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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 1.12 by jsr166, Tue Jul 21 18:11:44 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 63 | Line 44 | public class ForkJoinWorkerThread extend
44		* of tasks. To accomplish this, we shift the CAS arbitrating pop
45		* vs deq (steal) from being on the indices ("base" and "sp") to
46		* the slots themselves (mainly via method "casSlotNull()"). So,
47	<	* both a successful pop and deq mainly entail CAS'ing a nonnull
47	>	* both a successful pop and deq mainly entail CAS'ing a non-null
48		* slot to null.  Because we rely on CASes of references, we do
49		* not need tag bits on base or sp.  They are simple ints as used
50		* in any circular array-based queue (see for example ArrayDeque).
#	Line 75 | Line 56 | public class ForkJoinWorkerThread extend
56		* considered individually, is not wait-free. One thief cannot
57		* successfully continue until another in-progress one (or, if
58		* previously empty, a push) completes.  However, in the
59	<	* aggregate, we ensure at least probablistic non-blockingness. If
59	>	* aggregate, we ensure at least probabilistic non-blockingness. If
60		* an attempted steal fails, a thief always chooses a different
61		* random victim target to try next. So, in order for one thief to
62		* progress, it suffices for any in-progress deq or new push on
#	Line 94 | Line 75 | public class ForkJoinWorkerThread extend
75		* push) require store order and CASes (in pop and deq) require
76		* (volatile) CAS semantics. Since these combinations aren't
77		* supported using ordinary volatiles, the only way to accomplish
78	<	* these effciently is to use direct Unsafe calls. (Using external
78	>	* these efficiently is to use direct Unsafe calls. (Using external
79		* AtomicIntegers and AtomicReferenceArrays for the indices and
80		* array is significantly slower because of memory locality and
81		* indirection effects.) Further, performance on most platforms is
#	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.
208	+	*
209		* @param pool the pool this thread works in
210		* @throws NullPointerException if pool is null
211		*/
212		protected ForkJoinWorkerThread(ForkJoinPool pool) {
213		if (pool == null) throw new NullPointerException();
214		this.pool = pool;
215	<	// remaining initialization deferred to onStart
215	>	// Note: poolIndex is set by pool during construction
216	>	// Remaining initialization is deferred to onStart
217		}
218
219	<	//  Access methods used by Pool
219	>	// Public access methods
220
221		/**
222	<	* Get and clear steal count for accumulation by pool.  Called
223	<	* only when known to be idle (in pool.sync and termination).
222	>	* Returns the pool hosting this thread.
223	>	*
224	>	* @return the pool
225		*/
226	<	final int getAndClearStealCount() {
227	<	int sc = stealCount;
250	<	stealCount = 0;
251	<	return sc;
226	>	public ForkJoinPool getPool() {
227	>	return pool;
228		}
229
230		/**
231	<	* Returns estimate of the number of tasks in the queue, without
232	<	* correcting for transient negative values
231	>	* Returns the index number of this thread in its pool.  The
232	>	* returned value ranges from zero to the maximum number of
233	>	* threads (minus one) that have ever been created in the pool.
234	>	* This method may be useful for applications that track status or
235	>	* collect results per-worker rather than per-task.
236	>	*
237	>	* @return the index number
238		*/
239	<	final int getRawQueueSize() {
240	<	return sp - base;
239	>	public int getPoolIndex() {
240	>	return poolIndex;
241		}
242
243	<	// Intrinsics-based support for queue operations.
244	<	// Currently these three (setSp, setSlot, casSlotNull) are
245	<	// usually manually inlined to improve performance
243	>	/**
244	>	* Establishes local first-in-first-out scheduling mode for forked
245	>	* tasks that are never joined.
