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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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|
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package jsr166y; |
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import java.util.*; |
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import java.util.concurrent.*; |
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import java.util.concurrent.locks.*; |
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import java.util.concurrent.atomic.*; |
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import sun.misc.Unsafe; |
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import java.lang.reflect.*; |
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|
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/** |
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* An {@link ExecutorService} for running {@link ForkJoinTask}s. A |
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* 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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* |
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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 |
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* <tt>setAsyncMode</tt>, a ForkJoinPools may also be appropriate for |
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* use with fine-grained tasks that are never joined. Otherwise, other |
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* ExecutorService implementations are typically more appropriate |
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* choices. |
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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 <code>ManagedBlocker</code> 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 (<code>setParallelism</code>) |
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* and thread construction can be limited using methods |
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* <code>setMaximumPoolSize</code> and/or |
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* <code>setMaintainsParallelism</code>. |
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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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* <code>getStealCount</code>) that are intended to aid in developing, |
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* tuning, and monitoring fork/join applications. Also, method |
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* <code>toString</code> 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><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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*/ |
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public class ForkJoinPool extends AbstractExecutorService { |
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|
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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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*/ |
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|
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/** Mask for packing and unpacking shorts */ |
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private static final int shortMask = 0xffff; |
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|
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/** Max pool size -- must be a power of two minus 1 */ |
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private static final int MAX_THREADS = 0x7FFF; |
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|
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/** |
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* Factory for creating new ForkJoinWorkerThreads. A |
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* ForkJoinWorkerThreadFactory must be defined and used for |
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* ForkJoinWorkerThread subclasses that extend base functionality |
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* or initialize threads with different contexts. |
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*/ |
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public static interface ForkJoinWorkerThreadFactory { |
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/** |
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* Returns a new worker thread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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* @throws NullPointerException if pool is null; |
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*/ |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool); |
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} |
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|
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/** |
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* Default ForkJoinWorkerThreadFactory implementation, creates a |
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* new ForkJoinWorkerThread. |
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*/ |
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static class DefaultForkJoinWorkerThreadFactory |
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implements ForkJoinWorkerThreadFactory { |
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public ForkJoinWorkerThread newThread(ForkJoinPool pool) { |
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try { |
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return new ForkJoinWorkerThread(pool); |
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} catch (OutOfMemoryError oom) { |
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return null; |
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} |
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} |
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} |
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|
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/** |
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* Creates a new ForkJoinWorkerThread. This factory is used unless |
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* overridden in ForkJoinPool constructors. |
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*/ |
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public static final ForkJoinWorkerThreadFactory |
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defaultForkJoinWorkerThreadFactory = |
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new DefaultForkJoinWorkerThreadFactory(); |
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|
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/** |
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* Permission required for callers of methods that may start or |
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* kill threads. |
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*/ |
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private static final RuntimePermission modifyThreadPermission = |
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new RuntimePermission("modifyThread"); |
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|
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/** |
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* If there is a security manager, makes sure caller has |
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* permission to modify threads. |
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*/ |
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private static void checkPermission() { |
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SecurityManager security = System.getSecurityManager(); |
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if (security != null) |
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security.checkPermission(modifyThreadPermission); |
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} |
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|
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/** |
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* Generator for assigning sequence numbers as pool names. |
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*/ |
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private static final AtomicInteger poolNumberGenerator = |
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new AtomicInteger(); |
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|
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/** |
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* Array holding all worker threads in the pool. Initialized upon |
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* first use. Array size must be a power of two. Updates and |
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* replacements are protected by workerLock, but it is always kept |
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* in a consistent enough state to be randomly accessed without |
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* locking by workers performing work-stealing. |
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*/ |
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volatile ForkJoinWorkerThread[] workers; |
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|
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/** |
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* Lock protecting access to workers. |
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*/ |
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private final ReentrantLock workerLock; |
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|
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/** |
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* Condition for awaitTermination. |
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*/ |
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private final Condition termination; |
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|
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/** |
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* The uncaught exception handler used when any worker |
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* abrupty terminates |
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*/ |
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private Thread.UncaughtExceptionHandler ueh; |
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|
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/** |
