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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 1.53 by dl, Sun Oct 24 19:37:26 2010 UTC

#	Line 6 | Line 6
6
7		package jsr166y;
8
9	–	import java.util.concurrent.*;
10	–
9		import java.util.Random;
10		import java.util.Collection;
11		import java.util.concurrent.locks.LockSupport;
12	+	import java.util.concurrent.RejectedExecutionException;
13
14		/**
15		* A thread managed by a {@link ForkJoinPool}.  This class is
#	Line 83 | Line 82 | public class ForkJoinWorkerThread extend
82		* by the ForkJoinPool).  This allows use in message-passing
83		* frameworks in which tasks are never joined.
84		*
85	<	* Efficient implementation of this approach currently relies on
86	<	* an uncomfortable amount of "Unsafe" mechanics. To maintain
85	>	* When a worker would otherwise be blocked waiting to join a
86	>	* task, it first tries a form of linear helping: Each worker
87	>	* records (in field currentSteal) the most recent task it stole
88	>	* from some other worker. Plus, it records (in field currentJoin)
89	>	* the task it is currently actively joining. Method joinTask uses
90	>	* these markers to try to find a worker to help (i.e., steal back
91	>	* a task from and execute it) that could hasten completion of the
92	>	* actively joined task. In essence, the joiner executes a task
93	>	* that would be on its own local deque had the to-be-joined task
94	>	* not been stolen. This may be seen as a conservative variant of
95	>	* the approach in Wagner & Calder "Leapfrogging: a portable
96	>	* technique for implementing efficient futures" SIGPLAN Notices,
97	>	* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs
98	>	* in that: (1) We only maintain dependency links across workers
99	>	* upon steals, rather than use per-task bookkeeping.  This may
100	>	* require a linear scan of workers array to locate stealers, but
101	>	* usually doesn't because stealers leave hints (that may become
102	>	* stale/wrong) of where to locate them. This isolates cost to
103	>	* when it is needed, rather than adding to per-task overhead.
104	>	* (2) It is "shallow", ignoring nesting and potentially cyclic
105	>	* mutual steals.  (3) It is intentionally racy: field currentJoin
106	>	* is updated only while actively joining, which means that we
107	>	* miss links in the chain during long-lived tasks, GC stalls etc
108	>	* (which is OK since blocking in such cases is usually a good
109	>	* idea).  (4) We bound the number of attempts to find work (see
110	>	* MAX_HELP_DEPTH) and fall back to suspending the worker and if
111	>	* necessary replacing it with a spare (see
112	>	* ForkJoinPool.awaitJoin).
113	>	*
114	>	* Efficient implementation of these algorithms currently relies
115	>	* on an uncomfortable amount of "Unsafe" mechanics. To maintain
116		* correct orderings, reads and writes of variable base require
117		* volatile ordering.  Variable sp does not require volatile
118		* writes but still needs store-ordering, which we accomplish by
119		* pre-incrementing sp before filling the slot with an ordered
120		* store.  (Pre-incrementing also enables backouts used in
121	<	* scanWhileJoining.)  Because they are protected by volatile base
122	<	* reads, reads of the queue array and its slots by other threads
123	<	* do not need volatile load semantics, but writes (in push)
124	<	* require store order and CASes (in pop and deq) require
125	<	* (volatile) CAS semantics.  (Michael, Saraswat, and Vechev's
126	<	* algorithm has similar properties, but without support for
127	<	* nulling slots.)  Since these combinations aren't supported
128	<	* using ordinary volatiles, the only way to accomplish these
129	<	* efficiently is to use direct Unsafe calls. (Using external
130	<	* AtomicIntegers and AtomicReferenceArrays for the indices and
131	<	* array is significantly slower because of memory locality and
132	<	* indirection effects.)
121	>	* joinTask.)  Because they are protected by volatile base reads,
122	>	* reads of the queue array and its slots by other threads do not
123	>	* need volatile load semantics, but writes (in push) require
124	>	* store order and CASes (in pop and deq) require (volatile) CAS
125	>	* semantics.  (Michael, Saraswat, and Vechev's algorithm has
126	>	* similar properties, but without support for nulling slots.)
127	>	* Since these combinations aren't supported using ordinary
128	>	* volatiles, the only way to accomplish these efficiently is to
129	>	* use direct Unsafe calls. (Using external AtomicIntegers and
130	>	* AtomicReferenceArrays for the indices and array is
131	>	* significantly slower because of memory locality and indirection
132	>	* effects.)
133		*
134		* Further, performance on most platforms is very sensitive to
135		* placement and sizing of the (resizable) queue array.  Even
#	Line 126 | Line 154 | public class ForkJoinWorkerThread extend
154		private static final Random seedGenerator = new Random();
155
156		/**
157	<	* The timeout value for suspending spares. Spare workers that
158	<	* remain unsignalled for more than this time may be trimmed
159	<	* (killed and removed from pool).  Since our goal is to avoid
160	<	* long-term thread buildup, the exact value of timeout does not
161	<	* matter too much so long as it avoids most false-alarm timeouts
134	<	* under GC stalls or momentarily high system load.
