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package jsr166y; |
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import java.util.concurrent.*; |
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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.Condition; |
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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.atomic.AtomicLong; |
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import java.util.concurrent.CountDownLatch; |
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. |
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* A ForkJoinPool provides the entry point for submissions from |
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* non-ForkJoinTasks, as well as management and monitoring operations. |
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* Normally a single ForkJoinPool is used for a large number of |
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* submitted tasks. Otherwise, use would not usually outweigh the |
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* construction and bookkeeping overhead of creating a large set of |
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* threads. |
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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>ForkJoinPools differ from other kinds of Executors mainly in |
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* that they provide <em>work-stealing</em>: all threads in the pool |
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* attempt to find and execute subtasks created by other active tasks |
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* (eventually blocking if none exist). This makes them efficient when |
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* most tasks spawn other subtasks (as do most ForkJoinTasks), as well |
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* as the mixed execution of some plain Runnable- or Callable- based |
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* activities along with ForkJoinTasks. When setting {@linkplain |
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* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate |
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* for use with fine-grained tasks that are never joined. Otherwise, |
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* other ExecutorService implementations are typically more |
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* appropriate choices. |
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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 ForkJoinPool may be constructed with a given parallelism level |
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* (target pool size), which it attempts to maintain by dynamically |
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* adding, suspending, or resuming threads, even if some tasks are |
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* waiting to join others. However, no such adjustments are performed |
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* in the face of blocked IO or other unmanaged synchronization. The |
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* nested {@link ManagedBlocker} interface enables extension of |
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* the kinds of synchronization accommodated. The target parallelism |
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* level may also be changed dynamically ({@link #setParallelism}) |
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* and thread construction can be limited using methods |
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* {@link #setMaximumPoolSize} and/or |
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* {@link #setMaintainsParallelism}. |
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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 #toString} returns indications of pool state in a |
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* convenient form for informal monitoring. |
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* |
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* <p> As is the case with other ExecutorServices, there are three |
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* main task execution methods summarized in the following |
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* table. These are designed to be used by clients not already engaged |
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* in fork/join computations in the current pool. The main forms of |
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* these methods accept instances of {@code ForkJoinTask}, but |
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* overloaded forms also allow mixed execution of plain {@code |
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* Runnable}- or {@code Callable}- based activities as well. However, |
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* tasks that are already executing in a pool should normally |
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* <em>NOT</em> use these pool execution methods, but instead use the |
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* within-computation forms listed in the table. |
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* |
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* <table BORDER CELLPADDING=3 CELLSPACING=1> |
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* <tr> |
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* <td></td> |
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* <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td> |
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* <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td> |
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* </tr> |
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* <tr> |
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* <td> <b>Arrange async execution</td> |
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* <td> {@link #execute(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork}</td> |
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* </tr> |
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* <tr> |
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* <td> <b>Await and obtain result</td> |
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* <td> {@link #invoke(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#invoke}</td> |
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* </tr> |
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* <tr> |
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* <td> <b>Arrange exec and obtain Future</td> |
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* <td> {@link #submit(ForkJoinTask)}</td> |
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* <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td> |
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* </tr> |
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* </table> |
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* |
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* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is |
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* used for all parallel task execution in a program or subsystem. |
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* Otherwise, use would not usually outweigh the construction and |
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* bookkeeping overhead of creating a large set of threads. For |
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* example, a common pool could be used for the {@code SortTasks} |
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* illustrated in {@link RecursiveAction}. Because {@code |
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* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon |
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* daemon} mode, there is typically no need to explicitly {@link |
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* #shutdown} such a pool upon program exit. |
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* |
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* <pre> |
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* static final ForkJoinPool mainPool = new ForkJoinPool(); |
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* ... |
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* public void sort(long[] array) { |
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* mainPool.invoke(new SortTask(array, 0, array.length)); |
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* } |
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* </pre> |
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* |
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* <p><b>Implementation notes</b>: This implementation restricts the |
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* maximum number of running threads to 32767. Attempts to create |
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* pools with greater than the maximum result in |
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* IllegalArgumentExceptions. |
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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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public class ForkJoinPool extends AbstractExecutorService { |
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/* |
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* See the extended comments interspersed below for design, |
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* rationale, and walkthroughs. |
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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. Because 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 |
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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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* It is impossible to keep exactly the target (parallelism) |
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* number of threads running at any given time. Determining |
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* existence of conservatively safe helping targets, the |
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* availability of already-created spares, and the apparent need |
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* to create new spares are all racy and require heuristic |
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* guidance, so we rely on multiple retries of each. Compensation |
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* occurs in slow-motion. It is triggered only upon timeouts of |
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* Object.wait used for joins. This reduces poor decisions that |
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* would otherwise be made when threads are waiting for others |
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* that are stalled because of unrelated activities such as |
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* garbage collection. |
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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 artificially 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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* correspondence 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 at most two others. The |
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* net effect is a tree-like diffusion of signals, where released |
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* threads (and possibly others) help with unparks. To further |
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* reduce contention effects a bit, failed CASes to increment |
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* field 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 notices |
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* (usually upon timeout of a wait()) that there are too few |
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* running threads, we may create a new thread to maintain |
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* parallelism level, or at least avoid starvation. Usually, extra |
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* threads are needed for only very short periods, yet join |
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* dependencies are such that we sometimes need them in |
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* bursts. Rather than create new threads each time this happens, |
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* we suspend no-longer-needed extra ones as "spares". For most |
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* purposes, we don't distinguish "extra" spare threads from |
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* normal "core" threads: On each call to preStep (the only point |
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* at which we can do this) a worker checks to see if there are |
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* now too many running workers, and if so, suspends itself. |
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* Method helpMaintainParallelism looks for suspended threads to |
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* resume before considering creating a new replacement. The |
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* spares themselves are encoded on another variant of a Treiber |
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* Stack, headed at field "spareWaiters". Note that the use of |
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* spares is intrinsically racy. One thread may become a spare at |
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* about the same time as another is needlessly being created. We |
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* counteract this and related slop in part by requiring resumed |
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* spares to immediately recheck (in preStep) to see whether they |
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* should re-suspend. |
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* |
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* 6. Killing off unneeded workers. A timeout mechanism is used to |
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* shed unused workers: The oldest (first) event queue waiter uses |
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* a timed rather than hard wait. When this wait times out without |
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* a normal wakeup, it tries to shutdown any one (for convenience |
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* the newest) other spare or event waiter via |
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* tryShutdownUnusedWorker. This eventually reduces the number of |
