--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/24 22:05:22 1.20 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/08/02 17:55:51 1.39 @@ -5,57 +5,65 @@ */ package jsr166y; -import java.util.*; + import java.util.concurrent.*; -import java.util.concurrent.locks.*; -import java.util.concurrent.atomic.*; -import sun.misc.Unsafe; -import java.lang.reflect.*; + +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Collection; +import java.util.Collections; +import java.util.List; +import java.util.concurrent.locks.Condition; +import java.util.concurrent.locks.LockSupport; +import java.util.concurrent.locks.ReentrantLock; +import java.util.concurrent.atomic.AtomicInteger; +import java.util.concurrent.atomic.AtomicLong; /** - * An {@link ExecutorService} for running {@link ForkJoinTask}s. A - * ForkJoinPool provides the entry point for submissions from - * non-ForkJoinTasks, as well as management and monitoring operations. - * Normally a single ForkJoinPool is used for a large number of - * submitted tasks. Otherwise, use would not usually outweigh the - * construction and bookkeeping overhead of creating a large set of - * threads. + * An {@link ExecutorService} for running {@link ForkJoinTask}s. + * A {@code ForkJoinPool} provides the entry point for submissions + * from non-{@code ForkJoinTask}s, as well as management and + * monitoring operations. Normally a single {@code ForkJoinPool} is + * used for a large number of submitted tasks. Otherwise, use would + * not usually outweigh the construction and bookkeeping overhead of + * creating a large set of threads. * - *

ForkJoinPools differ from other kinds of Executors mainly in - * that they provide work-stealing: all threads in the pool - * attempt to find and execute subtasks created by other active tasks - * (eventually blocking if none exist). This makes them efficient when - * most tasks spawn other subtasks (as do most ForkJoinTasks), as well - * as the mixed execution of some plain Runnable- or Callable- based - * activities along with ForkJoinTasks. When setting - * {@code setAsyncMode}, a ForkJoinPools may also be appropriate for - * use with fine-grained tasks that are never joined. Otherwise, other - * ExecutorService implementations are typically more appropriate - * choices. + *

{@code ForkJoinPool}s differ from other kinds of {@link + * Executor}s mainly in that they provide work-stealing: all + * threads in the pool attempt to find and execute subtasks created by + * other active tasks (eventually blocking if none exist). This makes + * them efficient when most tasks spawn other subtasks (as do most + * {@code ForkJoinTask}s), as well as the mixed execution of some + * plain {@code Runnable}- or {@code Callable}- based activities along + * with {@code ForkJoinTask}s. When setting {@linkplain #setAsyncMode + * async mode}, a {@code ForkJoinPool} may also be appropriate for use + * with fine-grained tasks that are never joined. Otherwise, other + * {@code ExecutorService} implementations are typically more + * appropriate choices. * - *

A ForkJoinPool may be constructed with a given parallelism level - * (target pool size), which it attempts to maintain by dynamically - * adding, suspending, or resuming threads, even if some tasks are - * waiting to join others. However, no such adjustments are performed - * in the face of blocked IO or other unmanaged synchronization. The - * nested {@code ManagedBlocker} interface enables extension of - * the kinds of synchronization accommodated. The target parallelism - * level may also be changed dynamically ({@code setParallelism}) - * and thread construction can be limited using methods - * {@code setMaximumPoolSize} and/or - * {@code setMaintainsParallelism}. + *

A {@code ForkJoinPool} may be constructed with a given + * parallelism level (target pool size), which it attempts to maintain + * by dynamically adding, suspending, or resuming threads, even if + * some tasks are waiting to join others. However, no such adjustments + * are performed in the face of blocked IO or other unmanaged + * synchronization. The nested {@link ManagedBlocker} interface + * enables extension of the kinds of synchronization accommodated. + * The target parallelism level may also be changed dynamically + * ({@link #setParallelism}) and thread construction can be limited + * using methods {@link #setMaximumPoolSize} and/or {@link + * #setMaintainsParallelism}. * *

