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root/jsr166/jsr166/src/jsr166e/ForkJoinTask.java

Comparing jsr166/src/jsr166e/ForkJoinTask.java (file contents):
Revision 1.2 by dl, Sun Oct 28 22:35:45 2012 UTC vs.
Revision 1.15 by jsr166, Mon Jul 22 16:52:31 2013 UTC

#	Line 33 | Line 33 | import java.lang.reflect.Constructor;
33		* <p>A "main" {@code ForkJoinTask} begins execution when it is
34		* explicitly submitted to a {@link ForkJoinPool}, or, if not already
35		* engaged in a ForkJoin computation, commenced in the {@link
36	<	* ForkJoinPool#commonPool} via {@link #fork}, {@link #invoke}, or
36	>	* ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
37		* related methods.  Once started, it will usually in turn start other
38		* subtasks.  As indicated by the name of this class, many programs
39		* using {@code ForkJoinTask} employ only methods {@link #fork} and
#	Line 55 | Line 55 | import java.lang.reflect.Constructor;
55		* minimize other blocking synchronization apart from joining other
56		* tasks or using synchronizers such as Phasers that are advertised to
57		* cooperate with fork/join scheduling. Subdividable tasks should also
58	<	* not perform blocking IO, and should ideally access variables that
58	>	* not perform blocking I/O, and should ideally access variables that
59		* are completely independent of those accessed by other running
60		* tasks. These guidelines are loosely enforced by not permitting
61		* checked exceptions such as {@code IOExceptions} to be
#	Line 73 | Line 73 | import java.lang.reflect.Constructor;
73		* <p>It is possible to define and use ForkJoinTasks that may block,
74		* but doing do requires three further considerations: (1) Completion
75		* of few if any <em>other</em> tasks should be dependent on a task
76	<	* that blocks on external synchronization or IO. Event-style async
76	>	* that blocks on external synchronization or I/O. Event-style async
77		* tasks that are never joined (for example, those subclassing {@link
78		* CountedCompleter}) often fall into this category.  (2) To minimize
79		* resource impact, tasks should be small; ideally performing only the
#	Line 134 | Line 134 | import java.lang.reflect.Constructor;
134		* (DAG). Otherwise, executions may encounter a form of deadlock as
135		* tasks cyclically wait for each other.  However, this framework
136		* supports other methods and techniques (for example the use of
137	<	* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
137	>	* {@link java.util.concurrent.Phaser Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
138		* may be of use in constructing custom subclasses for problems that
139	<	* are not statically structured as DAGs. To support such usages a
139	>	* are not statically structured as DAGs. To support such usages, a
140		* ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
141		* value using {@link #setForkJoinTaskTag} or {@link
142		* #compareAndSetForkJoinTaskTag} and checked using {@link
#	Line 285 | Line 285 | public abstract class ForkJoinTask<V> im
285		*/
286		private int externalAwaitDone() {
287		int s;
288	<	boolean interrupted = false;
289	<	if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this))
290	<	s = doExec();
291	<	while (s >= 0) {
292	<	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
293	<	synchronized (this) {
294	<	if (status >= 0) {
295	<	try {
296	<	wait();
297	<	} catch (InterruptedException ie) {
298	<	interrupted = true;
288	>	ForkJoinPool cp = ForkJoinPool.common;
289	>	if ((s = status) >= 0) {
290	>	if (cp != null) {
291	>	if (this instanceof CountedCompleter)
292	>	s = cp.externalHelpComplete((CountedCompleter<?>)this);
293	>	else if (cp.tryExternalUnpush(this))
294	>	s = doExec();
295	>	}
296	>	if (s >= 0 && (s = status) >= 0) {
297	>	boolean interrupted = false;
298	>	do {
299	>	if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
300	>	synchronized (this) {
301	>	if (status >= 0) {
302	>	try {
303	>	wait();
304	>	} catch (InterruptedException ie) {
305	>	interrupted = true;
306	>	}
307	>	}
308	>	else
309	>	notifyAll();
310		}
311		}
312	<	else
313	<	notifyAll();
314	<	}
312	>	} while ((s = status) >= 0);
313	>	if (interrupted)
314	>	Thread.currentThread().interrupt();
315		}
305	–	s = status;
316		}
307	–	if (interrupted)
308	–	Thread.currentThread().interrupt();
317		return s;
318		}
319
#	Line 313 | Line 321 | public abstract class ForkJoinTask<V> im
321		* Blocks a non-worker-thread until completion or interruption.