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* worker threads to a minimum of one after a long enough period |
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* 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 impossible |
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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 |
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* presence of transient 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 parallelism to |
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* lapse for a while during joins, and use a timeout to see if, |
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* after the resulting settling, there is still a need for |
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* additional workers. This also better copes with the fact that |
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* some of the methods in this class tend to never become compiled |
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* (but are interpreted), so some components of the entire set of |
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* controls might execute 100 times faster than others. And |
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* similarly for cases where the apparent lack of work is just due |
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* to GC stalls and other 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 |
337 |
> |
* ForkJoinTask. For example, direct access to "workers" array by |
338 |
> |
* workers, and direct access to ForkJoinTask.status by both |
339 |
> |
* ForkJoinPool and ForkJoinWorkerThread. There is little point |
340 |
> |
* trying to reduce this, since any associated future changes in |
341 |
> |
* representations will need to be accompanied by algorithmic |
342 |
> |
* changes anyway. |
343 |
> |
* |
344 |
> |
* Style notes: There are lots of inline assignments (of form |
345 |
> |
* "while ((local = field) != 0)") which are usually the simplest |
346 |
> |
* way to ensure the required read orderings (which are sometimes |
347 |
> |
* critical). Also several occurrences of the unusual "do {} |
348 |
> |
* while (!cas...)" which is the simplest way to force an update of |
349 |
> |
* a CAS'ed variable. There are also other coding oddities that |
350 |
> |
* help some methods perform reasonably even when interpreted (not |
351 |
> |
* compiled), at the expense of some messy constructions that |
352 |
> |
* reduce byte code counts. |
353 |
> |
* |
354 |
> |
* The order of declarations in this file is: (1) statics (2) |
355 |
> |
* fields (along with constants used when unpacking some of them) |
356 |
> |
* (3) internal control methods (4) callbacks and other support |
357 |
> |
* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported |
358 |
> |
* methods (plus a few little helpers). |
359 |
|
*/ |
360 |
|
|
77 |
– |
/** Mask for packing and unpacking shorts */ |
78 |
– |
private static final int shortMask = 0xffff; |
79 |
– |
|
80 |
– |
/** Max pool size -- must be a power of two minus 1 */ |
81 |
– |
private static final int MAX_THREADS = 0x7FFF; |
82 |
– |
|
361 |
|
/** |
362 |
|
* Factory for creating new {@link ForkJoinWorkerThread}s. |
363 |
|
* A {@code ForkJoinWorkerThreadFactory} must be defined and used |
369 |
|
* Returns a new worker thread operating in the given pool. |
370 |
|
* |
371 |
|
* @param pool the pool this thread works in |
372 |
< |
* @throws NullPointerException if pool is null |
372 |
> |
* @throws NullPointerException if the pool is null |
373 |
|
*/ |
374 |
|
public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
375 |
|
} |
378 |
|
* Default ForkJoinWorkerThreadFactory implementation; creates a |
379 |
|
* new ForkJoinWorkerThread. |
380 |
|
*/ |
381 |
< |
static class DefaultForkJoinWorkerThreadFactory |
381 |
> |
static class DefaultForkJoinWorkerThreadFactory |
382 |
|
implements ForkJoinWorkerThreadFactory { |
383 |
|
public ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
384 |
< |
try { |
107 |
< |
return new ForkJoinWorkerThread(pool); |
108 |
< |
} catch (OutOfMemoryError oom) { |
109 |
< |
return null; |
110 |
< |
} |
384 |
> |
return new ForkJoinWorkerThread(pool); |
385 |
|
} |
386 |
|
} |
387 |
|
|
417 |
|
new AtomicInteger(); |
418 |
|
|
419 |
|
/** |
420 |
< |
* Array holding all worker threads in the pool. Initialized upon |
421 |
< |
* first use. Array size must be a power of two. Updates and |
422 |
< |
* replacements are protected by workerLock, but it is always kept |
423 |
< |
* in a consistent enough state to be randomly accessed without |
424 |
< |
* locking by workers performing work-stealing. |
420 |
> |
* The time to block in a join (see awaitJoin) before checking if |
421 |
> |
* a new worker should be (re)started to maintain parallelism |
422 |
> |
* level. The value should be short enough to maintain global |
423 |
> |
* responsiveness and progress but long enough to avoid |
424 |
> |
* counterproductive firings during GC stalls or unrelated system |
425 |
> |
* activity, and to not bog down systems with continual re-firings |
426 |
> |
* on GCs or legitimately long waits. |
427 |
|
*/ |
428 |
< |
volatile ForkJoinWorkerThread[] workers; |
428 |
> |
private static final long JOIN_TIMEOUT_MILLIS = 250L; // 4 per second |
429 |
|
|
430 |
|
/** |
431 |
< |
* Lock protecting access to workers. |
431 |
> |
* The wakeup interval (in nanoseconds) for the oldest worker |
432 |
> |
* waiting for an event invokes tryShutdownUnusedWorker to shrink |
433 |
> |
* the number of workers. The exact value does not matter too |
434 |
> |
* much, but should be long enough to slowly release resources |
435 |
> |
* during long periods without use without disrupting normal use. |
436 |
|
*/ |
437 |
< |
private final ReentrantLock workerLock; |
437 |
> |
private static final long SHRINK_RATE_NANOS = |
438 |
> |
30L * 1000L * 1000L * 1000L; // 2 per minute |
439 |
|
|
440 |
|
/** |
441 |
< |
* Condition for awaitTermination. |
441 |
> |
* Absolute bound for parallelism level. Twice this number plus |
442 |
> |
* one (i.e., 0xfff) must fit into a 16bit field to enable |
443 |
> |
* word-packing for some counts and indices. |
444 |
|
*/ |
445 |
< |
private final Condition termination; |
445 |
> |
private static final int MAX_WORKERS = 0x7fff; |
446 |
|
|
447 |
|
/** |
448 |
< |
* The uncaught exception handler used when any worker |
449 |
< |
* abruptly terminates |
448 |
> |
* Array holding all worker threads in the pool. Array size must |
449 |
> |
* be a power of two. Updates and replacements are protected by |
450 |
> |
* workerLock, but the array is always kept in a consistent enough |
451 |
> |
* state to be randomly accessed without locking by workers |
452 |
> |
* performing work-stealing, as well as other traversal-based |
453 |
> |
* methods in this class. All readers must tolerate that some |
454 |
> |
* array slots may be null. |
455 |
|
*/ |
456 |
< |
private Thread.UncaughtExceptionHandler ueh; |
456 |
> |
volatile ForkJoinWorkerThread[] workers; |
457 |
|
|
458 |
|
/** |
459 |
< |
* Creation factory for worker threads. |
459 |
> |
* Queue for external submissions. |
460 |
|
*/ |
461 |
< |
private final ForkJoinWorkerThreadFactory factory; |
461 |
> |
private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
462 |
|
|
463 |
|
/** |
464 |
< |
* Head of stack of threads that were created to maintain |
177 |
< |
* parallelism when other threads blocked, but have since |
178 |
< |
* suspended when the parallelism level rose. |
464 |
> |
* Lock protecting updates to workers array. |
465 |
|
*/ |
466 |
< |
private volatile WaitQueueNode spareStack; |
466 |
> |
private final ReentrantLock workerLock; |
467 |
|
|
468 |
|
/** |
469 |
< |
* Sum of per-thread steal counts, updated only when threads are |
184 |
< |
* idle or terminating. |
469 |
> |
* Latch released upon termination. |
470 |
|
*/ |
471 |
< |
private final AtomicLong stealCount; |
471 |
> |
private final Phaser termination; |
472 |
|
|
473 |
|
/** |
474 |
< |
* Queue for external submissions. |
474 |
> |
* Creation factory for worker threads. |
475 |
|
*/ |
476 |
< |
private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
476 |
> |
private final ForkJoinWorkerThreadFactory factory; |
477 |
|
|
478 |
|
/** |
479 |
< |
* Head of Treiber stack for barrier sync. See below for explanation. |
479 |
> |
* Sum of per-thread steal counts, updated only when threads are |
480 |
> |
* idle or terminating. |
481 |
|
*/ |
482 |
< |
private volatile WaitQueueNode syncStack; |
482 |
> |
private volatile long stealCount; |
483 |
|
|
484 |
|
/** |
485 |
< |
* The count for event barrier |
485 |
> |
* Encoded record of top of Treiber stack of threads waiting for |
486 |
> |
* events. The top 32 bits contain the count being waited for. The |
487 |
> |
* bottom 16 bits contains one plus the pool index of waiting |
488 |
> |
* worker thread. (Bits 16-31 are unused.) |
489 |
|
*/ |
490 |
< |
private volatile long eventCount; |
490 |
> |
private volatile long eventWaiters; |
491 |
|
|
492 |
< |
/** |
493 |
< |
* Pool number, just for assigning useful names to worker threads |
205 |
< |
*/ |
206 |
< |
private final int poolNumber; |
492 |
> |
private static final int EVENT_COUNT_SHIFT = 32; |
493 |
> |
private static final long WAITER_ID_MASK = (1L << 16) - 1L; |
494 |
|
|
495 |
|
/** |
496 |
< |
* The maximum allowed pool size |
496 |
> |
* A counter for events that may wake up worker threads: |
497 |
> |
* - Submission of a new task to the pool |
498 |
> |
* - A worker pushing a task on an empty queue |
499 |
> |
* - termination |
500 |
|
*/ |
501 |
< |
private volatile int maxPoolSize; |
501 |
> |
private volatile int eventCount; |
502 |
|
|
503 |
|
/** |
504 |
< |
* The desired parallelism level, updated only under workerLock. |
504 |
> |
* Encoded record of top of Treiber stack of spare threads waiting |
505 |
> |
* for resumption. The top 16 bits contain an arbitrary count to |
506 |
> |
* avoid ABA effects. The bottom 16bits contains one plus the pool |
507 |
> |
* index of waiting worker thread. |
508 |
|
*/ |
509 |
< |
private volatile int parallelism; |
509 |
> |
private volatile int spareWaiters; |
510 |
> |
|
511 |
> |
private static final int SPARE_COUNT_SHIFT = 16; |
512 |
> |
private static final int SPARE_ID_MASK = (1 << 16) - 1; |
513 |
|
|
514 |
|
/** |
515 |
< |
* True if use local fifo, not default lifo, for local polling |
515 |
> |
* Lifecycle control. The low word contains the number of workers |
516 |
> |
* that are (probably) executing tasks. This value is atomically |
517 |
> |
* incremented before a worker gets a task to run, and decremented |
518 |
> |
* when worker has no tasks and cannot find any. Bits 16-18 |
519 |
> |
* contain runLevel value. When all are zero, the pool is |
520 |
> |
* running. Level transitions are monotonic (running -> shutdown |
521 |
> |
* -> terminating -> terminated) so each transition adds a bit. |
522 |
> |
* These are bundled together to ensure consistent read for |
523 |
> |
* termination checks (i.e., that runLevel is at least SHUTDOWN |
524 |
> |
* and active threads is zero). |
525 |
> |
* |
526 |
> |
* Notes: Most direct CASes are dependent on these bitfield |
527 |
> |
* positions. Also, this field is non-private to enable direct |
528 |
> |
* performance-sensitive CASes in ForkJoinWorkerThread. |
529 |
|
*/ |
530 |
< |
private volatile boolean locallyFifo; |
530 |
> |
volatile int runState; |
531 |
> |
|
532 |
> |
// Note: The order among run level values matters. |
533 |
> |
private static final int RUNLEVEL_SHIFT = 16; |
534 |
> |
private static final int SHUTDOWN = 1 << RUNLEVEL_SHIFT; |
535 |
> |
private static final int TERMINATING = 1 << (RUNLEVEL_SHIFT + 1); |
536 |
> |
private static final int TERMINATED = 1 << (RUNLEVEL_SHIFT + 2); |
537 |
> |
private static final int ACTIVE_COUNT_MASK = (1 << RUNLEVEL_SHIFT) - 1; |
538 |
|
|
539 |
|
/** |
540 |
|
* Holds number of total (i.e., created and not yet terminated) |
541 |
|
* and running (i.e., not blocked on joins or other managed sync) |
542 |
< |
* threads, packed into one int to ensure consistent snapshot when |
542 |
> |
* threads, packed together to ensure consistent snapshot when |
543 |
|
* making decisions about creating and suspending spare |
544 |
< |
* threads. Updated only by CAS. Note: CASes in |
545 |
< |
* updateRunningCount and preJoin assume that running active count |
546 |
< |
* is in low word, so need to be modified if this changes. |
544 |
> |
* threads. Updated only by CAS. Note that adding a new worker |
545 |
> |
* requires incrementing both counts, since workers start off in |
546 |
> |
* running state. |
547 |
|
*/ |
548 |
|
private volatile int workerCounts; |
549 |
|
|
550 |
< |
private static int totalCountOf(int s) { return s >>> 16; } |
551 |
< |
private static int runningCountOf(int s) { return s & shortMask; } |
552 |
< |
private static int workerCountsFor(int t, int r) { return (t << 16) + r; } |
550 |
> |
private static final int TOTAL_COUNT_SHIFT = 16; |
551 |
> |
private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1; |
552 |
> |
private static final int ONE_RUNNING = 1; |
553 |
> |
private static final int ONE_TOTAL = 1 << TOTAL_COUNT_SHIFT; |
554 |
|
|
555 |
|
/** |
556 |
< |
* Adds delta (which may be negative) to running count. This must |
557 |
< |
* be called before (with negative arg) and after (with positive) |
241 |
< |
* any managed synchronization (i.e., mainly, joins). |
242 |
< |
* |
243 |
< |
* @param delta the number to add |
556 |
> |
* The target parallelism level. |
557 |
> |
* Accessed directly by ForkJoinWorkerThreads. |
558 |
|
*/ |
559 |
< |
final void updateRunningCount(int delta) { |
246 |
< |
int s; |
247 |
< |
do {} while (!casWorkerCounts(s = workerCounts, s + delta)); |
248 |
< |
} |
559 |
> |
final int parallelism; |
560 |
|
|
561 |
|
/** |
562 |
< |
* Adds delta (which may be negative) to both total and running |
563 |
< |
* count. This must be called upon creation and termination of |
253 |
< |
* worker threads. |
254 |
< |
* |
255 |
< |
* @param delta the number to add |
562 |
> |
* True if use local fifo, not default lifo, for local polling |
563 |
> |
* Read by, and replicated by ForkJoinWorkerThreads |
564 |
|
*/ |
565 |
< |
private void updateWorkerCount(int delta) { |
258 |
< |
int d = delta + (delta << 16); // add to both lo and hi parts |
259 |
< |
int s; |
260 |
< |
do {} while (!casWorkerCounts(s = workerCounts, s + d)); |
261 |
< |
} |
565 |
> |
final boolean locallyFifo; |
566 |
|
|
567 |
|
/** |
568 |
< |
* Lifecycle control. High word contains runState, low word |
569 |
< |
* contains the number of workers that are (probably) executing |
266 |
< |
* tasks. This value is atomically incremented before a worker |
267 |
< |
* gets a task to run, and decremented when worker has no tasks |
268 |
< |
* and cannot find any. These two fields are bundled together to |
269 |
< |
* support correct termination triggering. Note: activeCount |
270 |
< |
* CAS'es cheat by assuming active count is in low word, so need |
271 |
< |
* to be modified if this changes |
568 |
> |
* The uncaught exception handler used when any worker abruptly |
