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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.4 by dl, Wed Jan 7 20:51:36 2009 UTC vs.
Revision 1.5 by dl, Mon Jan 12 17:16:18 2009 UTC

#	Line 21 | Line 21 | import java.lang.reflect.*;
21		* do create such a subclass, you will also need to supply a custom
22		* ForkJoinWorkerThreadFactory to use it in a ForkJoinPool.
23		*
24	–	* <p>This class also provides methods for generating per-thread
25	–	* random numbers, with the same properties as {@link
26	–	* java.util.Random} but with each generator isolated from those of
27	–	* other threads.
24		*/
25		public class ForkJoinWorkerThread extends Thread {
26		/*
#	Line 134 | Line 130 | public class ForkJoinWorkerThread extend
130
131		/**
132		* Maximum work-stealing queue array size.  Must be less than or
133	<	* equal to 1 << 30 to ensure lack of index wraparound.
133	>	* equal to 1 << 28 to ensure lack of index wraparound. (This
134	>	* is less than usual bounds, because we need leftshift by 3
135	>	* to be in int range).
136		*/
137	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30;
137	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
138
139		/**
140	<	* Generator of seeds for per-thread random numbers.
140	>	* The pool this thread works in. Accessed directly by ForkJoinTask
141		*/
142	<	private static final Random randomSeedGenerator = new Random();
142	>	final ForkJoinPool pool;
143
144		/**
145		* The work-stealing queue array. Size must be a power of two.
146	+	* Initialized when thread starts, to improve memory locality.
147		*/
148		private ForkJoinTask<?>[] queue;
149
#	Line 163 | Line 162 | public class ForkJoinWorkerThread extend
162		private volatile int base;
163
164		/**
165	<	* The pool this thread works in.
166	<	*/
167	<	final ForkJoinPool pool;
168	<
170	<	/**
171	<	* Index of this worker in pool array. Set once by pool before
172	<	* running, and accessed directly by pool during cleanup etc
165	>	* Activity status. When true, this worker is considered active.
166	>	* Must be false upon construction. It must be true when executing
167	>	* tasks, and BEFORE stealing a task. It must be false before
168	>	* calling pool.sync
169		*/
170	<	int poolIndex;
170	>	private boolean active;
171
172		/**
173		* Run state of this worker. Supports simple versions of the usual
#	Line 179 | Line 175 | public class ForkJoinWorkerThread extend
175		*/
176		private volatile int runState;
177
182	–	// Runstate values. Order matters
183	–	private static final int RUNNING     = 0;
184	–	private static final int SHUTDOWN    = 1;
185	–	private static final int TERMINATING = 2;
186	–	private static final int TERMINATED  = 3;
187	–
178		/**
179	<	* Activity status. When true, this worker is considered active.
180	<	* Must be false upon construction. It must be true when executing
191	<	* tasks, and BEFORE stealing a task. It must be false before
192	<	* blocking on the Pool Barrier.
179	>	* Seed for random number generator for choosing steal victims.
180	>	* Uses Marsaglia xorshift. Must be nonzero upon initialization.
181		*/
182	<	private boolean active;
182	>	private int seed;
183
184		/**
185		* Number of steals, transferred to pool when idle
#	Line 199 | Line 187 | public class ForkJoinWorkerThread extend
187		private int stealCount;
188
189		/**
190	<	* Seed for random number generator for choosing steal victims
191	<	*/
204	<	private int randomVictimSeed;
205	<
206	<	/**
207	<	* Seed for embedded Jurandom
190	>	* Index of this worker in pool array. Set once by pool before
191	>	* running, and accessed directly by pool during cleanup etc
192		*/
193	<	private long juRandomSeed;
193	>	int poolIndex;
194
195		/**
196	<	* The last barrier event waited for
196	>	* The last barrier event waited for. Accessed in pool callback
197	>	* methods, but only by current thread.
198		*/
199	<	private long eventCount;
199	>	long lastEventCount;
200
201		/**
202		* Creates a ForkJoinWorkerThread operating in the given pool.