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* Creation factory for worker threads. |
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*/ |
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private final ForkJoinWorkerThreadFactory factory; |
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|
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/** |
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* Head of stack of threads that were created to maintain |
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* parallelism when other threads blocked, but have since |
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* suspended when the parallelism level rose. |
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*/ |
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private volatile WaitQueueNode spareStack; |
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|
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/** |
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* Sum of per-thread steal counts, updated only when threads are |
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* idle or terminating. |
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*/ |
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private final AtomicLong stealCount; |
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|
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/** |
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* Queue for external submissions. |
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*/ |
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private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue; |
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|
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/** |
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* Head of Treiber stack for barrier sync. See below for explanation |
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*/ |
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private volatile WaitQueueNode syncStack; |
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|
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/** |
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* The count for event barrier |
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*/ |
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private volatile long eventCount; |
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|
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/** |
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* Pool number, just for assigning useful names to worker threads |
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*/ |
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private final int poolNumber; |
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|
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/** |
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* The maximum allowed pool size |
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*/ |
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private volatile int maxPoolSize; |
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|
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/** |
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* The desired parallelism level, updated only under workerLock. |
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*/ |
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private volatile int parallelism; |
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|
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/** |
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* True if use local fifo, not default lifo, for local polling |
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*/ |
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private volatile boolean locallyFifo; |
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|
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/** |
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* Holds number of total (i.e., created and not yet terminated) |
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* and running (i.e., not blocked on joins or other managed sync) |
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* threads, packed into one int to ensure consistent snapshot when |
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* making decisions about creating and suspending spare |
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* threads. Updated only by CAS. Note: CASes in |
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* updateRunningCount and preJoin assume that running active count |
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* is in low word, so need to be modified if this changes |
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*/ |
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private volatile int workerCounts; |
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|
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private static int totalCountOf(int s) { return s >>> 16; } |
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private static int runningCountOf(int s) { return s & shortMask; } |
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private static int workerCountsFor(int t, int r) { return (t << 16) + r; } |
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|
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/** |
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* Add delta (which may be negative) to running count. This must |
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* be called before (with negative arg) and after (with positive) |
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* any managed synchronization (i.e., mainly, joins) |
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* @param delta the number to add |
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*/ |
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final void updateRunningCount(int delta) { |
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int s; |
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do;while (!casWorkerCounts(s = workerCounts, s + delta)); |
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} |
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|
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/** |
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* Add delta (which may be negative) to both total and running |
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* count. This must be called upon creation and termination of |
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* worker threads. |
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* @param delta the number to add |
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*/ |
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private void updateWorkerCount(int delta) { |
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int d = delta + (delta << 16); // add to both lo and hi parts |
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int s; |
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do;while (!casWorkerCounts(s = workerCounts, s + d)); |
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} |
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|
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/** |
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* Lifecycle control. High word contains runState, low word |
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* contains the number of workers that are (probably) executing |
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* tasks. This value is atomically incremented before a worker |
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* gets a task to run, and decremented when worker has no tasks |
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* and cannot find any. These two fields are bundled together to |
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* support correct termination triggering. Note: activeCount |
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* CAS'es cheat by assuming active count is in low word, so need |
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* to be modified if this changes |
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*/ |
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private volatile int runControl; |
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|
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// RunState values. Order among values matters |
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private static final int RUNNING = 0; |
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private static final int SHUTDOWN = 1; |
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private static final int TERMINATING = 2; |
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private static final int TERMINATED = 3; |
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|
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private static int runStateOf(int c) { return c >>> 16; } |
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private static int activeCountOf(int c) { return c & shortMask; } |
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private static int runControlFor(int r, int a) { return (r << 16) + a; } |
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|
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/** |
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* Try incrementing active count; fail on contention. Called by |
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* workers before/during executing tasks. |
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* @return true on success; |
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*/ |
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final boolean tryIncrementActiveCount() { |
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int c = runControl; |
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return casRunControl(c, c+1); |
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} |
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|
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/** |
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* Try decrementing active count; fail on contention. |
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* Possibly trigger termination on success |
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* Called by workers when they can't find tasks. |
