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root/jsr166/jsr166/src/jsr166y/ForkJoinTask.java

Comparing jsr166/src/jsr166y/ForkJoinTask.java (file contents):
Revision 1.86 by dl, Mon Feb 20 18:20:06 2012 UTC vs.
Revision 1.89 by dl, Mon Apr 9 13:11:44 2012 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	+
9		import java.io.Serializable;
10		import java.util.Collection;
11		import java.util.List;
#	Line 115 | Line 116 | import java.lang.reflect.Constructor;
116		* <p>The ForkJoinTask class is not usually directly subclassed.
117		* Instead, you subclass one of the abstract classes that support a
118		* particular style of fork/join processing, typically {@link
119	<	* RecursiveAction} for computations that do not return results, or
120	<	* {@link RecursiveTask} for those that do.  Normally, a concrete
121	<	* ForkJoinTask subclass declares fields comprising its parameters,
122	<	* established in a constructor, and then defines a {@code compute}
123	<	* method that somehow uses the control methods supplied by this base
124	<	* class. While these methods have {@code public} access (to allow
125	<	* instances of different task subclasses to call each other's
126	<	* methods), some of them may only be called from within other
127	<	* ForkJoinTasks (as may be determined using method {@link
128	<	* #inForkJoinPool}).  Attempts to invoke them in other contexts
129	<	* result in exceptions or errors, possibly including
130	<	* {@code ClassCastException}.
119	>	* RecursiveAction} for most computations that do not return results,
120	>	* {@link RecursiveTask} for those that do, and {@link
121	>	* CountedCompleter} for those in which completed actions trigger
122	>	* other actions.  Normally, a concrete ForkJoinTask subclass declares
123	>	* fields comprising its parameters, established in a constructor, and
124	>	* then defines a {@code compute} method that somehow uses the control
125	>	* methods supplied by this base class. While these methods have
126	>	* {@code public} access (to allow instances of different task
127	>	* subclasses to call each other's methods), some of them may only be
128	>	* called from within other ForkJoinTasks (as may be determined using
129	>	* method {@link #inForkJoinPool}).  Attempts to invoke them in other
130	>	* contexts result in exceptions or errors, possibly including {@code
131	>	* ClassCastException}.
132		*
133		* <p>Method {@link #join} and its variants are appropriate for use
134		* only when completion dependencies are acyclic; that is, the
#	Line 137 | Line 139 | import java.lang.reflect.Constructor;
139		* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
140		* may be of use in constructing custom subclasses for problems that
141		* are not statically structured as DAGs. To support such usages a
142	<	* ForkJoinTask may be atomically <em>marked</em> using {@link
143	<	* #markForkJoinTask} and checked for marking using {@link
144	<	* #isMarkedForkJoinTask}. The ForkJoinTask implementation does not
145	<	* use these {@code protected} methods or marks for any purpose, but
142	>	* ForkJoinTask may be atomically <em>tagged</em> with a {@code
143	>	* short} value using {@link #setForkJoinTaskTag} or {@link
144	>	* #compareAndSetForkJoinTaskTag} and checked using {@link
145	>	* #getForkJoinTaskTag}. The ForkJoinTask implementation does not
146	>	* use these {@code protected} methods or tags for any purpose, but
147		* they may be of use in the construction of specialized subclasses.
148		* For example, parallel graph traversals can use the supplied methods
149		* to avoid revisiting nodes/tasks that have already been processed.
150	<	* Also, completion based designs can use them to record that one
151	<	* subtask has completed. (Method names for marking are bulky in part
152	<	* to encourage definition of methods that reflect their usage
150	<	* patterns.)
150	>	* Also, completion based designs can use them to record that subtasks
151	>	* have completed. (Method names for tagging are bulky in part to
152	>	* encourage definition of methods that reflect their usage patterns.)
153		*
154		* <p>Most base support methods are {@code final}, to prevent
155		* overriding of implementations that are intrinsically tied to the
#	Line 213 | Line 215 | public abstract class ForkJoinTask<V> im
215		* thin-lock techniques, so use some odd coding idioms that tend
216		* to avoid them, mainly by arranging that every synchronized
217		* block performs a wait, notifyAll or both.
218	+	*
219	+	* These control bits occupy only (some of) the upper half (16
220	+	* bits) of status field. The lower bits are used for user-defined
221	+	* tags.
