ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

root/jsr166/jsr166/src/jsr166y/ForkJoinWorkerThread.java

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.33 by dl, Thu May 27 16:46:49 2010 UTC vs.
Revision 1.40 by dl, Wed Aug 11 18:45:12 2010 UTC

#	Line 83 | Line 83 | public class ForkJoinWorkerThread extend
83		* by the ForkJoinPool).  This allows use in message-passing
84		* frameworks in which tasks are never joined.
85		*
86	<	* Efficient implementation of this approach currently relies on
87	<	* an uncomfortable amount of "Unsafe" mechanics. To maintain
86	>	* When a worker would otherwise be blocked waiting to join a
87	>	* task, it first tries a form of linear helping: Each worker
88	>	* records (in field currentSteal) the most recent task it stole
89	>	* from some other worker. Plus, it records (in field currentJoin)
90	>	* the task it is currently actively joining. Method joinTask uses
91	>	* these markers to try to find a worker to help (i.e., steal back
92	>	* a task from and execute it) that could hasten completion of the
93	>	* actively joined task. In essence, the joiner executes a task
94	>	* that would be on its own local deque had the to-be-joined task
95	>	* not been stolen. This may be seen as a conservative variant of
96	>	* the approach in Wagner & Calder "Leapfrogging: a portable
97	>	* technique for implementing efficient futures" SIGPLAN Notices,
98	>	* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs
99	>	* in that: (1) We only maintain dependency links across workers
100	>	* upon steals, rather than use per-task bookkeeping.  This may
101	>	* require a linear scan of workers array to locate stealers, but
102	>	* usually doesn't because stealers leave hints (that may become
103	>	* stale/wrong) of where to locate them. This isolates cost to
104	>	* when it is needed, rather than adding to per-task overhead.
105	>	* (2) It is "shallow", ignoring nesting and potentially cyclic
106	>	* mutual steals.  (3) It is intentionally racy: field currentJoin
107	>	* is updated only while actively joining, which means that we
108	>	* miss links in the chain during long-lived tasks, GC stalls etc
109	>	* (which is OK since blocking in such cases is usually a good
110	>	* idea).  (4) We bound the number of attempts to find work (see
111	>	* MAX_HELP_DEPTH) and fall back to suspending the worker and if
112	>	* necessary replacing it with a spare (see
113	>	* ForkJoinPool.tryAwaitJoin).
114	>	*
115	>	* Efficient implementation of these algorithms currently relies
116	>	* on an uncomfortable amount of "Unsafe" mechanics. To maintain
117		* correct orderings, reads and writes of variable base require
118		* volatile ordering.  Variable sp does not require volatile
119		* writes but still needs store-ordering, which we accomplish by
120		* pre-incrementing sp before filling the slot with an ordered
121		* store.  (Pre-incrementing also enables backouts used in
122	<	* scanWhileJoining.)  Because they are protected by volatile base
123	<	* reads, reads of the queue array and its slots by other threads
124	<	* do not need volatile load semantics, but writes (in push)
125	<	* require store order and CASes (in pop and deq) require
126	<	* (volatile) CAS semantics.  (Michael, Saraswat, and Vechev's
127	<	* algorithm has similar properties, but without support for
128	<	* nulling slots.)  Since these combinations aren't supported
129	<	* using ordinary volatiles, the only way to accomplish these
130	<	* efficiently is to use direct Unsafe calls. (Using external
131	<	* AtomicIntegers and AtomicReferenceArrays for the indices and
132	<	* array is significantly slower because of memory locality and
133	<	* indirection effects.)
122	>	* joinTask.)  Because they are protected by volatile base reads,
123	>	* reads of the queue array and its slots by other threads do not
124	>	* need volatile load semantics, but writes (in push) require
125	>	* store order and CASes (in pop and deq) require (volatile) CAS
126	>	* semantics.  (Michael, Saraswat, and Vechev's algorithm has
127	>	* similar properties, but without support for nulling slots.)
128	>	* Since these combinations aren't supported using ordinary
129	>	* volatiles, the only way to accomplish these efficiently is to
130	>	* use direct Unsafe calls. (Using external AtomicIntegers and
131	>	* AtomicReferenceArrays for the indices and array is
132	>	* significantly slower because of memory locality and indirection
133	>	* effects.)
134		*
135		* Further, performance on most platforms is very sensitive to
136		* placement and sizing of the (resizable) queue array.  Even
#	Line 126 | Line 155 | public class ForkJoinWorkerThread extend
155		private static final Random seedGenerator = new Random();
156
157		/**
158	<	* The timeout value for suspending spares. Spare workers that
159	<	* remain unsignalled for more than this time may be trimmed
160	<	* (killed and removed from pool).  Since our goal is to avoid
161	<	* long-term thread buildup, the exact value of timeout does not
162	<	* matter too much so long as it avoids most false-alarm timeouts
163	<	* under GC stalls or momentarily high system load.
