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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.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.Random; |
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import java.util.concurrent.AbstractExecutorService; |
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import java.util.concurrent.Callable; |
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import java.util.concurrent.ExecutorService; |
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import java.util.concurrent.Future; |
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import java.util.concurrent.RejectedExecutionException; |
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import java.util.concurrent.RunnableFuture; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.TimeoutException; |
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import java.util.concurrent.atomic.AtomicInteger; |
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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.locks.Condition; |
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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>Arrange 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 exhausted. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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*/ |
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public class ForkJoinPool extends AbstractExecutorService { |
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|
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/* |
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* Implementation Overview |
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* |
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* This class 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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* Preference rules give first priority to processing tasks from |
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* their own queues (LIFO or FIFO, depending on mode), then to |
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* randomized FIFO steals of tasks in other worker queues, and |
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* lastly to new submissions. |
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* |
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* The main throughput advantages of work-stealing stem from |
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* decentralized control -- workers mostly take tasks from |
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* themselves or each other. We cannot negate this in the |
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* implementation of other management responsibilities. The main |
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* tactic for avoiding bottlenecks is packing nearly all |
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* essentially atomic control state into a single 64bit volatile |
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* variable ("ctl"). This variable is read on the order of 10-100 |
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* times as often as it is modified (always via CAS). (There is |
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* some additional control state, for example variable "shutdown" |
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* for which we can cope with uncoordinated updates.) This |
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* streamlines synchronization and control at the expense of messy |
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* constructions needed to repack status bits upon updates. |
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* Updates tend not to contend with each other except during |
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* bursts while submitted tasks begin or end. In some cases when |
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* they do contend, threads can instead do something else |
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* (usually, scan for tasks) until contention subsides. |
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* |
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* To enable packing, we restrict maximum parallelism to (1<<15)-1 |
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* (which is far in excess of normal operating range) to allow |
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* ids, counts, and their negations (used for thresholding) to fit |
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* into 16bit fields. |
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* |
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* Recording Workers. Workers are recorded in the "workers" array |
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* that is created upon pool construction and expanded if (rarely) |
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* necessary. 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 seqLock |
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* (scanGuard) 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. To avoid flailing during |
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* start-up, the array is presized to hold twice #parallelism |
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* workers (which is unlikely to need further resizing during |
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* execution). But to avoid dealing with so many null slots, |
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* variable scanGuard includes a mask for the nearest power of two |
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* that contains all current workers. All worker thread creation |
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* is on-demand, triggered by task submissions, replacement of |
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* terminated workers, and/or compensation for blocked |
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* workers. However, all other support code is set up to work with |
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* other policies. To ensure that we do not hold on to worker |
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* references that would prevent GC, ALL accesses to workers are |
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* via indices into the workers array (which is one source of some |
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* of the messy code constructions here). In essence, the workers |
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* array serves as a weak reference mechanism. Thus for example |
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* the wait queue field of ctl stores worker indices, not worker |
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* references. Access to the workers in associated methods (for |
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* example signalWork) must both index-check and null-check the |
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* IDs. All such accesses ignore bad IDs by returning out early |
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* from what they are doing, since this can only be associated |
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* with termination, in which case it is OK to give up. |
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* |
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* All uses of the workers array, as well as queue arrays, check |
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* that the array is non-null (even if previously non-null). This |
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* allows nulling during termination, which is currently not |
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* necessary, but remains an option for resource-revocation-based |
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* shutdown schemes. |
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* |
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* Wait Queuing. Unlike HPC work-stealing frameworks, we cannot |
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* let workers spin indefinitely scanning for tasks when none can |
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* be found immediately, and we cannot start/resume workers unless |
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* there appear to be tasks available. On the other hand, we must |
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* quickly prod them into action when new tasks are submitted or |
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* generated. We park/unpark workers after placing in an event |
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* wait queue when they cannot find work. This "queue" is actually |
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* a simple Treiber stack, headed by the "id" field of ctl, plus a |
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* 15bit counter value to both wake up waiters (by advancing their |
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* count) and avoid ABA effects. Successors are held in worker |
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* field "nextWait". Queuing deals with several intrinsic races, |
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* mainly that a task-producing thread can miss seeing (and |
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* signalling) another thread that gave up looking for work but |
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* has not yet entered the wait queue. We solve this by requiring |
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* a full sweep of all workers both before (in scan()) and after |
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* (in tryAwaitWork()) a newly waiting worker is added to the wait |
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* queue. During a rescan, the worker might release some other |
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* queued worker rather than itself, which has the same net |
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* effect. Because enqueued workers may actually be rescanning |
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* rather than waiting, we set and clear the "parked" field of |
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* ForkJoinWorkerThread to reduce unnecessary calls to unpark. |
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* (Use of the parked field requires a secondary recheck to avoid |
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* missed signals.) |
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* |
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* Signalling. We create or wake up workers only when there |
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* appears to be at least one task they might be able to find and |
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* execute. When a submission is added or another worker adds a |
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* task to a queue that previously had two or fewer tasks, they |
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* signal waiting workers (or trigger creation of new ones if |
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* fewer than the given parallelism level -- see signalWork). |