322		*/
323		private int externalInterruptibleAwaitDone() throws InterruptedException {
324	+	int s;
325	+	ForkJoinPool cp = ForkJoinPool.common;
326		if (Thread.interrupted())
327		throw new InterruptedException();
328	<	int s;
329	<	if ((s = status) >= 0 && ForkJoinPool.tryUnsubmitFromCommonPool(this))
330	<	s = doExec();
331	<	while (s >= 0) {
328	>	if ((s = status) >= 0 && cp != null) {
329	>	if (this instanceof CountedCompleter)
330	>	cp.externalHelpComplete((CountedCompleter<?>)this);
331	>	else if (cp.tryExternalUnpush(this))
332	>	doExec();
333	>	}
334	>	while ((s = status) >= 0) {
335		if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
336		synchronized (this) {
337		if (status >= 0)
#	Line 327 | Line 340 | public abstract class ForkJoinTask<V> im
340		notifyAll();
341		}
342		}
330	–	s = status;
343		}
344		return s;
345		}
346
347	+
348		/**
349		* Implementation for join, get, quietlyJoin. Directly handles
350		* only cases of already-completed, external wait, and
#	Line 438 | Line 451 | public abstract class ForkJoinTask<V> im
451		}
452
453		/**
454	<	* Records exception and possibly propagates
454	>	* Records exception and possibly propagates.
455		*
456		* @return status on exit
457		*/
#	Line 471 | Line 484 | public abstract class ForkJoinTask<V> im
484		}
485
486		/**
487	<	* Removes exception node and clears status
487	>	* Removes exception node and clears status.
488		*/
489		private void clearExceptionalCompletion() {
490		int h = System.identityHashCode(this);
#	Line 601 | Line 614 | public abstract class ForkJoinTask<V> im
614		}
615
616		/**
617	+	* A version of "sneaky throw" to relay exceptions
618	+	*/
619	+	static void rethrow(Throwable ex) {
620	+	if (ex != null)
621	+	ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
622	+	}
623	+
624	+	/**
625	+	* The sneaky part of sneaky throw, relying on generics
626	+	* limitations to evade compiler complaints about rethrowing
627	+	* unchecked exceptions
628	+	*/
629	+	@SuppressWarnings("unchecked") static <T extends Throwable>
630	+	void uncheckedThrow(Throwable t) throws T {
631	+	throw (T)t; // rely on vacuous cast
632	+	}
633	+
634	+	/**
635		* Throws exception, if any, associated with the given status.
636		*/
637		private void reportException(int s) {
638	<	Throwable ex = ((s == CANCELLED) ?  new CancellationException() :
639	<	(s == EXCEPTIONAL) ? getThrowableException() :
640	<	null);
641	<	if (ex != null)
611	<	U.throwException(ex);
638	>	if (s == CANCELLED)
639	>	throw new CancellationException();
640	>	if (s == EXCEPTIONAL)
641	>	rethrow(getThrowableException());
642		}
643
644		// public methods
#	Line 616 | Line 646 | public abstract class ForkJoinTask<V> im
646		/**
647		* Arranges to asynchronously execute this task in the pool the
648		* current task is running in, if applicable, or using the {@link
649	<	* ForkJoinPool#commonPool} if not {@link #inForkJoinPool}.  While
649	>	* ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}.  While
650		* it is not necessarily enforced, it is a usage error to fork a
651		* task more than once unless it has completed and been
652		* reinitialized.  Subsequent modifications to the state of this
#	Line 633 | Line 663 | public abstract class ForkJoinTask<V> im
663		if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
664		((ForkJoinWorkerThread)t).workQueue.push(this);
665		else
666	<	ForkJoinPool.submitToCommonPool(this);
666	>	ForkJoinPool.common.externalPush(this);
667		return this;
668		}
669
#	Line 735 | Line 765 | public abstract class ForkJoinTask<V> im
765		}
766		}
767		if (ex != null)
768	<	U.throwException(ex);
768	>	rethrow(ex);
769		}
770
771		/**
#	Line 752 | Line 782 | public abstract class ForkJoinTask<V> im
782		* unprocessed.