In addition to execution and lifecycle control methods, this * class provides status check methods (for example - * {@code getStealCount}) that are intended to aid in developing, + * {@link #getStealCount}) that are intended to aid in developing, * tuning, and monitoring fork/join applications. Also, method - * {@code toString} returns indications of pool state in a + * {@link #toString} returns indications of pool state in a * convenient form for informal monitoring. * *

Implementation notes: This implementation restricts the * maximum number of running threads to 32767. Attempts to create * pools with greater than the maximum result in - * IllegalArgumentExceptions. + * {@code IllegalArgumentException}. * * @since 1.7 * @author Doug Lea @@ -74,10 +82,10 @@ public class ForkJoinPool extends Abstra private static final int MAX_THREADS = 0x7FFF; /** - * Factory for creating new ForkJoinWorkerThreads. A - * ForkJoinWorkerThreadFactory must be defined and used for - * ForkJoinWorkerThread subclasses that extend base functionality - * or initialize threads with different contexts. + * Factory for creating new {@link ForkJoinWorkerThread}s. + * A {@code ForkJoinWorkerThreadFactory} must be defined and used + * for {@code ForkJoinWorkerThread} subclasses that extend base + * functionality or initialize threads with different contexts. */ public static interface ForkJoinWorkerThreadFactory { /** @@ -304,8 +312,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if argument represents zero active count and - * nonzero runstate, which is the triggering condition for + * Returns {@code true} if argument represents zero active count + * and nonzero runstate, which is the triggering condition for * terminating on shutdown. */ private static boolean canTerminateOnShutdown(int c) { @@ -541,6 +549,8 @@ public class ForkJoinPool extends Abstra * Common code for execute, invoke and submit */ private void doSubmit(ForkJoinTask task) { + if (task == null) + throw new NullPointerException(); if (isShutdown()) throw new RejectedExecutionException(); if (workers == null) @@ -569,93 +579,63 @@ public class ForkJoinPool extends Abstra * @throws NullPointerException if task is null * @throws RejectedExecutionException if pool is shut down */ - public void execute(ForkJoinTask task) { + public void execute(ForkJoinTask task) { doSubmit(task); } // AbstractExecutorService methods public void execute(Runnable task) { - doSubmit(new AdaptedRunnable(task, null)); + ForkJoinTask job; + if (task instanceof ForkJoinTask) // avoid re-wrap + job = (ForkJoinTask) task; + else + job = ForkJoinTask.adapt(task, null); + doSubmit(job); } public ForkJoinTask submit(Callable task) { - ForkJoinTask job = new AdaptedCallable(task); + ForkJoinTask job = ForkJoinTask.adapt(task); doSubmit(job); return job; } public ForkJoinTask submit(Runnable task, T result) { - ForkJoinTask job = new AdaptedRunnable(task, result); + ForkJoinTask job = ForkJoinTask.adapt(task, result); doSubmit(job); return job; } public ForkJoinTask submit(Runnable task) { - ForkJoinTask job = new AdaptedRunnable(task, null); + ForkJoinTask job; + if (task instanceof ForkJoinTask) // avoid re-wrap + job = (ForkJoinTask) task; + else + job = ForkJoinTask.adapt(task, null); doSubmit(job); return job; } /** - * Adaptor for Runnables. This implements RunnableFuture - * to be compliant with AbstractExecutorService constraints. + * Submits a ForkJoinTask for execution. + * + * @param task the task to submit + * @return the task + * @throws RejectedExecutionException if the task cannot be + * scheduled for execution + * @throws NullPointerException if the task is null */ - static final class AdaptedRunnable extends ForkJoinTask - implements RunnableFuture { - final Runnable runnable; - final T resultOnCompletion; - T result; - AdaptedRunnable(Runnable runnable, T result) { - if (runnable == null) throw new NullPointerException(); - this.runnable = runnable; - this.resultOnCompletion = result; - } - public T getRawResult() { return result; } - public void setRawResult(T v) { result = v; } - public boolean exec() { - runnable.run(); - result = resultOnCompletion; - return true; - } - public void run() { invoke(); } - private static final long serialVersionUID = 5232453952276885070L; + public ForkJoinTask submit(ForkJoinTask task) { + doSubmit(task); + return task; } - /** - * Adaptor for Callables - */ - static final class AdaptedCallable extends ForkJoinTask - implements RunnableFuture { - final Callable callable; - T result; - AdaptedCallable(Callable callable) { - if (callable == null) throw new NullPointerException(); - this.callable = callable; - } - public T getRawResult() { return result; } - public void