#	Line 221 | Line 206 | public class ForkJoinWorkerThread extend
206		protected ForkJoinWorkerThread(ForkJoinPool pool) {
207		if (pool == null) throw new NullPointerException();
208		this.pool = pool;
209	<	// remaining initialization deferred to onStart
209	>	// Note: poolIndex is set by pool during construction
210	>	// Remaining initialization is deferred to onStart
211		}
212
213	<	// public access methods
213	>	// Public access methods
214
215		/**
216		* Returns the pool hosting this thread
#	Line 239 | Line 225 | public class ForkJoinWorkerThread extend
225		* returned value ranges from zero to the maximum number of
226		* threads (minus one) that have ever been created in the pool.
227		* This method may be useful for applications that track status or
228	<	* collect results on a per-worker basis.
228	>	* collect results per-worker rather than per-task.
229		* @return the index number.
230		*/
231		public int getPoolIndex() {
232		return poolIndex;
233		}
234
235	<	//  Access methods used by Pool
235	>
236	>	// Runstate management
237	>
238	>	// Runstate values. Order matters
239	>	private static final int RUNNING     = 0;
240	>	private static final int SHUTDOWN    = 1;
241	>	private static final int TERMINATING = 2;
242	>	private static final int TERMINATED  = 3;
243	>
244	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
245	>	final boolean isTerminating() { return runState >= TERMINATING;  }
246	>	final boolean isTerminated()  { return runState == TERMINATED; }
247	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
248	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
249
250		/**
251	<	* Get and clear steal count for accumulation by pool.  Called
252	<	* only when known to be idle (in pool.sync and termination).
251	>	* Transition to at least the given state. Return true if not
252	>	* already at least given state.
253		*/
254	<	final int getAndClearStealCount() {
255	<	int sc = stealCount;
256	<	stealCount = 0;
257	<	return sc;
254	>	private boolean transitionRunStateTo(int state) {
255	>	for (;;) {
256	>	int s = runState;
257	>	if (s >= state)
258	>	return false;
259	>	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
260	>	return true;
261	>	}
262		}
263
264		/**
265	<	* Returns estimate of the number of tasks in the queue, without
263	<	* correcting for transient negative values
265	>	* Try to set status to active; fail on contention
266		*/
267	<	final int getRawQueueSize() {
268	<	return sp - base;
267	>	private boolean tryActivate() {
268	>	if (!active) {
269	>	if (!pool.tryIncrementActiveCount())
270	>	return false;
271	>	active = true;
272	>	}
273	>	return true;
274		}
275
276	<	// Intrinsics-based support for queue operations.
277	<	// Currently these three (setSp, setSlot, casSlotNull) are
278	<	// usually manually inlined to improve performance
276	>	/**
277	>	* Try to set status to active; fail on contention
278	>	*/
279	>	private boolean tryInactivate() {
280	>	if (active) {
281	>	if (!pool.tryDecrementActiveCount())
282	>	return false;
283	>	active = false;
284	>	}
285	>	return true;
286	>	}
287
288		/**
289	<	* Sets sp in store-order.
289	>	* Computes next value for random victim probe. Scans don't
290	>	* require a very high quality generator, but also not a crummy
291	>	* one. Marsaglia xor-shift is cheap and works well.
292		*/
293	<	private void setSp(int s) {
294	<	_unsafe.putOrderedInt(this, spOffset, s);
293	>	private static int xorShift(int r) {
294	>	r ^= r << 1;
295	>	r ^= r >>> 3;
296	>	r ^= r << 10;
297	>	return r;
298		}
299
300	+	// Lifecycle methods
301	+
302	+	/**
303	+	* This method is required to be public, but should never be
304	+	* called explicitly. It performs the main run loop to execute
305	+	* ForkJoinTasks.
306	+	*/
307	+	public void run() {
308	+	Throwable exception = null;
309	+	try {
310	+	onStart();
311	+	pool.sync(this); // await first pool event
312	+	mainLoop();
313	+	} catch (Throwable ex) {
314	+	exception = ex;
315	+	} finally {
316	+	onTermination(exception);
317	+	}
318	+	}
319	+
320	+	/**
321	+	* Execute tasks until shut down.