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* These primary signals are buttressed by signals during rescans |
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* as well as those performed when a worker steals a task and |
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* notices that there are more tasks too; together these cover the |
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* signals needed in cases when more than two tasks are pushed |
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* but untaken. |
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* |
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* Trimming workers. To release resources after periods of lack of |
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* use, a worker starting to wait when the pool is quiescent will |
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* time out and terminate if the pool has remained quiescent for |
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* SHRINK_RATE nanosecs. This will slowly propagate, eventually |
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* terminating all workers after long periods of non-use. |
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* |
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* Submissions. External submissions are maintained in an |
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* array-based queue that is structured identically to |
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* ForkJoinWorkerThread queues except for the use of |
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* submissionLock in method addSubmission. Unlike the case for |
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* worker queues, multiple external threads can add new |
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* submissions, so adding requires a lock. |
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* |
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* Compensation. Beyond work-stealing support and lifecycle |
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* control, the main responsibility of this framework is to take |
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* actions when one worker is waiting to join a task stolen (or |
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* always held by) another. Because we are multiplexing many |
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* tasks on to a pool of workers, we can't just let them block (as |
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* in Thread.join). We also cannot just reassign the joiner's |
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* run-time stack with another and replace it later, which would |
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* be a form of "continuation", that even if possible is not |
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* necessarily a good idea since we sometimes need both an |
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* unblocked task and its continuation to progress. 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.joinTask 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 tryPreBlock() may create or re-activate a spare |
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* thread to compensate for blocked joiners until they |
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* unblock. |
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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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* It is impossible to keep exactly the target parallelism number |
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* of threads running at any given time. Determining the |
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* existence of conservatively safe helping targets, the |
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* availability of already-created spares, and the apparent need |
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* to create new spares are all racy and require heuristic |
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* guidance, so we rely on multiple retries of each. Currently, |
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* in keeping with on-demand signalling policy, we compensate only |
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* if blocking would leave less than one active (non-waiting, |
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* non-blocked) worker. Additionally, to avoid some false alarms |
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* due to GC, lagging counters, system activity, etc, compensated |
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* blocking for joins is only attempted after rechecks stabilize |
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* (retries are interspersed with Thread.yield, for good |
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* citizenship). The variable blockedCount, incremented before |
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* blocking and decremented after, is sometimes needed to |
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* distinguish cases of waiting for work vs blocking on joins or |
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* other managed sync. Both cases are equivalent for most pool |
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* control, so we can update non-atomically. (Additionally, |
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* contention on blockedCount alleviates some contention on ctl). |
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* |
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* Shutdown and Termination. A call to shutdownNow atomically sets |
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* the ctl stop bit and then (non-atomically) sets each workers |
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* "terminate" status, cancels all unprocessed tasks, and wakes up |
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* all waiting workers. Detecting whether termination should |
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* commence after a non-abrupt shutdown() call requires more work |
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* and bookkeeping. We need consensus about quiesence (i.e., that |
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* there is no more work) which is reflected in active counts so |
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* long as there are no current blockers, as well as possible |
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* re-evaluations during independent changes in blocking or |
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* quiescing workers. |
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* |
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* Style notes: There is a lot of representation-level coupling |
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* among classes ForkJoinPool, ForkJoinWorkerThread, and |
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* ForkJoinTask. Most fields of ForkJoinWorkerThread maintain |
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* data structures managed by ForkJoinPool, so are directly |
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* accessed. Conversely we allow 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. All together, these low-level implementation |
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* choices produce as much as a factor of 4 performance |
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* improvement compared to naive implementations, and enable the |
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* processing of billions of tasks per second, at the expense of |
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* some ugliness. |
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* |
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* Methods signalWork() and scan() are the main bottlenecks so are |
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* especially heavily micro-optimized/mangled. There are lots of |
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* inline assignments (of form "while ((local = field) != 0)") |
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* which are usually the simplest way to ensure the required read |
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* orderings (which are sometimes critical). This leads to a |
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* "C"-like style of listing declarations of these locals at the |
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* heads of methods or blocks. There are several occurrences of |
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* the unusual "do {} while (!cas...)" which is the simplest way |
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* to force an update of a CAS'ed variable. There are also other |
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* coding oddities that help some methods perform reasonably even |
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* when interpreted (not compiled). |
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* |
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* The order of declarations in this file is: (1) declarations of |
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* statics (2) fields (along with constants used when unpacking |
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* some of them), listed in an order that tends to reduce |
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* contention among them a bit under most JVMs. (3) internal |
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* control methods (4) callbacks and other support for |
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* ForkJoinTask and ForkJoinWorkerThread classes, (5) exported |
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* methods (plus a few little helpers). (6) static block |
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* initializing all statics in a minimally dependent order. |
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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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|
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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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|
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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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|
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/** |
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* Generator for initial random seeds for worker victim |
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* selection. This is used only to create initial seeds. Random |
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* steals use a cheaper xorshift generator per steal attempt. We |
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* don't expect much contention on seedGenerator, so just use a |
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* plain Random. |
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*/ |
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static final Random workerSeedGenerator; |
