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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.1 by dl, Tue Jan 6 14:30:31 2009 UTC vs.
Revision 1.8 by jsr166, Mon Jul 20 21:45:06 2009 UTC

#	Line 13 | Line 13 | import sun.misc.Unsafe;
13		import java.lang.reflect.*;
14
15		/**
16	<	* A thread that is internally managed by a ForkJoinPool to execute
17	<	* ForkJoinTasks. This class additionally provides public
18	<	* <tt>static</tt> methods accessing some basic scheduling and
19	<	* execution mechanics for the <em>current</em>
20	<	* ForkJoinWorkerThread. These methods may be invoked only from within
21	<	* other ForkJoinTask computations. Attempts to invoke in other
22	<	* contexts result in exceptions or errors including
23	<	* ClassCastException.  These methods enable construction of
24	<	* special-purpose task classes, as well as specialized idioms
25	<	* occasionally useful in ForkJoinTask processing.
16	>	* A thread managed by a {@link ForkJoinPool}.  This class is
17	>	* subclassable solely for the sake of adding functionality -- there
18	>	* are no overridable methods dealing with scheduling or
19	>	* execution. However, you can override initialization and termination
20	>	* methods surrounding the main task processing loop.  If you do
21	>	* create such a subclass, you will also need to supply a custom
22	>	* ForkJoinWorkerThreadFactory to use it in a ForkJoinPool.
23		*
27	–	* <p>The form of supported static methods reflects the fact that
28	–	* worker threads may access and process tasks obtained in any of
29	–	* three ways. In preference order: <em>Local</em> tasks are processed
30	–	* in LIFO (newest first) order. <em>Stolen</em> tasks are obtained
31	–	* from other threads in FIFO (oldest first) order, only if there are
32	–	* no local tasks to run.  <em>Submissions</em> form a FIFO queue
33	–	* common to the entire pool, and are started only if no other
34	–	* work is available.
35	–	*
36	–	* <p> This class is subclassable solely for the sake of adding
37	–	* functionality -- there are no overridable methods dealing with
38	–	* scheduling or execution. However, you can override initialization
39	–	* and termination cleanup methods surrounding the main task
40	–	* processing loop.  If you do create such a subclass, you will also
41	–	* need to supply a custom ForkJoinWorkerThreadFactory to use it in a
42	–	* ForkJoinPool.
24		*/
25		public class ForkJoinWorkerThread extends Thread {
26		/*
#	Line 149 | 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 178 | 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	<
185	<	/**
186	<	* Index of this worker in pool array. Set once by pool before
187	<	* 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 194 | Line 175 | public class ForkJoinWorkerThread extend
175		*/
176		private volatile int runState;
177
197	–	// Runstate values. Order matters
198	–	private static final int RUNNING     = 0;
199	–	private static final int SHUTDOWN    = 1;
200	–	private static final int TERMINATING = 2;
201	–	private static final int TERMINATED  = 3;
202	–
178		/**
179	<	* Activity status. When true, this worker is considered active.
180	<	* Must be false upon construction. It must be true when executing
206	<	* tasks, and BEFORE stealing a task. It must be false before
207	<	* 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 214 | Line 187 | public class ForkJoinWorkerThread extend
187		private int stealCount;
188
189		/**
190	<	* Seed for random number generator for choosing steal victims
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 int randomVictimSeed;
193	>	int poolIndex;
194
195		/**
196	<	* Seed for embedded Jurandom
196	>	* The last barrier event waited for. Accessed in pool callback
197	>	* methods, but only by current thread.
198		*/
199	<	private long juRandomSeed;
199	>	long lastEventCount;
200
201		/**
202	<	* The last barrier event waited for
202	>	* True if use local fifo, not default lifo, for local polling
203		*/
204	<	private long eventCount;
204	>	private boolean locallyFifo;
205
206		/**
207		* Creates a ForkJoinWorkerThread operating in the given pool.
#	Line 236 | Line 211 | public class ForkJoinWorkerThread extend
211		protected ForkJoinWorkerThread(ForkJoinPool pool) {
212		if (pool == null) throw new NullPointerException();
213		this.pool = pool;
214	<	// remaining initialization deferred to onStart
214	>	// Note: poolIndex is set by pool during construction
215	>	// Remaining initialization is deferred to onStart
216		}
217
218	<	//  Access methods used by Pool
218	>	// Public access methods
219
220		/**
221	<	* Get and clear steal count for accumulation by pool.  Called
222	<	* only when known to be idle (in pool.sync and termination).
221	>	* Returns the pool hosting this thread
222	>	* @return the pool
223		*/
224	<	final int getAndClearStealCount() {
225	<	int sc = stealCount;
250	<	stealCount = 0;
251	<	return sc;
224	>	public ForkJoinPool getPool() {
225	>	return pool;
226		}
227
228		/**
229	<	* Returns estimate of the number of tasks in the queue, without
230	<	* correcting for transient negative values
229	>	* Returns the index number of this thread in its pool.  The
230	>	* returned value ranges from zero to the maximum number of
231	>	* threads (minus one) that have ever been created in the pool.
232	>	* This method may be useful for applications that track status or
233	>	* collect results per-worker rather than per-task.
234	>	* @return the index number.