322	+	*/
323	+	private void mainLoop() {
324	+	while (!isShutdown()) {
325	+	ForkJoinTask<?> t = pollTask();
326	+	if (t != null || (t = pollSubmission()) != null)
327	+	t.quietlyExec();
328	+	else if (tryInactivate())
329	+	pool.sync(this);
330	+	}
331	+	}
332	+
333	+	/**
334	+	* Initializes internal state after construction but before
335	+	* processing any tasks. If you override this method, you must
336	+	* invoke super.onStart() at the beginning of the method.
337	+	* Initialization requires care: Most fields must have legal
338	+	* default values, to ensure that attempted accesses from other
339	+	* threads work correctly even before this thread starts
340	+	* processing tasks.
341	+	*/
342	+	protected void onStart() {
343	+	// Allocate while starting to improve chances of thread-local
344	+	// isolation
345	+	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
346	+	// Initial value of seed need not be especially random but
347	+	// should differ across workers and must be nonzero
348	+	int p = poolIndex + 1;
349	+	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
350	+	}
351	+
352	+	/**
353	+	* Perform cleanup associated with termination of this worker
354	+	* thread.  If you override this method, you must invoke
355	+	* super.onTermination at the end of the overridden method.
356	+	*
357	+	* @param exception the exception causing this thread to abort due
358	+	* to an unrecoverable error, or null if completed normally.
359	+	*/
360	+	protected void onTermination(Throwable exception) {
361	+	// Execute remaining local tasks unless aborting or terminating
362	+	while (exception == null &&  !pool.isTerminating() && base != sp) {
363	+	try {
364	+	ForkJoinTask<?> t = popTask();
365	+	if (t != null)
366	+	t.quietlyExec();
367	+	} catch(Throwable ex) {
368	+	exception = ex;
369	+	}
370	+	}
371	+	// Cancel other tasks, transition status, notify pool, and
372	+	// propagate exception to uncaught exception handler
373	+	try {
374	+	do;while (!tryInactivate()); // ensure inactive
375	+	cancelTasks();
376	+	runState = TERMINATED;
377	+	pool.workerTerminated(this);
378	+	} catch (Throwable ex) {        // Shouldn't ever happen
379	+	if (exception == null)      // but if so, at least rethrown
380	+	exception = ex;
381	+	} finally {
382	+	if (exception != null)
383	+	ForkJoinTask.rethrowException(exception);
384	+	}
385	+	}
386	+
387	+	// Intrinsics-based support for queue operations.
388	+
389		/**
390		* Add in store-order the given task at given slot of q to
391		* null. Caller must ensure q is nonnull and index is in range.
#	Line 295 | Line 404 | public class ForkJoinWorkerThread extend
404		return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
405		}
406
407	+	/**
408	+	* Sets sp in store-order.
409	+	*/
410	+	private void storeSp(int s) {
411	+	_unsafe.putOrderedInt(this, spOffset, s);
412	+	}
413	+
414		// Main queue methods
415
416		/**
#	Line 305 | Line 421 | public class ForkJoinWorkerThread extend
421		ForkJoinTask<?>[] q = queue;
422		int mask = q.length - 1;
423		int s = sp;
424	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
425	<	_unsafe.putOrderedInt(this, spOffset, ++s);
424	>	setSlot(q, s & mask, t);
425	>	storeSp(++s);
426		if ((s -= base) == 1)
427	<	pool.signalNonEmptyWorkerQueue();
427	>	pool.signalWork();
428		else if (s >= mask)
429		growQueue();
430		}
#	Line 319 | Line 435 | public class ForkJoinWorkerThread extend
435		* @return a task, or null if none or contended.
436		*/
437		private ForkJoinTask<?> deqTask() {
322	–	ForkJoinTask<?>[] q;
438		ForkJoinTask<?> t;
439	+	ForkJoinTask<?>[] q;
440		int i;
441		int b;
442		if (sp != (b = base) &&
443		(q = queue) != null && // must read q after b
444		(t = q[i = (q.length - 1) & b]) != null &&
445	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
445	>	casSlotNull(q, i, t)) {
446		base = b + 1;
447		return t;
448		}
#	Line 334 | Line 450 | public class ForkJoinWorkerThread extend
450		}
451
452		/**
453	<	* Returns a popped task, or null if empty.  Called only by
454	<	* current thread.
453	>	* Returns a popped task, or null if empty. Ensures active status
454	>	* if nonnull. Called only by current thread.