222		*/
223
224		/** The run status of this task */
#	Line 221 | Line 227 | public abstract class ForkJoinTask<V> im
227		static final int NORMAL      = 0xf0000000;  // must be negative
228		static final int CANCELLED   = 0xc0000000;  // must be < NORMAL
229		static final int EXCEPTIONAL = 0x80000000;  // must be < CANCELLED
230	<	static final int SIGNAL      = 0x00000001;
231	<	static final int MARKED      = 0x00000002;
230	>	static final int SIGNAL      = 0x00010000;  // must be >= 1 << 16
231	>	static final int SMASK       = 0x0000ffff;  // short bits for tags
232
233		/**
234		* Marks completion and wakes up threads waiting to join this
235	<	* task. A specialization for NORMAL completion is in method
230	<	* doExec.
235	>	* task.
236		*
237		* @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
238		* @return completion status on exit
#	Line 237 | Line 242 | public abstract class ForkJoinTask<V> im
242		if ((s = status) < 0)
243		return s;
244		if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
245	<	if ((s & SIGNAL) != 0)
245	>	if ((s >>> 16) != 0)
246		synchronized (this) { notifyAll(); }
247		return completion;
248		}
#	Line 259 | Line 264 | public abstract class ForkJoinTask<V> im
264		} catch (Throwable rex) {
265		return setExceptionalCompletion(rex);
266		}
267	<	while ((s = status) >= 0 && completed) {
268	<	if (U.compareAndSwapInt(this, STATUS, s, s | NORMAL)) {
264	<	if ((s & SIGNAL) != 0)
265	<	synchronized (this) { notifyAll(); }
266	<	return NORMAL;
267	<	}
268	<	}
267	>	if (completed)
268	>	s = setCompletion(NORMAL);
269		}
270		return s;
271		}
272
273		/**
274	<	* Tries to set SIGNAL status. Used by ForkJoinPool. Other
275	<	* variants are directly incorporated into externalAwaitDone etc.
274	>	* Tries to set SIGNAL status unless already completed. Used by
275	>	* ForkJoinPool. Other variants are directly incorporated into
276	>	* externalAwaitDone etc.
277		*
278		* @return true if successful
279		*/
280		final boolean trySetSignal() {
281	<	int s;
282	<	return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL);
281	>	int s = status;
282	>	return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL);
283		}
284
285		/**
#	Line 328 | Line 329 | public abstract class ForkJoinTask<V> im
329		return s;
330		}
331
331	–
332		/**
333		* Implementation for join, get, quietlyJoin. Directly handles
334		* only cases of already-completed, external wait, and
#	Line 417 | Line 417 | public abstract class ForkJoinTask<V> im
417		* @return status on exit
418		*/
419		private int setExceptionalCompletion(Throwable ex) {
420	<	int h = System.identityHashCode(this);
421	<	final ReentrantLock lock = exceptionTableLock;
422	<	lock.lock();
423	<	try {
424	<	expungeStaleExceptions();
425	<	ExceptionNode[] t = exceptionTable;
426	<	int i = h & (t.length - 1);
427	<	for (ExceptionNode e = t[i]; ; e = e.next) {
428	<	if (e == null) {
429	<	t[i] = new ExceptionNode(this, ex, t[i]);
430	<	break;
420	>	int s;
421	>	if ((s = status) >= 0) {
422	>	int h = System.identityHashCode(this);
423	>	final ReentrantLock lock = exceptionTableLock;
424	>	lock.lock();
425	>	try {
426	>	expungeStaleExceptions();
427	>	ExceptionNode[] t = exceptionTable;
428	>	int i = h & (t.length - 1);
429	>	for (ExceptionNode e = t[i]; ; e = e.next) {
430	>	if (e == null) {
431	>	t[i] = new ExceptionNode(this, ex, t[i]);
432	>	break;
433	>	}
434	>	if (e.get() == this) // already present
435	>	break;
436		}
437	<	if (e.get() == this) // already present
438	<	break;
437	>	} finally {
438	>	lock.unlock();
439		}
440	<	} finally {
436	<	lock.unlock();
440	>	s = setCompletion(EXCEPTIONAL);
441		}
442	<	return setCompletion(EXCEPTIONAL);
442	>	ForkJoinTask<?> p = internalGetCompleter(); // propagate
443	>	if (p != null && p.status >= 0)
444	>	p.setExceptionalCompletion(ex);
445	>	return s;
446	>	}
447	>
448	>	/**
449	>	* Exception propagation support for tasks with completers.
450	>	*/
451	>	ForkJoinTask<?> internalGetCompleter() {
452	>	return null;
453		}
454
455		/**
#	Line 517 | Line 531 | public abstract class ForkJoinTask<V> im
531		Throwable ex;
532		if (e == null || (ex = e.ex) == null)
533		return null;
534	<	if (e.thrower != Thread.currentThread().getId()) {
534	>	if (false && e.thrower != Thread.currentThread().getId()) {
535		Class<? extends Throwable> ec = ex.getClass();
536		try {
537		Constructor<?> noArgCtor = null;
#	Line 907 | Line 921 | public abstract class ForkJoinTask<V> im
921		}
922
923		/**
924	+	* Completes this task normally without setting a value. The most
925	+	* recent value established by {@link #setRawResult} (or {@code
926	+	* null} by default) will be returned as the result of subsequent
927	+	* invocations of {@code join} and related operations.