158	>	* The maximum stolen->joining link depth allowed in helpJoinTask.
159	>	* Depths for legitimate chains are unbounded, but we use a fixed
160	>	* constant to avoid (otherwise unchecked) cycles and bound
161	>	* staleness of traversal parameters at the expense of sometimes
162	>	* blocking when we could be helping.
163	>	*/
164	>	private static final int MAX_HELP_DEPTH = 8;
165	>
166	>	/**
167	>	* The wakeup interval (in nanoseconds) for the first worker
168	>	* suspended as spare.  On each wakeup not signalled by a
169	>	* resumption, it may ask the pool to reduce the number of spares.
170		*/
171	<	private static final long SPARE_KEEPALIVE_NANOS =
137	<	5L * 1000L * 1000L * 1000L; // 5 secs
171	>	private static final long TRIM_RATE_NANOS = 200L * 1000L * 1000L;
172
173		/**
174		* Capacity of work-stealing queue array upon initialization.
175	<	* Must be a power of two. Initial size must be at least 2, but is
175	>	* Must be a power of two. Initial size must be at least 4, but is
176		* padded to minimize cache effects.
177		*/
178		private static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
#	Line 178 | Line 212 | public class ForkJoinWorkerThread extend
212		private int sp;
213
214		/**
215	+	* The index of most recent stealer, used as a hint to avoid
216	+	* traversal in method helpJoinTask. This is only a hint because a
217	+	* worker might have had multiple steals and this only holds one
218	+	* of them (usually the most current). Declared non-volatile,
219	+	* relying on other prevailing sync to keep reasonably current.
220	+	*/
221	+	private int stealHint;
222	+
223	+	/**
224		* Run state of this worker. In addition to the usual run levels,
225		* tracks if this worker is suspended as a spare, and if it was
226		* killed (trimmed) while suspended. However, "active" status is
#	Line 191 | Line 234 | public class ForkJoinWorkerThread extend
234		private static final int TRIMMED     = 0x08; // killed while suspended
235
236		/**
194	–	* Number of LockSupport.park calls to block this thread for
195	–	* suspension or event waits. Used for internal instrumention;
196	–	* currently not exported but included because volatile write upon
197	–	* park also provides a workaround for a JVM bug.
198	–	*/
199	–	private volatile int parkCount;
200	–
201	–	/**
237		* Number of steals, transferred and reset in pool callbacks pool
238		* when idle Accessed directly by pool.
239		*/
#	Line 218 | Line 253 | public class ForkJoinWorkerThread extend
253
254		/**
255		* True if use local fifo, not default lifo, for local polling.
256	<	* Shadows value from ForkJoinPool, which resets it if changed
222	<	* pool-wide.
256	>	* Shadows value from ForkJoinPool.
257		*/
258	<	private boolean locallyFifo;
258	>	private final boolean locallyFifo;
259
260		/**
261		* Index of this worker in pool array. Set once by pool before
#	Line 243 | Line 277 | public class ForkJoinWorkerThread extend
277		volatile long nextWaiter;
278
279		/**
280	+	* Number of times this thread suspended as spare
281	+	*/
282	+	int spareCount;
283	+
284	+	/**
285	+	* Encoded index and count of next spare waiter. Used only
286	+	* by ForkJoinPool for managing spares.
287	+	*/
288	+	volatile int nextSpare;
289	+
290	+	/**
291	+	* The task currently being joined, set only when actively trying
292	+	* to helpStealer. Written only by current thread, but read by
293	+	* others.
294	+	*/
295	+	private volatile ForkJoinTask<?> currentJoin;
296	+
297	+	/**
298	+	* The task most recently stolen from another worker (or
299	+	* submission queue).  Not volatile because always read/written in
300	+	* presence of related volatiles in those cases where it matters.
301	+	*/
302	+	private ForkJoinTask<?> currentSteal;
303	+
304	+	/**
305		* Creates a ForkJoinWorkerThread operating in the given pool.
