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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.43 by jsr166, Tue Aug 4 00:55:13 2009 UTC vs.
Revision 1.51 by dl, Fri Dec 4 15:46:38 2009 UTC

#	Line 23 | Line 23 | import java.util.concurrent.atomic.Atomi
23		* An {@link ExecutorService} for running {@link ForkJoinTask}s.
24		* A {@code ForkJoinPool} provides the entry point for submissions
25		* from non-{@code ForkJoinTask}s, as well as management and
26	<	* monitoring operations.
26	>	* monitoring operations.
27		*
28		* <p>A {@code ForkJoinPool} differs from other kinds of {@link
29		* ExecutorService} mainly by virtue of employing
#	Line 45 | Line 45 | import java.util.concurrent.atomic.Atomi
45		* #setMaintainsParallelism}, the pool attempts to maintain this
46		* number of active (or available) threads by dynamically adding,
47		* suspending, or resuming internal worker threads, even if some tasks
48	<	* are waiting to join others. However, no such adjustments are
49	<	* performed in the face of blocked IO or other unmanaged
48	>	* are stalled waiting to join others. However, no such adjustments
49	>	* are performed in the face of blocked IO or other unmanaged
50		* synchronization. The nested {@link ManagedBlocker} interface
51		* enables extension of the kinds of synchronization accommodated.
52		* The target parallelism level may also be changed dynamically
#	Line 82 | Line 82 | import java.util.concurrent.atomic.Atomi
82		*
83		* <p><b>Implementation notes</b>: This implementation restricts the
84		* maximum number of running threads to 32767. Attempts to create
85	<	* pools with greater than the maximum result in
85	>	* pools with greater than the maximum number result in
86		* {@code IllegalArgumentException}.
87		*
88	+	* <p>This implementation rejects submitted tasks (that is, by throwing
89	+	* {@link RejectedExecutionException}) only when the pool is shut down.
90	+	*
91		* @since 1.7
92		* @author Doug Lea
93		*/
#	Line 112 | Line 115 | public class ForkJoinPool extends Abstra
115		* Returns a new worker thread operating in the given pool.
116		*
117		* @param pool the pool this thread works in
118	<	* @throws NullPointerException if pool is null
118	>	* @throws NullPointerException if the pool is null
119		*/
120		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
121		}
#	Line 384 | Line 387 | public class ForkJoinPool extends Abstra
387		*
388		* @param parallelism the parallelism level
389		* @throws IllegalArgumentException if parallelism less than or
390	<	* equal to zero
390	>	*         equal to zero, or greater than implementation limit
391		* @throws SecurityException if a security manager exists and
392		*         the caller is not permitted to modify threads
393		*         because it does not hold {@link
#	Line 400 | Line 403 | public class ForkJoinPool extends Abstra
403		* thread factory.
404		*
405		* @param factory the factory for creating new threads
406	<	* @throws NullPointerException if factory is null
406	>	* @throws NullPointerException if the factory is null
407		* @throws SecurityException if a security manager exists and
408		*         the caller is not permitted to modify threads
409		*         because it does not hold {@link
#	Line 417 | Line 420 | public class ForkJoinPool extends Abstra
420		* @param parallelism the parallelism level
421		* @param factory the factory for creating new threads
422		* @throws IllegalArgumentException if parallelism less than or
423	<	* equal to zero, or greater than implementation limit
424	<	* @throws NullPointerException if factory is null
423	>	*         equal to zero, or greater than implementation limit
424	>	* @throws NullPointerException if the factory is null
425		* @throws SecurityException if a security manager exists and
426		*         the caller is not permitted to modify threads
427		*         because it does not hold {@link
#	Line 523 | Line 526 | public class ForkJoinPool extends Abstra
526		ws = workers;
527		if (ws == null) {
528		int ps = parallelism;
529	+	updateWorkerCount(ps);
530		ws = ensureWorkerArrayCapacity(ps);
531		for (int i = 0; i < ps; ++i) {
532		ForkJoinWorkerThread w = createWorker(i);
533		if (w != null) {
534		ws[i] = w;
535		w.start();
532	–	updateWorkerCount(1);
536		}
537	+	else
538	+	updateWorkerCount(-1);
539		}
540		}
541		} finally {
#	Line 594 | Line 599 | public class ForkJoinPool extends Abstra
599		*
600		* @param task the task
601		* @return the task's result
602	<	* @throws NullPointerException if task is null
603	<	* @throws RejectedExecutionException if pool is shut down
602	>	* @throws NullPointerException if the task is null
603	>	* @throws RejectedExecutionException if the task cannot be
604	>	*         scheduled for execution
605		*/
606		public <T> T invoke(ForkJoinTask<T> task) {
607		doSubmit(task);
#	Line 606 | Line 612 | public class ForkJoinPool extends Abstra
612		* Arranges for (asynchronous) execution of the given task.