157	>	* The maximum stolen->joining link depth allowed in helpJoinTask.
158	>	* Depths for legitimate chains are unbounded, but we use a fixed
159	>	* constant to avoid (otherwise unchecked) cycles and bound
160	>	* staleness of traversal parameters at the expense of sometimes
161	>	* blocking when we could be helping.
162		*/
163	<	private static final long SPARE_KEEPALIVE_NANOS =
137	<	5L * 1000L * 1000L * 1000L; // 5 secs
163	>	private static final int MAX_HELP_DEPTH = 8;
164
165		/**
166		* Capacity of work-stealing queue array upon initialization.
167	<	* Must be a power of two. Initial size must be at least 2, but is
167	>	* Must be a power of two. Initial size must be at least 4, but is
168		* padded to minimize cache effects.
169		*/
170		private static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
171
172		/**
173		* Maximum work-stealing queue array size.  Must be less than or
174	<	* equal to 1 << 28 to ensure lack of index wraparound. (This
175	<	* is less than usual bounds, because we need leftshift by 3
176	<	* to be in int range).
174	>	* equal to 1 << (31 - width of array entry) to ensure lack of
175	>	* index wraparound. The value is set in the static block
176	>	* at the end of this file after obtaining width.
177		*/
178	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
178	>	private static final int MAXIMUM_QUEUE_CAPACITY;
179
180		/**
181		* The pool this thread works in. Accessed directly by ForkJoinTask.
#	Line 178 | Line 204 | public class ForkJoinWorkerThread extend
204		private int sp;
205
206		/**
207	+	* The index of most recent stealer, used as a hint to avoid
208	+	* traversal in method helpJoinTask. This is only a hint because a
209	+	* worker might have had multiple steals and this only holds one
210	+	* of them (usually the most current). Declared non-volatile,
211	+	* relying on other prevailing sync to keep reasonably current.
212	+	*/
213	+	private int stealHint;
214	+
215	+	/**
216		* Run state of this worker. In addition to the usual run levels,
217		* tracks if this worker is suspended as a spare, and if it was
218		* killed (trimmed) while suspended. However, "active" status is
219	<	* maintained separately.
219	>	* maintained separately and modified only in conjunction with
220	>	* CASes of the pool's runState (which are currently sadly
221	>	* manually inlined for performance.)  Accessed directly by pool
222	>	* to simplify checks for normal (zero) status.
223		*/
224	<	private volatile int runState;
224	>	volatile int runState;
225
226		private static final int TERMINATING = 0x01;
227		private static final int TERMINATED  = 0x02;
#	Line 191 | Line 229 | public class ForkJoinWorkerThread extend
229		private static final int TRIMMED     = 0x08; // killed while suspended
230
231		/**
232	<	* Number of LockSupport.park calls to block this thread for
233	<	* 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	<	/**
202	<	* Number of steals, transferred and reset in pool callbacks pool
203	<	* when idle Accessed directly by pool.
232	>	* Number of steals. Directly accessed (and reset) by
233	>	* pool.tryAccumulateStealCount when idle.
234		*/
235		int stealCount;
236
#	Line 218 | Line 248 | public class ForkJoinWorkerThread extend
248
249		/**
250		* True if use local fifo, not default lifo, for local polling.
251	<	* Shadows value from ForkJoinPool, which resets it if changed
222	<	* pool-wide.
251	>	* Shadows value from ForkJoinPool.
252		*/
253	<	private boolean locallyFifo;
253	>	private final boolean locallyFifo;
254
255		/**
256		* Index of this worker in pool array. Set once by pool before
#	Line 237 | Line 266 | public class ForkJoinWorkerThread extend
266		int lastEventCount;
267
268		/**
269	<	* Encoded index and event count of next event waiter. Used only
270	<	* by ForkJoinPool for managing event waiters.
269	>	* Encoded index and event count of next event waiter. Accessed
270	>	* only by ForkJoinPool for managing event waiters.
271		*/
272		volatile long nextWaiter;
273
274		/**
275	+	* Number of times this thread suspended as spare. Accessed only
276	+	* by pool.
277	+	*/
278	+	int spareCount;
279	+
280	+	/**
281	+	* Encoded index and count of next spare waiter. Accessed only
282	+	* by ForkJoinPool for managing spares.
283	+	*/
284	+	volatile int nextSpare;
285	+
286	+	/**
287	+	* The task currently being joined, set only when actively trying
288	+	* to help other stealers in helpJoinTask. Written only by this
289	+	* thread, but read by others.
