status. These may include |
1561 |
* artificially generated or wrapped tasks. This method is |
1562 |
* designed to be invoked only when the pool is known to be |
1563 |
* quiescent. Invocations at other times may not remove all |
1564 |
* tasks. A failure encountered while attempting to add elements |
1565 |
* to collection {@code c} may result in elements being in |
1566 |
* neither, either or both collections when the associated |
1567 |
* exception is thrown. The behavior of this operation is |
1568 |
* undefined if the specified collection is modified while the |
1569 |
* operation is in progress. |
1570 |
* |
1571 |
* @param c the collection to transfer elements into |
1572 |
* @return the number of elements transferred |
1573 |
*/ |
1574 |
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1575 |
int count = submissionQueue.drainTo(c); |
1576 |
ForkJoinWorkerThread[] ws = workers; |
1577 |
int n = ws.length; |
1578 |
for (int i = 0; i < n; ++i) { |
1579 |
ForkJoinWorkerThread w = ws[i]; |
1580 |
if (w != null) |
1581 |
count += w.drainTasksTo(c); |
1582 |
} |
1583 |
return count; |
1584 |
} |
1585 |
|
1586 |
/** |
1587 |
* Returns a string identifying this pool, as well as its state, |
1588 |
* including indications of run state, parallelism level, and |
1589 |
* worker and task counts. |
1590 |
* |
1591 |
* @return a string identifying this pool, as well as its state |
1592 |
*/ |
1593 |
public String toString() { |
1594 |
long st = getStealCount(); |
1595 |
long qt = getQueuedTaskCount(); |
1596 |
long qs = getQueuedSubmissionCount(); |
1597 |
int wc = workerCounts; |
1598 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1599 |
int rc = wc & RUNNING_COUNT_MASK; |
1600 |
int pc = parallelism; |
1601 |
int rs = runState; |
1602 |
int ac = rs & ACTIVE_COUNT_MASK; |
1603 |
return super.toString() + |
1604 |
"[" + runLevelToString(rs) + |
1605 |
", parallelism = " + pc + |
1606 |
", size = " + tc + |
1607 |
", active = " + ac + |
1608 |
", running = " + rc + |
1609 |
", steals = " + st + |
1610 |
", tasks = " + qt + |
1611 |
", submissions = " + qs + |
1612 |
"]"; |
1613 |
} |
1614 |
|
1615 |
private static String runLevelToString(int s) { |
1616 |
return ((s & TERMINATED) != 0 ? "Terminated" : |
1617 |
((s & TERMINATING) != 0 ? "Terminating" : |
1618 |
((s & SHUTDOWN) != 0 ? "Shutting down" : |
1619 |
"Running"))); |
1620 |
} |
1621 |
|
1622 |
/** |
1623 |
* Initiates an orderly shutdown in which previously submitted |
1624 |
* tasks are executed, but no new tasks will be accepted. |
1625 |
* Invocation has no additional effect if already shut down. |
1626 |
* Tasks that are in the process of being submitted concurrently |
1627 |
* during the course of this method may or may not be rejected. |
1628 |
* |
1629 |
* @throws SecurityException if a security manager exists and |
1630 |
* the caller is not permitted to modify threads |
1631 |
* because it does not hold {@link |
1632 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1633 |
*/ |
1634 |
public void shutdown() { |
1635 |
checkPermission(); |
1636 |
advanceRunLevel(SHUTDOWN); |
1637 |
tryTerminate(false); |
1638 |
} |
1639 |
|
1640 |
/** |
1641 |
* Attempts to cancel and/or stop all tasks, and reject all |
1642 |
* subsequently submitted tasks. Tasks that are in the process of |
1643 |
* being submitted or executed concurrently during the course of |
1644 |
* this method may or may not be rejected. This method cancels |
1645 |
* both existing and unexecuted tasks, in order to permit |
1646 |
* termination in the presence of task dependencies. So the method |
1647 |
* always returns an empty list (unlike the case for some other |
1648 |
* Executors). |
1649 |
* |
1650 |
* @return an empty list |
1651 |
* @throws SecurityException if a security manager exists and |
1652 |
* the caller is not permitted to modify threads |
1653 |
* because it does not hold {@link |
1654 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1655 |
*/ |
1656 |
public List<Runnable> shutdownNow() { |
1657 |
checkPermission(); |
1658 |
tryTerminate(true); |
1659 |
return Collections.emptyList(); |
1660 |
} |
1661 |
|
1662 |
/** |
1663 |
* Returns {@code true} if all tasks have completed following shut down. |
1664 |
* |
1665 |
* @return {@code true} if all tasks have completed following shut down |