306		*
307		* @param pool the pool this thread works in
308		* @throws NullPointerException if pool is null
309		*/
310		protected ForkJoinWorkerThread(ForkJoinPool pool) {
252	–	if (pool == null) throw new NullPointerException();
311		this.pool = pool;
312	+	this.locallyFifo = pool.locallyFifo;
313	+	setDaemon(true);
314		// To avoid exposing construction details to subclasses,
315		// remaining initialization is in start() and onStart()
316		}
#	Line 258 | Line 318 | public class ForkJoinWorkerThread extend
318		/**
319		* Performs additional initialization and starts this thread
320		*/
321	<	final void start(int poolIndex, boolean locallyFifo,
262	<	UncaughtExceptionHandler ueh) {
321	>	final void start(int poolIndex, UncaughtExceptionHandler ueh) {
322		this.poolIndex = poolIndex;
264	–	this.locallyFifo = locallyFifo;
323		if (ueh != null)
324		setUncaughtExceptionHandler(ueh);
267	–	setDaemon(true);
325		start();
326		}
327
#	Line 305 | Line 362 | public class ForkJoinWorkerThread extend
362		int rs = seedGenerator.nextInt();
363		seed = rs == 0? 1 : rs; // seed must be nonzero
364
365	<	// Allocate name string and queue array in this thread
365	>	// Allocate name string and arrays in this thread
366		String pid = Integer.toString(pool.getPoolNumber());
367		String wid = Integer.toString(poolIndex);
368		setName("ForkJoinPool-" + pid + "-worker-" + wid);
#	Line 324 | Line 381 | public class ForkJoinWorkerThread extend
381		protected void onTermination(Throwable exception) {
382		try {
383		cancelTasks();
384	+	while (active)              // force inactive
385	+	active = !pool.tryDecrementActiveCount();
386		setTerminated();
387		pool.workerTerminated(this);
388		} catch (Throwable ex) {        // Shouldn't ever happen
#	Line 358 | Line 417 | public class ForkJoinWorkerThread extend
417		* Find and execute tasks and check status while running
418		*/
419		private void mainLoop() {
420	<	boolean ran = false; // true if ran task on previous step
420	>	int misses = 0; // track consecutive times failed to find work; max 2
421		ForkJoinPool p = pool;
422		for (;;) {
423	<	p.preStep(this, ran);
423	>	p.preStep(this, misses);
424		if (runState != 0)
425	<	return;
426	<	ForkJoinTask<?> t; // try to get and run stolen or submitted task
427	<	if (ran = (t = scan()) != null || (t = pollSubmission()) != null) {
369	<	t.tryExec();
370	<	if (base != sp)
371	<	runLocalTasks();
372	<	}
425	>	break;
426	>	misses = ((tryExecSteal() || tryExecSubmission()) ? 0 :
427	>	(misses < 2 ? misses + 1 : 2));
428		}
429		}
430
431		/**
432	<	* Runs local tasks until queue is empty or shut down.  Call only
433	<	* while active.
432	>	* Try to steal a task and execute it
433	>	*
434	>	* @return true if ran a task
435		*/
436	<	private void runLocalTasks() {
437	<	while (runState == 0) {
438	<	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
439	<	if (t != null)
440	<	t.tryExec();
441	<	else if (base == sp)
442	<	break;
436	>	private boolean tryExecSteal() {
437	>	ForkJoinTask<?> t;
438	>	if ((t  = scan()) != null) {
439	>	t.quietlyExec();
440	>	currentSteal = null;
441	>	if (sp != base)
442	>	execLocalTasks();
443	>	return true;
444		}
445	+	return false;
446		}
447
448		/**
449	<	* If a submission exists, try to activate and take it
449	>	* If a submission exists, try to activate and run it;
450		*
451	<	* @return a task, if available
451	>	* @return true if ran a task
452		*/
453	<	private ForkJoinTask<?> pollSubmission() {
453	>	private boolean tryExecSubmission() {
454		ForkJoinPool p = pool;
455		while (p.hasQueuedSubmissions()) {
456	+	ForkJoinTask<?> t;
457		if (active || (active = p.tryIncrementActiveCount())) {
458	<	ForkJoinTask<?> t = p.pollSubmission();
459	<	return t != null ? t : scan(); // if missed, rescan
458	>	if ((t = p.pollSubmission()) != null) {
459	>	currentSteal = t;
460	>	t.quietlyExec();
461	>	currentSteal = null;
462	>	if (sp != base)
463	>	execLocalTasks();
464	>	return true;
465	>	}
466		}
467		}
468	<	return null;
468	>	return false;
469	>	}
470	>
471	>	/**
472	>	* Runs local tasks until queue is empty or shut down.  Call only
473	>	* while active.
474	>	*/
475	>	private void execLocalTasks() {
476	>	while (runState == 0) {
477	>	ForkJoinTask<?> t = locallyFifo? locallyDeqTask() : popTask();
478	>	if (t != null)
479	>	t.quietlyExec();
480	>	else if (sp == base)
481	>	break;
482	>	}
483		}
484
485		/*
#	Line 447 | Line 526 | public class ForkJoinWorkerThread extend
526		* @param t the task. Caller must ensure non-null.
