--- jsr166/src/jsr166y/ForkJoinPool.java 2009/03/19 05:10:42 1.5 +++ jsr166/src/jsr166y/ForkJoinPool.java 2009/11/16 04:57:09 1.49 @@ -5,55 +5,91 @@ */ 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. * - *
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. Otherwise, other - * ExecutorService implementations are typically more appropriate - * choices. + *
A {@code ForkJoinPool} differs from other kinds of {@link + * ExecutorService} mainly by virtue of employing + * work-stealing: all threads in the pool attempt to find and + * execute subtasks created by other active tasks (eventually blocking + * waiting for work if none exist). This enables efficient processing + * when most tasks spawn other subtasks (as do most {@code + * ForkJoinTask}s). A {@code ForkJoinPool} may also be used for 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 of any form + * 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 ManagedBlocker
interface enables extension of
- * the kinds of synchronization accommodated. The target parallelism
- * level may also be changed dynamically (setParallelism
)
- * and dynamically thread construction can be limited using methods
- * setMaximumPoolSize
and/or
- * setMaintainsParallelism
.
+ *
A {@code ForkJoinPool} is constructed with a given target + * parallelism level; by default, equal to the number of available + * processors. Unless configured otherwise via {@link + * #setMaintainsParallelism}, the pool attempts to maintain this + * number of active (or available) threads by dynamically adding, + * suspending, or resuming internal worker threads, even if some tasks + * are stalled 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}). The total number of threads may be + * limited using method {@link #setMaximumPoolSize}, in which case it + * may become possible for the activities of a pool to stall due to + * the lack of available threads to process new tasks. * *
In addition to execution and lifecycle control methods, this
* class provides status check methods (for example
- * 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
- * toString
returns indications of pool state in a
+ * {@link #toString} returns indications of pool state in a
* convenient form for informal monitoring.
*
+ *
Sample Usage. Normally a single {@code ForkJoinPool} is + * used for all parallel task execution in a program or subsystem. + * Otherwise, use would not usually outweigh the construction and + * bookkeeping overhead of creating a large set of threads. For + * example, a common pool could be used for the {@code SortTasks} + * illustrated in {@link RecursiveAction}. Because {@code + * ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon + * daemon} mode, there is typically no need to explicitly {@link + * #shutdown} such a pool upon program exit. + * + *
+ * static final ForkJoinPool mainPool = new ForkJoinPool(); + * ... + * public void sort(long[] array) { + * mainPool.invoke(new SortTask(array, 0, array.length)); + * } + *+ * *
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. + * pools with greater than the maximum number result in + * {@code IllegalArgumentException}. + * + *
This implementation rejects submitted tasks (that is, by throwing
+ * {@link RejectedExecutionException}) only when the pool is shut down.
+ *
+ * @since 1.7
+ * @author Doug Lea
*/
public class ForkJoinPool extends AbstractExecutorService {
@@ -69,23 +105,23 @@ 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 {
/**
* Returns a new worker thread operating in the given pool.
*
* @param pool the pool this thread works in
- * @throws NullPointerException if pool is null;
+ * @throws NullPointerException if the pool is null
*/
public ForkJoinWorkerThread newThread(ForkJoinPool pool);
}
/**
- * Default ForkJoinWorkerThreadFactory implementation, creates a
+ * Default ForkJoinWorkerThreadFactory implementation; creates a
* new ForkJoinWorkerThread.
*/
static class DefaultForkJoinWorkerThreadFactory
@@ -131,11 +167,11 @@ public class ForkJoinPool extends Abstra
new AtomicInteger();
/**
- * Array holding all worker threads in the pool. Array size must
- * be a power of two. Updates and replacements are protected by
- * workerLock, but it is always kept in a consistent enough state
- * to be randomly accessed without locking by workers performing
- * work-stealing.
+ * Array holding all worker threads in the pool. Initialized upon
+ * first use. Array size must be a power of two. Updates and
+ * replacements are protected by workerLock, but it is always kept
+ * in a consistent enough state to be randomly accessed without
+ * locking by workers performing work-stealing.