235		*/
236	<	final int getRawQueueSize() {
237	<	return sp - base;
236	>	public int getPoolIndex() {
237	>	return poolIndex;
238		}
239
240	<	// Intrinsics-based support for queue operations.
241	<	// Currently these three (setSp, setSlot, casSlotNull) are
242	<	// usually manually inlined to improve performance
240	>	/**
241	>	* Establishes local first-in-first-out scheduling mode for forked
242	>	* tasks that are never joined.
243	>	* @param async if true, use locally FIFO scheduling
244	>	*/
245	>	void setAsyncMode(boolean async) {
246	>	locallyFifo = async;
247	>	}
248	>
249	>	// Runstate management
250	>
251	>	// Runstate values. Order matters
252	>	private static final int RUNNING     = 0;
253	>	private static final int SHUTDOWN    = 1;
254	>	private static final int TERMINATING = 2;
255	>	private static final int TERMINATED  = 3;
256	>
257	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
258	>	final boolean isTerminating() { return runState >= TERMINATING;  }
259	>	final boolean isTerminated()  { return runState == TERMINATED; }
260	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
261	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
262
263		/**
264	<	* Sets sp in store-order.
264	>	* Transition to at least the given state. Return true if not
265	>	* already at least given state.
266		*/
267	<	private void setSp(int s) {
268	<	_unsafe.putOrderedInt(this, spOffset, s);
267	>	private boolean transitionRunStateTo(int state) {
268	>	for (;;) {
269	>	int s = runState;
270	>	if (s >= state)
271	>	return false;
272	>	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
273	>	return true;
274	>	}
275	>	}
276	>
277	>	/**
278	>	* Try to set status to active; fail on contention
279	>	*/
280	>	private boolean tryActivate() {
281	>	if (!active) {
282	>	if (!pool.tryIncrementActiveCount())
283	>	return false;
284	>	active = true;
285	>	}
286	>	return true;
287	>	}
288	>
289	>	/**
290	>	* Try to set status to active; fail on contention
291	>	*/
292	>	private boolean tryInactivate() {
293	>	if (active) {
294	>	if (!pool.tryDecrementActiveCount())
295	>	return false;
296	>	active = false;
297	>	}
298	>	return true;
299	>	}
300	>
301	>	/**
302	>	* Computes next value for random victim probe. Scans don't
303	>	* require a very high quality generator, but also not a crummy
304	>	* one. Marsaglia xor-shift is cheap and works well.
305	>	*/
306	>	private static int xorShift(int r) {
307	>	r ^= r << 1;
308	>	r ^= r >>> 3;
309	>	r ^= r << 10;
310	>	return r;
311	>	}
312	>
313	>	// Lifecycle methods
314	>
315	>	/**
316	>	* This method is required to be public, but should never be
317	>	* called explicitly. It performs the main run loop to execute
318	>	* ForkJoinTasks.
319	>	*/
320	>	public void run() {
321	>	Throwable exception = null;
322	>	try {
323	>	onStart();
324	>	pool.sync(this); // await first pool event
325	>	mainLoop();
326	>	} catch (Throwable ex) {
327	>	exception = ex;
328	>	} finally {
329	>	onTermination(exception);
330	>	}
331	>	}
332	>
333	>	/**
334	>	* Execute tasks until shut down.
335	>	*/
336	>	private void mainLoop() {
337	>	while (!isShutdown()) {
338	>	ForkJoinTask<?> t = pollTask();
339	>	if (t != null || (t = pollSubmission()) != null)
340	>	t.quietlyExec();
341	>	else if (tryInactivate())
342	>	pool.sync(this);
343	>	}
344	>	}
345	>
346	>	/**
347	>	* Initializes internal state after construction but before
348	>	* processing any tasks. If you override this method, you must
349	>	* invoke super.onStart() at the beginning of the method.
350	>	* Initialization requires care: Most fields must have legal
351	>	* default values, to ensure that attempted accesses from other
352	>	* threads work correctly even before this thread starts
353	>	* processing tasks.
354	>	*/
355	>	protected void onStart() {
356	>	// Allocate while starting to improve chances of thread-local
357	>	// isolation
358	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
359	>	// Initial value of seed need not be especially random but
360	>	// should differ across workers and must be nonzero
361	>	int p = poolIndex + 1;
362	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
363	>	}
364	>
365	>	/**
366	>	* Perform cleanup associated with termination of this worker
367	>	* thread.  If you override this method, you must invoke
368	>	* super.onTermination at the end of the overridden method.
369	>	*
370	>	* @param exception the exception causing this thread to abort due
371	>	* to an unrecoverable error, or null if completed normally.
372	>	*/
373	>	protected void onTermination(Throwable exception) {
374	>	// Execute remaining local tasks unless aborting or terminating
375	>	while (exception == null &&  !pool.isTerminating() && base != sp) {
376	>	try {
377	>	ForkJoinTask<?> t = popTask();
378	>	if (t != null)
379	>	t.quietlyExec();
380	>	} catch(Throwable ex) {
381	>	exception = ex;
382	>	}
383	>	}
384	>	// Cancel other tasks, transition status, notify pool, and
385	>	// propagate exception to uncaught exception handler
386	>	try {
387	>	do;while (!tryInactivate()); // ensure inactive
388	>	cancelTasks();
389	>	runState = TERMINATED;
390	>	pool.workerTerminated(this);
391	>	} catch (Throwable ex) {        // Shouldn't ever happen
392	>	if (exception == null)      // but if so, at least rethrown
393	>	exception = ex;
394	>	} finally {
395	>	if (exception != null)
396	>	ForkJoinTask.rethrowException(exception);
397	>	}
398		}
399
400	+	// Intrinsics-based support for queue operations.