246	>	*
247	>	* @param async if true, use locally FIFO scheduling
248	>	*/
249	>	void setAsyncMode(boolean async) {
250	>	locallyFifo = async;
251	>	}
252	>
253	>	// Runstate management
254	>
255	>	// Runstate values. Order matters
256	>	private static final int RUNNING     = 0;
257	>	private static final int SHUTDOWN    = 1;
258	>	private static final int TERMINATING = 2;
259	>	private static final int TERMINATED  = 3;
260	>
261	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
262	>	final boolean isTerminating() { return runState >= TERMINATING;  }
263	>	final boolean isTerminated()  { return runState == TERMINATED; }
264	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
265	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
266
267		/**
268	<	* Sets sp in store-order.
268	>	* Transitions to at least the given state.  Returns true if not
269	>	* already at least at given state.
270	>	*/
271	>	private boolean transitionRunStateTo(int state) {
272	>	for (;;) {
273	>	int s = runState;
274	>	if (s >= state)
275	>	return false;
276	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
277	>	return true;
278	>	}
279	>	}
280	>
281	>	/**
282	>	* Tries to set status to active; fails on contention.
283		*/
284	<	private void setSp(int s) {
285	<	_unsafe.putOrderedInt(this, spOffset, s);
284	>	private boolean tryActivate() {
285	>	if (!active) {
286	>	if (!pool.tryIncrementActiveCount())
287	>	return false;
288	>	active = true;
289	>	}
290	>	return true;
291		}
292
293		/**
294	<	* Add in store-order the given task at given slot of q to
295	<	* null. Caller must ensure q is nonnull and index is in range.
294	>	* Tries to set status to active; fails on contention.
295	>	*/
296	>	private boolean tryInactivate() {
297	>	if (active) {
298	>	if (!pool.tryDecrementActiveCount())
299	>	return false;
300	>	active = false;
301	>	}
302	>	return true;
303	>	}
304	>
305	>	/**
306	>	* Computes next value for random victim probe.  Scans don't
307	>	* require a very high quality generator, but also not a crummy
308	>	* one.  Marsaglia xor-shift is cheap and works well.
309	>	*/
310	>	private static int xorShift(int r) {
311	>	r ^= r << 1;
312	>	r ^= r >>> 3;
313	>	r ^= r << 10;
314	>	return r;
315	>	}
316	>
317	>	// Lifecycle methods
318	>
319	>	/**
320	>	* This method is required to be public, but should never be
321	>	* called explicitly. It performs the main run loop to execute
322	>	* ForkJoinTasks.
323	>	*/
324	>	public void run() {
325	>	Throwable exception = null;
326	>	try {
327	>	onStart();
328	>	pool.sync(this); // await first pool event
329	>	mainLoop();
330	>	} catch (Throwable ex) {
331	>	exception = ex;
332	>	} finally {
333	>	onTermination(exception);
334	>	}
335	>	}
336	>
337	>	/**
338	>	* Executes tasks until shut down.
339	>	*/
340	>	private void mainLoop() {
341	>	while (!isShutdown()) {
342	>	ForkJoinTask<?> t = pollTask();
343	>	if (t != null || (t = pollSubmission()) != null)
344	>	t.quietlyExec();
345	>	else if (tryInactivate())
346	>	pool.sync(this);
347	>	}
348	>	}
349	>
350	>	/**
351	>	* Initializes internal state after construction but before
352	>	* processing any tasks. If you override this method, you must
353	>	* invoke super.onStart() at the beginning of the method.
354	>	* Initialization requires care: Most fields must have legal
355	>	* default values, to ensure that attempted accesses from other
356	>	* threads work correctly even before this thread starts
357	>	* processing tasks.
358	>	*/
359	>	protected void onStart() {
360	>	// Allocate while starting to improve chances of thread-local
361	>	// isolation
362	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
363	>	// Initial value of seed need not be especially random but
364	>	// should differ across workers and must be nonzero
365	>	int p = poolIndex + 1;
366	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
367	>	}
368	>
369	>	/**
370	>	* Performs cleanup associated with termination of this worker
371	>	* thread.  If you override this method, you must invoke
372	>	* super.onTermination at the end of the overridden method.