*/
volatile ForkJoinWorkerThread[] workers;
@@ -151,7 +187,7 @@ public class ForkJoinPool extends Abstra
/**
* The uncaught exception handler used when any worker
- * abrupty terminates
+ * abruptly terminates
*/
private Thread.UncaughtExceptionHandler ueh;
@@ -179,7 +215,7 @@ public class ForkJoinPool extends Abstra
private final LinkedTransferQueue 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:
- * If the caller is not a ForkJoinTask, this method is behaviorally
- * equivalent to
- * 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 {@link ForkJoinTask}, this method is
+ * behaviorally equivalent to
+ * ("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool() {
this(Runtime.getRuntime().availableProcessors(),
@@ -334,47 +381,51 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the indicated parellelism level
- * threads, and using the default ForkJoinWorkerThreadFactory,
- * @param parallelism the number of worker threads
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
+ *
+ * @param parallelism the parallelism level
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero
+ * equal to zero, or greater than implementation limit
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism) {
this(parallelism, defaultForkJoinWorkerThreadFactory);
}
/**
- * Creates a ForkJoinPool with parallelism equal to the number of
- * processors available on the system and using the given
- * ForkJoinWorkerThreadFactory,
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the given
+ * thread factory.
+ *
* @param factory the factory for creating new threads
- * @throws NullPointerException if factory is null
+ * @throws NullPointerException if the factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
this(Runtime.getRuntime().availableProcessors(), factory);
}
/**
- * Creates a ForkJoinPool with the given parallelism and factory.
+ * Creates a {@code ForkJoinPool} with the given parallelism and
+ * thread factory.
*
- * @param parallelism the targeted number of worker threads
+ * @param parallelism the parallelism level
* @param factory the factory for creating new threads
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero, or greater than implementation limit.
- * @throws NullPointerException if factory is null
+ * equal to zero, or greater than implementation limit
+ * @throws NullPointerException if the factory is null
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
if (parallelism <= 0 || parallelism > MAX_THREADS)
@@ -391,13 +442,14 @@ public class ForkJoinPool extends Abstra
this.termination = workerLock.newCondition();
this.stealCount = new AtomicLong();
this.submissionQueue = new LinkedTransferQueue("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public Thread.UncaughtExceptionHandler
setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
@@ -683,10 +764,12 @@ public class ForkJoinPool extends Abstra
old = ueh;
ueh = h;
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread w = ws[i];
- if (w != null)
- w.setUncaughtExceptionHandler(h);
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ w.setUncaughtExceptionHandler(h);
+ }
}
} finally {
lock.unlock();
@@ -696,14 +779,15 @@ public class ForkJoinPool extends Abstra
/**
- * Sets the target paralleism level of this pool.
+ * Sets the target parallelism level of this pool.
+ *
* @param parallelism the target parallelism
* @throws IllegalArgumentException if parallelism less than or
- * equal to zero or greater than maximum size bounds.
+ * equal to zero or greater than maximum size bounds
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public void setParallelism(int parallelism) {
checkPermission();
@@ -712,7 +796,7 @@ public class ForkJoinPool extends Abstra
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
- if (!isTerminating()) {
+ if (isProcessingTasks()) {
int p = this.parallelism;
this.parallelism = parallelism;
if (parallelism > p)
@@ -727,9 +811,9 @@ public class ForkJoinPool extends Abstra
}
/**
- * Returns the targeted number of worker threads in this pool.
+ * Returns the targeted parallelism level of this pool.
*
- * @return the targeted number of worker threads in this pool
+ * @return the targeted parallelism level of this pool
*/
public int getParallelism() {
return parallelism;
@@ -738,7 +822,7 @@ 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 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
@@ -749,7 +833,10 @@ public class ForkJoinPool extends Abstra
/**
* Returns the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
+ * pool. Unless set using {@link #setMaximumPoolSize}, the
+ * maximum is an implementation-defined value designed only to
+ * prevent runaway growth.