455		*/
456		final ForkJoinTask<?> popTask() {
341	–	ForkJoinTask<?> t;
342	–	int i;
343	–	ForkJoinTask<?>[] q = queue;
344	–	int mask = q.length - 1;
457		int s = sp;
458	<	if (s != base &&
459	<	(t = q[i = (s - 1) & mask]) != null &&
460	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
461	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
462	<	return t;
458	>	while (s != base) {
459	>	if (tryActivate()) {
460	>	ForkJoinTask<?>[] q = queue;
461	>	int mask = q.length - 1;
462	>	int i = (s - 1) & mask;
463	>	ForkJoinTask<?> t = q[i];
464	>	if (t == null || !casSlotNull(q, i, t))
465	>	break;
466	>	storeSp(s - 1);
467	>	return t;
468	>	}
469		}
470		return null;
471		}
#	Line 355 | Line 473 | public class ForkJoinWorkerThread extend
473		/**
474		* Specialized version of popTask to pop only if
475		* topmost element is the given task. Called only
476	<	* by current thread.
476	>	* by current thread while active.
477		* @param t the task. Caller must ensure nonnull
478		*/
479		final boolean unpushTask(ForkJoinTask<?> t) {
480		ForkJoinTask<?>[] q = queue;
481		int mask = q.length - 1;
482		int s = sp - 1;
483	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
484	<	t, null)) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
483	>	if (casSlotNull(q, s & mask, t)) {
484	>	storeSp(s);
485		return true;
486		}
487		return false;
#	Line 402 | Line 519 | public class ForkJoinWorkerThread extend
519		t = null;
520		setSlot(newQ, b & newMask, t);
521		} while (++b != bf);
522	<	pool.signalIdleWorkers(false);
522	>	pool.signalWork();
523		}
524
408	–	// Runstate management
409	–
410	–	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
411	–	final boolean isTerminating() { return runState >= TERMINATING;  }
412	–	final boolean isTerminated()  { return runState == TERMINATED; }
413	–	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
414	–	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
415	–
525		/**
526	<	* Transition to at least the given state. Return true if not
527	<	* already at least given state.
528	<	*/
529	<	private boolean transitionRunStateTo(int state) {
530	<	for (;;) {
531	<	int s = runState;
532	<	if (s >= state)
533	<	return false;
425	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
426	<	return true;
427	<	}
428	<	}
429	<
430	<	/**
431	<	* Ensure status is active and if necessary adjust pool active count
432	<	*/
433	<	final void activate() {
434	<	if (!active) {
435	<	active = true;
436	<	pool.incrementActiveCount();
437	<	}
438	<	}
439	<
440	<	/**
441	<	* Ensure status is inactive and if necessary adjust pool active count
442	<	*/
443	<	final void inactivate() {
444	<	if (active) {
445	<	active = false;
446	<	pool.decrementActiveCount();
447	<	}
448	<	}
449	<
450	<	// Lifecycle methods
451	<
452	<	/**
453	<	* Initializes internal state after construction but before
454	<	* processing any tasks. If you override this method, you must
455	<	* invoke super.onStart() at the beginning of the method.
456	<	* Initialization requires care: Most fields must have legal
457	<	* default values, to ensure that attempted accesses from other
458	<	* threads work correctly even before this thread starts
459	<	* processing tasks.
460	<	*/
461	<	protected void onStart() {
462	<	juRandomSeed = randomSeedGenerator.nextLong();
463	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
464	<	if (queue == null)
465	<	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
466	<
467	<	// Heuristically allow one initial thread to warm up; others wait
468	<	if (poolIndex < pool.getParallelism() - 1) {
469	<	eventCount = pool.sync(this, 0);
470	<	activate();
471	<	}
472	<	}
473	<
474	<	/**
475	<	* Perform cleanup associated with termination of this worker
476	<	* thread.  If you override this method, you must invoke
477	<	* super.onTermination at the end of the overridden method.
478	<	*
479	<	* @param exception the exception causing this thread to abort due
480	<	* to an unrecoverable error, or null if completed normally.