928	+	*
929	+	* @since 1.8
930	+	*/
931	+	public final void quietlyComplete() {
932	+	setCompletion(NORMAL);
933	+	}
934	+
935	+	/**
936		* Waits if necessary for the computation to complete, and then
937		* retrieves its result.
938		*
#	Line 1225 | Line 1251 | public abstract class ForkJoinTask<V> im
1251		protected abstract void setRawResult(V value);
1252
1253		/**
1254	<	* Immediately performs the base action of this task.  This method
1255	<	* is designed to support extensions, and should not in general be
1256	<	* called otherwise. The return value controls whether this task
1257	<	* is considered to be done normally. It may return false in
1254	>	* Immediately performs the base action of this task and returns
1255	>	* true if, upon return from this method, this task is guaranteed
1256	>	* to have completed normally. This method may return false
1257	>	* otherwise, to indicate that this task is not necessarily
1258	>	* complete (or is not known to be complete), for example in
1259		* asynchronous actions that require explicit invocations of
1260	<	* {@link #complete} to become joinable. It may also throw an
1261	<	* (unchecked) exception to indicate abnormal exit.
1260	>	* completion methods. This method may also throw an (unchecked)
1261	>	* exception to indicate abnormal exit. This method is designed to
1262	>	* support extensions, and should not in general be called
1263	>	* otherwise.
1264		*
1265	<	* @return {@code true} if completed normally
1265	>	* @return {@code true} if this task is known to have completed normally
1266		*/
1267		protected abstract boolean exec();
1268
#	Line 1302 | Line 1331 | public abstract class ForkJoinTask<V> im
1331		return wt.pool.nextTaskFor(wt.workQueue);
1332		}
1333
1334	<	// Mark-bit operations
1334	>	// tag operations
1335
1336		/**
1337	<	* Returns true if this task is marked.
1337	>	* Returns the tag for this task.
1338		*
1339	<	* @return true if this task is marked
1339	>	* @return the tag for this task
1340		* @since 1.8
1341		*/
1342	<	public final boolean isMarkedForkJoinTask() {
1343	<	return (status & MARKED) != 0;
1342	>	public final short getForkJoinTaskTag() {
1343	>	return (short)status;
1344		}
1345
1346		/**
1347	<	* Atomically sets the mark on this task.
1347	>	* Atomically sets the tag value for this task.
1348		*
1349	<	* @return true if this task was previously unmarked
1349	>	* @param tag the tag value
1350	>	* @return the previous value of the tag
1351		* @since 1.8
1352		*/
1353	<	public final boolean markForkJoinTask() {
1353	>	public final short setForkJoinTaskTag(short tag) {
1354		for (int s;;) {
1355	<	if (((s = status) & MARKED) != 0)
1356	<	return false;
1357	<	if (U.compareAndSwapInt(this, STATUS, s, s | MARKED))
1328	<	return true;
1355	>	if (U.compareAndSwapInt(this, STATUS, s = status,
1356	>	(s & ~SMASK) | (tag & SMASK)))
1357	>	return (short)s;
1358		}
1359		}
1360
1361		/**
1362	<	* Atomically clears the mark on this task.
1362	>	* Atomically conditionally sets the tag value for this task.
1363	>	* Among other applications, tags can be used as visit markers
1364	>	* in tasks operating on graphs, as in methods that check: {@code
1365	>	* if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1366	>	* before processing, otherwise exiting because the node has
1367	>	* already been visited.
1368		*
1369	<	* @return true if this task was previously marked
1369	>	* @param e the expected tag value
1370	>	* @param tag the new tag value
1371	>	* @return true if successful; i.e., the current value was
1372	>	* equal to e and is now tag.
1373		* @since 1.8
1374		*/
1375	<	public final boolean unmarkForkJoinTask() {
1375	>	public final boolean compareAndSetForkJoinTaskTag(short e, short tag) {
1376		for (int s;;) {
1377	<	if (((s = status) & MARKED) == 0)
1377	>	if ((short)(s = status) != e)
1378		return false;
1379	<	if (U.compareAndSwapInt(this, STATUS, s, s & ~MARKED))
1379	>	if (U.compareAndSwapInt(this, STATUS, s,
1380	>	(s & ~SMASK) | (tag & SMASK)))
1381		return true;
1382		}
1383		}

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