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|
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/** |
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* Array holding all worker threads in the pool. Initialized upon |
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* construction. Array size must be a power of two. Updates and |
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* replacements are protected by scanGuard, but the array is |
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* always kept in a consistent enough state to be randomly |
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* accessed without locking by workers performing work-stealing, |
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* as well as other traversal-based methods in this class, so long |
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* as reads memory-acquire by first reading ctl. All readers must |
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* tolerate that some array slots may be null. |
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*/ |
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ForkJoinWorkerThread[] workers; |
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|
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/** |
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* Initial size for submission queue array. Must be a power of |
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* two. In many applications, these always stay small so we use a |
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* small initial cap. |
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*/ |
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private static final int INITIAL_QUEUE_CAPACITY = 8; |
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|
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/** |
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* Maximum size for submission queue array. Must be a power of two |
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* less than or equal to 1 << (31 - width of array entry) to |
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* ensure lack of index wraparound, but is capped at a lower |
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* value to help users trap runaway computations. |
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*/ |
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private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 24; // 16M |
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|
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/** |
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* Array serving as submission queue. Initialized upon construction. |
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*/ |
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private ForkJoinTask<?>[] submissionQueue; |
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|
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/** |
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* Lock protecting submissions array for addSubmission |
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*/ |
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private final ReentrantLock submissionLock; |
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|
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/** |
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* Condition for awaitTermination, using submissionLock for |
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* convenience. |
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*/ |
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private final Condition 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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* The uncaught exception handler used when any worker abruptly |
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* terminates. |
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*/ |
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final Thread.UncaughtExceptionHandler ueh; |
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|
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/** |
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* Prefix for assigning names to worker threads |
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*/ |
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private final String workerNamePrefix; |
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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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* Main pool control -- a long packed with: |
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* AC: Number of active running workers minus target parallelism (16 bits) |
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* TC: Number of total workers minus target parallelism (16bits) |
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* ST: true if pool is terminating (1 bit) |
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* EC: the wait count of top waiting thread (15 bits) |
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* ID: ~poolIndex of top of Treiber stack of waiting threads (16 bits) |
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* |
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* When convenient, we can extract the upper 32 bits of counts and |
476 |
* the lower 32 bits of queue state, u = (int)(ctl >>> 32) and e = |
477 |
* (int)ctl. The ec field is never accessed alone, but always |
478 |
* together with id and st. The offsets of counts by the target |
479 |
* parallelism and the positionings of fields makes it possible to |
480 |
* perform the most common checks via sign tests of fields: When |
481 |
* ac is negative, there are not enough active workers, when tc is |
482 |
* negative, there are not enough total workers, when id is |
483 |
* negative, there is at least one waiting worker, and when e is |
484 |
* negative, the pool is terminating. To deal with these possibly |
485 |
* negative fields, we use casts in and out of "short" and/or |
486 |
* signed shifts to maintain signedness. |
487 |
*/ |
488 |
volatile long ctl; |
489 |
|
490 |
// bit positions/shifts for fields |
491 |
private static final int AC_SHIFT = 48; |
492 |
private static final int TC_SHIFT = 32; |
493 |
private static final int ST_SHIFT = 31; |
494 |
private static final int EC_SHIFT = 16; |
495 |
|
496 |
// bounds |
497 |
private static final int MAX_ID = 0x7fff; // max poolIndex |
498 |
private static final int SMASK = 0xffff; // mask short bits |
499 |
private static final int SHORT_SIGN = 1 << 15; |
500 |
private static final int INT_SIGN = 1 << 31; |
501 |
|
502 |
// masks |
503 |
private static final long STOP_BIT = 0x0001L << ST_SHIFT; |
504 |
private static final long AC_MASK = ((long)SMASK) << AC_SHIFT; |
505 |
private static final long TC_MASK = ((long)SMASK) << TC_SHIFT; |
506 |
|
507 |
// units for incrementing and decrementing |
508 |
private static final long TC_UNIT = 1L << TC_SHIFT; |
509 |
private static final long AC_UNIT = 1L << AC_SHIFT; |
510 |
|
511 |
// masks and units for dealing with u = (int)(ctl >>> 32) |
512 |
private static final int UAC_SHIFT = AC_SHIFT - 32; |
513 |
private static final int UTC_SHIFT = TC_SHIFT - 32; |
514 |
private static final int UAC_MASK = SMASK << UAC_SHIFT; |
515 |
private static final int UTC_MASK = SMASK << UTC_SHIFT; |
516 |
private static final int UAC_UNIT = 1 << UAC_SHIFT; |
517 |
private static final int UTC_UNIT = 1 << UTC_SHIFT; |
518 |
|
519 |
// masks and units for dealing with e = (int)ctl |
520 |
private static final int E_MASK = 0x7fffffff; // no STOP_BIT |
521 |
private static final int EC_UNIT = 1 << EC_SHIFT; |
522 |
|
523 |
/** |
524 |
* The target parallelism level. |
525 |
*/ |
526 |
final int parallelism; |
527 |
|
528 |
/** |
529 |
* Index (mod submission queue length) of next element to take |
530 |
* from submission queue. Usage is identical to that for |
531 |
* per-worker queues -- see ForkJoinWorkerThread internal |
532 |
* documentation. |
533 |
*/ |
534 |
volatile int queueBase; |
535 |
|
536 |
/** |
537 |
* Index (mod submission queue length) of next element to add |
538 |
* in submission queue. Usage is identical to that for |
539 |
* per-worker queues -- see ForkJoinWorkerThread internal |
540 |
* documentation. |
541 |
*/ |
542 |
int queueTop; |
543 |
|
544 |
/** |
545 |
* True when shutdown() has been called. |
546 |
*/ |
547 |
volatile boolean shutdown; |
548 |
|
549 |
/** |
550 |
* True if use local fifo, not default lifo, for local polling |
551 |
* Read by, and replicated by ForkJoinWorkerThreads |
552 |
*/ |
553 |
final boolean locallyFifo; |
554 |
|
555 |
/** |
556 |
* The number of threads in ForkJoinWorkerThreads.helpQuiescePool. |
557 |
* When non-zero, suppresses automatic shutdown when active |
558 |
* counts become zero. |
559 |
*/ |
560 |
volatile int quiescerCount; |
561 |
|
562 |
/** |
563 |
* The number of threads blocked in join. |
564 |
*/ |
565 |
volatile int blockedCount; |
566 |
|
567 |
/** |
568 |
* Counter for worker Thread names (unrelated to their poolIndex) |
569 |
*/ |
570 |
private volatile int nextWorkerNumber; |
571 |
|
572 |
/** |
573 |
* The index for the next created worker. Accessed under scanGuard. |
574 |
*/ |
575 |
private int nextWorkerIndex; |
576 |
|
577 |
/** |
578 |
* SeqLock and index masking for updates to workers array. Locked |
579 |
* when SG_UNIT is set. Unlocking clears bit by adding |
580 |
* SG_UNIT. Staleness of read-only operations can be checked by |
581 |
* comparing scanGuard to value before the reads. The low 16 bits |
582 |
* (i.e, anding with SMASK) hold (the smallest power of two |
583 |
* covering all worker indices, minus one, and is used to avoid |
584 |
* dealing with large numbers of null slots when the workers array |
585 |
* is overallocated. |
586 |
*/ |
587 |
volatile int scanGuard; |
588 |
|
589 |
private static final int SG_UNIT = 1 << 16; |
590 |
|
591 |
/** |
592 |
* The wakeup interval (in nanoseconds) for a worker waiting for a |
593 |
* task when the pool is quiescent to instead try to shrink the |
594 |
* number of workers. The exact value does not matter too |
595 |
* much. It must be short enough to release resources during |
596 |
* sustained periods of idleness, but not so short that threads |
597 |
* are continually re-created. |
598 |
*/ |
599 |
private static final long SHRINK_RATE = |
600 |
4L * 1000L * 1000L * 1000L; // 4 seconds |
601 |
|
602 |
/** |
603 |
* Top-level loop for worker threads: On each step: if the |
604 |
* previous step swept through all queues and found no tasks, or |
605 |
* there are excess threads, then possibly blocks. Otherwise, |
606 |
* scans for and, if found, executes a task. Returns when pool |
607 |
* and/or worker terminate. |
608 |
* |
609 |
* @param w the worker |
610 |
*/ |
611 |
final void work(ForkJoinWorkerThread w) { |
612 |
boolean swept = false; // true on empty scans |
613 |
long c; |
614 |
while (!w.terminate && (int)(c = ctl) >= 0) { |
615 |
int a; // active count |
616 |
if (!swept && (a = (int)(c >> AC_SHIFT)) <= 0) |
617 |
swept = scan(w, a); |
618 |
else if (tryAwaitWork(w, c)) |
619 |
swept = false; |
620 |
} |
621 |
} |
622 |
|
623 |
// Signalling |
624 |
|
625 |
/** |
626 |
* Wakes up or creates a worker. |
627 |
*/ |
628 |
final void signalWork() { |
629 |
/* |
630 |
* The while condition is true if: (there is are too few total |
