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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package jsr166y; |
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|
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import java.util.concurrent.*; |
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|
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import java.util.ArrayList; |
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import java.util.Arrays; |
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import java.util.Collection; |
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import java.util.Collections; |
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import java.util.List; |
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import java.util.concurrent.locks.LockSupport; |
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import java.util.concurrent.locks.ReentrantLock; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.CountDownLatch; |
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|
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
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* A {@code ForkJoinPool} provides the entry point for submissions |
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* from non-{@code ForkJoinTask} clients, as well as management and |
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* monitoring operations. |
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* |
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* <p>A {@code ForkJoinPool} differs from other kinds of {@link |
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* ExecutorService} mainly by virtue of employing |
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* <em>work-stealing</em>: all threads in the pool attempt to find and |
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* execute subtasks created by other active tasks (eventually blocking |
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* waiting for work if none exist). This enables efficient processing |
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* when most tasks spawn other subtasks (as do most {@code |
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* ForkJoinTask}s). When setting <em>asyncMode</em> to true in |
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* constructors, {@code ForkJoinPool}s may also be appropriate for use |
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* with event-style tasks that are never joined. |
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* |
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* <p>A {@code ForkJoinPool} is constructed with a given target |
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* parallelism level; by default, equal to the number of available |
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* processors. The pool attempts to maintain enough active (or |
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* available) threads by dynamically adding, suspending, or resuming |
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* internal worker threads, even if some tasks are stalled waiting to |
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* join others. However, no such adjustments are guaranteed in the |
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* face of blocked IO or other unmanaged synchronization. The nested |
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* {@link ManagedBlocker} interface enables extension of the kinds of |
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* synchronization accommodated. |
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* |
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* <p>In addition to execution and lifecycle control methods, this |
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* class provides status check methods (for example |
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* {@link #getStealCount}) that are intended to aid in developing, |
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* tuning, and monitoring fork/join applications. Also, method |
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* {@link #toString} returns indications of pool state in a |
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* convenient form for informal monitoring. |
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* |
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* <p> As is the case with other ExecutorServices, there are three |
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* main task execution methods summarized in the following |
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* table. These are designed to be used by clients not already engaged |
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* in fork/join computations in the current pool. The main forms of |
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* these methods accept instances of {@code ForkJoinTask}, but |
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* overloaded forms also allow mixed execution of plain {@code |
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* Runnable}- or {@code Callable}- based activities as well. However, |
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* tasks that are already executing in a pool should normally |
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* <em>NOT</em> use these pool execution methods, but instead use the |
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* within-computation forms listed in the table. |
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* |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <tr> |
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* <td></td> |
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* <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
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* <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
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* </tr> |
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* <tr> |
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* <td> <b>Arange async execution</td> |
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* <td> {@link #execute(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork}</td> |
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* </tr> |
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* <tr> |
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* <td> <b>Await and obtain result</td> |
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* <td> {@link #invoke(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#invoke}</td> |
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* </tr> |
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* <tr> |
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* <td> <b>Arrange exec and obtain Future</td> |
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* <td> {@link #submit(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
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* </tr> |
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* </table> |
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* |
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* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is |
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* used for all parallel task execution in a program or subsystem. |
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* Otherwise, use would not usually outweigh the construction and |
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* bookkeeping overhead of creating a large set of threads. For |
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* example, a common pool could be used for the {@code SortTasks} |
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* illustrated in {@link RecursiveAction}. Because {@code |
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* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon |
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* daemon} mode, there is typically no need to explicitly {@link |
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* #shutdown} such a pool upon program exit. |
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* |
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* <pre> |
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* static final ForkJoinPool mainPool = new ForkJoinPool(); |
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* ... |
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* public void sort(long[] array) { |
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* mainPool.invoke(new SortTask(array, 0, array.length)); |
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* } |
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* </pre> |
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* |
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* <p><b>Implementation notes</b>: This implementation restricts the |
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* maximum number of running threads to 32767. Attempts to create |
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* pools with greater than the maximum number result in |
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* {@code IllegalArgumentException}. |
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* |
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* <p>This implementation rejects submitted tasks (that is, by throwing |
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* {@link RejectedExecutionException}) only when the pool is shut down |
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* or internal resources have been 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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* The main work-stealing mechanics implemented in class |
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* ForkJoinWorkerThread give first priority to processing tasks |
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* from their own queues (LIFO or FIFO, depending on mode), then |
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* to randomized FIFO steals of tasks in other worker queues, and |
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* lastly to new submissions. These mechanics do not consider |
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* affinities, loads, cache localities, etc, so rarely provide the |
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* best possible performance on a given machine, but portably |
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* provide good throughput by averaging over these factors. |
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* (Further, even if we did try to use such information, we do not |
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* usually have a basis for exploiting it. For example, some sets |
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* of tasks profit from cache affinities, but others are harmed by |
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* cache pollution effects.) |
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* |
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* Beyond work-stealing support and essential bookkeeping, the |
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* main responsibility of this framework is to take actions when |
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* one worker is waiting to join a task stolen (or always held by) |
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* another. Becauae we are multiplexing many tasks on to a pool |
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* of workers, we can't just let them block (as in Thread.join). |
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* We also cannot just reassign the joiner's run-time stack with |
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* another and replace it later, which would be a form of |
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* "continuation", that even if possible is not necessarily a good |
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* idea. Given that the creation costs of most threads on most |
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* systems mainly surrounds setting up runtime stacks, thread |
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* creation and switching is usually not much more expensive than |