290	+	*/
291	+	private volatile ForkJoinTask<?> currentJoin;
292	+
293	+	/**
294	+	* The task most recently stolen from another worker (or
295	+	* submission queue).  Written only by this thread, but read by
296	+	* others.
297	+	*/
298	+	private volatile ForkJoinTask<?> currentSteal;
299	+
300	+	/**
301		* Creates a ForkJoinWorkerThread operating in the given pool.
302		*
303		* @param pool the pool this thread works in
304		* @throws NullPointerException if pool is null
305		*/
306		protected ForkJoinWorkerThread(ForkJoinPool pool) {
252	–	if (pool == null) throw new NullPointerException();
307		this.pool = pool;
308	+	this.locallyFifo = pool.locallyFifo;
309	+	setDaemon(true);
310		// To avoid exposing construction details to subclasses,
311		// remaining initialization is in start() and onStart()
312		}
313
314		/**
315	<	* Performs additional initialization and starts this thread
315	>	* Performs additional initialization and starts this thread.
316		*/
317	<	final void start(int poolIndex, boolean locallyFifo,
262	<	UncaughtExceptionHandler ueh) {
317	>	final void start(int poolIndex, UncaughtExceptionHandler ueh) {
318		this.poolIndex = poolIndex;
264	–	this.locallyFifo = locallyFifo;
319		if (ueh != null)
320		setUncaughtExceptionHandler(ueh);
267	–	setDaemon(true);
321		start();
322		}
323
#	Line 295 | Line 348 | public class ForkJoinWorkerThread extend
348		/**
349		* Initializes internal state after construction but before
350		* processing any tasks. If you override this method, you must
351	<	* invoke super.onStart() at the beginning of the method.
351	>	* invoke @code{super.onStart()} at the beginning of the method.
352		* Initialization requires care: Most fields must have legal
353		* default values, to ensure that attempted accesses from other
354		* threads work correctly even before this thread starts
#	Line 305 | Line 358 | public class ForkJoinWorkerThread extend
358		int rs = seedGenerator.nextInt();
359		seed = rs == 0? 1 : rs; // seed must be nonzero
360
361	<	// Allocate name string and queue array in this thread
361	>	// Allocate name string and arrays in this thread
362		String pid = Integer.toString(pool.getPoolNumber());
363		String wid = Integer.toString(poolIndex);
364		setName("ForkJoinPool-" + pid + "-worker-" + wid);
#	Line 323 | Line 376 | public class ForkJoinWorkerThread extend
376		*/
377		protected void onTermination(Throwable exception) {
378		try {
379	+	ForkJoinPool p = pool;
380	+	if (active) {
381	+	int a; // inline p.tryDecrementActiveCount
382	+	active = false;
383	+	do {} while (!UNSAFE.compareAndSwapInt
384	+	(p, poolRunStateOffset, a = p.runState, a - 1));
385	+	}
386		cancelTasks();
387		setTerminated();
388	<	pool.workerTerminated(this);
388	>	p.workerTerminated(this);
389		} catch (Throwable ex) {        // Shouldn't ever happen
390		if (exception == null)      // but if so, at least rethrown
391		exception = ex;
#	Line 355 | Line 415 | public class ForkJoinWorkerThread extend
415		// helpers for run()
416
417		/**
418	<	* Find and execute tasks and check status while running
418	>	* Finds and executes tasks, and checks status while running.
419		*/
420		private void mainLoop() {
421	<	boolean ran = false; // true if ran task on previous step
421	>	boolean ran = false; // true if ran a task on last step
422		ForkJoinPool p = pool;
423		for (;;) {
424		p.preStep(this, ran);
425		if (runState != 0)
426	<	return;
427	<	ForkJoinTask<?> t; // try to get and run stolen or submitted task
368	<	if (ran = (t = scan()) != null || (t = pollSubmission()) != null) {
369	<	t.tryExec();
370	<	if (base != sp)
371	<	runLocalTasks();
372	<	}
426	>	break;
427	>	ran = tryExecSteal() || tryExecSubmission();
428		}
429		}
430
431		/**
432	<	* Runs local tasks until queue is empty or shut down.  Call only
433	<	* while active.
432	>	* Tries 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	>	UNSAFE.putOrderedObject(this, currentStealOffset, 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	+	// This loop is needed in case attempt to activate fails, in
456	+	// which case we only retry if there still appears to be a
457	+	// submission.
458		while (p.hasQueuedSubmissions()) {
459	<	if (active || (active = p.tryIncrementActiveCount())) {
460	<	ForkJoinTask<?> t = p.pollSubmission();
461	<	return t != null ? t : scan(); // if missed, rescan
459	>	ForkJoinTask<?> t; int a;
460	>	if (active || // inline p.tryIncrementActiveCount
461	>	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
462	>	a = p.runState, a + 1))) {
463	>	if ((t = p.pollSubmission()) != null) {
464	>	UNSAFE.putOrderedObject(this, currentStealOffset, t);
465	>	t.quietlyExec();
466	>	UNSAFE.putOrderedObject(this, currentStealOffset, null);
467	>	if (sp != base)
468	>	execLocalTasks();
469	>	return true;
470	>	}
471		}
472		}
473	<	return null;
473	>	return false;
474	>	}
475	>
476	>	/**
477	>	* Runs local tasks until queue is empty or shut down.  Call only
478	>	* while active.