569 |
> |
* terminates. |
570 |
|
*/ |
571 |
< |
private volatile int runControl; |
571 |
> |
private final Thread.UncaughtExceptionHandler ueh; |
572 |
|
|
573 |
< |
// RunState values. Order among values matters |
574 |
< |
private static final int RUNNING = 0; |
575 |
< |
private static final int SHUTDOWN = 1; |
576 |
< |
private static final int TERMINATING = 2; |
279 |
< |
private static final int TERMINATED = 3; |
573 |
> |
/** |
574 |
> |
* Pool number, just for assigning useful names to worker threads |
575 |
> |
*/ |
576 |
> |
private final int poolNumber; |
577 |
|
|
578 |
< |
private static int runStateOf(int c) { return c >>> 16; } |
579 |
< |
private static int activeCountOf(int c) { return c & shortMask; } |
283 |
< |
private static int runControlFor(int r, int a) { return (r << 16) + a; } |
578 |
> |
// Utilities for CASing fields. Note that most of these |
579 |
> |
// are usually manually inlined by callers |
580 |
|
|
581 |
|
/** |
582 |
< |
* Tries incrementing active count; fails on contention. |
287 |
< |
* Called by workers before/during executing tasks. |
288 |
< |
* |
289 |
< |
* @return true on success |
582 |
> |
* Increments running count part of workerCounts |
583 |
|
*/ |
584 |
< |
final boolean tryIncrementActiveCount() { |
585 |
< |
int c = runControl; |
586 |
< |
return casRunControl(c, c+1); |
584 |
> |
final void incrementRunningCount() { |
585 |
> |
int c; |
586 |
> |
do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
587 |
> |
c = workerCounts, |
588 |
> |
c + ONE_RUNNING)); |
589 |
|
} |
590 |
|
|
591 |
|
/** |
592 |
< |
* Tries decrementing active count; fails on contention. |
298 |
< |
* Possibly triggers termination on success. |
299 |
< |
* Called by workers when they can't find tasks. |
300 |
< |
* |
301 |
< |
* @return true on success |
592 |
> |
* Tries to decrement running count unless already zero |
593 |
|
*/ |
594 |
< |
final boolean tryDecrementActiveCount() { |
595 |
< |
int c = runControl; |
596 |
< |
int nextc = c - 1; |
306 |
< |
if (!casRunControl(c, nextc)) |
594 |
> |
final boolean tryDecrementRunningCount() { |
595 |
> |
int wc = workerCounts; |
596 |
> |
if ((wc & RUNNING_COUNT_MASK) == 0) |
597 |
|
return false; |
598 |
< |
if (canTerminateOnShutdown(nextc)) |
599 |
< |
terminateOnShutdown(); |
310 |
< |
return true; |
598 |
> |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
599 |
> |
wc, wc - ONE_RUNNING); |
600 |
|
} |
601 |
|
|
602 |
|
/** |
603 |
< |
* Returns {@code true} if argument represents zero active count |
604 |
< |
* and nonzero runstate, which is the triggering condition for |
605 |
< |
* terminating on shutdown. |
603 |
> |
* Forces decrement of encoded workerCounts, awaiting nonzero if |
604 |
> |
* (rarely) necessary when other count updates lag. |
605 |
> |
* |
606 |
> |
* @param dr -- either zero or ONE_RUNNING |
607 |
> |
* @param dt == either zero or ONE_TOTAL |
608 |
|
*/ |
609 |
< |
private static boolean canTerminateOnShutdown(int c) { |
610 |
< |
// i.e. least bit is nonzero runState bit |
611 |
< |
return ((c & -c) >>> 16) != 0; |
609 |
> |
private void decrementWorkerCounts(int dr, int dt) { |
610 |
> |
for (;;) { |
611 |
> |
int wc = workerCounts; |
612 |
> |
if ((wc & RUNNING_COUNT_MASK) - dr < 0 || |
613 |
> |
(wc >>> TOTAL_COUNT_SHIFT) - dt < 0) { |
614 |
> |
if ((runState & TERMINATED) != 0) |
615 |
> |
return; // lagging termination on a backout |
616 |
> |
Thread.yield(); |
617 |
> |
} |
618 |
> |
if (UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
619 |
> |
wc, wc - (dr + dt))) |
620 |
> |
return; |
621 |
> |
} |
622 |
> |
} |
623 |
> |
|
624 |
> |
/** |
625 |
> |
* Tries decrementing active count; fails on contention. |
626 |
> |
* Called when workers cannot find tasks to run. |
627 |
> |
*/ |
628 |
> |
final boolean tryDecrementActiveCount() { |
629 |
> |
int c; |
630 |
> |
return UNSAFE.compareAndSwapInt(this, runStateOffset, |
631 |
> |
c = runState, c - 1); |
632 |
|
} |
633 |
|
|
634 |
|
/** |
635 |
< |
* Transition run state to at least the given state. Return true |
636 |
< |
* if not already at least given state. |
635 |
> |
* Advances to at least the given level. Returns true if not |
636 |
> |
* already in at least the given level. |
637 |
|
*/ |
638 |
< |
private boolean transitionRunStateTo(int state) { |
638 |
> |
private boolean advanceRunLevel(int level) { |
639 |
|
for (;;) { |
640 |
< |
int c = runControl; |
641 |
< |
if (runStateOf(c) >= state) |
640 |
> |
int s = runState; |
641 |
> |
if ((s & level) != 0) |
642 |
|
return false; |
643 |
< |
if (casRunControl(c, runControlFor(state, activeCountOf(c)))) |
643 |
> |
if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level)) |
644 |
|
return true; |
645 |
|
} |
646 |
|
} |
647 |
|
|
648 |
+ |
// workers array maintenance |
649 |
+ |
|
650 |
|
/** |
651 |
< |
* Controls whether to add spares to maintain parallelism |
651 |
> |
* Records and returns a workers array index for new worker. |
652 |
|
*/ |
653 |
< |
private volatile boolean maintainsParallelism; |
653 |
> |
private int recordWorker(ForkJoinWorkerThread w) { |
654 |
> |
// Try using slot totalCount-1. If not available, scan and/or resize |
655 |
> |
int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1; |
656 |
> |
final ReentrantLock lock = this.workerLock; |
657 |
> |
lock.lock(); |
658 |
> |
try { |
659 |
> |
ForkJoinWorkerThread[] ws = workers; |
660 |
> |
int n = ws.length; |
661 |
> |
if (k < 0 || k >= n || ws[k] != null) { |
662 |
> |
for (k = 0; k < n && ws[k] != null; ++k) |
663 |
> |
; |
664 |
> |
if (k == n) |
665 |
> |
ws = Arrays.copyOf(ws, n << 1); |
666 |
> |
} |
667 |
> |
ws[k] = w; |
668 |
> |
workers = ws; // volatile array write ensures slot visibility |
669 |
> |
} finally { |
670 |
> |
lock.unlock(); |
671 |
> |
} |
672 |
> |
return k; |
673 |
> |
} |
674 |
|
|
675 |
< |
// Constructors |
675 |
> |
/** |
676 |
> |
* Nulls out record of worker in workers array. |
677 |
> |
*/ |
678 |
> |
private void forgetWorker(ForkJoinWorkerThread w) { |
679 |
> |
int idx = w.poolIndex; |
680 |
> |
// Locking helps method recordWorker avoid unnecessary expansion |
681 |
> |
final ReentrantLock lock = this.workerLock; |
682 |
> |
lock.lock(); |
683 |
> |
try { |
684 |
> |
ForkJoinWorkerThread[] ws = workers; |
685 |
> |
if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify |
686 |
> |
ws[idx] = null; |
687 |
> |
} finally { |
688 |
> |
lock.unlock(); |
689 |
> |
} |
690 |
> |
} |
691 |
|
|
692 |
|
/** |
693 |
< |
* Creates a ForkJoinPool with a pool size equal to the number of |
694 |
< |
* processors available on the system, using the default |
695 |
< |
* ForkJoinWorkerThreadFactory. |
693 |
> |
* Final callback from terminating worker. Removes record of |
694 |
> |
* worker from array, and adjusts counts. If pool is shutting |
695 |
> |
* down, tries to complete termination. |
696 |
|
* |
697 |
< |
* @throws SecurityException if a security manager exists and |
350 |
< |
* the caller is not permitted to modify threads |
351 |
< |
* because it does not hold {@link |
352 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
697 |
> |
* @param w the worker |
698 |
|
*/ |
699 |
< |
public ForkJoinPool() { |
700 |
< |
this(Runtime.getRuntime().availableProcessors(), |
701 |
< |
defaultForkJoinWorkerThreadFactory); |
699 |
> |
final void workerTerminated(ForkJoinWorkerThread w) { |
700 |
> |
forgetWorker(w); |
701 |
> |
decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL); |
702 |
> |
while (w.stealCount != 0) // collect final count |
703 |
> |
tryAccumulateStealCount(w); |
704 |
> |
tryTerminate(false); |
705 |
|
} |
706 |
|
|
707 |
+ |
// Waiting for and signalling events |
708 |
+ |
|
709 |
|
/** |
710 |
< |
* Creates a ForkJoinPool with the indicated parallelism level |
711 |
< |
* threads and using the default ForkJoinWorkerThreadFactory. |
712 |
< |
* |
713 |
< |
* @param parallelism the number of worker threads |
364 |
< |
* @throws IllegalArgumentException if parallelism less than or |
365 |
< |
* equal to zero |
366 |
< |
* @throws SecurityException if a security manager exists and |
367 |
< |
* the caller is not permitted to modify threads |
368 |
< |
* because it does not hold {@link |
369 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
710 |
> |
* Releases workers blocked on a count not equal to current count. |
711 |
> |
* Normally called after precheck that eventWaiters isn't zero to |
712 |
> |
* avoid wasted array checks. Gives up upon a change in count or |
713 |
> |
* upon releasing two workers, letting others take over. |
714 |
|
*/ |
715 |
< |
public ForkJoinPool(int parallelism) { |
716 |
< |
this(parallelism, defaultForkJoinWorkerThreadFactory); |
715 |
> |
private void releaseEventWaiters() { |
716 |
> |
ForkJoinWorkerThread[] ws = workers; |
717 |
> |
int n = ws.length; |
718 |
> |
long h = eventWaiters; |
719 |
> |
int ec = eventCount; |
720 |
> |
boolean releasedOne = false; |
721 |
> |
ForkJoinWorkerThread w; int id; |
722 |
> |
while ((id = ((int)(h & WAITER_ID_MASK)) - 1) >= 0 && |
723 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) != ec && |
724 |
> |
id < n && (w = ws[id]) != null) { |
725 |
> |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
726 |
> |
h, w.nextWaiter)) { |
727 |
> |
LockSupport.unpark(w); |
728 |
> |
if (releasedOne) // exit on second release |
729 |
> |
break; |
730 |
> |
releasedOne = true; |
731 |
> |
} |
732 |
> |
if (eventCount != ec) |
733 |
> |
break; |
734 |
> |
h = eventWaiters; |
735 |
> |
} |
736 |
|
} |
737 |
|
|
738 |
|
/** |
739 |
< |
* Creates a ForkJoinPool with parallelism equal to the number of |
740 |
< |
* processors available on the system and using the given |
378 |
< |
* ForkJoinWorkerThreadFactory. |
379 |
< |
* |
380 |
< |
* @param factory the factory for creating new threads |
381 |
< |
* @throws NullPointerException if factory is null |
382 |
< |
* @throws SecurityException if a security manager exists and |
383 |
< |
* the caller is not permitted to modify threads |
384 |
< |
* because it does not hold {@link |
385 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
739 |
> |
* Tries to advance eventCount and releases waiters. Called only |
740 |
> |
* from workers. |
741 |
|
*/ |
742 |
< |
public ForkJoinPool(ForkJoinWorkerThreadFactory factory) { |
743 |
< |
this(Runtime.getRuntime().availableProcessors(), factory); |
742 |
> |
final void signalWork() { |
743 |
> |
int c; // try to increment event count -- CAS failure OK |
744 |
> |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1); |
745 |
> |
if (eventWaiters != 0L) |
746 |
> |
releaseEventWaiters(); |
747 |
|
} |
748 |
|
|
749 |
|
/** |
750 |
< |
* Creates a ForkJoinPool with the given parallelism and factory. |
750 |
> |
* Adds the given worker to event queue and blocks until |
751 |
> |
* terminating or event count advances from the given value |
752 |
|
* |
753 |
< |
* @param parallelism the targeted number of worker threads |
754 |
< |
* @param factory the factory for creating new threads |
396 |
< |
* @throws IllegalArgumentException if parallelism less than or |
397 |
< |
* equal to zero, or greater than implementation limit |
398 |
< |
* @throws NullPointerException if factory is null |
399 |
< |
* @throws SecurityException if a security manager exists and |
400 |
< |
* the caller is not permitted to modify threads |
401 |
< |
* because it does not hold {@link |
402 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
753 |
> |
* @param w the calling worker thread |
754 |
> |
* @param ec the count |
755 |
|
*/ |
756 |
< |
public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) { |
757 |
< |
if (parallelism <= 0 || parallelism > MAX_THREADS) |
758 |
< |
throw new IllegalArgumentException(); |
759 |
< |
if (factory == null) |
760 |
< |
throw new NullPointerException(); |
761 |
< |
checkPermission(); |
762 |
< |
this.factory = factory; |
763 |
< |
this.parallelism = parallelism; |
764 |
< |
this.maxPoolSize = MAX_THREADS; |
765 |
< |
this.maintainsParallelism = true; |
766 |
< |
this.poolNumber = poolNumberGenerator.incrementAndGet(); |
767 |
< |
this.workerLock = new ReentrantLock(); |
768 |
< |
this.termination = workerLock.newCondition(); |
417 |
< |
this.stealCount = new AtomicLong(); |
418 |
< |
this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
419 |
< |
// worker array and workers are lazily constructed |
756 |
> |
private void eventSync(ForkJoinWorkerThread w, int ec) { |
757 |
> |
long nh = (((long)ec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1)); |
758 |
> |
long h; |
759 |
> |
while ((runState < SHUTDOWN || !tryTerminate(false)) && |
760 |
> |
(((int)((h = eventWaiters) & WAITER_ID_MASK)) == 0 || |
761 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) == ec) && |
762 |
> |
eventCount == ec) { |
763 |
> |
if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset, |
764 |
> |
w.nextWaiter = h, nh)) { |
765 |
> |
awaitEvent(w, ec); |
766 |
> |
break; |
767 |
> |
} |
768 |
> |
} |
769 |
|
} |
770 |
|
|
771 |
|
/** |
772 |
< |
* Creates a new worker thread using factory. |
772 |
> |
* Blocks the given worker (that has already been entered as an |
773 |
> |
* event waiter) until terminating or event count advances from |
774 |
> |
* the given value. The oldest (first) waiter uses a timed wait to |
775 |
> |
* occasionally one-by-one shrink the number of workers (to a |
776 |
> |
* minimum of one) if the pool has not been used for extended |
777 |
> |
* periods. |
778 |
|
* |
779 |
< |
* @param index the index to assign worker |
780 |
< |
* @return new worker, or null of factory failed |
779 |
> |
* @param w the calling worker thread |
780 |
> |
* @param ec the count |
781 |
|
*/ |
782 |
< |
private ForkJoinWorkerThread createWorker(int index) { |
783 |
< |
Thread.UncaughtExceptionHandler h = ueh; |
784 |
< |
ForkJoinWorkerThread w = factory.newThread(this); |
785 |
< |
if (w != null) { |
786 |
< |
w.poolIndex = index; |
787 |
< |
w.setDaemon(true); |
788 |
< |
w.setAsyncMode(locallyFifo); |
789 |
< |
w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index); |
790 |
< |
if (h != null) |
791 |
< |
w.setUncaughtExceptionHandler(h); |
782 |
> |
private void awaitEvent(ForkJoinWorkerThread w, int ec) { |
783 |
> |
while (eventCount == ec) { |
784 |
> |
if (tryAccumulateStealCount(w)) { // transfer while idle |
785 |
> |
boolean untimed = (w.nextWaiter != 0L || |
786 |
> |
(workerCounts & RUNNING_COUNT_MASK) <= 1); |
787 |
> |
long startTime = untimed? 0 : System.nanoTime(); |
788 |
> |
Thread.interrupted(); // clear/ignore interrupt |
789 |
> |
if (eventCount != ec || w.runState != 0 || |
790 |
> |
runState >= TERMINATING) // recheck after clear |
791 |
> |
break; |
792 |
> |
if (untimed) |
793 |
> |
LockSupport.park(w); |
794 |
> |
else { |
795 |
> |
LockSupport.parkNanos(w, SHRINK_RATE_NANOS); |
796 |
> |
if (eventCount != ec || w.runState != 0 || |
797 |
> |
runState >= TERMINATING) |
798 |
> |
break; |
799 |
> |
if (System.nanoTime() - startTime >= SHRINK_RATE_NANOS) |
800 |
> |
tryShutdownUnusedWorker(ec); |
801 |
> |
} |
802 |
> |
} |
803 |
|
} |
439 |
– |
return w; |
804 |
|
} |
805 |
|
|
806 |
+ |
// Maintaining parallelism |
807 |
+ |
|
808 |
|
/** |
809 |