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* @return true on success |
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*/ |
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final boolean tryDecrementActiveCount() { |
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int c = runControl; |
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int nextc = c - 1; |
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if (!casRunControl(c, nextc)) |
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return false; |
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if (canTerminateOnShutdown(nextc)) |
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terminateOnShutdown(); |
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return true; |
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} |
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|
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/** |
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* Return true if argument represents zero active count and |
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* nonzero runstate, which is the triggering condition for |
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* terminating on shutdown. |
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*/ |
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private static boolean canTerminateOnShutdown(int c) { |
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return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit |
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} |
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|
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/** |
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* Transition run state to at least the given state. Return true |
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* if not already at least given state. |
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*/ |
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private boolean transitionRunStateTo(int state) { |
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for (;;) { |
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int c = runControl; |
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if (runStateOf(c) >= state) |
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return false; |
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if (casRunControl(c, runControlFor(state, activeCountOf(c)))) |
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return true; |
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} |
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} |
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|
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/** |
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* Controls whether to add spares to maintain parallelism |
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*/ |
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private volatile boolean maintainsParallelism; |
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|
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// Constructors |
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|
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/** |
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* Creates a ForkJoinPool with a pool size equal to the number of |
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* processors available on the system and using the default |
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* ForkJoinWorkerThreadFactory, |
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* @throws SecurityException if a security manager exists and |
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* the caller is not permitted to modify threads |
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* because it does not hold {@link |
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* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
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*/ |
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public ForkJoinPool() { |
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this(Runtime.getRuntime().availableProcessors(), |
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defaultForkJoinWorkerThreadFactory); |
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} |
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|
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/** |
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* Creates a ForkJoinPool with the indicated parellelism level |
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* threads, and using the default ForkJoinWorkerThreadFactory, |
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* @param parallelism the number of worker threads |
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* @throws IllegalArgumentException if parallelism less than or |
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* equal to zero |
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* @throws SecurityException if a security manager exists and |
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* the caller is not permitted to modify threads |
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* because it does not hold {@link |
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* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
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*/ |
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public ForkJoinPool(int parallelism) { |
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this(parallelism, defaultForkJoinWorkerThreadFactory); |
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} |
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|
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/** |
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* Creates a ForkJoinPool with parallelism equal to the number of |
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* processors available on the system and using the given |
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* ForkJoinWorkerThreadFactory, |
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* @param factory the factory for creating new threads |
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* @throws NullPointerException if factory is null |
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* @throws SecurityException if a security manager exists and |
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* the caller is not permitted to modify threads |
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* because it does not hold {@link |
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* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
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*/ |
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public ForkJoinPool(ForkJoinWorkerThreadFactory factory) { |
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this(Runtime.getRuntime().availableProcessors(), factory); |
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} |
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|
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/** |
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* Creates a ForkJoinPool with the given parallelism and factory. |
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* |
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* @param parallelism the targeted number of worker threads |
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* @param factory the factory for creating new threads |
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* @throws IllegalArgumentException if parallelism less than or |
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* equal to zero, or greater than implementation limit. |
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* @throws NullPointerException if factory is null |
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* @throws SecurityException if a security manager exists and |
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* the caller is not permitted to modify threads |
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* because it does not hold {@link |
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* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
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*/ |
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public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) { |
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if (parallelism <= 0 || parallelism > MAX_THREADS) |
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throw new IllegalArgumentException(); |
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if (factory == null) |
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throw new NullPointerException(); |
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checkPermission(); |
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this.factory = factory; |
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this.parallelism = parallelism; |
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this.maxPoolSize = MAX_THREADS; |
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this.maintainsParallelism = true; |
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this.poolNumber = poolNumberGenerator.incrementAndGet(); |
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this.workerLock = new ReentrantLock(); |
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this.termination = workerLock.newCondition(); |
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this.stealCount = new AtomicLong(); |
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this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>(); |
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// worker array and workers are lazily constructed |
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} |
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|
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/** |
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* Create new worker using factory. |
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* @param index the index to assign worker |
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* @return new worker, or null of factory failed |
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*/ |
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private ForkJoinWorkerThread createWorker(int index) { |