631 |
* workers OR there is at least one waiter) AND (there are too |
632 |
* few active workers OR the pool is terminating). The value |
633 |
* of e distinguishes the remaining cases: zero (no waiters) |
634 |
* for create, negative if terminating (in which case do |
635 |
* nothing), else release a waiter. The secondary checks for |
636 |
* release (non-null array etc) can fail if the pool begins |
637 |
* terminating after the test, and don't impose any added cost |
638 |
* because JVMs must perform null and bounds checks anyway. |
639 |
*/ |
640 |
long c; int e, u; |
641 |
while ((((e = (int)(c = ctl)) | (u = (int)(c >>> 32))) & |
642 |
(INT_SIGN|SHORT_SIGN)) == (INT_SIGN|SHORT_SIGN) && e >= 0) { |
643 |
if (e > 0) { // release a waiting worker |
644 |
int i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; |
645 |
if ((ws = workers) == null || |
646 |
(i = ~e & SMASK) >= ws.length || |
647 |
(w = ws[i]) == null) |
648 |
break; |
649 |
long nc = (((long)(w.nextWait & E_MASK)) | |
650 |
((long)(u + UAC_UNIT) << 32)); |
651 |
if (w.eventCount == e && |
652 |
UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { |
653 |
w.eventCount = (e + EC_UNIT) & E_MASK; |
654 |
if (w.parked) |
655 |
UNSAFE.unpark(w); |
656 |
break; |
657 |
} |
658 |
} |
659 |
else if (UNSAFE.compareAndSwapLong |
660 |
(this, ctlOffset, c, |
661 |
(long)(((u + UTC_UNIT) & UTC_MASK) | |
662 |
((u + UAC_UNIT) & UAC_MASK)) << 32)) { |
663 |
addWorker(); |
664 |
break; |
665 |
} |
666 |
} |
667 |
} |
668 |
|
669 |
/** |
670 |
* Variant of signalWork to help release waiters on rescans. |
671 |
* Tries once to release a waiter if active count < 0. |
672 |
* |
673 |
* @return false if failed due to contention, else true |
674 |
*/ |
675 |
private boolean tryReleaseWaiter() { |
676 |
long c; int e, i; ForkJoinWorkerThread w; ForkJoinWorkerThread[] ws; |
677 |
if ((e = (int)(c = ctl)) > 0 && |
678 |
(int)(c >> AC_SHIFT) < 0 && |
679 |
(ws = workers) != null && |
680 |
(i = ~e & SMASK) < ws.length && |
681 |
(w = ws[i]) != null) { |
682 |
long nc = ((long)(w.nextWait & E_MASK) | |
683 |
((c + AC_UNIT) & (AC_MASK|TC_MASK))); |
684 |
if (w.eventCount != e || |
685 |
!UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) |
686 |
return false; |
687 |
w.eventCount = (e + EC_UNIT) & E_MASK; |
688 |
if (w.parked) |
689 |
UNSAFE.unpark(w); |
690 |
} |
691 |
return true; |
692 |
} |
693 |
|
694 |
// Scanning for tasks |
695 |
|
696 |
/** |
697 |
* Scans for and, if found, executes one task. Scans start at a |
698 |
* random index of workers array, and randomly select the first |
699 |
* (2*#workers)-1 probes, and then, if all empty, resort to 2 |
700 |
* circular sweeps, which is necessary to check quiescence. and |
701 |
* taking a submission only if no stealable tasks were found. The |
702 |
* steal code inside the loop is a specialized form of |
703 |
* ForkJoinWorkerThread.deqTask, followed bookkeeping to support |
704 |
* helpJoinTask and signal propagation. The code for submission |
705 |
* queues is almost identical. On each steal, the worker completes |
706 |
* not only the task, but also all local tasks that this task may |
707 |
* have generated. On detecting staleness or contention when |
708 |
* trying to take a task, this method returns without finishing |
709 |
* sweep, which allows global state rechecks before retry. |
710 |
* |
711 |
* @param w the worker |
712 |
* @param a the number of active workers |
713 |
* @return true if swept all queues without finding a task |
714 |
*/ |
715 |
private boolean scan(ForkJoinWorkerThread w, int a) { |
716 |
int g = scanGuard; // mask 0 avoids useless scans if only one active |
717 |
int m = parallelism == 1 - a? 0 : g & SMASK; |
718 |
ForkJoinWorkerThread[] ws = workers; |
719 |
if (ws == null || ws.length <= m) // staleness check |
720 |
return false; |
721 |
for (int r = w.seed, k = r, j = -(m + m); j <= m + m; ++j) { |
722 |
ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; |
723 |
ForkJoinWorkerThread v = ws[k & m]; |
724 |
if (v != null && (b = v.queueBase) != v.queueTop && |
725 |
(q = v.queue) != null && (i = (q.length - 1) & b) >= 0) { |
726 |
long u = (i << ASHIFT) + ABASE; |
727 |
if ((t = q[i]) != null && v.queueBase == b && |
728 |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
729 |
int d = (v.queueBase = b + 1) - v.queueTop; |
730 |
v.stealHint = w.poolIndex; |
731 |
if (d != 0) |
732 |
signalWork(); // propagate if nonempty |
733 |
w.execTask(t); |
734 |
} |
735 |
r ^= r << 13; r ^= r >>> 17; w.seed = r ^ (r << 5); |
736 |
return false; // store next seed |
737 |
} |
738 |
else if (j < 0) { // xorshift |
739 |
r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5; |
740 |
} |
741 |
else |
742 |
++k; |
743 |
} |
744 |
if (scanGuard != g) // staleness check |
745 |
return false; |
746 |
else { // try to take submission |
747 |
ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; |
748 |
if ((b = queueBase) != queueTop && |
749 |
(q = submissionQueue) != null && |
750 |
(i = (q.length - 1) & b) >= 0) { |
751 |
long u = (i << ASHIFT) + ABASE; |
752 |
if ((t = q[i]) != null && queueBase == b && |
753 |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
754 |
queueBase = b + 1; |
755 |
w.execTask(t); |
756 |
} |
757 |
return false; |
758 |
} |
759 |
return true; // all queues empty |
760 |
} |
761 |
} |
762 |
|
763 |
/** |
764 |
* Tries to enqueue worker w in wait queue and await change in |
765 |
* worker's eventCount. If the pool is quiescent, possibly |
766 |
* terminates worker upon exit. Otherwise, before blocking, |
767 |
* rescans queues to avoid missed signals. Upon finding work, |
768 |
* releases at least one worker (which may be the current |
769 |
* worker). Rescans restart upon detected staleness or failure to |
770 |
* release due to contention. Note the unusual conventions about |
771 |
* Thread.interrupt here and elsewhere: Because interrupts are |
772 |
* used solely to alert threads to check termination, which is |
773 |
* checked here anyway, we clear status (using Thread.interrupted) |
774 |
* before any call to park, so that park does not immediately |
775 |
* return due to status being set via some other unrelated call to |
776 |
* interrupt in user code. |
777 |
* |
778 |
* @param w the calling worker |
779 |
* @param c the ctl value on entry |
780 |
* @return true if waited or another thread was released upon enq |
781 |
*/ |
782 |
private boolean tryAwaitWork(ForkJoinWorkerThread w, long c) { |
783 |
int v = w.eventCount; |
784 |
w.nextWait = (int)c; // w's successor record |
785 |
long nc = (long)(v & E_MASK) | ((c - AC_UNIT) & (AC_MASK|TC_MASK)); |
786 |
if (ctl != c || !UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { |
787 |
long d = ctl; // return true if lost to a deq, to force scan |
788 |
return (int)d != (int)c && ((d - c) & AC_MASK) >= 0L; |
789 |
} |
790 |
for (int sc = w.stealCount; sc != 0;) { // accumulate stealCount |
791 |
long s = stealCount; |
792 |
if (UNSAFE.compareAndSwapLong(this, stealCountOffset, s, s + sc)) |
793 |
sc = w.stealCount = 0; |
794 |
else if (w.eventCount != v) |
795 |
return true; // update next time |
796 |
} |
797 |
if (parallelism + (int)(nc >> AC_SHIFT) == 0 && |
798 |
blockedCount == 0 && quiescerCount == 0) |
799 |
idleAwaitWork(w, nc, c, v); // quiescent |
800 |
for (boolean rescanned = false;;) { |
801 |
if (w.eventCount != v) |
802 |
return true; |
803 |
if (!rescanned) { |
804 |
int g = scanGuard, m = g & SMASK; |
805 |
ForkJoinWorkerThread[] ws = workers; |
806 |
if (ws != null && m < ws.length) { |
807 |
rescanned = true; |
808 |
for (int i = 0; i <= m; ++i) { |
809 |
ForkJoinWorkerThread u = ws[i]; |
810 |
if (u != null) { |
811 |
if (u.queueBase != u.queueTop && |
812 |
!tryReleaseWaiter()) |
813 |
rescanned = false; // contended |
814 |
if (w.eventCount != v) |
815 |
return true; |
816 |
} |
817 |
} |
818 |
} |
819 |
if (scanGuard != g || // stale |
820 |
(queueBase != queueTop && !tryReleaseWaiter())) |
821 |
rescanned = false; |
822 |
if (!rescanned) |
823 |
Thread.yield(); // reduce contention |
824 |
else |
825 |
Thread.interrupted(); // clear before park |
826 |
} |
827 |
else { |
828 |
w.parked = true; // must recheck |
829 |
if (w.eventCount != v) { |
830 |
w.parked = false; |
831 |
return true; |
832 |
} |
833 |
LockSupport.park(this); |
834 |
rescanned = w.parked = false; |
835 |
} |
836 |
} |
837 |
} |
838 |
|
839 |
/** |
840 |
* If inactivating worker w has caused pool to become |
841 |
* quiescent, check for pool termination, and wait for event |
842 |
* for up to SHRINK_RATE nanosecs (rescans are unnecessary in |
843 |
* this case because quiescence reflects consensus about lack |
844 |
* of work). On timeout, if ctl has not changed, terminate the |
845 |
* worker. Upon its termination (see deregisterWorker), it may |
846 |
* wake up another worker to possibly repeat this process. |
847 |
* |
848 |
* @param w the calling worker |
849 |
* @param currentCtl the ctl value after enqueuing w |
850 |
* @param prevCtl the ctl value if w terminated |
851 |
* @param v the eventCount w awaits change |
852 |
*/ |
853 |
private void idleAwaitWork(ForkJoinWorkerThread w, long currentCtl, |
854 |
long prevCtl, int v) { |
855 |
if (w.eventCount == v) { |
856 |
if (shutdown) |
857 |
tryTerminate(false); |
858 |
ForkJoinTask.helpExpungeStaleExceptions(); // help clean weak refs |
859 |
while (ctl == currentCtl) { |
860 |
long startTime = System.nanoTime(); |
861 |
w.parked = true; |
862 |
if (w.eventCount == v) // must recheck |
863 |
LockSupport.parkNanos(this, SHRINK_RATE); |
864 |
w.parked = false; |
865 |
if (w.eventCount != v) |
866 |
break; |
867 |
else if (System.nanoTime() - startTime < SHRINK_RATE) |
868 |
Thread.interrupted(); // spurious wakeup |
869 |
else if (UNSAFE.compareAndSwapLong(this, ctlOffset, |
870 |
currentCtl, prevCtl)) { |
871 |
w.terminate = true; // restore previous |
872 |
w.eventCount = ((int)currentCtl + EC_UNIT) & E_MASK; |
873 |
break; |
874 |
} |
875 |
} |
876 |
} |
877 |
} |
878 |
|
879 |
// Submissions |
880 |
|
881 |
/** |
882 |
* Enqueues the given task in the submissionQueue. Same idea as |
883 |
* ForkJoinWorkerThread.pushTask except for use of submissionLock. |
884 |
* |
885 |
* @param t the task |
886 |
*/ |
887 |
private void addSubmission(ForkJoinTask<?> t) { |
888 |
final ReentrantLock lock = this.submissionLock; |
889 |
lock.lock(); |
890 |
try { |
891 |
ForkJoinTask<?>[] q; int s, m; |
892 |
if ((q = submissionQueue) != null) { // ignore if queue removed |
893 |
long u = (((s = queueTop) & (m = q.length-1)) << ASHIFT)+ABASE; |
894 |
UNSAFE.putOrderedObject(q, u, t); |
895 |
queueTop = s + 1; |
896 |
if (s - queueBase == m) |
897 |
growSubmissionQueue(); |
898 |
} |
899 |
} finally { |
900 |
lock.unlock(); |
901 |
} |
902 |
signalWork(); |
903 |
} |
904 |
|
905 |
// (pollSubmission is defined below with exported methods) |
906 |
|
907 |
/** |
908 |
* Creates or doubles submissionQueue array. |
909 |
* Basically identical to ForkJoinWorkerThread version. |
910 |
*/ |
911 |
private void growSubmissionQueue() { |
912 |
ForkJoinTask<?>[] oldQ = submissionQueue; |
913 |
int size = oldQ != null ? oldQ.length << 1 : INITIAL_QUEUE_CAPACITY; |
914 |
if (size > MAXIMUM_QUEUE_CAPACITY) |
915 |
throw new RejectedExecutionException("Queue capacity exceeded"); |
916 |
if (size < INITIAL_QUEUE_CAPACITY) |
917 |
size = INITIAL_QUEUE_CAPACITY; |
918 |
ForkJoinTask<?>[] q = submissionQueue = new ForkJoinTask<?>[size]; |
919 |
int mask = size - 1; |
920 |
int top = queueTop; |