< |
* Returns a good size for worker array given pool size. |
444 |
< |
* Currently requires size to be a power of two. |
809 |
> |
* Pushes worker onto the spare stack |
810 |
|
*/ |
811 |
< |
private static int arraySizeFor(int poolSize) { |
812 |
< |
return (poolSize <= 1) ? 1 : |
813 |
< |
(1 << (32 - Integer.numberOfLeadingZeros(poolSize-1))); |
811 |
> |
final void pushSpare(ForkJoinWorkerThread w) { |
812 |
> |
int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex + 1); |
813 |
> |
do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
814 |
> |
w.nextSpare = spareWaiters,ns)); |
815 |
|
} |
816 |
|
|
817 |
|
/** |
818 |
< |
* Creates or resizes array if necessary to hold newLength. |
819 |
< |
* Call only under exclusion. |
454 |
< |
* |
455 |
< |
* @return the array |
818 |
> |
* Tries (once) to resume a spare if the number of running |
819 |
> |
* threads is less than target. |
820 |
|
*/ |
821 |
< |
private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) { |
821 |
> |
private void tryResumeSpare() { |
822 |
> |
int sw, id; |
823 |
|
ForkJoinWorkerThread[] ws = workers; |
824 |
< |
if (ws == null) |
825 |
< |
return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)]; |
826 |
< |
else if (newLength > ws.length) |
827 |
< |
return workers = Arrays.copyOf(ws, arraySizeFor(newLength)); |
828 |
< |
else |
829 |
< |
return ws; |
824 |
> |
int n = ws.length; |
825 |
> |
ForkJoinWorkerThread w; |
826 |
> |
if ((sw = spareWaiters) != 0 && |
827 |
> |
(id = (sw & SPARE_ID_MASK) - 1) >= 0 && |
828 |
> |
id < n && (w = ws[id]) != null && |
829 |
> |
(workerCounts & RUNNING_COUNT_MASK) < parallelism && |
830 |
> |
spareWaiters == sw && |
831 |
> |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
832 |
> |
sw, w.nextSpare)) { |
833 |
> |
int c; // increment running count before resume |
834 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
835 |
> |
(this, workerCountsOffset, |
836 |
> |
c = workerCounts, c + ONE_RUNNING)); |
837 |
> |
if (w.tryUnsuspend()) |
838 |
> |
LockSupport.unpark(w); |
839 |
> |
else // back out if w was shutdown |
840 |
> |
decrementWorkerCounts(ONE_RUNNING, 0); |
841 |
> |
} |
842 |
|
} |
843 |
|
|
844 |
|
/** |
845 |
< |
* Tries to shrink workers into smaller array after one or more terminate. |
846 |
< |
*/ |
847 |
< |
private void tryShrinkWorkerArray() { |
848 |
< |
ForkJoinWorkerThread[] ws = workers; |
849 |
< |
if (ws != null) { |
850 |
< |
int len = ws.length; |
851 |
< |
int last = len - 1; |
852 |
< |
while (last >= 0 && ws[last] == null) |
853 |
< |
--last; |
854 |
< |
int newLength = arraySizeFor(last+1); |
855 |
< |
if (newLength < len) |
856 |
< |
workers = Arrays.copyOf(ws, newLength); |
845 |
> |
* Tries to increase the number of running workers if below target |
846 |
> |
* parallelism: If a spare exists tries to resume it via |
847 |
> |
* tryResumeSpare. Otherwise, if not enough total workers or all |
848 |
> |
* existing workers are busy, adds a new worker. In all cases also |
849 |
> |
* helps wake up releasable workers waiting for work. |
850 |
> |
*/ |
851 |
> |
private void helpMaintainParallelism() { |
852 |
> |
int pc = parallelism; |
853 |
> |
int wc, rs, tc; |
854 |
> |
while (((wc = workerCounts) & RUNNING_COUNT_MASK) < pc && |
855 |
> |
(rs = runState) < TERMINATING) { |
856 |
> |
if (spareWaiters != 0) |
857 |
> |
tryResumeSpare(); |
858 |
> |
else if ((tc = wc >>> TOTAL_COUNT_SHIFT) >= MAX_WORKERS || |
859 |
> |
(tc >= pc && (rs & ACTIVE_COUNT_MASK) != tc)) |
860 |
> |
break; // enough total |
861 |
> |
else if (runState == rs && workerCounts == wc && |
862 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc, |
863 |
> |
wc + (ONE_RUNNING|ONE_TOTAL))) { |
864 |
> |
ForkJoinWorkerThread w = null; |
865 |
> |
try { |
866 |
> |
w = factory.newThread(this); |
867 |
> |
} finally { // adjust on null or exceptional factory return |
868 |
> |
if (w == null) { |
869 |
> |
decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL); |
870 |
> |
tryTerminate(false); // handle failure during shutdown |
871 |
> |
} |
872 |
> |
} |
873 |
> |
if (w == null) |
874 |
> |
break; |
875 |
> |
w.start(recordWorker(w), ueh); |
876 |
> |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) >= pc) { |
877 |
> |
int c; // advance event count |
878 |
> |
UNSAFE.compareAndSwapInt(this, eventCountOffset, |
879 |
> |
c = eventCount, c+1); |
880 |
> |
break; // add at most one unless total below target |
881 |
> |
} |
882 |
> |
} |
883 |
|
} |
884 |
+ |
if (eventWaiters != 0L) |
885 |
+ |
releaseEventWaiters(); |
886 |
|
} |
887 |
|
|
888 |
|
/** |
889 |
< |
* Initializes workers if necessary. |
889 |
> |
* Callback from the oldest waiter in awaitEvent waking up after a |
890 |
> |
* period of non-use. If all workers are idle, tries (once) to |
891 |
> |
* shutdown an event waiter or a spare, if one exists. Note that |
892 |
> |
* we don't need CAS or locks here because the method is called |
893 |
> |
* only from one thread occasionally waking (and even misfires are |
894 |
> |
* OK). Note that until the shutdown worker fully terminates, |
895 |
> |
* workerCounts will overestimate total count, which is tolerable. |
896 |
> |
* |
897 |
> |
* @param ec the event count waited on by caller (to abort |
898 |
> |
* attempt if count has since changed). |
899 |
|
*/ |
900 |
< |
final void ensureWorkerInitialization() { |
901 |
< |
ForkJoinWorkerThread[] ws = workers; |
902 |
< |
if (ws == null) { |
903 |
< |
final ReentrantLock lock = this.workerLock; |
904 |
< |
lock.lock(); |
905 |
< |
try { |
906 |
< |
ws = workers; |
907 |
< |
if (ws == null) { |
908 |
< |
int ps = parallelism; |
909 |
< |
ws = ensureWorkerArrayCapacity(ps); |
910 |
< |
for (int i = 0; i < ps; ++i) { |
911 |
< |
ForkJoinWorkerThread w = createWorker(i); |
912 |
< |
if (w != null) { |
913 |
< |
ws[i] = w; |
914 |
< |
w.start(); |
915 |
< |
updateWorkerCount(1); |
916 |
< |
} |
917 |
< |
} |
900 |
> |
private void tryShutdownUnusedWorker(int ec) { |
901 |
> |
if (runState == 0 && eventCount == ec) { // only trigger if all idle |
902 |
> |
ForkJoinWorkerThread[] ws = workers; |
903 |
> |
int n = ws.length; |
904 |
> |
ForkJoinWorkerThread w = null; |
905 |
> |
boolean shutdown = false; |
906 |
> |
int sw; |
907 |
> |
long h; |
908 |
> |
if ((sw = spareWaiters) != 0) { // prefer killing spares |
909 |
> |
int id = (sw & SPARE_ID_MASK) - 1; |
910 |
> |
if (id >= 0 && id < n && (w = ws[id]) != null && |
911 |
> |
UNSAFE.compareAndSwapInt(this, spareWaitersOffset, |
912 |
> |
sw, w.nextSpare)) |
913 |
> |
shutdown = true; |
914 |
> |
} |
915 |
> |
else if ((h = eventWaiters) != 0L) { |
916 |
> |
long nh; |
917 |
> |
int id = ((int)(h & WAITER_ID_MASK)) - 1; |
918 |
> |
if (id >= 0 && id < n && (w = ws[id]) != null && |
919 |
> |
(nh = w.nextWaiter) != 0L && // keep at least one worker |
920 |
> |
UNSAFE.compareAndSwapLong(this, eventWaitersOffset, h, nh)) |
921 |
> |
shutdown = true; |
922 |
> |
} |
923 |
> |
if (w != null && shutdown) { |
924 |
> |
w.shutdown(); |
925 |
> |
LockSupport.unpark(w); |
926 |
> |
} |
927 |
> |
} |
928 |
> |
releaseEventWaiters(); // in case of interference |
929 |
> |
} |
930 |
> |
|
931 |
> |
/** |
932 |
> |
* Callback from workers invoked upon each top-level action (i.e., |
933 |
> |
* stealing a task or taking a submission and running it). |
934 |
> |
* Performs one or more of the following: |
935 |
> |
* |
936 |
> |
* 1. If the worker is active and either did not run a task |
937 |
> |
* or there are too many workers, try to set its active status |
938 |
> |
* to inactive and update activeCount. On contention, we may |
939 |
> |
* try again in this or a subsequent call. |
940 |
> |
* |
941 |
> |
* 2. If not enough total workers, help create some. |
942 |
> |
* |
943 |
> |
* 3. If there are too many running workers, suspend this worker |
944 |
> |
* (first forcing inactive if necessary). If it is not needed, |
945 |
> |
* it may be shutdown while suspended (via |
946 |
> |
* tryShutdownUnusedWorker). Otherwise, upon resume it |
947 |
> |
* rechecks running thread count and need for event sync. |
948 |
> |
* |
949 |
> |
* 4. If worker did not run a task, await the next task event via |
950 |
> |
* eventSync if necessary (first forcing inactivation), upon |
951 |
> |
* which the worker may be shutdown via |
952 |
> |
* tryShutdownUnusedWorker. Otherwise, help release any |
953 |
> |
* existing event waiters that are now releasable, |
954 |
> |
* |
955 |
> |
* @param w the worker |
956 |
> |
* @param ran true if worker ran a task since last call to this method |
957 |
> |
*/ |
958 |
> |
final void preStep(ForkJoinWorkerThread w, boolean ran) { |
959 |
> |
int wec = w.lastEventCount; |
960 |
> |
boolean active = w.active; |
961 |
> |
boolean inactivate = false; |
962 |
> |
int pc = parallelism; |
963 |
> |
int rs; |
964 |
> |
while (w.runState == 0 && (rs = runState) < TERMINATING) { |
965 |
> |
if ((inactivate || (active && (rs & ACTIVE_COUNT_MASK) >= pc)) && |
966 |
> |
UNSAFE.compareAndSwapInt(this, runStateOffset, rs, rs - 1)) |
967 |
> |
inactivate = active = w.active = false; |
968 |
> |
int wc = workerCounts; |
969 |
> |
if ((wc & RUNNING_COUNT_MASK) > pc) { |
970 |
> |
if (!(inactivate |= active) && // must inactivate to suspend |
971 |
> |
workerCounts == wc && // try to suspend as spare |
972 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
973 |
> |
wc, wc - ONE_RUNNING)) |
974 |
> |
w.suspendAsSpare(); |
975 |
> |
} |
976 |
> |
else if ((wc >>> TOTAL_COUNT_SHIFT) < pc) |
977 |
> |
helpMaintainParallelism(); // not enough workers |
978 |
> |
else if (!ran) { |
979 |
> |
long h = eventWaiters; |
980 |
> |
int ec = eventCount; |
981 |
> |
if (h != 0L && (int)(h >>> EVENT_COUNT_SHIFT) != ec) |
982 |
> |
releaseEventWaiters(); // release others before waiting |
983 |
> |
else if (ec != wec) { |
984 |
> |
w.lastEventCount = ec; // no need to wait |
985 |
> |
break; |
986 |
|
} |
987 |
< |
} finally { |
988 |
< |
lock.unlock(); |
987 |
> |
else if (!(inactivate |= active)) |
988 |
> |
eventSync(w, wec); // must inactivate before sync |
989 |
|
} |
990 |
+ |
else |
991 |
+ |
break; |
992 |
|
} |
993 |
|
} |
994 |
|
|
995 |
|
/** |
996 |
< |
* Worker creation and startup for threads added via setParallelism. |
996 |
> |
* Helps and/or blocks awaiting join of the given task. |
997 |
> |
* See above for explanation. |
998 |
> |
* |
999 |
> |
* @param joinMe the task to join |
1000 |
> |
* @param worker the current worker thread |
1001 |
|
*/ |
1002 |
< |
private void createAndStartAddedWorkers() { |
1003 |
< |
resumeAllSpares(); // Allow spares to convert to nonspare |
1004 |
< |
int ps = parallelism; |
1005 |
< |
ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps); |
1006 |
< |
int len = ws.length; |
1007 |
< |
// Sweep through slots, to keep lowest indices most populated |
1008 |
< |
int k = 0; |
1009 |
< |
while (k < len) { |
1010 |
< |
if (ws[k] != null) { |
1011 |
< |
++k; |
1012 |
< |
continue; |
1002 |
> |
final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) { |
1003 |
> |
int retries = 2 + (parallelism >> 2); // #helpJoins before blocking |
1004 |
> |
while (joinMe.status >= 0) { |
1005 |
> |
int wc; |
1006 |
> |
worker.helpJoinTask(joinMe); |
1007 |
> |
if (joinMe.status < 0) |
1008 |
> |
break; |
1009 |
> |
else if (retries > 0) |
1010 |
> |
--retries; |
1011 |
> |
else if (((wc = workerCounts) & RUNNING_COUNT_MASK) != 0 && |
1012 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1013 |
> |
wc, wc - ONE_RUNNING)) { |
1014 |
> |
int stat, c; long h; |
1015 |
> |
while ((stat = joinMe.status) >= 0 && |
1016 |
> |
(h = eventWaiters) != 0L && // help release others |
1017 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) != eventCount) |
1018 |
> |
releaseEventWaiters(); |
1019 |
> |
if (stat >= 0 && |
1020 |
> |
((workerCounts & RUNNING_COUNT_MASK) == 0 || |
1021 |
> |
(stat = |
1022 |
> |
joinMe.internalAwaitDone(JOIN_TIMEOUT_MILLIS)) >= 0)) |
1023 |
> |
helpMaintainParallelism(); // timeout or no running workers |
1024 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
1025 |
> |
(this, workerCountsOffset, |
1026 |
> |
c = workerCounts, c + ONE_RUNNING)); |
1027 |
> |
if (stat < 0) |
1028 |
> |
break; // else restart |
1029 |
|
} |
1030 |
< |
int s = workerCounts; |
1031 |
< |
int tc = totalCountOf(s); |
1032 |
< |
int rc = runningCountOf(s); |
1033 |
< |
if (rc >= ps || tc >= ps) |
1030 |
> |
} |
1031 |
> |
} |
1032 |
> |
|
1033 |
> |
/** |
1034 |
> |
* Same idea as awaitJoin, but no helping, retries, or timeouts. |
1035 |
> |
*/ |
1036 |
> |
final void awaitBlocker(ManagedBlocker blocker) |
1037 |
> |
throws InterruptedException { |
1038 |
> |
while (!blocker.isReleasable()) { |
1039 |
> |
int wc = workerCounts; |
1040 |
> |
if ((wc & RUNNING_COUNT_MASK) != 0 && |
1041 |
> |
UNSAFE.compareAndSwapInt(this, workerCountsOffset, |
1042 |
> |
wc, wc - ONE_RUNNING)) { |
1043 |
> |
try { |
1044 |
> |
while (!blocker.isReleasable()) { |
1045 |
> |
long h = eventWaiters; |
1046 |
> |
if (h != 0L && |
1047 |
> |
(int)(h >>> EVENT_COUNT_SHIFT) != eventCount) |
1048 |
> |
releaseEventWaiters(); |
1049 |
> |
else if ((workerCounts & RUNNING_COUNT_MASK) == 0 && |
1050 |
> |
runState < TERMINATING) |
1051 |
> |
helpMaintainParallelism(); |
1052 |
> |
else if (blocker.block()) |
1053 |
> |
break; |
1054 |
> |
} |
1055 |
> |
} finally { |
1056 |
> |
int c; |
1057 |
> |
do {} while (!UNSAFE.compareAndSwapInt |
1058 |
> |
(this, workerCountsOffset, |
1059 |
> |
c = workerCounts, c + ONE_RUNNING)); |
1060 |
> |
} |
1061 |
|
break; |
1062 |
< |
if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) { |
1063 |
< |
ForkJoinWorkerThread w = createWorker(k); |
1062 |
> |
} |
1063 |
> |
} |
1064 |
> |
} |
1065 |
> |
|
1066 |
> |
/** |
1067 |
> |
* Possibly initiates and/or completes termination. |
1068 |
> |
* |
1069 |
> |
* @param now if true, unconditionally terminate, else only |
1070 |
> |
* if shutdown and empty queue and no active workers |
1071 |
> |
* @return true if now terminating or terminated |
1072 |
> |
*/ |
1073 |
> |
private boolean tryTerminate(boolean now) { |
1074 |
> |
if (now) |
1075 |
> |
advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN |
1076 |
> |
else if (runState < SHUTDOWN || |
1077 |
> |
!submissionQueue.isEmpty() || |
1078 |
> |
(runState & ACTIVE_COUNT_MASK) != 0) |
1079 |
> |
return false; |
1080 |
> |
|
1081 |
> |
if (advanceRunLevel(TERMINATING)) |
1082 |
> |
startTerminating(); |
1083 |
> |
|
1084 |
> |
// Finish now if all threads terminated; else in some subsequent call |
1085 |
> |
if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) { |
1086 |
> |
advanceRunLevel(TERMINATED); |
1087 |
> |
termination.arrive(); |
1088 |
> |
} |
1089 |
> |
return true; |
1090 |
> |
} |
1091 |
> |
|
1092 |
> |
/** |
1093 |
> |
* Actions on transition to TERMINATING |
1094 |
> |
* |
1095 |
> |
* Runs up to four passes through workers: (0) shutting down each |
1096 |
> |
* (without waking up if parked) to quickly spread notifications |
1097 |
> |
* without unnecessary bouncing around event queues etc (1) wake |
1098 |
> |
* up and help cancel tasks (2) interrupt (3) mop up races with |
1099 |
> |
* interrupted workers |
1100 |
> |
*/ |
1101 |
> |