401	+
402		/**
403		* Add in store-order the given task at given slot of q to
404		* null. Caller must ensure q is nonnull and index is in range.
#	Line 288 | Line 417 | public class ForkJoinWorkerThread extend
417		return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
418		}
419
420	+	/**
421	+	* Sets sp in store-order.
422	+	*/
423	+	private void storeSp(int s) {
424	+	_unsafe.putOrderedInt(this, spOffset, s);
425	+	}
426	+
427		// Main queue methods
428
429		/**
#	Line 298 | Line 434 | public class ForkJoinWorkerThread extend
434		ForkJoinTask<?>[] q = queue;
435		int mask = q.length - 1;
436		int s = sp;
437	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
438	<	_unsafe.putOrderedInt(this, spOffset, ++s);
437	>	setSlot(q, s & mask, t);
438	>	storeSp(++s);
439		if ((s -= base) == 1)
440	<	pool.signalNonEmptyWorkerQueue();
440	>	pool.signalWork();
441		else if (s >= mask)
442		growQueue();
443		}
#	Line 311 | Line 447 | public class ForkJoinWorkerThread extend
447		* either empty or contended.
448		* @return a task, or null if none or contended.
449		*/
450	<	private ForkJoinTask<?> deqTask() {
315	<	ForkJoinTask<?>[] q;
450	>	final ForkJoinTask<?> deqTask() {
451		ForkJoinTask<?> t;
452	+	ForkJoinTask<?>[] q;
453		int i;
454		int b;
455		if (sp != (b = base) &&
456		(q = queue) != null && // must read q after b
457		(t = q[i = (q.length - 1) & b]) != null &&
458	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
458	>	casSlotNull(q, i, t)) {
459		base = b + 1;
460		return t;
461		}
#	Line 327 | Line 463 | public class ForkJoinWorkerThread extend
463		}
464
465		/**
466	<	* Returns a popped task, or null if empty.  Called only by
467	<	* current thread.
466	>	* Returns a popped task, or null if empty. Ensures active status
467	>	* if nonnull. Called only by current thread.
468		*/
469		final ForkJoinTask<?> popTask() {
334	–	ForkJoinTask<?> t;
335	–	int i;
336	–	ForkJoinTask<?>[] q = queue;
337	–	int mask = q.length - 1;
470		int s = sp;
471	<	if (s != base &&
472	<	(t = q[i = (s - 1) & mask]) != null &&
473	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
474	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
475	<	return t;
471	>	while (s != base) {
472	>	if (tryActivate()) {
473	>	ForkJoinTask<?>[] q = queue;
474	>	int mask = q.length - 1;
475	>	int i = (s - 1) & mask;
476	>	ForkJoinTask<?> t = q[i];
477	>	if (t == null || !casSlotNull(q, i, t))
478	>	break;
479	>	storeSp(s - 1);
480	>	return t;
481	>	}
482		}
483		return null;
484		}
#	Line 348 | Line 486 | public class ForkJoinWorkerThread extend
486		/**
487		* Specialized version of popTask to pop only if
488		* topmost element is the given task. Called only
489	<	* by current thread.
489	>	* by current thread while active.
490		* @param t the task. Caller must ensure nonnull
491		*/
492		final boolean unpushTask(ForkJoinTask<?> t) {
493		ForkJoinTask<?>[] q = queue;
494		int mask = q.length - 1;
495		int s = sp - 1;
496	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
497	<	t, null)) {
360	<	_unsafe.putOrderedInt(this, spOffset, s);
496	>	if (casSlotNull(q, s & mask, t)) {
497	>	storeSp(s);
498		return true;
499		}
500		return false;
501		}
502
503		/**
504	<	* Returns next task to pop.
504	>	* Returns next task.
505		*/
506	<	private ForkJoinTask<?> peekTask() {
506	>	final ForkJoinTask<?> peekTask() {
507		ForkJoinTask<?>[] q = queue;
508	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
508	>	if (q == null)
509	>	return null;
510	>	int mask = q.length - 1;
511	>	int i = locallyFifo? base : (sp - 1);
512	>	return q[i & mask];
513		}
514
515		/**
#	Line 395 | Line 536 | public class ForkJoinWorkerThread extend
536		t = null;
537		setSlot(newQ, b & newMask, t);
538		} while (++b != bf);
539	<	pool.signalIdleWorkers(false);
539	>	pool.signalWork();
540		}
541
401	–	// Runstate management
402	–
403	–	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
404	–	final boolean isTerminating() { return runState >= TERMINATING;  }
405	–	final boolean isTerminated()  { return runState == TERMINATED; }
406	–	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
407	–	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
408	–
542		/**
543	<	* Transition to at least the given state. Return true if not
544	<	* already at least given state.