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Thread.UncaughtExceptionHandler h = ueh; |
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ForkJoinWorkerThread w = factory.newThread(this); |
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if (w != null) { |
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w.poolIndex = index; |
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w.setDaemon(true); |
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w.setAsyncMode(locallyFifo); |
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w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index); |
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if (h != null) |
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w.setUncaughtExceptionHandler(h); |
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} |
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return w; |
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} |
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|
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/** |
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* Return a good size for worker array given pool size. |
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* Currently requires size to be a power of two. |
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*/ |
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private static int arraySizeFor(int ps) { |
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return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1))); |
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} |
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|
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/** |
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* Create or resize array if necessary to hold newLength. |
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* Call only under exclusion |
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* @return the array |
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*/ |
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private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) { |
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ForkJoinWorkerThread[] ws = workers; |
438 |
if (ws == null) |
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return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)]; |
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else if (newLength > ws.length) |
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return workers = Arrays.copyOf(ws, arraySizeFor(newLength)); |
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else |
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return ws; |
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} |
445 |
|
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/** |
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* Try to shrink workers into smaller array after one or more terminate |
448 |
*/ |
449 |
private void tryShrinkWorkerArray() { |
450 |
ForkJoinWorkerThread[] ws = workers; |
451 |
if (ws != null) { |
452 |
int len = ws.length; |
453 |
int last = len - 1; |
454 |
while (last >= 0 && ws[last] == null) |
455 |
--last; |
456 |
int newLength = arraySizeFor(last+1); |
457 |
if (newLength < len) |
458 |
workers = Arrays.copyOf(ws, newLength); |
459 |
} |
460 |
} |
461 |
|
462 |
/** |
463 |
* Initialize workers if necessary |
464 |
*/ |
465 |
final void ensureWorkerInitialization() { |
466 |
ForkJoinWorkerThread[] ws = workers; |
467 |
if (ws == null) { |
468 |
final ReentrantLock lock = this.workerLock; |
469 |
lock.lock(); |
470 |
try { |
471 |
ws = workers; |
472 |
if (ws == null) { |
473 |
int ps = parallelism; |
474 |
ws = ensureWorkerArrayCapacity(ps); |
475 |
for (int i = 0; i < ps; ++i) { |
476 |
ForkJoinWorkerThread w = createWorker(i); |
477 |
if (w != null) { |
478 |
ws[i] = w; |
479 |
w.start(); |
480 |
updateWorkerCount(1); |
481 |
} |
482 |
} |
483 |
} |
484 |
} finally { |
485 |
lock.unlock(); |
486 |
} |
487 |
} |
488 |
} |
489 |
|
490 |
/** |
491 |
* Worker creation and startup for threads added via setParallelism. |
492 |
*/ |
493 |
private void createAndStartAddedWorkers() { |
494 |
resumeAllSpares(); // Allow spares to convert to nonspare |
495 |
int ps = parallelism; |
496 |
ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps); |
497 |
int len = ws.length; |
498 |
// Sweep through slots, to keep lowest indices most populated |
499 |
int k = 0; |
500 |
while (k < len) { |
501 |
if (ws[k] != null) { |
502 |
++k; |
503 |
continue; |
504 |
} |
505 |
int s = workerCounts; |
506 |
int tc = totalCountOf(s); |
507 |
int rc = runningCountOf(s); |
508 |
if (rc >= ps || tc >= ps) |
509 |
break; |
510 |
if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) { |
511 |
ForkJoinWorkerThread w = createWorker(k); |
512 |
if (w != null) { |
513 |
ws[k++] = w; |
514 |
w.start(); |
515 |
} |
516 |
else { |
517 |
updateWorkerCount(-1); // back out on failed creation |
518 |
break; |
519 |
} |
520 |
} |
521 |
} |
522 |
} |
523 |
|
524 |
// Execution methods |
525 |
|
526 |
/** |
527 |
* Common code for execute, invoke and submit |
528 |
*/ |
529 |
private <T> void doSubmit(ForkJoinTask<T> task) { |
530 |
if (isShutdown()) |
531 |
throw new RejectedExecutionException(); |
532 |
if (workers == null) |
533 |
ensureWorkerInitialization(); |
534 |
submissionQueue.offer(task); |
535 |
signalIdleWorkers(); |
536 |
} |
537 |
|
538 |
/** |
539 |
* Performs the given task; returning its result upon completion |
540 |
* @param task the task |
541 |
* @return the task's result |
542 |
* @throws NullPointerException if task is null |
543 |
* @throws RejectedExecutionException if pool is shut down |
544 |
*/ |
545 |
public <T> T invoke(ForkJoinTask<T> task) { |
546 |
doSubmit(task); |
547 |
return task.join(); |
548 |
} |
549 |
|
550 |
/** |
551 |
* Arranges for (asynchronous) execution of the given task. |
552 |
* @param task the task |
553 |
* @throws NullPointerException if task is null |
554 |
* @throws RejectedExecutionException if pool is shut down |
555 |
*/ |
556 |
public <T> void execute(ForkJoinTask<T> task) { |
557 |
doSubmit(task); |
558 |
} |
559 |
|
560 |
// AbstractExecutorService methods |
561 |
|
562 |
public void execute(Runnable task) { |
563 |
doSubmit(new AdaptedRunnable<Void>(task, null)); |
564 |
} |
565 |
|
566 |
public <T> ForkJoinTask<T> submit(Callable<T> task) { |
567 |
ForkJoinTask<T> job = new AdaptedCallable<T>(task); |
568 |
doSubmit(job); |
569 |
return job; |
570 |
} |
571 |
|
572 |
public <T> ForkJoinTask<T> submit(Runnable task, T result) { |
573 |
ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result); |
574 |
doSubmit(job); |
575 |
return job; |
576 |
} |
577 |
|
578 |
public ForkJoinTask<?> submit(Runnable task) { |
579 |
ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null); |
580 |
doSubmit(job); |
581 |
return job; |
582 |
} |
583 |
|
584 |
/** |
585 |
* Adaptor for Runnables. This implements RunnableFuture |
586 |
* to be compliant with AbstractExecutorService constraints |
587 |
*/ |
588 |
static final class AdaptedRunnable<T> extends ForkJoinTask<T> |
589 |
implements RunnableFuture<T> { |
590 |
final Runnable runnable; |
591 |
final T resultOnCompletion; |
592 |
T result; |
593 |
AdaptedRunnable(Runnable runnable, T result) { |
594 |
if (runnable == null) throw new NullPointerException(); |
595 |
this.runnable = runnable; |
596 |
this.resultOnCompletion = result; |
597 |
} |
598 |
public T getRawResult() { return result; } |
599 |
public void setRawResult(T v) { result = v; } |
600 |
public boolean exec() { |
601 |
runnable.run(); |
602 |
result = resultOnCompletion; |
603 |
return true; |
604 |
} |
605 |
public void run() { invoke(); } |
606 |
} |
607 |
|
608 |
/** |
609 |
* Adaptor for Callables |
610 |
*/ |
611 |
static final class AdaptedCallable<T> extends ForkJoinTask<T> |
612 |
implements RunnableFuture<T> { |
613 |
final Callable<T> callable; |
614 |
T result; |
615 |
AdaptedCallable(Callable<T> callable) { |
616 |
if (callable == null) throw new NullPointerException(); |
617 |
this.callable = callable; |
618 |
} |
619 |
public T getRawResult() { return result; } |
620 |
public void setRawResult(T v) { result = v; } |
621 |
public boolean exec() { |
622 |
try { |
623 |
result = callable.call(); |
624 |
return true; |
625 |
} catch (Error err) { |
626 |
throw err; |
627 |
} catch (RuntimeException rex) { |
628 |
throw rex; |
629 |
} catch (Exception ex) { |
630 |
throw new RuntimeException(ex); |
631 |
} |
632 |
} |
633 |
public void run() { invoke(); } |
634 |
} |
635 |
|
636 |
public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) { |
637 |
ArrayList<ForkJoinTask<T>> ts = |
638 |
new ArrayList<ForkJoinTask<T>>(tasks.size()); |
639 |
for (Callable<T> c : tasks) |
640 |
ts.add(new AdaptedCallable<T>(c)); |
641 |
invoke(new InvokeAll<T>(ts)); |
642 |
return (List<Future<T>>)(List)ts; |
643 |
} |
644 |
|
645 |
static final class InvokeAll<T> extends RecursiveAction { |
646 |
final ArrayList<ForkJoinTask<T>> tasks; |
647 |
InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; } |
648 |
public void compute() { |
649 |
try { invokeAll(tasks); } catch(Exception ignore) {} |
650 |
} |
651 |
} |
652 |
|
653 |
// Configuration and status settings and queries |
654 |
|
655 |
/** |
656 |
* Returns the factory used for constructing new workers |
657 |
* |
658 |
* @return the factory used for constructing new workers |
659 |
*/ |
660 |
public ForkJoinWorkerThreadFactory getFactory() { |
661 |
return factory; |
662 |
} |
663 |
|
664 |
/** |
665 |
* Returns the handler for internal worker threads that terminate |
666 |
* due to unrecoverable errors encountered while executing tasks. |
667 |
* @return the handler, or null if none |
668 |
*/ |
669 |
public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { |
670 |
Thread.UncaughtExceptionHandler h; |
671 |
final ReentrantLock lock = this.workerLock; |
672 |
lock.lock(); |
673 |
try { |
674 |
h = ueh; |
675 |
} finally { |
676 |
lock.unlock(); |
677 |
} |
678 |
return h; |
679 |
} |
680 |
|
681 |
/** |
682 |
* Sets the handler for internal worker threads that terminate due |
683 |
* to unrecoverable errors encountered while executing tasks. |
684 |
* Unless set, the current default or ThreadGroup handler is used |
685 |
* as handler. |
686 |
* |
687 |
* @param h the new handler |
688 |
* @return the old handler, or null if none |
689 |
* @throws SecurityException if a security manager exists and |
690 |
* the caller is not permitted to modify threads |
691 |
* because it does not hold {@link |
692 |
* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
693 |
*/ |
694 |
public Thread.UncaughtExceptionHandler |
695 |
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) { |
696 |
checkPermission(); |
697 |
Thread.UncaughtExceptionHandler old = null; |
698 |
final ReentrantLock lock = this.workerLock; |
699 |
lock.lock(); |
700 |
try { |
701 |
old = ueh; |
702 |
ueh = h; |
703 |
ForkJoinWorkerThread[] ws = workers; |
704 |
if (ws != null) { |
705 |
for (int i = 0; i < ws.length; ++i) { |
706 |
ForkJoinWorkerThread w = ws[i]; |
707 |
if (w != null) |
708 |
w.setUncaughtExceptionHandler(h); |
709 |
} |
710 |
} |
711 |
} finally { |
712 |
lock.unlock(); |
713 |
} |
714 |
return old; |
715 |
} |
716 |
|
717 |
|
718 |
/** |
719 |
* Sets the target paralleism level of this pool. |
720 |
* @param parallelism the target parallelism |
721 |
* @throws IllegalArgumentException if parallelism less than or |
722 |
* equal to zero or greater than maximum size bounds. |
723 |
* @throws SecurityException if a security manager exists and |
724 |
* the caller is not permitted to modify threads |
725 |
* because it does not hold {@link |
726 |
* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
727 |
*/ |
728 |
public void setParallelism(int parallelism) { |
729 |
checkPermission(); |
730 |
if (parallelism <= 0 || parallelism > maxPoolSize) |
731 |
throw new IllegalArgumentException(); |
732 |
final ReentrantLock lock = this.workerLock; |
733 |
lock.lock(); |
734 |
try { |
735 |
if (!isTerminating()) { |
736 |
int p = this.parallelism; |
737 |
this.parallelism = parallelism; |
738 |
if (parallelism > p) |
739 |
createAndStartAddedWorkers(); |
740 |
else |
741 |
trimSpares(); |
742 |
} |
743 |
} finally { |
744 |
lock.unlock(); |
745 |
} |
746 |
signalIdleWorkers(); |
747 |
} |
748 |
|
749 |
/** |
750 |
* Returns the targeted number of worker threads in this pool. |
751 |
* |
752 |
* @return the targeted number of worker threads in this pool |
753 |
*/ |
754 |
public int getParallelism() { |
755 |
return parallelism; |
756 |
} |
757 |
|
758 |
/** |
759 |
* Returns the number of worker threads that have started but not |
760 |
* yet terminated. This result returned by this method may differ |
761 |
* from <code>getParallelism</code> when threads are created to |
762 |
* maintain parallelism when others are cooperatively blocked. |
763 |
* |
764 |
* @return the number of worker threads |
765 |
*/ |
766 |
public int getPoolSize() { |
767 |
return totalCountOf(workerCounts); |
768 |
} |
769 |
|
770 |
/** |
771 |
* Returns the maximum number of threads allowed to exist in the |
772 |
* pool, even if there are insufficient unblocked running threads. |
773 |
* @return the maximum |
774 |
*/ |
775 |
public int getMaximumPoolSize() { |
776 |
return maxPoolSize; |
777 |
} |
778 |
|
779 |
/** |
780 |
* Sets the maximum number of threads allowed to exist in the |
781 |
* pool, even if there are insufficient unblocked running threads. |
782 |
* Setting this value has no effect on current pool size. It |
783 |
* controls construction of new threads. |
784 |
* @throws IllegalArgumentException if negative or greater then |
785 |
* internal implementation limit. |
786 |
*/ |
787 |
public void setMaximumPoolSize(int newMax) { |
788 |
if (newMax < 0 || newMax > MAX_THREADS) |
789 |
throw new IllegalArgumentException(); |
790 |
maxPoolSize = newMax; |
791 |
} |
792 |
|
793 |
|
794 |
/** |
795 |
* Returns true if this pool dynamically maintains its target |
796 |
* parallelism level. If false, new threads are added only to |
797 |
* avoid possible starvation. |
798 |
* This setting is by default true; |
799 |
* @return true if maintains parallelism |
800 |
*/ |
801 |
public boolean getMaintainsParallelism() { |
802 |
return maintainsParallelism; |
803 |
} |
804 |
|
805 |
/** |
806 |
* Sets whether this pool dynamically maintains its target |
807 |
* parallelism level. If false, new threads are added only to |
808 |
* avoid possible starvation. |
809 |
* @param enable true to maintains parallelism |
810 |
*/ |
811 |
public void setMaintainsParallelism(boolean enable) { |
812 |
maintainsParallelism = enable; |
813 |
} |
814 |
|
815 |
/** |
816 |
* Establishes local first-in-first-out scheduling mode for forked |
817 |
* tasks that are never joined. This mode may be more appropriate |
818 |
* than default locally stack-based mode in applications in which |
819 |
* worker threads only process asynchronous tasks. This method is |
820 |
* designed to be invoked only when pool is quiescent, and |
821 |
* typically only before any tasks are submitted. The effects of |
822 |
* invocations at ather times may be unpredictable. |
823 |
* |
824 |
* @param async if true, use locally FIFO scheduling |
825 |
* @return the previous mode. |
826 |
*/ |
827 |
public boolean setAsyncMode(boolean async) { |
828 |
boolean oldMode = locallyFifo; |
829 |
locallyFifo = async; |
830 |
ForkJoinWorkerThread[] ws = workers; |
831 |
if (ws != null) { |
832 |
for (int i = 0; i < ws.length; ++i) { |
833 |
ForkJoinWorkerThread t = ws[i]; |
834 |
if (t != null) |
835 |
t.setAsyncMode(async); |
836 |
} |
837 |
} |
838 |
return oldMode; |
839 |
} |
840 |
|
841 |
/** |
842 |
* Returns true if this pool uses local first-in-first-out |
843 |
* scheduling mode for forked tasks that are never joined. |
844 |
* |
845 |
* @return true if this pool uses async mode. |
846 |
*/ |
847 |
public boolean getAsyncMode() { |
848 |
return locallyFifo; |
849 |
} |
850 |
|
851 |
/** |
852 |
* Returns an estimate of the number of worker threads that are |
853 |
* not blocked waiting to join tasks or for other managed |
854 |
* synchronization. |
855 |
* |
856 |
* @return the number of worker threads |
857 |
*/ |
858 |
public int getRunningThreadCount() { |
859 |
return runningCountOf(workerCounts); |
860 |
} |
861 |
|
862 |
/** |
863 |
* Returns an estimate of the number of threads that are currently |
864 |
* stealing or executing tasks. This method may overestimate the |
865 |
* number of active threads. |
866 |
* @return the number of active threads. |
867 |
*/ |
868 |
public int getActiveThreadCount() { |
869 |
return activeCountOf(runControl); |
870 |
} |
871 |
|
872 |
/** |
873 |
* Returns an estimate of the number of threads that are currently |
874 |
* idle waiting for tasks. This method may underestimate the |
875 |
* number of idle threads. |
876 |
* @return the number of idle threads. |
877 |
*/ |
878 |
final int getIdleThreadCount() { |
879 |
int c = runningCountOf(workerCounts) - activeCountOf(runControl); |
880 |
return (c <= 0)? 0 : c; |
881 |
} |
882 |
|
883 |
/** |
884 |
* Returns true if all worker threads are currently idle. An idle |
885 |
* worker is one that cannot obtain a task to execute because none |
886 |
* are available to steal from other threads, and there are no |
887 |
* pending submissions to the pool. This method is conservative: |
888 |
* It might not return true immediately upon idleness of all |
889 |
* threads, but will eventually become true if threads remain |
890 |
* inactive. |
891 |
* @return true if all threads are currently idle |
892 |
*/ |
893 |
public boolean isQuiescent() { |
894 |
return activeCountOf(runControl) == 0; |
895 |
} |
896 |
|
897 |
/** |
898 |
* Returns an estimate of the total number of tasks stolen from |
899 |
* one thread's work queue by another. The reported value |
900 |
* underestimates the actual total number of steals when the pool |
901 |
* is not quiescent. This value may be useful for monitoring and |
902 |
* tuning fork/join programs: In general, steal counts should be |
903 |
* high enough to keep threads busy, but low enough to avoid |
904 |
* overhead and contention across threads. |
905 |
* @return the number of steals. |
906 |
*/ |
907 |
public long getStealCount() { |
908 |
return stealCount.get(); |
909 |
} |
910 |
|
911 |
/** |
912 |
* Accumulate steal count from a worker. Call only |
913 |
* when worker known to be idle. |
914 |
*/ |
915 |
private void updateStealCount(ForkJoinWorkerThread w) { |
916 |
int sc = w.getAndClearStealCount(); |
917 |
if (sc != 0) |
918 |
stealCount.addAndGet(sc); |
919 |
} |
920 |
|
921 |
/** |
922 |
* Returns an estimate of the total number of tasks currently held |
923 |
* in queues by worker threads (but not including tasks submitted |
924 |
* to the pool that have not begun executing). This value is only |
925 |
* an approximation, obtained by iterating across all threads in |
926 |
* the pool. This method may be useful for tuning task |
927 |
* granularities. |
928 |
* @return the number of queued tasks. |
929 |
*/ |
930 |
public long getQueuedTaskCount() { |
931 |
long count = 0; |
932 |
ForkJoinWorkerThread[] ws = workers; |
933 |
if (ws != null) { |
934 |
for (int i = 0; i < ws.length; ++i) { |
935 |
ForkJoinWorkerThread t = ws[i]; |
936 |
if (t != null) |
937 |
count += t.getQueueSize(); |
938 |
} |
939 |
} |
940 |
return count; |
941 |
} |
942 |
|
943 |
/** |
944 |
* Returns an estimate of the number tasks submitted to this pool |
945 |
* that have not yet begun executing. This method takes time |
946 |
* proportional to the number of submissions. |
947 |
* @return the number of queued submissions. |
948 |
*/ |
949 |
public int getQueuedSubmissionCount() { |
950 |
return submissionQueue.size(); |
951 |
} |
952 |
|
953 |
/** |
954 |
* Returns true if there are any tasks submitted to this pool |
955 |
* that have not yet begun executing. |
956 |
* @return <code>true</code> if there are any queued submissions. |
957 |
*/ |
958 |
public boolean hasQueuedSubmissions() { |
959 |
return !submissionQueue.isEmpty(); |
960 |
} |
961 |
|
962 |
/** |
963 |
* Removes and returns the next unexecuted submission if one is |
964 |
* available. This method may be useful in extensions to this |
965 |
* class that re-assign work in systems with multiple pools. |
966 |
* @return the next submission, or null if none |
967 |
*/ |
968 |
protected ForkJoinTask<?> pollSubmission() { |
969 |
return submissionQueue.poll(); |
970 |
} |
971 |
|
972 |
/** |
973 |
* Removes all available unexecuted submitted and forked tasks |
974 |
* from scheduling queues and adds them to the given collection, |
975 |
* without altering their execution status. These may include |
976 |
* artifically generated or wrapped tasks. This method id designed |
977 |
* to be invoked only when the pool is known to be |
978 |
* quiescent. Invocations at other times may not remove all |
979 |
* tasks. A failure encountered while attempting to add elements |
980 |
* to collection <tt>c</tt> may result in elements being in |
981 |
* neither, either or both collections when the associated |
982 |
* exception is thrown. The behavior of this operation is |