private void startTerminating() { |
1102 |
> |
cancelSubmissions(); |
1103 |
> |
for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) { |
1104 |
> |
int c; // advance event count |
1105 |
> |
UNSAFE.compareAndSwapInt(this, eventCountOffset, |
1106 |
> |
c = eventCount, c+1); |
1107 |
> |
eventWaiters = 0L; // clobber lists |
1108 |
> |
spareWaiters = 0; |
1109 |
> |
for (ForkJoinWorkerThread w : workers) { |
1110 |
|
if (w != null) { |
1111 |
< |
ws[k++] = w; |
1112 |
< |
w.start(); |
1113 |
< |
} |
1114 |
< |
else { |
1115 |
< |
updateWorkerCount(-1); // back out on failed creation |
1116 |
< |
break; |
1111 |
> |
w.shutdown(); |
1112 |
> |
if (passes > 0 && !w.isTerminated()) { |
1113 |
> |
w.cancelTasks(); |
1114 |
> |
LockSupport.unpark(w); |
1115 |
> |
if (passes > 1) { |
1116 |
> |
try { |
1117 |
> |
w.interrupt(); |
1118 |
> |
} catch (SecurityException ignore) { |
1119 |
> |
} |
1120 |
> |
} |
1121 |
> |
} |
1122 |
|
} |
1123 |
|
} |
1124 |
|
} |
1125 |
|
} |
1126 |
|
|
1127 |
+ |
/** |
1128 |
+ |
* Clears out and cancels submissions, ignoring exceptions. |
1129 |
+ |
*/ |
1130 |
+ |
private void cancelSubmissions() { |
1131 |
+ |
ForkJoinTask<?> task; |
1132 |
+ |
while ((task = submissionQueue.poll()) != null) { |
1133 |
+ |
try { |
1134 |
+ |
task.cancel(false); |
1135 |
+ |
} catch (Throwable ignore) { |
1136 |
+ |
} |
1137 |
+ |
} |
1138 |
+ |
} |
1139 |
+ |
|
1140 |
+ |
// misc support for ForkJoinWorkerThread |
1141 |
+ |
|
1142 |
+ |
/** |
1143 |
+ |
* Returns pool number. |
1144 |
+ |
*/ |
1145 |
+ |
final int getPoolNumber() { |
1146 |
+ |
return poolNumber; |
1147 |
+ |
} |
1148 |
+ |
|
1149 |
+ |
/** |
1150 |
+ |
* Tries to accumulate steal count from a worker, clearing |
1151 |
+ |
* the worker's value if successful. |
1152 |
+ |
* |
1153 |
+ |
* @return true if worker steal count now zero |
1154 |
+ |
*/ |
1155 |
+ |
final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) { |
1156 |
+ |
int sc = w.stealCount; |
1157 |
+ |
long c = stealCount; |
1158 |
+ |
// CAS even if zero, for fence effects |
1159 |
+ |
if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) { |
1160 |
+ |
if (sc != 0) |
1161 |
+ |
w.stealCount = 0; |
1162 |
+ |
return true; |
1163 |
+ |
} |
1164 |
+ |
return sc == 0; |
1165 |
+ |
} |
1166 |
+ |
|
1167 |
+ |
/** |
1168 |
+ |
* Returns the approximate (non-atomic) number of idle threads per |
1169 |
+ |
* active thread. |
1170 |
+ |
*/ |
1171 |
+ |
final int idlePerActive() { |
1172 |
+ |
int pc = parallelism; // use parallelism, not rc |
1173 |
+ |
int ac = runState; // no mask -- artificially boosts during shutdown |
1174 |
+ |
// Use exact results for small values, saturate past 4 |
1175 |
+ |
return ((pc <= ac) ? 0 : |
1176 |
+ |
(pc >>> 1 <= ac) ? 1 : |
1177 |
+ |
(pc >>> 2 <= ac) ? 3 : |
1178 |
+ |
pc >>> 3); |
1179 |
+ |
} |
1180 |
+ |
|
1181 |
+ |
// Public and protected methods |
1182 |
+ |
|
1183 |
+ |
// Constructors |
1184 |
+ |
|
1185 |
+ |
/** |
1186 |
+ |
* Creates a {@code ForkJoinPool} with parallelism equal to {@link |
1187 |
+ |
* java.lang.Runtime#availableProcessors}, using the {@linkplain |
1188 |
+ |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1189 |
+ |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1190 |
+ |
* |
1191 |
+ |
* @throws SecurityException if a security manager exists and |
1192 |
+ |
* the caller is not permitted to modify threads |
1193 |
+ |
* because it does not hold {@link |
1194 |
+ |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1195 |
+ |
*/ |
1196 |
+ |
public ForkJoinPool() { |
1197 |
+ |
this(Runtime.getRuntime().availableProcessors(), |
1198 |
+ |
defaultForkJoinWorkerThreadFactory, null, false); |
1199 |
+ |
} |
1200 |
+ |
|
1201 |
+ |
/** |
1202 |
+ |
* Creates a {@code ForkJoinPool} with the indicated parallelism |
1203 |
+ |
* level, the {@linkplain |
1204 |
+ |
* #defaultForkJoinWorkerThreadFactory default thread factory}, |
1205 |
+ |
* no UncaughtExceptionHandler, and non-async LIFO processing mode. |
1206 |
+ |
* |
1207 |
+ |
* @param parallelism the parallelism level |
1208 |
+ |
* @throws IllegalArgumentException if parallelism less than or |
1209 |
+ |
* equal to zero, or greater than implementation limit |
1210 |
+ |
* @throws SecurityException if a security manager exists and |
1211 |
+ |
* the caller is not permitted to modify threads |
1212 |
+ |
* because it does not hold {@link |
1213 |
+ |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1214 |
+ |
*/ |
1215 |
+ |
public ForkJoinPool(int parallelism) { |
1216 |
+ |
this(parallelism, defaultForkJoinWorkerThreadFactory, null, false); |
1217 |
+ |
} |
1218 |
+ |
|
1219 |
+ |
/** |
1220 |
+ |
* Creates a {@code ForkJoinPool} with the given parameters. |
1221 |
+ |
* |
1222 |
+ |
* @param parallelism the parallelism level. For default value, |
1223 |
+ |
* use {@link java.lang.Runtime#availableProcessors}. |
1224 |
+ |
* @param factory the factory for creating new threads. For default value, |
1225 |
+ |
* use {@link #defaultForkJoinWorkerThreadFactory}. |
1226 |
+ |
* @param handler the handler for internal worker threads that |
1227 |
+ |
* terminate due to unrecoverable errors encountered while executing |
1228 |
+ |
* tasks. For default value, use {@code null}. |
1229 |
+ |
* @param asyncMode if true, |
1230 |
+ |
* establishes local first-in-first-out scheduling mode for forked |
1231 |
+ |
* tasks that are never joined. This mode may be more appropriate |
1232 |
+ |
* than default locally stack-based mode in applications in which |
1233 |
+ |
* worker threads only process event-style asynchronous tasks. |
1234 |
+ |
* For default value, use {@code false}. |
1235 |
+ |
* @throws IllegalArgumentException if parallelism less than or |
1236 |
+ |
* equal to zero, or greater than implementation limit |
1237 |
+ |
* @throws NullPointerException if the factory is null |
1238 |
+ |
* @throws SecurityException if a security manager exists and |
1239 |
+ |
* the caller is not permitted to modify threads |
1240 |
+ |
* because it does not hold {@link |
1241 |
+ |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
1242 |
+ |
*/ |
1243 |
+ |
public ForkJoinPool(int parallelism, |
1244 |
+ |
ForkJoinWorkerThreadFactory factory, |
1245 |
+ |
Thread.UncaughtExceptionHandler handler, |
1246 |
+ |
boolean asyncMode) { |
1247 |
+ |
checkPermission(); |
1248 |
+ |
if (factory == null) |
1249 |
+ |
throw new NullPointerException(); |
1250 |
+ |
if (parallelism <= 0 || parallelism > MAX_WORKERS) |
1251 |
+ |
throw new IllegalArgumentException(); |
1252 |
+ |
this.parallelism = parallelism; |
1253 |
+ |
this.factory = factory; |
1254 |
+ |
this.ueh = handler; |
1255 |
+ |
this.locallyFifo = asyncMode; |
1256 |
+ |
int arraySize = initialArraySizeFor(parallelism); |
1257 |
+ |
this.workers = new ForkJoinWorkerThread[arraySize]; |
1258 |
+ |
this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
1259 |
+ |
this.workerLock = new ReentrantLock(); |
1260 |
+ |
this.termination = new Phaser(1); |
1261 |
+ |
this.poolNumber = poolNumberGenerator.incrementAndGet(); |
1262 |
+ |
} |
1263 |
+ |
|
1264 |
+ |
/** |
1265 |
+ |
* Returns initial power of two size for workers array. |
1266 |
+ |
* @param pc the initial parallelism level |
1267 |
+ |
*/ |
1268 |
+ |
private static int initialArraySizeFor(int pc) { |
1269 |
+ |
// If possible, initially allocate enough space for one spare |
1270 |
+ |
int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS; |
1271 |
+ |
// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16) |
1272 |
+ |
size |= size >>> 1; |
1273 |
+ |
size |= size >>> 2; |
1274 |
+ |
size |= size >>> 4; |
1275 |
+ |
size |= size >>> 8; |
1276 |
+ |
return size + 1; |
1277 |
+ |
} |
1278 |
+ |
|
1279 |
|
// Execution methods |
1280 |
|
|
1281 |
|
/** |
1284 |
|
private <T> void doSubmit(ForkJoinTask<T> task) { |
1285 |
|
if (task == null) |
1286 |
|
throw new NullPointerException(); |
1287 |
< |
if (isShutdown()) |
1287 |
> |
if (runState >= SHUTDOWN) |
1288 |
|
throw new RejectedExecutionException(); |
555 |
– |
if (workers == null) |
556 |
– |
ensureWorkerInitialization(); |
1289 |
|
submissionQueue.offer(task); |
1290 |
< |
signalIdleWorkers(); |
1290 |
> |
int c; // try to increment event count -- CAS failure OK |
1291 |
> |
UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1); |
1292 |
> |
helpMaintainParallelism(); // create, start, or resume some workers |
1293 |
|
} |
1294 |
|
|
1295 |
|
/** |
1297 |
|
* |
1298 |
|
* @param task the task |
1299 |
|
* @return the task's result |
1300 |
< |
* @throws NullPointerException if task is null |
1301 |
< |
* @throws RejectedExecutionException if pool is shut down |
1300 |
> |
* @throws NullPointerException if the task is null |
1301 |
> |
* @throws RejectedExecutionException if the task cannot be |
1302 |
> |
* scheduled for execution |
1303 |
|
*/ |
1304 |
|
public <T> T invoke(ForkJoinTask<T> task) { |
1305 |
|
doSubmit(task); |
1310 |
|
* Arranges for (asynchronous) execution of the given task. |
1311 |
|
* |
1312 |
|
* @param task the task |
1313 |
< |
* @throws NullPointerException if task is null |
1314 |
< |
* @throws RejectedExecutionException if pool is shut down |
1313 |
> |
* @throws NullPointerException if the task is null |
1314 |
> |
* @throws RejectedExecutionException if the task cannot be |
1315 |
> |
* scheduled for execution |
1316 |
|
*/ |
1317 |
< |
public <T> void execute(ForkJoinTask<T> task) { |
1317 |
> |
public void execute(ForkJoinTask<?> task) { |
1318 |
|
doSubmit(task); |
1319 |
|
} |
1320 |
|
|
1321 |
|
// AbstractExecutorService methods |
1322 |
|
|
1323 |
+ |
/** |
1324 |
+ |
* @throws NullPointerException if the task is null |
1325 |
+ |
* @throws RejectedExecutionException if the task cannot be |
1326 |
+ |
* scheduled for execution |
1327 |
+ |
*/ |
1328 |
|
public void execute(Runnable task) { |
1329 |
|
ForkJoinTask<?> job; |
1330 |
|
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1334 |
|
doSubmit(job); |
1335 |
|
} |
1336 |
|
|
1337 |
+ |
/** |
1338 |
+ |
* Submits a ForkJoinTask for execution. |
1339 |
+ |
* |
1340 |
+ |
* @param task the task to submit |
1341 |
+ |
* @return the task |
1342 |
+ |
* @throws NullPointerException if the task is null |
1343 |
+ |
* @throws RejectedExecutionException if the task cannot be |
1344 |
+ |
* scheduled for execution |
1345 |
+ |
*/ |
1346 |
+ |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
1347 |
+ |
doSubmit(task); |
1348 |
+ |
return task; |
1349 |
+ |
} |
1350 |
+ |
|
1351 |
+ |
/** |
1352 |
+ |
* @throws NullPointerException if the task is null |
1353 |
+ |
* @throws RejectedExecutionException if the task cannot be |
1354 |
+ |
* scheduled for execution |
1355 |
+ |
*/ |
1356 |
|
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
1357 |
|
ForkJoinTask<T> job = ForkJoinTask.adapt(task); |
1358 |
|
doSubmit(job); |
1359 |
|
return job; |
1360 |
|
} |
1361 |
|
|
1362 |
+ |
/** |
1363 |
+ |
* @throws NullPointerException if the task is null |
1364 |
+ |
* @throws RejectedExecutionException if the task cannot be |
1365 |
+ |
* scheduled for execution |
1366 |
+ |
*/ |
1367 |
|
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
1368 |
|
ForkJoinTask<T> job = ForkJoinTask.adapt(task, result); |
1369 |
|
doSubmit(job); |
1370 |
|
return job; |
1371 |
|
} |
1372 |
|
|
1373 |
+ |
/** |
1374 |
+ |
* @throws NullPointerException if the task is null |
1375 |
+ |
* @throws RejectedExecutionException if the task cannot be |
1376 |
+ |
* scheduled for execution |
1377 |
+ |
*/ |
1378 |
|
public ForkJoinTask<?> submit(Runnable task) { |
1379 |
|
ForkJoinTask<?> job; |
1380 |
|
if (task instanceof ForkJoinTask<?>) // avoid re-wrap |
1386 |
|
} |
1387 |
|
|
1388 |
|
/** |
1389 |
< |
* Submits a ForkJoinTask for execution. |
1390 |
< |
* |
621 |
< |
* @param task the task to submit |
622 |
< |
* @return the task |
623 |
< |
* @throws RejectedExecutionException if the task cannot be |
624 |
< |
* scheduled for execution |
625 |
< |
* @throws NullPointerException if the task is null |
1389 |
> |
* @throws NullPointerException {@inheritDoc} |
1390 |
> |
* @throws RejectedExecutionException {@inheritDoc} |
1391 |
|
*/ |
627 |
– |
public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) { |
628 |
– |
doSubmit(task); |
629 |
– |
return task; |
630 |
– |
} |
631 |
– |
|
632 |
– |
|
1392 |
|
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
1393 |
|
ArrayList<ForkJoinTask<T>> forkJoinTasks = |
1394 |
|
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
1397 |
|
invoke(new InvokeAll<T>(forkJoinTasks)); |
1398 |
|
|
1399 |
|
@SuppressWarnings({"unchecked", "rawtypes"}) |
1400 |
< |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1400 |
> |
List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks; |
1401 |
|
return futures; |
1402 |
|
} |
1403 |
|
|
1411 |
|
private static final long serialVersionUID = -7914297376763021607L; |
1412 |
|
} |
1413 |
|
|
655 |
– |
// Configuration and status settings and queries |
656 |
– |
|
1414 |
|
/** |
1415 |
|
* Returns the factory used for constructing new workers. |
1416 |
|
* |
1427 |
|
* @return the handler, or {@code null} if none |
1428 |
|
*/ |
1429 |
|
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
1430 |
< |
Thread.UncaughtExceptionHandler h; |
674 |
< |
final ReentrantLock lock = this.workerLock; |
675 |
< |
lock.lock(); |
676 |
< |
try { |
677 |
< |
h = ueh; |
678 |
< |
} finally { |
679 |
< |
lock.unlock(); |
680 |
< |
} |
681 |
< |
return h; |
682 |
< |
} |
683 |
< |
|
684 |
< |
/** |
685 |
< |
* Sets the handler for internal worker threads that terminate due |
686 |
< |
* to unrecoverable errors encountered while executing tasks. |
687 |
< |
* Unless set, the current default or ThreadGroup handler is used |
688 |
< |
* as handler. |
689 |
< |
* |
690 |
< |
* @param h the new handler |
691 |
< |
* @return the old handler, or {@code null} if none |
692 |
< |
* @throws SecurityException if a security manager exists and |
693 |
< |
* the caller is not permitted to modify threads |
694 |
< |
* because it does not hold {@link |
695 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
696 |
< |
*/ |
697 |
< |
public Thread.UncaughtExceptionHandler |
698 |
< |
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) { |
699 |
< |
checkPermission(); |
700 |
< |
Thread.UncaughtExceptionHandler old = null; |
701 |
< |
final ReentrantLock lock = this.workerLock; |
702 |
< |
lock.lock(); |
703 |
< |
try { |
704 |
< |
old = ueh; |
705 |
< |
ueh = h; |
706 |
< |
ForkJoinWorkerThread[] ws = workers; |
707 |
< |
if (ws != null) { |
708 |
< |
for (int i = 0; i < ws.length; ++i) { |
709 |
< |
ForkJoinWorkerThread w = ws[i]; |
710 |
< |
if (w != null) |
711 |
< |
w.setUncaughtExceptionHandler(h); |
712 |
< |
} |
713 |
< |
} |
714 |
< |
} finally { |
715 |
< |
lock.unlock(); |
716 |
< |
} |
717 |
< |
return old; |
718 |
< |
} |
719 |
< |
|
720 |
< |
|
721 |
< |
/** |
722 |
< |
* Sets the target parallelism level of this pool. |
723 |
< |
* |
724 |
< |
* @param parallelism the target parallelism |
725 |
< |
* @throws IllegalArgumentException if parallelism less than or |
726 |
< |
* equal to zero or greater than maximum size bounds |
727 |
< |
* @throws SecurityException if a security manager exists and |