+ *
* @return the maximum
*/
public int getMaximumPoolSize() {
@@ -758,11 +845,13 @@ public class ForkJoinPool extends Abstra
/**
* Sets the maximum number of threads allowed to exist in the
- * pool, even if there are insufficient unblocked running threads.
- * Setting this value has no effect on current pool size. It
- * controls construction of new threads.
- * @throws IllegalArgumentException if negative or greater then
- * internal implementation limit.
+ * pool. The given value should normally be greater than or equal
+ * to the {@link #getParallelism parallelism} level. Setting this
+ * value has no effect on current pool size. It controls
+ * construction of new threads.
+ *
+ * @throws IllegalArgumentException if negative or greater than
+ * internal implementation limit
*/
public void setMaximumPoolSize(int newMax) {
if (newMax < 0 || newMax > MAX_THREADS)
@@ -772,11 +861,11 @@ 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;
- * @return true if maintains parallelism
+ * 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 {@code true} if maintains parallelism
*/
public boolean getMaintainsParallelism() {
return maintainsParallelism;
@@ -786,13 +875,52 @@ public class ForkJoinPool extends Abstra
* Sets whether this pool dynamically maintains its target
* 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;
}
/**
+ * Establishes local first-in-first-out scheduling mode for forked
+ * 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 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 {@code true}, use locally FIFO scheduling
+ * @return the previous mode
+ * @see #getAsyncMode
+ */
+ public boolean setAsyncMode(boolean async) {
+ boolean oldMode = locallyFifo;
+ locallyFifo = async;
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.setAsyncMode(async);
+ }
+ }
+ return oldMode;
+ }
+
+ /**
+ * Returns {@code true} if this pool uses local first-in-first-out
+ * scheduling mode for forked tasks that are never joined.
+ *
+ * @return {@code true} if this pool uses async mode
+ * @see #setAsyncMode
+ */
+ public boolean getAsyncMode() {
+ return locallyFifo;
+ }
+
+ /**
* Returns an estimate of the number of worker threads that are
* not blocked waiting to join tasks or for other managed
* synchronization.
@@ -807,7 +935,8 @@ public class ForkJoinPool extends Abstra
* Returns an estimate of the number of threads that are currently
* stealing or executing tasks. This method may overestimate the
* number of active threads.
- * @return the number of active threads.
+ *
+ * @return the number of active threads
*/
public int getActiveThreadCount() {
return activeCountOf(runControl);
@@ -817,22 +946,24 @@ public class ForkJoinPool extends Abstra
* Returns an estimate of the number of threads that are currently
* idle waiting for tasks. This method may underestimate the
* number of idle threads.
- * @return the number of idle threads.
+ *
+ * @return the number of idle threads
*/
final int getIdleThreadCount() {
int c = runningCountOf(workerCounts) - activeCountOf(runControl);
- return (c <= 0)? 0 : c;
+ return (c <= 0) ? 0 : c;
}
/**
- * 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.
- * @return true if all threads are currently idle
+ * 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 {@code true} if all threads are currently idle
*/
public boolean isQuiescent() {
return activeCountOf(runControl) == 0;
@@ -843,18 +974,19 @@ public class ForkJoinPool extends Abstra
* one thread's work queue by another. The reported value
* underestimates the actual total number of steals when the pool
* is not quiescent. This value may be useful for monitoring and
- * tuning fork/join programs: In general, steal counts should be
+ * tuning fork/join programs: in general, steal counts should be
* high enough to keep threads busy, but low enough to avoid
* overhead and contention across threads.
- * @return the number of steals.
+ *
+ * @return the number of steals
*/
public long getStealCount() {
return stealCount.get();
}
/**
- * Accumulate steal count from a worker. Call only
- * when worker known to be idle.
+ * Accumulates steal count from a worker.
+ * Call only when worker known to be idle.