479	>	*/
480	>	private void execLocalTasks() {
481	>	while (runState == 0) {
482	>	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
483	>	if (t != null)
484	>	t.quietlyExec();
485	>	else if (sp == base)
486	>	break;
487	>	}
488		}
489
490		/*
491		* Intrinsics-based atomic writes for queue slots. These are
492	<	* basically the same as methods in AtomicObjectArray, but
492	>	* basically the same as methods in AtomicReferenceArray, but
493		* specialized for (1) ForkJoinTask elements (2) requirement that
494		* nullness and bounds checks have already been performed by
495		* callers and (3) effective offsets are known not to overflow
496		* from int to long (because of MAXIMUM_QUEUE_CAPACITY). We don't
497		* need corresponding version for reads: plain array reads are OK
498	<	* because they protected by other volatile reads and are
498	>	* because they are protected by other volatile reads and are
499		* confirmed by CASes.
500		*
501		* Most uses don't actually call these methods, but instead contain
#	Line 435 | Line 519 | public class ForkJoinWorkerThread extend
519		* range. This method is used only during resets and backouts.
520		*/
521		private static final void writeSlot(ForkJoinTask<?>[] q, int i,
522	<	ForkJoinTask<?> t) {
522	>	ForkJoinTask<?> t) {
523		UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t);
524		}
525
#	Line 447 | Line 531 | public class ForkJoinWorkerThread extend
531		* @param t the task. Caller must ensure non-null.
532		*/
533		final void pushTask(ForkJoinTask<?> t) {
450	–	int s;
534		ForkJoinTask<?>[] q = queue;
535		int mask = q.length - 1; // implicit assert q != null
536	<	UNSAFE.putOrderedObject(q, (((s = sp++) & mask) << qShift) + qBase, t);
537	<	if ((s -= base) <= 0)
538	<	pool.signalWork();
539	<	else if (s + 1 >= mask)
540	<	growQueue();
536	>	int s = sp++;            // ok to increment sp before slot write
537	>	UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
538	>	if ((s -= base) == 0)
539	>	pool.signalWork();   // was empty
540	>	else if (s == mask)
541	>	growQueue();         // is full
542		}
543
544		/**
545		* Tries to take a task from the base of the queue, failing if
546		* empty or contended. Note: Specializations of this code appear
547	<	* in scan and scanWhileJoining.
547	>	* in locallyDeqTask and elsewhere.
548		*
549		* @return a task, or null if none or contended
550		*/
#	Line 468 | Line 552 | public class ForkJoinWorkerThread extend
552		ForkJoinTask<?> t;
553		ForkJoinTask<?>[] q;
554		int b, i;
555	<	if ((b = base) != sp &&
555	>	if (sp != (b = base) &&
556		(q = queue) != null && // must read q after b
557	<	(t = q[i = (q.length - 1) & b]) != null &&
557	>	(t = q[i = (q.length - 1) & b]) != null && base == b &&
558		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
559		base = b + 1;
560		return t;
#	Line 480 | Line 564 | public class ForkJoinWorkerThread extend
564
565		/**
566		* Tries to take a task from the base of own queue. Assumes active
567	<	* status.  Called only by current thread.
567	>	* status.  Called only by this thread.
568		*
569		* @return a task, or null if none
570		*/
#	Line 490 | Line 574 | public class ForkJoinWorkerThread extend
574		ForkJoinTask<?> t;
575		int b, i;
576		while (sp != (b = base)) {
577	<	if ((t = q[i = (q.length - 1) & b]) != null &&
577	>	if ((t = q[i = (q.length - 1) & b]) != null && base == b &&
578		UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase,
579		t, null)) {
580		base = b + 1;
#	Line 503 | Line 587 | public class ForkJoinWorkerThread extend
587
588		/**
589		* Returns a popped task, or null if empty. Assumes active status.
590	<	* Called only by current thread. (Note: a specialization of this
507	<	* code appears in popWhileJoining.)
590	>	* Called only by this thread.