728 |
< |
* the caller is not permitted to modify threads |
729 |
< |
* because it does not hold {@link |
730 |
< |
* java.lang.RuntimePermission}{@code ("modifyThread")} |
731 |
< |
*/ |
732 |
< |
public void setParallelism(int parallelism) { |
733 |
< |
checkPermission(); |
734 |
< |
if (parallelism <= 0 || parallelism > maxPoolSize) |
735 |
< |
throw new IllegalArgumentException(); |
736 |
< |
final ReentrantLock lock = this.workerLock; |
737 |
< |
lock.lock(); |
738 |
< |
try { |
739 |
< |
if (!isTerminating()) { |
740 |
< |
int p = this.parallelism; |
741 |
< |
this.parallelism = parallelism; |
742 |
< |
if (parallelism > p) |
743 |
< |
createAndStartAddedWorkers(); |
744 |
< |
else |
745 |
< |
trimSpares(); |
746 |
< |
} |
747 |
< |
} finally { |
748 |
< |
lock.unlock(); |
749 |
< |
} |
750 |
< |
signalIdleWorkers(); |
1430 |
> |
return ueh; |
1431 |
|
} |
1432 |
|
|
1433 |
|
/** |
1434 |
< |
* Returns the targeted number of worker threads in this pool. |
1434 |
> |
* Returns the targeted parallelism level of this pool. |
1435 |
|
* |
1436 |
< |
* @return the targeted number of worker threads in this pool |
1436 |
> |
* @return the targeted parallelism level of this pool |
1437 |
|
*/ |
1438 |
|
public int getParallelism() { |
1439 |
|
return parallelism; |
1448 |
|
* @return the number of worker threads |
1449 |
|
*/ |
1450 |
|
public int getPoolSize() { |
1451 |
< |
return totalCountOf(workerCounts); |
772 |
< |
} |
773 |
< |
|
774 |
< |
/** |
775 |
< |
* Returns the maximum number of threads allowed to exist in the |
776 |
< |
* pool, even if there are insufficient unblocked running threads. |
777 |
< |
* |
778 |
< |
* @return the maximum |
779 |
< |
*/ |
780 |
< |
public int getMaximumPoolSize() { |
781 |
< |
return maxPoolSize; |
782 |
< |
} |
783 |
< |
|
784 |
< |
/** |
785 |
< |
* Sets the maximum number of threads allowed to exist in the |
786 |
< |
* pool, even if there are insufficient unblocked running threads. |
787 |
< |
* Setting this value has no effect on current pool size. It |
788 |
< |
* controls construction of new threads. |
789 |
< |
* |
790 |
< |
* @throws IllegalArgumentException if negative or greater then |
791 |
< |
* internal implementation limit |
792 |
< |
*/ |
793 |
< |
public void setMaximumPoolSize(int newMax) { |
794 |
< |
if (newMax < 0 || newMax > MAX_THREADS) |
795 |
< |
throw new IllegalArgumentException(); |
796 |
< |
maxPoolSize = newMax; |
797 |
< |
} |
798 |
< |
|
799 |
< |
|
800 |
< |
/** |
801 |
< |
* Returns {@code true} if this pool dynamically maintains its |
802 |
< |
* target parallelism level. If false, new threads are added only |
803 |
< |
* to avoid possible starvation. This setting is by default true. |
804 |
< |
* |
805 |
< |
* @return {@code true} if maintains parallelism |
806 |
< |
*/ |
807 |
< |
public boolean getMaintainsParallelism() { |
808 |
< |
return maintainsParallelism; |
809 |
< |
} |
810 |
< |
|
811 |
< |
/** |
812 |
< |
* Sets whether this pool dynamically maintains its target |
813 |
< |
* parallelism level. If false, new threads are added only to |
814 |
< |
* avoid possible starvation. |
815 |
< |
* |
816 |
< |
* @param enable {@code true} to maintain parallelism |
817 |
< |
*/ |
818 |
< |
public void setMaintainsParallelism(boolean enable) { |
819 |
< |
maintainsParallelism = enable; |
820 |
< |
} |
821 |
< |
|
822 |
< |
/** |
823 |
< |
* Establishes local first-in-first-out scheduling mode for forked |
824 |
< |
* tasks that are never joined. This mode may be more appropriate |
825 |
< |
* than default locally stack-based mode in applications in which |
826 |
< |
* worker threads only process asynchronous tasks. This method is |
827 |
< |
* designed to be invoked only when the pool is quiescent, and |
828 |
< |
* typically only before any tasks are submitted. The effects of |
829 |
< |
* invocations at other times may be unpredictable. |
830 |
< |
* |
831 |
< |
* @param async if {@code true}, use locally FIFO scheduling |
832 |
< |
* @return the previous mode |
833 |
< |
* @see #getAsyncMode |
834 |
< |
*/ |
835 |
< |
public boolean setAsyncMode(boolean async) { |
836 |
< |
boolean oldMode = locallyFifo; |
837 |
< |
locallyFifo = async; |
838 |
< |
ForkJoinWorkerThread[] ws = workers; |
839 |
< |
if (ws != null) { |
840 |
< |
for (int i = 0; i < ws.length; ++i) { |
841 |
< |
ForkJoinWorkerThread t = ws[i]; |
842 |
< |
if (t != null) |
843 |
< |
t.setAsyncMode(async); |
844 |
< |
} |
845 |
< |
} |
846 |
< |
return oldMode; |
1451 |
> |
return workerCounts >>> TOTAL_COUNT_SHIFT; |
1452 |
|
} |
1453 |
|
|
1454 |
|
/** |
1456 |
|
* scheduling mode for forked tasks that are never joined. |
1457 |
|
* |
1458 |
|
* @return {@code true} if this pool uses async mode |
854 |
– |
* @see #setAsyncMode |
1459 |
|
*/ |
1460 |
|
public boolean getAsyncMode() { |
1461 |
|
return locallyFifo; |
1464 |
|
/** |
1465 |
|
* Returns an estimate of the number of worker threads that are |
1466 |
|
* not blocked waiting to join tasks or for other managed |
1467 |
< |
* synchronization. |
1467 |
> |
* synchronization. This method may overestimate the |
1468 |
> |
* number of running threads. |
1469 |
|
* |
1470 |
|
* @return the number of worker threads |
1471 |
|
*/ |
1472 |
|
public int getRunningThreadCount() { |
1473 |
< |
return runningCountOf(workerCounts); |
1473 |
> |
return workerCounts & RUNNING_COUNT_MASK; |
1474 |
|
} |
1475 |
|
|
1476 |
|
/** |
1481 |
|
* @return the number of active threads |
1482 |
|
*/ |
1483 |
|
public int getActiveThreadCount() { |
1484 |
< |
return activeCountOf(runControl); |
880 |
< |
} |
881 |
< |
|
882 |
< |
/** |
883 |
< |
* Returns an estimate of the number of threads that are currently |
884 |
< |
* idle waiting for tasks. This method may underestimate the |
885 |
< |
* number of idle threads. |
886 |
< |
* |
887 |
< |
* @return the number of idle threads |
888 |
< |
*/ |
889 |
< |
final int getIdleThreadCount() { |
890 |
< |
int c = runningCountOf(workerCounts) - activeCountOf(runControl); |
891 |
< |
return (c <= 0) ? 0 : c; |
1484 |
> |
return runState & ACTIVE_COUNT_MASK; |
1485 |
|
} |
1486 |
|
|
1487 |
|
/** |
1496 |
|
* @return {@code true} if all threads are currently idle |
1497 |
|
*/ |
1498 |
|
public boolean isQuiescent() { |
1499 |
< |
return activeCountOf(runControl) == 0; |
1499 |
> |
return (runState & ACTIVE_COUNT_MASK) == 0; |
1500 |
|
} |
1501 |
|
|
1502 |
|
/** |
1511 |
|
* @return the number of steals |
1512 |
|
*/ |
1513 |
|
public long getStealCount() { |
1514 |
< |
return stealCount.get(); |
922 |
< |
} |
923 |
< |
|
924 |
< |
/** |
925 |
< |
* Accumulates steal count from a worker. |
926 |
< |
* Call only when worker known to be idle. |
927 |
< |
*/ |
928 |
< |
private void updateStealCount(ForkJoinWorkerThread w) { |
929 |
< |
int sc = w.getAndClearStealCount(); |
930 |
< |
if (sc != 0) |
931 |
< |
stealCount.addAndGet(sc); |
1514 |
> |
return stealCount; |
1515 |
|
} |
1516 |
|
|
1517 |
|
/** |
1526 |
|
*/ |
1527 |
|
public long getQueuedTaskCount() { |
1528 |
|
long count = 0; |
1529 |
< |
ForkJoinWorkerThread[] ws = workers; |
1530 |
< |
if (ws != null) { |
1531 |
< |
for (int i = 0; i < ws.length; ++i) { |
949 |
< |
ForkJoinWorkerThread t = ws[i]; |
950 |
< |
if (t != null) |
951 |
< |
count += t.getQueueSize(); |
952 |
< |
} |
953 |
< |
} |
1529 |
> |
for (ForkJoinWorkerThread w : workers) |
1530 |
> |
if (w != null) |
1531 |
> |
count += w.getQueueSize(); |
1532 |
|
return count; |
1533 |
|
} |
1534 |
|
|
1535 |
|
/** |
1536 |
< |
* Returns an estimate of the number tasks submitted to this pool |
1537 |
< |
* that have not yet begun executing. This method takes time |
1536 |
> |
* Returns an estimate of the number of tasks submitted to this |
1537 |
> |
* pool that have not yet begun executing. This method takes time |
1538 |
|
* proportional to the number of submissions. |
1539 |
|
* |
1540 |
|
* @return the number of queued submissions |
1568 |
|
* Removes all available unexecuted submitted and forked tasks |
1569 |
|
* from scheduling queues and adds them to the given collection, |
1570 |
|
* without altering their execution status. These may include |
1571 |
< |
* artificially generated or wrapped tasks. This method is designed |
1572 |
< |
* to be invoked only when the pool is known to be |
1571 |
> |
* artificially generated or wrapped tasks. This method is |
1572 |
> |
* designed to be invoked only when the pool is known to be |
1573 |
|
* quiescent. Invocations at other times may not remove all |
1574 |
|
* tasks. A failure encountered while attempting to add elements |
1575 |
|
* to collection {@code c} may result in elements being in |
1582 |
|
* @return the number of elements transferred |
1583 |
|
*/ |
1584 |
|
protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) { |
1585 |
< |
int n = submissionQueue.drainTo(c); |
1586 |
< |
ForkJoinWorkerThread[] ws = workers; |
1587 |
< |
if (ws != null) { |
1588 |
< |
for (int i = 0; i < ws.length; ++i) { |
1589 |
< |
ForkJoinWorkerThread w = ws[i]; |
1012 |
< |
if (w != null) |
1013 |
< |
n += w.drainTasksTo(c); |
1014 |
< |
} |
1015 |
< |
} |
1016 |
< |
return n; |
1585 |
> |
int count = submissionQueue.drainTo(c); |
1586 |
> |
for (ForkJoinWorkerThread w : workers) |
1587 |
> |
if (w != null) |
1588 |
> |
count += w.drainTasksTo(c); |
1589 |
> |
return count; |
1590 |
|
} |
1591 |
|
|
1592 |
|
/** |
1597 |
|
* @return a string identifying this pool, as well as its state |
1598 |
|
*/ |
1599 |
|
public String toString() { |
1027 |
– |
int ps = parallelism; |
1028 |
– |
int wc = workerCounts; |
1029 |
– |
int rc = runControl; |
1600 |
|
long st = getStealCount(); |
1601 |
|
long qt = getQueuedTaskCount(); |
1602 |
|
long qs = getQueuedSubmissionCount(); |
1603 |
+ |
int wc = workerCounts; |
1604 |
+ |
int tc = wc >>> TOTAL_COUNT_SHIFT; |
1605 |
+ |
int rc = wc & RUNNING_COUNT_MASK; |
1606 |
+ |
int pc = parallelism; |
1607 |
+ |
int rs = runState; |
1608 |
+ |
int ac = rs & ACTIVE_COUNT_MASK; |
1609 |
|
return super.toString() + |
1610 |
< |
"[" + runStateToString(runStateOf(rc)) + |
1611 |
< |
", parallelism = " + ps + |
1612 |
< |
", size = " + totalCountOf(wc) + |
1613 |
< |
", active = " + activeCountOf(rc) + |
1614 |
< |
", running = " + runningCountOf(wc) + |
1610 |
> |
"[" + runLevelToString(rs) + |
1611 |
> |
", parallelism = " + pc + |
1612 |
> |
", size = " + tc + |
1613 |
> |
", active = " + ac + |
1614 |
> |
", running = " + rc + |
1615 |
|
", steals = " + st + |
1616 |
|
", tasks = " + qt + |
1617 |
|
", submissions = " + qs + |
1618 |
|
"]"; |
1619 |
|
} |
1620 |
|
|
1621 |
< |
private static String runStateToString(int rs) { |
1622 |
< |
switch(rs) { |
1623 |
< |
case RUNNING: return "Running"; |
1624 |
< |
case SHUTDOWN: return "Shutting down"; |
1625 |
< |
case TERMINATING: return "Terminating"; |
1050 |
< |
case TERMINATED: return "Terminated"; |
1051 |
< |
default: throw new Error("Unknown run state"); |
1052 |
< |
} |
1621 |
> |
private static String runLevelToString(int s) { |
1622 |
> |
return ((s & TERMINATED) != 0 ? "Terminated" : |
1623 |
> |
((s & TERMINATING) != 0 ? "Terminating" : |
1624 |
> |
((s & SHUTDOWN) != 0 ? "Shutting down" : |
1625 |
> |
"Running"))); |
1626 |
|
} |
1627 |
|
|
1055 |
– |
// lifecycle control |
1056 |
– |
|
1628 |
|
/** |
1629 |
|
* Initiates an orderly shutdown in which previously submitted |
1630 |
|
* tasks are executed, but no new tasks will be accepted. |
1639 |
|
*/ |
1640 |
|
public void shutdown() { |
1641 |
|
checkPermission(); |
1642 |
< |
transitionRunStateTo(SHUTDOWN); |
1643 |
< |
if (canTerminateOnShutdown(runControl)) { |
1073 |
< |
if (workers == null) { // shutting down before workers created |
1074 |
< |
final ReentrantLock lock = this.workerLock; |
1075 |
< |
lock.lock(); |
1076 |
< |
try { |
1077 |
< |
if (workers == null) { |
1078 |
< |
terminate(); |
1079 |
< |
transitionRunStateTo(TERMINATED); |
1080 |
< |
termination.signalAll(); |
1081 |
< |
} |
1082 |
< |
} finally { |
1083 |
< |
lock.unlock(); |
1084 |
< |
} |
1085 |
< |
} |
1086 |
< |
terminateOnShutdown(); |
1087 |
< |
} |
1642 |
> |
advanceRunLevel(SHUTDOWN); |
1643 |
> |
tryTerminate(false); |
1644 |
|
} |
1645 |
|
|
1646 |
|
/** |
1647 |
< |
* Attempts to stop all actively executing tasks, and cancels all |
1648 |
< |
* waiting tasks. Tasks that are in the process of being |
1649 |
< |
* submitted or executed concurrently during the course of this |
1650 |
< |
* method may or may not be rejected. Unlike some other executors, |
1651 |
< |
* this method cancels rather than collects non-executed tasks |
1652 |
< |
* upon termination, so always returns an empty list. However, you |
1653 |
< |
* can use method {@link #drainTasksTo} before invoking this |
1654 |
< |
* method to transfer unexecuted tasks to another collection. |
1647 |
> |
* Attempts to cancel and/or stop all tasks, and reject all |
1648 |
> |
* subsequently submitted tasks. Tasks that are in the process of |
1649 |
> |
* being submitted or executed concurrently during the course of |
1650 |
> |
* this method may or may not be rejected. This method cancels |
1651 |
> |
* both existing and unexecuted tasks, in order to permit |
1652 |
> |
* termination in the presence of task dependencies. So the method |
1653 |
> |
* always returns an empty list (unlike the case for some other |
1654 |
> |
* Executors). |
1655 |
|
* |
1656 |
|
* @return an empty list |
1657 |
|
* @throws SecurityException if a security manager exists and |
1661 |
|
*/ |
1662 |
|
public List<Runnable> shutdownNow() { |
1663 |
|
checkPermission(); |
1664 |
< |
terminate(); |
1664 |
> |
tryTerminate(true); |
1665 |
|
return Collections.emptyList(); |
1666 |
|
} |
1667 |
|
|
1671 |
|
* @return {@code true} if all tasks have completed following shut down |
1672 |
|
*/ |
1673 |
|
public boolean isTerminated() { |
1674 |
< |
return runStateOf(runControl) == TERMINATED; |
1674 |
> |
return runState >= TERMINATED; |
1675 |
|
} |
1676 |
|
|
1677 |
|
/** |
1678 |
|
* Returns {@code true} if the process of termination has |
1679 |
< |
* commenced but possibly not yet completed. |
1679 |
> |
* commenced but not yet completed. This method may be useful for |
1680 |
> |
* debugging. A return of {@code true} reported a sufficient |
1681 |
> |
* period after shutdown may indicate that submitted tasks have |
1682 |
> |
* ignored or suppressed interruption, causing this executor not |
1683 |
> |
* to properly terminate. |
1684 |
|
* |
1685 |
< |
* @return {@code true} if terminating |
1685 |
> |
* @return {@code true} if terminating but not yet terminated |
1686 |
|
*/ |
1687 |
|
public boolean isTerminating() { |
1688 |
< |
return runStateOf(runControl) >= TERMINATING; |
1688 |
> |
return (runState & (TERMINATING|TERMINATED)) == TERMINATING; |
1689 |
|
} |
1690 |
|
|
1691 |
|
/** |
1694 |
|
* @return {@code true} if this pool has been shut down |
1695 |
|
*/ |
1696 |
|
public boolean isShutdown() { |
1697 |
< |
return runStateOf(runControl) >= SHUTDOWN; |
1697 |
> |
return runState >= SHUTDOWN; |
1698 |
|
} |
1699 |
|
|
1700 |
|
/** |
1710 |
|
*/ |
1711 |
|
public boolean awaitTermination(long timeout, TimeUnit unit) |
1712 |
|
throws InterruptedException { |
1153 |
– |
long nanos = unit.toNanos(timeout); |
1154 |
– |
final ReentrantLock lock = this.workerLock; |
1155 |
– |
lock.lock(); |
1156 |
– |
try { |
1157 |
– |
for (;;) { |
1158 |
– |
if (isTerminated()) |
1159 |
– |
return true; |
1160 |
– |
if (nanos <= 0) |
1161 |
– |
return false; |
1162 |
– |
nanos = termination.awaitNanos(nanos); |
1163 |
– |
} |
1164 |
– |
} finally { |
1165 |
– |
lock.unlock(); |
1166 |
– |
} |
1167 |
– |
} |
1168 |
– |
|
1169 |
– |
// Shutdown and termination support |
1170 |
– |
|
1171 |
– |
/** |
1172 |
– |
* Callback from terminating worker. Nulls out the corresponding |
1173 |
– |
* workers slot, and if terminating, tries to terminate; else |
1174 |
– |
* tries to shrink workers array. |
1175 |
– |
* |
1176 |
– |
* @param w the worker |
1177 |
– |
*/ |
1178 |
– |
final void workerTerminated(ForkJoinWorkerThread w) { |
1179 |
– |
updateStealCount(w); |
1180 |
– |
updateWorkerCount(-1); |
1181 |
– |
final ReentrantLock lock = this.workerLock; |
1182 |
– |
lock.lock(); |
1183 |
– |
try { |
1184 |
– |
ForkJoinWorkerThread[] ws = workers; |
1185 |
– |
if (ws != null) { |
1186 |
– |
int idx = w.poolIndex; |
1187 |
– |
if (idx >= 0 && idx < ws.length && ws[idx] == w) |
1188 |
– |
ws[idx] = null; |
1189 |
– |
if (totalCountOf(workerCounts) == 0) { |
1190 |
– |
terminate(); // no-op if already terminating |
1191 |
– |
transitionRunStateTo(TERMINATED); |
1192 |
– |
termination.signalAll(); |
1193 |
– |
} |
1194 |
– |
else if (!isTerminating()) { |
1195 |
– |
tryShrinkWorkerArray(); |
1196 |
– |
tryResumeSpare(true); // allow replacement |
1197 |
– |
} |
1198 |
– |
} |
1199 |
– |
} finally { |
1200 |
– |
lock.unlock(); |
1201 |
– |
} |
1202 |
– |
signalIdleWorkers(); |
1203 |
– |
} |
1204 |
– |
|
1205 |
– |
/** |
1206 |
– |
* Initiates termination. |
1207 |
– |
*/ |
1208 |
– |
private void terminate() { |
1209 |
– |
if (transitionRunStateTo(TERMINATING)) { |
1210 |
– |
stopAllWorkers(); |
1211 |
– |
resumeAllSpares(); |
1212 |
– |
signalIdleWorkers(); |
1213 |
– |
cancelQueuedSubmissions(); |
1214 |
– |
cancelQueuedWorkerTasks(); |
1215 |
– |
interruptUnterminatedWorkers(); |
1216 |
– |
signalIdleWorkers(); // resignal after interrupt |
1217 |
– |
} |
1218 |
– |
} |
1219 |
– |
|
1220 |
– |
/** |
1221 |
– |
* Possibly terminates when on shutdown state. |
1222 |
– |
*/ |
1223 |
– |
private void terminateOnShutdown() { |
1224 |
– |
if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) |
1225 |
– |
terminate(); |
1226 |
– |
} |
1227 |
– |
|
1228 |
– |
/** |
1229 |
– |
* Clears out and cancels submissions. |
1230 |
– |
*/ |
1231 |
– |
private void cancelQueuedSubmissions() { |
1232 |
– |
ForkJoinTask<?> task; |
1233 |
– |
while ((task = pollSubmission()) != null) |
1234 |
– |
task.cancel(false); |
1235 |
– |
} |
1236 |
– |
|
1237 |
– |
/** |
1238 |
– |
* Cleans out worker queues. |
1239 |
– |
*/ |
1240 |
– |
private void cancelQueuedWorkerTasks() { |
1241 |
– |
final ReentrantLock lock = this.workerLock; |
1242 |
– |
lock.lock(); |
1713 |
|
try { |
1714 |
< |
ForkJoinWorkerThread[] ws = workers; |
1715 |
< |
if (ws != null) { |
1246 |
< |
for (int i = 0; i < ws.length; ++i) { |
1247 |
< |
ForkJoinWorkerThread t = ws[i]; |
1248 |
< |
if (t != null) |
1249 |
< |
t.cancelTasks(); |
1250 |
< |
} |
1251 |
< |
} |
1252 |
< |
} finally { |
1253 |
< |
lock.unlock(); |
1254 |
< |
} |
1255 |
< |
} |
1256 |
< |
|
1257 |
< |
/** |
1258 |
< |
* Sets each worker's status to terminating. Requires lock to avoid |
1259 |
< |
* conflicts with add/remove. |
1260 |
< |
*/ |
1261 |
< |
private void stopAllWorkers() { |
1262 |
< |
final ReentrantLock lock = this.workerLock; |
1263 |
< |
lock.lock(); |
1264 |
< |
try { |
1265 |
< |
ForkJoinWorkerThread[] ws = workers; |
1266 |
< |
if (ws != null) { |
1267 |
< |
for (int i = 0; i < ws.length; ++i) { |
1268 |
< |
ForkJoinWorkerThread t = ws[i]; |
1269 |
< |
if (t != null) |
1270 |
< |
t.shutdownNow(); |
1271 |
< |
} |
1272 |
< |
} |
1273 |
< |
} finally { |
1274 |
< |
lock.unlock(); |
1275 |
< |
} |
1276 |
< |
} |
1277 |
< |
|
1278 |
< |
/** |
1279 |
< |
* Interrupts all unterminated workers. This is not required for |
1280 |
< |
* sake of internal control, but may help unstick user code during |
1281 |
< |
* shutdown. |
1282 |
< |
*/ |
1283 |
< |
private void interruptUnterminatedWorkers() { |
1284 |
< |
final ReentrantLock lock = this.workerLock; |
1285 |
< |
lock.lock(); |
1286 |
< |
try { |
1287 |
< |
ForkJoinWorkerThread[] ws = workers; |
1288 |
< |
if (ws != null) { |
1289 |
< |
for (int i = 0; i < ws.length; ++i) { |
1290 |
< |
ForkJoinWorkerThread t = ws[i]; |
1291 |
< |
if (t != null && !t.isTerminated()) { |
1292 |
< |
try { |
1293 |
< |
t.interrupt(); |
1294 |
< |
} catch (SecurityException ignore) { |
1295 |
< |
} |
1296 |
< |
} |
1297 |
< |
} |
1298 |
< |
} |
1299 |
< |
} finally { |
1300 |
< |
lock.unlock(); |
1301 |
< |
} |
1302 |
< |
} |
1303 |
< |
|
1304 |
< |
|
1305 |
< |
/* |
1306 |
< |
* Nodes for event barrier to manage idle threads. Queue nodes |
1307 |
< |
* are basic Treiber stack nodes, also used for spare stack. |
1308 |
< |
* |
1309 |
< |
* The event barrier has an event count and a wait queue (actually |
1310 |
< |
* a Treiber stack). Workers are enabled to look for work when |
1311 |
< |
* the eventCount is incremented. If they fail to find work, they |
1312 |
< |
* may wait for next count. Upon release, threads help others wake |
1313 |
< |
* up. |
1314 |
< |
* |
1315 |
< |
* Synchronization events occur only in enough contexts to |
1316 |
< |
* maintain overall liveness: |
1317 |
< |
* |
1318 |
< |
* - Submission of a new task to the pool |
1319 |
< |
* - Resizes or other changes to the workers array |
1320 |
< |
* - pool termination |
1321 |
< |
* - A worker pushing a task on an empty queue |
1322 |
< |
* |
1323 |
< |
* The case of pushing a task occurs often enough, and is heavy |
1324 |
< |
* enough compared to simple stack pushes, to require special |
1325 |
< |
* handling: Method signalWork returns without advancing count if |
1326 |
< |
* the queue appears to be empty. This would ordinarily result in |
1327 |
< |
* races causing some queued waiters not to be woken up. To avoid |
1328 |
< |
* this, the first worker enqueued in method sync (see |
1329 |
< |
* syncIsReleasable) rescans for tasks after being enqueued, and |
1330 |
< |
* helps signal if any are found. This works well because the |
1331 |
< |
* worker has nothing better to do, and so might as well help |
1332 |
< |
* alleviate the overhead and contention on the threads actually |
1333 |
< |
* doing work. Also, since event counts increments on task |
1334 |
< |
* availability exist to maintain liveness (rather than to force |
1335 |
< |
* refreshes etc), it is OK for callers to exit early if |
1336 |
< |
* contending with another signaller. |
1337 |
< |
*/ |
1338 |
< |
static final class WaitQueueNode { |
1339 |
< |
WaitQueueNode next; // only written before enqueued |
1340 |
< |
volatile ForkJoinWorkerThread thread; // nulled to cancel wait |
1341 |
< |
final long count; // unused for spare stack |
1342 |
< |
|
1343 |
< |
WaitQueueNode(long c, ForkJoinWorkerThread w) { |
1344 |
< |
count = c; |
1345 |
< |
thread = w; |
1346 |
< |
} |
1347 |
< |
|
1348 |
< |
/** |
1349 |
< |
* Wakes up waiter, returning false if known to already |
1350 |
< |
*/ |
1351 |
< |
boolean signal() { |
1352 |
< |
ForkJoinWorkerThread t = thread; |
1353 |
< |
if (t == null) |
1354 |
< |
return false; |
1355 |
< |
thread = null; |
1356 |
< |
LockSupport.unpark(t); |
1357 |
< |
return true; |
1358 |
< |
} |
1359 |
< |
|
1360 |
< |
/** |
1361 |
< |
* Awaits release on sync. |
1362 |
< |
*/ |
1363 |
< |
void awaitSyncRelease(ForkJoinPool p) { |
1364 |
< |
while (thread != null && !p.syncIsReleasable(this)) |
1365 |
< |
LockSupport.park(this); |
1366 |
< |
} |
1367 |
< |
|
1368 |
< |
/** |
1369 |
< |
* Awaits resumption as spare. |
1370 |
< |
*/ |
1371 |
< |
void awaitSpareRelease() { |
1372 |
< |
while (thread != null) { |
1373 |
< |
if (!Thread.interrupted()) |
1374 |
< |
LockSupport.park(this); |
1375 |
< |
} |
1376 |
< |
} |
1377 |
< |
} |
1378 |
< |
|
1379 |
< |
/** |
1380 |
< |
* Ensures that no thread is waiting for count to advance from the |
1381 |
< |
* current value of eventCount read on entry to this method, by |
1382 |
< |
* releasing waiting threads if necessary. |
1383 |
< |
* |
1384 |
< |
* @return the count |
1385 |
< |
*/ |
1386 |
< |
final long ensureSync() { |
1387 |
< |
long c = eventCount; |
1388 |
< |
WaitQueueNode q; |
1389 |
< |
while ((q = syncStack) != null && q.count < c) { |
1390 |
< |
if (casBarrierStack(q, null)) { |
1391 |
< |
do { |
1392 |
< |
q.signal(); |
1393 |
< |
} while ((q = q.next) != null); |
1394 |
< |
break; |
1395 |
< |
} |
1396 |
< |
} |
1397 |
< |
return c; |
1398 |
< |
} |
1399 |
< |
|
1400 |
< |
/** |
1401 |
< |
* Increments event count and releases waiting threads. |
1402 |
< |
*/ |
1403 |
< |
private void signalIdleWorkers() { |
1404 |
< |
long c; |
1405 |
< |
do {} while (!casEventCount(c = eventCount, c+1)); |
1406 |
< |
ensureSync(); |
1407 |
< |
} |
1408 |
< |
|
1409 |
< |
/** |
1410 |
< |
* Signals threads waiting to poll a task. Because method sync |
1411 |
< |
* rechecks availability, it is OK to only proceed if queue |
1412 |
< |
* appears to be non-empty, and OK to skip under contention to |
1413 |
< |
* increment count (since some other thread succeeded). |
1414 |
< |
*/ |
1415 |
< |
final void signalWork() { |
1416 |
< |
long c; |
1417 |
< |
WaitQueueNode q; |
1418 |
< |
if (syncStack != null && |
1419 |
< |
casEventCount(c = eventCount, c+1) && |
1420 |
< |
(((q = syncStack) != null && q.count <= c) && |
1421 |
< |
(!casBarrierStack(q, q.next) || !q.signal()))) |
1422 |
< |
ensureSync(); |
1423 |
< |
} |
1424 |
< |
|
1425 |
< |
/** |
1426 |
< |
* Waits until event count advances from last value held by |
1427 |
< |
* caller, or if excess threads, caller is resumed as spare, or |
1428 |
< |
* caller or pool is terminating. Updates caller's event on exit. |
1429 |
< |
* |
1430 |
< |
* @param w the calling worker thread |
1431 |
< |
*/ |
1432 |
< |
final void sync(ForkJoinWorkerThread w) { |
1433 |
< |
updateStealCount(w); // Transfer w's count while it is idle |
1434 |
< |
|
1435 |
< |
while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { |
1436 |
< |
long prev = w.lastEventCount; |
1437 |
< |
WaitQueueNode node = null; |
1438 |
< |
WaitQueueNode h; |
1439 |
< |
while (eventCount == prev && |
1440 |
< |
((h = syncStack) == null || h.count == prev)) { |
1441 |
< |
if (node == null) |
1442 |
< |
node = new WaitQueueNode(prev, w); |
1443 |
< |
if (casBarrierStack(node.next = h, node)) { |
1444 |
< |
node.awaitSyncRelease(this); |
1445 |
< |
break; |
1446 |
< |
} |
1447 |
< |
} |
1448 |
< |
long ec = ensureSync(); |
1449 |
< |
if (ec != prev) { |
1450 |
< |
w.lastEventCount = ec; |
1451 |
< |
break; |
1452 |
< |
} |
1453 |
< |
} |
1454 |
< |
} |
1455 |
< |
|
1456 |
< |
/** |
1457 |
< |
* Returns {@code true} if worker waiting on sync can proceed: |
1458 |
< |
* - on signal (thread == null) |
1459 |
< |
* - on event count advance (winning race to notify vs signaller) |
1460 |
< |
* - on interrupt |
1461 |
< |
* - if the first queued node, we find work available |
1462 |
< |
* If node was not signalled and event count not advanced on exit, |
1463 |
< |
* then we also help advance event count. |
1464 |
< |
* |
1465 |
< |
* @return {@code true} if node can be released |
1466 |
< |
*/ |
1467 |
< |
final boolean syncIsReleasable(WaitQueueNode node) { |
1468 |
< |
long prev = node.count; |
1469 |
< |
if (!Thread.interrupted() && node.thread != null && |
1470 |
< |
(node.next != null || |
1471 |
< |
!ForkJoinWorkerThread.hasQueuedTasks(workers)) && |
1472 |
< |
eventCount == prev) |
1473 |
< |
return false; |
1474 |
< |
if (node.thread != null) { |
1475 |
< |
node.thread = null; |
1476 |
< |
long ec = eventCount; |
1477 |
< |
if (prev <= ec) // help signal |
1478 |
< |
casEventCount(ec, ec+1); |
1479 |
< |
} |
1480 |
< |
return true; |
1481 |
< |
} |
1482 |
< |
|
1483 |
< |
/** |
1484 |
< |
* Returns {@code true} if a new sync event occurred since last |
1485 |
< |
* call to sync or this method, if so, updating caller's count. |
1486 |
< |
*/ |
1487 |
< |
final boolean hasNewSyncEvent(ForkJoinWorkerThread w) { |
1488 |
< |
long lc = w.lastEventCount; |
1489 |
< |
long ec = ensureSync(); |
1490 |
< |
if (ec == lc) |
1714 |
> |
return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0; |
1715 |
> |
} catch (TimeoutException ex) { |
1716 |
|
return false; |
1492 |
– |
w.lastEventCount = ec; |
1493 |
– |
return true; |
1494 |
– |
} |
1495 |
– |
|
1496 |
– |
// Parallelism maintenance |
1497 |
– |
|
1498 |
– |
/** |
1499 |
– |
* Decrements running count; if too low, adds spare. |
1500 |
– |
* |
1501 |
– |
* Conceptually, all we need to do here is add or resume a |
1502 |
– |
* spare thread when one is about to block (and remove or |
1503 |
– |
* suspend it later when unblocked -- see suspendIfSpare). |
1504 |
– |
* However, implementing this idea requires coping with |
1505 |
– |
* several problems: we have imperfect information about the |
1506 |
– |
* states of threads. Some count updates can and usually do |
1507 |
– |
* lag run state changes, despite arrangements to keep them |
1508 |
– |
* accurate (for example, when possible, updating counts |
1509 |
– |
* before signalling or resuming), especially when running on |
1510 |
– |
* dynamic JVMs that don't optimize the infrequent paths that |
1511 |
– |
* update counts. Generating too many threads can make these |
1512 |
– |
* problems become worse, because excess threads are more |
1513 |
– |
* likely to be context-switched with others, slowing them all |
1514 |
– |
* down, especially if there is no work available, so all are |
1515 |
– |
* busy scanning or idling. Also, excess spare threads can |
1516 |
– |
* only be suspended or removed when they are idle, not |
1517 |
– |
* immediately when they aren't needed. So adding threads will |
1518 |
– |
* raise parallelism level for longer than necessary. Also, |
1519 |
– |
* FJ applications often encounter highly transient peaks when |
1520 |
– |
* many threads are blocked joining, but for less time than it |
1521 |
– |
* takes to create or resume spares. |
1522 |
– |
* |
1523 |
– |
* @param joinMe if non-null, return early if done |
1524 |
– |
* @param maintainParallelism if true, try to stay within |
1525 |
– |
* target counts, else create only to avoid starvation |
1526 |
– |
* @return true if joinMe known to be done |
1527 |
– |
*/ |
1528 |
– |
final boolean preJoin(ForkJoinTask<?> joinMe, |
1529 |
– |
boolean maintainParallelism) { |
1530 |
– |
maintainParallelism &= maintainsParallelism; // overrride |
1531 |
– |
boolean dec = false; // true when running count decremented |
1532 |
– |
while (spareStack == null || !tryResumeSpare(dec)) { |
1533 |
– |
int counts = workerCounts; |
1534 |
– |
if (dec || (dec = casWorkerCounts(counts, --counts))) { |
1535 |
– |
// CAS cheat |
1536 |
– |
if (!needSpare(counts, maintainParallelism)) |
1537 |
– |
break; |
1538 |
– |
if (joinMe.status < 0) |
1539 |
– |
return true; |
1540 |
– |
if (tryAddSpare(counts)) |
1541 |
– |
break; |
1542 |
– |
} |
1543 |
– |
} |
1544 |
– |
return false; |
1545 |