921 |
int oldMask; |
922 |
if (oldQ != null && (oldMask = oldQ.length - 1) >= 0) { |
923 |
for (int b = queueBase; b != top; ++b) { |
924 |
long u = ((b & oldMask) << ASHIFT) + ABASE; |
925 |
Object x = UNSAFE.getObjectVolatile(oldQ, u); |
926 |
if (x != null && UNSAFE.compareAndSwapObject(oldQ, u, x, null)) |
927 |
UNSAFE.putObjectVolatile |
928 |
(q, ((b & mask) << ASHIFT) + ABASE, x); |
929 |
} |
930 |
} |
931 |
} |
932 |
|
933 |
// Blocking support |
934 |
|
935 |
/** |
936 |
* Tries to increment blockedCount, decrement active count |
937 |
* (sometimes implicitly) and possibly release or create a |
938 |
* compensating worker in preparation for blocking. Fails |
939 |
* on contention or termination. |
940 |
* |
941 |
* @return true if the caller can block, else should recheck and retry |
942 |
*/ |
943 |
private boolean tryPreBlock() { |
944 |
int b = blockedCount; |
945 |
if (UNSAFE.compareAndSwapInt(this, blockedCountOffset, b, b + 1)) { |
946 |
int pc = parallelism; |
947 |
do { |
948 |
ForkJoinWorkerThread[] ws; ForkJoinWorkerThread w; |
949 |
int e, ac, tc, rc, i; |
950 |
long c = ctl; |
951 |
int u = (int)(c >>> 32); |
952 |
if ((e = (int)c) < 0) { |
953 |
// skip -- terminating |
954 |
} |
955 |
else if ((ac = (u >> UAC_SHIFT)) <= 0 && e != 0 && |
956 |
(ws = workers) != null && |
957 |
(i = ~e & SMASK) < ws.length && |
958 |
(w = ws[i]) != null) { |
959 |
long nc = ((long)(w.nextWait & E_MASK) | |
960 |
(c & (AC_MASK|TC_MASK))); |
961 |
if (w.eventCount == e && |
962 |
UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { |
963 |
w.eventCount = (e + EC_UNIT) & E_MASK; |
964 |
if (w.parked) |
965 |
UNSAFE.unpark(w); |
966 |
return true; // release an idle worker |
967 |
} |
968 |
} |
969 |
else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) { |
970 |
long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK); |
971 |
if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) |
972 |
return true; // no compensation needed |
973 |
} |
974 |
else if (tc + pc < MAX_ID) { |
975 |
long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK); |
976 |
if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, nc)) { |
977 |
addWorker(); |
978 |
return true; // create a replacement |
979 |
} |
980 |
} |
981 |
// try to back out on any failure and let caller retry |
982 |
} while (!UNSAFE.compareAndSwapInt(this, blockedCountOffset, |
983 |
b = blockedCount, b - 1)); |
984 |
} |
985 |
return false; |
986 |
} |
987 |
|
988 |
/** |
989 |
* Decrements blockedCount and increments active count |
990 |
*/ |
991 |
private void postBlock() { |
992 |
long c; |
993 |
do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, // no mask |
994 |
c = ctl, c + AC_UNIT)); |
995 |
int b; |
996 |
do {} while(!UNSAFE.compareAndSwapInt(this, blockedCountOffset, |
997 |
b = blockedCount, b - 1)); |
998 |
} |
999 |
|
1000 |
/** |
1001 |
* Possibly blocks waiting for the given task to complete, or |
1002 |
* cancels the task if terminating. Fails to wait if contended. |
1003 |
* |
1004 |
* @param joinMe the task |
1005 |
*/ |
1006 |
final void tryAwaitJoin(ForkJoinTask<?> joinMe) { |
1007 |
int s; |
1008 |
Thread.interrupted(); // clear interrupts before checking termination |
1009 |
if (joinMe.status >= 0) { |
1010 |
if (tryPreBlock()) { |
1011 |
joinMe.tryAwaitDone(0L); |
1012 |
postBlock(); |
1013 |
} |
1014 |
else if ((ctl & STOP_BIT) != 0L) |
1015 |
joinMe.cancelIgnoringExceptions(); |
1016 |
} |
1017 |
} |
1018 |
|
1019 |
/** |
1020 |
* Possibly blocks the given worker waiting for joinMe to |
1021 |
* complete or timeout |
1022 |
* |
1023 |
* @param joinMe the task |
1024 |
* @param millis the wait time for underlying Object.wait |
1025 |
*/ |
1026 |
final void timedAwaitJoin(ForkJoinTask<?> joinMe, long nanos) { |
1027 |
while (joinMe.status >= 0) { |
1028 |
Thread.interrupted(); |
1029 |
if ((ctl & STOP_BIT) != 0L) { |
1030 |
joinMe.cancelIgnoringExceptions(); |
1031 |
break; |
1032 |
} |
1033 |
if (tryPreBlock()) { |
1034 |
long last = System.nanoTime(); |
1035 |
while (joinMe.status >= 0) { |
1036 |
long millis = TimeUnit.NANOSECONDS.toMillis(nanos); |
1037 |
if (millis <= 0) |
1038 |
break; |
1039 |
joinMe.tryAwaitDone(millis); |
1040 |
if (joinMe.status < 0) |
1041 |
break; |
1042 |
if ((ctl & STOP_BIT) != 0L) { |
1043 |
joinMe.cancelIgnoringExceptions(); |
1044 |
break; |
1045 |
} |
1046 |
long now = System.nanoTime(); |
1047 |
nanos -= now - last; |
1048 |
last = now; |
1049 |
} |
1050 |
postBlock(); |
1051 |
break; |
1052 |
} |
1053 |
} |
1054 |
} |
1055 |
|
1056 |
/** |
1057 |
* If necessary, compensates for blocker, and blocks |
1058 |
*/ |
1059 |
private void awaitBlocker(ManagedBlocker blocker) |
1060 |
throws InterruptedException { |
1061 |
while (!blocker.isReleasable()) { |
1062 |
if (tryPreBlock()) { |
1063 |
try { |
1064 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1065 |
} finally { |
1066 |
postBlock(); |
1067 |
} |
1068 |
break; |
1069 |
} |
1070 |
} |
1071 |
} |
1072 |
|
1073 |
// Creating, registering and deregistring workers |
1074 |
|
1075 |
/** |
1076 |
* Tries to create and start a worker; minimally rolls back counts |
1077 |
* on failure. |
1078 |
*/ |
1079 |
private void addWorker() { |
1080 |
Throwable ex = null; |
1081 |
ForkJoinWorkerThread t = null; |
1082 |
try { |
1083 |
t = factory.newThread(this); |
1084 |
} catch (Throwable e) { |
1085 |
ex = e; |
1086 |
} |
1087 |
if (t == null) { // null or exceptional factory return |
1088 |
long c; // adjust counts |
1089 |
do {} while (!UNSAFE.compareAndSwapLong |
1090 |
(this, ctlOffset, c = ctl, |
1091 |
(((c - AC_UNIT) & AC_MASK) | |
1092 |
((c - TC_UNIT) & TC_MASK) | |
1093 |
(c & ~(AC_MASK|TC_MASK))))); |
1094 |
// Propagate exception if originating from an external caller |
1095 |
if (!tryTerminate(false) && ex != null && |
1096 |
!(Thread.currentThread() instanceof ForkJoinWorkerThread)) |
1097 |
UNSAFE.throwException(ex); |
1098 |
} |
1099 |
else |
1100 |
t.start(); |
1101 |
} |
1102 |
|
1103 |
/** |
1104 |
* Callback from ForkJoinWorkerThread constructor to assign a |
1105 |
* public name |
1106 |
*/ |
1107 |
final String nextWorkerName() { |
1108 |
for (int n;;) { |
1109 |
if (UNSAFE.compareAndSwapInt(this, nextWorkerNumberOffset, |
1110 |
n = nextWorkerNumber, ++n)) |
1111 |
return workerNamePrefix + n; |
1112 |
} |
1113 |
} |
1114 |
|
1115 |
/** |
1116 |
* Callback from ForkJoinWorkerThread constructor to |
1117 |
* determine its poolIndex and record in workers array. |
1118 |
* |
1119 |
* @param w the worker |
1120 |
* @return the worker's pool index |
1121 |
*/ |
1122 |
final int registerWorker(ForkJoinWorkerThread w) { |
1123 |
/* |
1124 |
* In the typical case, a new worker acquires the lock, uses |
1125 |
* next available index and returns quickly. Since we should |
1126 |
* not block callers (ultimately from signalWork or |
1127 |
* tryPreBlock) waiting for the lock needed to do this, we |
1128 |
* instead help release other workers while waiting for the |
1129 |
* lock. |
1130 |
*/ |
1131 |
for (int g;;) { |
1132 |
ForkJoinWorkerThread[] ws; |
1133 |
if (((g = scanGuard) & SG_UNIT) == 0 && |
1134 |
UNSAFE.compareAndSwapInt(this, scanGuardOffset, |
1135 |
g, g | SG_UNIT)) { |
1136 |
int k = nextWorkerIndex; |
1137 |
try { |
1138 |
if ((ws = workers) != null) { // ignore on shutdown |
1139 |
int n = ws.length; |
1140 |
if (k < 0 || k >= n || ws[k] != null) { |
1141 |
for (k = 0; k < n && ws[k] != null; ++k) |
1142 |
; |
1143 |
if (k == n) |
1144 |
ws = workers = Arrays.copyOf(ws, n << 1); |
1145 |
} |
1146 |
ws[k] = w; |
1147 |
nextWorkerIndex = k + 1; |
1148 |
int m = g & SMASK; |
1149 |
g = k >= m? ((m << 1) + 1) & SMASK : g + (SG_UNIT<<1); |
1150 |
} |
1151 |
} finally { |
1152 |
scanGuard = g; |
1153 |
} |
1154 |
return k; |
1155 |
} |
1156 |
else if ((ws = workers) != null) { // help release others |
1157 |
for (ForkJoinWorkerThread u : ws) { |
1158 |
if (u != null && u.queueBase != u.queueTop) { |
1159 |
if (tryReleaseWaiter()) |
1160 |
break; |
1161 |
} |
1162 |
} |
1163 |
} |
1164 |
} |
1165 |
} |
1166 |
|
1167 |
/** |
1168 |
* Final callback from terminating worker. Removes record of |
1169 |
* worker from array, and adjusts counts. If pool is shutting |
1170 |
* down, tries to complete termination. |
1171 |
* |
1172 |
* @param w the worker |
1173 |
*/ |
1174 |
final void deregisterWorker(ForkJoinWorkerThread w, Throwable ex) { |
1175 |
int idx = w.poolIndex; |
1176 |
int sc = w.stealCount; |
1177 |
int steps = 0; |
1178 |
// Remove from array, adjust worker counts and collect steal count. |
1179 |
// We can intermix failed removes or adjusts with steal updates |
1180 |
do { |
1181 |
long s, c; |
1182 |
int g; |
1183 |
if (steps == 0 && ((g = scanGuard) & SG_UNIT) == 0 && |
1184 |
UNSAFE.compareAndSwapInt(this, scanGuardOffset, |
1185 |
g, g |= SG_UNIT)) { |
1186 |
ForkJoinWorkerThread[] ws = workers; |
1187 |
if (ws != null && idx >= 0 && |
1188 |
idx < ws.length && ws[idx] == w) |
1189 |
ws[idx] = null; // verify |
1190 |
nextWorkerIndex = idx; |
1191 |
scanGuard = g + SG_UNIT; |
1192 |
steps = 1; |
1193 |
} |
1194 |
if (steps == 1 && |
1195 |
UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl, |
1196 |
(((c - AC_UNIT) & AC_MASK) | |
1197 |
((c - TC_UNIT) & TC_MASK) | |
1198 |
(c & ~(AC_MASK|TC_MASK))))) |
1199 |
steps = 2; |
1200 |
if (sc != 0 && |
1201 |
UNSAFE.compareAndSwapLong(this, stealCountOffset, |
1202 |
s = stealCount, s + sc)) |
1203 |
sc = 0; |
1204 |
} while (steps != 2 || sc != 0); |
1205 |
if (!tryTerminate(false)) { |
1206 |
if (ex != null) // possibly replace if died abnormally |
1207 |
signalWork(); |
1208 |
else |
1209 |
tryReleaseWaiter(); |
1210 |
} |
1211 |
} |
1212 |
|
1213 |
// Shutdown and termination |
1214 |
|
1215 |
/** |
1216 |
* Possibly initiates and/or completes termination. |
1217 |
* |
1218 |
* @param now if true, unconditionally terminate, else only |
1219 |
* if shutdown and empty queue and no active workers |
1220 |
* @return true if now terminating or terminated |
1221 |
*/ |
1222 |
private boolean tryTerminate(boolean now) { |
1223 |
long c; |
1224 |
while (((c = ctl) & STOP_BIT) == 0) { |
1225 |
if (!now) { |
1226 |
if ((int)(c >> AC_SHIFT) != -parallelism) |
1227 |
return false; |
1228 |
if (!shutdown || blockedCount != 0 || quiescerCount != 0 || |
1229 |
queueBase != queueTop) { |
1230 |
if (ctl == c) // staleness check |
1231 |
return false; |
1232 |
continue; |
1233 |
} |
1234 |
} |
1235 |
if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, c | STOP_BIT)) |
1236 |
startTerminating(); |
1237 |
} |
1238 |
if ((short)(c >>> TC_SHIFT) == -parallelism) { // signal when 0 workers |
1239 |
final ReentrantLock lock = this.submissionLock; |
1240 |
lock.lock(); |
1241 |
try { |
1242 |
termination.signalAll(); |
1243 |
} finally { |
1244 |
lock.unlock(); |
1245 |
} |
1246 |
} |
1247 |
return true; |
1248 |
} |
1249 |
|
1250 |
/** |
1251 |
* Runs up to three passes through workers: (0) Setting |
1252 |
* termination status for each worker, followed by wakeups up to |
1253 |
* queued workers; (1) helping cancel tasks; (2) interrupting |
1254 |
* lagging threads (likely in external tasks, but possibly also |
1255 |
* blocked in joins). Each pass repeats previous steps because of |
1256 |
* potential lagging thread creation. |
1257 |
*/ |
1258 |
private void startTerminating() { |
1259 |
cancelSubmissions(); |
1260 |
for (int pass = 0; pass < 3; ++pass) { |
1261 |
ForkJoinWorkerThread[] ws = workers; |
1262 |
if (ws != null) { |
1263 |
for (ForkJoinWorkerThread w : ws) { |
1264 |
if (w != null) { |