527		*/
528		final void pushTask(ForkJoinTask<?> t) {
450	–	int s;
529		ForkJoinTask<?>[] q = queue;
530		int mask = q.length - 1; // implicit assert q != null
531	<	UNSAFE.putOrderedObject(q, (((s = sp++) & mask) << qShift) + qBase, t);
532	<	if ((s -= base) <= 0)
533	<	pool.signalWork();
534	<	else if (s + 1 >= mask)
535	<	growQueue();
531	>	int s = sp++;            // ok to increment sp before slot write
532	>	UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
533	>	if ((s -= base) == 0)
534	>	pool.signalWork();   // was empty
535	>	else if (s == mask)
536	>	growQueue();         // is full
537		}
538
539		/**
540		* Tries to take a task from the base of the queue, failing if
541		* empty or contended. Note: Specializations of this code appear
542	<	* in scan and scanWhileJoining.
542	>	* in locallyDeqTask and elsewhere.
543		*
544		* @return a task, or null if none or contended
545		*/
#	Line 468 | Line 547 | public class ForkJoinWorkerThread extend
547		ForkJoinTask<?> t;
548		ForkJoinTask<?>[] q;
549		int b, i;
550	<	if ((b = base) != sp &&
550	>	if (sp != (b = base) &&
551		(q = queue) != null && // must read q after b
552	<	(t = q[i = (q.length - 1) & b]) != null &&
552	>	(t = q[i = (q.length - 1) & b]) != null && base == b &&
553		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
554		base = b + 1;
555		return t;
#	Line 490 | Line 569 | public class ForkJoinWorkerThread extend
569		ForkJoinTask<?> t;
570		int b, i;
571		while (sp != (b = base)) {
572	<	if ((t = q[i = (q.length - 1) & b]) != null &&
572	>	if ((t = q[i = (q.length - 1) & b]) != null && base == b &&
573		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase,
574		t, null)) {
575		base = b + 1;
#	Line 503 | Line 582 | public class ForkJoinWorkerThread extend
582
583		/**
584		* Returns a popped task, or null if empty. Assumes active status.
585	<	* Called only by current thread. (Note: a specialization of this
507	<	* code appears in popWhileJoining.)
585	>	* Called only by current thread.
586		*/
587	<	final ForkJoinTask<?> popTask() {
588	<	int s;
589	<	ForkJoinTask<?>[] q;
590	<	if (base != (s = sp) && (q = queue) != null) {
591	<	int i = (q.length - 1) & --s;
592	<	ForkJoinTask<?> t = q[i];
593	<	if (t != null && UNSAFE.compareAndSwapObject
594	<	(q, (i << qShift) + qBase, t, null)) {
595	<	sp = s;
596	<	return t;
587	>	private ForkJoinTask<?> popTask() {
588	>	ForkJoinTask<?>[] q = queue;
589	>	if (q != null) {
590	>	int s;
591	>	while ((s = sp) != base) {
592	>	int i = (q.length - 1) & --s;
593	>	long u = (i << qShift) + qBase; // raw offset
594	>	ForkJoinTask<?> t = q[i];
595	>	if (t == null)   // lost to stealer
596	>	break;
597	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
598	>	sp = s; // putOrderedInt may encourage more timely write
599	>	// UNSAFE.putOrderedInt(this, spOffset, s);
600	>	return t;
601	>	}
602		}
603		}
604		return null;
#	Line 530 | Line 613 | public class ForkJoinWorkerThread extend
613		*/
614		final boolean unpushTask(ForkJoinTask<?> t) {
615		int s;
616	<	ForkJoinTask<?>[] q;
617	<	if (base != (s = sp) && (q = queue) != null &&
616	>	ForkJoinTask<?>[] q = queue;
617	>	if ((s = sp) != base && q != null &&
618		UNSAFE.compareAndSwapObject
619		(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
620		sp = s;
621	+	// UNSAFE.putOrderedInt(this, spOffset, s);
622		return true;
623		}
624		return false;
#	Line 623 | Line 707 | public class ForkJoinWorkerThread extend
707		ForkJoinWorkerThread v = ws[k & mask];
708		r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
709		if (v != null && v.base != v.sp) {
710	<	int b, i;             // inline specialized deqTask
711	<	ForkJoinTask<?>[] q;
628	<	ForkJoinTask<?> t;
629	<	if ((canSteal ||      // ensure active status
710	>	ForkJoinTask<?>[] q; int b;
711	>	if ((canSteal ||       // ensure active status
712		(canSteal = active = p.tryIncrementActiveCount())) &&
713	<	(q = v.queue) != null &&
714	<	(t = q[i = (q.length - 1) & (b = v.base)]) != null &&
715	<	UNSAFE.compareAndSwapObject
716	<	(q, (i << qShift) + qBase, t, null)) {
717	<	v.base = b + 1;
718	<	seed = r;
719	<	++stealCount;
720	<	return t;
713	>	(q = v.queue) != null && (b = v.base) != v.sp) {
714	>	int i = (q.length - 1) & b;
715	>	long u = (i << qShift) + qBase; // raw offset
716	>	ForkJoinTask<?> t = q[i];
717	>	if (v.base == b && t != null &&
718	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
719	>	int pid = poolIndex;
720	>	currentSteal = t;
721	>	v.stealHint = pid;
722	>	v.base = b + 1;
723	>	seed = r;
724	>	++stealCount;
725	>	return t;
726	>	}
727		}
728		j = -n;
729		k = r;                // restart on contention
#	Line 654 | Line 742 | public class ForkJoinWorkerThread extend
742		// Run State management
743
744		// status check methods used mainly by ForkJoinPool
745	+	final boolean isRunning()     { return runState == 0; }
746		final boolean isTerminating() { return (runState & TERMINATING) != 0; }
747		final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
748		final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
749		final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
750
751		/**
752	<	* Sets state to TERMINATING, also resuming if suspended.