481	<	*/
482	<	protected void onTermination(Throwable exception) {
483	<	try {
484	<	clearLocalTasks();
485	<	inactivate();
486	<	cancelTasks();
487	<	} finally {
488	<	terminate(exception);
489	<	}
490	<	}
491	<
492	<	/**
493	<	* Notify pool of termination and, if exception is nonnull,
494	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
495	<	*/
496	<	private void terminate(Throwable exception) {
497	<	transitionRunStateTo(TERMINATED);
498	<	try {
499	<	pool.workerTerminated(this);
500	<	} finally {
501	<	if (exception != null)
502	<	ForkJoinTask.rethrowException(exception);
503	<	}
504	<	}
505	<
506	<	/**
507	<	* Run local tasks on exit from main.
508	<	*/
509	<	private void clearLocalTasks() {
510	<	while (base != sp && !pool.isTerminating()) {
511	<	ForkJoinTask<?> t = popTask();
512	<	if (t != null) {
513	<	activate(); // ensure active status
514	<	t.quietlyExec();
515	<	}
516	<	}
517	<	}
518	<
519	<	/**
520	<	* Removes and cancels all tasks in queue.  Can be called from any
521	<	* thread.
522	<	*/
523	<	final void cancelTasks() {
524	<	while (base != sp) {
525	<	ForkJoinTask<?> t = deqTask();
526	<	if (t != null)
527	<	t.cancelIgnoringExceptions();
528	<	}
529	<	}
530	<
531	<	/**
532	<	* This method is required to be public, but should never be
533	<	* called explicitly. It performs the main run loop to execute
534	<	* ForkJoinTasks.
535	<	*/
536	<	public void run() {
537	<	Throwable exception = null;
538	<	try {
539	<	onStart();
540	<	while (!isShutdown())
541	<	step();
542	<	} catch (Throwable ex) {
543	<	exception = ex;
544	<	} finally {
545	<	onTermination(exception);
546	<	}
547	<	}
548	<
549	<	/**
550	<	* Main top-level action.
551	<	*/
552	<	private void step() {
553	<	ForkJoinTask<?> t = sp != base? popTask() : null;
554	<	if (t != null || (t = scan(null, true)) != null) {
555	<	activate();
556	<	t.quietlyExec();
557	<	}
558	<	else {
559	<	inactivate();
560	<	eventCount = pool.sync(this, eventCount);
561	<	}
562	<	}
563	<
564	<	// scanning for and stealing tasks
565	<
566	<	/**
567	<	* Computes next value for random victim probe. Scans don't
568	<	* require a very high quality generator, but also not a crummy
569	<	* one. Marsaglia xor-shift is cheap and works well.
570	<	*
571	<	* This is currently unused, and manually inlined
572	<	*/
573	<	private static int xorShift(int r) {
574	<	r ^= r << 1;
575	<	r ^= r >>> 3;
576	<	r ^= r << 10;
577	<	return r;
578	<	}
579	<
580	<	/**
581	<	* Tries to steal a task from another worker and/or, if enabled,
582	<	* submission queue. Starts at a random index of workers array,
583	<	* and probes workers until finding one with non-empty queue or
584	<	* finding that all are empty.  It randomly selects the first n-1
585	<	* probes. If these are empty, it resorts to full circular
586	<	* traversal, which is necessary to accurately set active status
587	<	* by caller. Also restarts if pool barrier has tripped since last
588	<	* scan, which forces refresh of workers array, in case barrier
589	<	* was associated with resize.
526	>	* Tries to steal a task from another worker. Starts at a random
527	>	* index of workers array, and probes workers until finding one
528	>	* with non-empty queue or finding that all are empty.  It
529	>	* randomly selects the first n probes. If these are empty, it
530	>	* resorts to a full circular traversal, which is necessary to
531	>	* accurately set active status by caller. Also restarts if pool
532	>	* events occurred since last scan, which forces refresh of
533	>	* workers array, in case barrier was associated with resize.
534		*
535		* This method must be both fast and quiet -- usually avoiding
536		* memory accesses that could disrupt cache sharing etc other than
537		* those needed to check for and take tasks. This accounts for,
538		* among other things, updating random seed in place without
539	<	* storing it until exit. (Note that we only need to store it if
596	<	* we found a task; otherwise it doesn't matter if we start at the
597	<	* same place next time.)
539	>	* storing it until exit.