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* stack creation and switching, and is more flexible). Instead we |
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* combine two tactics: |
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* |
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* Helping: Arranging for the joiner to execute some task that it |
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* would be running if the steal had not occurred. Method |
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* ForkJoinWorkerThread.helpJoinTask tracks joining->stealing |
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* links to try to find such a task. |
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* |
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* Compensating: Unless there are already enough live threads, |
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* method helpMaintainParallelism() may create or or |
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* re-activate a spare thread to compensate for blocked |
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* joiners until they unblock. |
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* |
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* Because the determining existence of conservatively safe |
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* helping targets, the availability of already-created spares, |
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* and the apparent need to create new spares are all racy and |
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* require heuristic guidance, we rely on multiple retries of |
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* each. Further, because it is impossible to keep exactly the |
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* target (parallelism) number of threads running at any given |
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* time, we allow compensation during joins to fail, and enlist |
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* all other threads to help out whenever they are not otherwise |
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* occupied (i.e., mainly in method preStep). |
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* |
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* The ManagedBlocker extension API can't use helping so relies |
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* only on compensation in method awaitBlocker. |
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* |
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* The main throughput advantages of work-stealing stem from |
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* decentralized control -- workers mostly steal tasks from each |
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* other. We do not want to negate this by creating bottlenecks |
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* implementing other management responsibilities. So we use a |
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* collection of techniques that avoid, reduce, or cope well with |
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* contention. These entail several instances of bit-packing into |
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* CASable fields to maintain only the minimally required |
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* atomicity. To enable such packing, we restrict maximum |
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* parallelism to (1<<15)-1 (enabling twice this (to accommodate |
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* unbalanced increments and decrements) to fit into a 16 bit |
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* field, which is far in excess of normal operating range. Even |
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* though updates to some of these bookkeeping fields do sometimes |
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* contend with each other, they don't normally cache-contend with |
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* updates to others enough to warrant memory padding or |
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* isolation. So they are all held as fields of ForkJoinPool |
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* objects. The main capabilities are as follows: |
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* |
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* 1. Creating and removing workers. Workers are recorded in the |
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* "workers" array. This is an array as opposed to some other data |
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* structure to support index-based random steals by workers. |
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* Updates to the array recording new workers and unrecording |
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* terminated ones are protected from each other by a lock |
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* (workerLock) but the array is otherwise concurrently readable, |
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* and accessed directly by workers. To simplify index-based |
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* operations, the array size is always a power of two, and all |
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* readers must tolerate null slots. Currently, all worker thread |
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* creation is on-demand, triggered by task submissions, |
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* replacement of terminated workers, and/or compensation for |
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* blocked workers. However, all other support code is set up to |
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* work with other policies. |
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* |
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* To ensure that we do not hold on to worker references that |
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* would prevent GC, ALL accesses to workers are via indices into |
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* the workers array (which is one source of some of the unusual |
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* code constructions here). In essence, the workers array serves |
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* as a WeakReference mechanism. Thus for example the event queue |
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* stores worker indices, not worker references. Access to the |
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* workers in associated methods (for example releaseEventWaiters) |
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* must both index-check and null-check the IDs. All such accesses |
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* ignore bad IDs by returning out early from what they are doing, |
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* since this can only be associated with shutdown, in which case |
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* it is OK to give up. On termination, we just clobber these |
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* data structures without trying to use them. |
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* |
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* 2. Bookkeeping for dynamically adding and removing workers. We |
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* aim to approximately maintain the given level of parallelism. |
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* When some workers are known to be blocked (on joins or via |
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* ManagedBlocker), we may create or resume others to take their |
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* place until they unblock (see below). Implementing this |
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* requires counts of the number of "running" threads (i.e., those |
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* that are neither blocked nor artifically suspended) as well as |
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* the total number. These two values are packed into one field, |
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* "workerCounts" because we need accurate snapshots when deciding |
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* to create, resume or suspend. Note however that the |
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* correspondance of these counts to reality is not guaranteed. In |
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* particular updates for unblocked threads may lag until they |
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* actually wake up. |
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* |
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* 3. Maintaining global run state. The run state of the pool |
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* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to |
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* those in other Executor implementations, as well as a count of |
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* "active" workers -- those that are, or soon will be, or |
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* recently were executing tasks. The runLevel and active count |
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* are packed together in order to correctly trigger shutdown and |
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* termination. Without care, active counts can be subject to very |
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* high contention. We substantially reduce this contention by |
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* relaxing update rules. A worker must claim active status |
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* prospectively, by activating if it sees that a submitted or |
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* stealable task exists (it may find after activating that the |
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* task no longer exists). It stays active while processing this |
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* task (if it exists) and any other local subtasks it produces, |
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* until it cannot find any other tasks. It then tries |
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* inactivating (see method preStep), but upon update contention |
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* instead scans for more tasks, later retrying inactivation if it |
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* doesn't find any. |
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* |
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* 4. Managing idle workers waiting for tasks. We cannot let |
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* workers spin indefinitely scanning for tasks when none are |
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* available. On the other hand, we must quickly prod them into |
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* action when new tasks are submitted or generated. We |
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* park/unpark these idle workers using an event-count scheme. |
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* Field eventCount is incremented upon events that may enable |
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* workers that previously could not find a task to now find one: |
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* Submission of a new task to the pool, or another worker pushing |
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* a task onto a previously empty queue. (We also use this |
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* mechanism for configuration and termination actions that |
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* require wakeups of idle workers). Each worker maintains its |
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* last known event count, and blocks when a scan for work did not |
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* find a task AND its lastEventCount matches the current |