752	>	* Sets state to TERMINATING, also, unless "quiet", unparking if
753	>	* not already terminated
754	>	*
755	>	* @param quiet don't unpark (used for faster status updates on
756	>	* pool termination)
757		*/
758	<	final void shutdown() {
758	>	final void shutdown(boolean quiet) {
759		for (;;) {
760		int s = runState;
761	+	if ((s & (TERMINATING|TERMINATED)) != 0)
762	+	break;
763		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
764		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
765		(s & ~SUSPENDED) |
766	<	(TRIMMED|TERMINATING))) {
672	<	LockSupport.unpark(this);
766	>	(TRIMMED|TERMINATING)))
767		break;
674	–	}
768		}
769		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
770		s | TERMINATING))
771		break;
772		}
773	+	if (!quiet && (runState & TERMINATED) != 0)
774	+	LockSupport.unpark(this);
775		}
776
777		/**
778	<	* Sets state to TERMINATED. Called only by this thread.
778	>	* Sets state to TERMINATED. Called only by onTermination()
779		*/
780		private void setTerminated() {
781		int s;
#	Line 690 | Line 785 | public class ForkJoinWorkerThread extend
785		}
786
787		/**
788	<	* Instrumented version of park. Also used by ForkJoinPool.awaitEvent
694	<	*/
695	<	final void doPark() {
696	<	++parkCount;
697	<	LockSupport.park(this);
698	<	}
699	<
700	<	/**
701	<	* If suspended, tries to set status to unsuspended.
702	<	* Caller must unpark to actually resume
788	>	* If suspended, tries to set status to unsuspended and unparks.
789		*
790		* @return true if successful
791		*/
792		final boolean tryUnsuspend() {
793		int s;
794	<	return (((s = runState) & SUSPENDED) != 0 &&
795	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
796	<	s & ~SUSPENDED));
794	>	while (((s = runState) & SUSPENDED) != 0) {
795	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
796	>	s & ~SUSPENDED))
797	>	return true;
798	>	}
799	>	return false;
800		}
801
802		/**
803	<	* Sets suspended status and blocks as spare until resumed,
804	<	* shutdown, or timed out.
805	<	*
717	<	* @return false if trimmed
803	>	* Sets suspended status and blocks as spare until resumed
804	>	* or shutdown.
805	>	* @returns true if still running on exit
806		*/
807		final boolean suspendAsSpare() {
808	<	for (;;) {               // set suspended unless terminating
808	>	lastEventCount = 0;         // reset upon resume
809	>	for (;;) {                  // set suspended unless terminating
810		int s = runState;
811		if ((s & TERMINATING) != 0) { // must kill
812		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
#	Line 728 | Line 817 | public class ForkJoinWorkerThread extend
817		s | SUSPENDED))
818		break;
819		}
731	–	lastEventCount = 0;      // reset upon resume
820		ForkJoinPool p = pool;
821	<	p.releaseWaiters();      // help others progress
734	<	p.accumulateStealCount(this);
735	<	interrupted();           // clear/ignore interrupts
736	<	if (poolIndex < p.getParallelism()) { // untimed wait
737	<	while ((runState & SUSPENDED) != 0)
738	<	doPark();
739	<	return true;
740	<	}
741	<	return timedSuspend();   // timed wait if apparently non-core
742	<	}
743	<
744	<	/**
745	<	* Blocks as spare until resumed or timed out
746	<	* @return false if trimmed
747	<	*/
748	<	private boolean timedSuspend() {
749	<	long nanos = SPARE_KEEPALIVE_NANOS;
750	<	long startTime = System.nanoTime();
821	>	p.pushSpare(this);
822		while ((runState & SUSPENDED) != 0) {
823	<	++parkCount;
824	<	if ((nanos -= (System.nanoTime() - startTime)) > 0)
825	<	LockSupport.parkNanos(this, nanos);
826	<	else { // try to trim on timeout
827	<	int s = runState;
828	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
829	<	(s & ~SUSPENDED) |
830	<	(TRIMMED|TERMINATING)))
831	<	return false;
823	>	if (!p.tryAccumulateStealCount(this))
824	>	continue;
825	>	interrupted();          // clear/ignore interrupts
826	>	if ((runState & SUSPENDED) == 0)
827	>	break;
828	>	if (nextSpare != 0)     // untimed
829	>	LockSupport.park(this);
830	>	else {
831	>	long startTime = System.nanoTime();
832	>	LockSupport.parkNanos(this, TRIM_RATE_NANOS);
833	>	if ((runState & SUSPENDED) == 0)
834	>	break;
835	>	long now = System.nanoTime();
836	>	if (now - startTime >= TRIM_RATE_NANOS)
837	>	pool.tryTrimSpare(now);
838		}
839		}
840	<	return true;
840	>	return runState == 0;
841		}
842
843		// Misc support methods for ForkJoinPool
#	Line 770 | Line 847 | public class ForkJoinWorkerThread extend
847		* used by ForkJoinTask.