983 |
* undefined if the specified collection is modified while the |
984 |
* operation is in progress. |
985 |
* @param c the collection to transfer elements into |
986 |
* @return the number of elements transferred |
987 |
*/ |
988 |
protected int drainTasksTo(Collection<ForkJoinTask<?>> c) { |
989 |
int n = submissionQueue.drainTo(c); |
990 |
ForkJoinWorkerThread[] ws = workers; |
991 |
if (ws != null) { |
992 |
for (int i = 0; i < ws.length; ++i) { |
993 |
ForkJoinWorkerThread w = ws[i]; |
994 |
if (w != null) |
995 |
n += w.drainTasksTo(c); |
996 |
} |
997 |
} |
998 |
return n; |
999 |
} |
1000 |
|
1001 |
/** |
1002 |
* Returns a string identifying this pool, as well as its state, |
1003 |
* including indications of run state, parallelism level, and |
1004 |
* worker and task counts. |
1005 |
* |
1006 |
* @return a string identifying this pool, as well as its state |
1007 |
*/ |
1008 |
public String toString() { |
1009 |
int ps = parallelism; |
1010 |
int wc = workerCounts; |
1011 |
int rc = runControl; |
1012 |
long st = getStealCount(); |
1013 |
long qt = getQueuedTaskCount(); |
1014 |
long qs = getQueuedSubmissionCount(); |
1015 |
return super.toString() + |
1016 |
"[" + runStateToString(runStateOf(rc)) + |
1017 |
", parallelism = " + ps + |
1018 |
", size = " + totalCountOf(wc) + |
1019 |
", active = " + activeCountOf(rc) + |
1020 |
", running = " + runningCountOf(wc) + |
1021 |
", steals = " + st + |
1022 |
", tasks = " + qt + |
1023 |
", submissions = " + qs + |
1024 |
"]"; |
1025 |
} |
1026 |
|
1027 |
private static String runStateToString(int rs) { |
1028 |
switch(rs) { |
1029 |
case RUNNING: return "Running"; |
1030 |
case SHUTDOWN: return "Shutting down"; |
1031 |
case TERMINATING: return "Terminating"; |
1032 |
case TERMINATED: return "Terminated"; |
1033 |
default: throw new Error("Unknown run state"); |
1034 |
} |
1035 |
} |
1036 |
|
1037 |
// lifecycle control |
1038 |
|
1039 |
/** |
1040 |
* Initiates an orderly shutdown in which previously submitted |
1041 |
* tasks are executed, but no new tasks will be accepted. |
1042 |
* Invocation has no additional effect if already shut down. |
1043 |
* Tasks that are in the process of being submitted concurrently |
1044 |
* during the course of this method may or may not be rejected. |
1045 |
* @throws SecurityException if a security manager exists and |
1046 |
* the caller is not permitted to modify threads |
1047 |
* because it does not hold {@link |
1048 |
* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
1049 |
*/ |
1050 |
public void shutdown() { |
1051 |
checkPermission(); |
1052 |
transitionRunStateTo(SHUTDOWN); |
1053 |
if (canTerminateOnShutdown(runControl)) |
1054 |
terminateOnShutdown(); |
1055 |
} |
1056 |
|
1057 |
/** |
1058 |
* Attempts to stop all actively executing tasks, and cancels all |
1059 |
* waiting tasks. Tasks that are in the process of being |
1060 |
* submitted or executed concurrently during the course of this |
1061 |
* method may or may not be rejected. Unlike some other executors, |
1062 |
* this method cancels rather than collects non-executed tasks |
1063 |
* upon termination, so always returns an empty list. However, you |
1064 |
* can use method <code>drainTasksTo</code> before invoking this |
1065 |
* method to transfer unexecuted tasks to another collection. |
1066 |
* @return an empty list |
1067 |
* @throws SecurityException if a security manager exists and |
1068 |
* the caller is not permitted to modify threads |
1069 |
* because it does not hold {@link |
1070 |
* java.lang.RuntimePermission}<code>("modifyThread")</code>, |
1071 |
*/ |
1072 |
public List<Runnable> shutdownNow() { |
1073 |
checkPermission(); |
1074 |
terminate(); |
1075 |
return Collections.emptyList(); |
1076 |
} |
1077 |
|
1078 |
/** |
1079 |
* Returns <code>true</code> if all tasks have completed following shut down. |
1080 |
* |
1081 |
* @return <code>true</code> if all tasks have completed following shut down |
1082 |
*/ |
1083 |
public boolean isTerminated() { |
1084 |
return runStateOf(runControl) == TERMINATED; |
1085 |
} |
1086 |
|
1087 |
/** |
1088 |
* Returns <code>true</code> if the process of termination has |
1089 |
* commenced but possibly not yet completed. |
1090 |
* |
1091 |
* @return <code>true</code> if terminating |
1092 |
*/ |
1093 |
public boolean isTerminating() { |
1094 |
return runStateOf(runControl) >= TERMINATING; |
1095 |
} |
1096 |
|
1097 |
/** |
1098 |
* Returns <code>true</code> if this pool has been shut down. |
1099 |
* |
1100 |
* @return <code>true</code> if this pool has been shut down |
1101 |
*/ |
1102 |
public boolean isShutdown() { |
1103 |
return runStateOf(runControl) >= SHUTDOWN; |
1104 |
} |
1105 |
|
1106 |
/** |
1107 |
* Blocks until all tasks have completed execution after a shutdown |
1108 |
* request, or the timeout occurs, or the current thread is |
1109 |
* interrupted, whichever happens first. |
1110 |
* |
1111 |
* @param timeout the maximum time to wait |
1112 |
* @param unit the time unit of the timeout argument |
1113 |
* @return <code>true</code> if this executor terminated and |
1114 |
* <code>false</code> if the timeout elapsed before termination |
1115 |
* @throws InterruptedException if interrupted while waiting |
1116 |
*/ |
1117 |
public boolean awaitTermination(long timeout, TimeUnit unit) |
1118 |
throws InterruptedException { |
1119 |
long nanos = unit.toNanos(timeout); |
1120 |
final ReentrantLock lock = this.workerLock; |
1121 |
lock.lock(); |
1122 |
try { |
1123 |
for (;;) { |
1124 |
if (isTerminated()) |
1125 |
return true; |
1126 |
if (nanos <= 0) |
1127 |
return false; |
1128 |
nanos = termination.awaitNanos(nanos); |
1129 |
} |
1130 |
} finally { |
1131 |
lock.unlock(); |
1132 |
} |
1133 |
} |
1134 |
|
1135 |
// Shutdown and termination support |
1136 |
|
1137 |
/** |
1138 |
* Callback from terminating worker. Null out the corresponding |
1139 |
* workers slot, and if terminating, try to terminate, else try to |
1140 |
* shrink workers array. |
1141 |
* @param w the worker |
1142 |
*/ |
1143 |
final void workerTerminated(ForkJoinWorkerThread w) { |
1144 |
updateStealCount(w); |
1145 |
updateWorkerCount(-1); |
1146 |
final ReentrantLock lock = this.workerLock; |
1147 |
lock.lock(); |
1148 |
try { |
1149 |
ForkJoinWorkerThread[] ws = workers; |
1150 |
if (ws != null) { |
1151 |
int idx = w.poolIndex; |
1152 |
if (idx >= 0 && idx < ws.length && ws[idx] == w) |
1153 |
ws[idx] = null; |
1154 |
if (totalCountOf(workerCounts) == 0) { |
1155 |
terminate(); // no-op if already terminating |
1156 |
transitionRunStateTo(TERMINATED); |
1157 |
termination.signalAll(); |
1158 |
} |
1159 |
else if (!isTerminating()) { |
1160 |
tryShrinkWorkerArray(); |
1161 |
tryResumeSpare(true); // allow replacement |
1162 |
} |
1163 |
} |
1164 |
} finally { |
1165 |
lock.unlock(); |
1166 |
} |
1167 |
signalIdleWorkers(); |
1168 |
} |
1169 |
|
1170 |
/** |
1171 |
* Initiate termination. |
1172 |
*/ |
1173 |
private void terminate() { |
1174 |
if (transitionRunStateTo(TERMINATING)) { |
1175 |
stopAllWorkers(); |
1176 |
resumeAllSpares(); |
1177 |
signalIdleWorkers(); |
1178 |
cancelQueuedSubmissions(); |
1179 |
cancelQueuedWorkerTasks(); |
1180 |
interruptUnterminatedWorkers(); |
1181 |
signalIdleWorkers(); // resignal after interrupt |
1182 |
} |
1183 |
} |
1184 |
|
1185 |
/** |
1186 |
* Possibly terminate when on shutdown state |
1187 |
*/ |
1188 |
private void terminateOnShutdown() { |
1189 |
if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl)) |
1190 |
terminate(); |
1191 |
} |
1192 |
|
1193 |
/** |
1194 |
* Clear out and cancel submissions |
1195 |
*/ |
1196 |
private void cancelQueuedSubmissions() { |
1197 |
ForkJoinTask<?> task; |
1198 |
while ((task = pollSubmission()) != null) |
1199 |
task.cancel(false); |
1200 |
} |
1201 |
|
1202 |
/** |
1203 |
* Clean out worker queues. |
1204 |
*/ |
1205 |
private void cancelQueuedWorkerTasks() { |
1206 |
final ReentrantLock lock = this.workerLock; |
1207 |
lock.lock(); |
1208 |
try { |
1209 |
ForkJoinWorkerThread[] ws = workers; |
1210 |
if (ws != null) { |
1211 |
for (int i = 0; i < ws.length; ++i) { |
1212 |
ForkJoinWorkerThread t = ws[i]; |
1213 |
if (t != null) |
1214 |
t.cancelTasks(); |
1215 |
} |
1216 |
} |
1217 |
} finally { |
1218 |
lock.unlock(); |
1219 |
} |
1220 |
} |
1221 |
|
1222 |
/** |
1223 |
* Set each worker's status to terminating. Requires lock to avoid |
1224 |
* conflicts with add/remove |
1225 |
*/ |
1226 |
private void stopAllWorkers() { |
1227 |
final ReentrantLock lock = this.workerLock; |
1228 |
lock.lock(); |
1229 |
try { |
1230 |
ForkJoinWorkerThread[] ws = workers; |
1231 |
if (ws != null) { |
1232 |
for (int i = 0; i < ws.length; ++i) { |
1233 |
ForkJoinWorkerThread t = ws[i]; |
1234 |
if (t != null) |
1235 |
t.shutdownNow(); |
1236 |
} |
1237 |
} |
1238 |
} finally { |
1239 |
lock.unlock(); |
1240 |
} |
1241 |
} |
1242 |
|
1243 |
/** |
1244 |
* Interrupt all unterminated workers. This is not required for |
1245 |
* sake of internal control, but may help unstick user code during |
1246 |
* shutdown. |
1247 |
*/ |
1248 |
private void interruptUnterminatedWorkers() { |
1249 |
final ReentrantLock lock = this.workerLock; |
1250 |
lock.lock(); |
1251 |
try { |
1252 |
ForkJoinWorkerThread[] ws = workers; |
1253 |
if (ws != null) { |
1254 |
for (int i = 0; i < ws.length; ++i) { |
1255 |
ForkJoinWorkerThread t = ws[i]; |
1256 |
if (t != null && !t.isTerminated()) { |
1257 |
try { |
1258 |
t.interrupt(); |
1259 |
} catch (SecurityException ignore) { |
1260 |
} |
1261 |
} |
1262 |
} |
1263 |
} |
1264 |
} finally { |
1265 |
lock.unlock(); |
1266 |
} |
1267 |
} |
1268 |
|
1269 |
|
1270 |
/* |
1271 |
* Nodes for event barrier to manage idle threads. Queue nodes |
1272 |
* are basic Treiber stack nodes, also used for spare stack. |
1273 |
* |
1274 |
* The event barrier has an event count and a wait queue (actually |
1275 |
* a Treiber stack). Workers are enabled to look for work when |
1276 |
* the eventCount is incremented. If they fail to find work, they |
1277 |
* may wait for next count. Upon release, threads help others wake |
1278 |
* up. |
1279 |
* |
1280 |
* Synchronization events occur only in enough contexts to |
1281 |
* maintain overall liveness: |
1282 |
* |
1283 |
* - Submission of a new task to the pool |
1284 |
* - Resizes or other changes to the workers array |
1285 |
* - pool termination |
1286 |
* - A worker pushing a task on an empty queue |
1287 |
* |
1288 |
* The case of pushing a task occurs often enough, and is heavy |
1289 |
* enough compared to simple stack pushes, to require special |
1290 |
* handling: Method signalWork returns without advancing count if |