783		*
784		* @param tasks the collection of tasks
785	+	* @param <T> the type of the values returned from the tasks
786		* @return the tasks argument, to simplify usage
787		* @throws NullPointerException if tasks or any element are null
788		*/
#	Line 786 | Line 817 | public abstract class ForkJoinTask<V> im
817		}
818		}
819		if (ex != null)
820	<	U.throwException(ex);
820	>	rethrow(ex);
821		return tasks;
822		}
823
#	Line 809 | Line 840 | public abstract class ForkJoinTask<V> im
840		* <p>This method is designed to be invoked by <em>other</em>
841		* tasks. To terminate the current task, you can just return or
842		* throw an unchecked exception from its computation method, or
843	<	* invoke {@link #completeExceptionally}.
843	>	* invoke {@link #completeExceptionally(Throwable)}.
844		*
845		* @param mayInterruptIfRunning this value has no effect in the
846		* default implementation because interrupts are not used to
#	Line 959 | Line 990 | public abstract class ForkJoinTask<V> im
990		if (Thread.interrupted())
991		throw new InterruptedException();
992		// Messy in part because we measure in nanosecs, but wait in millisecs
993	<	int s; long ns, ms;
994	<	if ((s = status) >= 0 && (ns = unit.toNanos(timeout)) > 0L) {
993	>	int s; long ms;
994	>	long ns = unit.toNanos(timeout);
995	>	ForkJoinPool cp;
996	>	if ((s = status) >= 0 && ns > 0L) {
997		long deadline = System.nanoTime() + ns;
998		ForkJoinPool p = null;
999		ForkJoinPool.WorkQueue w = null;
#	Line 969 | Line 1002 | public abstract class ForkJoinTask<V> im
1002		ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1003		p = wt.pool;
1004		w = wt.workQueue;
1005	<	s = p.helpJoinOnce(w, this); // no retries on failure
1005	>	p.helpJoinOnce(w, this); // no retries on failure
1006	>	}
1007	>	else if ((cp = ForkJoinPool.common) != null) {
1008	>	if (this instanceof CountedCompleter)
1009	>	cp.externalHelpComplete((CountedCompleter<?>)this);
1010	>	else if (cp.tryExternalUnpush(this))
1011	>	doExec();
1012		}
1013		boolean canBlock = false;
1014		boolean interrupted = false;
1015		try {
1016		while ((s = status) >= 0) {
1017	<	if (w != null && w.runState < 0)
1017	>	if (w != null && w.qlock < 0)
1018		cancelIgnoringExceptions(this);
1019		else if (!canBlock) {
1020	<	if (p == null || p.tryCompensate(this, null))
1020	>	if (p == null || p.tryCompensate(p.ctl))
1021		canBlock = true;
1022		}
1023		else {
#	Line 1054 | Line 1093 | public abstract class ForkJoinTask<V> im
1093		wt.pool.helpQuiescePool(wt.workQueue);
1094		}
1095		else
1096	<	ForkJoinPool.externalHelpQuiescePool();
1096	>	ForkJoinPool.quiesceCommonPool();
1097		}
1098
1099		/**
#	Line 1117 | Line 1156 | public abstract class ForkJoinTask<V> im
1156		*/
1157		public boolean tryUnfork() {
1158		Thread t;
1159	<	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1160	<	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1161	<	ForkJoinPool.tryUnsubmitFromCommonPool(this);
1159	>	return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1160	>	((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1161	>	ForkJoinPool.common.tryExternalUnpush(this));
1162		}
1163
1164		/**
#	Line 1131 | Line 1170 | public abstract class ForkJoinTask<V> im
1170		* @return the number of tasks
1171		*/
1172		public static int getQueuedTaskCount() {
1173	<	Thread t;
1174	<	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1175	<	((ForkJoinWorkerThread)t).workQueue.queueSize() :
1176	<	ForkJoinPool.getEstimatedSubmitterQueueLength();
1173	>	Thread t; ForkJoinPool.WorkQueue q;
1174	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1175	>	q = ((ForkJoinWorkerThread)t).workQueue;
1176	>	else
1177	>	q = ForkJoinPool.commonSubmitterQueue();
1178	>	return (q == null) ? 0 : q.queueSize();
1179		}
1180
1181		/**
#	Line 1151 | Line 1192 | public abstract class ForkJoinTask<V> im
1192		* @return the surplus number of tasks, which may be negative
1193		*/
1194		public static int getSurplusQueuedTaskCount() {
1195	<	/*
1155	<	* The aim of this method is to return a cheap heuristic guide
1156	<	* for task partitioning when programmers, frameworks, tools,
1157	<	* or languages have little or no idea about task granularity.
1158	<	* In essence by offering this method, we ask users only about
1159	<	* tradeoffs in overhead vs expected throughput and its
1160	<	* variance, rather than how finely to partition tasks.
