--- jsr166/src/jsr166y/ForkJoinPool.java 2009/07/31 16:27:08 1.33
+++ jsr166/src/jsr166y/ForkJoinPool.java 2009/12/05 11:39:03 1.52
@@ -21,36 +21,39 @@ import java.util.concurrent.atomic.Atomi
/**
* 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.
+ * 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. When setting {@linkplain
- * #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
- * for use with fine-grained tasks that are never joined. 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 {@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}.
+ *
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
@@ -59,10 +62,31 @@ import java.util.concurrent.atomic.Atomi
* {@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
@@ -81,17 +105,17 @@ 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);
}
@@ -342,9 +366,9 @@ public class ForkJoinPool extends Abstra
// Constructors
/**
- * Creates a ForkJoinPool with a pool size equal to the number of
- * processors available on the system, using the default
- * ForkJoinWorkerThreadFactory.
+ * Creates a {@code ForkJoinPool} with parallelism equal to {@link
+ * java.lang.Runtime#availableProcessors}, and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
*
* @throws SecurityException if a security manager exists and
* the caller is not permitted to modify threads
@@ -357,12 +381,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Creates a ForkJoinPool with the indicated parallelism level
- * threads and using the default ForkJoinWorkerThreadFactory.
+ * Creates a {@code ForkJoinPool} with the indicated parallelism
+ * level and using the {@linkplain
+ * #defaultForkJoinWorkerThreadFactory default thread factory}.
*
- * @param parallelism the number of worker threads
+ * @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
@@ -373,12 +398,12 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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
@@ -389,13 +414,14 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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
@@ -423,7 +449,7 @@ public class ForkJoinPool extends Abstra
* Creates a new worker thread using factory.
*
* @param index the index to assign worker
- * @return new worker, or null of factory failed
+ * @return new worker, or null if factory failed
*/
private ForkJoinWorkerThread createWorker(int index) {
Thread.UncaughtExceptionHandler h = ueh;
@@ -444,8 +470,16 @@ public class ForkJoinPool extends Abstra
* Currently requires size to be a power of two.
*/
private static int arraySizeFor(int poolSize) {
- return (poolSize <= 1) ? 1 :
- (1 << (32 - Integer.numberOfLeadingZeros(poolSize-1)));
+ if (poolSize <= 1)
+ return 1;
+ // See Hackers Delight, sec 3.2
+ int c = poolSize >= MAX_THREADS ? MAX_THREADS : (poolSize - 1);
+ c |= c >>> 1;
+ c |= c >>> 2;
+ c |= c >>> 4;
+ c |= c >>> 8;
+ c |= c >>> 16;
+ return c + 1;
}
/**
@@ -492,14 +526,16 @@ public class ForkJoinPool extends Abstra
ws = workers;
if (ws == null) {
int ps = parallelism;
+ updateWorkerCount(ps);
ws = ensureWorkerArrayCapacity(ps);
for (int i = 0; i < ps; ++i) {
ForkJoinWorkerThread w = createWorker(i);
if (w != null) {
ws[i] = w;
w.start();
- updateWorkerCount(1);
}
+ else
+ updateWorkerCount(-1);
}
}
} finally {
@@ -563,8 +599,9 @@ public class ForkJoinPool extends Abstra
*
* @param task the task
* @return the task's result
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
public T invoke(ForkJoinTask task) {
doSubmit(task);
@@ -575,15 +612,21 @@ public class ForkJoinPool extends Abstra
* Arranges for (asynchronous) execution of the given task.