setRawResult(T v) { result = v; } - public boolean exec() { - try { - result = callable.call(); - return true; - } catch (Error err) { - throw err; - } catch (RuntimeException rex) { - throw rex; - } catch (Exception ex) { - throw new RuntimeException(ex); - } - } - public void run() { invoke(); } - private static final long serialVersionUID = 2838392045355241008L; - } public List> invokeAll(Collection> tasks) { ArrayList> forkJoinTasks = new ArrayList>(tasks.size()); for (Callable task : tasks) - forkJoinTasks.add(new AdaptedCallable(task)); + forkJoinTasks.add(ForkJoinTask.adapt(task)); invoke(new InvokeAll(forkJoinTasks)); @SuppressWarnings({"unchecked", "rawtypes"}) @@ -688,7 +668,7 @@ public class ForkJoinPool extends Abstra * Returns the handler for internal worker threads that terminate * due to unrecoverable errors encountered while executing tasks. * - * @return the handler, or null if none + * @return the handler, or {@code null} if none */ public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() { Thread.UncaughtExceptionHandler h; @@ -709,7 +689,7 @@ public class ForkJoinPool extends Abstra * as handler. * * @param h the new handler - * @return the old handler, or null if none + * @return the old handler, or {@code null} if none * @throws SecurityException if a security manager exists and * the caller is not permitted to modify threads * because it does not hold {@link @@ -783,7 +763,7 @@ public class ForkJoinPool extends Abstra /** * Returns the number of worker threads that have started but not * yet terminated. This result returned by this method may differ - * from {@code getParallelism} when threads are created to + * from {@link #getParallelism} when threads are created to * maintain parallelism when others are cooperatively blocked. * * @return the number of worker threads @@ -808,7 +788,7 @@ public class ForkJoinPool extends Abstra * Setting this value has no effect on current pool size. It * controls construction of new threads. * - * @throws IllegalArgumentException if negative or greater then + * @throws IllegalArgumentException if negative or greater than * internal implementation limit */ public void setMaximumPoolSize(int newMax) { @@ -819,12 +799,11 @@ public class ForkJoinPool extends Abstra /** - * Returns true if this pool dynamically maintains its target - * parallelism level. If false, new threads are added only to - * avoid possible starvation. - * This setting is by default true. + * Returns {@code true} if this pool dynamically maintains its + * target parallelism level. If false, new threads are added only + * to avoid possible starvation. This setting is by default true. * - * @return true if maintains parallelism + * @return {@code true} if maintains parallelism */ public boolean getMaintainsParallelism() { return maintainsParallelism; @@ -835,7 +814,7 @@ public class ForkJoinPool extends Abstra * parallelism level. If false, new threads are added only to * avoid possible starvation. * - * @param enable true to maintains parallelism + * @param enable {@code true} to maintain parallelism */ public void setMaintainsParallelism(boolean enable) { maintainsParallelism = enable; @@ -846,12 +825,13 @@ public class ForkJoinPool extends Abstra * tasks that are never joined. This mode may be more appropriate * than default locally stack-based mode in applications in which * worker threads only process asynchronous tasks. This method is - * designed to be invoked only when pool is quiescent, and + * designed to be invoked only when the pool is quiescent, and * typically only before any tasks are submitted. The effects of * invocations at other times may be unpredictable. * - * @param async if true, use locally FIFO scheduling + * @param async if {@code true}, use locally FIFO scheduling * @return the previous mode + * @see #getAsyncMode */ public boolean setAsyncMode(boolean async) { boolean oldMode = locallyFifo; @@ -868,10 +848,11 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if this pool uses local first-in-first-out + * Returns {@code true} if this pool uses local first-in-first-out * scheduling mode for forked tasks that are never joined. * - * @return true if this pool uses async mode + * @return {@code true} if this pool uses async mode + * @see #setAsyncMode */ public boolean getAsyncMode() { return locallyFifo; @@ -912,15 +893,15 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if all worker threads are currently idle. An idle - * worker is one that cannot obtain a task to execute because none - * are available to steal from other threads, and there are no - * pending submissions to the pool. This method is conservative; - * it might not return true immediately upon idleness of all - * threads, but will eventually become true if threads remain - * inactive. + * Returns {@code true} if all worker threads are currently idle. + * An idle worker is one that cannot obtain a task to execute + * because none are available to steal from other threads, and + * there are no pending submissions to the pool. This method is + * conservative; it might not return {@code true} immediately upon + * idleness of all threads, but will eventually become true if + * threads remain inactive. * - * @return true if all threads are currently idle + * @return {@code true} if all threads are currently idle */ public boolean isQuiescent() { return activeCountOf(runControl) == 0; @@ -986,8 +967,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if there are any tasks submitted to this pool - * that have not yet begun executing. + * Returns {@code true} if there are any tasks submitted to this + * pool that have not yet begun executing. * * @return {@code true} if there are any queued submissions */ @@ -1000,7 +981,7 @@ public class ForkJoinPool extends Abstra * available. This method may be useful in extensions to this * class that re-assign work in systems with multiple pools. * - * @return the next submission, or null if none + * @return the next submission, or {@code null} if none */ protected ForkJoinTask pollSubmission() { return submissionQueue.poll(); @@ -1023,7 +1004,7 @@ public class ForkJoinPool extends Abstra * @param c the collection to transfer elements into * @return the number of elements transferred */ - protected int drainTasksTo(Collection> c) { + protected int drainTasksTo(Collection> c) { int n = submissionQueue.drainTo(c); ForkJoinWorkerThread[] ws = workers; if (ws != null) { @@ -1089,8 +1070,22 @@ public class ForkJoinPool extends Abstra public void shutdown() { checkPermission(); transitionRunStateTo(SHUTDOWN); - if (canTerminateOnShutdown(runControl)) + if (canTerminateOnShutdown(runControl)) { + if (workers == null) { // shutting down before workers created + final ReentrantLock lock = this.workerLock; + lock.lock(); + try { + if (workers == null) { + terminate(); + transitionRunStateTo(TERMINATED); + termination.signalAll(); + } + } finally { + lock.unlock(); + } + } terminateOnShutdown(); + } } /** @@ -1100,7 +1095,7 @@ public class ForkJoinPool extends Abstra * method may or may not be rejected. Unlike some other executors, * this method cancels rather than collects non-executed tasks * upon termination, so always returns an empty list. However, you - * can use method {@code drainTasksTo} before invoking this + * can use method {@link #drainTasksTo} before invoking this * method to transfer unexecuted tasks to another collection. * * @return an empty list @@ -1460,7 +1455,7 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if worker waiting on sync can proceed: + * Returns {@code true} if worker waiting on sync can proceed: * - on signal (thread == null) * - on event count advance (winning race to notify vs signaller) * - on interrupt @@ -1468,7 +1463,7 @@ public class ForkJoinPool extends Abstra * If node was not signalled and event count not advanced on exit, * then we also help advance event count. * - * @return true if node can be released + * @return {@code true} if node can be released */ final boolean syncIsReleasable(WaitQueueNode node) { long prev = node.count; @@ -1487,8 +1482,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if a new sync event occurred since last call to - * sync or this method, if so, updating caller's count. + * Returns {@code true} if a new sync event occurred since last + * call to sync or this method, if so, updating caller's count. */ final boolean hasNewSyncEvent(ForkJoinWorkerThread w) { long lc = w.lastEventCount; @@ -1572,8 +1567,8 @@ public class ForkJoinPool extends Abstra } /** - * Returns true if a spare thread appears to be needed. If - * maintaining parallelism, returns true when the deficit in + * Returns {@code true} if a spare thread appears to be needed. + * If maintaining parallelism, returns true when the deficit in * running threads is more than the surplus of total threads, and * there is apparently some work to do. This self-limiting rule * means that the more threads that have already been added, the @@ -1741,11 +1736,13 @@ public class ForkJoinPool extends Abstra /** * Interface for extending managed parallelism for tasks running - * in ForkJoinPools. A ManagedBlocker provides two methods. - * Method {@code isReleasable} must return true if blocking is not - * necessary. Method {@code block} blocks the current thread if - * necessary (perhaps internally invoking {@code isReleasable} - * before actually blocking.). + * in {@link ForkJoinPool}s. + * + *