1666 |
*/ |
1667 |
public boolean isTerminated() { |
1668 |
return runState >= TERMINATED; |
1669 |
} |
1670 |
|
1671 |
/** |
1672 |
* Returns {@code true} if the process of termination has |
1673 |
* commenced but not yet completed. This method may be useful for |
1674 |
* debugging. A return of {@code true} reported a sufficient |
1675 |
* period after shutdown may indicate that submitted tasks have |
1676 |
* ignored or suppressed interruption, causing this executor not |
1677 |
* to properly terminate. |
1678 |
* |
1679 |
* @return {@code true} if terminating but not yet terminated |
1680 |
*/ |
1681 |
public boolean isTerminating() { |
1682 |
return (runState & (TERMINATING|TERMINATED)) == TERMINATING; |
1683 |
} |
1684 |
|
1685 |
/** |
1686 |
* Returns {@code true} if this pool has been shut down. |
1687 |
* |
1688 |
* @return {@code true} if this pool has been shut down |
1689 |
*/ |
1690 |
public boolean isShutdown() { |
1691 |
return runState >= SHUTDOWN; |
1692 |
} |
1693 |
|
1694 |
/** |
1695 |
* Blocks until all tasks have completed execution after a shutdown |
1696 |
* request, or the timeout occurs, or the current thread is |
1697 |
* interrupted, whichever happens first. |
1698 |
* |
1699 |
* @param timeout the maximum time to wait |
1700 |
* @param unit the time unit of the timeout argument |
1701 |
* @return {@code true} if this executor terminated and |
1702 |
* {@code false} if the timeout elapsed before termination |
1703 |
* @throws InterruptedException if interrupted while waiting |
1704 |
*/ |
1705 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1706 |
throws InterruptedException { |
1707 |
try { |
1708 |
return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
1709 |
} catch(TimeoutException ex) { |
1710 |
return false; |
1711 |
} |
1712 |
} |
1713 |
|
1714 |
/** |
1715 |
* Interface for extending managed parallelism for tasks running |
1716 |
* in {@link ForkJoinPool}s. |
1717 |
* |
1718 |
* <p>A {@code ManagedBlocker} provides two methods. Method |
1719 |
* {@code isReleasable} must return {@code true} if blocking is |
1720 |
* not necessary. Method {@code block} blocks the current thread |
1721 |
* if necessary (perhaps internally invoking {@code isReleasable} |
1722 |
* before actually blocking). The unusual methods in this API |
1723 |
* accommodate synchronizers that may, but don't usually, block |
1724 |
* for long periods. Similarly, they allow more efficient internal |
1725 |
* handling of cases in which additional workers may be, but |
1726 |
* usually are not, needed to ensure sufficient parallelism. |
1727 |
* Toward this end, implementations of method {@code isReleasable} |
1728 |
* must be amenable to repeated invocation. |
1729 |
* |
1730 |
* <p>For example, here is a ManagedBlocker based on a |
1731 |
* ReentrantLock: |
1732 |
* <pre> {@code |
1733 |
* class ManagedLocker implements ManagedBlocker { |
1734 |
* final ReentrantLock lock; |
1735 |
* boolean hasLock = false; |
1736 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
1737 |
* public boolean block() { |
1738 |
* if (!hasLock) |
1739 |
* lock.lock(); |
1740 |
* return true; |
1741 |
* } |
1742 |
* public boolean isReleasable() { |
1743 |
* return hasLock || (hasLock = lock.tryLock()); |
1744 |
* } |
1745 |
* }}</pre> |
1746 |
* |
1747 |
* <p>Here is a class that possibly blocks waiting for an |
1748 |
* item on a given queue: |
1749 |
* <pre> {@code |
1750 |
* class QueueTaker<E> implements ManagedBlocker { |
1751 |
* final BlockingQueue<E> queue; |
1752 |
* volatile E item = null; |
1753 |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
1754 |
* public boolean block() throws InterruptedException { |
1755 |
* if (item == null) |
1756 |
* item = queue.take |
1757 |
* return true; |
1758 |
* } |
1759 |
* public boolean isReleasable() { |
1760 |
* return item != null || (item = queue.poll) != null; |
1761 |
* } |
1762 |
* public E getItem() { // call after pool.managedBlock completes |
1763 |
* return item; |
1764 |
* } |
1765 |
* }}</pre> |
1766 |
*/ |
1767 |
public static interface ManagedBlocker { |
1768 |
/** |
1769 |
* Possibly blocks the current thread, for example waiting for |
1770 |
* a lock or condition. |
1771 |
* |
1772 |
* @return {@code true} if no additional blocking is necessary |