*
* @param task the task
- * @throws NullPointerException if task is null
- * @throws RejectedExecutionException if pool is shut down
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
*/
- public void execute(ForkJoinTask task) {
+ public void execute(ForkJoinTask task) {
doSubmit(task);
}
// AbstractExecutorService methods
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public void execute(Runnable task) {
ForkJoinTask job;
if (task instanceof ForkJoinTask) // avoid re-wrap
@@ -593,18 +636,33 @@ public class ForkJoinPool extends Abstra
doSubmit(job);
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Callable task) {
ForkJoinTask job = ForkJoinTask.adapt(task);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task, T result) {
ForkJoinTask job = ForkJoinTask.adapt(task, result);
doSubmit(job);
return job;
}
+ /**
+ * @throws NullPointerException if the task is null
+ * @throws RejectedExecutionException if the task cannot be
+ * scheduled for execution
+ */
public ForkJoinTask submit(Runnable task) {
ForkJoinTask job;
if (task instanceof ForkJoinTask) // avoid re-wrap
@@ -620,9 +678,9 @@ public class ForkJoinPool extends Abstra
*
* @param task the task to submit
* @return the task
+ * @throws NullPointerException if the task is null
* @throws RejectedExecutionException if the task cannot be
* scheduled for execution
- * @throws NullPointerException if the task is null
*/
public ForkJoinTask submit(ForkJoinTask task) {
doSubmit(task);
@@ -630,6 +688,10 @@ public class ForkJoinPool extends Abstra
}
+ /**
+ * @throws NullPointerException {@inheritDoc}
+ * @throws RejectedExecutionException {@inheritDoc}
+ */
public List> invokeAll(Collection> tasks) {
ArrayList> forkJoinTasks =
new ArrayList>(tasks.size());
@@ -736,13 +798,15 @@ 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)
- createAndStartAddedWorkers();
- else
- trimSpares();
+ if (workers != null) {
+ if (parallelism > p)
+ createAndStartAddedWorkers();
+ else
+ trimSpares();
+ }
}
} finally {
lock.unlock();
@@ -751,9 +815,9 @@ 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;
@@ -773,7 +837,9 @@ 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
*/
@@ -783,11 +849,12 @@ 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.
+ * 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 then
+ * @throws IllegalArgumentException if negative or greater than
* internal implementation limit
*/
public void setMaximumPoolSize(int newMax) {
@@ -955,8 +1022,8 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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
@@ -990,8 +1057,8 @@ public class ForkJoinPool extends Abstra
* 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
+ * 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
@@ -1043,7 +1110,7 @@ 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";
@@ -1088,14 +1155,14 @@ public class ForkJoinPool extends Abstra
}
/**
- * 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
- * upon termination, so always returns an empty list. However, you
- * can use method {@link #drainTasksTo} before invoking this
- * method to transfer unexecuted tasks to another collection.
+ * 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
@@ -1120,12 +1187,16 @@ public class ForkJoinPool extends Abstra
/**
* Returns {@code true} if the process of termination has
- * commenced but possibly not yet completed.
+ * 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 {@code true} if terminating
+ * @return {@code true} if terminating but not yet terminated
*/
public boolean isTerminating() {
- return runStateOf(runControl) >= TERMINATING;
+ return runStateOf(runControl) == TERMINATING;
}
/**
@@ -1138,6 +1209,14 @@ public class ForkJoinPool extends Abstra
}
/**
+ * 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.
@@ -1191,7 +1270,7 @@ public class ForkJoinPool extends Abstra
transitionRunStateTo(TERMINATED);
termination.signalAll();
}
- else if (!isTerminating()) {
+ else if (isProcessingTasks()) {
tryShrinkWorkerArray();
tryResumeSpare(true); // allow replacement
}
@@ -1301,7 +1380,6 @@ public class ForkJoinPool extends Abstra
}
}
-
/*
* Nodes for event barrier to manage idle threads. Queue nodes
* are basic Treiber stack nodes, also used for spare stack.
@@ -1325,15 +1403,14 @@ public class ForkJoinPool extends Abstra
* handling: Method signalWork returns without advancing count if
* the queue appears to be empty. This would ordinarily result in
* races causing some queued waiters not to be woken up. To avoid
- * this, the first worker enqueued in method sync (see
- * syncIsReleasable) rescans for tasks after being enqueued, and
- * helps signal if any are found. This works well because the
- * worker has nothing better to do, and so might as well help
- * alleviate the overhead and contention on the threads actually
- * doing work. Also, since event counts increments on task
- * availability exist to maintain liveness (rather than to force
- * refreshes etc), it is OK for callers to exit early if
- * contending with another signaller.