A {@code ManagedBlocker} provides two methods. + * Method {@code isReleasable} must return {@code true} if + * blocking is not necessary. Method {@code block} blocks the + * current thread if necessary (perhaps internally invoking + * {@code isReleasable} before actually blocking.). * *

For example, here is a ManagedBlocker based on a * ReentrantLock: @@ -1769,46 +1766,48 @@ public class ForkJoinPool extends Abstra * Possibly blocks the current thread, for example waiting for * a lock or condition. * - * @return true if no additional blocking is necessary (i.e., - * if isReleasable would return true) + * @return {@code true} if no additional blocking is necessary + * (i.e., if isReleasable would return true) * @throws InterruptedException if interrupted while waiting * (the method is not required to do so, but is allowed to) */ boolean block() throws InterruptedException; /** - * Returns true if blocking is unnecessary. + * Returns {@code true} if blocking is unnecessary. */ boolean isReleasable(); } /** * Blocks in accord with the given blocker. If the current thread - * is a ForkJoinWorkerThread, this method possibly arranges for a - * spare thread to be activated if necessary to ensure parallelism - * while the current thread is blocked. If - * {@code maintainParallelism} is true and the pool supports - * it ({@link #getMaintainsParallelism}), this method attempts to - * maintain the pool's nominal parallelism. Otherwise it activates - * a thread only if necessary to avoid complete starvation. This - * option may be preferable when blockages use timeouts, or are - * almost always brief. + * is a {@link ForkJoinWorkerThread}, this method possibly + * arranges for a spare thread to be activated if necessary to + * ensure parallelism while the current thread is blocked. + * + *

If {@code maintainParallelism} is {@code true} and the pool + * supports it ({@link #getMaintainsParallelism}), this method + * attempts to maintain the pool's nominal parallelism. Otherwise + * it activates a thread only if necessary to avoid complete + * starvation. This option may be preferable when blockages use + * timeouts, or are almost always brief. * - *

If the caller is not a ForkJoinTask, this method is behaviorally - * equivalent to + *

If the caller is not a {@link ForkJoinTask}, this method is + * behaviorally equivalent to * 