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* eventCount. Waiting idle workers are recorded in a variant of |
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* Treiber stack headed by field eventWaiters which, when nonzero, |
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* encodes the thread index and count awaited for by the worker |
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* thread most recently calling eventSync. This thread in turn has |
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* a record (field nextEventWaiter) for the next waiting worker. |
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* In addition to allowing simpler decisions about need for |
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* wakeup, the event count bits in eventWaiters serve the role of |
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* tags to avoid ABA errors in Treiber stacks. Upon any wakeup, |
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* released threads also try to release others (but give up upon |
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* contention to reduce useless flailing). The net effect is a |
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* tree-like diffusion of signals, where released threads (and |
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* possibly others) help with unparks. To further reduce |
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* contention effects a bit, failed CASes to increment field |
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* eventCount are tolerated without retries in signalWork. |
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* Conceptually they are merged into the same event, which is OK |
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* when their only purpose is to enable workers to scan for work. |
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* |
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* 5. Managing suspension of extra workers. When a worker is about |
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* to block waiting for a join (or via ManagedBlockers), we may |
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* create a new thread to maintain parallelism level, or at least |
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* avoid starvation. Usually, extra threads are needed for only |
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* very short periods, yet join dependencies are such that we |
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* sometimes need them in bursts. Rather than create new threads |
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* each time this happens, we suspend no-longer-needed extra ones |
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* as "spares". For most purposes, we don't distinguish "extra" |
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* spare threads from normal "core" threads: On each call to |
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* preStep (the only point at which we can do this) a worker |
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* checks to see if there are now too many running workers, and if |
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* so, suspends itself. Method helpMaintainParallelism looks for |
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* suspended threads to resume before considering creating a new |
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* replacement. The spares themselves are encoded on another |
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* variant of a Treiber Stack, headed at field "spareWaiters". |
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* Note that the use of spares is intrinsically racy. One thread |
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* may become a spare at about the same time as another is |
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* needlessly being created. We counteract this and related slop |
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* in part by requiring resumed spares to immediately recheck (in |
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* preStep) to see whether they they should re-suspend. |
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* |
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* 6. Killing off unneeded workers. The Spare and Event queues use |
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* similar mechanisms to shed unused workers: The oldest (first) |
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* waiter uses a timed rather than hard wait. When this wait times |
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* out without a normal wakeup, it tries to shutdown any one (for |
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* convenience the newest) other waiter via tryShutdownSpare or |
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* tryShutdownWaiter, respectively. The wakeup rates for spares |
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* are much shorter than for waiters. Together, they will |
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* eventually reduce the number of worker threads to a minimum of |
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* one after a long enough period without use. |
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* |
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* 7. Deciding when to create new workers. The main dynamic |
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* control in this class is deciding when to create extra threads |
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* in method helpMaintainParallelism. We would like to keep |
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* exactly #parallelism threads running, which is an impossble |
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* task. We always need to create one when the number of running |
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* threads would become zero and all workers are busy. Beyond |
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* this, we must rely on heuristics that work well in the the |
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* presence of transients phenomena such as GC stalls, dynamic |
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* compilation, and wake-up lags. These transients are extremely |
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* common -- we are normally trying to fully saturate the CPUs on |
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* a machine, so almost any activity other than running tasks |
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* impedes accuracy. Our main defense is to allow some slack in |
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* creation thresholds, using rules that reflect the fact that the |
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* more threads we have running, the more likely that we are |
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* underestimating the number running threads. (We also include |
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* some heuristic use of Thread.yield when all workers appear to |
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* be busy, to improve likelihood of counts settling.) The rules |
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* also better cope with the fact that some of the methods in this |
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* class tend to never become compiled (but are interpreted), so |
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* some components of the entire set of controls might execute 100 |
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* times faster than others. And similarly for cases where the |
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* apparent lack of work is just due to GC stalls and other |
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* transient system activity. |
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* |
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* Beware that there is a lot of representation-level coupling |
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* among classes ForkJoinPool, ForkJoinWorkerThread, and |
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* ForkJoinTask. For example, direct access to "workers" array by |
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* workers, and direct access to ForkJoinTask.status by both |
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* ForkJoinPool and ForkJoinWorkerThread. There is little point |
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* trying to reduce this, since any associated future changes in |
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* representations will need to be accompanied by algorithmic |
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* changes anyway. |
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* |
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* Style notes: There are lots of inline assignments (of form |
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* "while ((local = field) != 0)") which are usually the simplest |
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* way to ensure the required read orderings (which are sometimes |
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* critical). Also several occurrences of the unusual "do {} |
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* while(!cas...)" which is the simplest way to force an update of |
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* a CAS'ed variable. There are also other coding oddities that |
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* help some methods perform reasonably even when interpreted (not |
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* compiled), at the expense of some messy constructions that |
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* reduce byte code counts. |
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* |
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* The order of declarations in this file is: (1) statics (2) |
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* fields (along with constants used when unpacking some of them) |
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* (3) internal control methods (4) callbacks and other support |
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* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported |
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* methods (plus a few little helpers). |
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*/ |
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|
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/** |
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* Factory for creating new {@link ForkJoinWorkerThread}s. |
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* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
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* for {@code ForkJoinWorkerThread} subclasses that extend base |
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* functionality or initialize threads with different contexts. |
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*/ |
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public static interface ForkJoinWorkerThreadFactory { |
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/** |
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* Returns a new worker thread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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* @throws NullPointerException if the pool is null |
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*/ |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
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} |
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|
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/** |
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* Default ForkJoinWorkerThreadFactory implementation; creates a |
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* new ForkJoinWorkerThread. |
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*/ |
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static class DefaultForkJoinWorkerThreadFactory |
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implements ForkJoinWorkerThreadFactory { |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