591		*/
592	<	final ForkJoinTask<?> popTask() {
593	<	int s;
594	<	ForkJoinTask<?>[] q;
595	<	if (base != (s = sp) && (q = queue) != null) {
596	<	int i = (q.length - 1) & --s;
597	<	ForkJoinTask<?> t = q[i];
598	<	if (t != null && UNSAFE.compareAndSwapObject
599	<	(q, (i << qShift) + qBase, t, null)) {
600	<	sp = s;
601	<	return t;
592	>	private ForkJoinTask<?> popTask() {
593	>	ForkJoinTask<?>[] q = queue;
594	>	if (q != null) {
595	>	int s;
596	>	while ((s = sp) != base) {
597	>	int i = (q.length - 1) & --s;
598	>	long u = (i << qShift) + qBase; // raw offset
599	>	ForkJoinTask<?> t = q[i];
600	>	if (t == null)   // lost to stealer
601	>	break;
602	>	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
603	>	sp = s; // putOrderedInt may encourage more timely write
604	>	// UNSAFE.putOrderedInt(this, spOffset, s);
605	>	return t;
606	>	}
607		}
608		}
609		return null;
#	Line 523 | Line 611 | public class ForkJoinWorkerThread extend
611
612		/**
613		* Specialized version of popTask to pop only if topmost element
614	<	* is the given task. Called only by current thread while
527	<	* active.
614	>	* is the given task. Called only by this thread while active.
615		*
616		* @param t the task. Caller must ensure non-null.
617		*/
618		final boolean unpushTask(ForkJoinTask<?> t) {
619		int s;
620	<	ForkJoinTask<?>[] q;
621	<	if (base != (s = sp) && (q = queue) != null &&
620	>	ForkJoinTask<?>[] q = queue;
621	>	if ((s = sp) != base && q != null &&
622		UNSAFE.compareAndSwapObject
623		(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
624	<	sp = s;
624	>	sp = s; // putOrderedInt may encourage more timely write
625	>	// UNSAFE.putOrderedInt(this, spOffset, s);
626		return true;
627		}
628		return false;
629		}
630
631		/**
632	<	* Returns next task or null if empty or contended
632	>	* Returns next task, or null if empty or contended.
633		*/
634		final ForkJoinTask<?> peekTask() {
635		ForkJoinTask<?>[] q = queue;
#	Line 583 | Line 671 | public class ForkJoinWorkerThread extend
671		* Computes next value for random victim probe in scan().  Scans
672		* don't require a very high quality generator, but also not a
673		* crummy one.  Marsaglia xor-shift is cheap and works well enough.
674	<	* Note: This is manually inlined in scan()
674	>	* Note: This is manually inlined in scan().
675		*/
676		private static final int xorShift(int r) {
677		r ^= r << 13;
#	Line 622 | Line 710 | public class ForkJoinWorkerThread extend
710		for (;;) {
711		ForkJoinWorkerThread v = ws[k & mask];
712		r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
713	<	if (v != null && v.base != v.sp) {
714	<	int b, i;             // inline specialized deqTask
715	<	ForkJoinTask<?>[] q;
716	<	ForkJoinTask<?> t;
717	<	if ((canSteal ||      // ensure active status
718	<	(canSteal = active = p.tryIncrementActiveCount())) &&
719	<	(q = v.queue) != null &&
720	<	(t = q[i = (q.length - 1) & (b = v.base)]) != null &&
721	<	UNSAFE.compareAndSwapObject
722	<	(q, (i << qShift) + qBase, t, null)) {
723	<	v.base = b + 1;
724	<	seed = r;
725	<	++stealCount;
726	<	return t;
713	>	ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a;
714	>	if (v != null && (b = v.base) != v.sp &&
715	>	(q = v.queue) != null) {
716	>	int i = (q.length - 1) & b;
717	>	long u = (i << qShift) + qBase; // raw offset
718	>	int pid = poolIndex;
719	>	if ((t = q[i]) != null) {
720	>	if (!canSteal &&  // inline p.tryIncrementActiveCount
721	>	UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
722	>	a = p.runState, a + 1))
723	>	canSteal = active = true;
724	>	if (canSteal && v.base == b++ &&
725	>	UNSAFE.compareAndSwapObject(q, u, t, null)) {
726	>	v.base = b;
727	>	v.stealHint = pid;
728	>	UNSAFE.putOrderedObject(this,
729	>	currentStealOffset, t);
730	>	seed = r;
731	>	++stealCount;
732	>	return t;
733	>	}
734		}
735		j = -n;
736		k = r;                // restart on contention
#	Line 654 | Line 749 | public class ForkJoinWorkerThread extend
749		// Run State management
750
751		// status check methods used mainly by ForkJoinPool
752	<	final boolean isTerminating() { return (runState & TERMINATING) != 0; }
753	<	final boolean isTerminated()  { return (runState & TERMINATED) != 0; }
754	<	final boolean isSuspended()   { return (runState & SUSPENDED) != 0; }
755	<	final boolean isTrimmed()     { return (runState & TRIMMED) != 0; }
752	>	final boolean isRunning()    { return runState == 0; }
753	>	final boolean isTerminated() { return (runState & TERMINATED) != 0; }
754	>	final boolean isSuspended()  { return (runState & SUSPENDED) != 0; }
755	>	final boolean isTrimmed()    { return (runState & TRIMMED) != 0; }
756	>
757	>	final boolean isTerminating() {
758	>	if ((runState & TERMINATING) != 0)
759	>	return true;
760	>	if (pool.isAtLeastTerminating()) { // propagate pool state
761	>	shutdown();
762	>	return true;
763	>	}
764	>	return false;
765	>	}
766
767		/**
768	<	* Sets state to TERMINATING, also resuming if suspended.