1161	<	*
1162	<	* In a steady state strict (tree-structured) computation,
1163	<	* each thread makes available for stealing enough tasks for
1164	<	* other threads to remain active. Inductively, if all threads
1165	<	* play by the same rules, each thread should make available
1166	<	* only a constant number of tasks.
1167	<	*
1168	<	* The minimum useful constant is just 1. But using a value of
1169	<	* 1 would require immediate replenishment upon each steal to
1170	<	* maintain enough tasks, which is infeasible.  Further,
1171	<	* partitionings/granularities of offered tasks should
1172	<	* minimize steal rates, which in general means that threads
1173	<	* nearer the top of computation tree should generate more
1174	<	* than those nearer the bottom. In perfect steady state, each
1175	<	* thread is at approximately the same level of computation
1176	<	* tree. However, producing extra tasks amortizes the
1177	<	* uncertainty of progress and diffusion assumptions.
1178	<	*
1179	<	* So, users will want to use values larger, but not much
1180	<	* larger than 1 to both smooth over transient shortages and
1181	<	* hedge against uneven progress; as traded off against the
1182	<	* cost of extra task overhead. We leave the user to pick a
1183	<	* threshold value to compare with the results of this call to
1184	<	* guide decisions, but recommend values such as 3.
1185	<	*
1186	<	* When all threads are active, it is on average OK to
1187	<	* estimate surplus strictly locally. In steady-state, if one
1188	<	* thread is maintaining say 2 surplus tasks, then so are
1189	<	* others. So we can just use estimated queue length.
1190	<	* However, this strategy alone leads to serious mis-estimates
1191	<	* in some non-steady-state conditions (ramp-up, ramp-down,
1192	<	* other stalls). We can detect many of these by further
1193	<	* considering the number of "idle" threads, that are known to
1194	<	* have zero queued tasks, so compensate by a factor of
1195	<	* (#idle/#active) threads.
1196	<	*/
1197	<	Thread t; ForkJoinWorkerThread wt;
1198	<	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1199	<	(wt = (ForkJoinWorkerThread)t).workQueue.queueSize() - wt.pool.idlePerActive() :
1200	<	0;
1195	>	return ForkJoinPool.getSurplusQueuedTaskCount();
1196		}
1197
1198		// Extension methods
#	Line 1241 | Line 1236 | public abstract class ForkJoinTask<V> im
1236		/**
1237		* Returns, but does not unschedule or execute, a task queued by
1238		* the current thread but not yet executed, if one is immediately
1239	<	* available and the current thread is operating in a
1240	<	* ForkJoinPool. There is no guarantee that this task will
1241	<	* actually be polled or executed next. Conversely, this method
1242	<	* may return null even if a task exists but cannot be accessed
1248	<	* without contention with other threads.  This method is designed
1239	>	* available. There is no guarantee that this task will actually
1240	>	* be polled or executed next. Conversely, this method may return
1241	>	* null even if a task exists but cannot be accessed without
1242	>	* contention with other threads.  This method is designed
1243		* primarily to support extensions, and is unlikely to be useful
1244		* otherwise.
1245		*
1246		* @return the next task, or {@code null} if none are available
1247		*/
1248		protected static ForkJoinTask<?> peekNextLocalTask() {
1249	<	Thread t;
1250	<	return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1251	<	((ForkJoinWorkerThread)t).workQueue.peek() :
1252	<	null;
1249	>	Thread t; ForkJoinPool.WorkQueue q;
1250	>	if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1251	>	q = ((ForkJoinWorkerThread)t).workQueue;
1252	>	else
1253	>	q = ForkJoinPool.commonSubmitterQueue();
1254	>	return (q == null) ? null : q.peek();
1255		}
1256
1257		/**
#	Line 1331 | Line 1327 | public abstract class ForkJoinTask<V> im
1327		*
1328		* @param e the expected tag value
1329		* @param tag the new tag value
1330	<	* @return true if successful; i.e., the current value was
1330	>	* @return {@code true} if successful; i.e., the current value was
1331		* equal to e and is now tag.