*/
private void updateStealCount(ForkJoinWorkerThread w) {
int sc = w.getAndClearStealCount();
@@ -869,33 +1001,38 @@ public class ForkJoinPool extends Abstra
* an approximation, obtained by iterating across all threads in
* the pool. This method may be useful for tuning task
* granularities.
- * @return the number of queued tasks.
+ *
+ * @return the number of queued tasks
*/
public long getQueuedTaskCount() {
long count = 0;
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- count += t.getQueueSize();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ count += t.getQueueSize();
+ }
}
return count;
}
/**
- * Returns an estimate of the number tasks submitted to this pool
- * that have not yet begun executing. This method takes time
+ * Returns an estimate of the number of tasks submitted to this
+ * pool that have not yet begun executing. This method takes time
* proportional to the number of submissions.
- * @return the number of queued submissions.
+ *
+ * @return the number of queued submissions
*/
public int getQueuedSubmissionCount() {
return submissionQueue.size();
}
/**
- * Returns true if there are any tasks submitted to this pool
- * that have not yet begun executing.
- * @return true
if there are any queued submissions.
+ * 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
*/
public boolean hasQueuedSubmissions() {
return !submissionQueue.isEmpty();
@@ -905,13 +1042,44 @@ public class ForkJoinPool extends Abstra
* Removes and returns the next unexecuted submission if one is
* 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();
}
/**
+ * Removes all available unexecuted submitted and forked tasks
+ * from scheduling queues and adds them to the given collection,
+ * without altering their execution status. These may include
+ * artificially generated or wrapped tasks. This method is
+ * designed to be invoked only when the pool is known to be
+ * quiescent. Invocations at other times may not remove all
+ * tasks. A failure encountered while attempting to add elements
+ * to collection {@code c} may result in elements being in
+ * neither, either or both collections when the associated
+ * exception is thrown. The behavior of this operation is
+ * undefined if the specified collection is modified while the
+ * operation is in progress.
+ *
+ * @param c the collection to transfer elements into
+ * @return the number of elements transferred
+ */
+ protected int drainTasksTo(Collection super ForkJoinTask>> c) {
+ int n = submissionQueue.drainTo(c);
+ ForkJoinWorkerThread[] ws = workers;
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread w = ws[i];
+ if (w != null)
+ n += w.drainTasksTo(c);
+ }
+ }
+ return n;
+ }
+
+ /**
* Returns a string identifying this pool, as well as its state,
* including indications of run state, parallelism level, and
* worker and task counts.
@@ -938,7 +1106,7 @@ public class ForkJoinPool extends Abstra
}
private static String runStateToString(int rs) {
- switch(rs) {
+ switch (rs) {
case RUNNING: return "Running";
case SHUTDOWN: return "Shutting down";
case TERMINATING: return "Terminating";
@@ -955,30 +1123,48 @@ public class ForkJoinPool extends Abstra
* Invocation has no additional effect if already shut down.
* Tasks that are in the process of being submitted concurrently
* during the course of this method may or may not be rejected.
+ *
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
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();
+ }
}
/**
- * Attempts to stop all actively executing tasks, and cancels all
- * waiting tasks. Tasks that are in the process of being
- * submitted or executed concurrently during the course of this
- * method may or may not be rejected. Unlike some other executors,
- * this method cancels rather than collects non-executed tasks,
- * so always returns an empty list.
+ * Attempts to cancel and/or stop all tasks, and reject all
+ * subsequently submitted tasks. Tasks that are in the process of
+ * being submitted or executed concurrently during the course of
+ * this method may or may not be rejected. This method cancels
+ * both existing and unexecuted tasks, in order to permit
+ * termination in the presence of task dependencies. So the method
+ * always returns an empty list (unlike the case for some other
+ * Executors).
+ *
* @return an empty list
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
* because it does not hold {@link
- * java.lang.RuntimePermission}("modifyThread")
,
+ * java.lang.RuntimePermission}{@code ("modifyThread")}
*/
public Listtrue
if all tasks have completed following shut down.
+ * Returns {@code true} if all tasks have completed following shut down.
*
- * @return true
if all tasks have completed following shut down
+ * @return {@code true} if all tasks have completed following shut down
*/
public boolean isTerminated() {
return runStateOf(runControl) == TERMINATED;
}
/**
- * Returns true
if the process of termination has
- * commenced but possibly not yet completed.
+ * Returns {@code true} if the process of termination has
+ * commenced but not yet completed. This method may be useful for
+ * debugging. A return of {@code true} reported a sufficient
+ * period after shutdown may indicate that submitted tasks have
+ * ignored or suppressed interruption, causing this executor not
+ * to properly terminate.
*
- * @return true
if terminating
+ * @return {@code true} if terminating but not yet terminated
*/
public boolean isTerminating() {
- return runStateOf(runControl) >= TERMINATING;
+ return runStateOf(runControl) == TERMINATING;
}
/**
- * Returns true
if this pool has been shut down.
+ * Returns {@code true} if this pool has been shut down.
*
- * @return true
if this pool has been shut down
+ * @return {@code true} if this pool has been shut down
*/
public boolean isShutdown() {
return runStateOf(runControl) >= SHUTDOWN;
}
/**
+ * Returns true if pool is not terminating or terminated.
+ * Used internally to suppress execution when terminating.
+ */
+ final boolean isProcessingTasks() {
+ return runStateOf(runControl) < TERMINATING;
+ }
+
+ /**
* Blocks until all tasks have completed execution after a shutdown
* request, or the timeout occurs, or the current thread is
* interrupted, whichever happens first.
*
* @param timeout the maximum time to wait
* @param unit the time unit of the timeout argument
- * @return true
if this executor terminated and
- * false
if the timeout elapsed before termination
+ * @return {@code true} if this executor terminated and
+ * {@code false} if the timeout elapsed before termination
* @throws InterruptedException if interrupted while waiting
*/
public boolean awaitTermination(long timeout, TimeUnit unit)
@@ -1046,9 +1244,10 @@ public class ForkJoinPool extends Abstra
// Shutdown and termination support
/**
- * Callback from terminating worker. Null out the corresponding
- * workers slot, and if terminating, try to terminate, else try to
- * shrink workers array.
+ * Callback from terminating worker. Nulls out the corresponding
+ * workers slot, and if terminating, tries to terminate; else
+ * tries to shrink workers array.
+ *
* @param w the worker
*/
final void workerTerminated(ForkJoinWorkerThread w) {
@@ -1058,17 +1257,19 @@ public class ForkJoinPool extends Abstra
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- int idx = w.poolIndex;
- if (idx >= 0 && idx < ws.length && ws[idx] == w)
- ws[idx] = null;
- if (totalCountOf(workerCounts) == 0) {
- terminate(); // no-op if already terminating
- transitionRunStateTo(TERMINATED);
- termination.signalAll();
- }
- else if (!isTerminating()) {
- tryShrinkWorkerArray();
- tryResumeSpare(true); // allow replacement
+ if (ws != null) {
+ int idx = w.poolIndex;
+ if (idx >= 0 && idx < ws.length && ws[idx] == w)
+ ws[idx] = null;
+ if (totalCountOf(workerCounts) == 0) {
+ terminate(); // no-op if already terminating
+ transitionRunStateTo(TERMINATED);
+ termination.signalAll();
+ }
+ else if (isProcessingTasks()) {
+ tryShrinkWorkerArray();
+ tryResumeSpare(true); // allow replacement
+ }
}
} finally {
lock.unlock();
@@ -1077,7 +1278,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Initiate termination.
+ * Initiates termination.
*/
private void terminate() {
if (transitionRunStateTo(TERMINATING)) {
@@ -1092,7 +1293,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Possibly terminate when on shutdown state
+ * Possibly terminates when on shutdown state.