373	>	*
374	>	* @param exception the exception causing this thread to abort due
375	>	* to an unrecoverable error, or null if completed normally
376	>	*/
377	>	protected void onTermination(Throwable exception) {
378	>	// Execute remaining local tasks unless aborting or terminating
379	>	while (exception == null &&  !pool.isTerminating() && base != sp) {
380	>	try {
381	>	ForkJoinTask<?> t = popTask();
382	>	if (t != null)
383	>	t.quietlyExec();
384	>	} catch(Throwable ex) {
385	>	exception = ex;
386	>	}
387	>	}
388	>	// Cancel other tasks, transition status, notify pool, and
389	>	// propagate exception to uncaught exception handler
390	>	try {
391	>	do;while (!tryInactivate()); // ensure inactive
392	>	cancelTasks();
393	>	runState = TERMINATED;
394	>	pool.workerTerminated(this);
395	>	} catch (Throwable ex) {        // Shouldn't ever happen
396	>	if (exception == null)      // but if so, at least rethrown
397	>	exception = ex;
398	>	} finally {
399	>	if (exception != null)
400	>	ForkJoinTask.rethrowException(exception);
401	>	}
402	>	}
403	>
404	>	// Intrinsics-based support for queue operations.
405	>
406	>	/**
407	>	* Adds in store-order the given task at given slot of q to null.
408	>	* Caller must ensure q is non-null and index is in range.
409		*/
410		private static void setSlot(ForkJoinTask<?>[] q, int i,
411		ForkJoinTask<?> t){
412	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
412	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
413		}
414
415		/**
416	<	* CAS given slot of q to null. Caller must ensure q is nonnull
416	>	* CAS given slot of q to null. Caller must ensure q is non-null
417		* and index is in range.
418		*/
419		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
420		ForkJoinTask<?> t) {
421	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
421	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
422	>	}
423	>
424	>	/**
425	>	* Sets sp in store-order.
426	>	*/
427	>	private void storeSp(int s) {
428	>	UNSAFE.putOrderedInt(this, spOffset, s);
429		}
430
431		// Main queue methods
432
433		/**
434		* Pushes a task. Called only by current thread.
435	<	* @param t the task. Caller must ensure nonnull
435	>	*
436	>	* @param t the task. Caller must ensure non-null.
437		*/
438		final void pushTask(ForkJoinTask<?> t) {
439		ForkJoinTask<?>[] q = queue;
440		int mask = q.length - 1;
441		int s = sp;
442	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
443	<	_unsafe.putOrderedInt(this, spOffset, ++s);
442	>	setSlot(q, s & mask, t);
443	>	storeSp(++s);
444		if ((s -= base) == 1)
445	<	pool.signalNonEmptyWorkerQueue();
445	>	pool.signalWork();
446		else if (s >= mask)
447		growQueue();
448		}
#	Line 309 | Line 450 | public class ForkJoinWorkerThread extend
450		/**
451		* Tries to take a task from the base of the queue, failing if
452		* either empty or contended.
453	<	* @return a task, or null if none or contended.
453	>	*
454	>	* @return a task, or null if none or contended
455		*/
456	<	private ForkJoinTask<?> deqTask() {
315	<	ForkJoinTask<?>[] q;
456	>	final ForkJoinTask<?> deqTask() {
457		ForkJoinTask<?> t;
458	+	ForkJoinTask<?>[] q;
459		int i;
460		int b;
461		if (sp != (b = base) &&
462		(q = queue) != null && // must read q after b
463		(t = q[i = (q.length - 1) & b]) != null &&
464	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
464	>	casSlotNull(q, i, t)) {
465		base = b + 1;
466		return t;
467		}
#	Line 327 | Line 469 | public class ForkJoinWorkerThread extend
469		}
470
471		/**
472	<	* Returns a popped task, or null if empty.  Called only by
473	<	* current thread.
472	>	* Returns a popped task, or null if empty. Ensures active status
473	>	* if non-null. Called only by current thread.