545	<	*/
546	<	private boolean transitionRunStateTo(int state) {
547	<	for (;;) {
548	<	int s = runState;
549	<	if (s >= state)
550	<	return false;
418	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
419	<	return true;
420	<	}
421	<	}
422	<
423	<	/**
424	<	* Ensure status is active and if necessary adjust pool active count
425	<	*/
426	<	final void activate() {
427	<	if (!active) {
428	<	active = true;
429	<	pool.incrementActiveCount();
430	<	}
431	<	}
432	<
433	<	/**
434	<	* Ensure status is inactive and if necessary adjust pool active count
435	<	*/
436	<	final void inactivate() {
437	<	if (active) {
438	<	active = false;
439	<	pool.decrementActiveCount();
440	<	}
441	<	}
442	<
443	<	// Lifecycle methods
444	<
445	<	/**
446	<	* Initializes internal state after construction but before
447	<	* processing any tasks. If you override this method, you must
448	<	* invoke super.onStart() at the beginning of the method.
449	<	* Initialization requires care: Most fields must have legal
450	<	* default values, to ensure that attempted accesses from other
451	<	* threads work correctly even before this thread starts
452	<	* processing tasks.
453	<	*/
454	<	protected void onStart() {
455	<	juRandomSeed = randomSeedGenerator.nextLong();
456	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
457	<	if (queue == null)
458	<	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
459	<
460	<	// Heuristically allow one initial thread to warm up; others wait
461	<	if (poolIndex < pool.getParallelism() - 1) {
462	<	eventCount = pool.sync(this, 0);
463	<	activate();
464	<	}
465	<	}
466	<
467	<	/**
468	<	* Perform cleanup associated with termination of this worker
469	<	* thread.  If you override this method, you must invoke
470	<	* super.onTermination at the end of the overridden method.
471	<	*
472	<	* @param exception the exception causing this thread to abort due
473	<	* to an unrecoverable error, or null if completed normally.
474	<	*/
475	<	protected void onTermination(Throwable exception) {
476	<	try {
477	<	clearLocalTasks();
478	<	inactivate();
479	<	cancelTasks();
480	<	} finally {
481	<	terminate(exception);
482	<	}
483	<	}
484	<
485	<	/**
486	<	* Notify pool of termination and, if exception is nonnull,
487	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
488	<	*/
489	<	private void terminate(Throwable exception) {
490	<	transitionRunStateTo(TERMINATED);
491	<	try {
492	<	pool.workerTerminated(this);
493	<	} finally {
494	<	if (exception != null)
495	<	ForkJoinTask.rethrowException(exception);
496	<	}
497	<	}
498	<
499	<	/**
500	<	* Run local tasks on exit from main.
501	<	*/
502	<	private void clearLocalTasks() {
503	<	while (base != sp && !pool.isTerminating()) {
504	<	ForkJoinTask<?> t = popTask();
505	<	if (t != null) {
506	<	activate(); // ensure active status
507	<	t.quietlyExec();
508	<	}
509	<	}
510	<	}
511	<
512	<	/**
513	<	* Removes and cancels all tasks in queue.  Can be called from any
514	<	* thread.
515	<	*/
516	<	final void cancelTasks() {
517	<	while (base != sp) {
518	<	ForkJoinTask<?> t = deqTask();
519	<	if (t != null)
520	<	t.cancelIgnoreExceptions();
521	<	}
522	<	}
523	<
524	<	/**
525	<	* This method is required to be public, but should never be
526	<	* called explicitly. It performs the main run loop to execute
527	<	* ForkJoinTasks.
528	<	*/
529	<	public void run() {
530	<	Throwable exception = null;
531	<	try {
532	<	onStart();
533	<	while (!isShutdown())
534	<	step();
535	<	} catch (Throwable ex) {
536	<	exception = ex;
537	<	} finally {
538	<	onTermination(exception);
539	<	}
540	<	}
541	<
542	<	/**
543	<	* Main top-level action.
544	<	*/
545	<	private void step() {
546	<	ForkJoinTask<?> t = sp != base? popTask() : null;
547	<	if (t != null || (t = scan(null, true)) != null) {
548	<	activate();
549	<	t.quietlyExec();
550	<	}
551	<	else {
552	<	inactivate();
553	<	eventCount = pool.sync(this, eventCount);
554	<	}
555	<	}
556	<
557	<	// scanning for and stealing tasks
558	<
559	<	/**
560	<	* Computes next value for random victim probe. Scans don't
561	<	* require a very high quality generator, but also not a crummy
562	<	* one. Marsaglia xor-shift is cheap and works well.
563	<	*
564	<	* This is currently unused, and manually inlined
565	<	*/
566	<	private static int xorShift(int r) {
567	<	r ^= r << 1;
568	<	r ^= r >>> 3;
569	<	r ^= r << 10;
570	<	return r;
571	<	}
572	<
573	<	/**
574	<	* Tries to steal a task from another worker and/or, if enabled,
575	<	* submission queue. Starts at a random index of workers array,
576	<	* and probes workers until finding one with non-empty queue or
577	<	* finding that all are empty.  It randomly selects the first n-1
578	<	* probes. If these are empty, it resorts to full circular
579	<	* traversal, which is necessary to accurately set active status
580	<	* by caller. Also restarts if pool barrier has tripped since last
581	<	* scan, which forces refresh of workers array, in case barrier
582	<	* was associated with resize.