– |
} |
1546 |
– |
|
1547 |
– |
/** |
1548 |
– |
* Same idea as preJoin |
1549 |
– |
*/ |
1550 |
– |
final boolean preBlock(ManagedBlocker blocker, |
1551 |
– |
boolean maintainParallelism) { |
1552 |
– |
maintainParallelism &= maintainsParallelism; |
1553 |
– |
boolean dec = false; |
1554 |
– |
while (spareStack == null || !tryResumeSpare(dec)) { |
1555 |
– |
int counts = workerCounts; |
1556 |
– |
if (dec || (dec = casWorkerCounts(counts, --counts))) { |
1557 |
– |
if (!needSpare(counts, maintainParallelism)) |
1558 |
– |
break; |
1559 |
– |
if (blocker.isReleasable()) |
1560 |
– |
return true; |
1561 |
– |
if (tryAddSpare(counts)) |
1562 |
– |
break; |
1563 |
– |
} |
1564 |
– |
} |
1565 |
– |
return false; |
1566 |
– |
} |
1567 |
– |
|
1568 |
– |
/** |
1569 |
– |
* Returns {@code true} if a spare thread appears to be needed. |
1570 |
– |
* If maintaining parallelism, returns true when the deficit in |
1571 |
– |
* running threads is more than the surplus of total threads, and |
1572 |
– |
* there is apparently some work to do. This self-limiting rule |
1573 |
– |
* means that the more threads that have already been added, the |
1574 |
– |
* less parallelism we will tolerate before adding another. |
1575 |
– |
* |
1576 |
– |
* @param counts current worker counts |
1577 |
– |
* @param maintainParallelism try to maintain parallelism |
1578 |
– |
*/ |
1579 |
– |
private boolean needSpare(int counts, boolean maintainParallelism) { |
1580 |
– |
int ps = parallelism; |
1581 |
– |
int rc = runningCountOf(counts); |
1582 |
– |
int tc = totalCountOf(counts); |
1583 |
– |
int runningDeficit = ps - rc; |
1584 |
– |
int totalSurplus = tc - ps; |
1585 |
– |
return (tc < maxPoolSize && |
1586 |
– |
(rc == 0 || totalSurplus < 0 || |
1587 |
– |
(maintainParallelism && |
1588 |
– |
runningDeficit > totalSurplus && |
1589 |
– |
ForkJoinWorkerThread.hasQueuedTasks(workers)))); |
1590 |
– |
} |
1591 |
– |
|
1592 |
– |
/** |
1593 |
– |
* Adds a spare worker if lock available and no more than the |
1594 |
– |
* expected numbers of threads exist. |
1595 |
– |
* |
1596 |
– |
* @return true if successful |
1597 |
– |
*/ |
1598 |
– |
private boolean tryAddSpare(int expectedCounts) { |
1599 |
– |
final ReentrantLock lock = this.workerLock; |
1600 |
– |
int expectedRunning = runningCountOf(expectedCounts); |
1601 |
– |
int expectedTotal = totalCountOf(expectedCounts); |
1602 |
– |
boolean success = false; |
1603 |
– |
boolean locked = false; |
1604 |
– |
// confirm counts while locking; CAS after obtaining lock |
1605 |
– |
try { |
1606 |
– |
for (;;) { |
1607 |
– |
int s = workerCounts; |
1608 |
– |
int tc = totalCountOf(s); |
1609 |
– |
int rc = runningCountOf(s); |
1610 |
– |
if (rc > expectedRunning || tc > expectedTotal) |
1611 |
– |
break; |
1612 |
– |
if (!locked && !(locked = lock.tryLock())) |
1613 |
– |
break; |
1614 |
– |
if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) { |
1615 |
– |
createAndStartSpare(tc); |
1616 |
– |
success = true; |
1617 |
– |
break; |
1618 |
– |
} |
1619 |
– |
} |
1620 |
– |
} finally { |
1621 |
– |
if (locked) |
1622 |
– |
lock.unlock(); |
1623 |
– |
} |
1624 |
– |
return success; |
1625 |
– |
} |
1626 |
– |
|
1627 |
– |
/** |
1628 |
– |
* Adds the kth spare worker. On entry, pool counts are already |
1629 |
– |
* adjusted to reflect addition. |
1630 |
– |
*/ |
1631 |
– |
private void createAndStartSpare(int k) { |
1632 |
– |
ForkJoinWorkerThread w = null; |
1633 |
– |
ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1); |
1634 |
– |
int len = ws.length; |
1635 |
– |
// Probably, we can place at slot k. If not, find empty slot |
1636 |
– |
if (k < len && ws[k] != null) { |
1637 |
– |
for (k = 0; k < len && ws[k] != null; ++k) |
1638 |
– |
; |
1639 |
– |
} |
1640 |
– |
if (k < len && !isTerminating() && (w = createWorker(k)) != null) { |
1641 |
– |
ws[k] = w; |
1642 |
– |
w.start(); |
1643 |
– |
} |
1644 |
– |
else |
1645 |
– |
updateWorkerCount(-1); // adjust on failure |
1646 |
– |
signalIdleWorkers(); |
1647 |
– |
} |
1648 |
– |
|
1649 |
– |
/** |
1650 |
– |
* Suspends calling thread w if there are excess threads. Called |
1651 |
– |
* only from sync. Spares are enqueued in a Treiber stack using |
1652 |
– |
* the same WaitQueueNodes as barriers. They are resumed mainly |
1653 |
– |
* in preJoin, but are also woken on pool events that require all |
1654 |
– |
* threads to check run state. |
1655 |
– |
* |
1656 |
– |
* @param w the caller |
1657 |
– |
*/ |
1658 |
– |
private boolean suspendIfSpare(ForkJoinWorkerThread w) { |
1659 |
– |
WaitQueueNode node = null; |
1660 |
– |
int s; |
1661 |
– |
while (parallelism < runningCountOf(s = workerCounts)) { |
1662 |
– |
if (node == null) |
1663 |
– |
node = new WaitQueueNode(0, w); |
1664 |
– |
if (casWorkerCounts(s, s-1)) { // representation-dependent |
1665 |
– |
// push onto stack |
1666 |
– |
do {} while (!casSpareStack(node.next = spareStack, node)); |
1667 |
– |
// block until released by resumeSpare |
1668 |
– |
node.awaitSpareRelease(); |
1669 |
– |
return true; |
1670 |
– |
} |
1671 |
– |
} |
1672 |
– |
return false; |
1673 |
– |
} |
1674 |
– |
|
1675 |
– |
/** |
1676 |
– |
* Tries to pop and resume a spare thread. |
1677 |
– |
* |
1678 |
– |
* @param updateCount if true, increment running count on success |
1679 |
– |
* @return true if successful |
1680 |
– |
*/ |
1681 |
– |
private boolean tryResumeSpare(boolean updateCount) { |
1682 |
– |
WaitQueueNode q; |
1683 |
– |
while ((q = spareStack) != null) { |
1684 |
– |
if (casSpareStack(q, q.next)) { |
1685 |
– |
if (updateCount) |
1686 |
– |
updateRunningCount(1); |
1687 |
– |
q.signal(); |
1688 |
– |
return true; |
1689 |
– |
} |
1690 |
– |
} |
1691 |
– |
return false; |
1692 |
– |
} |
1693 |
– |
|
1694 |
– |
/** |
1695 |
– |
* Pops and resumes all spare threads. Same idea as ensureSync. |
1696 |
– |
* |
1697 |
– |
* @return true if any spares released |
1698 |
– |
*/ |
1699 |
– |
private boolean resumeAllSpares() { |
1700 |
– |
WaitQueueNode q; |
1701 |
– |
while ( (q = spareStack) != null) { |
1702 |
– |
if (casSpareStack(q, null)) { |
1703 |
– |
do { |
1704 |
– |
updateRunningCount(1); |
1705 |
– |
q.signal(); |
1706 |
– |
} while ((q = q.next) != null); |
1707 |
– |
return true; |
1708 |
– |
} |
1709 |
– |
} |
1710 |
– |
return false; |
1711 |
– |
} |
1712 |
– |
|
1713 |
– |
/** |
1714 |
– |
* Pops and shuts down excessive spare threads. Call only while |
1715 |
– |
* holding lock. This is not guaranteed to eliminate all excess |
1716 |
– |
* threads, only those suspended as spares, which are the ones |
1717 |
– |
* unlikely to be needed in the future. |
1718 |
– |
*/ |
1719 |
– |
private void trimSpares() { |
1720 |
– |
int surplus = totalCountOf(workerCounts) - parallelism; |
1721 |
– |
WaitQueueNode q; |
1722 |
– |
while (surplus > 0 && (q = spareStack) != null) { |
1723 |
– |
if (casSpareStack(q, null)) { |
1724 |
– |
do { |
1725 |
– |
updateRunningCount(1); |
1726 |
– |
ForkJoinWorkerThread w = q.thread; |
1727 |
– |
if (w != null && surplus > 0 && |
1728 |
– |
runningCountOf(workerCounts) > 0 && w.shutdown()) |
1729 |
– |
--surplus; |
1730 |
– |
q.signal(); |
1731 |
– |
} while ((q = q.next) != null); |
1732 |
– |
} |
1717 |
|
} |
1718 |
|
} |
1719 |
|
|
1721 |
|
* Interface for extending managed parallelism for tasks running |
1722 |
|
* in {@link ForkJoinPool}s. |
1723 |
|
* |
1724 |
< |
* <p>A {@code ManagedBlocker} provides two methods. |
1725 |
< |
* Method {@code isReleasable} must return {@code true} if |
1726 |
< |
* blocking is not necessary. Method {@code block} blocks the |
1727 |
< |
* current thread if necessary (perhaps internally invoking |
1728 |
< |
* {@code isReleasable} before actually blocking.). |
1724 |
> |
* <p>A {@code ManagedBlocker} provides two methods. Method |
1725 |
> |
* {@code isReleasable} must return {@code true} if blocking is |
1726 |
> |
* not necessary. Method {@code block} blocks the current thread |
1727 |
> |
* if necessary (perhaps internally invoking {@code isReleasable} |
1728 |
> |
* before actually blocking). The unusual methods in this API |
1729 |
> |
* accommodate synchronizers that may, but don't usually, block |
1730 |
> |
* for long periods. Similarly, they allow more efficient internal |
1731 |
> |
* handling of cases in which additional workers may be, but |
1732 |
> |
* usually are not, needed to ensure sufficient parallelism. |
1733 |
> |
* Toward this end, implementations of method {@code isReleasable} |
1734 |
> |
* must be amenable to repeated invocation. |
1735 |
|
* |
1736 |
|
* <p>For example, here is a ManagedBlocker based on a |
1737 |
|
* ReentrantLock: |
1749 |
|
* return hasLock || (hasLock = lock.tryLock()); |
1750 |
|
* } |
1751 |
|
* }}</pre> |
1752 |
+ |
* |
1753 |
+ |
* <p>Here is a class that possibly blocks waiting for an |
1754 |
+ |
* item on a given queue: |
1755 |
+ |
* <pre> {@code |
1756 |
+ |
* class QueueTaker<E> implements ManagedBlocker { |
1757 |
+ |
* final BlockingQueue<E> queue; |
1758 |
+ |
* volatile E item = null; |
1759 |
+ |
* QueueTaker(BlockingQueue<E> q) { this.queue = q; } |
1760 |
+ |
* public boolean block() throws InterruptedException { |
1761 |
+ |
* if (item == null) |
1762 |
+ |
* item = queue.take(); |
1763 |
+ |
* return true; |
1764 |
+ |
* } |
1765 |
+ |
* public boolean isReleasable() { |
1766 |
+ |
* return item != null || (item = queue.poll()) != null; |
1767 |
+ |
* } |
1768 |
+ |
* public E getItem() { // call after pool.managedBlock completes |
1769 |
+ |
* return item; |
1770 |
+ |
* } |
1771 |
+ |
* }}</pre> |
1772 |
|
*/ |
1773 |
|
public static interface ManagedBlocker { |
1774 |
|
/** |
1790 |
|
|
1791 |
|
/** |
1792 |
|
* Blocks in accord with the given blocker. If the current thread |
1793 |
< |
* is a ForkJoinWorkerThread, this method possibly arranges for a |
1794 |
< |
* spare thread to be activated if necessary to ensure parallelism |
1795 |
< |
* while the current thread is blocked. If |
1786 |
< |
* {@code maintainParallelism} is {@code true} and the pool supports |
1787 |
< |
* it ({@link #getMaintainsParallelism}), this method attempts to |
1788 |
< |
* maintain the pool's nominal parallelism. Otherwise it activates |
1789 |
< |
* a thread only if necessary to avoid complete starvation. This |
1790 |
< |
* option may be preferable when blockages use timeouts, or are |
1791 |
< |
* almost always brief. |
1793 |
> |
* is a {@link ForkJoinWorkerThread}, this method possibly |
1794 |
> |
* arranges for a spare thread to be activated if necessary to |
1795 |
> |
* ensure sufficient parallelism while the current thread is blocked. |
1796 |
|
* |
1797 |
< |
* <p> If the caller is not a ForkJoinTask, this method is behaviorally |
1798 |
< |
* equivalent to |
1797 |
> |
* <p>If the caller is not a {@link ForkJoinTask}, this method is |
1798 |
> |
* behaviorally equivalent to |
1799 |
|
* <pre> {@code |
1800 |
|
* while (!blocker.isReleasable()) |
1801 |
|
* if (blocker.block()) |
1802 |
|
* return; |
1803 |
|
* }</pre> |
1804 |
< |
* If the caller is a ForkJoinTask, then the pool may first |
1805 |
< |
* be expanded to ensure parallelism, and later adjusted. |
1804 |
> |
* |
1805 |
> |
* If the caller is a {@code ForkJoinTask}, then the pool may |
1806 |
> |
* first be expanded to ensure parallelism, and later adjusted. |
1807 |
|
* |
1808 |
|
* @param blocker the blocker |
1804 |
– |
* @param maintainParallelism if {@code true} and supported by |
1805 |
– |
* this pool, attempt to maintain the pool's nominal parallelism; |
1806 |
– |
* otherwise activate a thread only if necessary to avoid |
1807 |
– |
* complete starvation. |
1809 |
|
* @throws InterruptedException if blocker.block did so |
1810 |
|
*/ |
1811 |
< |
public static void managedBlock(ManagedBlocker blocker, |
1811 |
< |
boolean maintainParallelism) |
1811 |
> |
public static void managedBlock(ManagedBlocker blocker) |
1812 |
|
throws InterruptedException { |
1813 |
|
Thread t = Thread.currentThread(); |
1814 |
< |
ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ? |
1815 |
< |
((ForkJoinWorkerThread) t).pool : null); |
1816 |
< |
if (!blocker.isReleasable()) { |
1817 |
< |
try { |
1818 |
< |
if (pool == null || |
1819 |
< |
!pool.preBlock(blocker, maintainParallelism)) |
1820 |
< |
awaitBlocker(blocker); |
1821 |
< |
} finally { |
1822 |
< |
if (pool != null) |
1823 |
< |
pool.updateRunningCount(1); |
1824 |
< |
} |
1814 |
> |
if (t instanceof ForkJoinWorkerThread) { |
1815 |
> |
ForkJoinWorkerThread w = (ForkJoinWorkerThread) t; |
1816 |
> |
w.pool.awaitBlocker(blocker); |
1817 |
> |
} |
1818 |
> |
else { |
1819 |
> |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1820 |
|
} |
1826 |
– |
} |
1827 |
– |
|
1828 |
– |
private static void awaitBlocker(ManagedBlocker blocker) |
1829 |
– |
throws InterruptedException { |
1830 |
– |
do {} while (!blocker.isReleasable() && !blocker.block()); |
1821 |
|
} |
1822 |
|
|
1823 |
|
// AbstractExecutorService overrides. These rely on undocumented |
1835 |
|
// Unsafe mechanics |
1836 |
|
|
1837 |
|
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
1848 |
– |
private static final long eventCountOffset = |
1849 |
– |
objectFieldOffset("eventCount", ForkJoinPool.class); |
1838 |
|
private static final long workerCountsOffset = |
1839 |
|
objectFieldOffset("workerCounts", ForkJoinPool.class); |
1840 |
< |
private static final long runControlOffset = |
1841 |
< |
objectFieldOffset("runControl", ForkJoinPool.class); |
1842 |
< |
private static final long syncStackOffset = |
1843 |
< |
objectFieldOffset("syncStack",ForkJoinPool.class); |
1844 |
< |
private static final long spareStackOffset = |
1845 |
< |
objectFieldOffset("spareStack", ForkJoinPool.class); |
1846 |
< |
|
1847 |
< |
private boolean casEventCount(long cmp, long val) { |
1848 |
< |
return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val); |
1849 |
< |
} |
1862 |
< |
private boolean casWorkerCounts(int cmp, int val) { |
1863 |
< |
return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val); |
1864 |
< |
} |
1865 |
< |
private boolean casRunControl(int cmp, int val) { |
1866 |
< |
return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val); |
1867 |
< |
} |
1868 |
< |
private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) { |
1869 |
< |
return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val); |
1870 |
< |
} |
1871 |
< |
private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { |
1872 |
< |
return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val); |
1873 |
< |
} |
1840 |
> |
private static final long runStateOffset = |
1841 |
> |
objectFieldOffset("runState", ForkJoinPool.class); |
1842 |
> |
private static final long eventCountOffset = |
1843 |
> |
objectFieldOffset("eventCount", ForkJoinPool.class); |
1844 |
> |
private static final long eventWaitersOffset = |
1845 |
> |
objectFieldOffset("eventWaiters",ForkJoinPool.class); |
1846 |
> |
private static final long stealCountOffset = |
1847 |
> |
objectFieldOffset("stealCount",ForkJoinPool.class); |
1848 |
> |
private static final long spareWaitersOffset = |
1849 |
> |
objectFieldOffset("spareWaiters",ForkJoinPool.class); |
1850 |
|
|
1851 |
|
private static long objectFieldOffset(String field, Class<?> klazz) { |
1852 |
|
try { |