474		*/
475		final ForkJoinTask<?> popTask() {
334	–	ForkJoinTask<?> t;
335	–	int i;
336	–	ForkJoinTask<?>[] q = queue;
337	–	int mask = q.length - 1;
476		int s = sp;
477	<	if (s != base &&
478	<	(t = q[i = (s - 1) & mask]) != null &&
479	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
480	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
481	<	return t;
477	>	while (s != base) {
478	>	if (tryActivate()) {
479	>	ForkJoinTask<?>[] q = queue;
480	>	int mask = q.length - 1;
481	>	int i = (s - 1) & mask;
482	>	ForkJoinTask<?> t = q[i];
483	>	if (t == null || !casSlotNull(q, i, t))
484	>	break;
485	>	storeSp(s - 1);
486	>	return t;
487	>	}
488		}
489		return null;
490		}
#	Line 348 | Line 492 | public class ForkJoinWorkerThread extend
492		/**
493		* Specialized version of popTask to pop only if
494		* topmost element is the given task. Called only
495	<	* by current thread.
496	<	* @param t the task. Caller must ensure nonnull
495	>	* by current thread while active.
496	>	*
497	>	* @param t the task. Caller must ensure non-null.
498		*/
499		final boolean unpushTask(ForkJoinTask<?> t) {
500		ForkJoinTask<?>[] q = queue;
501		int mask = q.length - 1;
502		int s = sp - 1;
503	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
504	<	t, null)) {
360	<	_unsafe.putOrderedInt(this, spOffset, s);
503	>	if (casSlotNull(q, s & mask, t)) {
504	>	storeSp(s);
505		return true;
506		}
507		return false;
508		}
509
510		/**
511	<	* Returns next task to pop.
511	>	* Returns next task.
512		*/
513	<	private ForkJoinTask<?> peekTask() {
513	>	final ForkJoinTask<?> peekTask() {
514		ForkJoinTask<?>[] q = queue;
515	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
515	>	if (q == null)
516	>	return null;
517	>	int mask = q.length - 1;
518	>	int i = locallyFifo? base : (sp - 1);
519	>	return q[i & mask];
520		}
521
522		/**
#	Line 395 | Line 543 | public class ForkJoinWorkerThread extend
543		t = null;
544		setSlot(newQ, b & newMask, t);
545		} while (++b != bf);
546	<	pool.signalIdleWorkers(false);
399	<	}
400	<
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	<
409	<	/**
410	<	* Transition to at least the given state. Return true if not
411	<	* already at least given state.
412	<	*/
413	<	private boolean transitionRunStateTo(int state) {
414	<	for (;;) {
415	<	int s = runState;
416	<	if (s >= state)
417	<	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	<	}
546	>	pool.signalWork();
547		}
548
549		/**
550	<	* Ensure status is inactive and if necessary adjust pool active count
550	>	* Tries to steal a task from another worker. Starts at a random
551	>	* index of workers array, and probes workers until finding one
552	>	* with non-empty queue or finding that all are empty.  It
553	>	* randomly selects the first n probes. If these are empty, it
554	>	* resorts to a full circular traversal, which is necessary to
555	>	* accurately set active status by caller. Also restarts if pool
556	>	* events occurred since last scan, which forces refresh of
557	>	* workers array, in case barrier was associated with resize.
558	>	*
559	>	* This method must be both fast and quiet -- usually avoiding
560	>	* memory accesses that could disrupt cache sharing etc other than
561	>	* those needed to check for and take tasks. This accounts for,
562	>	* among other things, updating random seed in place without
563	>	* storing it until exit.
564	>	*
565	>	* @return a task, or null if none found
566		*/
567	<	final void inactivate() {
568	<	if (active) {
569	<	active = false;
570	<	pool.decrementActiveCount();
571	<	}
567	>	private ForkJoinTask<?> scan() {
568	>	ForkJoinTask<?> t = null;
569	>	int r = seed;                    // extract once to keep scan quiet
570	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
571	>	int mask;                        // must be power 2 minus 1 and > 0
572	>	outer:do {
573	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
574	>	int idx = r;
575	>	int probes = ~mask;      // use random index while negative
576	>	for (;;) {
577	>	r = xorShift(r);     // update random seed
578	>	ForkJoinWorkerThread v = ws[mask & idx];
579	>	if (v == null || v.sp == v.base) {
580	>	if (probes <= mask)
581	>	idx = (probes++ < 0)? r : (idx + 1);
582	>	else
583	>	break;
584	>	}
585	>	else if (!tryActivate() || (t = v.deqTask()) == null)
586	>	continue outer;  // restart on contention
587	>	else
588	>	break outer;
589	>	}
590	>	}
591	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
592	>	seed = r;
593	>	return t;
594		}
595
443	–	// Lifecycle methods
444	–
596		/**
597	<	* Initializes internal state after construction but before
598	<	* processing any tasks. If you override this method, you must
599	<	* 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.
597	>	* Gets and removes a local or stolen task.
598	>	*
599	>	* @return a task, if available
600		*/
601	<	protected void onStart() {
602	<	juRandomSeed = randomSeedGenerator.nextLong();
603	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
604	<	if (queue == null)
605	<	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	<	}
601	>	final ForkJoinTask<?> pollTask() {
602	>	ForkJoinTask<?> t = locallyFifo? deqTask() : popTask();
603	>	if (t == null && (t = scan()) != null)
604	>	++stealCount;
605	>	return t;
606		}
607
608		/**
609	<	* 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.
609	>	* Gets a local task.
610		*
611	<	* @param exception the exception causing this thread to abort due
473	<	* to an unrecoverable error, or null if completed normally.
611	>	* @return a task, if available
612		*/
613	<	protected void onTermination(Throwable exception) {
614	<	try {
477	<	clearLocalTasks();
478	<	inactivate();
479	<	cancelTasks();
480	<	} finally {
481	<	terminate(exception);
482	<	}
613	>	final ForkJoinTask<?> pollLocalTask() {
614	>	return locallyFifo? deqTask() : popTask();
615		}
616
617		/**
618	<	* Notify pool of termination and, if exception is nonnull,
619	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
618	>	* Returns a pool submission, if one exists, activating first.
619	>	*
620	>	* @return a submission, if available
621		*/
622	<	private void terminate(Throwable exception) {
623	<	transitionRunStateTo(TERMINATED);
624	<	try {
625	<	pool.workerTerminated(this);
626	<	} finally {
627	<	if (exception != null)
495	<	ForkJoinTask.rethrowException(exception);
622	>	private ForkJoinTask<?> pollSubmission() {
623	>	ForkJoinPool p = pool;
624	>	while (p.hasQueuedSubmissions()) {
625	>	ForkJoinTask<?> t;
626	>	if (tryActivate() && (t = p.pollSubmission()) != null)
627	>	return t;
628		}
629	+	return null;
630		}
631
632	<	/**
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	<	}
632	>	// Methods accessed only by Pool
633
634		/**
635		* Removes and cancels all tasks in queue.  Can be called from any
636		* thread.
637		*/
638		final void cancelTasks() {
639	<	while (base != sp) {
640	<	ForkJoinTask<?> t = deqTask();
641	<	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	<	}
639	>	ForkJoinTask<?> t;
640	>	while (base != sp && (t = deqTask()) != null)
641	>	t.cancelIgnoringExceptions();
642		}
643
644		/**
645	<	* Main top-level action.
645	>	* Drains tasks to given collection c.