540		*
599	–	* @param joinMe if non null; exit early if done
600	–	* @param checkSubmissions true if OK to take submissions
541		* @return a task, or null if none found
542		*/
543	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
544	<	boolean checkSubmissions) {
545	<	ForkJoinPool p = pool;
546	<	if (p == null)                    // Never null, but avoids
547	<	return null;                  //   implicit nullchecks below
548	<	int r = randomVictimSeed;         // extract once to keep scan quiet
549	<	restart:                          // outer loop refreshes ws array
610	<	while (joinMe == null || joinMe.status >= 0) {
611	<	int mask;
612	<	ForkJoinWorkerThread[] ws = p.workers;
613	<	if (ws != null && (mask = ws.length - 1) > 0) {
614	<	int probes = -mask;       // use random index while negative
543	>	private ForkJoinTask<?> scan() {
544	>	ForkJoinTask<?> t = null;
545	>	int r = seed;                    // extract once to keep scan quiet
546	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
547	>	int mask;                        // must be power 2 minus 1 and > 0
548	>	outer:do {
549	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
550		int idx = r;
551	+	int probes = ~mask;      // use random index while negative
552		for (;;) {
553	<	ForkJoinWorkerThread v;
554	<	// inlined xorshift to update seed
555	<	r ^= r << 1;  r ^= r >>> 3; r ^= r << 10;
556	<	if ((v = ws[mask & idx]) != null && v.sp != v.base) {
557	<	ForkJoinTask<?> t;
558	<	activate();
559	<	if ((joinMe == null || joinMe.status >= 0) &&
624	<	(t = v.deqTask()) != null) {
625	<	randomVictimSeed = r;
626	<	++stealCount;
627	<	return t;
628	<	}
629	<	continue restart; // restart on contention
553	>	r = xorShift(r);     // update random seed
554	>	ForkJoinWorkerThread v = ws[mask & idx];
555	>	if (v == null || v.sp == v.base) {
556	>	if (probes <= mask)
557	>	idx = (probes++ < 0)? r : (idx + 1);
558	>	else
559	>	break;
560		}
561	<	if ((probes >> 1) <= mask) // n-1 random then circular
562	<	idx = (probes++ < 0)? r : (idx + 1);
561	>	else if (!tryActivate() || (t = v.deqTask()) == null)
562	>	continue outer;  // restart on contention
563		else
564	<	break;
564	>	break outer;
565		}
566		}
567	<	if (checkSubmissions && p.hasQueuedSubmissions()) {
568	<	activate();
569	<	ForkJoinTask<?> t = p.pollSubmission();
640	<	if (t != null)
641	<	return t;
642	<	}
643	<	else {
644	<	long ec = eventCount;     // restart on pool event
645	<	if ((eventCount = p.getEventCount()) == ec)
646	<	break;
647	<	}
648	<	}
649	<	return null;
567	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
568	>	seed = r;
569	>	return t;
570		}
571
572		/**
573	<	* Callback from pool.sync to rescan before blocking.  If a
574	<	* task is found, it is pushed so it can be executed upon return.
575	<	* @return true if found and pushed a task
576	<	*/
577	<	final boolean prescan() {
578	<	ForkJoinTask<?> t = scan(null, true);
579	<	if (t != null) {
580	<	pushTask(t);
661	<	return true;
662	<	}
663	<	else {
664	<	inactivate();
665	<	return false;
666	<	}
573	>	* Pops or steals a task
574	>	* @return a task, if available
575	>	*/
576	>	final ForkJoinTask<?> pollTask() {
577	>	ForkJoinTask<?> t = popTask();
578	>	if (t == null && (t = scan()) != null)
579	>	++stealCount;
580	>	return t;
581		}
582
669	–	// Support for ForkJoinTask methods
670	–
583		/**
584	<	* Scan, returning early if joinMe done
584	>	* Returns a pool submission, if one exists, activating first.
585	>	* @return a submission, if available
586		*/
587	<	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
588	<	ForkJoinTask<?> t = scan(joinMe, false);
589	<	if (t != null && joinMe.status < 0 && sp == base) {
590	<	pushTask(t); // unsteal if done and this task would be stealable
591	<	t = null;
587	>	private ForkJoinTask<?> pollSubmission() {
588	>	ForkJoinPool p = pool;
589	>	while (p.hasQueuedSubmissions()) {
590	>	ForkJoinTask<?> t;
591	>	if (tryActivate() && (t = p.pollSubmission()) != null)
592	>	return t;
593		}
594	<	return t;
594	>	return null;
595		}
596	<
596	>
597	>	// Methods accessed only by Pool
598	>
599		/**
600	<	* Pops or steals a task
601	<	* @return task, or null if none available
600	>	* Removes and cancels all tasks in queue.  Can be called from any
601	>	* thread.
602		*/
603	<	final ForkJoinTask<?> pollLocalOrStolenTask() {
603	>	final void cancelTasks() {
604		ForkJoinTask<?> t;
605	<	return (t = popTask()) == null? scan(null, false) : t;
605	>	while (base != sp && (t = deqTask()) != null)
606	>	t.cancelIgnoringExceptions();
607		}
608
609		/**
610	<	* Runs tasks until pool isQuiescent
610	>	* Get and clear steal count for accumulation by pool.  Called
611	>	* only when known to be idle (in pool.sync and termination).
612		*/
613	<	final void helpQuiescePool() {
614	<	for (;;) {
615	<	ForkJoinTask<?> t = pollLocalOrStolenTask();
616	<	if (t != null) {
617	<	activate();
618	<	t.quietlyExec();
619	<	}
620	<	else {
621	<	inactivate();
622	<	if (pool.isQuiescent()) {
623	<	activate(); // re-activate on exit
624	<	break;
613	>	final int getAndClearStealCount() {
614	>	int sc = stealCount;
615	>	stealCount = 0;
616	>	return sc;
617	>	}
618	>
619	>	/**
620	>	* Returns true if at least one worker in the given array appears
621	>	* to have at least one queued task.
622	>	* @param ws array of workers
623	>	*/
624	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
625	>	if (ws != null) {
626	>	int len = ws.length;
627	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
628	>	for (int i = 0; i < len; ++i) {
629	>	ForkJoinWorkerThread w = ws[i];
630	>	if (w != null && w.sp != w.base)
631	>	return true;
632		}
633		}
634		}
635	+	return false;
636		}
637
638	+	// Support methods for ForkJoinTask
639	+
640		/**
641		* Returns an estimate of the number of tasks in the queue.
642		*/
643		final int getQueueSize() {
644		int n = sp - base;
645	<	return n <= 0? 0 : n; // suppress momentarily negative values
645	>	return n < 0? 0 : n; // suppress momentarily negative values
646		}
647
648		/**
#	Line 726 | Line 654 | public class ForkJoinWorkerThread extend
654		return (sp - base) - (pool.getIdleThreadCount() >>> 1);
655		}
656
729	–	// Per-worker exported random numbers
730	–
731	–	// Same constants as java.util.Random
732	–	final static long JURandomMultiplier = 0x5DEECE66DL;
733	–	final static long JURandomAddend = 0xBL;
734	–	final static long JURandomMask = (1L << 48) - 1;
735	–
736	–	private final int nextJURandom(int bits) {
737	–	long next = (juRandomSeed * JURandomMultiplier + JURandomAddend) &
738	–	JURandomMask;
739	–	juRandomSeed = next;
740	–	return (int)(next >>> (48 - bits));
741	–	}
742	–
743	–	private final int nextJURandomInt(int n) {
744	–	if (n <= 0)
745	–	throw new IllegalArgumentException("n must be positive");
746	–	int bits = nextJURandom(31);
747	–	if ((n & -n) == n)
748	–	return (int)((n * (long)bits) >> 31);
749	–
750	–	for (;;) {
751	–	int val = bits % n;
752	–	if (bits - val + (n-1) >= 0)
753	–	return val;
754	–	bits = nextJURandom(31);
755	–	}
756	–	}
757	–
758	–	private final long nextJURandomLong() {
759	–	return ((long)(nextJURandom(32)) << 32) + nextJURandom(32);
760	–	}
761	–
762	–	private final long nextJURandomLong(long n) {
763	–	if (n <= 0)
764	–	throw new IllegalArgumentException("n must be positive");
765	–	long offset = 0;
766	–	while (n >= Integer.MAX_VALUE) { // randomly pick half range
767	–	int bits = nextJURandom(2); // 2nd bit for odd vs even split
768	–	long half = n >>> 1;
769	–	long nextn = ((bits & 2) == 0)? half : n - half;
770	–	if ((bits & 1) == 0)
771	–	offset += n - nextn;
772	–	n = nextn;
773	–	}
774	–	return offset + nextJURandomInt((int)n);
775	–	}
776	–
777	–	private final double nextJURandomDouble() {
778	–	return (((long)(nextJURandom(26)) << 27) + nextJURandom(27))
779	–	/ (double)(1L << 53);
780	–	}
781	–
657		/**
658	<	* Returns a random integer using a per-worker random
784	<	* number generator with the same properties as
785	<	* {@link java.util.Random#nextInt}
786	<	* @return the next pseudorandom, uniformly distributed {@code int}
787	<	*         value from this worker's random number generator's sequence
788	<	*/
789	<	public static int nextRandomInt() {
790	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
791	<	nextJURandom(32);
792	<	}
793	<
794	<	/**
795	<	* Returns a random integer using a per-worker random
796	<	* number generator with the same properties as
797	<	* {@link java.util.Random#nextInt(int)}
798	<	* @param n the bound on the random number to be returned.  Must be
799	<	*        positive.
800	<	* @return the next pseudorandom, uniformly distributed {@code int}
801	<	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
802	<	*         from this worker's random number generator's sequence
803	<	* @throws IllegalArgumentException if n is not positive
804	<	*/
805	<	public static int nextRandomInt(int n) {
806	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
807	<	nextJURandomInt(n);
808	<	}
809	<
810	<	/**
811	<	* Returns a random long using a per-worker random
812	<	* number generator with the same properties as
813	<	* {@link java.util.Random#nextLong}
814	<	* @return the next pseudorandom, uniformly distributed {@code long}
815	<	*         value from this worker's random number generator's sequence
816	<	*/
817	<	public static long nextRandomLong() {
818	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
819	<	nextJURandomLong();
820	<	}
821	<
822	<	/**
823	<	* Returns a random integer using a per-worker random
824	<	* number generator with the same properties as
825	<	* {@link java.util.Random#nextInt(int)}
826	<	* @param n the bound on the random number to be returned.  Must be
827	<	*        positive.
828	<	* @return the next pseudorandom, uniformly distributed {@code int}
829	<	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
830	<	*         from this worker's random number generator's sequence
831	<	* @throws IllegalArgumentException if n is not positive
658	>	* Scan, returning early if joinMe done
659		*/
660	<	public static long nextRandomLong(long n) {
661	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
662	<	nextJURandomLong(n);
660	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
661	>	ForkJoinTask<?> t = pollTask();
662	>	if (t != null && joinMe.status < 0 && sp == base) {
663	>	pushTask(t); // unsteal if done and this task would be stealable
664	>	t = null;
665	>	}
666	>	return t;
667		}
668	<
668	>
669		/**
670	<	* Returns a random double using a per-worker random
840	<	* number generator with the same properties as
841	<	* {@link java.util.Random#nextDouble}
842	<	* @return the next pseudorandom, uniformly distributed {@code double}
843	<	*         value between {@code 0.0} and {@code 1.0} from this
844	<	*         worker's random number generator's sequence
670	>	* Runs tasks until pool isQuiescent
671		*/
672	<	public static double nextRandomDouble() {
673	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
674	<	nextJURandomDouble();
672	>	final void helpQuiescePool() {
673	>	for (;;) {
674	>	ForkJoinTask<?> t = pollTask();
675	>	if (t != null)
676	>	t.quietlyExec();
677	>	else if (tryInactivate() && pool.isQuiescent())
678	>	break;
679	>	}
680	>	do;while (!tryActivate()); // re-activate on exit
681		}
682
683		// Temporary Unsafe mechanics for preliminary release
#	Line 853 | Line 685 | public class ForkJoinWorkerThread extend
685		static final Unsafe _unsafe;
686		static final long baseOffset;
687		static final long spOffset;
688	+	static final long runStateOffset;
689		static final long qBase;
690		static final int qShift;
858	–	static final long runStateOffset;
691		static {
692		try {
693		if (ForkJoinWorkerThread.class.getClassLoader() != null) {

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