1265 |
w.terminate = true; |
1266 |
if (pass > 0) { |
1267 |
w.cancelTasks(); |
1268 |
if (pass > 1 && !w.isInterrupted()) { |
1269 |
try { |
1270 |
w.interrupt(); |
1271 |
} catch (SecurityException ignore) { |
1272 |
} |
1273 |
} |
1274 |
} |
1275 |
} |
1276 |
} |
1277 |
terminateWaiters(); |
1278 |
} |
1279 |
} |
1280 |
} |
1281 |
|
1282 |
/** |
1283 |
* Polls and cancels all submissions. Called only during termination. |
1284 |
*/ |
1285 |
private void cancelSubmissions() { |
1286 |
while (queueBase != queueTop) { |
1287 |
ForkJoinTask<?> task = pollSubmission(); |
1288 |
if (task != null) { |
1289 |
try { |
1290 |
task.cancel(false); |
1291 |
} catch (Throwable ignore) { |
1292 |
} |
1293 |
} |
1294 |
} |
1295 |
} |
1296 |
|
1297 |
/** |
1298 |
* Tries to set the termination status of waiting workers, and |
1299 |
* then wakes them up (after which they will terminate). |
1300 |
*/ |
1301 |
private void terminateWaiters() { |
1302 |
ForkJoinWorkerThread[] ws = workers; |
1303 |
if (ws != null) { |
1304 |
ForkJoinWorkerThread w; long c; int i, e; |
1305 |
int n = ws.length; |
1306 |
while ((i = ~(e = (int)(c = ctl)) & SMASK) < n && |
1307 |
(w = ws[i]) != null && w.eventCount == (e & E_MASK)) { |
1308 |
if (UNSAFE.compareAndSwapLong(this, ctlOffset, c, |
1309 |
(long)(w.nextWait & E_MASK) | |
1310 |
((c + AC_UNIT) & AC_MASK) | |
1311 |
(c & (TC_MASK|STOP_BIT)))) { |
1312 |
w.terminate = true; |
1313 |
w.eventCount = e + EC_UNIT; |
1314 |
if (w.parked) |
1315 |
UNSAFE.unpark(w); |
1316 |
} |
1317 |
} |
1318 |
} |
1319 |
} |
1320 |
|
1321 |
// misc ForkJoinWorkerThread support |
1322 |
|
1323 |
/** |
1324 |
* Increment or decrement quiescerCount. Needed only to prevent |
1325 |
* triggering shutdown if a worker is transiently inactive while |
1326 |
* checking quiescence. |
1327 |
* |
1328 |
* @param delta 1 for increment, -1 for decrement |
1329 |
*/ |
1330 |
final void addQuiescerCount(int delta) { |
1331 |
int c; |
1332 |
do {} while(!UNSAFE.compareAndSwapInt(this, quiescerCountOffset, |
1333 |
c = quiescerCount, c + delta)); |
1334 |
} |
1335 |
|
1336 |
/** |
1337 |
* Directly increment or decrement active count without |
1338 |
* queuing. This method is used to transiently assert inactivation |
1339 |
* while checking quiescence. |
1340 |
* |
1341 |
* @param delta 1 for increment, -1 for decrement |
1342 |
*/ |
1343 |
final void addActiveCount(int delta) { |
1344 |
long d = delta < 0 ? -AC_UNIT : AC_UNIT; |
1345 |
long c; |
1346 |
do {} while (!UNSAFE.compareAndSwapLong(this, ctlOffset, c = ctl, |
1347 |
((c + d) & AC_MASK) | |
1348 |
(c & ~AC_MASK))); |
1349 |
} |
1350 |
|
1351 |
/** |
1352 |
* Returns the approximate (non-atomic) number of idle threads per |
1353 |
* active thread. |
1354 |
*/ |
1355 |
final int idlePerActive() { |
1356 |
// Approximate at powers of two for small values, saturate past 4 |
1357 |
int p = parallelism; |
1358 |
int a = p + (int)(ctl >> AC_SHIFT); |
1359 |
return (a > (p >>>= 1) ? 0 : |
1360 |
a > (p >>>= 1) ? 1 : |
1361 |
a > (p >>>= 1) ? 2 : |
1362 |
a > (p >>>= 1) ? 4 : |
1363 |
8); |
1364 |
} |
1365 |
|
1366 |
// Exported methods |
1367 |
|
1368 |
// Constructors |
1369 |
|
1370 |
/** |
1371 |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
1372 |
* java.lang.Runtime#availableProcessors}, using the {@linkplain |
1373 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1374 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1375 |
* |
1376 |
* @throws SecurityException if a security manager exists and |
1377 |
* the caller is not permitted to modify threads |
1378 |
* because it does not hold {@link |
1379 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1380 |
*/ |
1381 |
public ForkJoinPool() { |
1382 |
this(Runtime.getRuntime().availableProcessors(), |
1383 |
defaultForkJoinWorkerThreadFactory, null, false); |
1384 |
} |
1385 |
|
1386 |
/** |
1387 |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
1388 |
* level, the {@linkplain |
1389 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1390 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1391 |
* |
1392 |
* @param parallelism the parallelism level |
1393 |
* @throws IllegalArgumentException if parallelism less than or |
1394 |
* equal to zero, or greater than implementation limit |
1395 |
* @throws SecurityException if a security manager exists and |
1396 |
* the caller is not permitted to modify threads |
1397 |
* because it does not hold {@link |
1398 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1399 |
*/ |
1400 |
public ForkJoinPool(int parallelism) { |
1401 |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
1402 |
} |
1403 |
|
1404 |
/** |
1405 |
* Creates a {@code ForkJoinPool} with the given parameters. |
1406 |
* |
1407 |
* @param parallelism the parallelism level. For default value, |
1408 |
* use {@link java.lang.Runtime#availableProcessors}. |
1409 |
* @param factory the factory for creating new threads. For default value, |
1410 |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
1411 |
* @param handler the handler for internal worker threads that |
1412 |
* terminate due to unrecoverable errors encountered while executing |
1413 |
* tasks. For default value, use {@code null}. |
1414 |
* @param asyncMode if true, |
1415 |
* establishes local first-in-first-out scheduling mode for forked |
1416 |
* tasks that are never joined. This mode may be more appropriate |
1417 |
* than default locally stack-based mode in applications in which |
1418 |
* worker threads only process event-style asynchronous tasks. |
1419 |
* For default value, use {@code false}. |
1420 |
* @throws IllegalArgumentException if parallelism less than or |
1421 |
* equal to zero, or greater than implementation limit |
1422 |
* @throws NullPointerException if the factory is null |
1423 |
* @throws SecurityException if a security manager exists and |
1424 |
* the caller is not permitted to modify threads |
1425 |
* because it does not hold {@link |
1426 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1427 |
*/ |
1428 |
public ForkJoinPool(int parallelism, |
1429 |
ForkJoinWorkerThreadFactory factory, |
1430 |
Thread.UncaughtExceptionHandler handler, |
1431 |
boolean asyncMode) { |
1432 |
checkPermission(); |
1433 |
if (factory == null) |
1434 |
throw new NullPointerException(); |
1435 |
if (parallelism <= 0 || parallelism > MAX_ID) |
1436 |
throw new IllegalArgumentException(); |
1437 |
this.parallelism = parallelism; |
1438 |
this.factory = factory; |
1439 |
this.ueh = handler; |
1440 |
this.locallyFifo = asyncMode; |
1441 |
long np = (long)(-parallelism); // offset ctl counts |
1442 |
this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK); |
1443 |
this.submissionQueue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY]; |
1444 |
// initialize workers array with room for 2*parallelism if possible |
1445 |
int n = parallelism << 1; |
1446 |
if (n >= MAX_ID) |
1447 |
n = MAX_ID; |
1448 |
else { // See Hackers Delight, sec 3.2, where n < (1 << 16) |
1449 |
n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; |
1450 |
} |
1451 |
workers = new ForkJoinWorkerThread[n + 1]; |
1452 |
this.submissionLock = new ReentrantLock(); |
1453 |
this.termination = submissionLock.newCondition(); |
1454 |
StringBuilder sb = new StringBuilder("ForkJoinPool-"); |
1455 |
sb.append(poolNumberGenerator.incrementAndGet()); |
1456 |
sb.append("-worker-"); |
1457 |
this.workerNamePrefix = sb.toString(); |
1458 |
} |
1459 |
|
1460 |
// Execution methods |
1461 |
|
1462 |
/** |
1463 |
* Performs the given task, returning its result upon completion. |
1464 |
* If the computation encounters an unchecked Exception or Error, |
1465 |
* it is rethrown as the outcome of this invocation. Rethrown |
1466 |
* exceptions behave in the same way as regular exceptions, but, |
1467 |
* when possible, contain stack traces (as displayed for example |
1468 |
* using {@code ex.printStackTrace()}) of both the current thread |
1469 |
* as well as the thread actually encountering the exception; |
1470 |
* minimally only the latter. |
1471 |
* |
1472 |
* @param task the task |
1473 |
* @return the task's result |
1474 |
* @throws NullPointerException if the task is null |
1475 |
* @throws RejectedExecutionException if the task cannot be |
1476 |
* scheduled for execution |
1477 |
*/ |
1478 |
public <T> T invoke(ForkJoinTask<T> task) { |
1479 |
Thread t = Thread.currentThread(); |
1480 |
if (task == null) |
1481 |
throw new NullPointerException(); |
1482 |
if (shutdown) |
1483 |
throw new RejectedExecutionException(); |
1484 |
if ((t instanceof ForkJoinWorkerThread) && |
1485 |
((ForkJoinWorkerThread)t).pool == this) |
1486 |
return task.invoke(); // bypass submit if in same pool |
1487 |
else { |
1488 |
addSubmission(task); |
1489 |
return task.join(); |
1490 |
} |
1491 |
} |
1492 |
|
1493 |
/** |
1494 |
* Unless terminating, forks task if within an ongoing FJ |
1495 |
* computation in the current pool, else submits as external task. |
1496 |
*/ |
1497 |
private <T> void forkOrSubmit(ForkJoinTask<T> task) { |
1498 |
ForkJoinWorkerThread w; |
1499 |
Thread t = Thread.currentThread(); |
1500 |
if (shutdown) |
1501 |
throw new RejectedExecutionException(); |
1502 |
if ((t instanceof ForkJoinWorkerThread) && |
1503 |
(w = (ForkJoinWorkerThread)t).pool == this) |
1504 |
w.pushTask(task); |
1505 |
else |
1506 |
addSubmission(task); |
1507 |
} |
1508 |
|
1509 |
/** |
1510 |
* Arranges for (asynchronous) execution of the given task. |
1511 |
* |
1512 |
* @param task the task |
1513 |
* @throws NullPointerException if the task is null |
1514 |
* @throws RejectedExecutionException if the task cannot be |
1515 |
* scheduled for execution |
1516 |
*/ |
1517 |
public void execute(ForkJoinTask<?> task) { |
1518 |
if (task == null) |
1519 |
throw new NullPointerException(); |
1520 |
forkOrSubmit(task); |
1521 |
} |
1522 |
|
1523 |
// AbstractExecutorService methods |
1524 |
|
1525 |
/** |
1526 |
* @throws NullPointerException if the task is null |
1527 |
* @throws RejectedExecutionException if the task cannot be |
1528 |
* scheduled for execution |
1529 |
*/ |
1530 |
public void execute(Runnable task) { |
1531 |
if (task == null) |
1532 |
throw new NullPointerException(); |
1533 |
ForkJoinTask<?> job; |
1534 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1535 |
job = (ForkJoinTask<?>) task; |
1536 |
else |
1537 |
job = ForkJoinTask.adapt(task, null); |
1538 |
forkOrSubmit(job); |
1539 |
} |
1540 |
|
1541 |
/** |
1542 |
* Submits a ForkJoinTask for execution. |
1543 |
* |
1544 |
* @param task the task to submit |
1545 |
* @return the task |
1546 |
* @throws NullPointerException if the task is null |
1547 |
* @throws RejectedExecutionException if the task cannot be |
1548 |
* scheduled for execution |
1549 |
*/ |
1550 |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
1551 |
if (task == null) |
1552 |
throw new NullPointerException(); |
1553 |
forkOrSubmit(task); |
1554 |
return task; |
1555 |
} |
1556 |
|
1557 |
/** |
1558 |
* @throws NullPointerException if the task is null |
1559 |
* @throws RejectedExecutionException if the task cannot be |
1560 |
* scheduled for execution |
1561 |
*/ |
1562 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
1563 |
if (task == null) |
1564 |
throw new NullPointerException(); |
1565 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task); |
1566 |
forkOrSubmit(job); |
1567 |
return job; |
1568 |
} |
1569 |
|
1570 |
/** |
1571 |
* @throws NullPointerException if the task is null |
1572 |
* @throws RejectedExecutionException if the task cannot be |