613		*
614		* @param task the task
615	<	* @throws NullPointerException if task is null
616	<	* @throws RejectedExecutionException if pool is shut down
615	>	* @throws NullPointerException if the task is null
616	>	* @throws RejectedExecutionException if the task cannot be
617	>	*         scheduled for execution
618		*/
619		public void execute(ForkJoinTask<?> task) {
620		doSubmit(task);
#	Line 615 | Line 622 | public class ForkJoinPool extends Abstra
622
623		// AbstractExecutorService methods
624
625	+	/**
626	+	* @throws NullPointerException if the task is null
627	+	* @throws RejectedExecutionException if the task cannot be
628	+	*         scheduled for execution
629	+	*/
630		public void execute(Runnable task) {
631		ForkJoinTask<?> job;
632		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 624 | Line 636 | public class ForkJoinPool extends Abstra
636		doSubmit(job);
637		}
638
639	+	/**
640	+	* @throws NullPointerException if the task is null
641	+	* @throws RejectedExecutionException if the task cannot be
642	+	*         scheduled for execution
643	+	*/
644		public <T> ForkJoinTask<T> submit(Callable<T> task) {
645		ForkJoinTask<T> job = ForkJoinTask.adapt(task);
646		doSubmit(job);
647		return job;
648		}
649
650	+	/**
651	+	* @throws NullPointerException if the task is null
652	+	* @throws RejectedExecutionException if the task cannot be
653	+	*         scheduled for execution
654	+	*/
655		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
656		ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
657		doSubmit(job);
658		return job;
659		}
660
661	+	/**
662	+	* @throws NullPointerException if the task is null
663	+	* @throws RejectedExecutionException if the task cannot be
664	+	*         scheduled for execution
665	+	*/
666		public ForkJoinTask<?> submit(Runnable task) {
667		ForkJoinTask<?> job;
668		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
#	Line 651 | Line 678 | public class ForkJoinPool extends Abstra
678		*
679		* @param task the task to submit
680		* @return the task
681	+	* @throws NullPointerException if the task is null
682		* @throws RejectedExecutionException if the task cannot be
683		*         scheduled for execution
656	–	* @throws NullPointerException if the task is null
684		*/
685		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
686		doSubmit(task);
#	Line 661 | Line 688 | public class ForkJoinPool extends Abstra
688		}
689
690
691	+	/**
692	+	* @throws NullPointerException       {@inheritDoc}
693	+	* @throws RejectedExecutionException {@inheritDoc}
694	+	*/
695		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
696		ArrayList<ForkJoinTask<T>> forkJoinTasks =
697		new ArrayList<ForkJoinTask<T>>(tasks.size());
#	Line 770 | Line 801 | public class ForkJoinPool extends Abstra
801		if (isProcessingTasks()) {
802		int p = this.parallelism;
803		this.parallelism = parallelism;
804	<	if (parallelism > p)
805	<	createAndStartAddedWorkers();
806	<	else
807	<	trimSpares();
804	>	if (workers != null) {
805	>	if (parallelism > p)
806	>	createAndStartAddedWorkers();
807	>	else
808	>	trimSpares();
809	>	}
810		}
811		} finally {
812		lock.unlock();
#	Line 804 | Line 837 | public class ForkJoinPool extends Abstra
837
838		/**
839		* Returns the maximum number of threads allowed to exist in the
840	<	* pool.  Unless set using {@link #setMaximumPoolSize}, the
840	>	* pool. Unless set using {@link #setMaximumPoolSize}, the
841		* maximum is an implementation-defined value designed only to
842		* prevent runaway growth.
843		*
#	Line 816 | Line 849 | public class ForkJoinPool extends Abstra
849
850		/**
851		* Sets the maximum number of threads allowed to exist in the
852	<	* pool.  Setting this value has no effect on current pool
853	<	* size. It controls construction of new threads.
852	>	* pool. The given value should normally be greater than or equal
853	>	* to the {@link #getParallelism parallelism} level. Setting this
854	>	* value has no effect on current pool size. It controls
855	>	* construction of new threads.
856		*
857		* @throws IllegalArgumentException if negative or greater than
858		* internal implementation limit
#	Line 1075 | Line 1110 | public class ForkJoinPool extends Abstra
1110		}
1111
1112		private static String runStateToString(int rs) {
1113	<	switch(rs) {
1113	>	switch (rs) {
1114		case RUNNING: return "Running";
1115		case SHUTDOWN: return "Shutting down";
1116		case TERMINATING: return "Terminating";
#	Line 1345 | Line 1380 | public class ForkJoinPool extends Abstra
1380		}
1381		}
1382
1348	–
1383		/*
1384		* Nodes for event barrier to manage idle threads.  Queue nodes
1385		* are basic Treiber stack nodes, also used for spare stack.