543	>	* Tries to steal a task from another worker. Starts at a random
544	>	* index of workers array, and probes workers until finding one
545	>	* with non-empty queue or finding that all are empty.  It
546	>	* randomly selects the first n probes. If these are empty, it
547	>	* resorts to a full circular traversal, which is necessary to
548	>	* accurately set active status by caller. Also restarts if pool
549	>	* events occurred since last scan, which forces refresh of
550	>	* workers array, in case barrier was associated with resize.
551		*
552		* This method must be both fast and quiet -- usually avoiding
553		* memory accesses that could disrupt cache sharing etc other than
554		* those needed to check for and take tasks. This accounts for,
555		* among other things, updating random seed in place without
556	<	* storing it until exit. (Note that we only need to store it if
589	<	* we found a task; otherwise it doesn't matter if we start at the
590	<	* same place next time.)
556	>	* storing it until exit.
557		*
592	–	* @param joinMe if non null; exit early if done
593	–	* @param checkSubmissions true if OK to take submissions
558		* @return a task, or null if none found
559		*/
560	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
561	<	boolean checkSubmissions) {
562	<	ForkJoinPool p = pool;
563	<	if (p == null)                    // Never null, but avoids
564	<	return null;                  //   implicit nullchecks below
565	<	int r = randomVictimSeed;         // extract once to keep scan quiet
566	<	restart:                          // outer loop refreshes ws array
603	<	while (joinMe == null || joinMe.status >= 0) {
604	<	int mask;
605	<	ForkJoinWorkerThread[] ws = p.workers;
606	<	if (ws != null && (mask = ws.length - 1) > 0) {
607	<	int probes = -mask;       // use random index while negative
560	>	private ForkJoinTask<?> scan() {
561	>	ForkJoinTask<?> t = null;
562	>	int r = seed;                    // extract once to keep scan quiet
563	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
564	>	int mask;                        // must be power 2 minus 1 and > 0
565	>	outer:do {
566	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
567		int idx = r;
568	+	int probes = ~mask;      // use random index while negative
569		for (;;) {
570	<	ForkJoinWorkerThread v;
571	<	// inlined xorshift to update seed
572	<	r ^= r << 1;  r ^= r >>> 3; r ^= r << 10;
573	<	if ((v = ws[mask & idx]) != null && v.sp != v.base) {
574	<	ForkJoinTask<?> t;
575	<	activate();
576	<	if ((joinMe == null || joinMe.status >= 0) &&
617	<	(t = v.deqTask()) != null) {
618	<	randomVictimSeed = r;
619	<	++stealCount;
620	<	return t;
621	<	}
622	<	continue restart; // restart on contention
570	>	r = xorShift(r);     // update random seed
571	>	ForkJoinWorkerThread v = ws[mask & idx];
572	>	if (v == null || v.sp == v.base) {
573	>	if (probes <= mask)
574	>	idx = (probes++ < 0)? r : (idx + 1);
575	>	else
576	>	break;
577		}
578	<	if ((probes >> 1) <= mask) // n-1 random then circular
579	<	idx = (probes++ < 0)? r : (idx + 1);
578	>	else if (!tryActivate() || (t = v.deqTask()) == null)
579	>	continue outer;  // restart on contention
580		else
581	<	break;
581	>	break outer;
582		}
583		}
584	<	if (checkSubmissions && p.hasQueuedSubmissions()) {
585	<	activate();
586	<	ForkJoinTask<?> t = p.pollSubmission();
633	<	if (t != null)
634	<	return t;
635	<	}
636	<	else {
637	<	long ec = eventCount;     // restart on pool event
638	<	if ((eventCount = p.getEventCount()) == ec)
639	<	break;
640	<	}
641	<	}
642	<	return null;
584	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
585	>	seed = r;
586	>	return t;
587		}
588
589		/**
590	<	* Callback from pool.sync to rescan before blocking.  If a
591	<	* task is found, it is pushed so it can be executed upon return.
648	<	* @return true if found and pushed a task
649	<	*/
650	<	final boolean prescan() {
651	<	ForkJoinTask<?> t = scan(null, true);
652	<	if (t != null) {
653	<	pushTask(t);
654	<	return true;
655	<	}
656	<	else {
657	<	inactivate();
658	<	return false;
659	<	}
660	<	}
661	<
662	<	/**
663	<	* Implements ForkJoinTask.helpJoin
590	>	* gets and removes a local or stolen a task
591	>	* @return a task, if available
592		*/
593	<	final int helpJoinTask(ForkJoinTask<?> joinMe) {
594	<	ForkJoinTask<?> t = null;
595	<	int s;
596	<	while ((s = joinMe.status) >= 0) {
597	<	if (t == null) {
670	<	if ((t = scan(joinMe, false)) == null)  // block if no work
671	<	return joinMe.awaitDone(this, false);
672	<	// else recheck status before exec
673	<	}
674	<	else {
675	<	t.quietlyExec();
676	<	t = null;
677	<	}
678	<	}
679	<	if (t != null) // unsteal
680	<	pushTask(t);
681	<	return s;
593	>	final ForkJoinTask<?> pollTask() {
594	>	ForkJoinTask<?> t = locallyFifo? deqTask() : popTask();
595	>	if (t == null && (t = scan()) != null)
596	>	++stealCount;
597	>	return t;
598		}
599
684	–	// Support for public static and/or ForkJoinTask methods
685	–
600		/**
601	<	* Returns an estimate of the number of tasks in the queue.
601	>	* gets a local task
602	>	* @return a task, if available
603		*/
604	<	final int getQueueSize() {
605	<	int b = base;
691	<	int n = sp - b;
692	<	return n <= 0? 0 : n; // suppress momentarily negative values
604	>	final ForkJoinTask<?> pollLocalTask() {
605	>	return locallyFifo? deqTask() : popTask();
606		}
607
608		/**
609	<	* Runs one popped task, if available
610	<	* @return true if ran a task
609	>	* Returns a pool submission, if one exists, activating first.
610	>	* @return a submission, if available
611		*/
612	<	private boolean runLocalTask() {
613	<	ForkJoinTask<?> t = popTask();
614	<	if (t == null)
615	<	return false;
616	<	t.quietlyExec();
617	<	return true;
612	>	private ForkJoinTask<?> pollSubmission() {
613	>	ForkJoinPool p = pool;
614	>	while (p.hasQueuedSubmissions()) {
615	>	ForkJoinTask<?> t;
616	>	if (tryActivate() && (t = p.pollSubmission()) != null)
617	>	return t;
618	>	}
619	>	return null;
620		}
621
622	<	/**
708	<	* Pops or steals a task
709	<	* @return task, or null if none available
710	<	*/
711	<	private ForkJoinTask<?> getLocalOrStolenTask() {
712	<	ForkJoinTask<?> t = popTask();
713	<	return t != null? t : scan(null, false);
714	<	}
622	>	// Methods accessed only by Pool
623
624		/**
625	<	* Runs a popped or stolen task, if available
626	<	* @return true if ran a task
625	>	* Removes and cancels all tasks in queue.  Can be called from any
626	>	* thread.
627		*/
628	<	private boolean runLocalOrStolenTask() {
629	<	ForkJoinTask<?> t = getLocalOrStolenTask();
630	<	if (t == null)
631	<	return false;
724	<	t.quietlyExec();
725	<	return true;
628	>	final void cancelTasks() {
629	>	ForkJoinTask<?> t;
630	>	while (base != sp && (t = deqTask()) != null)
631	>	t.cancelIgnoringExceptions();
632		}
633
634		/**
635	<	* Runs tasks until pool isQuiescent
635	>	* Drains tasks to given collection c
636	>	* @return the number of tasks drained
637		*/
638	<	final void helpQuiescePool() {
639	<	activate();
640	<	for (;;) {
641	<	if (!runLocalOrStolenTask()) {
642	<	inactivate();
643	<	if (pool.isQuiescent()) {
737	<	activate(); // re-activate on exit
738	<	break;
739	<	}
740	<	}
638	>	final int drainTasksTo(Collection<ForkJoinTask<?>> c) {
639	>	int n = 0;
640	>	ForkJoinTask<?> t;
641	>	while (base != sp && (t = deqTask()) != null) {
642	>	c.add(t);
643	>	++n;
644		}
645	+	return n;
646		}
647
648		/**
649	<	* Returns an estimate of the number of tasks, offset by a
650	<	* function of number of idle workers.
747	<	*/
748	<	final int getEstimatedSurplusTaskCount() {
749	<	return (sp - base) - (pool.getIdleThreadCount() >>> 1);
750	<	}
751	<
752	<	// Public methods on current thread
753	<
754	<	/**
755	<	* Returns the pool hosting the current task execution.
756	<	* @return the pool
757	<	*/
758	<	public static ForkJoinPool getPool() {
759	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pool;
760	<	}
761	<
762	<	/**
763	<	* Returns the index number of the current worker thread in its
764	<	* pool.  The returned value ranges from zero to the maximum
765	<	* number of threads (minus one) that have ever been created in
766	<	* the pool.  This method may be useful for applications that
767	<	* track status or collect results per-worker rather than
768	<	* per-task.
769	<	* @return the index number.
649	>	* Get and clear steal count for accumulation by pool.  Called
650	>	* only when known to be idle (in pool.sync and termination).
651		*/
652	<	public static int getPoolIndex() {
653	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex;
652	>	final int getAndClearStealCount() {
653	>	int sc = stealCount;
654	>	stealCount = 0;
655	>	return sc;
656		}
657
658		/**
659	<	* Returns an estimate of the number of tasks waiting to be run by
660	<	* the current worker thread. This value may be useful for
661	<	* heuristic decisions about whether to fork other tasks.
662	<	* @return the number of tasks
663	<	*/
664	<	public static int getLocalQueueSize() {
665	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
666	<	getQueueSize();
659	>	* Returns true if at least one worker in the given array appears
660	>	* to have at least one queued task.
661	>	* @param ws array of workers
662	>	*/
663	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
664	>	if (ws != null) {
665	>	int len = ws.length;
666	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
667	>	for (int i = 0; i < len; ++i) {
668	>	ForkJoinWorkerThread w = ws[i];
669	>	if (w != null && w.sp != w.base)
670	>	return true;
671	>	}
672	>	}
673	>	}
674	>	return false;
675		}
676
677	<	/**
787	<	* Returns, but does not remove or execute, the next task locally
788	<	* queued for execution by the current worker thread. There is no
789	<	* guarantee that this task will be the next one actually returned
790	<	* or executed from other polling or execution methods.
791	<	* @return the next task or null if none
792	<	*/
793	<	public static ForkJoinTask<?> peekLocalTask() {
794	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).peekTask();
795	<	}
677	>	// Support methods for ForkJoinTask
678
679		/**
680	<	* Removes and returns, without executing, the next task queued
799	<	* for execution in the current worker thread's local queue.
800	<	* @return the next task to execute, or null if none
680	>	* Returns an estimate of the number of tasks in the queue.
681		*/
682	<	public static ForkJoinTask<?> pollLocalTask() {
683	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask();
682	>	final int getQueueSize() {
683	>	int n = sp - base;
684	>	return n < 0? 0 : n; // suppress momentarily negative values
685		}
686
687		/**
688	<	* Execute the next task locally queued by the current worker, if
689	<	* one is available.
809	<	* @return true if a task was run; a false return indicates
810	<	* that no task was available.
688	>	* Returns an estimate of the number of tasks, offset by a
689	>	* function of number of idle workers.
690		*/
691	<	public static boolean executeLocalTask() {
692	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
693	<	runLocalTask();
691	>	final int getEstimatedSurplusTaskCount() {
692	>	// The halving approximates weighting idle vs non-idle workers
693	>	return (sp - base) - (pool.getIdleThreadCount() >>> 1);
694		}
695
696		/**
697	<	* Removes and returns, without executing, the next task queued
819	<	* for execution in the current worker thread's local queue or if
820	<	* none, a task stolen from another worker, if one is available.
821	<	* A null return does not necessarily imply that all tasks are
822	<	* completed, only that there are currently none available.
823	<	* @return the next task to execute, or null if none
697	>	* Scan, returning early if joinMe done
698		*/
699	<	public static ForkJoinTask<?> pollTask() {
700	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
701	<	getLocalOrStolenTask();
699	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
700	>	ForkJoinTask<?> t = pollTask();
701	>	if (t != null && joinMe.status < 0 && sp == base) {
702	>	pushTask(t); // unsteal if done and this task would be stealable
703	>	t = null;
704	>	}
705	>	return t;
706		}
707
708		/**
709	<	* Helps this program complete by processing a local or stolen
832	<	* task, if one is available.  This method may be useful when
833	<	* several tasks are forked, and only one of them must be joined,
834	<	* as in:
835	<	*
836	<	* <pre>
837	<	*   while (!t1.isDone() &amp;&amp; !t2.isDone())
838	<	*     ForkJoinWorkerThread.executeTask();
839	<	* </pre>
840	<	*
841	<	* @return true if a task was run; a false return indicates
842	<	* that no task was available.
709	>	* Runs tasks until pool isQuiescent
710		*/
711	<	public static boolean executeTask() {
845	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
846	<	runLocalOrStolenTask();
847	<	}
848	<
849	<	// Per-worker exported random numbers
850	<
851	<	// Same constants as java.util.Random
852	<	final static long JURandomMultiplier = 0x5DEECE66DL;
853	<	final static long JURandomAddend = 0xBL;
854	<	final static long JURandomMask = (1L << 48) - 1;
855	<
856	<	private final int nextJURandom(int bits) {
857	<	long next = (juRandomSeed * JURandomMultiplier + JURandomAddend) &
858	<	JURandomMask;
859	<	juRandomSeed = next;
860	<	return (int)(next >>> (48 - bits));
861	<	}
862	<
863	<	private final int nextJURandomInt(int n) {
864	<	if (n <= 0)
865	<	throw new IllegalArgumentException("n must be positive");
866	<	int bits = nextJURandom(31);
867	<	if ((n & -n) == n)
868	<	return (int)((n * (long)bits) >> 31);
869	<
711	>	final void helpQuiescePool() {
712		for (;;) {
713	<	int val = bits % n;
714	<	if (bits - val + (n-1) >= 0)
715	<	return val;
716	<	bits = nextJURandom(31);
713	>	ForkJoinTask<?> t = pollTask();
714	>	if (t != null)
715	>	t.quietlyExec();
716	>	else if (tryInactivate() && pool.isQuiescent())
717	>	break;
718		}
719	+	do;while (!tryActivate()); // re-activate on exit
720		}
721
722	<	private final long nextJURandomLong() {
723	<	return ((long)(nextJURandom(32)) << 32) + nextJURandom(32);
724	<	}
725	<
726	<	private final long nextJURandomLong(long n) {
727	<	if (n <= 0)
728	<	throw new IllegalArgumentException("n must be positive");
729	<	long offset = 0;
730	<	while (n >= Integer.MAX_VALUE) { // randomly pick half range
731	<	int bits = nextJURandom(2); // 2nd bit for odd vs even split
732	<	long half = n >>> 1;
733	<	long nextn = ((bits & 2) == 0)? half : n - half;
734	<	if ((bits & 1) == 0)
735	<	offset += n - nextn;
892	<	n = nextn;
722	>	// Temporary Unsafe mechanics for preliminary release
723	>	private static Unsafe getUnsafe() throws Throwable {
724	>	try {
725	>	return Unsafe.getUnsafe();
726	>	} catch (SecurityException se) {
727	>	try {
728	>	return java.security.AccessController.doPrivileged
729	>	(new java.security.PrivilegedExceptionAction<Unsafe>() {
730	>	public Unsafe run() throws Exception {
731	>	return getUnsafePrivileged();
732	>	}});
733	>	} catch (java.security.PrivilegedActionException e) {
734	>	throw e.getCause();
735	>	}
736		}
894	–	return offset + nextJURandomInt((int)n);
737		}
738
739	<	private final double nextJURandomDouble() {
740	<	return (((long)(nextJURandom(26)) << 27) + nextJURandom(27))
741	<	/ (double)(1L << 53);
739	>	private static Unsafe getUnsafePrivileged()
740	>	throws NoSuchFieldException, IllegalAccessException {
741	>	Field f = Unsafe.class.getDeclaredField("theUnsafe");
742	>	f.setAccessible(true);
743	>	return (Unsafe) f.get(null);
744		}
745
746	<	/**
747	<	* Returns a random integer using a per-worker random
748	<	* number generator with the same properties as
749	<	* {@link java.util.Random#nextInt}
906	<	* @return the next pseudorandom, uniformly distributed {@code int}
907	<	*         value from this worker's random number generator's sequence
908	<	*/
909	<	public static int nextRandomInt() {
910	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
911	<	nextJURandom(32);
746	>	private static long fieldOffset(String fieldName)
747	>	throws NoSuchFieldException {
748	>	return _unsafe.objectFieldOffset
749	>	(ForkJoinWorkerThread.class.getDeclaredField(fieldName));
750		}
751
914	–	/**
915	–	* Returns a random integer using a per-worker random
916	–	* number generator with the same properties as
917	–	* {@link java.util.Random#nextInt(int)}
918	–	* @param n the bound on the random number to be returned.  Must be
919	–	*        positive.
920	–	* @return the next pseudorandom, uniformly distributed {@code int}
921	–	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
922	–	*         from this worker's random number generator's sequence
923	–	* @throws IllegalArgumentException if n is not positive
924	–	*/
925	–	public static int nextRandomInt(int n) {
926	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
927	–	nextJURandomInt(n);
928	–	}
929	–
930	–	/**
931	–	* Returns a random long using a per-worker random
932	–	* number generator with the same properties as
933	–	* {@link java.util.Random#nextLong}
934	–	* @return the next pseudorandom, uniformly distributed {@code long}
935	–	*         value from this worker's random number generator's sequence
936	–	*/
937	–	public static long nextRandomLong() {
938	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
939	–	nextJURandomLong();
940	–	}
941	–
942	–	/**
943	–	* Returns a random integer using a per-worker random
944	–	* number generator with the same properties as
945	–	* {@link java.util.Random#nextInt(int)}
946	–	* @param n the bound on the random number to be returned.  Must be
947	–	*        positive.
948	–	* @return the next pseudorandom, uniformly distributed {@code int}
949	–	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
950	–	*         from this worker's random number generator's sequence
951	–	* @throws IllegalArgumentException if n is not positive
952	–	*/
953	–	public static long nextRandomLong(long n) {
954	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
955	–	nextJURandomLong(n);
956	–	}
957	–
958	–	/**
959	–	* Returns a random double using a per-worker random
960	–	* number generator with the same properties as
961	–	* {@link java.util.Random#nextDouble}
962	–	* @return the next pseudorandom, uniformly distributed {@code double}
963	–	*         value between {@code 0.0} and {@code 1.0} from this
964	–	*         worker's random number generator's sequence
965	–	*/
966	–	public static double nextRandomDouble() {
967	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
968	–	nextJURandomDouble();
969	–	}
970	–
971	–	// Temporary Unsafe mechanics for preliminary release
972	–
752		static final Unsafe _unsafe;
753		static final long baseOffset;
754		static final long spOffset;
755	+	static final long runStateOffset;
756		static final long qBase;
757		static final int qShift;
978	–	static final long runStateOffset;
758		static {
759		try {
760	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
761	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
762	<	f.setAccessible(true);
763	<	_unsafe = (Unsafe)f.get(null);
985	<	}
986	<	else
987	<	_unsafe = Unsafe.getUnsafe();
988	<	baseOffset = _unsafe.objectFieldOffset
989	<	(ForkJoinWorkerThread.class.getDeclaredField("base"));
990	<	spOffset = _unsafe.objectFieldOffset
991	<	(ForkJoinWorkerThread.class.getDeclaredField("sp"));
992	<	runStateOffset = _unsafe.objectFieldOffset
993	<	(ForkJoinWorkerThread.class.getDeclaredField("runState"));
760	>	_unsafe = getUnsafe();
761	>	baseOffset = fieldOffset("base");
762	>	spOffset = fieldOffset("sp");
763	>	runStateOffset = fieldOffset("runState");
764		qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class);
765		int s = _unsafe.arrayIndexScale(ForkJoinTask[].class);
766		if ((s & (s-1)) != 0)
767		throw new Error("data type scale not a power of two");
768		qShift = 31 - Integer.numberOfLeadingZeros(s);
769	<	} catch (Exception e) {
769	>	} catch (Throwable e) {
770		throw new RuntimeException("Could not initialize intrinsics", e);
771		}
772		}

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