1332		* @since 1.8
1333		*/
#	Line 1384 | Line 1380 | public abstract class ForkJoinTask<V> im
1380		}
1381
1382		/**
1383	+	* Adaptor for Runnables in which failure forces worker exception
1384	+	*/
1385	+	static final class RunnableExecuteAction extends ForkJoinTask<Void> {
1386	+	final Runnable runnable;
1387	+	RunnableExecuteAction(Runnable runnable) {
1388	+	if (runnable == null) throw new NullPointerException();
1389	+	this.runnable = runnable;
1390	+	}
1391	+	public final Void getRawResult() { return null; }
1392	+	public final void setRawResult(Void v) { }
1393	+	public final boolean exec() { runnable.run(); return true; }
1394	+	void internalPropagateException(Throwable ex) {
1395	+	rethrow(ex); // rethrow outside exec() catches.
1396	+	}
1397	+	private static final long serialVersionUID = 5232453952276885070L;
1398	+	}
1399	+
1400	+	/**
1401		* Adaptor for Callables
1402		*/
1403		static final class AdaptedCallable<T> extends ForkJoinTask<T>
#	Line 1431 | Line 1445 | public abstract class ForkJoinTask<V> im
1445		*
1446		* @param runnable the runnable action
1447		* @param result the result upon completion
1448	+	* @param <T> the type of the result
1449		* @return the task
1450		*/
1451		public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
#	Line 1444 | Line 1459 | public abstract class ForkJoinTask<V> im
1459		* encountered into {@code RuntimeException}.
1460		*
1461		* @param callable the callable action
1462	+	* @param <T> the type of the callable's result
1463		* @return the task
1464		*/
1465		public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
#	Line 1457 | Line 1473 | public abstract class ForkJoinTask<V> im
1473		/**
1474		* Saves this task to a stream (that is, serializes it).
1475		*
1476	+	* @param s the stream
1477	+	* @throws java.io.IOException if an I/O error occurs
1478		* @serialData the current run status and the exception thrown
1479		* during execution, or {@code null} if none
1480		*/
#	Line 1468 | Line 1486 | public abstract class ForkJoinTask<V> im
1486
1487		/**
1488		* Reconstitutes this task from a stream (that is, deserializes it).
1489	+	* @param s the stream
1490	+	* @throws ClassNotFoundException if the class of a serialized object
1491	+	*         could not be found
1492	+	* @throws java.io.IOException if an I/O error occurs
1493		*/
1494		private void readObject(java.io.ObjectInputStream s)
1495		throws java.io.IOException, ClassNotFoundException {
#	Line 1480 | Line 1502 | public abstract class ForkJoinTask<V> im
1502		// Unsafe mechanics
1503		private static final sun.misc.Unsafe U;
1504		private static final long STATUS;
1505	+
1506		static {
1507		exceptionTableLock = new ReentrantLock();
1508		exceptionTableRefQueue = new ReferenceQueue<Object>();
1509		exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1510		try {
1511		U = getUnsafe();
1512	+	Class<?> k = ForkJoinTask.class;
1513		STATUS = U.objectFieldOffset
1514	<	(ForkJoinTask.class.getDeclaredField("status"));
1514	>	(k.getDeclaredField("status"));
1515		} catch (Exception e) {
1516		throw new Error(e);
1517		}
#	Line 1503 | Line 1527 | public abstract class ForkJoinTask<V> im
1527		private static sun.misc.Unsafe getUnsafe() {
1528		try {
1529		return sun.misc.Unsafe.getUnsafe();
1530	<	} catch (SecurityException se) {
1531	<	try {
1532	<	return java.security.AccessController.doPrivileged
1533	<	(new java.security
1534	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1535	<	public sun.misc.Unsafe run() throws Exception {
1536	<	java.lang.reflect.Field f = sun.misc
1537	<	.Unsafe.class.getDeclaredField("theUnsafe");
1538	<	f.setAccessible(true);
1539	<	return (sun.misc.Unsafe) f.get(null);
1540	<	}});
1541	<	} catch (java.security.PrivilegedActionException e) {
1542	<	throw new RuntimeException("Could not initialize intrinsics",
1543	<	e.getCause());
1544	<	}
1530	>	} catch (SecurityException tryReflectionInstead) {}
1531	>	try {
1532	>	return java.security.AccessController.doPrivileged
1533	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1534	>	public sun.misc.Unsafe run() throws Exception {
1535	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1536	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1537	>	f.setAccessible(true);
1538	>	Object x = f.get(null);
1539	>	if (k.isInstance(x))
1540	>	return k.cast(x);
1541	>	}
1542	>	throw new NoSuchFieldError("the Unsafe");
1543	>	}});
1544	>	} catch (java.security.PrivilegedActionException e) {
1545	>	throw new RuntimeException("Could not initialize intrinsics",
1546	>	e.getCause());
1547		}
1548		}
1549		}

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