1773 |
* (i.e., if isReleasable would return true) |
1774 |
* @throws InterruptedException if interrupted while waiting |
1775 |
* (the method is not required to do so, but is allowed to) |
1776 |
*/ |
1777 |
boolean block() throws InterruptedException; |
1778 |
|
1779 |
/** |
1780 |
* Returns {@code true} if blocking is unnecessary. |
1781 |
*/ |
1782 |
boolean isReleasable(); |
1783 |
} |
1784 |
|
1785 |
/** |
1786 |
* Blocks in accord with the given blocker. If the current thread |
1787 |
* is a {@link ForkJoinWorkerThread}, this method possibly |
1788 |
* arranges for a spare thread to be activated if necessary to |
1789 |
* ensure sufficient parallelism while the current thread is blocked. |
1790 |
* |
1791 |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
1792 |
* behaviorally equivalent to |
1793 |
* <pre> {@code |
1794 |
* while (!blocker.isReleasable()) |
1795 |
* if (blocker.block()) |
1796 |
* return; |
1797 |
* }</pre> |
1798 |
* |
1799 |
* If the caller is a {@code ForkJoinTask}, then the pool may |
1800 |
* first be expanded to ensure parallelism, and later adjusted. |
1801 |
* |
1802 |
* @param blocker the blocker |
1803 |
* @throws InterruptedException if blocker.block did so |
1804 |
*/ |
1805 |
public static void managedBlock(ManagedBlocker blocker) |
1806 |
throws InterruptedException { |
1807 |
Thread t = Thread.currentThread(); |
1808 |
if (t instanceof ForkJoinWorkerThread) { |
1809 |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
1810 |
w.pool.awaitBlocker(blocker); |
1811 |
} |
1812 |
else { |
1813 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1814 |
} |
1815 |
} |
1816 |
|
1817 |
// AbstractExecutorService overrides. These rely on undocumented |
1818 |
// fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
1819 |
// implement RunnableFuture. |
1820 |
|
1821 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
1822 |
return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); |
1823 |
} |
1824 |
|
1825 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
1826 |
return (RunnableFuture<T>) ForkJoinTask.adapt(callable); |
1827 |
} |
1828 |
|
1829 |
// Unsafe mechanics |
1830 |
|
1831 |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1832 |
private static final long workerCountsOffset = |
1833 |
objectFieldOffset("workerCounts", ForkJoinPool.class); |
1834 |
private static final long runStateOffset = |
1835 |
objectFieldOffset("runState", ForkJoinPool.class); |
1836 |
private static final long eventCountOffset = |
1837 |
objectFieldOffset("eventCount", ForkJoinPool.class); |
1838 |
private static final long eventWaitersOffset = |
1839 |
objectFieldOffset("eventWaiters",ForkJoinPool.class); |
1840 |
private static final long stealCountOffset = |
1841 |
objectFieldOffset("stealCount",ForkJoinPool.class); |
1842 |
private static final long spareWaitersOffset = |
1843 |
objectFieldOffset("spareWaiters",ForkJoinPool.class); |
1844 |
|
1845 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
1846 |
try { |
1847 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1848 |
} catch (NoSuchFieldException e) { |
1849 |
// Convert Exception to corresponding Error |
1850 |
NoSuchFieldError error = new NoSuchFieldError(field); |
1851 |
error.initCause(e); |
1852 |
throw error; |
1853 |
} |
1854 |
} |
1855 |
|
1856 |
/** |
1857 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1858 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1859 |
* into a jdk. |
1860 |
* |
1861 |
* @return a sun.misc.Unsafe |
1862 |
*/ |
1863 |
private static sun.misc.Unsafe getUnsafe() { |
1864 |
try { |
1865 |
return sun.misc.Unsafe.getUnsafe(); |
1866 |
} catch (SecurityException se) { |
1867 |
try { |
1868 |
return java.security.AccessController.doPrivileged |
1869 |
(new java.security |
1870 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1871 |
public sun.misc.Unsafe run() throws Exception { |
1872 |
java.lang.reflect.Field f = sun.misc |
1873 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1874 |
f.setAccessible(true); |
1875 |
return (sun.misc.Unsafe) f.get(null); |
1876 |
}}); |
1877 |
} catch (java.security.PrivilegedActionException e) { |
1878 |
throw new RuntimeException("Could not initialize intrinsics", |
1879 |
e.getCause()); |
1880 |
} |
1881 |
} |
1882 |
} |
1883 |
} |