646	>	*
647	>	* @return the number of tasks drained
648		*/
649	<	private void step() {
650	<	ForkJoinTask<?> t = sp != base? popTask() : null;
651	<	if (t != null || (t = scan(null, true)) != null) {
652	<	activate();
653	<	t.quietlyExec();
654	<	}
551	<	else {
552	<	inactivate();
553	<	eventCount = pool.sync(this, eventCount);
649	>	final int drainTasksTo(Collection<ForkJoinTask<?>> c) {
650	>	int n = 0;
651	>	ForkJoinTask<?> t;
652	>	while (base != sp && (t = deqTask()) != null) {
653	>	c.add(t);
654	>	++n;
655		}
656	+	return n;
657		}
658
557	–	// scanning for and stealing tasks
558	–
659		/**
660	<	* Computes next value for random victim probe. Scans don't
661	<	* 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
660	>	* Gets and clears steal count for accumulation by pool.  Called
661	>	* only when known to be idle (in pool.sync and termination).
662		*/
663	<	private static int xorShift(int r) {
664	<	r ^= r << 1;
665	<	r ^= r >>> 3;
666	<	r ^= r << 10;
570	<	return r;
663	>	final int getAndClearStealCount() {
664	>	int sc = stealCount;
665	>	stealCount = 0;
666	>	return sc;
667		}
668
669		/**
670	<	* Tries to steal a task from another worker and/or, if enabled,
671	<	* submission queue. Starts at a random index of workers array,
672	<	* and probes workers until finding one with non-empty queue or
673	<	* finding that all are empty.  It randomly selects the first n-1
674	<	* probes. If these are empty, it resorts to full circular
675	<	* traversal, which is necessary to accurately set active status
676	<	* by caller. Also restarts if pool barrier has tripped since last
677	<	* scan, which forces refresh of workers array, in case barrier
678	<	* was associated with resize.
679	<	*
680	<	* This method must be both fast and quiet -- usually avoiding
681	<	* memory accesses that could disrupt cache sharing etc other than
586	<	* those needed to check for and take tasks. This accounts for,
587	<	* among other things, updating random seed in place without
588	<	* 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.)
591	<	*
592	<	* @param joinMe if non null; exit early if done
593	<	* @param checkSubmissions true if OK to take submissions
594	<	* @return a task, or null if none found
595	<	*/
596	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
597	<	boolean checkSubmissions) {
598	<	ForkJoinPool p = pool;
599	<	if (p == null)                    // Never null, but avoids
600	<	return null;                  //   implicit nullchecks below
601	<	int r = randomVictimSeed;         // extract once to keep scan quiet
602	<	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
608	<	int idx = r;
609	<	for (;;) {
610	<	ForkJoinWorkerThread v;
611	<	// inlined xorshift to update seed
612	<	r ^= r << 1;  r ^= r >>> 3; r ^= r << 10;
613	<	if ((v = ws[mask & idx]) != null && v.sp != v.base) {
614	<	ForkJoinTask<?> t;
615	<	activate();
616	<	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
623	<	}
624	<	if ((probes >> 1) <= mask) // n-1 random then circular
625	<	idx = (probes++ < 0)? r : (idx + 1);
626	<	else
627	<	break;
670	>	* Returns true if at least one worker in the given array appears
671	>	* to have at least one queued task.
672	>	* @param ws array of workers
673	>	*/
674	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
675	>	if (ws != null) {
676	>	int len = ws.length;
677	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
678	>	for (int i = 0; i < len; ++i) {
679	>	ForkJoinWorkerThread w = ws[i];
680	>	if (w != null && w.sp != w.base)
681	>	return true;
682		}
683		}
630	–	if (checkSubmissions && p.hasQueuedSubmissions()) {
631	–	activate();
632	–	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;
643	–	}
644	–
645	–	/**
646	–	* Callback from pool.sync to rescan before blocking.  If a
647	–	* 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
664	–	*/
665	–	final int helpJoinTask(ForkJoinTask<?> joinMe) {
666	–	ForkJoinTask<?> t = null;
667	–	int s;
668	–	while ((s = joinMe.status) >= 0) {
669	–	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	–	}
684		}
685	<	if (t != null) // unsteal
680	<	pushTask(t);
681	<	return s;
685	>	return false;
686		}
687
688	<	// Support for public static and/or ForkJoinTask methods
688	>	// Support methods for ForkJoinTask
689
690		/**
691		* Returns an estimate of the number of tasks in the queue.