848		*/
849		final int getQueueSize() {
850	<	return -base + sp;
851	<	}
775	<
776	<	/**
777	<	* Set locallyFifo mode. Called only by ForkJoinPool
778	<	*/
779	<	final void setAsyncMode(boolean async) {
780	<	locallyFifo = async;
850	>	int n; // external calls must read base first
851	>	return (n = -base + sp) <= 0 ? 0 : n;
852		}
853
854		/**
#	Line 785 | Line 856 | public class ForkJoinWorkerThread extend
856		* thread.
857		*/
858		final void cancelTasks() {
859	+	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
860	+	if (cj != null) {
861	+	currentJoin = null;
862	+	cj.cancelIgnoringExceptions();
863	+	try {
864	+	this.interrupt(); // awaken wait
865	+	} catch (SecurityException ignore) {
866	+	}
867	+	}
868	+	ForkJoinTask<?> cs = currentSteal;
869	+	if (cs != null) {
870	+	currentSteal = null;
871	+	cs.cancelIgnoringExceptions();
872	+	}
873		while (base != sp) {
874		ForkJoinTask<?> t = deqTask();
875		if (t != null)
#	Line 812 | Line 897 | public class ForkJoinWorkerThread extend
897		// Support methods for ForkJoinTask
898
899		/**
900	+	* Gets and removes a local task.
901	+	*
902	+	* @return a task, if available
903	+	*/
904	+	final ForkJoinTask<?> pollLocalTask() {
905	+	while (sp != base) {
906	+	if (active || (active = pool.tryIncrementActiveCount()))
907	+	return locallyFifo? locallyDeqTask() : popTask();
908	+	}
909	+	return null;
910	+	}
911	+
912	+	/**
913	+	* Gets and removes a local or stolen task.
914	+	*
915	+	* @return a task, if available
916	+	*/
917	+	final ForkJoinTask<?> pollTask() {
918	+	ForkJoinTask<?> t = pollLocalTask();
919	+	if (t == null) {
920	+	t = scan();
921	+	currentSteal = null; // cannot retain/track/help
922	+	}
923	+	return t;
924	+	}
925	+
926	+	/**
927	+	* Possibly runs some tasks and/or blocks, until task is done.
928	+	*
929	+	* @param joinMe the task to join
930	+	*/
931	+	final void joinTask(ForkJoinTask<?> joinMe) {
932	+	// currentJoin only written by this thread; only need ordered store
933	+	ForkJoinTask<?> prevJoin = currentJoin;
934	+	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
935	+	if (sp != base)
936	+	localHelpJoinTask(joinMe);
937	+	if (joinMe.status >= 0)
938	+	pool.awaitJoin(joinMe, this);
939	+	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
940	+	}
941	+
942	+	/**
943	+	* Run tasks in local queue until given task is done.
944	+	*
945	+	* @param joinMe the task to join
946	+	*/
947	+	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
948	+	int s;
949	+	ForkJoinTask<?>[] q;
950	+	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
951	+	int i = (q.length - 1) & --s;
952	+	long u = (i << qShift) + qBase; // raw offset
953	+	ForkJoinTask<?> t = q[i];
954	+	if (t == null)  // lost to a stealer
955	+	break;
956	+	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
957	+	/*
958	+	* This recheck (and similarly in helpJoinTask)
959	+	* handles cases where joinMe is independently
960	+	* cancelled or forced even though there is other work
961	+	* available. Back out of the pop by putting t back
962	+	* into slot before we commit by writing sp.