*/
private void terminateOnShutdown() {
if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
@@ -1100,7 +1301,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Clear out and cancel submissions
+ * Clears out and cancels submissions.
*/
private void cancelQueuedSubmissions() {
ForkJoinTask> task;
@@ -1109,17 +1310,19 @@ public class ForkJoinPool extends Abstra
}
/**
- * Clean out worker queues.
+ * Cleans out worker queues.
*/
private void cancelQueuedWorkerTasks() {
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.cancelTasks();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.cancelTasks();
+ }
}
} finally {
lock.unlock();
@@ -1127,18 +1330,20 @@ public class ForkJoinPool extends Abstra
}
/**
- * Set each worker's status to terminating. Requires lock to avoid
- * conflicts with add/remove
+ * Sets each worker's status to terminating. Requires lock to avoid
+ * conflicts with add/remove.
*/
private void stopAllWorkers() {
final ReentrantLock lock = this.workerLock;
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null)
- t.shutdownNow();
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null)
+ t.shutdownNow();
+ }
}
} finally {
lock.unlock();
@@ -1146,7 +1351,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Interrupt all unterminated workers. This is not required for
+ * Interrupts all unterminated workers. This is not required for
* sake of internal control, but may help unstick user code during
* shutdown.
*/
@@ -1155,12 +1360,14 @@ public class ForkJoinPool extends Abstra
lock.lock();
try {
ForkJoinWorkerThread[] ws = workers;
- for (int i = 0; i < ws.length; ++i) {
- ForkJoinWorkerThread t = ws[i];
- if (t != null && !t.isTerminated()) {
- try {
- t.interrupt();
- } catch (SecurityException ignore) {
+ if (ws != null) {
+ for (int i = 0; i < ws.length; ++i) {
+ ForkJoinWorkerThread t = ws[i];
+ if (t != null && !t.isTerminated()) {
+ try {
+ t.interrupt();
+ } catch (SecurityException ignore) {
+ }
}
}
}
@@ -1214,7 +1421,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Wake up waiter, returning false if known to already
+ * Wakes up waiter, returning false if known to already
*/
boolean signal() {
ForkJoinWorkerThread t = thread;
@@ -1226,7 +1433,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Await release on sync
+ * Awaits release on sync.
*/
void awaitSyncRelease(ForkJoinPool p) {
while (thread != null && !p.syncIsReleasable(this))
@@ -1234,7 +1441,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Await resumption as spare
+ * Awaits resumption as spare.
*/
void awaitSpareRelease() {
while (thread != null) {
@@ -1248,6 +1455,7 @@ public class ForkJoinPool extends Abstra
* Ensures that no thread is waiting for count to advance from the
* current value of eventCount read on entry to this method, by
* releasing waiting threads if necessary.
+ *
* @return the count
*/
final long ensureSync() {
@@ -1269,12 +1477,12 @@ public class ForkJoinPool extends Abstra
*/
private void signalIdleWorkers() {
long c;
- do;while (!casEventCount(c = eventCount, c+1));
+ do {} while (!casEventCount(c = eventCount, c+1));
ensureSync();
}
/**
- * Signal threads waiting to poll a task. Because method sync
+ * Signals threads waiting to poll a task. Because method sync
* rechecks availability, it is OK to only proceed if queue
* appears to be non-empty, and OK to skip under contention to
* increment count (since some other thread succeeded).
@@ -1293,12 +1501,13 @@ public class ForkJoinPool extends Abstra
* Waits until event count advances from last value held by
* caller, or if excess threads, caller is resumed as spare, or
* caller or pool is terminating. Updates caller's event on exit.
+ *
* @param w the calling worker thread
*/
final void sync(ForkJoinWorkerThread w) {
updateStealCount(w); // Transfer w's count while it is idle
- while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
+ while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
long prev = w.lastEventCount;
WaitQueueNode node = null;
WaitQueueNode h;
@@ -1320,14 +1529,15 @@ 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
+ * - on interrupt
* - if the first queued node, we find work available
* 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;
@@ -1346,8 +1556,8 @@ 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;
@@ -1361,13 +1571,13 @@ public class ForkJoinPool extends Abstra
// Parallelism maintenance
/**
- * Decrement running count; if too low, add spare.