692		*/
693		final int getQueueSize() {
694	<	int b = base;
695	<	int n = sp - b;
692	<	return n <= 0? 0 : n; // suppress momentarily negative values
693	<	}
694	<
695	<	/**
696	<	* Runs one popped task, if available
697	<	* @return true if ran a task
698	<	*/
699	<	private boolean runLocalTask() {
700	<	ForkJoinTask<?> t = popTask();
701	<	if (t == null)
702	<	return false;
703	<	t.quietlyExec();
704	<	return true;
705	<	}
706	<
707	<	/**
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	<	}
715	<
716	<	/**
717	<	* Runs a popped or stolen task, if available
718	<	* @return true if ran a task
719	<	*/
720	<	private boolean runLocalOrStolenTask() {
721	<	ForkJoinTask<?> t = getLocalOrStolenTask();
722	<	if (t == null)
723	<	return false;
724	<	t.quietlyExec();
725	<	return true;
726	<	}
727	<
728	<	/**
729	<	* Runs tasks until pool isQuiescent
730	<	*/
731	<	final void helpQuiescePool() {
732	<	activate();
733	<	for (;;) {
734	<	if (!runLocalOrStolenTask()) {
735	<	inactivate();
736	<	if (pool.isQuiescent()) {
737	<	activate(); // re-activate on exit
738	<	break;
739	<	}
740	<	}
741	<	}
694	>	int n = sp - base;
695	>	return n < 0? 0 : n; // suppress momentarily negative values
696		}
697
698		/**
#	Line 746 | Line 700 | public class ForkJoinWorkerThread extend
700		* function of number of idle workers.
701		*/
702		final int getEstimatedSurplusTaskCount() {
703	+	// The halving approximates weighting idle vs non-idle workers
704		return (sp - base) - (pool.getIdleThreadCount() >>> 1);
705		}
706
752	–	// Public methods on current thread
753	–
707		/**
708	<	* Returns the pool hosting the current task execution.
756	<	* @return the pool
708	>	* Scans, returning early if joinMe done
709		*/
710	<	public static ForkJoinPool getPool() {
711	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pool;
712	<	}
713	<
714	<	/**
715	<	* Returns the index number of the current worker thread in its
716	<	* 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.
770	<	*/
771	<	public static int getPoolIndex() {
772	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex;
773	<	}
774	<
775	<	/**
776	<	* Returns an estimate of the number of tasks waiting to be run by
777	<	* the current worker thread. This value may be useful for
778	<	* heuristic decisions about whether to fork other tasks.
779	<	* @return the number of tasks
780	<	*/
781	<	public static int getLocalQueueSize() {
782	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
783	<	getQueueSize();
784	<	}
785	<
786	<	/**
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	<	}
796	<
797	<	/**
798	<	* 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
801	<	*/
802	<	public static ForkJoinTask<?> pollLocalTask() {
803	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).popTask();
804	<	}
805	<
806	<	/**
807	<	* Execute the next task locally queued by the current worker, if
808	<	* one is available.
809	<	* @return true if a task was run; a false return indicates
810	<	* that no task was available.
811	<	*/
812	<	public static boolean executeLocalTask() {
813	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
814	<	runLocalTask();
815	<	}
816	<
817	<	/**
818	<	* 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
824	<	*/
825	<	public static ForkJoinTask<?> pollTask() {
826	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
827	<	getLocalOrStolenTask();
710	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
711	>	ForkJoinTask<?> t = pollTask();
712	>	if (t != null && joinMe.status < 0 && sp == base) {
713	>	pushTask(t); // unsteal if done and this task would be stealable
714	>	t = null;
715	>	}
716	>	return t;
717		}
718
719		/**
720	<	* 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.
720	>	* Runs tasks until pool isQuiescent.