 {@code
      * while (!blocker.isReleasable())
      *   if (blocker.block())
      *     return;
      * }
- * If the caller is a ForkJoinTask, then the pool may first - * be expanded to ensure parallelism, and later adjusted. + * + * If the caller is a {@code ForkJoinTask}, then the pool may + * first be expanded to ensure parallelism, and later adjusted. * * @param blocker the blocker - * @param maintainParallelism if true and supported by this pool, - * attempt to maintain the pool's nominal parallelism; otherwise - * activate a thread only if necessary to avoid complete - * starvation. + * @param maintainParallelism if {@code true} and supported by + * this pool, attempt to maintain the pool's nominal parallelism; + * otherwise activate a thread only if necessary to avoid + * complete starvation. * @throws InterruptedException if blocker.block did so */ public static void managedBlock(ManagedBlocker blocker, @@ -1834,66 +1833,31 @@ public class ForkJoinPool extends Abstra do {} while (!blocker.isReleasable() && !blocker.block()); } - // AbstractExecutorService overrides + // AbstractExecutorService overrides. These rely on undocumented + // fact that ForkJoinTask.adapt returns ForkJoinTasks that also + // implement RunnableFuture. protected RunnableFuture newTaskFor(Runnable runnable, T value) { - return new AdaptedRunnable(runnable, value); + return (RunnableFuture) ForkJoinTask.adapt(runnable, value); } protected RunnableFuture newTaskFor(Callable callable) { - return new AdaptedCallable(callable); + return (RunnableFuture) ForkJoinTask.adapt(callable); } + // Unsafe mechanics - // Temporary Unsafe mechanics for preliminary release - private static Unsafe getUnsafe() throws Throwable { - try { - return Unsafe.getUnsafe(); - } catch (SecurityException se) { - try { - return java.security.AccessController.doPrivileged - (new java.security.PrivilegedExceptionAction() { - public Unsafe run() throws Exception { - return getUnsafePrivileged(); - }}); - } catch (java.security.PrivilegedActionException e) { - throw e.getCause(); - } - } - } - - private static Unsafe getUnsafePrivileged() - throws NoSuchFieldException, IllegalAccessException { - Field f = Unsafe.class.getDeclaredField("theUnsafe"); - f.setAccessible(true); - return (Unsafe) f.get(null); - } - - private static long fieldOffset(String fieldName) - throws NoSuchFieldException { - return UNSAFE.objectFieldOffset - (ForkJoinPool.class.getDeclaredField(fieldName)); - } - - static final Unsafe UNSAFE; - static final long eventCountOffset; - static final long workerCountsOffset; - static final long runControlOffset; - static final long syncStackOffset; - static final long spareStackOffset; - - static { - try { - UNSAFE = getUnsafe(); - eventCountOffset = fieldOffset("eventCount"); - workerCountsOffset = fieldOffset("workerCounts"); - runControlOffset = fieldOffset("runControl"); - syncStackOffset = fieldOffset("syncStack"); - spareStackOffset = fieldOffset("spareStack"); - } catch (Throwable e) { - throw new RuntimeException("Could not initialize intrinsics", e); - } - } + private static final sun.misc.Unsafe UNSAFE = getUnsafe(); + private static final long eventCountOffset = + objectFieldOffset("eventCount", ForkJoinPool.class); + private static final long workerCountsOffset = + objectFieldOffset("workerCounts", ForkJoinPool.class); + private static final long runControlOffset = + objectFieldOffset("runControl", ForkJoinPool.class); + private static final long syncStackOffset = + objectFieldOffset("syncStack",ForkJoinPool.class); + private static final long spareStackOffset = + objectFieldOffset("spareStack", ForkJoinPool.class); private boolean casEventCount(long cmp, long val) { return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val); @@ -1910,4 +1874,43 @@ public class ForkJoinPool extends Abstra private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) { return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val); } + + private static long objectFieldOffset(String field, Class klazz) { + try { + return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); + } catch (NoSuchFieldException e) { + // Convert Exception to corresponding Error + NoSuchFieldError error = new NoSuchFieldError(field); + error.initCause(e); + throw error; + } + } + + /** + * Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. + * Replace with a simple call to Unsafe.getUnsafe when integrating + * into a jdk. + * + * @return a sun.misc.Unsafe + */ + private static sun.misc.Unsafe getUnsafe() { + try { + return sun.misc.Unsafe.getUnsafe(); + } catch (SecurityException se) { + try { + return java.security.AccessController.doPrivileged + (new java.security + .PrivilegedExceptionAction() { + public sun.misc.Unsafe run() throws Exception { + java.lang.reflect.Field f = sun.misc + .Unsafe.class.getDeclaredField("theUnsafe"); + f.setAccessible(true); + return (sun.misc.Unsafe) f.get(null); + }}); + } catch (java.security.PrivilegedActionException e) { + throw new RuntimeException("Could not initialize intrinsics", + e.getCause()); + } + } + } }