#	Line 1369 | Line 1403 | public class ForkJoinPool extends Abstra
1403		* handling: Method signalWork returns without advancing count if
1404		* the queue appears to be empty.  This would ordinarily result in
1405		* races causing some queued waiters not to be woken up. To avoid
1406	<	* this, the first worker enqueued in method sync (see
1407	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1408	<	* helps signal if any are found. This works well because the
1409	<	* worker has nothing better to do, and so might as well help
1410	<	* alleviate the overhead and contention on the threads actually
1411	<	* doing work.  Also, since event counts increments on task
1412	<	* availability exist to maintain liveness (rather than to force
1413	<	* refreshes etc), it is OK for callers to exit early if
1380	<	* contending with another signaller.
1406	>	* this, the first worker enqueued in method sync rescans for
1407	>	* tasks after being enqueued, and helps signal if any are
1408	>	* found. This works well because the worker has nothing better to
1409	>	* do, and so might as well help alleviate the overhead and
1410	>	* contention on the threads actually doing work.  Also, since
1411	>	* event counts increments on task availability exist to maintain
1412	>	* liveness (rather than to force refreshes etc), it is OK for
1413	>	* callers to exit early if contending with another signaller.
1414		*/
1415		static final class WaitQueueNode {
1416		WaitQueueNode next; // only written before enqueued
#	Line 1390 | Line 1423 | public class ForkJoinPool extends Abstra
1423		}
1424
1425		/**
1426	<	* Wakes up waiter, returning false if known to already
1426	>	* Wakes up waiter, returning false if known to already be awake
1427		*/
1428		boolean signal() {
1429		ForkJoinWorkerThread t = thread;
#	Line 1400 | Line 1433 | public class ForkJoinPool extends Abstra
1433		LockSupport.unpark(t);
1434		return true;
1435		}
1403	–
1404	–	/**
1405	–	* Awaits release on sync.
1406	–	*/
1407	–	void awaitSyncRelease(ForkJoinPool p) {
1408	–	while (thread != null && !p.syncIsReleasable(this))
1409	–	LockSupport.park(this);
1410	–	}
1411	–
1412	–	/**
1413	–	* Awaits resumption as spare.
1414	–	*/
1415	–	void awaitSpareRelease() {
1416	–	while (thread != null) {
1417	–	if (!Thread.interrupted())
1418	–	LockSupport.park(this);
1419	–	}
1420	–	}
1436		}
1437
1438		/**
1439		* Ensures that no thread is waiting for count to advance from the
1440		* current value of eventCount read on entry to this method, by
1441		* releasing waiting threads if necessary.
1427	–	*
1428	–	* @return the count
1442		*/
1443	<	final long ensureSync() {
1443	>	final void ensureSync() {
1444		long c = eventCount;
1445		WaitQueueNode q;
1446		while ((q = syncStack) != null && q.count < c) {
#	Line 1438 | Line 1451 | public class ForkJoinPool extends Abstra
1451		break;
1452		}
1453		}
1441	–	return c;
1454		}
1455
1456		/**
#	Line 1453 | Line 1465 | public class ForkJoinPool extends Abstra
1465		/**
1466		* Signals threads waiting to poll a task. Because method sync
1467		* rechecks availability, it is OK to only proceed if queue
1468	<	* appears to be non-empty, and OK to skip under contention to
1469	<	* increment count (since some other thread succeeded).
1468	>	* appears to be non-empty, and OK if CAS to increment count
1469	>	* fails (since some other thread succeeded).