721		*/
722	<	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	<
722	>	final void helpQuiescePool() {
723		for (;;) {
724	<	int val = bits % n;
725	<	if (bits - val + (n-1) >= 0)
726	<	return val;
727	<	bits = nextJURandom(31);
724	>	ForkJoinTask<?> t = pollTask();
725	>	if (t != null)
726	>	t.quietlyExec();
727	>	else if (tryInactivate() && pool.isQuiescent())
728	>	break;
729		}
730	+	do;while (!tryActivate()); // re-activate on exit
731		}
732
733	<	private final long nextJURandomLong() {
734	<	return ((long)(nextJURandom(32)) << 32) + nextJURandom(32);
735	<	}
736	<
737	<	private final long nextJURandomLong(long n) {
738	<	if (n <= 0)
739	<	throw new IllegalArgumentException("n must be positive");
740	<	long offset = 0;
741	<	while (n >= Integer.MAX_VALUE) { // randomly pick half range
742	<	int bits = nextJURandom(2); // 2nd bit for odd vs even split
743	<	long half = n >>> 1;
744	<	long nextn = ((bits & 2) == 0)? half : n - half;
745	<	if ((bits & 1) == 0)
746	<	offset += n - nextn;
892	<	n = nextn;
733	>	// Temporary Unsafe mechanics for preliminary release
734	>	private static Unsafe getUnsafe() throws Throwable {
735	>	try {
736	>	return Unsafe.getUnsafe();
737	>	} catch (SecurityException se) {
738	>	try {
739	>	return java.security.AccessController.doPrivileged
740	>	(new java.security.PrivilegedExceptionAction<Unsafe>() {
741	>	public Unsafe run() throws Exception {
742	>	return getUnsafePrivileged();
743	>	}});
744	>	} catch (java.security.PrivilegedActionException e) {
745	>	throw e.getCause();
746	>	}
747		}
894	–	return offset + nextJURandomInt((int)n);
748		}
749
750	<	private final double nextJURandomDouble() {
751	<	return (((long)(nextJURandom(26)) << 27) + nextJURandom(27))
752	<	/ (double)(1L << 53);
750	>	private static Unsafe getUnsafePrivileged()
751	>	throws NoSuchFieldException, IllegalAccessException {
752	>	Field f = Unsafe.class.getDeclaredField("theUnsafe");
753	>	f.setAccessible(true);
754	>	return (Unsafe) f.get(null);
755		}
756
757	<	/**
758	<	* Returns a random integer using a per-worker random
759	<	* number generator with the same properties as
760	<	* {@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);
757	>	private static long fieldOffset(String fieldName)
758	>	throws NoSuchFieldException {
759	>	return UNSAFE.objectFieldOffset
760	>	(ForkJoinWorkerThread.class.getDeclaredField(fieldName));
761		}
762
763	<	/**
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	<
973	<	static final Unsafe _unsafe;
763	>	static final Unsafe UNSAFE;
764		static final long baseOffset;
765		static final long spOffset;
766	+	static final long runStateOffset;
767		static final long qBase;
768		static final int qShift;
978	–	static final long runStateOffset;
769		static {
770		try {
771	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
772	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
773	<	f.setAccessible(true);
774	<	_unsafe = (Unsafe)f.get(null);
775	<	}
776	<	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"));
994	<	qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class);
995	<	int s = _unsafe.arrayIndexScale(ForkJoinTask[].class);
771	>	UNSAFE = getUnsafe();
772	>	baseOffset = fieldOffset("base");
773	>	spOffset = fieldOffset("sp");
774	>	runStateOffset = fieldOffset("runState");
775	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
776	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
777		if ((s & (s-1)) != 0)
778		throw new Error("data type scale not a power of two");
779		qShift = 31 - Integer.numberOfLeadingZeros(s);
780	<	} catch (Exception e) {
780	>	} catch (Throwable e) {
781		throw new RuntimeException("Could not initialize intrinsics", e);
782		}
783		}

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