1291 |
* the queue appears to be empty. This would ordinarily result in |
1292 |
* races causing some queued waiters not to be woken up. To avoid |
1293 |
* this, the first worker enqueued in method sync (see |
1294 |
* syncIsReleasable) rescans for tasks after being enqueued, and |
1295 |
* helps signal if any are found. This works well because the |
1296 |
* worker has nothing better to do, and so might as well help |
1297 |
* alleviate the overhead and contention on the threads actually |
1298 |
* doing work. Also, since event counts increments on task |
1299 |
* availability exist to maintain liveness (rather than to force |
1300 |
* refreshes etc), it is OK for callers to exit early if |
1301 |
* contending with another signaller. |
1302 |
*/ |
1303 |
static final class WaitQueueNode { |
1304 |
WaitQueueNode next; // only written before enqueued |
1305 |
volatile ForkJoinWorkerThread thread; // nulled to cancel wait |
1306 |
final long count; // unused for spare stack |
1307 |
|
1308 |
WaitQueueNode(long c, ForkJoinWorkerThread w) { |
1309 |
count = c; |
1310 |
thread = w; |
1311 |
} |
1312 |
|
1313 |
/** |
1314 |
* Wake up waiter, returning false if known to already |
1315 |
*/ |
1316 |
boolean signal() { |
1317 |
ForkJoinWorkerThread t = thread; |
1318 |
if (t == null) |
1319 |
return false; |
1320 |
thread = null; |
1321 |
LockSupport.unpark(t); |
1322 |
return true; |
1323 |
} |
1324 |
|
1325 |
/** |
1326 |
* Await release on sync |
1327 |
*/ |
1328 |
void awaitSyncRelease(ForkJoinPool p) { |
1329 |
while (thread != null && !p.syncIsReleasable(this)) |
1330 |
LockSupport.park(this); |
1331 |
} |
1332 |
|
1333 |
/** |
1334 |
* Await resumption as spare |
1335 |
*/ |
1336 |
void awaitSpareRelease() { |
1337 |
while (thread != null) { |
1338 |
if (!Thread.interrupted()) |
1339 |
LockSupport.park(this); |
1340 |
} |
1341 |
} |
1342 |
} |
1343 |
|
1344 |
/** |
1345 |
* Ensures that no thread is waiting for count to advance from the |
1346 |
* current value of eventCount read on entry to this method, by |
1347 |
* releasing waiting threads if necessary. |
1348 |
* @return the count |
1349 |
*/ |
1350 |
final long ensureSync() { |
1351 |
long c = eventCount; |
1352 |
WaitQueueNode q; |
1353 |
while ((q = syncStack) != null && q.count < c) { |
1354 |
if (casBarrierStack(q, null)) { |
1355 |
do { |
1356 |
q.signal(); |
1357 |
} while ((q = q.next) != null); |
1358 |
break; |
1359 |
} |
1360 |
} |
1361 |
return c; |
1362 |
} |
1363 |
|
1364 |
/** |
1365 |
* Increments event count and releases waiting threads. |
1366 |
*/ |
1367 |
private void signalIdleWorkers() { |
1368 |
long c; |
1369 |
do;while (!casEventCount(c = eventCount, c+1)); |
1370 |
ensureSync(); |
1371 |
} |
1372 |
|
1373 |
/** |
1374 |
* Signal threads waiting to poll a task. Because method sync |
1375 |
* rechecks availability, it is OK to only proceed if queue |
1376 |
* appears to be non-empty, and OK to skip under contention to |
1377 |
* increment count (since some other thread succeeded). |
1378 |
*/ |
1379 |
final void signalWork() { |
1380 |
long c; |
1381 |
WaitQueueNode q; |
1382 |
if (syncStack != null && |
1383 |
casEventCount(c = eventCount, c+1) && |
1384 |
(((q = syncStack) != null && q.count <= c) && |
1385 |
(!casBarrierStack(q, q.next) || !q.signal()))) |
1386 |
ensureSync(); |
1387 |
} |
1388 |
|
1389 |
/** |
1390 |
* Waits until event count advances from last value held by |
1391 |
* caller, or if excess threads, caller is resumed as spare, or |
1392 |
* caller or pool is terminating. Updates caller's event on exit. |
1393 |
* @param w the calling worker thread |
1394 |
*/ |
1395 |
final void sync(ForkJoinWorkerThread w) { |
1396 |
updateStealCount(w); // Transfer w's count while it is idle |
1397 |
|
1398 |
while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) { |
1399 |
long prev = w.lastEventCount; |
1400 |
WaitQueueNode node = null; |
1401 |
WaitQueueNode h; |
1402 |
while (eventCount == prev && |
1403 |
((h = syncStack) == null || h.count == prev)) { |
1404 |
if (node == null) |
1405 |
node = new WaitQueueNode(prev, w); |
1406 |
if (casBarrierStack(node.next = h, node)) { |
1407 |
node.awaitSyncRelease(this); |
1408 |
break; |
1409 |
} |
1410 |
} |
1411 |
long ec = ensureSync(); |
1412 |
if (ec != prev) { |
1413 |
w.lastEventCount = ec; |
1414 |
break; |
1415 |
} |
1416 |
} |
1417 |
} |
1418 |
|
1419 |
/** |
1420 |
* Returns true if worker waiting on sync can proceed: |
1421 |
* - on signal (thread == null) |
1422 |
* - on event count advance (winning race to notify vs signaller) |
1423 |
* - on Interrupt |
1424 |
* - if the first queued node, we find work available |
1425 |
* If node was not signalled and event count not advanced on exit, |
1426 |
* then we also help advance event count. |
1427 |
* @return true if node can be released |
1428 |
*/ |
1429 |
final boolean syncIsReleasable(WaitQueueNode node) { |
1430 |
long prev = node.count; |
1431 |
if (!Thread.interrupted() && node.thread != null && |
1432 |
(node.next != null || |
1433 |
!ForkJoinWorkerThread.hasQueuedTasks(workers)) && |
1434 |
eventCount == prev) |
1435 |
return false; |
1436 |
if (node.thread != null) { |
1437 |
node.thread = null; |
1438 |
long ec = eventCount; |
1439 |
if (prev <= ec) // help signal |
1440 |
casEventCount(ec, ec+1); |
1441 |
} |
1442 |
return true; |
1443 |
} |
1444 |
|
1445 |
/** |
1446 |
* Returns true if a new sync event occurred since last call to |
1447 |
* sync or this method, if so, updating caller's count. |
1448 |
*/ |
1449 |
final boolean hasNewSyncEvent(ForkJoinWorkerThread w) { |
1450 |
long lc = w.lastEventCount; |
1451 |
long ec = ensureSync(); |
1452 |
if (ec == lc) |
1453 |
return false; |
1454 |
w.lastEventCount = ec; |
1455 |
return true; |
1456 |
} |
1457 |
|
1458 |
// Parallelism maintenance |
1459 |
|
1460 |
/** |
1461 |
* Decrement running count; if too low, add spare. |
1462 |
* |
1463 |
* Conceptually, all we need to do here is add or resume a |
1464 |
* spare thread when one is about to block (and remove or |
1465 |
* suspend it later when unblocked -- see suspendIfSpare). |
1466 |
* However, implementing this idea requires coping with |
1467 |
* several problems: We have imperfect information about the |
1468 |
* states of threads. Some count updates can and usually do |
1469 |
* lag run state changes, despite arrangements to keep them |
1470 |
* accurate (for example, when possible, updating counts |
1471 |
* before signalling or resuming), especially when running on |
1472 |
* dynamic JVMs that don't optimize the infrequent paths that |
1473 |
* update counts. Generating too many threads can make these |
1474 |
* problems become worse, because excess threads are more |
1475 |
* likely to be context-switched with others, slowing them all |
1476 |
* down, especially if there is no work available, so all are |
1477 |
* busy scanning or idling. Also, excess spare threads can |
1478 |
* only be suspended or removed when they are idle, not |
1479 |
* immediately when they aren't needed. So adding threads will |
1480 |
* raise parallelism level for longer than necessary. Also, |
1481 |
* FJ applications often enounter highly transient peaks when |
1482 |
* many threads are blocked joining, but for less time than it |
1483 |
* takes to create or resume spares. |
1484 |
* |
1485 |
* @param joinMe if non-null, return early if done |
1486 |
* @param maintainParallelism if true, try to stay within |
1487 |
* target counts, else create only to avoid starvation |
1488 |
* @return true if joinMe known to be done |
1489 |
*/ |
1490 |
final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) { |
1491 |
maintainParallelism &= maintainsParallelism; // overrride |
1492 |
boolean dec = false; // true when running count decremented |
1493 |
while (spareStack == null || !tryResumeSpare(dec)) { |
1494 |
int counts = workerCounts; |
1495 |
if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat |
1496 |
if (!needSpare(counts, maintainParallelism)) |
1497 |
break; |
1498 |
if (joinMe.status < 0) |
1499 |
return true; |
1500 |
if (tryAddSpare(counts)) |
1501 |
break; |
1502 |
} |
1503 |
} |
1504 |
return false; |
1505 |
} |
1506 |
|
1507 |
/** |
1508 |
* Same idea as preJoin |
1509 |
*/ |
1510 |
final boolean preBlock(ManagedBlocker blocker, |
1511 |
boolean maintainParallelism) { |
1512 |
maintainParallelism &= maintainsParallelism; |
1513 |
boolean dec = false; |
1514 |
while (spareStack == null || !tryResumeSpare(dec)) { |
1515 |
int counts = workerCounts; |
1516 |
if (dec || (dec = casWorkerCounts(counts, --counts))) { |
1517 |
if (!needSpare(counts, maintainParallelism)) |
1518 |
break; |
1519 |
if (blocker.isReleasable()) |
1520 |
return true; |
1521 |
if (tryAddSpare(counts)) |
1522 |
break; |
1523 |
} |
1524 |
} |
1525 |
return false; |
1526 |
} |
1527 |
|
1528 |
/** |
1529 |
* Returns true if a spare thread appears to be needed. If |
1530 |
* maintaining parallelism, returns true when the deficit in |
1531 |
* running threads is more than the surplus of total threads, and |
1532 |
* there is apparently some work to do. This self-limiting rule |
1533 |
* means that the more threads that have already been added, the |
1534 |
* less parallelism we will tolerate before adding another. |
1535 |
* @param counts current worker counts |
1536 |
* @param maintainParallelism try to maintain parallelism |
1537 |
*/ |
1538 |
private boolean needSpare(int counts, boolean maintainParallelism) { |
1539 |
int ps = parallelism; |
1540 |
int rc = runningCountOf(counts); |
1541 |
int tc = totalCountOf(counts); |
1542 |
int runningDeficit = ps - rc; |
1543 |
int totalSurplus = tc - ps; |
1544 |
return (tc < maxPoolSize && |
1545 |
(rc == 0 || totalSurplus < 0 || |
1546 |
(maintainParallelism && |
1547 |
runningDeficit > totalSurplus && |
1548 |
ForkJoinWorkerThread.hasQueuedTasks(workers)))); |
1549 |
} |
1550 |
|
1551 |
/** |
1552 |
* Add a spare worker if lock available and no more than the |
1553 |
* expected numbers of threads exist |
1554 |
* @return true if successful |
1555 |
*/ |
1556 |
private boolean tryAddSpare(int expectedCounts) { |
1557 |
final ReentrantLock lock = this.workerLock; |
1558 |
int expectedRunning = runningCountOf(expectedCounts); |
1559 |
int expectedTotal = totalCountOf(expectedCounts); |
1560 |
boolean success = false; |
1561 |
boolean locked = false; |
1562 |
// confirm counts while locking; CAS after obtaining lock |
1563 |
try { |
1564 |
for (;;) { |
1565 |
int s = workerCounts; |
1566 |
int tc = totalCountOf(s); |
1567 |
int rc = runningCountOf(s); |
1568 |
if (rc > expectedRunning || tc > expectedTotal) |
1569 |
break; |
1570 |
if (!locked && !(locked = lock.tryLock())) |