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return new ForkJoinWorkerThread(pool); |
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} |
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} |
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|
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/** |
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* Creates a new ForkJoinWorkerThread. This factory is used unless |
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* overridden in ForkJoinPool constructors. |
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*/ |
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public static final ForkJoinWorkerThreadFactory |
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defaultForkJoinWorkerThreadFactory = |
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new DefaultForkJoinWorkerThreadFactory(); |
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|
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/** |
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* Permission required for callers of methods that may start or |
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* kill threads. |
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*/ |
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private static final RuntimePermission modifyThreadPermission = |
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new RuntimePermission("modifyThread"); |
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|
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/** |
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* If there is a security manager, makes sure caller has |
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* permission to modify threads. |
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*/ |
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private static void checkPermission() { |
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SecurityManager security = System.getSecurityManager(); |
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if (security != null) |
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security.checkPermission(modifyThreadPermission); |
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} |
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|
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/** |
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* Generator for assigning sequence numbers as pool names. |
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*/ |
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private static final AtomicInteger poolNumberGenerator = |
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new AtomicInteger(); |
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|
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/** |
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* The wakeup interval (in nanoseconds) for the oldest worker |
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* worker waiting for an event invokes tryShutdownWaiter to shrink |
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* the number of workers. The exact value does not matter too |
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* much, but should be long enough to slowly release resources |
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* during long periods without use without disrupting normal use. |
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*/ |
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private static final long SHRINK_RATE_NANOS = |
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60L * 1000L * 1000L * 1000L; // one minute |
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|
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/** |
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* Absolute bound for parallelism level. Twice this number plus |
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* one (i.e., 0xfff) must fit into a 16bit field to enable |
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* word-packing for some counts and indices. |
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*/ |
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private static final int MAX_WORKERS = 0x7fff; |
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|
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/** |
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* Array holding all worker threads in the pool. Array size must |
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* be a power of two. Updates and replacements are protected by |
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* workerLock, but the array is always kept in a consistent enough |
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* state to be randomly accessed without locking by workers |
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* performing work-stealing, as well as other traversal-based |
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* methods in this class. All readers must tolerate that some |
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* array slots may be null. |
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*/ |
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volatile ForkJoinWorkerThread[] workers; |
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|
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/** |
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* Queue for external submissions. |
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*/ |
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private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
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|
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/** |
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* Lock protecting updates to workers array. |
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*/ |
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private final ReentrantLock workerLock; |
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|
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/** |
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* Latch released upon termination. |
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*/ |
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private final Phaser termination; |
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|
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/** |
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* Creation factory for worker threads. |
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*/ |
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private final ForkJoinWorkerThreadFactory factory; |
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|
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/** |
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* Sum of per-thread steal counts, updated only when threads are |
472 |
* idle or terminating. |
473 |
*/ |
474 |
private volatile long stealCount; |
475 |
|
476 |
/** |
477 |
* Encoded record of top of treiber stack of threads waiting for |
478 |
* events. The top 32 bits contain the count being waited for. The |
479 |
* bottom 16 bits contains one plus the pool index of waiting |
480 |
* worker thread. (Bits 16-31 are unused.) |
481 |
*/ |
482 |
private volatile long eventWaiters; |
483 |
|
484 |
private static final int EVENT_COUNT_SHIFT = 32; |
485 |
private static final long WAITER_ID_MASK = (1L << 16) - 1L; |
486 |
|
487 |
/** |
488 |
* A counter for events that may wake up worker threads: |
489 |
* - Submission of a new task to the pool |
490 |
* - A worker pushing a task on an empty queue |
491 |
* - termination |
492 |
*/ |
493 |
private volatile int eventCount; |
494 |
|
495 |
/** |
496 |
* Encoded record of top of treiber stack of spare threads waiting |
497 |
* for resumption. The top 16 bits contain an arbitrary count to |
498 |
* avoid ABA effects. The bottom 16bits contains one plus the pool |
499 |
* index of waiting worker thread. |
500 |
*/ |
501 |
private volatile int spareWaiters; |
502 |
|
503 |
private static final int SPARE_COUNT_SHIFT = 16; |
504 |
private static final int SPARE_ID_MASK = (1 << 16) - 1; |
505 |
|
506 |
/** |
507 |
* Lifecycle control. The low word contains the number of workers |
508 |
* that are (probably) executing tasks. This value is atomically |
509 |
* incremented before a worker gets a task to run, and decremented |
510 |
* when worker has no tasks and cannot find any. Bits 16-18 |
511 |
* contain runLevel value. When all are zero, the pool is |
512 |
* running. Level transitions are monotonic (running -> shutdown |
513 |
* -> terminating -> terminated) so each transition adds a bit. |
514 |
* These are bundled together to ensure consistent read for |
515 |
* termination checks (i.e., that runLevel is at least SHUTDOWN |
516 |
* and active threads is zero). |
517 |
* |
518 |
* Notes: Most direct CASes are dependent on these bitfield |
519 |
* positions. Also, this field is non-private to enable direct |
520 |
* performance-sensitive CASes in ForkJoinWorkerThread. |
521 |
*/ |
522 |
volatile int runState; |
523 |
|
524 |
// Note: The order among run level values matters. |
525 |
private static final int RUNLEVEL_SHIFT = 16; |
526 |
private static final int SHUTDOWN = 1 << RUNLEVEL_SHIFT; |
527 |
private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1); |
528 |
private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2); |
529 |
private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1; |
530 |
|
531 |
/** |
532 |
* Holds number of total (i.e., created and not yet terminated) |
533 |
* and running (i.e., not blocked on joins or other managed sync) |
534 |
* threads, packed together to ensure consistent snapshot when |
535 |
* making decisions about creating and suspending spare |
536 |
* threads. Updated only by CAS. Note that adding a new worker |
537 |
* requires incrementing both counts, since workers start off in |
538 |
* running state. |
539 |
*/ |
540 |
private volatile int workerCounts; |
541 |
|
542 |
private static final int TOTAL_COUNT_SHIFT = 16; |
543 |
private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1; |
544 |
private static final int ONE_RUNNING = 1; |
545 |
private static final int ONE_TOTAL = 1 << TOTAL_COUNT_SHIFT; |
546 |
|
547 |
/** |
548 |
* The target parallelism level. |
549 |
* Accessed directly by ForkJoinWorkerThreads. |
550 |
*/ |
551 |
final int parallelism; |
552 |
|
553 |
/** |
554 |
* True if use local fifo, not default lifo, for local polling |
555 |
* Read by, and replicated by ForkJoinWorkerThreads |
556 |
*/ |
557 |
final boolean locallyFifo; |
558 |
|
559 |
/** |
560 |
* The uncaught exception handler used when any worker abruptly |
561 |
* terminates. |
562 |
*/ |
563 |
private final Thread.UncaughtExceptionHandler ueh; |
564 |
|
565 |
/** |
566 |
* Pool number, just for assigning useful names to worker threads |
567 |
*/ |
568 |
private final int poolNumber; |
569 |
|
570 |
|
571 |
// Utilities for CASing fields. Note that most of these |
572 |
// are usually manually inlined by callers |
573 |
|
574 |
/** |
575 |
* Increments running count part of workerCounts |
576 |
*/ |
577 |
final void incrementRunningCount() { |
578 |
int c; |
579 |
do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
580 |
c = workerCounts, |
581 |
c + ONE_RUNNING)); |
582 |
} |
583 |
|
584 |
/** |
585 |
* Tries to decrement running count unless already zero |
586 |
*/ |
587 |
final boolean tryDecrementRunningCount() { |
588 |
int wc = workerCounts; |
589 |
if ((wc & RUNNING_COUNT_MASK) == 0) |
590 |
return false; |
591 |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
592 |
wc, wc - ONE_RUNNING); |
593 |
} |
594 |
|
595 |
/** |
596 |
* Forces decrement of encoded workerCounts, awaiting nonzero if |
597 |
* (rarely) necessary when other count updates lag. |
598 |
* |
599 |
* @param dr -- either zero or ONE_RUNNING |
600 |
* @param dt == either zero or ONE_TOTAL |
601 |
*/ |
602 |
private void decrementWorkerCounts(int dr, int dt) { |
603 |
for (;;) { |
604 |
int wc = workerCounts; |
605 |
if ((wc & RUNNING_COUNT_MASK) - dr < 0 || |
606 |
(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) { |
607 |
if ((runState & TERMINATED) != 0) |
608 |
return; // lagging termination on a backout |
609 |
Thread.yield(); |
610 |
} |
611 |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
612 |
wc, wc - (dr + dt))) |