768	>	* Sets state to TERMINATING. Does NOT unpark or interrupt
769	>	* to wake up if currently blocked. Callers must do so if desired.
770		*/
771		final void shutdown() {
772		for (;;) {
773		int s = runState;
774	+	if ((s & (TERMINATING|TERMINATED)) != 0)
775	+	break;
776		if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
777		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
778		(s & ~SUSPENDED) |
779	<	(TRIMMED|TERMINATING))) {
672	<	LockSupport.unpark(this);
779	>	(TRIMMED|TERMINATING)))
780		break;
674	–	}
781		}
782		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
783		s | TERMINATING))
#	Line 680 | Line 786 | public class ForkJoinWorkerThread extend
786		}
787
788		/**
789	<	* Sets state to TERMINATED. Called only by this thread.
789	>	* Sets state to TERMINATED. Called only by onTermination().
790		*/
791		private void setTerminated() {
792		int s;
#	Line 690 | Line 796 | public class ForkJoinWorkerThread extend
796		}
797
798		/**
693	–	* Instrumented version of park. Also used by ForkJoinPool.awaitEvent
694	–	*/
695	–	final void doPark() {
696	–	++parkCount;
697	–	LockSupport.park(this);
698	–	}
699	–
700	–	/**
799		* If suspended, tries to set status to unsuspended.
800	<	* Caller must unpark to actually resume
800	>	* Does NOT wake up if blocked.
801		*
802		* @return true if successful
803		*/
804		final boolean tryUnsuspend() {
805		int s;
806	<	return (((s = runState) & SUSPENDED) != 0 &&
807	<	UNSAFE.compareAndSwapInt(this, runStateOffset, s,
808	<	s & ~SUSPENDED));
806	>	while (((s = runState) & SUSPENDED) != 0) {
807	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
808	>	s & ~SUSPENDED))
809	>	return true;
810	>	}
811	>	return false;
812		}
813
814		/**
815	<	* Sets suspended status and blocks as spare until resumed,
816	<	* shutdown, or timed out.
716	<	*
717	<	* @return false if trimmed
815	>	* Sets suspended status and blocks as spare until resumed
816	>	* or shutdown.
817		*/
818	<	final boolean suspendAsSpare() {
819	<	for (;;) {               // set suspended unless terminating
818	>	final void suspendAsSpare() {
819	>	for (;;) {                  // set suspended unless terminating
820		int s = runState;
821		if ((s & TERMINATING) != 0) { // must kill
822		if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
823		s | (TRIMMED | TERMINATING)))
824	<	return false;
824	>	return;
825		}
826		else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
827		s | SUSPENDED))
828		break;
829		}
731	–	lastEventCount = 0;      // reset upon resume
830		ForkJoinPool p = pool;
831	<	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();
831	>	p.pushSpare(this);
832		while ((runState & SUSPENDED) != 0) {
833	<	++parkCount;
834	<	if ((nanos -= (System.nanoTime() - startTime)) > 0)
835	<	LockSupport.parkNanos(this, nanos);
836	<	else { // try to trim on timeout
837	<	int s = runState;
757	<	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
758	<	(s & ~SUSPENDED) |
759	<	(TRIMMED|TERMINATING)))
760	<	return false;
833	>	if (p.tryAccumulateStealCount(this)) {
834	>	interrupted();          // clear/ignore interrupts
835	>	if ((runState & SUSPENDED) == 0)
836	>	break;
837	>	LockSupport.park(this);
838		}
839		}
763	–	return true;
840		}
841
842		// Misc support methods for ForkJoinPool
#	Line 770 | Line 846 | public class ForkJoinWorkerThread extend
846		* used by ForkJoinTask.
847		*/
848		final int getQueueSize() {
849	<	return -base + sp;
850	<	}
775	<
776	<	/**
777	<	* Set locallyFifo mode. Called only by ForkJoinPool
778	<	*/
779	<	final void setAsyncMode(boolean async) {
780	<	locallyFifo = async;
849	>	int n; // external calls must read base first
850	>	return (n = -base + sp) <= 0 ? 0 : n;
851		}
852
853		/**
#	Line 785 | Line 855 | public class ForkJoinWorkerThread extend
855		* thread.