963	+	*/
964	+	if (joinMe.status < 0) {
965	+	UNSAFE.putObjectVolatile(q, u, t);
966	+	break;
967	+	}
968	+	sp = s;
969	+	// UNSAFE.putOrderedInt(this, spOffset, s);
970	+	t.quietlyExec();
971	+	}
972	+	}
973	+	}
974	+
975	+	/**
976	+	* Tries to locate and help perform tasks for a stealer of the
977	+	* given task, or in turn one of its stealers.  Traces
978	+	* currentSteal->currentJoin links looking for a thread working on
979	+	* a descendant of the given task and with a non-empty queue to
980	+	* steal back and execute tasks from.
981	+	*
982	+	* The implementation is very branchy to cope with the potential
983	+	* inconsistencies or loops encountering chains that are stale,
984	+	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
985	+	* of these cases are dealt with by just returning back to the
986	+	* caller, who is expected to retry if other join mechanisms also
987	+	* don't work out.
988	+	*
989	+	* @param joinMe the task to join
990	+	*/
991	+	final void helpJoinTask(ForkJoinTask<?> joinMe) {
992	+	ForkJoinWorkerThread[] ws = pool.workers;
993	+	int n; // need at least 2 workers
994	+	if (ws != null && (n = ws.length) > 1 && joinMe.status >= 0) {
995	+	ForkJoinTask<?> task = joinMe;        // base of chain
996	+	ForkJoinWorkerThread thread = this;   // thread with stolen task
997	+	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
998	+	// Try to find v, the stealer of task, by first using hint
999	+	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1000	+	if (v == null || v.currentSteal != task) {
1001	+	for (int j = 0; ; ++j) {      // search array
1002	+	if (j < n) {
1003	+	if ((v = ws[j]) != null) {
1004	+	if (task.status < 0)
1005	+	return;       // stale or done
1006	+	if (v.currentSteal == task) {
1007	+	thread.stealHint = j;
1008	+	break;        // save hint for next time
1009	+	}
1010	+	}
1011	+	}
1012	+	else
1013	+	return;               // no stealer
1014	+	}
1015	+	}
1016	+	// Try to help v, using specialized form of deqTask
1017	+	int b;
1018	+	ForkJoinTask<?>[] q;
1019	+	while ((b = v.base) != v.sp && (q = v.queue) != null) {
1020	+	int i = (q.length - 1) & b;
1021	+	long u = (i << qShift) + qBase;
1022	+	ForkJoinTask<?> t = q[i];
1023	+	if (task.status < 0)
1024	+	return;                   // stale or done
1025	+	if (v.base == b) {
1026	+	if (t == null)
1027	+	return;               // producer stalled
1028	+	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
1029	+	if (joinMe.status < 0) {
1030	+	UNSAFE.putObjectVolatile(q, u, t);
1031	+	return;           // back out on cancel
1032	+	}
1033	+	int pid = poolIndex;
1034	+	ForkJoinTask<?> prevSteal = currentSteal;
1035	+	currentSteal = t;
1036	+	v.stealHint = pid;
1037	+	v.base = b + 1;
1038	+	t.quietlyExec();
1039	+	currentSteal = prevSteal;
1040	+	}
1041	+	}
1042	+	if (joinMe.status < 0)
1043	+	return;
1044	+	}
1045	+	// Try to descend to find v's stealer
1046	+	ForkJoinTask<?> next = v.currentJoin;
1047	+	if (task.status < 0 || next == null || next == task ||
1048	+	joinMe.status < 0)
1049	+	return;
1050	+	task = next;
1051	+	thread = v;
1052	+	}
1053	+	}
1054	+	}
1055	+
1056	+	/**
1057		* Returns an estimate of the number of tasks, offset by a
1058		* function of number of idle workers.
1059		*
#	Line 863 | Line 1105 | public class ForkJoinWorkerThread extend
1105		}
1106
1107		/**
866	–	* Gets and removes a local task.
867	–	*
868	–	* @return a task, if available
869	–	*/
870	–	final ForkJoinTask<?> pollLocalTask() {
871	–	while (base != sp) {
872	–	if (active || (active = pool.tryIncrementActiveCount()))
873	–	return locallyFifo? locallyDeqTask() : popTask();
874	–	}
875	–	return null;
876	–	}
877	–
878	–	/**
879	–	* Gets and removes a local or stolen task.
880	–	*
881	–	* @return a task, if available
882	–	*/
883	–	final ForkJoinTask<?> pollTask() {
884	–	ForkJoinTask<?> t;
885	–	return (t = pollLocalTask()) != null ? t : scan();
886	–	}
887	–
888	–	/**
889	–	* Executes or processes other tasks awaiting the given task
890	–	* @return task completion status
891	–	*/
892	–	final int execWhileJoining(ForkJoinTask<?> joinMe) {
893	–	int s;
894	–	while ((s = joinMe.status) >= 0) {
895	–	ForkJoinTask<?> t = base != sp?