613 |
return; |
614 |
} |
615 |
} |
616 |
|
617 |
/** |
618 |
* Increments event count |
619 |
*/ |
620 |
private void advanceEventCount() { |
621 |
int c; |
622 |
do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset, |
623 |
c = eventCount, c+1)); |
624 |
} |
625 |
|
626 |
/** |
627 |
* Tries incrementing active count; fails on contention. |
628 |
* Called by workers before executing tasks. |
629 |
* |
630 |
* @return true on success |
631 |
*/ |
632 |
final boolean tryIncrementActiveCount() { |
633 |
int c; |
634 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
635 |
c = runState, c + 1); |
636 |
} |
637 |
|
638 |
/** |
639 |
* Tries decrementing active count; fails on contention. |
640 |
* Called when workers cannot find tasks to run. |
641 |
*/ |
642 |
final boolean tryDecrementActiveCount() { |
643 |
int c; |
644 |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
645 |
c = runState, c - 1); |
646 |
} |
647 |
|
648 |
/** |
649 |
* Advances to at least the given level. Returns true if not |
650 |
* already in at least the given level. |
651 |
*/ |
652 |
private boolean advanceRunLevel(int level) { |
653 |
for (;;) { |
654 |
int s = runState; |
655 |
if ((s & level) != 0) |
656 |
return false; |
657 |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level)) |
658 |
return true; |
659 |
} |
660 |
} |
661 |
|
662 |
// workers array maintenance |
663 |
|
664 |
/** |
665 |
* Records and returns a workers array index for new worker. |
666 |
*/ |
667 |
private int recordWorker(ForkJoinWorkerThread w) { |
668 |
// Try using slot totalCount-1. If not available, scan and/or resize |
669 |
int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1; |
670 |
final ReentrantLock lock = this.workerLock; |
671 |
lock.lock(); |
672 |
try { |
673 |
ForkJoinWorkerThread[] ws = workers; |
674 |
int n = ws.length; |
675 |
if (k < 0 || k >= n || ws[k] != null) { |
676 |
for (k = 0; k < n && ws[k] != null; ++k) |
677 |
; |
678 |
if (k == n) |
679 |
ws = Arrays.copyOf(ws, n << 1); |
680 |
} |
681 |
ws[k] = w; |
682 |
workers = ws; // volatile array write ensures slot visibility |
683 |
} finally { |
684 |
lock.unlock(); |
685 |
} |
686 |
return k; |
687 |
} |
688 |
|
689 |
/** |
690 |
* Nulls out record of worker in workers array |
691 |
*/ |
692 |
private void forgetWorker(ForkJoinWorkerThread w) { |
693 |
int idx = w.poolIndex; |
694 |
// Locking helps method recordWorker avoid unecessary expansion |
695 |
final ReentrantLock lock = this.workerLock; |
696 |
lock.lock(); |
697 |
try { |
698 |
ForkJoinWorkerThread[] ws = workers; |
699 |
if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify |
700 |
ws[idx] = null; |
701 |
} finally { |
702 |
lock.unlock(); |
703 |
} |
704 |
} |
705 |
|
706 |
// adding and removing workers |
707 |
|
708 |
/** |
709 |
* Tries to create and add new worker. Assumes that worker counts |
710 |
* are already updated to accommodate the worker, so adjusts on |
711 |
* failure. |
712 |
* |
713 |
* @return the worker, or null on failure |
714 |
*/ |
715 |
private ForkJoinWorkerThread addWorker() { |
716 |
ForkJoinWorkerThread w = null; |
717 |
try { |
718 |
w = factory.newThread(this); |
719 |
} finally { // Adjust on either null or exceptional factory return |
720 |
if (w == null) { |
721 |
decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL); |
722 |
tryTerminate(false); // in case of failure during shutdown |
723 |
} |
724 |
} |
725 |
if (w != null) { |
726 |
w.start(recordWorker(w), ueh); |
727 |
advanceEventCount(); |
728 |
} |
729 |
return w; |
730 |
} |
731 |
|
732 |
/** |
733 |
* Final callback from terminating worker. Removes record of |
734 |
* worker from array, and adjusts counts. If pool is shutting |
735 |
* down, tries to complete terminatation. |
736 |
* |
737 |
* @param w the worker |
738 |
*/ |
739 |
final void workerTerminated(ForkJoinWorkerThread w) { |
740 |
forgetWorker(w); |
741 |
decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL); |
742 |
while (w.stealCount != 0) // collect final count |
743 |
tryAccumulateStealCount(w); |
744 |
tryTerminate(false); |
745 |
} |
746 |
|
747 |
// Waiting for and signalling events |
748 |
|
749 |
/** |
750 |
* Releases workers blocked on a count not equal to current count. |
751 |
* Normally called after precheck that eventWaiters isn't zero to |
752 |
* avoid wasted array checks. Gives up upon a change in count or |
753 |
* contention, letting other workers take over. |
754 |
*/ |
755 |
private void releaseEventWaiters() { |
756 |
ForkJoinWorkerThread[] ws = workers; |
757 |
int n = ws.length; |
758 |
long h = eventWaiters; |
759 |
int ec = eventCount; |
760 |
ForkJoinWorkerThread w; int id; |
761 |
while ((int)(h >>> EVENT_COUNT_SHIFT) != ec && |
762 |
(id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 && |
763 |
id < n && (w = ws[id]) != null && |
764 |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
765 |
h, h = w.nextWaiter)) { |
766 |
LockSupport.unpark(w); |
767 |
if (eventWaiters != h || eventCount != ec) |
768 |
break; |
769 |
} |
770 |
} |
771 |
|
772 |
/** |
773 |
* Tries to advance eventCount and releases waiters. Called only |
774 |
* from workers. |
775 |
*/ |
776 |
final void signalWork() { |
777 |
int c; // try to increment event count -- CAS failure OK |
778 |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1); |
779 |
if (eventWaiters != 0L) |
780 |
releaseEventWaiters(); |
781 |
} |
782 |
|
783 |
/** |
784 |
* Adds the given worker to event queue and blocks until |
785 |
* terminating or event count advances from the workers |
786 |
* lastEventCount value |
787 |
* |
788 |
* @param w the calling worker thread |
789 |
*/ |
790 |
private void eventSync(ForkJoinWorkerThread w) { |
791 |
int ec = w.lastEventCount; |
792 |
long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1)); |
793 |
long h; |
794 |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
795 |
(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 || |
796 |
(int)(h >>> EVENT_COUNT_SHIFT) == ec) && |
797 |
eventCount == ec) { |
798 |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
799 |
w.nextWaiter = h, nh)) { |
800 |
awaitEvent(w, ec); |
801 |
break; |
802 |
} |
803 |
} |
804 |
} |
805 |
|
806 |
/** |
807 |
* Blocks the given worker (that has already been entered as an |
808 |
* event waiter) until terminating or event count advances from |
809 |
* the given value. The oldest (first) waiter uses a timed wait to |
810 |
* occasionally one-by-one shrink the number of workers (to a |
811 |
* minumum of one) if the pool has not been used for extended |
812 |
* periods. |
813 |
* |
814 |
* @param w the calling worker thread |
815 |
* @param ec the count |
816 |
*/ |
817 |
private void awaitEvent(ForkJoinWorkerThread w, int ec) { |
818 |
while (eventCount == ec) { |
819 |
if (tryAccumulateStealCount(w)) { // transfer while idle |
820 |
boolean untimed = (w.nextWaiter != 0L || |
821 |
(workerCounts & RUNNING_COUNT_MASK) <= 1); |
822 |
long startTime = untimed? 0 : System.nanoTime(); |
823 |
Thread.interrupted(); // clear/ignore interrupt |
824 |
if (eventCount != ec || !w.isRunning() || |
825 |
runState >= TERMINATING) // recheck after clear |
826 |
break; |
827 |
if (untimed) |
828 |
LockSupport.park(w); |
829 |
else { |
830 |
LockSupport.parkNanos(w, SHRINK_RATE_NANOS); |
831 |
if (eventCount != ec || !w.isRunning() || |
832 |
runState >= TERMINATING) |
833 |
break; |
834 |
if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS) |
835 |
tryShutdownWaiter(ec); |
836 |
} |
837 |
} |
838 |
} |
839 |
} |
840 |
|
841 |
/** |
842 |
* Callback from the oldest waiter in awaitEvent waking up after a |
843 |
* period of non-use. Tries (once) to shutdown an event waiter (or |
844 |
* a spare, if one exists). Note that we don't need CAS or locks |
845 |
* here because the method is called only from one thread |
846 |
* occasionally waking (and even misfires are OK). Note that |
847 |
* until the shutdown worker fully terminates, workerCounts |
848 |
* will overestimate total count, which is tolerable. |
849 |
* |
850 |
* @param ec the event count waited on by caller (to abort |
851 |
* attempt if count has since changed). |
852 |
*/ |
853 |
private void tryShutdownWaiter(int ec) { |
854 |
if (spareWaiters != 0) { // prefer killing spares |
855 |
tryShutdownSpare(); |
856 |
return; |
857 |
} |
858 |
ForkJoinWorkerThread[] ws = workers; |
859 |
int n = ws.length; |
860 |
long h = eventWaiters; |
861 |
ForkJoinWorkerThread w; int id; long nh; |
862 |
if (runState == 0 && |
863 |
submissionQueue.isEmpty() && |
864 |
eventCount == ec && |
865 |
(id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 && |
866 |
id < n && (w = ws[id]) != null && |
867 |
(nh = w.nextWaiter) != 0L && // keep at least one worker |
868 |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh)) { |
869 |
w.shutdown(); |
870 |
LockSupport.unpark(w); |
871 |
} |
872 |
releaseEventWaiters(); |
873 |
} |
874 |
|
875 |
// Maintaining spares |
876 |
|
877 |
/** |
878 |
* Pushes worker onto the spare stack |
879 |
*/ |
880 |
final void pushSpare(ForkJoinWorkerThread w) { |
881 |
int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1); |
882 |
do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
883 |
w.nextSpare = spareWaiters,ns)); |
884 |
} |
885 |
|
886 |
/** |
887 |
* Callback from oldest spare occasionally waking up. Tries |
888 |
* (once) to shutdown a spare. Same idea as tryShutdownWaiter. |
889 |
*/ |
890 |
final void tryShutdownSpare() { |
891 |
int sw, id; |
892 |
ForkJoinWorkerThread w; |
893 |
ForkJoinWorkerThread[] ws; |
894 |
if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
895 |
id < (ws = workers).length && (w = ws[id]) != null && |
896 |
(workerCounts & RUNNING_COUNT_MASK) >= parallelism && |
897 |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
898 |
sw, w.nextSpare)) { |
899 |
w.shutdown(); |
900 |
LockSupport.unpark(w); |
901 |
advanceEventCount(); |
902 |
} |
903 |
} |
904 |
|
905 |
/** |
906 |
* Tries (once) to resume a spare if worker counts match |
907 |
* the given count. |
908 |
* |
909 |
* @param wc workerCounts value on invocation of this method |
910 |
*/ |
911 |
private void tryResumeSpare(int wc) { |
912 |
ForkJoinWorkerThread[] ws = workers; |
913 |
int n = ws.length; |
914 |
int sw, id, rs; ForkJoinWorkerThread w; |
915 |
if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 && |
916 |
id < n && (w = ws[id]) != null && |
917 |
(rs = runState) < TERMINATING && |
918 |
eventWaiters == 0L && workerCounts == wc) { |
919 |
// In case all workers busy, heuristically back off to let settle |
920 |
Thread.yield(); |
921 |
if (eventWaiters == 0L && runState == rs && // recheck |
922 |
workerCounts == wc && spareWaiters == sw && |
923 |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
924 |
sw, w.nextSpare)) { |
925 |
int c; // increment running count before resume |
926 |
do {} while(!UNSAFE.compareAndSwapInt |
927 |
(this, workerCountsOffset, |
928 |
c = workerCounts, c + ONE_RUNNING)); |
929 |
if (w.tryUnsuspend()) |
930 |
LockSupport.unpark(w); |
931 |
else // back out if w was shutdown |
932 |
decrementWorkerCounts(ONE_RUNNING, 0); |
933 |
} |
934 |
} |
935 |
} |
936 |
|
937 |
// adding workers on demand |
938 |
|
939 |
/** |
940 |
* Adds one or more workers if needed to establish target parallelism. |
941 |
* Retries upon contention. |
942 |
*/ |
943 |
private void addWorkerIfBelowTarget() { |
944 |
int pc = parallelism; |
945 |
int wc; |
946 |
while (((wc = workerCounts) >>> TOTAL_COUNT_SHIFT) < pc && |
947 |
runState < TERMINATING) { |
948 |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
949 |
wc + (ONE_RUNNING|ONE_TOTAL))) { |
950 |
if (addWorker() == null) |
951 |
break; |
952 |
} |
953 |
} |
954 |
} |
955 |
|
956 |
/** |
957 |
* Tries (once) to add a new worker if all existing workers are |
958 |
* busy, and there are either no running workers or the deficit is |
959 |
* at least twice the surplus. |
960 |
* |
961 |
* @param wc workerCounts value on invocation of this method |
962 |
*/ |
963 |
private void tryAddWorkerIfBusy(int wc) { |
964 |
int tc, rc, rs; |
965 |
int pc = parallelism; |
966 |
if ((tc = wc >>> TOTAL_COUNT_SHIFT) < MAX_WORKERS && |
967 |
((rc = wc & RUNNING_COUNT_MASK) == 0 || |
968 |
rc < pc - ((tc - pc) << 1)) && |
969 |
(rs = runState) < TERMINATING && |
970 |
(rs & ACTIVE_COUNT_MASK) == tc) { |
971 |
// Since all workers busy, heuristically back off to let settle |
972 |
Thread.yield(); |
973 |
if (eventWaiters == 0L && spareWaiters == 0 && // recheck |
974 |
runState == rs && workerCounts == wc && |
975 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
976 |
wc + (ONE_RUNNING|ONE_TOTAL))) |
977 |
addWorker(); |
978 |
} |
979 |
} |
980 |
|
981 |
/** |
982 |
* Does at most one of: |
983 |
* |
984 |
* 1. Help wake up existing workers waiting for work via |
985 |
* releaseEventWaiters. (If any exist, then it doesn't |
986 |
* matter right now if under target parallelism level.) |
987 |
* |
988 |
* 2. If a spare exists, try (once) to resume it via tryResumeSpare. |
989 |
* |
990 |
* 3. If there are not enough total workers, add some |
991 |
* via addWorkerIfBelowTarget; |
992 |
* |
993 |
* 4. Try (once) to add a new worker if all existing workers |
994 |
* are busy, via tryAddWorkerIfBusy |
995 |
*/ |
996 |
private void helpMaintainParallelism() { |
997 |
long h; int pc, wc; |
998 |
if (((int)((h = eventWaiters) & WAITER_ID_MASK)) != 0) { |
999 |
if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount) |
1000 |
releaseEventWaiters(); // avoid useless call |
1001 |
} |
1002 |
else if ((pc = parallelism) > |
1003 |
((wc = workerCounts) & RUNNING_COUNT_MASK)) { |
1004 |
if (spareWaiters != 0) |
1005 |
tryResumeSpare(wc); |
1006 |
else if ((wc >>> TOTAL_COUNT_SHIFT) < pc) |
1007 |
addWorkerIfBelowTarget(); |
1008 |
else |
1009 |
tryAddWorkerIfBusy(wc); |
1010 |
} |
1011 |
} |
1012 |
|
1013 |
/** |
1014 |
* Callback from workers invoked upon each top-level action (i.e., |
1015 |
* stealing a task or taking a submission and running it). |
1016 |
* Performs one or more of the following: |
1017 |
* |
1018 |
* 1. If the worker is active, try to set its active status to |
1019 |
* inactive and update activeCount. On contention, we may try |
1020 |
* again on this or subsequent call. |
1021 |
* |
1022 |
* 2. Release any existing event waiters that are now relesable |
1023 |
* |
1024 |
* 3. If there are too many running threads, suspend this worker |
1025 |
* (first forcing inactive if necessary). If it is not |
1026 |
* needed, it may be killed while suspended via |
1027 |
* tryShutdownSpare. Otherwise, upon resume it rechecks to make |
1028 |
* sure that it is still needed. |
1029 |
* |
1030 |
* 4. If more than 1 miss, await the next task event via |
1031 |
* eventSync (first forcing inactivation if necessary), upon |
1032 |
* which worker may also be killed, via tryShutdownWaiter. |
1033 |
* |
1034 |
* 5. Help reactivate other workers via helpMaintainParallelism |
1035 |
* |
1036 |
* @param w the worker |
1037 |
* @param misses the number of scans by caller failing to find work |
1038 |
* (saturating at 2 to avoid wraparound) |
1039 |
*/ |
1040 |
final void preStep(ForkJoinWorkerThread w, int misses) { |
1041 |
boolean active = w.active; |
1042 |
int pc = parallelism; |
1043 |
for (;;) { |
1044 |
int rs, wc, rc, ec; long h; |
1045 |
if (active && UNSAFE.compareAndSwapInt(this, runStateOffset, |
1046 |
rs = runState, rs - 1)) |
1047 |
active = w.active = false; |
1048 |
if (((int)((h = eventWaiters) & WAITER_ID_MASK)) != 0 && |
1049 |
(int)(h >>> EVENT_COUNT_SHIFT) != eventCount) { |
1050 |
releaseEventWaiters(); |
1051 |
if (misses > 1) |
1052 |
continue; // clear before sync below |
1053 |
} |
1054 |
if ((rc = ((wc = workerCounts) & RUNNING_COUNT_MASK)) > pc) { |
1055 |
if (!active && // must inactivate to suspend |
1056 |
workerCounts == wc && // try to suspend as spare |
1057 |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1058 |
wc, wc - ONE_RUNNING)) { |
1059 |
w.suspendAsSpare(); |
1060 |
if (!w.isRunning()) |
1061 |
break; // was killed while spare |
1062 |
} |
1063 |
continue; |
1064 |
} |
1065 |
if (misses > 0) { |
1066 |
if ((ec = eventCount) == w.lastEventCount && misses > 1) { |
1067 |
if (!active) { // must inactivate to sync |
1068 |
eventSync(w); |
1069 |
if (w.isRunning()) |
1070 |
misses = 1; // don't re-sync |
1071 |
else |
1072 |
break; // was killed while waiting |
1073 |
} |
1074 |
continue; |
1075 |
} |
1076 |
w.lastEventCount = ec; |
1077 |
} |
1078 |
if (rc < pc) |
1079 |
helpMaintainParallelism(); |
1080 |
break; |
1081 |
} |
1082 |
} |
1083 |
|
1084 |
/** |
1085 |
* Helps and/or blocks awaiting join of the given task. |
1086 |
* Alternates between helpJoinTask() and helpMaintainParallelism() |
1087 |
* as many times as there is a deficit in running count (or longer |
1088 |
* if running count would become zero), then blocks if task still |
1089 |
* not done. |
1090 |
* |
1091 |
* @param joinMe the task to join |
1092 |
*/ |
1093 |
final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) { |
1094 |
int threshold = parallelism; // descend blocking thresholds |
1095 |
while (joinMe.status >= 0) { |
1096 |
boolean block; int wc; |
1097 |
worker.helpJoinTask(joinMe); |
1098 |
if (joinMe.status < 0) |
1099 |
break; |
1100 |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
1101 |
if (threshold > 0) |
1102 |
--threshold; |
1103 |
else |
1104 |
advanceEventCount(); // force release |
1105 |
block = false; |
1106 |
} |
1107 |
else |
1108 |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1109 |
wc, wc - ONE_RUNNING); |
1110 |
helpMaintainParallelism(); |
1111 |
if (block) { |
1112 |
int c; |
1113 |
joinMe.internalAwaitDone(); |
1114 |
do {} while (!UNSAFE.compareAndSwapInt |
1115 |
(this, workerCountsOffset, |
1116 |
c = workerCounts, c + ONE_RUNNING)); |
1117 |
break; |
1118 |
} |
1119 |
} |
1120 |
} |
1121 |
|
1122 |
/** |
1123 |
* Same idea as awaitJoin, but no helping |
1124 |
*/ |
1125 |
final void awaitBlocker(ManagedBlocker blocker) |
1126 |
throws InterruptedException { |
1127 |
int threshold = parallelism; |
1128 |
while (!blocker.isReleasable()) { |
1129 |
boolean block; int wc; |
1130 |
if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) { |
1131 |
if (threshold > 0) |
1132 |
--threshold; |
1133 |
else |
1134 |
advanceEventCount(); |
1135 |
block = false; |
1136 |
} |
1137 |
else |
1138 |
block = UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1139 |
wc, wc - ONE_RUNNING); |
1140 |
helpMaintainParallelism(); |
1141 |
if (block) { |
1142 |
try { |
1143 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1144 |
} finally { |
1145 |
int c; |
1146 |
do {} while (!UNSAFE.compareAndSwapInt |
1147 |
(this, workerCountsOffset, |
1148 |
c = workerCounts, c + ONE_RUNNING)); |
1149 |
} |
1150 |
break; |
1151 |
} |
1152 |
} |
1153 |
} |
1154 |
|
1155 |
/** |
1156 |
* Possibly initiates and/or completes termination. |
1157 |
* |
1158 |
* @param now if true, unconditionally terminate, else only |
1159 |
* if shutdown and empty queue and no active workers |
1160 |
* @return true if now terminating or terminated |
1161 |
*/ |
1162 |
private boolean tryTerminate(boolean now) { |
1163 |
if (now) |
1164 |
advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN |
1165 |
else if (runState < SHUTDOWN || |
1166 |
!submissionQueue.isEmpty() || |
1167 |
(runState & ACTIVE_COUNT_MASK) != 0) |
1168 |
return false; |
1169 |
|
1170 |
if (advanceRunLevel(TERMINATING)) |
1171 |
startTerminating(); |
1172 |
|
1173 |
// Finish now if all threads terminated; else in some subsequent call |
1174 |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) { |
1175 |
advanceRunLevel(TERMINATED); |
1176 |
termination.arrive(); |
1177 |
} |
1178 |
return true; |
1179 |
} |
1180 |
|
1181 |
/** |
1182 |
* Actions on transition to TERMINATING |
1183 |
* |
1184 |
* Runs up to four passes through workers: (0) shutting down each |
1185 |
* (without waking up if parked) to quickly spread notifications |
1186 |
* without unnecessary bouncing around event queues etc (1) wake |
1187 |
* up and help cancel tasks (2) interrupt (3) mop up races with |
1188 |
* interrupted workers |
1189 |
*/ |
1190 |
private void startTerminating() { |
1191 |
cancelSubmissions(); |
1192 |
for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) { |
1193 |
advanceEventCount(); |
1194 |
eventWaiters = 0L; // clobber lists |
1195 |
spareWaiters = 0; |
1196 |
ForkJoinWorkerThread[] ws = workers; |
1197 |
int n = ws.length; |
1198 |
for (int i = 0; i < n; ++i) { |
1199 |
ForkJoinWorkerThread w = ws[i]; |
1200 |
if (w != null) { |
1201 |
w.shutdown(); |
1202 |
if (passes > 0 && !w.isTerminated()) { |
1203 |
w.cancelTasks(); |
1204 |
LockSupport.unpark(w); |
1205 |
if (passes > 1) { |
1206 |
try { |
1207 |
w.interrupt(); |
1208 |
} catch (SecurityException ignore) { |
1209 |
} |
1210 |
} |
1211 |
} |
1212 |
} |
1213 |
} |
1214 |
} |
1215 |
} |
1216 |
|
1217 |
/** |
1218 |
* Clear out and cancel submissions, ignoring exceptions |
1219 |
*/ |
1220 |
private void cancelSubmissions() { |
1221 |
ForkJoinTask<?> task; |
1222 |
while ((task = submissionQueue.poll()) != null) { |
1223 |
try { |
1224 |
task.cancel(false); |
1225 |
} catch (Throwable ignore) { |
1226 |
} |
1227 |
} |
1228 |
} |
1229 |
|
1230 |
// misc support for ForkJoinWorkerThread |
1231 |
|
1232 |
/** |
1233 |
* Returns pool number |
1234 |
*/ |
1235 |
final int getPoolNumber() { |
1236 |
return poolNumber; |
1237 |
} |
1238 |
|
1239 |
/** |
1240 |
* Tries to accumulates steal count from a worker, clearing |
1241 |
* the worker's value. |
1242 |
* |
1243 |
* @return true if worker steal count now zero |
1244 |
*/ |
1245 |
final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) { |
1246 |
int sc = w.stealCount; |
1247 |
long c = stealCount; |
1248 |
// CAS even if zero, for fence effects |
1249 |
if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) { |
1250 |
if (sc != 0) |
1251 |
w.stealCount = 0; |
1252 |
return true; |
1253 |
} |
1254 |
return sc == 0; |
1255 |
} |
1256 |
|
1257 |
/** |
1258 |
* Returns the approximate (non-atomic) number of idle threads per |
1259 |
* active thread. |
1260 |
*/ |
1261 |
final int idlePerActive() { |
1262 |
int pc = parallelism; // use parallelism, not rc |
1263 |
int ac = runState; // no mask -- artifically boosts during shutdown |
1264 |
// Use exact results for small values, saturate past 4 |
1265 |
return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3; |
1266 |
} |
1267 |
|
1268 |
// Public and protected methods |
1269 |
|
1270 |
// Constructors |
1271 |
|
1272 |
/** |
1273 |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
1274 |
* java.lang.Runtime#availableProcessors}, using the {@linkplain |
1275 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1276 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1277 |
* |
1278 |
* @throws SecurityException if a security manager exists and |
1279 |
* the caller is not permitted to modify threads |
1280 |
* because it does not hold {@link |
1281 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1282 |
*/ |
1283 |
public ForkJoinPool() { |
1284 |
this(Runtime.getRuntime().availableProcessors(), |
1285 |
defaultForkJoinWorkerThreadFactory, null, false); |
1286 |
} |
1287 |
|
1288 |
/** |
1289 |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
1290 |
* level, the {@linkplain |
1291 |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1292 |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1293 |
* |
1294 |
* @param parallelism the parallelism level |
1295 |
* @throws IllegalArgumentException if parallelism less than or |
1296 |
* equal to zero, or greater than implementation limit |
1297 |
* @throws SecurityException if a security manager exists and |
1298 |
* the caller is not permitted to modify threads |
1299 |
* because it does not hold {@link |
1300 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1301 |
*/ |
1302 |
public ForkJoinPool(int parallelism) { |
1303 |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
1304 |
} |
1305 |
|
1306 |
/** |
1307 |
* Creates a {@code ForkJoinPool} with the given parameters. |
1308 |
* |
1309 |
* @param parallelism the parallelism level. For default value, |
1310 |
* use {@link java.lang.Runtime#availableProcessors}. |
1311 |
* @param factory the factory for creating new threads. For default value, |
1312 |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
1313 |
* @param handler the handler for internal worker threads that |
1314 |
* terminate due to unrecoverable errors encountered while executing |
1315 |
* tasks. For default value, use <code>null</code>. |
1316 |
* @param asyncMode if true, |
1317 |
* establishes local first-in-first-out scheduling mode for forked |
1318 |
* tasks that are never joined. This mode may be more appropriate |
1319 |
* than default locally stack-based mode in applications in which |
1320 |
* worker threads only process event-style asynchronous tasks. |
1321 |
* For default value, use <code>false</code>. |
1322 |
* @throws IllegalArgumentException if parallelism less than or |
1323 |
* equal to zero, or greater than implementation limit |
1324 |
* @throws NullPointerException if the factory is null |
1325 |
* @throws SecurityException if a security manager exists and |
1326 |
* the caller is not permitted to modify threads |
1327 |
* because it does not hold {@link |
1328 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1329 |
*/ |
1330 |
public ForkJoinPool(int parallelism, |
1331 |
ForkJoinWorkerThreadFactory factory, |
1332 |
Thread.UncaughtExceptionHandler handler, |
1333 |
boolean asyncMode) { |
1334 |
checkPermission(); |
1335 |
if (factory == null) |
1336 |
throw new NullPointerException(); |
1337 |
if (parallelism <= 0 || parallelism > MAX_WORKERS) |
1338 |
throw new IllegalArgumentException(); |
1339 |
this.parallelism = parallelism; |
1340 |
this.factory = factory; |
1341 |
this.ueh = handler; |
1342 |
this.locallyFifo = asyncMode; |
1343 |
int arraySize = initialArraySizeFor(parallelism); |
1344 |
this.workers = new ForkJoinWorkerThread[arraySize]; |
1345 |
this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
1346 |
this.workerLock = new ReentrantLock(); |
1347 |
this.termination = new Phaser(1); |
1348 |
this.poolNumber = poolNumberGenerator.incrementAndGet(); |
1349 |
} |
1350 |
|
1351 |
/** |
1352 |
* Returns initial power of two size for workers array. |
1353 |
* @param pc the initial parallelism level |
1354 |
*/ |
1355 |
private static int initialArraySizeFor(int pc) { |
1356 |
// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16) |
1357 |
int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS; |
1358 |
size |= size >>> 1; |
1359 |
size |= size >>> 2; |
1360 |
size |= size >>> 4; |
1361 |
size |= size >>> 8; |
1362 |
return size + 1; |
1363 |
} |
1364 |
|
1365 |
// Execution methods |
1366 |
|
1367 |
/** |
1368 |
* Common code for execute, invoke and submit |
1369 |
*/ |
1370 |
private <T> void doSubmit(ForkJoinTask<T> task) { |
1371 |
if (task == null) |
1372 |
throw new NullPointerException(); |
1373 |
if (runState >= SHUTDOWN) |
1374 |
throw new RejectedExecutionException(); |
1375 |
submissionQueue.offer(task); |
1376 |
advanceEventCount(); |
1377 |
if (eventWaiters != 0L) |
1378 |
releaseEventWaiters(); |
1379 |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) < parallelism) |
1380 |
addWorkerIfBelowTarget(); |
1381 |
} |
1382 |
|
1383 |
/** |
1384 |
* Performs the given task, returning its result upon completion. |
1385 |
* |
1386 |
* @param task the task |
1387 |
* @return the task's result |
1388 |
* @throws NullPointerException if the task is null |
1389 |
* @throws RejectedExecutionException if the task cannot be |
1390 |
* scheduled for execution |
1391 |
*/ |
1392 |
public <T> T invoke(ForkJoinTask<T> task) { |
1393 |
doSubmit(task); |
1394 |
return task.join(); |
1395 |
} |
1396 |
|
1397 |
/** |
1398 |
* Arranges for (asynchronous) execution of the given task. |
1399 |
* |
1400 |
* @param task the task |
1401 |
* @throws NullPointerException if the task is null |
1402 |
* @throws RejectedExecutionException if the task cannot be |
1403 |
* scheduled for execution |
1404 |
*/ |
1405 |
public void execute(ForkJoinTask<?> task) { |
1406 |
doSubmit(task); |
1407 |
} |
1408 |
|
1409 |
// AbstractExecutorService methods |
1410 |
|
1411 |
/** |
1412 |
* @throws NullPointerException if the task is null |
1413 |
* @throws RejectedExecutionException if the task cannot be |
1414 |
* scheduled for execution |
1415 |
*/ |
1416 |
public void execute(Runnable task) { |
1417 |
ForkJoinTask<?> job; |
1418 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1419 |
job = (ForkJoinTask<?>) task; |
1420 |
else |
1421 |
job = ForkJoinTask.adapt(task, null); |
1422 |
doSubmit(job); |
1423 |
} |
1424 |
|
1425 |
/** |
1426 |
* Submits a ForkJoinTask for execution. |
1427 |
* |
1428 |
* @param task the task to submit |
1429 |
* @return the task |
1430 |
* @throws NullPointerException if the task is null |
1431 |
* @throws RejectedExecutionException if the task cannot be |
1432 |
* scheduled for execution |
1433 |
*/ |
1434 |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
1435 |
doSubmit(task); |
1436 |
return task; |
1437 |
} |
1438 |
|
1439 |
/** |
1440 |
* @throws NullPointerException if the task is null |
1441 |
* @throws RejectedExecutionException if the task cannot be |
1442 |
* scheduled for execution |
1443 |
*/ |
1444 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
1445 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task); |
1446 |
doSubmit(job); |
1447 |
return job; |
1448 |
} |
1449 |
|
1450 |
/** |
1451 |
* @throws NullPointerException if the task is null |
1452 |
* @throws RejectedExecutionException if the task cannot be |
1453 |
* scheduled for execution |
1454 |
*/ |
1455 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
1456 |
ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); |
1457 |
doSubmit(job); |
1458 |
return job; |
1459 |
} |
1460 |
|
1461 |
/** |
1462 |
* @throws NullPointerException if the task is null |
1463 |
* @throws RejectedExecutionException if the task cannot be |
1464 |
* scheduled for execution |
1465 |
*/ |
1466 |
public ForkJoinTask<?> submit(Runnable task) { |
1467 |
ForkJoinTask<?> job; |
1468 |
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1469 |
job = (ForkJoinTask<?>) task; |
1470 |
else |
1471 |
job = ForkJoinTask.adapt(task, null); |
1472 |
doSubmit(job); |
1473 |
return job; |
1474 |
} |
1475 |
|
1476 |
/** |
1477 |
* @throws NullPointerException {@inheritDoc} |
1478 |
* @throws RejectedExecutionException {@inheritDoc} |
1479 |
*/ |
1480 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
1481 |
ArrayList<ForkJoinTask<T>> forkJoinTasks = |
1482 |
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
1483 |
for (Callable<T> task : tasks) |
1484 |
forkJoinTasks.add(ForkJoinTask.adapt(task)); |
1485 |
invoke(new InvokeAll<T>(forkJoinTasks)); |
1486 |
|
1487 |
@SuppressWarnings({"unchecked", "rawtypes"}) |
1488 |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1489 |
return futures; |
1490 |
} |
1491 |
|
1492 |
static final class InvokeAll<T> extends RecursiveAction { |
1493 |
final ArrayList<ForkJoinTask<T>> tasks; |
1494 |
InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } |
1495 |
public void compute() { |
1496 |
try { invokeAll(tasks); } |
1497 |
catch (Exception ignore) {} |
1498 |
} |
1499 |
private static final long serialVersionUID = -7914297376763021607L; |
1500 |
} |
1501 |
|
1502 |
/** |
1503 |
* Returns the factory used for constructing new workers. |
1504 |
* |
1505 |
* @return the factory used for constructing new workers |
1506 |
*/ |
1507 |
public ForkJoinWorkerThreadFactory getFactory() { |
1508 |
return factory; |
1509 |
} |
1510 |
|
1511 |
/** |
1512 |
* Returns the handler for internal worker threads that terminate |
1513 |
* due to unrecoverable errors encountered while executing tasks. |
1514 |
* |
1515 |
* @return the handler, or {@code null} if none |
1516 |
*/ |
1517 |
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
1518 |
return ueh; |
1519 |
} |
1520 |
|
1521 |
/** |
1522 |
* Returns the targeted parallelism level of this pool. |
1523 |
* |
1524 |
* @return the targeted parallelism level of this pool |
1525 |
*/ |
1526 |
public int getParallelism() { |
1527 |
return parallelism; |
1528 |
} |
1529 |
|
1530 |
/** |
1531 |
* Returns the number of worker threads that have started but not |
1532 |
* yet terminated. This result returned by this method may differ |
1533 |
* from {@link #getParallelism} when threads are created to |
1534 |
* maintain parallelism when others are cooperatively blocked. |
1535 |
* |
1536 |
* @return the number of worker threads |
1537 |
*/ |
1538 |
public int getPoolSize() { |
1539 |
return workerCounts >>> TOTAL_COUNT_SHIFT; |
1540 |
} |
1541 |
|
1542 |
/** |
1543 |
* Returns {@code true} if this pool uses local first-in-first-out |
1544 |
* scheduling mode for forked tasks that are never joined. |
1545 |
* |
1546 |
* @return {@code true} if this pool uses async mode |
1547 |
*/ |
1548 |
public boolean getAsyncMode() { |
1549 |
return locallyFifo; |
1550 |
} |
1551 |
|
1552 |
/** |
1553 |
* Returns an estimate of the number of worker threads that are |
1554 |
* not blocked waiting to join tasks or for other managed |
1555 |
* synchronization. This method may overestimate the |
1556 |
* number of running threads. |
1557 |
* |
1558 |
* @return the number of worker threads |
1559 |
*/ |
1560 |
public int getRunningThreadCount() { |
1561 |
return workerCounts & RUNNING_COUNT_MASK; |
1562 |
} |
1563 |
|
1564 |
/** |
1565 |
* Returns an estimate of the number of threads that are currently |
1566 |
* stealing or executing tasks. This method may overestimate the |
1567 |
* number of active threads. |
1568 |
* |
1569 |
* @return the number of active threads |
1570 |
*/ |
1571 |
public int getActiveThreadCount() { |
1572 |
return runState & ACTIVE_COUNT_MASK; |
1573 |
} |
1574 |
|
1575 |
/** |
1576 |
* Returns {@code true} if all worker threads are currently idle. |
1577 |
* An idle worker is one that cannot obtain a task to execute |
1578 |
* because none are available to steal from other threads, and |
1579 |
* there are no pending submissions to the pool. This method is |
1580 |
* conservative; it might not return {@code true} immediately upon |
1581 |
* idleness of all threads, but will eventually become true if |
1582 |
* threads remain inactive. |
1583 |
* |
1584 |
* @return {@code true} if all threads are currently idle |
1585 |
*/ |
1586 |
public boolean isQuiescent() { |
1587 |
return (runState & ACTIVE_COUNT_MASK) == 0; |
1588 |
} |
1589 |
|
1590 |
/** |
1591 |
* Returns an estimate of the total number of tasks stolen from |
1592 |
* one thread's work queue by another. The reported value |
1593 |
* underestimates the actual total number of steals when the pool |
1594 |
* is not quiescent. This value may be useful for monitoring and |
1595 |
* tuning fork/join programs: in general, steal counts should be |
1596 |
* high enough to keep threads busy, but low enough to avoid |
1597 |
* overhead and contention across threads. |
1598 |
* |
1599 |
* @return the number of steals |
1600 |
*/ |
1601 |
public long getStealCount() { |
1602 |
return stealCount; |
1603 |
} |
1604 |
|
1605 |
/** |
1606 |
* Returns an estimate of the total number of tasks currently held |
1607 |
* in queues by worker threads (but not including tasks submitted |
1608 |
* to the pool that have not begun executing). This value is only |
1609 |
* an approximation, obtained by iterating across all threads in |
1610 |
* the pool. This method may be useful for tuning task |
1611 |
* granularities. |
1612 |
* |
1613 |
* @return the number of queued tasks |
1614 |
*/ |
1615 |
public long getQueuedTaskCount() { |
1616 |
long count = 0; |
1617 |
ForkJoinWorkerThread[] ws = workers; |
1618 |
int n = ws.length; |
1619 |
for (int i = 0; i < n; ++i) { |
1620 |
ForkJoinWorkerThread w = ws[i]; |
1621 |
if (w != null) |
1622 |
count += w.getQueueSize(); |
1623 |
} |
1624 |
return count; |
1625 |
} |
1626 |
|
1627 |
/** |
1628 |
* Returns an estimate of the number of tasks submitted to this |
1629 |
* pool that have not yet begun executing. This method takes time |
1630 |
* proportional to the number of submissions. |
1631 |
* |
1632 |
* @return the number of queued submissions |
1633 |
*/ |
1634 |
public int getQueuedSubmissionCount() { |
1635 |
return submissionQueue.size(); |
1636 |
} |
1637 |
|
1638 |
/** |
1639 |
* Returns {@code true} if there are any tasks submitted to this |
1640 |
* pool that have not yet begun executing. |
1641 |
* |
1642 |
* @return {@code true} if there are any queued submissions |
1643 |
*/ |
1644 |
public boolean hasQueuedSubmissions() { |
1645 |
return !submissionQueue.isEmpty(); |
1646 |
} |
1647 |
|
1648 |
/** |
1649 |
* Removes and returns the next unexecuted submission if one is |
1650 |
* available. This method may be useful in extensions to this |
1651 |
* class that re-assign work in systems with multiple pools. |
1652 |
* |
1653 |
* @return the next submission, or {@code null} if none |
1654 |
*/ |
1655 |
protected ForkJoinTask<?> pollSubmission() { |
1656 |
return submissionQueue.poll(); |
1657 |
} |
1658 |
|
1659 |
/** |
1660 |
* Removes all available unexecuted submitted and forked tasks |
1661 |
* from scheduling queues and adds them to the given collection, |
1662 |
* without altering their execution status. These may include |
1663 |
* artificially generated or wrapped tasks. This method is |
1664 |
* designed to be invoked only when the pool is known to be |
1665 |
* quiescent. Invocations at other times may not remove all |
1666 |
* tasks. A failure encountered while attempting to add elements |
1667 |