1573 |
* scheduled for execution |
1574 |
*/ |
1575 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
1576 |
if (task == null) |
1577 |
throw new NullPointerException(); |
1578 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); |
1579 |
forkOrSubmit(job); |
1580 |
return job; |
1581 |
} |
1582 |
|
1583 |
/** |
1584 |
* @throws NullPointerException if the task is null |
1585 |
* @throws RejectedExecutionException if the task cannot be |
1586 |
* scheduled for execution |
1587 |
*/ |
1588 |
public ForkJoinTask<?> submit(Runnable task) { |
1589 |
if (task == null) |
1590 |
throw new NullPointerException(); |
1591 |
ForkJoinTask<?> job; |
1592 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1593 |
job = (ForkJoinTask<?>) task; |
1594 |
else |
1595 |
job = ForkJoinTask.adapt(task, null); |
1596 |
forkOrSubmit(job); |
1597 |
return job; |
1598 |
} |
1599 |
|
1600 |
/** |
1601 |
* @throws NullPointerException {@inheritDoc} |
1602 |
* @throws RejectedExecutionException {@inheritDoc} |
1603 |
*/ |
1604 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
1605 |
ArrayList<ForkJoinTask<T>> forkJoinTasks = |
1606 |
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
1607 |
for (Callable<T> task : tasks) |
1608 |
forkJoinTasks.add(ForkJoinTask.adapt(task)); |
1609 |
invoke(new InvokeAll<T>(forkJoinTasks)); |
1610 |
|
1611 |
@SuppressWarnings({"unchecked", "rawtypes"}) |
1612 |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1613 |
return futures; |
1614 |
} |
1615 |
|
1616 |
static final class InvokeAll<T> extends RecursiveAction { |
1617 |
final ArrayList<ForkJoinTask<T>> tasks; |
1618 |
InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } |
1619 |
public void compute() { |
1620 |
try { invokeAll(tasks); } |
1621 |
catch (Exception ignore) {} |
1622 |
} |
1623 |
private static final long serialVersionUID = -7914297376763021607L; |
1624 |
} |
1625 |
|
1626 |
/** |
1627 |
* Returns the factory used for constructing new workers. |
1628 |
* |
1629 |
* @return the factory used for constructing new workers |
1630 |
*/ |
1631 |
public ForkJoinWorkerThreadFactory getFactory() { |
1632 |
return factory; |
1633 |
} |
1634 |
|
1635 |
/** |
1636 |
* Returns the handler for internal worker threads that terminate |
1637 |
* due to unrecoverable errors encountered while executing tasks. |
1638 |
* |
1639 |
* @return the handler, or {@code null} if none |
1640 |
*/ |
1641 |
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
1642 |
return ueh; |
1643 |
} |
1644 |
|
1645 |
/** |
1646 |
* Returns the targeted parallelism level of this pool. |
1647 |
* |
1648 |
* @return the targeted parallelism level of this pool |
1649 |
*/ |
1650 |
public int getParallelism() { |
1651 |
return parallelism; |
1652 |
} |
1653 |
|
1654 |
/** |
1655 |
* Returns the number of worker threads that have started but not |
1656 |
* yet terminated. The result returned by this method may differ |
1657 |
* from {@link #getParallelism} when threads are created to |
1658 |
* maintain parallelism when others are cooperatively blocked. |
1659 |
* |
1660 |
* @return the number of worker threads |
1661 |
*/ |
1662 |
public int getPoolSize() { |
1663 |
return parallelism + (short)(ctl >>> TC_SHIFT); |
1664 |
} |
1665 |
|
1666 |
/** |
1667 |
* Returns {@code true} if this pool uses local first-in-first-out |
1668 |
* scheduling mode for forked tasks that are never joined. |
1669 |
* |
1670 |
* @return {@code true} if this pool uses async mode |
1671 |
*/ |
1672 |
public boolean getAsyncMode() { |
1673 |
return locallyFifo; |
1674 |
} |
1675 |
|
1676 |
/** |
1677 |
* Returns an estimate of the number of worker threads that are |
1678 |
* not blocked waiting to join tasks or for other managed |
1679 |
* synchronization. This method may overestimate the |
1680 |
* number of running threads. |
1681 |
* |
1682 |
* @return the number of worker threads |
1683 |
*/ |
1684 |
public int getRunningThreadCount() { |
1685 |
int r = parallelism + (int)(ctl >> AC_SHIFT); |
1686 |
return r <= 0? 0 : r; // suppress momentarily negative values |
1687 |
} |
1688 |
|
1689 |
/** |
1690 |
* Returns an estimate of the number of threads that are currently |
1691 |
* stealing or executing tasks. This method may overestimate the |
1692 |
* number of active threads. |
1693 |
* |
1694 |
* @return the number of active threads |
1695 |
*/ |
1696 |
public int getActiveThreadCount() { |
1697 |
int r = parallelism + (int)(ctl >> AC_SHIFT) + blockedCount; |
1698 |
return r <= 0? 0 : r; // suppress momentarily negative values |
1699 |
} |
1700 |
|
1701 |
/** |
1702 |
* Returns {@code true} if all worker threads are currently idle. |
1703 |
* An idle worker is one that cannot obtain a task to execute |
1704 |
* because none are available to steal from other threads, and |
1705 |
* there are no pending submissions to the pool. This method is |
1706 |
* conservative; it might not return {@code true} immediately upon |
1707 |
* idleness of all threads, but will eventually become true if |
1708 |
* threads remain inactive. |
1709 |
* |
1710 |
* @return {@code true} if all threads are currently idle |
1711 |
*/ |
1712 |
public boolean isQuiescent() { |
1713 |
return parallelism + (int)(ctl >> AC_SHIFT) + blockedCount == 0; |
1714 |
} |
1715 |
|
1716 |
/** |
1717 |
* Returns an estimate of the total number of tasks stolen from |
1718 |
* one thread's work queue by another. The reported value |
1719 |
* underestimates the actual total number of steals when the pool |
1720 |
* is not quiescent. This value may be useful for monitoring and |
1721 |
* tuning fork/join programs: in general, steal counts should be |
1722 |
* high enough to keep threads busy, but low enough to avoid |
1723 |
* overhead and contention across threads. |
1724 |
* |
1725 |
* @return the number of steals |
1726 |
*/ |
1727 |
public long getStealCount() { |
1728 |
return stealCount; |
1729 |
} |
1730 |
|
1731 |
/** |
1732 |
* Returns an estimate of the total number of tasks currently held |
1733 |
* in queues by worker threads (but not including tasks submitted |
1734 |
* to the pool that have not begun executing). This value is only |
1735 |
* an approximation, obtained by iterating across all threads in |
1736 |
* the pool. This method may be useful for tuning task |
1737 |
* granularities. |
1738 |
* |
1739 |
* @return the number of queued tasks |
1740 |
*/ |
1741 |
public long getQueuedTaskCount() { |
1742 |
long count = 0; |
1743 |
ForkJoinWorkerThread[] ws; |
1744 |
if ((short)(ctl >>> TC_SHIFT) > -parallelism && |
1745 |
(ws = workers) != null) { |
1746 |
for (ForkJoinWorkerThread w : ws) |
1747 |
if (w != null) |
1748 |
count -= w.queueBase - w.queueTop; // must read base first |
1749 |
} |
1750 |
return count; |
1751 |
} |
1752 |
|
1753 |
/** |
1754 |
* Returns an estimate of the number of tasks submitted to this |
1755 |
* pool that have not yet begun executing. This method may take |
1756 |
* time proportional to the number of submissions. |
1757 |
* |
1758 |
* @return the number of queued submissions |
1759 |
*/ |
1760 |
public int getQueuedSubmissionCount() { |
1761 |
return -queueBase + queueTop; |
1762 |
} |
1763 |
|
1764 |
/** |
1765 |
* Returns {@code true} if there are any tasks submitted to this |
1766 |
* pool that have not yet begun executing. |
1767 |
* |
1768 |
* @return {@code true} if there are any queued submissions |
1769 |
*/ |
1770 |
public boolean hasQueuedSubmissions() { |
1771 |
return queueBase != queueTop; |
1772 |
} |
1773 |
|
1774 |
/** |
1775 |
* Removes and returns the next unexecuted submission if one is |
1776 |
* available. This method may be useful in extensions to this |
1777 |
* class that re-assign work in systems with multiple pools. |
1778 |
* |
1779 |
* @return the next submission, or {@code null} if none |
1780 |
*/ |
1781 |
protected ForkJoinTask<?> pollSubmission() { |
1782 |
ForkJoinTask<?> t; ForkJoinTask<?>[] q; int b, i; |
1783 |
while ((b = queueBase) != queueTop && |
1784 |
(q = submissionQueue) != null && |
1785 |
(i = (q.length - 1) & b) >= 0) { |
1786 |
long u = (i << ASHIFT) + ABASE; |
1787 |
if ((t = q[i]) != null && |
1788 |
queueBase == b && |
1789 |
UNSAFE.compareAndSwapObject(q, u, t, null)) { |
1790 |
queueBase = b + 1; |
1791 |
return t; |
1792 |
} |
1793 |
} |
1794 |
return null; |
1795 |
} |
1796 |
|
1797 |
/** |
1798 |
* Removes all available unexecuted submitted and forked tasks |
1799 |
* from scheduling queues and adds them to the given collection, |
1800 |
* without altering their execution status. These may include |
1801 |
* artificially generated or wrapped tasks. This method is |
1802 |
* designed to be invoked only when the pool is known to be |
1803 |
* quiescent. Invocations at other times may not remove all |
1804 |
* tasks. A failure encountered while attempting to add elements |
1805 |
* to collection {@code c} may result in elements being in |
1806 |
* neither, either or both collections when the associated |
1807 |
* exception is thrown. The behavior of this operation is |
1808 |
* undefined if the specified collection is modified while the |
1809 |
* operation is in progress. |
1810 |
* |
1811 |
* @param c the collection to transfer elements into |
1812 |
* @return the number of elements transferred |
1813 |
*/ |
1814 |
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1815 |
int count = 0; |
1816 |
while (queueBase != queueTop) { |
1817 |
ForkJoinTask<?> t = pollSubmission(); |
1818 |
if (t != null) { |
1819 |
c.add(t); |
1820 |
++count; |
1821 |
} |
1822 |
} |
1823 |
ForkJoinWorkerThread[] ws; |
1824 |
if ((short)(ctl >>> TC_SHIFT) > -parallelism && |
1825 |
(ws = workers) != null) { |
1826 |
for (ForkJoinWorkerThread w : ws) |
1827 |
if (w != null) |
1828 |
count += w.drainTasksTo(c); |
1829 |
} |
1830 |
return count; |
1831 |
} |
1832 |
|
1833 |
/** |
1834 |
* Returns a string identifying this pool, as well as its state, |
1835 |
* including indications of run state, parallelism level, and |
1836 |
* worker and task counts. |
1837 |
* |
1838 |
* @return a string identifying this pool, as well as its state |
1839 |
*/ |
1840 |
public String toString() { |
1841 |
long st = getStealCount(); |
1842 |
long qt = getQueuedTaskCount(); |
1843 |
long qs = getQueuedSubmissionCount(); |
1844 |
int pc = parallelism; |
1845 |
long c = ctl; |
1846 |
int tc = pc + (short)(c >>> TC_SHIFT); |
1847 |
int rc = pc + (int)(c >> AC_SHIFT); |
1848 |
if (rc < 0) // ignore transient negative |
1849 |
rc = 0; |
1850 |
int ac = rc + blockedCount; |
1851 |
String level; |
1852 |
if ((c & STOP_BIT) != 0) |
1853 |
level = (tc == 0)? "Terminated" : "Terminating"; |
1854 |
else |
1855 |
level = shutdown? "Shutting down" : "Running"; |
1856 |
return super.toString() + |
1857 |
"[" + level + |
1858 |
", parallelism = " + pc + |
1859 |
", size = " + tc + |
1860 |
", active = " + ac + |
1861 |
", running = " + rc + |
1862 |
", steals = " + st + |
1863 |
", tasks = " + qt + |
1864 |
", submissions = " + qs + |
1865 |
"]"; |
1866 |
} |
1867 |
|
1868 |
/** |
1869 |
* Initiates an orderly shutdown in which previously submitted |
1870 |
* tasks are executed, but no new tasks will be accepted. |
1871 |
* Invocation has no additional effect if already shut down. |
1872 |
* Tasks that are in the process of being submitted concurrently |
1873 |
* during the course of this method may or may not be rejected. |
1874 |
* |
1875 |
* @throws SecurityException if a security manager exists and |
1876 |
* the caller is not permitted to modify threads |
1877 |