1470		*/
1471		final void signalWork() {
1472	<	long c;
1473	<	WaitQueueNode q;
1474	<	if (syncStack != null &&
1475	<	casEventCount(c = eventCount, c+1) &&
1476	<	(((q = syncStack) != null && q.count <= c) &&
1477	<	(!casBarrierStack(q, q.next) || !q.signal())))
1478	<	ensureSync();
1472	>	if (syncStack != null) {
1473	>	long c;
1474	>	casEventCount(c = eventCount, c+1);
1475	>	WaitQueueNode q = syncStack;
1476	>	if (q != null && q.count <= c &&
1477	>	(!casBarrierStack(q, q.next) || !q.signal()))
1478	>	ensureSync();
1479	>	}
1480		}
1481
1482		/**
#	Line 1476 | Line 1489 | public class ForkJoinPool extends Abstra
1489		final void sync(ForkJoinWorkerThread w) {
1490		updateStealCount(w); // Transfer w's count while it is idle
1491
1492	<	while (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1492	>	if (!w.isShutdown() && isProcessingTasks() && !suspendIfSpare(w)) {
1493		long prev = w.lastEventCount;
1494		WaitQueueNode node = null;
1495		WaitQueueNode h;
1496	<	while (eventCount == prev &&
1496	>	long ec;
1497	>	while ((ec = eventCount) == prev &&
1498		((h = syncStack) == null || h.count == prev)) {
1499		if (node == null)
1500		node = new WaitQueueNode(prev, w);
1501		if (casBarrierStack(node.next = h, node)) {
1502	<	node.awaitSyncRelease(this);
1502	>	if (!Thread.interrupted() &&
1503	>	node.thread != null &&
1504	>	eventCount == prev &&
1505	>	(h != null || // cover signalWork race
1506	>	(!ForkJoinWorkerThread.hasQueuedTasks(workers) &&
1507	>	eventCount == prev)))
1508	>	LockSupport.park(this);
1509	>	ec = eventCount;
1510	>	if (node.thread != null) {
1511	>	node.thread = null;
1512	>	if (ec == prev)
1513	>	casEventCount(prev, prev + 1); // help signal
1514	>	}
1515		break;
1516		}
1517		}
1518	<	long ec = ensureSync();
1519	<	if (ec != prev) {
1494	<	w.lastEventCount = ec;
1495	<	break;
1496	<	}
1497	<	}
1498	<	}
1499	<
1500	<	/**
1501	<	* Returns {@code true} if worker waiting on sync can proceed:
1502	<	*  - on signal (thread == null)
1503	<	*  - on event count advance (winning race to notify vs signaller)
1504	<	*  - on interrupt
1505	<	*  - if the first queued node, we find work available
1506	<	* If node was not signalled and event count not advanced on exit,
1507	<	* then we also help advance event count.
1508	<	*
1509	<	* @return {@code true} if node can be released
1510	<	*/
1511	<	final boolean syncIsReleasable(WaitQueueNode node) {
1512	<	long prev = node.count;
1513	<	if (!Thread.interrupted() && node.thread != null &&
1514	<	(node.next != null ||
1515	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1516	<	eventCount == prev)
1517	<	return false;
1518	<	if (node.thread != null) {
1519	<	node.thread = null;
1520	<	long ec = eventCount;
1521	<	if (prev <= ec) // help signal
1522	<	casEventCount(ec, ec+1);
1518	>	w.lastEventCount = ec;
1519	>	ensureSync();
1520		}
1524	–	return true;
1521		}
1522
1523		/**
#	Line 1530 | Line 1526 | public class ForkJoinPool extends Abstra
1526		*/
1527		final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1528		long lc = w.lastEventCount;
1529	<	long ec = ensureSync();
1530	<	if (ec == lc)
1531	<	return false;
1532	<	w.lastEventCount = ec;
1533	<	return true;
1529	>	long ec = eventCount;
1530	>	if (lc != ec)
1531	>	w.lastEventCount = ec;
1532	>	ensureSync();
1533	>	return lc != ec || lc != eventCount;
1534		}
1535
1536		//  Parallelism maintenance
#	Line 1576 | Line 1572 | public class ForkJoinPool extends Abstra
1572		while (spareStack == null || !tryResumeSpare(dec)) {
1573		int counts = workerCounts;
1574		if (dec || (dec = casWorkerCounts(counts, --counts))) {
1579	–	// CAS cheat
1575		if (!needSpare(counts, maintainParallelism))
1576		break;
1577		if (joinMe.status < 0)
#	Line 1701 | Line 1696 | public class ForkJoinPool extends Abstra
1696		*/
1697		private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1698		WaitQueueNode node = null;
1699	<	int s;
1700	<	while (parallelism < runningCountOf(s = workerCounts)) {
1699	>	for (;;) {
1700	>	int p = parallelism;
1701	>	int s = workerCounts;
1702	>	int r = runningCountOf(s);
1703	>	int t = totalCountOf(s);
1704	>	// use t as bound if r transiently out of sync
1705	>	if (t <= p || r <= p)
1706	>	return false; // not a spare
1707		if (node == null)
1708		node = new WaitQueueNode(0, w);
1709	<	if (casWorkerCounts(s, s-1)) { // representation-dependent
1710	<	// push onto stack
1710	<	do {} while (!casSpareStack(node.next = spareStack, node));
1711	<	// block until released by resumeSpare
1712	<	node.awaitSpareRelease();
1713	<	return true;
1714	<	}
1709	>	if (casWorkerCounts(s, workerCountsFor(t, r - 1)))
1710	>	break;
1711		}
1712	<	return false;
1712	>	// push onto stack
1713	>	do {} while (!casSpareStack(node.next = spareStack, node));
1714	>	// block until released by resumeSpare
1715	>	while (!Thread.interrupted() && node.thread != null)
1716	>	LockSupport.park(this);
1717	>	return true;
1718		}
1719
1720		/**

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