* to collection {@code c} may result in elements being in |
1668 |
* neither, either or both collections when the associated |
1669 |
* exception is thrown. The behavior of this operation is |
1670 |
* undefined if the specified collection is modified while the |
1671 |
* operation is in progress. |
1672 |
* |
1673 |
* @param c the collection to transfer elements into |
1674 |
* @return the number of elements transferred |
1675 |
*/ |
1676 |
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1677 |
int count = submissionQueue.drainTo(c); |
1678 |
ForkJoinWorkerThread[] ws = workers; |
1679 |
int n = ws.length; |
1680 |
for (int i = 0; i < n; ++i) { |
1681 |
ForkJoinWorkerThread w = ws[i]; |
1682 |
if (w != null) |
1683 |
count += w.drainTasksTo(c); |
1684 |
} |
1685 |
return count; |
1686 |
} |
1687 |
|
1688 |
/** |
1689 |
* Returns a string identifying this pool, as well as its state, |
1690 |
* including indications of run state, parallelism level, and |
1691 |
* worker and task counts. |
1692 |
* |
1693 |
* @return a string identifying this pool, as well as its state |
1694 |
*/ |
1695 |
public String toString() { |
1696 |
long st = getStealCount(); |
1697 |
long qt = getQueuedTaskCount(); |
1698 |
long qs = getQueuedSubmissionCount(); |
1699 |
int wc = workerCounts; |
1700 |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1701 |
int rc = wc & RUNNING_COUNT_MASK; |
1702 |
int pc = parallelism; |
1703 |
int rs = runState; |
1704 |
int ac = rs & ACTIVE_COUNT_MASK; |
1705 |
return super.toString() + |
1706 |
"[" + runLevelToString(rs) + |
1707 |
", parallelism = " + pc + |
1708 |
", size = " + tc + |
1709 |
", active = " + ac + |
1710 |
", running = " + rc + |
1711 |
", steals = " + st + |
1712 |
", tasks = " + qt + |
1713 |
", submissions = " + qs + |
1714 |
"]"; |
1715 |
} |
1716 |
|
1717 |
private static String runLevelToString(int s) { |
1718 |
return ((s & TERMINATED) != 0 ? "Terminated" : |
1719 |
((s & TERMINATING) != 0 ? "Terminating" : |
1720 |
((s & SHUTDOWN) != 0 ? "Shutting down" : |
1721 |
"Running"))); |
1722 |
} |
1723 |
|
1724 |
/** |
1725 |
* Initiates an orderly shutdown in which previously submitted |
1726 |
* tasks are executed, but no new tasks will be accepted. |
1727 |
* Invocation has no additional effect if already shut down. |
1728 |
* Tasks that are in the process of being submitted concurrently |
1729 |
* during the course of this method may or may not be rejected. |
1730 |
* |
1731 |
* @throws SecurityException if a security manager exists and |
1732 |
* the caller is not permitted to modify threads |
1733 |
* because it does not hold {@link |
1734 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1735 |
*/ |
1736 |
public void shutdown() { |
1737 |
checkPermission(); |
1738 |
advanceRunLevel(SHUTDOWN); |
1739 |
tryTerminate(false); |
1740 |
} |
1741 |
|
1742 |
/** |
1743 |
* Attempts to cancel and/or stop all tasks, and reject all |
1744 |
* subsequently submitted tasks. Tasks that are in the process of |
1745 |
* being submitted or executed concurrently during the course of |
1746 |
* this method may or may not be rejected. This method cancels |
1747 |
* both existing and unexecuted tasks, in order to permit |
1748 |
* termination in the presence of task dependencies. So the method |
1749 |
* always returns an empty list (unlike the case for some other |
1750 |
* Executors). |
1751 |
* |
1752 |
* @return an empty list |
1753 |
* @throws SecurityException if a security manager exists and |
1754 |
* the caller is not permitted to modify threads |
1755 |
* because it does not hold {@link |
1756 |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1757 |
*/ |
1758 |
public List<Runnable> shutdownNow() { |
1759 |
checkPermission(); |
1760 |
tryTerminate(true); |
1761 |
return Collections.emptyList(); |
1762 |
} |
1763 |
|
1764 |
/** |
1765 |
* Returns {@code true} if all tasks have completed following shut down. |
1766 |
* |
1767 |
* @return {@code true} if all tasks have completed following shut down |
1768 |
*/ |
1769 |
public boolean isTerminated() { |
1770 |
return runState >= TERMINATED; |
1771 |
} |
1772 |
|
1773 |
/** |
1774 |
* Returns {@code true} if the process of termination has |
1775 |
* commenced but not yet completed. This method may be useful for |
1776 |
* debugging. A return of {@code true} reported a sufficient |
1777 |
* period after shutdown may indicate that submitted tasks have |
1778 |
* ignored or suppressed interruption, causing this executor not |
1779 |
* to properly terminate. |
1780 |
* |
1781 |
* @return {@code true} if terminating but not yet terminated |
1782 |
*/ |
1783 |
public boolean isTerminating() { |
1784 |
return (runState & (TERMINATING|TERMINATED)) == TERMINATING; |
1785 |
} |
1786 |
|
1787 |
/** |
1788 |
* Returns {@code true} if this pool has been shut down. |
1789 |
* |
1790 |
* @return {@code true} if this pool has been shut down |
1791 |
*/ |
1792 |
public boolean isShutdown() { |
1793 |
return runState >= SHUTDOWN; |
1794 |
} |
1795 |
|
1796 |
/** |
1797 |
* Blocks until all tasks have completed execution after a shutdown |
1798 |
* request, or the timeout occurs, or the current thread is |
1799 |
* interrupted, whichever happens first. |
1800 |
* |
1801 |
* @param timeout the maximum time to wait |
1802 |
* @param unit the time unit of the timeout argument |
1803 |
* @return {@code true} if this executor terminated and |
1804 |
* {@code false} if the timeout elapsed before termination |
1805 |
* @throws InterruptedException if interrupted while waiting |
1806 |
*/ |
1807 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1808 |
throws InterruptedException { |
1809 |
try { |
1810 |
return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
1811 |
} catch(TimeoutException ex) { |
1812 |
return false; |
1813 |
} |
1814 |
} |
1815 |
|
1816 |
/** |
1817 |
* Interface for extending managed parallelism for tasks running |
1818 |
* in {@link ForkJoinPool}s. |
1819 |
* |
1820 |
* <p>A {@code ManagedBlocker} provides two methods. Method |
1821 |
* {@code isReleasable} must return {@code true} if blocking is |
1822 |
* not necessary. Method {@code block} blocks the current thread |
1823 |
* if necessary (perhaps internally invoking {@code isReleasable} |
1824 |
* before actually blocking). The unusual methods in this API |
1825 |
* accommodate synchronizers that may, but don't usually, block |
1826 |
* for long periods. Similarly, they allow more efficient internal |
1827 |
* handling of cases in which additional workers may be, but |
1828 |
* usually are not, needed to ensure sufficient parallelism. |
1829 |
* Toward this end, implementations of method {@code isReleasable} |
1830 |
* must be amenable to repeated invocation. |
1831 |
* |
1832 |
* <p>For example, here is a ManagedBlocker based on a |
1833 |
* ReentrantLock: |
1834 |
* <pre> {@code |
1835 |
* class ManagedLocker implements ManagedBlocker { |
1836 |
* final ReentrantLock lock; |
1837 |
* boolean hasLock = false; |
1838 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
1839 |
* public boolean block() { |
1840 |
* if (!hasLock) |
1841 |
* lock.lock(); |
1842 |
* return true; |
1843 |
* } |
1844 |
* public boolean isReleasable() { |
1845 |
* return hasLock || (hasLock = lock.tryLock()); |
1846 |
* } |
1847 |
* }}</pre> |
1848 |
* |
1849 |
* <p>Here is a class that possibly blocks waiting for an |
1850 |
* item on a given queue: |
1851 |
* <pre> {@code |
1852 |
* class QueueTaker<E> implements ManagedBlocker { |
1853 |
* final BlockingQueue<E> queue; |
1854 |
* volatile E item = null; |
1855 |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
1856 |
* public boolean block() throws InterruptedException { |
1857 |
* if (item == null) |
1858 |
* item = queue.take |
1859 |
* return true; |
1860 |
* } |
1861 |
* public boolean isReleasable() { |
1862 |
* return item != null || (item = queue.poll) != null; |
1863 |
* } |
1864 |
* public E getItem() { // call after pool.managedBlock completes |
1865 |
* return item; |
1866 |
* } |
1867 |
* }}</pre> |
1868 |
*/ |
1869 |
public static interface ManagedBlocker { |
1870 |
/** |
1871 |
* Possibly blocks the current thread, for example waiting for |
1872 |
* a lock or condition. |
1873 |
* |
1874 |
* @return {@code true} if no additional blocking is necessary |
1875 |
* (i.e., if isReleasable would return true) |
1876 |
* @throws InterruptedException if interrupted while waiting |
1877 |
* (the method is not required to do so, but is allowed to) |
1878 |
*/ |
1879 |
boolean block() throws InterruptedException; |
1880 |
|
1881 |
/** |
1882 |
* Returns {@code true} if blocking is unnecessary. |
1883 |
*/ |
1884 |
boolean isReleasable(); |
1885 |
} |
1886 |
|
1887 |
/** |
1888 |
* Blocks in accord with the given blocker. If the current thread |
1889 |
* is a {@link ForkJoinWorkerThread}, this method possibly |
1890 |
* arranges for a spare thread to be activated if necessary to |
1891 |
* ensure sufficient parallelism while the current thread is blocked. |
1892 |
* |
1893 |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
1894 |
* behaviorally equivalent to |
1895 |
* <pre> {@code |
1896 |
* while (!blocker.isReleasable()) |
1897 |
* if (blocker.block()) |
1898 |
* return; |
1899 |
* }</pre> |
1900 |
* |
1901 |
* If the caller is a {@code ForkJoinTask}, then the pool may |
1902 |
* first be expanded to ensure parallelism, and later adjusted. |
1903 |
* |
1904 |
* @param blocker the blocker |
1905 |
* @throws InterruptedException if blocker.block did so |
1906 |
*/ |
1907 |
public static void managedBlock(ManagedBlocker blocker) |
1908 |
throws InterruptedException { |
1909 |
Thread t = Thread.currentThread(); |
1910 |
if (t instanceof ForkJoinWorkerThread) { |
1911 |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
1912 |
w.pool.awaitBlocker(blocker); |
1913 |
} |
1914 |
else { |
1915 |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1916 |
} |
1917 |
} |
1918 |
|
1919 |
// AbstractExecutorService overrides. These rely on undocumented |
1920 |
// fact that ForkJoinTask.adapt returns ForkJoinTasks that also |
1921 |
// implement RunnableFuture. |
1922 |
|
1923 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
1924 |
return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value); |
1925 |
} |
1926 |
|
1927 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
1928 |
return (RunnableFuture<T>) ForkJoinTask.adapt(callable); |
1929 |
} |
1930 |
|
1931 |
// Unsafe mechanics |
1932 |
|
1933 |
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1934 |
private static final long workerCountsOffset = |
1935 |
objectFieldOffset("workerCounts", ForkJoinPool.class); |
1936 |
private static final long runStateOffset = |
1937 |
objectFieldOffset("runState", ForkJoinPool.class); |
1938 |
private static final long eventCountOffset = |
1939 |
objectFieldOffset("eventCount", ForkJoinPool.class); |
1940 |
private static final long eventWaitersOffset = |
1941 |
objectFieldOffset("eventWaiters",ForkJoinPool.class); |
1942 |
private static final long stealCountOffset = |
1943 |
objectFieldOffset("stealCount",ForkJoinPool.class); |
1944 |
private static final long spareWaitersOffset = |
1945 |
objectFieldOffset("spareWaiters",ForkJoinPool.class); |
1946 |
|
1947 |
private static long objectFieldOffset(String field, Class<?> klazz) { |
1948 |
try { |
1949 |
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
1950 |
} catch (NoSuchFieldException e) { |
1951 |
// Convert Exception to corresponding Error |
1952 |
NoSuchFieldError error = new NoSuchFieldError(field); |
1953 |
error.initCause(e); |
1954 |
throw error; |
1955 |
} |
1956 |
} |
1957 |
|
1958 |
/** |
1959 |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
1960 |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
1961 |
* into a jdk. |
1962 |
* |
1963 |
* @return a sun.misc.Unsafe |
1964 |
*/ |
1965 |
private static sun.misc.Unsafe getUnsafe() { |
1966 |
try { |
1967 |
return sun.misc.Unsafe.getUnsafe(); |
1968 |
} catch (SecurityException se) { |
1969 |
try { |
1970 |
return java.security.AccessController.doPrivileged |
1971 |
(new java.security |
1972 |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1973 |
public sun.misc.Unsafe run() throws Exception { |
1974 |
java.lang.reflect.Field f = sun.misc |
1975 |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1976 |
f.setAccessible(true); |
1977 |
return (sun.misc.Unsafe) f.get(null); |
1978 |
}}); |
1979 |
} catch (java.security.PrivilegedActionException e) { |
1980 |
throw new RuntimeException("Could not initialize intrinsics", |
1981 |
e.getCause()); |
1982 |
} |
1983 |
} |
1984 |
} |
1985 |
} |