856		*/
857		final void cancelTasks() {
858	+	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
859	+	if (cj != null) {
860	+	currentJoin = null;
861	+	cj.cancelIgnoringExceptions();
862	+	try {
863	+	this.interrupt(); // awaken wait
864	+	} catch (SecurityException ignore) {
865	+	}
866	+	}
867	+	ForkJoinTask<?> cs = currentSteal;
868	+	if (cs != null) {
869	+	currentSteal = null;
870	+	cs.cancelIgnoringExceptions();
871	+	}
872		while (base != sp) {
873		ForkJoinTask<?> t = deqTask();
874		if (t != null)
#	Line 812 | Line 896 | public class ForkJoinWorkerThread extend
896		// Support methods for ForkJoinTask
897
898		/**
899	+	* Gets and removes a local task.
900	+	*
901	+	* @return a task, if available
902	+	*/
903	+	final ForkJoinTask<?> pollLocalTask() {
904	+	ForkJoinPool p = pool;
905	+	while (sp != base) {
906	+	int a; // inline p.tryIncrementActiveCount
907	+	if (active ||
908	+	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
909	+	a = p.runState, a + 1)))
910	+	return locallyFifo ? locallyDeqTask() : popTask();
911	+	}
912	+	return null;
913	+	}
914	+
915	+	/**
916	+	* Gets and removes a local or stolen task.
917	+	*
918	+	* @return a task, if available
919	+	*/
920	+	final ForkJoinTask<?> pollTask() {
921	+	ForkJoinTask<?> t = pollLocalTask();
922	+	if (t == null) {
923	+	t = scan();
924	+	// cannot retain/track/help steal
925	+	UNSAFE.putOrderedObject(this, currentStealOffset, null);
926	+	}
927	+	return t;
928	+	}
929	+
930	+	/**
931	+	* Possibly runs some tasks and/or blocks, until task is done.
932	+	*
933	+	* @param joinMe the task to join
934	+	* @param timed true if use timed wait
935	+	* @param nanos wait time if timed
936	+	*/
937	+	final void joinTask(ForkJoinTask<?> joinMe, boolean timed, long nanos) {
938	+	// currentJoin only written by this thread; only need ordered store
939	+	ForkJoinTask<?> prevJoin = currentJoin;
940	+	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
941	+	if (isTerminating())                // cancel if shutting down
942	+	joinMe.cancelIgnoringExceptions();
943	+	else {
944	+	if (sp != base)
945	+	localHelpJoinTask(joinMe);
946	+	if (joinMe.status >= 0)
947	+	pool.awaitJoin(joinMe, this, timed, nanos);
948	+	}
949	+	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
950	+	}
951	+
952	+	/**
953	+	* Run tasks in local queue until given task is done.
954	+	*
955	+	* @param joinMe the task to join
956	+	*/
957	+	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
958	+	int s;
959	+	ForkJoinTask<?>[] q;
960	+	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
961	+	int i = (q.length - 1) & --s;
962	+	long u = (i << qShift) + qBase; // raw offset
963	+	ForkJoinTask<?> t = q[i];
964	+	if (t == null)  // lost to a stealer
965	+	break;
966	+	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
967	+	/*
968	+	* This recheck (and similarly in helpJoinTask)
969	+	* handles cases where joinMe is independently
970	+	* cancelled or forced even though there is other work
971	+	* available. Back out of the pop by putting t back
972	+	* into slot before we commit by writing sp.
973	+	*/
974	+	if (joinMe.status < 0) {
975	+	UNSAFE.putObjectVolatile(q, u, t);
976	+	break;
977	+	}
978	+	sp = s;
979	+	// UNSAFE.putOrderedInt(this, spOffset, s);
980	+	t.quietlyExec();
981	+	}
982	+	}
983	+	}
984	+
985	+	/**
986	+	* Tries to locate and help perform tasks for a stealer of the
987	+	* given task, or in turn one of its stealers.  Traces
988	+	* currentSteal->currentJoin links looking for a thread working on
989	+	* a descendant of the given task and with a non-empty queue to
990	+	* steal back and execute tasks from.
991	+	*
992	+	* The implementation is very branchy to cope with potential
993	+	* inconsistencies or loops encountering chains that are stale,
994	+	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
995	+	* of these cases are dealt with by just returning back to the
996	+	* caller, who is expected to retry if other join mechanisms also
997	+	* don't work out.