+ * this, the first worker enqueued in method sync rescans for
+ * tasks after being enqueued, and helps signal if any are
+ * found. This works well because the worker has nothing better to
+ * do, and so might as well help alleviate the overhead and
+ * contention on the threads actually doing work. Also, since
+ * event counts increments on task availability exist to maintain
+ * liveness (rather than to force refreshes etc), it is OK for
+ * callers to exit early if contending with another signaller.
*/
static final class WaitQueueNode {
WaitQueueNode next; // only written before enqueued
@@ -1346,32 +1423,13 @@ public class ForkJoinPool extends Abstra
}
/**
- * Wakes up waiter, returning false if known to already
+ * Wakes up waiter, also clearing thread field
*/
- boolean signal() {
+ void signal() {
ForkJoinWorkerThread t = thread;
- if (t == null)
- return false;
- thread = null;
- LockSupport.unpark(t);
- return true;
- }
-
- /**
- * Awaits release on sync.
- */
- void awaitSyncRelease(ForkJoinPool p) {
- while (thread != null && !p.syncIsReleasable(this))
- LockSupport.park(this);
- }
-
- /**
- * Awaits resumption as spare.
- */
- void awaitSpareRelease() {
- while (thread != null) {
- if (!Thread.interrupted())
- LockSupport.park(this);
+ if (t != null) {
+ thread = null;
+ LockSupport.unpark(t);
}
}
}
@@ -1380,10 +1438,8 @@ 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() {
+ final void ensureSync() {
long c = eventCount;
WaitQueueNode q;
while ((q = syncStack) != null && q.count < c) {
@@ -1394,7 +1450,6 @@ public class ForkJoinPool extends Abstra
break;
}
}
- return c;
}
/**
@@ -1409,22 +1464,26 @@ public class ForkJoinPool extends Abstra
/**
* 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).
+ * appears to be non-empty, and OK if CAS to increment count
+ * fails (since some other thread succeeded).
*/
final void signalWork() {
- long c;
- WaitQueueNode q;
- if (syncStack != null &&
- casEventCount(c = eventCount, c+1) &&
- (((q = syncStack) != null && q.count <= c) &&
- (!casBarrierStack(q, q.next) || !q.signal())))
- ensureSync();
+ if (syncStack != null) {
+ long c = eventCount;
+ casEventCount(c, c+1);
+ WaitQueueNode q = syncStack;
+ if (q != null && q.count <= c) {
+ if (casBarrierStack(q, q.next))
+ q.signal();
+ else
+ ensureSync(); // awaken all on contention
+ }
+ }
}
/**
- * Waits until event count advances from last value held by
- * caller, or if excess threads, caller is resumed as spare, or
+ * Possibly blocks 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
@@ -1432,52 +1491,35 @@ public class ForkJoinPool extends Abstra
final void sync(ForkJoinWorkerThread w) {
updateStealCount(w); // Transfer w's count while it is idle
- while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
+ if (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
long prev = w.lastEventCount;
WaitQueueNode node = null;
WaitQueueNode h;
- while (eventCount == prev &&
+ long c;
+ while ((c = eventCount) == prev &&
((h = syncStack) == null || h.count == prev)) {
if (node == null)
node = new WaitQueueNode(prev, w);
if (casBarrierStack(node.next = h, node)) {
- node.awaitSyncRelease(this);
+ if (!Thread.interrupted() &&
+ node.thread != null &&
+ eventCount == prev &&
+ (h != null || // cover signalWork race
+ (!ForkJoinWorkerThread.hasQueuedTasks(workers) &&
+ eventCount == prev)))
+ LockSupport.park(this);
+ c = eventCount;
+ if (node.thread != null) { // help signal if not unparked
+ node.thread = null;
+ if (c == prev)
+ casEventCount(prev, prev + 1);
+ }
break;
}
}
- long ec = ensureSync();
- if (ec != prev) {
- w.lastEventCount = ec;
- break;
- }
- }
- }
-
- /**
- * 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
- * - 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 {@code true} if node can be released
- */
- final boolean syncIsReleasable(WaitQueueNode node) {
- long prev = node.count;
- if (!Thread.interrupted() && node.thread != null &&
- (node.next != null ||
- !ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
- eventCount == prev)
- return false;
- if (node.thread != null) {
- node.thread = null;
- long ec = eventCount;
- if (prev <= ec) // help signal
- casEventCount(ec, ec+1);
+ w.lastEventCount = c;
+ ensureSync();
}
- return true;
}
/**
@@ -1485,12 +1527,12 @@ public class ForkJoinPool extends Abstra
* call to sync or this method, if so, updating caller's count.