1571 |
break; |
1572 |
if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) { |
1573 |
createAndStartSpare(tc); |
1574 |
success = true; |
1575 |
break; |
1576 |
} |
1577 |
} |
1578 |
} finally { |
1579 |
if (locked) |
1580 |
lock.unlock(); |
1581 |
} |
1582 |
return success; |
1583 |
} |
1584 |
|
1585 |
/** |
1586 |
* Add the kth spare worker. On entry, pool coounts are already |
1587 |
* adjusted to reflect addition. |
1588 |
*/ |
1589 |
private void createAndStartSpare(int k) { |
1590 |
ForkJoinWorkerThread w = null; |
1591 |
ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1); |
1592 |
int len = ws.length; |
1593 |
// Probably, we can place at slot k. If not, find empty slot |
1594 |
if (k < len && ws[k] != null) { |
1595 |
for (k = 0; k < len && ws[k] != null; ++k) |
1596 |
; |
1597 |
} |
1598 |
if (k < len && !isTerminating() && (w = createWorker(k)) != null) { |
1599 |
ws[k] = w; |
1600 |
w.start(); |
1601 |
} |
1602 |
else |
1603 |
updateWorkerCount(-1); // adjust on failure |
1604 |
signalIdleWorkers(); |
1605 |
} |
1606 |
|
1607 |
/** |
1608 |
* Suspend calling thread w if there are excess threads. Called |
1609 |
* only from sync. Spares are enqueued in a Treiber stack |
1610 |
* using the same WaitQueueNodes as barriers. They are resumed |
1611 |
* mainly in preJoin, but are also woken on pool events that |
1612 |
* require all threads to check run state. |
1613 |
* @param w the caller |
1614 |
*/ |
1615 |
private boolean suspendIfSpare(ForkJoinWorkerThread w) { |
1616 |
WaitQueueNode node = null; |
1617 |
int s; |
1618 |
while (parallelism < runningCountOf(s = workerCounts)) { |
1619 |
if (node == null) |
1620 |
node = new WaitQueueNode(0, w); |
1621 |
if (casWorkerCounts(s, s-1)) { // representation-dependent |
1622 |
// push onto stack |
1623 |
do;while (!casSpareStack(node.next = spareStack, node)); |
1624 |
// block until released by resumeSpare |
1625 |
node.awaitSpareRelease(); |
1626 |
return true; |
1627 |
} |
1628 |
} |
1629 |
return false; |
1630 |
} |
1631 |
|
1632 |
/** |
1633 |
* Try to pop and resume a spare thread. |
1634 |
* @param updateCount if true, increment running count on success |
1635 |
* @return true if successful |
1636 |
*/ |
1637 |
private boolean tryResumeSpare(boolean updateCount) { |
1638 |
WaitQueueNode q; |
1639 |
while ((q = spareStack) != null) { |
1640 |
if (casSpareStack(q, q.next)) { |
1641 |
if (updateCount) |
1642 |
updateRunningCount(1); |
1643 |
q.signal(); |
1644 |
return true; |
1645 |
} |
1646 |
} |
1647 |
return false; |
1648 |
} |
1649 |
|
1650 |
/** |
1651 |
* Pop and resume all spare threads. Same idea as ensureSync. |
1652 |
* @return true if any spares released |
1653 |
*/ |
1654 |
private boolean resumeAllSpares() { |
1655 |
WaitQueueNode q; |
1656 |
while ( (q = spareStack) != null) { |
1657 |
if (casSpareStack(q, null)) { |
1658 |
do { |
1659 |
updateRunningCount(1); |
1660 |
q.signal(); |
1661 |
} while ((q = q.next) != null); |
1662 |
return true; |
1663 |
} |
1664 |
} |
1665 |
return false; |
1666 |
} |
1667 |
|
1668 |
/** |
1669 |
* Pop and shutdown excessive spare threads. Call only while |
1670 |
* holding lock. This is not guaranteed to eliminate all excess |
1671 |
* threads, only those suspended as spares, which are the ones |
1672 |
* unlikely to be needed in the future. |
1673 |
*/ |
1674 |
private void trimSpares() { |
1675 |
int surplus = totalCountOf(workerCounts) - parallelism; |
1676 |
WaitQueueNode q; |
1677 |
while (surplus > 0 && (q = spareStack) != null) { |
1678 |
if (casSpareStack(q, null)) { |
1679 |
do { |
1680 |
updateRunningCount(1); |
1681 |
ForkJoinWorkerThread w = q.thread; |
1682 |
if (w != null && surplus > 0 && |
1683 |
runningCountOf(workerCounts) > 0 && w.shutdown()) |
1684 |
--surplus; |
1685 |
q.signal(); |
1686 |
} while ((q = q.next) != null); |
1687 |
} |
1688 |
} |
1689 |
} |
1690 |
|
1691 |
/** |
1692 |
* Interface for extending managed parallelism for tasks running |
1693 |
* in ForkJoinPools. A ManagedBlocker provides two methods. |
1694 |
* Method <code>isReleasable</code> must return true if blocking is not |
1695 |
* necessary. Method <code>block</code> blocks the current thread |
1696 |
* if necessary (perhaps internally invoking isReleasable before |
1697 |
* actually blocking.). |
1698 |
* <p>For example, here is a ManagedBlocker based on a |
1699 |
* ReentrantLock: |
1700 |
* <pre> |
1701 |
* class ManagedLocker implements ManagedBlocker { |
1702 |
* final ReentrantLock lock; |
1703 |
* boolean hasLock = false; |
1704 |
* ManagedLocker(ReentrantLock lock) { this.lock = lock; } |
1705 |
* public boolean block() { |
1706 |
* if (!hasLock) |
1707 |
* lock.lock(); |
1708 |
* return true; |
1709 |
* } |
1710 |
* public boolean isReleasable() { |
1711 |
* return hasLock || (hasLock = lock.tryLock()); |
1712 |
* } |
1713 |
* } |
1714 |
* </pre> |
1715 |
*/ |
1716 |
public static interface ManagedBlocker { |
1717 |
/** |
1718 |
* Possibly blocks the current thread, for example waiting for |
1719 |
* a lock or condition. |
1720 |
* @return true if no additional blocking is necessary (i.e., |
1721 |
* if isReleasable would return true). |
1722 |
* @throws InterruptedException if interrupted while waiting |
1723 |
* (the method is not required to do so, but is allowe to). |
1724 |
*/ |
1725 |
boolean block() throws InterruptedException; |
1726 |
|
1727 |
/** |
1728 |
* Returns true if blocking is unnecessary. |
1729 |
*/ |
1730 |
boolean isReleasable(); |
1731 |
} |
1732 |
|
1733 |
/** |
1734 |
* Blocks in accord with the given blocker. If the current thread |
1735 |
* is a ForkJoinWorkerThread, this method possibly arranges for a |
1736 |
* spare thread to be activated if necessary to ensure parallelism |
1737 |
* while the current thread is blocked. If |
1738 |
* <code>maintainParallelism</code> is true and the pool supports |
1739 |
* it ({@link #getMaintainsParallelism}), this method attempts to |
1740 |
* maintain the pool's nominal parallelism. Otherwise if activates |
1741 |
* a thread only if necessary to avoid complete starvation. This |
1742 |
* option may be preferable when blockages use timeouts, or are |
1743 |
* almost always brief. |
1744 |
* |
1745 |
* <p> If the caller is not a ForkJoinTask, this method is behaviorally |
1746 |
* equivalent to |
1747 |
* <pre> |
1748 |
* while (!blocker.isReleasable()) |
1749 |
* if (blocker.block()) |
1750 |
* return; |
1751 |
* </pre> |
1752 |
* If the caller is a ForkJoinTask, then the pool may first |
1753 |
* be expanded to ensure parallelism, and later adjusted. |
1754 |
* |
1755 |
* @param blocker the blocker |
1756 |
* @param maintainParallelism if true and supported by this pool, |
1757 |
* attempt to maintain the pool's nominal parallelism; otherwise |
1758 |
* activate a thread only if necessary to avoid complete |
1759 |
* starvation. |
1760 |
* @throws InterruptedException if blocker.block did so. |
1761 |
*/ |
1762 |
public static void managedBlock(ManagedBlocker blocker, |
1763 |
boolean maintainParallelism) |
1764 |
throws InterruptedException { |
1765 |
Thread t = Thread.currentThread(); |
1766 |
ForkJoinPool pool = (t instanceof ForkJoinWorkerThread? |
1767 |
((ForkJoinWorkerThread)t).pool : null); |
1768 |
if (!blocker.isReleasable()) { |
1769 |
try { |
1770 |
if (pool == null || |
1771 |
!pool.preBlock(blocker, maintainParallelism)) |
1772 |
awaitBlocker(blocker); |
1773 |
} finally { |
1774 |
if (pool != null) |
1775 |
pool.updateRunningCount(1); |
1776 |
} |
1777 |
} |
1778 |
} |
1779 |
|
1780 |
private static void awaitBlocker(ManagedBlocker blocker) |
1781 |
throws InterruptedException { |
1782 |
do;while (!blocker.isReleasable() && !blocker.block()); |
1783 |
} |
1784 |
|
1785 |
// AbstractExecutorService overrides |
1786 |
|
1787 |
protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) { |
1788 |
return new AdaptedRunnable(runnable, value); |
1789 |
} |
1790 |
|
1791 |
protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) { |
1792 |
return new AdaptedCallable(callable); |
1793 |
} |
1794 |
|
1795 |
|
1796 |
// Temporary Unsafe mechanics for preliminary release |
1797 |
private static Unsafe getUnsafe() throws Throwable { |
1798 |
try { |
1799 |
return Unsafe.getUnsafe(); |
1800 |
} catch (SecurityException se) { |
1801 |
try { |
1802 |
return java.security.AccessController.doPrivileged |
1803 |
(new java.security.PrivilegedExceptionAction<Unsafe>() { |
1804 |
public Unsafe run() throws Exception { |
1805 |
return getUnsafePrivileged(); |
1806 |
}}); |
1807 |
} catch (java.security.PrivilegedActionException e) { |
1808 |
throw e.getCause(); |
1809 |
} |
1810 |
} |
1811 |
} |
1812 |
|
1813 |
private static Unsafe getUnsafePrivileged() |
1814 |
throws NoSuchFieldException, IllegalAccessException { |
1815 |
Field f = Unsafe.class.getDeclaredField("theUnsafe"); |
1816 |
f.setAccessible(true); |
1817 |
return (Unsafe) f.get(null); |
1818 |
} |
1819 |
|
1820 |
private static long fieldOffset(String fieldName) |
1821 |
throws NoSuchFieldException { |
1822 |
return _unsafe.objectFieldOffset |
1823 |
(ForkJoinPool.class.getDeclaredField(fieldName)); |
1824 |
} |
1825 |
|
1826 |
static final Unsafe _unsafe; |
1827 |
static final long eventCountOffset; |
1828 |
static final long workerCountsOffset; |
1829 |
static final long runControlOffset; |
1830 |
static final long syncStackOffset; |
1831 |
static final long spareStackOffset; |
1832 |
|
1833 |
static { |
1834 |
try { |
1835 |
_unsafe = getUnsafe(); |
1836 |
eventCountOffset = fieldOffset("eventCount"); |
1837 |
workerCountsOffset = fieldOffset("workerCounts"); |
1838 |
runControlOffset = fieldOffset("runControl"); |
1839 |
syncStackOffset = fieldOffset("syncStack"); |
1840 |
spareStackOffset = fieldOffset("spareStack"); |
1841 |
} catch (Throwable e) { |
1842 |
throw new RuntimeException("Could not initialize intrinsics", e); |
1843 |
} |
1844 |
} |
1845 |
|
1846 |
private boolean casEventCount(long cmp, long val) { |
1847 |
return _unsafe.compareAndSwapLong(this, eventCountOffset, cmp, val); |
1848 |
} |
1849 |
private boolean casWorkerCounts(int cmp, int val) { |
1850 |
return _unsafe.compareAndSwapInt(this, workerCountsOffset, cmp, val); |
1851 |
} |
1852 |
private boolean casRunControl(int cmp, int val) { |
1853 |
return _unsafe.compareAndSwapInt(this, runControlOffset, cmp, val); |
1854 |
} |
1855 |
private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) { |
1856 |
return _unsafe.compareAndSwapObject(this, spareStackOffset, cmp, val); |
1857 |
} |
1858 |
private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { |
1859 |
return _unsafe.compareAndSwapObject(this, syncStackOffset, cmp, val); |
1860 |
} |
1861 |
} |