998	+	*
999	+	* @param joinMe the task to join
1000	+	*/
1001	+	final void helpJoinTask(ForkJoinTask<?> joinMe) {
1002	+	ForkJoinWorkerThread[] ws;
1003	+	int n;
1004	+	if (joinMe.status < 0)                // already done
1005	+	return;
1006	+	if ((ws = pool.workers) == null || (n = ws.length) <= 1)
1007	+	return;                           // need at least 2 workers
1008	+
1009	+	ForkJoinTask<?> task = joinMe;        // base of chain
1010	+	ForkJoinWorkerThread thread = this;   // thread with stolen task
1011	+	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1012	+	// Try to find v, the stealer of task, by first using hint
1013	+	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1014	+	if (v == null || v.currentSteal != task) {
1015	+	for (int j = 0; ; ++j) {      // search array
1016	+	if (j < n) {
1017	+	ForkJoinTask<?> vs;
1018	+	if ((v = ws[j]) != null &&
1019	+	(vs = v.currentSteal) != null) {
1020	+	if (joinMe.status < 0 || task.status < 0)
1021	+	return;       // stale or done
1022	+	if (vs == task) {
1023	+	thread.stealHint = j;
1024	+	break;        // save hint for next time
1025	+	}
1026	+	}
1027	+	}
1028	+	else
1029	+	return;               // no stealer
1030	+	}
1031	+	}
1032	+	for (;;) { // Try to help v, using specialized form of deqTask
1033	+	if (joinMe.status < 0)
1034	+	return;
1035	+	int b = v.base;
1036	+	ForkJoinTask<?>[] q = v.queue;
1037	+	if (b == v.sp || q == null)
1038	+	break;
1039	+	int i = (q.length - 1) & b;
1040	+	long u = (i << qShift) + qBase;
1041	+	ForkJoinTask<?> t = q[i];
1042	+	int pid = poolIndex;
1043	+	ForkJoinTask<?> ps = currentSteal;
1044	+	if (task.status < 0)
1045	+	return;                   // stale or done
1046	+	if (t != null && v.base == b++ &&
1047	+	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1048	+	if (joinMe.status < 0) {
1049	+	UNSAFE.putObjectVolatile(q, u, t);
1050	+	return;               // back out on cancel
1051	+	}
1052	+	v.base = b;
1053	+	v.stealHint = pid;
1054	+	UNSAFE.putOrderedObject(this, currentStealOffset, t);
1055	+	t.quietlyExec();
1056	+	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1057	+	}
1058	+	}
1059	+	// Try to descend to find v's stealer
1060	+	ForkJoinTask<?> next = v.currentJoin;
1061	+	if (task.status < 0 || next == null || next == task ||
1062	+	joinMe.status < 0)
1063	+	return;
1064	+	task = next;
1065	+	thread = v;
1066	+	}
1067	+	}
1068	+
1069	+	/**
1070	+	* Implements ForkJoinTask.getSurplusQueuedTaskCount().
1071		* Returns an estimate of the number of tasks, offset by a
1072		* function of number of idle workers.
1073		*
#	Line 863 | Line 1119 | public class ForkJoinWorkerThread extend
1119		}
1120
1121		/**
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	–	/**
1122		* Runs tasks until {@code pool.isQuiescent()}.
1123		*/
1124		final void helpQuiescePool() {
1125	+	ForkJoinTask<?> ps = currentSteal; // to restore below
1126		for (;;) {
1127		ForkJoinTask<?> t = pollLocalTask();
1128		if (t != null || (t = scan()) != null)
1129	<	t.tryExec();
1129	>	t.quietlyExec();
1130		else {
1131		ForkJoinPool p = pool;
1132	+	int a; // to inline CASes
1133		if (active) {
1134	+	if (!UNSAFE.compareAndSwapInt
1135	+	(p, poolRunStateOffset, a = p.runState, a - 1))
1136	+	continue;   // retry later
1137		active = false; // inactivate
1138	<	do {} while (!p.tryDecrementActiveCount());
1138	>	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1139		}
1140		if (p.isQuiescent()) {
1141		active = true; // re-activate
1142	<	do {} while (!p.tryIncrementActiveCount());
1142	>	do {} while (!UNSAFE.compareAndSwapInt
1143	>	(p, poolRunStateOffset, a = p.runState, a+1));
1144		return;
1145		}
1146		}
#	Line 1008 | Line 1150 | public class ForkJoinWorkerThread extend
1150		// Unsafe mechanics
1151
1152		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1153	+	private static final long spOffset =
1154	+	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1155		private static final long runStateOffset =
1156		objectFieldOffset("runState", ForkJoinWorkerThread.class);
1157	+	private static final long currentJoinOffset =
1158	+	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1159	+	private static final long currentStealOffset =
1160	+	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1161		private static final long qBase =
1162		UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1163	+	private static final long poolRunStateOffset = // to inline CAS
1164	+	objectFieldOffset("runState", ForkJoinPool.class);
1165	+
1166		private static final int qShift;
1167
1168		static {
#	Line 1019 | Line 1170 | public class ForkJoinWorkerThread extend
1170		if ((s & (s-1)) != 0)
1171		throw new Error("data type scale not a power of two");
1172		qShift = 31 - Integer.numberOfLeadingZeros(s);
1173	+	MAXIMUM_QUEUE_CAPACITY = 1 << (31 - qShift);
1174		}
1175
1176		private static long objectFieldOffset(String field, Class<?> klazz) {

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