*/
final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
- long lc = w.lastEventCount;
- long ec = ensureSync();
- if (ec == lc)
- return false;
- w.lastEventCount = ec;
- return true;
+ long wc = w.lastEventCount;
+ long c = eventCount;
+ if (wc != c)
+ w.lastEventCount = c;
+ ensureSync();
+ return wc != c || wc != eventCount;
}
// Parallelism maintenance
@@ -1532,7 +1574,6 @@ public class ForkJoinPool extends Abstra
while (spareStack == null || !tryResumeSpare(dec)) {
int counts = workerCounts;
if (dec || (dec = casWorkerCounts(counts, --counts))) {
- // CAS cheat
if (!needSpare(counts, maintainParallelism))
break;
if (joinMe.status < 0)
@@ -1637,7 +1678,7 @@ 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();
}
@@ -1657,19 +1698,25 @@ public class ForkJoinPool extends Abstra
*/
private boolean suspendIfSpare(ForkJoinWorkerThread w) {
WaitQueueNode node = null;
- int s;
- while (parallelism < runningCountOf(s = workerCounts)) {
+ for (;;) {
+ int s = workerCounts;
+ int rc = runningCountOf(s);
+ int tc = totalCountOf(s);
+ int ps = parallelism;
+ // use tc as bound if rc transiently out of sync
+ if (tc <= ps || rc <= ps)
+ return false; // not a spare
if (node == null)
node = new WaitQueueNode(0, w);
- if (casWorkerCounts(s, s-1)) { // representation-dependent
- // push onto stack
- do {} while (!casSpareStack(node.next = spareStack, node));
- // block until released by resumeSpare
- node.awaitSpareRelease();
- return true;
- }
+ if (casWorkerCounts(s, workerCountsFor(tc, rc - 1)))
+ break;
}
- return false;
+ // push onto stack
+ do {} while (!casSpareStack(node.next = spareStack, node));
+ // block until released by resumeSpare
+ while (!Thread.interrupted() && node.thread != null)
+ LockSupport.park(this);
+ return true;
}
/**
@@ -1735,11 +1782,13 @@ public class ForkJoinPool extends Abstra
/**
* Interface for extending managed parallelism for tasks running
- * in ForkJoinPools. A ManagedBlocker provides two methods.
+ * 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.).
+ * {@code isReleasable} before actually blocking).
*
*
For example, here is a ManagedBlocker based on a
* ReentrantLock:
@@ -1778,25 +1827,27 @@ public class ForkJoinPool extends Abstra
/**
* 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 {@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.
+ * 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 {@code true} and supported by
@@ -1833,11 +1884,11 @@ public class ForkJoinPool extends Abstra
// implement RunnableFuture.
protected RunnableFuture newTaskFor(Runnable runnable, T value) {
- return (RunnableFuture)ForkJoinTask.adapt(runnable, value);
+ return (RunnableFuture) ForkJoinTask.adapt(runnable, value);
}
protected RunnableFuture newTaskFor(Callable callable) {
- return (RunnableFuture)ForkJoinTask.adapt(callable);
+ return (RunnableFuture) ForkJoinTask.adapt(callable);
}
// Unsafe mechanics