* because it does not hold {@link |
1878 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1879 |
*/ |
1880 |
public void shutdown() { |
1881 |
checkPermission(); |
1882 |
shutdown = true; |
1883 |
tryTerminate(false); |
1884 |
} |
1885 |
|
1886 |
/** |
1887 |
* Attempts to cancel and/or stop all tasks, and reject all |
1888 |
* subsequently submitted tasks. Tasks that are in the process of |
1889 |
* being submitted or executed concurrently during the course of |
1890 |
* this method may or may not be rejected. This method cancels |
1891 |
* both existing and unexecuted tasks, in order to permit |
1892 |
* termination in the presence of task dependencies. So the method |
1893 |
* always returns an empty list (unlike the case for some other |
1894 |
* Executors). |
1895 |
* |
1896 |
* @return an empty list |
1897 |
* @throws SecurityException if a security manager exists and |
1898 |
* the caller is not permitted to modify threads |
1899 |
* because it does not hold {@link |
1900 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1901 |
*/ |
1902 |
public List<Runnable> shutdownNow() { |
1903 |
checkPermission(); |
1904 |
shutdown = true; |
1905 |
tryTerminate(true); |
1906 |
return Collections.emptyList(); |
1907 |
} |
1908 |
|
1909 |
/** |
1910 |
* Returns {@code true} if all tasks have completed following shut down. |
1911 |
* |
1912 |
* @return {@code true} if all tasks have completed following shut down |
1913 |
*/ |
1914 |
public boolean isTerminated() { |
1915 |
long c = ctl; |
1916 |
return ((c & STOP_BIT) != 0L && |
1917 |
(short)(c >>> TC_SHIFT) == -parallelism); |
1918 |
} |
1919 |
|
1920 |
/** |
1921 |
* Returns {@code true} if the process of termination has |
1922 |
* commenced but not yet completed. This method may be useful for |
1923 |
* debugging. A return of {@code true} reported a sufficient |
1924 |
* period after shutdown may indicate that submitted tasks have |
1925 |
* ignored or suppressed interruption, or are waiting for IO, |
1926 |
* causing this executor not to properly terminate. (See the |
1927 |
* advisory notes for class {@link ForkJoinTask} stating that |
1928 |
* tasks should not normally entail blocking operations. But if |
1929 |
* they do, they must abort them on interrupt.) |
1930 |
* |
1931 |
* @return {@code true} if terminating but not yet terminated |
1932 |
*/ |
1933 |
public boolean isTerminating() { |
1934 |
long c = ctl; |
1935 |
return ((c & STOP_BIT) != 0L && |
1936 |
(short)(c >>> TC_SHIFT) != -parallelism); |
1937 |
} |
1938 |
|
1939 |
/** |
1940 |
* Returns true if terminating or terminated. Used by ForkJoinWorkerThread. |
1941 |
*/ |
1942 |
final boolean isAtLeastTerminating() { |
1943 |
return (ctl & STOP_BIT) != 0L; |
1944 |
} |
1945 |
|
1946 |
/** |
1947 |
* Returns {@code true} if this pool has been shut down. |
1948 |
* |
1949 |
* @return {@code true} if this pool has been shut down |
1950 |
*/ |
1951 |
public boolean isShutdown() { |
1952 |
return shutdown; |
1953 |
} |
1954 |
|
1955 |
/** |
1956 |
* Blocks until all tasks have completed execution after a shutdown |
1957 |
* request, or the timeout occurs, or the current thread is |
1958 |
* interrupted, whichever happens first. |
1959 |
* |
1960 |
* @param timeout the maximum time to wait |
1961 |
* @param unit the time unit of the timeout argument |
1962 |
* @return {@code true} if this executor terminated and |
1963 |
* {@code false} if the timeout elapsed before termination |
1964 |
* @throws InterruptedException if interrupted while waiting |
1965 |
*/ |
1966 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1967 |
throws InterruptedException { |
1968 |
long nanos = unit.toNanos(timeout); |
1969 |
final ReentrantLock lock = this.submissionLock; |
1970 |
lock.lock(); |
1971 |
try { |
1972 |
for (;;) { |
1973 |
if (isTerminated()) |
1974 |
return true; |
1975 |
if (nanos <= 0) |
1976 |
return false; |
1977 |
nanos = termination.awaitNanos(nanos); |
1978 |
} |
1979 |
} finally { |
1980 |
lock.unlock(); |
1981 |
} |
1982 |
} |
1983 |
|
1984 |
/** |
1985 |
* Interface for extending managed parallelism for tasks running |
1986 |
* in {@link ForkJoinPool}s. |
1987 |
* |
1988 |
* <p>A {@code ManagedBlocker} provides two methods. Method |
1989 |
* {@code isReleasable} must return {@code true} if blocking is |
1990 |
* not necessary. Method {@code block} blocks the current thread |
1991 |
* if necessary (perhaps internally invoking {@code isReleasable} |
1992 |
* before actually blocking). These actions are performed by any |
1993 |
* thread invoking {@link ForkJoinPool#managedBlock}. The |
1994 |
* unusual methods in this API accommodate synchronizers that may, |
1995 |
* but don't usually, block for long periods. Similarly, they |
1996 |
* allow more efficient internal handling of cases in which |
1997 |
* additional workers may be, but usually are not, needed to |
1998 |
* ensure sufficient parallelism. Toward this end, |
1999 |
* implementations of method {@code isReleasable} must be amenable |
2000 |
* to repeated invocation. |
2001 |
* |
2002 |
* <p>For example, here is a ManagedBlocker based on a |
2003 |
* ReentrantLock: |
2004 |
* <pre> {@code |
2005 |
* class ManagedLocker implements ManagedBlocker { |
2006 |
* final ReentrantLock lock; |
2007 |
* boolean hasLock = false; |
2008 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
2009 |
* public boolean block() { |
2010 |
* if (!hasLock) |
2011 |
* lock.lock(); |
2012 |
* return true; |
2013 |
* } |
2014 |
* public boolean isReleasable() { |
2015 |
* return hasLock || (hasLock = lock.tryLock()); |
2016 |
* } |
2017 |
* }}</pre> |
2018 |
* |
2019 |
* <p>Here is a class that possibly blocks waiting for an |
2020 |
* item on a given queue: |
2021 |
* <pre> {@code |
2022 |
* class QueueTaker<E> implements ManagedBlocker { |
2023 |
* final BlockingQueue<E> queue; |
2024 |
* volatile E item = null; |
2025 |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
2026 |
* public boolean block() throws InterruptedException { |
2027 |
* if (item == null) |
2028 |
* item = queue.take(); |
2029 |
* return true; |
2030 |
* } |
2031 |
* public boolean isReleasable() { |
2032 |
* return item != null || (item = queue.poll()) != null; |
2033 |
* } |
2034 |
* public E getItem() { // call after pool.managedBlock completes |
2035 |
* return item; |
2036 |
* } |
2037 |
* }}</pre> |
2038 |
*/ |
2039 |
public static interface ManagedBlocker { |
2040 |
/** |
2041 |
* Possibly blocks the current thread, for example waiting for |
2042 |
* a lock or condition. |
2043 |
* |
2044 |
* @return {@code true} if no additional blocking is necessary |
2045 |
* (i.e., if isReleasable would return true) |
2046 |
* @throws InterruptedException if interrupted while waiting |
2047 |
* (the method is not required to do so, but is allowed to) |
2048 |
*/ |
2049 |
boolean block() throws InterruptedException; |
2050 |
|
2051 |
/** |
2052 |
* Returns {@code true} if blocking is unnecessary. |
2053 |
*/ |
2054 |
boolean isReleasable(); |
2055 |
} |
2056 |
|
2057 |
/** |
2058 |
* Blocks in accord with the given blocker. If the current thread |
2059 |
* is a {@link ForkJoinWorkerThread}, this method possibly |
2060 |
* arranges for a spare thread to be activated if necessary to |
2061 |
* ensure sufficient parallelism while the current thread is blocked. |
2062 |
* |
2063 |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
2064 |
* behaviorally equivalent to |
2065 |
* <pre> {@code |
2066 |
* while (!blocker.isReleasable()) |
2067 |
* if (blocker.block()) |
2068 |
* return; |
2069 |
* }</pre> |
2070 |
* |
2071 |
* If the caller is a {@code ForkJoinTask}, then the pool may |
2072 |
* first be expanded to ensure parallelism, and later adjusted. |
2073 |
* |
2074 |
* @param blocker the blocker |
2075 |
* @throws InterruptedException if blocker.block did so |
2076 |
*/ |
2077 |
public static void managedBlock(ManagedBlocker blocker) |
2078 |
throws InterruptedException { |
2079 |
Thread t = Thread.currentThread(); |
2080 |
if (t instanceof ForkJoinWorkerThread) { |
2081 |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
2082 |
w.pool.awaitBlocker(blocker); |
2083 |
} |
2084 |
else { |
2085 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
2086 |
} |
2087 |
} |
2088 |
|
2089 |
// AbstractExecutorService overrides. These rely on undocumented |
2090 |
// fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
2091 |
// implement RunnableFuture. |
2092 |
|
2093 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
2094 |
return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); |
2095 |
} |
2096 |
|
2097 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
2098 |
return (RunnableFuture<T>) ForkJoinTask.adapt(callable); |
2099 |
} |
2100 |
|
2101 |
// Unsafe mechanics |
2102 |
private static final sun.misc.Unsafe UNSAFE; |
2103 |
private static final long ctlOffset; |
2104 |
private static final long stealCountOffset; |
2105 |
private static final long blockedCountOffset; |
2106 |
private static final long quiescerCountOffset; |
2107 |
private static final long scanGuardOffset; |
2108 |
private static final long nextWorkerNumberOffset; |
2109 |
private static final long ABASE; |
2110 |
private static final int ASHIFT; |
2111 |
|
2112 |
static { |
2113 |
poolNumberGenerator = new AtomicInteger(); |
2114 |
workerSeedGenerator = new Random(); |
2115 |
modifyThreadPermission = new RuntimePermission("modifyThread"); |
2116 |
defaultForkJoinWorkerThreadFactory = |
2117 |
new DefaultForkJoinWorkerThreadFactory(); |
2118 |
int s; |
2119 |
try { |
2120 |
UNSAFE = getUnsafe(); |
2121 |
Class k = ForkJoinPool.class; |
2122 |
ctlOffset = UNSAFE.objectFieldOffset |
2123 |
(k.getDeclaredField("ctl")); |
2124 |
stealCountOffset = UNSAFE.objectFieldOffset |
2125 |
(k.getDeclaredField("stealCount")); |
2126 |
blockedCountOffset = UNSAFE.objectFieldOffset |
2127 |
(k.getDeclaredField("blockedCount")); |
2128 |
quiescerCountOffset = UNSAFE.objectFieldOffset |
2129 |
(k.getDeclaredField("quiescerCount")); |
2130 |
scanGuardOffset = UNSAFE.objectFieldOffset |
2131 |
(k.getDeclaredField("scanGuard")); |
2132 |
nextWorkerNumberOffset = UNSAFE.objectFieldOffset |
2133 |
(k.getDeclaredField("nextWorkerNumber")); |
2134 |
Class a = ForkJoinTask[].class; |
2135 |
ABASE = UNSAFE.arrayBaseOffset(a); |
2136 |
s = UNSAFE.arrayIndexScale(a); |
2137 |
} catch (Exception e) { |
2138 |
throw new Error(e); |
2139 |
} |
2140 |
if ((s & (s-1)) != 0) |
2141 |
throw new Error("data type scale not a power of two"); |
2142 |
ASHIFT = 31 - Integer.numberOfLeadingZeros(s); |
2143 |
} |
2144 |
|
2145 |
/** |
2146 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
2147 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
2148 |
* into a jdk. |
2149 |
* |
2150 |
* @return a sun.misc.Unsafe |
2151 |
*/ |
2152 |
private static sun.misc.Unsafe getUnsafe() { |
2153 |
try { |
2154 |
return sun.misc.Unsafe.getUnsafe(); |
2155 |
} catch (SecurityException se) { |
2156 |
try { |
2157 |
return java.security.AccessController.doPrivileged |
2158 |
(new java.security |
2159 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
2160 |
public sun.misc.Unsafe run() throws Exception { |
2161 |
java.lang.reflect.Field f = sun.misc |
2162 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
2163 |
f.setAccessible(true); |
2164 |
return (sun.misc.Unsafe) f.get(null); |
2165 |
}}); |
2166 |
} catch (java.security.PrivilegedActionException e) { |
2167 |
throw new RuntimeException("Could not initialize intrinsics", |
2168 |
e.getCause()); |
2169 |
} |
2170 |
} |
2171 |
} |
2172 |
} |