+ * Decrements running count; if too low, adds spare.
*
* Conceptually, all we need to do here is add or resume a
* spare thread when one is about to block (and remove or
* suspend it later when unblocked -- see suspendIfSpare).
* However, implementing this idea requires coping with
- * several problems: We have imperfect information about the
+ * several problems: we have imperfect information about the
* states of threads. Some count updates can and usually do
* lag run state changes, despite arrangements to keep them
* accurate (for example, when possible, updating counts
@@ -1381,7 +1591,7 @@ public class ForkJoinPool extends Abstra
* only be suspended or removed when they are idle, not
* immediately when they aren't needed. So adding threads will
* raise parallelism level for longer than necessary. Also,
- * FJ applications often enounter highly transient peaks when
+ * FJ applications often encounter highly transient peaks when
* many threads are blocked joining, but for less time than it
* takes to create or resume spares.
*
@@ -1390,12 +1600,13 @@ public class ForkJoinPool extends Abstra
* target counts, else create only to avoid starvation
* @return true if joinMe known to be done
*/
- final boolean preJoin(ForkJoinTask> joinMe, boolean maintainParallelism) {
+ final boolean preJoin(ForkJoinTask> joinMe,
+ boolean maintainParallelism) {
maintainParallelism &= maintainsParallelism; // overrride
boolean dec = false; // true when running count decremented
while (spareStack == null || !tryResumeSpare(dec)) {
int counts = workerCounts;
- if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
+ if (dec || (dec = casWorkerCounts(counts, --counts))) {
if (!needSpare(counts, maintainParallelism))
break;
if (joinMe.status < 0)
@@ -1410,7 +1621,8 @@ public class ForkJoinPool extends Abstra
/**
* Same idea as preJoin
*/
- final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
+ final boolean preBlock(ManagedBlocker blocker,
+ boolean maintainParallelism) {
maintainParallelism &= maintainsParallelism;
boolean dec = false;
while (spareStack == null || !tryResumeSpare(dec)) {
@@ -1428,12 +1640,13 @@ 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
* less parallelism we will tolerate before adding another.
+ *
* @param counts current worker counts
* @param maintainParallelism try to maintain parallelism
*/
@@ -1451,8 +1664,9 @@ public class ForkJoinPool extends Abstra
}
/**
- * Add a spare worker if lock available and no more than the
- * expected numbers of threads exist
+ * Adds a spare worker if lock available and no more than the
+ * expected numbers of threads exist.
+ *
* @return true if successful
*/
private boolean tryAddSpare(int expectedCounts) {
@@ -1485,7 +1699,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Add the kth spare worker. On entry, pool coounts are already
+ * Adds the kth spare worker. On entry, pool counts are already
* adjusted to reflect addition.
*/
private void createAndStartSpare(int k) {
@@ -1497,7 +1711,7 @@ public class ForkJoinPool extends Abstra
for (k = 0; k < len && ws[k] != null; ++k)
;
}
- if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
+ if (k < len && isProcessingTasks() && (w = createWorker(k)) != null) {
ws[k] = w;
w.start();
}
@@ -1507,11 +1721,12 @@ public class ForkJoinPool extends Abstra
}
/**
- * Suspend calling thread w if there are excess threads. Called
- * only from sync. Spares are enqueued in a Treiber stack
- * using the same WaitQueueNodes as barriers. They are resumed
- * mainly in preJoin, but are also woken on pool events that
- * require all threads to check run state.
+ * Suspends calling thread w if there are excess threads. Called
+ * only from sync. Spares are enqueued in a Treiber stack using
+ * the same WaitQueueNodes as barriers. They are resumed mainly
+ * in preJoin, but are also woken on pool events that require all
+ * threads to check run state.
+ *
* @param w the caller
*/
private boolean suspendIfSpare(ForkJoinWorkerThread w) {
@@ -1522,7 +1737,7 @@ public class ForkJoinPool extends Abstra
node = new WaitQueueNode(0, w);
if (casWorkerCounts(s, s-1)) { // representation-dependent
// push onto stack
- do;while (!casSpareStack(node.next = spareStack, node));
+ do {} while (!casSpareStack(node.next = spareStack, node));
// block until released by resumeSpare
node.awaitSpareRelease();
return true;
@@ -1532,7 +1747,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Try to pop and resume a spare thread.
+ * Tries to pop and resume a spare thread.
+ *
* @param updateCount if true, increment running count on success
* @return true if successful
*/
@@ -1550,7 +1766,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * Pop and resume all spare threads. Same idea as ensureSync.
+ * Pops and resumes all spare threads. Same idea as ensureSync.
+ *
* @return true if any spares released
*/
private boolean resumeAllSpares() {
@@ -1568,7 +1785,7 @@ public class ForkJoinPool extends Abstra
}
/**
- * Pop and shutdown excessive spare threads. Call only while
+ * Pops and shuts down excessive spare threads. Call only while
* holding lock. This is not guaranteed to eliminate all excess
* threads, only those suspended as spares, which are the ones
* unlikely to be needed in the future.
@@ -1592,81 +1809,86 @@ public class ForkJoinPool extends Abstra
/**
* Interface for extending managed parallelism for tasks running
- * in ForkJoinPools. A ManagedBlocker provides two methods.
- * Method isReleasable
must return true if blocking is not
- * necessary. Method block
blocks the current thread
- * if necessary (perhaps internally invoking isReleasable before
- * actually blocking.).
+ * in {@link ForkJoinPool}s.
+ *
+ *
- * class ManagedLocker implements ManagedBlocker {
- * final ReentrantLock lock;
- * boolean hasLock = false;
- * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
- * public boolean block() {
- * if (!hasLock)
- * lock.lock();
- * return true;
- * }
- * public boolean isReleasable() {
- * return hasLock || (hasLock = lock.tryLock());
- * }
+ *
*/
public static interface ManagedBlocker {
/**
* 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 allowe to).
+ * (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
+ * class ManagedLocker implements ManagedBlocker {
+ * final ReentrantLock lock;
+ * boolean hasLock = false;
+ * ManagedLocker(ReentrantLock lock) { this.lock = lock; }
+ * public boolean block() {
+ * if (!hasLock)
+ * lock.lock();
+ * return true;
+ * }
+ * public boolean isReleasable() {
+ * return hasLock || (hasLock = lock.tryLock());
* }
- *
+ * }}maintainParallelism
is true and the pool supports
- * it ({@link #getMaintainsParallelism}), this method attempts to
- * maintain the pool's nominal parallelism. Otherwise if activates
- * a thread only if necessary to avoid complete starvation. This
- * option may be preferable when blockages use timeouts, or are
- * almost always brief.
- *
- *
- * 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.
+ * 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.
+ *
+ * {@code
+ * while (!blocker.isReleasable())
+ * if (blocker.block())
+ * return;
+ * }
+ *
+ * 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.
- * @throws InterruptedException if blocker.block did so.
+ * @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,
boolean maintainParallelism)
throws InterruptedException {
Thread t = Thread.currentThread();
- ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
- ((ForkJoinWorkerThread)t).pool : null);
+ ForkJoinPool pool = ((t instanceof ForkJoinWorkerThread) ?
+ ((ForkJoinWorkerThread) t).pool : null);
if (!blocker.isReleasable()) {
try {
if (pool == null ||
@@ -1681,83 +1903,87 @@ public class ForkJoinPool extends Abstra
private static void awaitBlocker(ManagedBlocker blocker)
throws InterruptedException {
- do;while (!blocker.isReleasable() && !blocker.block());
+ 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