896	–	popWhileJoining(joinMe) :
897	–	scanWhileJoining(joinMe);
898	–	if (t != null)
899	–	t.tryExec();
900	–	}
901	–	return s;
902	–	}
903	–
904	–	/**
905	–	* Returns or stolen task, if available, unless joinMe is done
906	–	*
907	–	* This method is intrinsically nonmodular. To maintain the
908	–	* property that tasks are never stolen if the awaited task is
909	–	* ready, we must interleave mechanics of scan with status
910	–	* checks. We rely here on the commit points of deq that allow us
911	–	* to cancel a steal even after CASing slot to null, but before
912	–	* adjusting base index: If, after the CAS, we see that joinMe is
913	–	* ready, we can back out by placing the task back into the slot,
914	–	* without adjusting index. The loop is otherwise a variant of the
915	–	* one in scan().
916	–	*
917	–	*/
918	–	private ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
919	–	int r = seed;
920	–	ForkJoinPool p = pool;
921	–	ForkJoinWorkerThread[] ws;
922	–	int n;
923	–	outer:while ((ws = p.workers) != null && (n = ws.length) > 1) {
924	–	int mask = n - 1;
925	–	int k = r;
926	–	boolean contended = false; // to retry loop if deq contends
927	–	for (int j = -n; j <= n; ++j) {
928	–	if (joinMe.status < 0)
929	–	break outer;
930	–	int b;
931	–	ForkJoinTask<?>[] q;
932	–	ForkJoinWorkerThread v = ws[k & mask];
933	–	r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // xorshift
934	–	if (v != null && (b=v.base) != v.sp && (q=v.queue) != null) {
935	–	int i = (q.length - 1) & b;
936	–	ForkJoinTask<?> t = q[i];
937	–	if (t != null && UNSAFE.compareAndSwapObject
938	–	(q, (i << qShift) + qBase, t, null)) {
939	–	if (joinMe.status >= 0) {
940	–	v.base = b + 1;
941	–	seed = r;
942	–	++stealCount;
943	–	return t;
944	–	}
945	–	UNSAFE.putObjectVolatile(q, (i<<qShift)+qBase, t);
946	–	break outer; // back out
947	–	}
948	–	contended = true;
949	–	}
950	–	k = j < 0 ? r : (k + ((n >>> 1) | 1));
951	–	}
952	–	if (!contended && p.tryAwaitBusyJoin(joinMe))
953	–	break;
954	–	}
955	–	return null;
956	–	}
957	–
958	–	/**
959	–	* Version of popTask with join checks surrounding extraction.
960	–	* Uses the same backout strategy as helpJoinTask. Note that
961	–	* we ignore locallyFifo flag for local tasks here since helping
962	–	* joins only make sense in LIFO mode.
963	–	*
964	–	* @return a popped task, if available, unless joinMe is done
965	–	*/
966	–	private ForkJoinTask<?> popWhileJoining(ForkJoinTask<?> joinMe) {
967	–	int s;
968	–	ForkJoinTask<?>[] q;
969	–	while ((s = sp) != base && (q = queue) != null && joinMe.status >= 0) {
970	–	int i = (q.length - 1) & --s;
971	–	ForkJoinTask<?> t = q[i];
972	–	if (t != null && UNSAFE.compareAndSwapObject
973	–	(q, (i << qShift) + qBase, t, null)) {
974	–	if (joinMe.status >= 0) {
975	–	sp = s;
976	–	return t;
977	–	}
978	–	UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t);
979	–	break;  // back out
980	–	}
981	–	}
982	–	return null;
983	–	}
984	–
985	–	/**
1108		* Runs tasks until {@code pool.isQuiescent()}.
1109		*/
1110		final void helpQuiescePool() {
1111		for (;;) {
1112		ForkJoinTask<?> t = pollLocalTask();
1113	<	if (t != null || (t = scan()) != null)
1114	<	t.tryExec();
1113	>	if (t != null || (t = scan()) != null) {
1114	>	t.quietlyExec();
1115	>	currentSteal = null;
1116	>	}
1117		else {
1118		ForkJoinPool p = pool;
1119		if (active) {
1120	+	if (!p.tryDecrementActiveCount())
1121	+	continue;   // retry later
1122		active = false; // inactivate
997	–	do {} while (!p.tryDecrementActiveCount());
1123		}
1124		if (p.isQuiescent()) {
1125		active = true; // re-activate
#	Line 1008 | Line 1133 | public class ForkJoinWorkerThread extend
1133		// Unsafe mechanics
1134
1135		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1136	+	private static final long spOffset =
1137	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1138		private static final long runStateOffset =
1139		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1140	+	private static final long currentJoinOffset =
1141	+	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1142	+	private static final long currentStealOffset =
1143	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1144		private static final long qBase =
1145		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1146	+
1147		private static final int qShift;
1148
1149		static {

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines