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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.3 by dl, Wed Jan 7 19:12:36 2009 UTC vs.
Revision 1.16 by jsr166, Thu Jul 23 23:07:57 2009 UTC

#	Line 17 | Line 17 | import java.lang.reflect.*;
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	<	* cleanup methods surrounding the main task processing loop.  If you
21	<	* do create such a subclass, you will also need to supply a custom
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	<	*
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.
23	>	*
24	>	* @since 1.7
25	>	* @author Doug Lea
26		*/
27		public class ForkJoinWorkerThread extends Thread {
28		/*
#	Line 48 | Line 46 | public class ForkJoinWorkerThread extend
46		* of tasks. To accomplish this, we shift the CAS arbitrating pop
47		* vs deq (steal) from being on the indices ("base" and "sp") to
48		* the slots themselves (mainly via method "casSlotNull()"). So,
49	<	* both a successful pop and deq mainly entail CAS'ing a nonnull
49	>	* both a successful pop and deq mainly entail CAS'ing a non-null
50		* slot to null.  Because we rely on CASes of references, we do
51		* not need tag bits on base or sp.  They are simple ints as used
52		* in any circular array-based queue (see for example ArrayDeque).
#	Line 60 | Line 58 | public class ForkJoinWorkerThread extend
58		* considered individually, is not wait-free. One thief cannot
59		* successfully continue until another in-progress one (or, if
60		* previously empty, a push) completes.  However, in the
61	<	* aggregate, we ensure at least probablistic non-blockingness. If
61	>	* aggregate, we ensure at least probabilistic non-blockingness. If
62		* an attempted steal fails, a thief always chooses a different
63		* random victim target to try next. So, in order for one thief to
64		* progress, it suffices for any in-progress deq or new push on
#	Line 79 | Line 77 | public class ForkJoinWorkerThread extend
77		* push) require store order and CASes (in pop and deq) require
78		* (volatile) CAS semantics. Since these combinations aren't
79		* supported using ordinary volatiles, the only way to accomplish
80	<	* these effciently is to use direct Unsafe calls. (Using external
80	>	* these efficiently is to use direct Unsafe calls. (Using external
81		* AtomicIntegers and AtomicReferenceArrays for the indices and
82		* array is significantly slower because of memory locality and
83		* indirection effects.) Further, performance on most platforms is
#	Line 134 | Line 132 | public class ForkJoinWorkerThread extend
132
133		/**
134		* Maximum work-stealing queue array size.  Must be less than or
135	<	* equal to 1 << 30 to ensure lack of index wraparound.
135	>	* equal to 1 << 28 to ensure lack of index wraparound. (This
136	>	* is less than usual bounds, because we need leftshift by 3
137	>	* to be in int range).
138		*/
139	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30;
139	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
140
141		/**
142	<	* Generator of seeds for per-thread random numbers.
142	>	* The pool this thread works in. Accessed directly by ForkJoinTask.
143		*/
144	<	private static final Random randomSeedGenerator = new Random();
144	>	final ForkJoinPool pool;
145
146		/**
147		* The work-stealing queue array. Size must be a power of two.
148	+	* Initialized when thread starts, to improve memory locality.
149		*/
150		private ForkJoinTask<?>[] queue;
151
#	Line 163 | Line 164 | public class ForkJoinWorkerThread extend
164		private volatile int base;
165
166		/**
167	<	* The pool this thread works in.
168	<	*/
169	<	final ForkJoinPool pool;
170	<
170	<	/**
171	<	* Index of this worker in pool array. Set once by pool before
172	<	* running, and accessed directly by pool during cleanup etc
167	>	* Activity status. When true, this worker is considered active.
168	>	* Must be false upon construction. It must be true when executing
169	>	* tasks, and BEFORE stealing a task. It must be false before
170	>	* calling pool.sync.
171		*/
172	<	int poolIndex;
172	>	private boolean active;
173
174		/**
175		* Run state of this worker. Supports simple versions of the usual
#	Line 179 | Line 177 | public class ForkJoinWorkerThread extend
177		*/
178		private volatile int runState;
179
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	–
180		/**
181	<	* Activity status. When true, this worker is considered active.
182	<	* 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.
181	>	* Seed for random number generator for choosing steal victims.
182	>	* Uses Marsaglia xorshift. Must be nonzero upon initialization.
183		*/
184	<	private boolean active;
184	>	private int seed;
185
186		/**
187		* Number of steals, transferred to pool when idle
#	Line 199 | Line 189 | public class ForkJoinWorkerThread extend
189		private int stealCount;
190
191		/**
192	<	* Seed for random number generator for choosing steal victims
192	>	* Index of this worker in pool array. Set once by pool before
193	>	* running, and accessed directly by pool during cleanup etc.
194		*/
195	<	private int randomVictimSeed;
195	>	int poolIndex;
196
197		/**
198	<	* Seed for embedded Jurandom
198	>	* The last barrier event waited for. Accessed in pool callback
199	>	* methods, but only by current thread.
200		*/
201	<	private long juRandomSeed;
201	>	long lastEventCount;
202
203		/**
204	<	* The last barrier event waited for
204	>	* True if use local fifo, not default lifo, for local polling
205		*/
206	<	private long eventCount;
206	>	private boolean locallyFifo;
207
208		/**
209		* Creates a ForkJoinWorkerThread operating in the given pool.
210	+	*
211		* @param pool the pool this thread works in
212		* @throws NullPointerException if pool is null
213		*/
214		protected ForkJoinWorkerThread(ForkJoinPool pool) {
215		if (pool == null) throw new NullPointerException();
216		this.pool = pool;
217	<	// remaining initialization deferred to onStart
217	>	// Note: poolIndex is set by pool during construction
218	>	// Remaining initialization is deferred to onStart
219		}
220
221	<	// public access methods
221	>	// Public access methods
222
223		/**
224	<	* Returns the pool hosting the current task execution.
224	>	* Returns the pool hosting this thread.
225	>	*
226		* @return the pool
227		*/
228	<	public static ForkJoinPool getPool() {
229	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pool;
228	>	public ForkJoinPool getPool() {
229	>	return pool;
230		}
231
232		/**
233	<	* Returns the index number of the current worker thread in its
234	<	* pool.  The returned value ranges from zero to the maximum
235	<	* number of threads (minus one) that have ever been created in
236	<	* the pool.  This method may be useful for applications that
237	<	* track status or collect results on a per-worker basis.
238	<	* @return the index number.
233	>	* Returns the index number of this thread in its pool.  The
234	>	* returned value ranges from zero to the maximum number of
235	>	* threads (minus one) that have ever been created in the pool.
236	>	* This method may be useful for applications that track status or
237	>	* collect results per-worker rather than per-task.
238	>	*
239	>	* @return the index number
240		*/
241	<	public static int getPoolIndex() {
242	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex;
241	>	public int getPoolIndex() {
242	>	return poolIndex;
243		}
244
245	<	//  Access methods used by Pool
245	>	/**
246	>	* Establishes local first-in-first-out scheduling mode for forked
247	>	* tasks that are never joined.
248	>	*
249	>	* @param async if true, use locally FIFO scheduling
250	>	*/
251	>	void setAsyncMode(boolean async) {
252	>	locallyFifo = async;
253	>	}
254	>
255	>	// Runstate management
256	>
257	>	// Runstate values. Order matters
258	>	private static final int RUNNING     = 0;
259	>	private static final int SHUTDOWN    = 1;
260	>	private static final int TERMINATING = 2;
261	>	private static final int TERMINATED  = 3;
262	>
263	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
264	>	final boolean isTerminating() { return runState >= TERMINATING;  }
265	>	final boolean isTerminated()  { return runState == TERMINATED; }
266	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
267	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
268
269		/**
270	<	* Get and clear steal count for accumulation by pool.  Called
271	<	* only when known to be idle (in pool.sync and termination).
270	>	* Transitions to at least the given state.  Returns true if not
271	>	* already at least at given state.
272		*/
273	<	final int getAndClearStealCount() {
274	<	int sc = stealCount;
275	<	stealCount = 0;
276	<	return sc;
273	>	private boolean transitionRunStateTo(int state) {
274	>	for (;;) {
275	>	int s = runState;
276	>	if (s >= state)
277	>	return false;
278	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
279	>	return true;
280	>	}
281		}
282
283		/**
284	<	* Returns estimate of the number of tasks in the queue, without
263	<	* correcting for transient negative values
284	>	* Tries to set status to active; fails on contention.
285		*/
286	<	final int getRawQueueSize() {
287	<	return sp - base;
286	>	private boolean tryActivate() {
287	>	if (!active) {
288	>	if (!pool.tryIncrementActiveCount())
289	>	return false;
290	>	active = true;
291	>	}
292	>	return true;
293		}
294
295	<	// Intrinsics-based support for queue operations.
296	<	// Currently these three (setSp, setSlot, casSlotNull) are
297	<	// usually manually inlined to improve performance
295	>	/**
296	>	* Tries to set status to inactive; fails on contention.
297	>	*/
298	>	private boolean tryInactivate() {
299	>	if (active) {
300	>	if (!pool.tryDecrementActiveCount())
301	>	return false;
302	>	active = false;
303	>	}
304	>	return true;
305	>	}
306
307		/**
308	<	* Sets sp in store-order.
308	>	* Computes next value for random victim probe.  Scans don't
309	>	* require a very high quality generator, but also not a crummy
310	>	* one.  Marsaglia xor-shift is cheap and works well.
311		*/
312	<	private void setSp(int s) {
313	<	_unsafe.putOrderedInt(this, spOffset, s);
312	>	private static int xorShift(int r) {
313	>	r ^= r << 1;
314	>	r ^= r >>> 3;
315	>	r ^= r << 10;
316	>	return r;
317		}
318
319	+	// Lifecycle methods
320	+
321		/**
322	<	* Add in store-order the given task at given slot of q to
323	<	* null. Caller must ensure q is nonnull and index is in range.
322	>	* This method is required to be public, but should never be
323	>	* called explicitly. It performs the main run loop to execute
324	>	* ForkJoinTasks.
325	>	*/
326	>	public void run() {
327	>	Throwable exception = null;
328	>	try {
329	>	onStart();
330	>	pool.sync(this); // await first pool event
331	>	mainLoop();
332	>	} catch (Throwable ex) {
333	>	exception = ex;
334	>	} finally {
335	>	onTermination(exception);
336	>	}
337	>	}
338	>
339	>	/**
340	>	* Executes tasks until shut down.
341	>	*/
342	>	private void mainLoop() {
343	>	while (!isShutdown()) {
344	>	ForkJoinTask<?> t = pollTask();
345	>	if (t != null || (t = pollSubmission()) != null)
346	>	t.quietlyExec();
347	>	else if (tryInactivate())
348	>	pool.sync(this);
349	>	}
350	>	}
351	>
352	>	/**
353	>	* Initializes internal state after construction but before
354	>	* processing any tasks. If you override this method, you must
355	>	* invoke super.onStart() at the beginning of the method.
356	>	* Initialization requires care: Most fields must have legal
357	>	* default values, to ensure that attempted accesses from other
358	>	* threads work correctly even before this thread starts
359	>	* processing tasks.
360	>	*/
361	>	protected void onStart() {
362	>	// Allocate while starting to improve chances of thread-local
363	>	// isolation
364	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
365	>	// Initial value of seed need not be especially random but
366	>	// should differ across workers and must be nonzero
367	>	int p = poolIndex + 1;
368	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
369	>	}
370	>
371	>	/**
372	>	* Performs cleanup associated with termination of this worker
373	>	* thread.  If you override this method, you must invoke
374	>	* {@code super.onTermination} at the end of the overridden method.
375	>	*
376	>	* @param exception the exception causing this thread to abort due
377	>	* to an unrecoverable error, or null if completed normally
378	>	*/
379	>	protected void onTermination(Throwable exception) {
380	>	// Execute remaining local tasks unless aborting or terminating
381	>	while (exception == null &&  !pool.isTerminating() && base != sp) {
382	>	try {
383	>	ForkJoinTask<?> t = popTask();
384	>	if (t != null)
385	>	t.quietlyExec();
386	>	} catch (Throwable ex) {
387	>	exception = ex;
388	>	}
389	>	}
390	>	// Cancel other tasks, transition status, notify pool, and
391	>	// propagate exception to uncaught exception handler
392	>	try {
393	>	do {} while (!tryInactivate()); // ensure inactive
394	>	cancelTasks();
395	>	runState = TERMINATED;
396	>	pool.workerTerminated(this);
397	>	} catch (Throwable ex) {        // Shouldn't ever happen
398	>	if (exception == null)      // but if so, at least rethrown
399	>	exception = ex;
400	>	} finally {
401	>	if (exception != null)
402	>	ForkJoinTask.rethrowException(exception);
403	>	}
404	>	}
405	>
406	>	// Intrinsics-based support for queue operations.
407	>
408	>	/**
409	>	* Adds in store-order the given task at given slot of q to null.
410	>	* Caller must ensure q is non-null and index is in range.
411		*/
412		private static void setSlot(ForkJoinTask<?>[] q, int i,
413	<	ForkJoinTask<?> t){
414	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
413	>	ForkJoinTask<?> t) {
414	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
415		}
416
417		/**
418	<	* CAS given slot of q to null. Caller must ensure q is nonnull
418	>	* CAS given slot of q to null. Caller must ensure q is non-null
419		* and index is in range.
420		*/
421		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
422		ForkJoinTask<?> t) {
423	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
423	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
424	>	}
425	>
426	>	/**
427	>	* Sets sp in store-order.
428	>	*/
429	>	private void storeSp(int s) {
430	>	UNSAFE.putOrderedInt(this, spOffset, s);
431		}
432
433		// Main queue methods
434
435		/**
436		* Pushes a task. Called only by current thread.
437	<	* @param t the task. Caller must ensure nonnull
437	>	*
438	>	* @param t the task. Caller must ensure non-null.
439		*/
440		final void pushTask(ForkJoinTask<?> t) {
441		ForkJoinTask<?>[] q = queue;
442		int mask = q.length - 1;
443		int s = sp;
444	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
445	<	_unsafe.putOrderedInt(this, spOffset, ++s);
444	>	setSlot(q, s & mask, t);
445	>	storeSp(++s);
446		if ((s -= base) == 1)
447	<	pool.signalNonEmptyWorkerQueue();
447	>	pool.signalWork();
448		else if (s >= mask)
449		growQueue();
450		}
#	Line 316 | Line 452 | public class ForkJoinWorkerThread extend
452		/**
453		* Tries to take a task from the base of the queue, failing if
454		* either empty or contended.
455	<	* @return a task, or null if none or contended.
455	>	*
456	>	* @return a task, or null if none or contended
457		*/
458	<	private ForkJoinTask<?> deqTask() {
322	<	ForkJoinTask<?>[] q;
458	>	final ForkJoinTask<?> deqTask() {
459		ForkJoinTask<?> t;
460	+	ForkJoinTask<?>[] q;
461		int i;
462		int b;
463		if (sp != (b = base) &&
464		(q = queue) != null && // must read q after b
465		(t = q[i = (q.length - 1) & b]) != null &&
466	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
466	>	casSlotNull(q, i, t)) {
467		base = b + 1;
468		return t;
469		}
#	Line 334 | Line 471 | public class ForkJoinWorkerThread extend
471		}
472
473		/**
474	<	* Returns a popped task, or null if empty.  Called only by
475	<	* current thread.
474	>	* Returns a popped task, or null if empty. Ensures active status
475	>	* if non-null. Called only by current thread.
476		*/
477		final ForkJoinTask<?> popTask() {
341	–	ForkJoinTask<?> t;
342	–	int i;
343	–	ForkJoinTask<?>[] q = queue;
344	–	int mask = q.length - 1;
478		int s = sp;
479	<	if (s != base &&
480	<	(t = q[i = (s - 1) & mask]) != null &&
481	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
482	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
483	<	return t;
479	>	while (s != base) {
480	>	if (tryActivate()) {
481	>	ForkJoinTask<?>[] q = queue;
482	>	int mask = q.length - 1;
483	>	int i = (s - 1) & mask;
484	>	ForkJoinTask<?> t = q[i];
485	>	if (t == null || !casSlotNull(q, i, t))
486	>	break;
487	>	storeSp(s - 1);
488	>	return t;
489	>	}
490		}
491		return null;
492		}
#	Line 355 | Line 494 | public class ForkJoinWorkerThread extend
494		/**
495		* Specialized version of popTask to pop only if
496		* topmost element is the given task. Called only
497	<	* by current thread.
498	<	* @param t the task. Caller must ensure nonnull
497	>	* by current thread while active.
498	>	*
499	>	* @param t the task. Caller must ensure non-null.
500		*/
501		final boolean unpushTask(ForkJoinTask<?> t) {
502		ForkJoinTask<?>[] q = queue;
503		int mask = q.length - 1;
504		int s = sp - 1;
505	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
506	<	t, null)) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
505	>	if (casSlotNull(q, s & mask, t)) {
506	>	storeSp(s);
507		return true;
508		}
509		return false;
510		}
511
512		/**
513	<	* Returns next task to pop.
513	>	* Returns next task.
514		*/
515		final ForkJoinTask<?> peekTask() {
516		ForkJoinTask<?>[] q = queue;
517	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
517	>	if (q == null)
518	>	return null;
519	>	int mask = q.length - 1;
520	>	int i = locallyFifo ? base : (sp - 1);
521	>	return q[i & mask];
522		}
523
524		/**
#	Line 402 | Line 545 | public class ForkJoinWorkerThread extend
545		t = null;
546		setSlot(newQ, b & newMask, t);
547		} while (++b != bf);
548	<	pool.signalIdleWorkers(false);
406	<	}
407	<
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	<
416	<	/**
417	<	* Transition to at least the given state. Return true if not
418	<	* already at least given state.
419	<	*/
420	<	private boolean transitionRunStateTo(int state) {
421	<	for (;;) {
422	<	int s = runState;
423	<	if (s >= state)
424	<	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	<	}
548	>	pool.signalWork();
549		}
550
551		/**
552	<	* Ensure status is inactive and if necessary adjust pool active count
552	>	* Tries to steal a task from another worker. Starts at a random
553	>	* index of workers array, and probes workers until finding one
554	>	* with non-empty queue or finding that all are empty.  It
555	>	* randomly selects the first n probes. If these are empty, it
556	>	* resorts to a full circular traversal, which is necessary to
557	>	* accurately set active status by caller. Also restarts if pool
558	>	* events occurred since last scan, which forces refresh of
559	>	* workers array, in case barrier was associated with resize.
560	>	*
561	>	* This method must be both fast and quiet -- usually avoiding
562	>	* memory accesses that could disrupt cache sharing etc other than
563	>	* those needed to check for and take tasks. This accounts for,
564	>	* among other things, updating random seed in place without
565	>	* storing it until exit.
566	>	*
567	>	* @return a task, or null if none found
568		*/
569	<	final void inactivate() {
570	<	if (active) {
571	<	active = false;
572	<	pool.decrementActiveCount();
573	<	}
569	>	private ForkJoinTask<?> scan() {
570	>	ForkJoinTask<?> t = null;
571	>	int r = seed;                    // extract once to keep scan quiet
572	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
573	>	int mask;                        // must be power 2 minus 1 and > 0
574	>	outer:do {
575	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
576	>	int idx = r;
577	>	int probes = ~mask;      // use random index while negative
578	>	for (;;) {
579	>	r = xorShift(r);     // update random seed
580	>	ForkJoinWorkerThread v = ws[mask & idx];
581	>	if (v == null || v.sp == v.base) {
582	>	if (probes <= mask)
583	>	idx = (probes++ < 0) ? r : (idx + 1);
584	>	else
585	>	break;
586	>	}
587	>	else if (!tryActivate() || (t = v.deqTask()) == null)
588	>	continue outer;  // restart on contention
589	>	else
590	>	break outer;
591	>	}
592	>	}
593	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
594	>	seed = r;
595	>	return t;
596		}
597
450	–	// Lifecycle methods
451	–
598		/**
599	<	* Initializes internal state after construction but before
600	<	* processing any tasks. If you override this method, you must
601	<	* 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.
599	>	* Gets and removes a local or stolen task.
600	>	*
601	>	* @return a task, if available
602		*/
603	<	protected void onStart() {
604	<	juRandomSeed = randomSeedGenerator.nextLong();
605	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
606	<	if (queue == null)
607	<	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	<	}
603	>	final ForkJoinTask<?> pollTask() {
604	>	ForkJoinTask<?> t = locallyFifo ? deqTask() : popTask();
605	>	if (t == null && (t = scan()) != null)
606	>	++stealCount;
607	>	return t;
608		}
609
610		/**
611	<	* 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.
611	>	* Gets a local task.
612		*
613	<	* @param exception the exception causing this thread to abort due
480	<	* to an unrecoverable error, or null if completed normally.
613	>	* @return a task, if available
614		*/
615	<	protected void onTermination(Throwable exception) {
616	<	try {
484	<	clearLocalTasks();
485	<	inactivate();
486	<	cancelTasks();
487	<	} finally {
488	<	terminate(exception);
489	<	}
615	>	final ForkJoinTask<?> pollLocalTask() {
616	>	return locallyFifo ? deqTask() : popTask();
617		}
618
619		/**
620	<	* Notify pool of termination and, if exception is nonnull,
621	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
620	>	* Returns a pool submission, if one exists, activating first.
621	>	*
622	>	* @return a submission, if available
623		*/
624	<	private void terminate(Throwable exception) {
625	<	transitionRunStateTo(TERMINATED);
626	<	try {
627	<	pool.workerTerminated(this);
628	<	} finally {
629	<	if (exception != null)
502	<	ForkJoinTask.rethrowException(exception);
624	>	private ForkJoinTask<?> pollSubmission() {
625	>	ForkJoinPool p = pool;
626	>	while (p.hasQueuedSubmissions()) {
627	>	ForkJoinTask<?> t;
628	>	if (tryActivate() && (t = p.pollSubmission()) != null)
629	>	return t;
630		}
631	+	return null;
632		}
633
634	<	/**
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	<	}
634	>	// Methods accessed only by Pool
635
636		/**
637		* Removes and cancels all tasks in queue.  Can be called from any
638		* thread.
639		*/
640		final void cancelTasks() {
641	<	while (base != sp) {
642	<	ForkJoinTask<?> t = deqTask();
643	<	if (t != null)
527	<	t.cancelIgnoringExceptions();
528	<	}
641	>	ForkJoinTask<?> t;
642	>	while (base != sp && (t = deqTask()) != null)
643	>	t.cancelIgnoringExceptions();
644		}
645
646		/**
647	<	* This method is required to be public, but should never be
648	<	* called explicitly. It performs the main run loop to execute
649	<	* ForkJoinTasks.
647	>	* Drains tasks to given collection c.
648	>	*
649	>	* @return the number of tasks drained
650		*/
651	<	public void run() {
652	<	Throwable exception = null;
653	<	try {
654	<	onStart();
655	<	while (!isShutdown())
656	<	step();
542	<	} catch (Throwable ex) {
543	<	exception = ex;
544	<	} finally {
545	<	onTermination(exception);
651	>	final int drainTasksTo(Collection<ForkJoinTask<?>> c) {
652	>	int n = 0;
653	>	ForkJoinTask<?> t;
654	>	while (base != sp && (t = deqTask()) != null) {
655	>	c.add(t);
656	>	++n;
657		}
658	+	return n;
659		}
660
661		/**
662	<	* Main top-level action.
662	>	* Gets and clears steal count for accumulation by pool.  Called
663	>	* only when known to be idle (in pool.sync and termination).
664		*/
665	<	private void step() {
666	<	ForkJoinTask<?> t = sp != base? popTask() : null;
667	<	if (t != null || (t = scan(null, true)) != null) {
668	<	activate();
556	<	t.quietlyExec();
557	<	}
558	<	else {
559	<	inactivate();
560	<	eventCount = pool.sync(this, eventCount);
561	<	}
665	>	final int getAndClearStealCount() {
666	>	int sc = stealCount;
667	>	stealCount = 0;
668	>	return sc;
669		}
670
564	–	// scanning for and stealing tasks
565	–
671		/**
672	<	* Computes next value for random victim probe. Scans don't
673	<	* require a very high quality generator, but also not a crummy
569	<	* one. Marsaglia xor-shift is cheap and works well.
672	>	* Returns true if at least one worker in the given array appears
673	>	* to have at least one queued task.
674		*
675	<	* This is currently unused, and manually inlined
675	>	* @param ws array of workers
676		*/
677	<	private static int xorShift(int r) {
678	<	r ^= r << 1;
679	<	r ^= r >>> 3;
680	<	r ^= r << 10;
681	<	return r;
682	<	}
683	<
684	<	/**
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.
590	<	*
591	<	* This method must be both fast and quiet -- usually avoiding
592	<	* memory accesses that could disrupt cache sharing etc other than
593	<	* those needed to check for and take tasks. This accounts for,
594	<	* among other things, updating random seed in place without
595	<	* 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.)
598	<	*
599	<	* @param joinMe if non null; exit early if done
600	<	* @param checkSubmissions true if OK to take submissions
601	<	* @return a task, or null if none found
602	<	*/
603	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
604	<	boolean checkSubmissions) {
605	<	ForkJoinPool p = pool;
606	<	if (p == null)                    // Never null, but avoids
607	<	return null;                  //   implicit nullchecks below
608	<	int r = randomVictimSeed;         // extract once to keep scan quiet
609	<	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
615	<	int idx = r;
616	<	for (;;) {
617	<	ForkJoinWorkerThread v;
618	<	// inlined xorshift to update seed
619	<	r ^= r << 1;  r ^= r >>> 3; r ^= r << 10;
620	<	if ((v = ws[mask & idx]) != null && v.sp != v.base) {
621	<	ForkJoinTask<?> t;
622	<	activate();
623	<	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
630	<	}
631	<	if ((probes >> 1) <= mask) // n-1 random then circular
632	<	idx = (probes++ < 0)? r : (idx + 1);
633	<	else
634	<	break;
677	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
678	>	if (ws != null) {
679	>	int len = ws.length;
680	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
681	>	for (int i = 0; i < len; ++i) {
682	>	ForkJoinWorkerThread w = ws[i];
683	>	if (w != null && w.sp != w.base)
684	>	return true;
685		}
686		}
637	–	if (checkSubmissions && p.hasQueuedSubmissions()) {
638	–	activate();
639	–	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;
650	–	}
651	–
652	–	/**
653	–	* Callback from pool.sync to rescan before blocking.  If a
654	–	* task is found, it is pushed so it can be executed upon return.
655	–	* @return true if found and pushed a task
656	–	*/
657	–	final boolean prescan() {
658	–	ForkJoinTask<?> t = scan(null, true);
659	–	if (t != null) {
660	–	pushTask(t);
661	–	return true;
662	–	}
663	–	else {
664	–	inactivate();
665	–	return false;
687		}
688	+	return false;
689		}
690
691	<	// Support for ForkJoinTask methods
670	<
671	<	/**
672	<	* Scan, returning early if joinMe done
673	<	*/
674	<	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
675	<	ForkJoinTask<?> t = scan(joinMe, false);
676	<	if (t != null && joinMe.status < 0 && sp == base) {
677	<	pushTask(t); // unsteal if done and this task would be stealable
678	<	t = null;
679	<	}
680	<	return t;
681	<	}
682	<
683	<	/**
684	<	* Pops or steals a task
685	<	* @return task, or null if none available
686	<	*/
687	<	final ForkJoinTask<?> pollLocalOrStolenTask() {
688	<	ForkJoinTask<?> t;
689	<	return (t = popTask()) == null? scan(null, false) : t;
690	<	}
691	<
692	<	/**
693	<	* Runs tasks until pool isQuiescent
694	<	*/
695	<	final void helpQuiescePool() {
696	<	for (;;) {
697	<	ForkJoinTask<?> t = pollLocalOrStolenTask();
698	<	if (t != null) {
699	<	activate();
700	<	t.quietlyExec();
701	<	}
702	<	else {
703	<	inactivate();
704	<	if (pool.isQuiescent()) {
705	<	activate(); // re-activate on exit
706	<	break;
707	<	}
708	<	}
709	<	}
710	<	}
691	>	// Support methods for ForkJoinTask
692
693		/**
694		* Returns an estimate of the number of tasks in the queue.
695		*/
696		final int getQueueSize() {
697	<	int n = sp - base;
698	<	return n <= 0? 0 : n; // suppress momentarily negative values
697	>	// suppress momentarily negative values
698	>	return Math.max(0, sp - base);
699		}
700
701		/**
#	Line 726 | Line 707 | public class ForkJoinWorkerThread extend
707		return (sp - base) - (pool.getIdleThreadCount() >>> 1);
708		}
709
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	–
710		/**
711	<	* 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
711	>	* Scans, returning early if joinMe done.
712		*/
713	<	public static int nextRandomInt() {
714	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
715	<	nextJURandom(32);
713	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
714	>	ForkJoinTask<?> t = pollTask();
715	>	if (t != null && joinMe.status < 0 && sp == base) {
716	>	pushTask(t); // unsteal if done and this task would be stealable
717	>	t = null;
718	>	}
719	>	return t;
720		}
721
722		/**
723	<	* 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
723	>	* Runs tasks until {@code pool.isQuiescent()}.
724		*/
725	<	public static int nextRandomInt(int n) {
726	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
727	<	nextJURandomInt(n);
725	>	final void helpQuiescePool() {
726	>	for (;;) {
727	>	ForkJoinTask<?> t = pollTask();
728	>	if (t != null)
729	>	t.quietlyExec();
730	>	else if (tryInactivate() && pool.isQuiescent())
731	>	break;
732	>	}
733	>	do {} while (!tryActivate()); // re-activate on exit
734		}
735
736	<	/**
737	<	* Returns a random long using a per-worker random
738	<	* number generator with the same properties as
739	<	* {@link java.util.Random#nextLong}
740	<	* @return the next pseudorandom, uniformly distributed {@code long}
741	<	*         value from this worker's random number generator's sequence
742	<	*/
743	<	public static long nextRandomLong() {
744	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
745	<	nextJURandomLong();
736	>	// Temporary Unsafe mechanics for preliminary release
737	>	private static Unsafe getUnsafe() throws Throwable {
738	>	try {
739	>	return Unsafe.getUnsafe();
740	>	} catch (SecurityException se) {
741	>	try {
742	>	return java.security.AccessController.doPrivileged
743	>	(new java.security.PrivilegedExceptionAction<Unsafe>() {
744	>	public Unsafe run() throws Exception {
745	>	return getUnsafePrivileged();
746	>	}});
747	>	} catch (java.security.PrivilegedActionException e) {
748	>	throw e.getCause();
749	>	}
750	>	}
751		}
752
753	<	/**
754	<	* Returns a random integer using a per-worker random
755	<	* number generator with the same properties as
756	<	* {@link java.util.Random#nextInt(int)}
757	<	* @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
832	<	*/
833	<	public static long nextRandomLong(long n) {
834	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
835	<	nextJURandomLong(n);
753	>	private static Unsafe getUnsafePrivileged()
754	>	throws NoSuchFieldException, IllegalAccessException {
755	>	Field f = Unsafe.class.getDeclaredField("theUnsafe");
756	>	f.setAccessible(true);
757	>	return (Unsafe) f.get(null);
758		}
759
760	<	/**
761	<	* Returns a random double using a per-worker random
762	<	* number generator with the same properties as
763	<	* {@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
845	<	*/
846	<	public static double nextRandomDouble() {
847	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
848	<	nextJURandomDouble();
760	>	private static long fieldOffset(String fieldName)
761	>	throws NoSuchFieldException {
762	>	return UNSAFE.objectFieldOffset
763	>	(ForkJoinWorkerThread.class.getDeclaredField(fieldName));
764		}
765
766	<	// Temporary Unsafe mechanics for preliminary release
852	<
853	<	static final Unsafe _unsafe;
766	>	static final Unsafe UNSAFE;
767		static final long baseOffset;
768		static final long spOffset;
769	+	static final long runStateOffset;
770		static final long qBase;
771		static final int qShift;
858	–	static final long runStateOffset;
772		static {
773		try {
774	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
775	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
776	<	f.setAccessible(true);
777	<	_unsafe = (Unsafe)f.get(null);
778	<	}
779	<	else
867	<	_unsafe = Unsafe.getUnsafe();
868	<	baseOffset = _unsafe.objectFieldOffset
869	<	(ForkJoinWorkerThread.class.getDeclaredField("base"));
870	<	spOffset = _unsafe.objectFieldOffset
871	<	(ForkJoinWorkerThread.class.getDeclaredField("sp"));
872	<	runStateOffset = _unsafe.objectFieldOffset
873	<	(ForkJoinWorkerThread.class.getDeclaredField("runState"));
874	<	qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class);
875	<	int s = _unsafe.arrayIndexScale(ForkJoinTask[].class);
774	>	UNSAFE = getUnsafe();
775	>	baseOffset = fieldOffset("base");
776	>	spOffset = fieldOffset("sp");
777	>	runStateOffset = fieldOffset("runState");
778	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
779	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
780		if ((s & (s-1)) != 0)
781		throw new Error("data type scale not a power of two");
782		qShift = 31 - Integer.numberOfLeadingZeros(s);
783	<	} catch (Exception e) {
783	>	} catch (Throwable e) {
784		throw new RuntimeException("Could not initialize intrinsics", e);
785		}
786		}

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