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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.2 by dl, Wed Jan 7 16:07:37 2009 UTC vs.
Revision 1.21 by jsr166, Mon Jul 27 20:57:44 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
8	>
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.atomic.*;
11	<	import java.util.concurrent.locks.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
10	>
11	>	import java.util.Collection;
12
13		/**
14		* A thread managed by a {@link ForkJoinPool}.  This class is
15		* subclassable solely for the sake of adding functionality -- there
16		* are no overridable methods dealing with scheduling or
17		* execution. However, you can override initialization and termination
18	<	* cleanup methods surrounding the main task processing loop.  If you
19	<	* do create such a subclass, you will also need to supply a custom
18	>	* methods surrounding the main task processing loop.  If you do
19	>	* create such a subclass, you will also need to supply a custom
20		* ForkJoinWorkerThreadFactory to use it in a ForkJoinPool.
21	<	*
22	<	* <p>This class also provides methods for generating per-thread
23	<	* random numbers, with the same properties as {@link
26	<	* java.util.Random} but with each generator isolated from those of
27	<	* other threads.
21	>	*
22	>	* @since 1.7
23	>	* @author Doug Lea
24		*/
25		public class ForkJoinWorkerThread extends Thread {
26		/*
#	Line 48 | 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 60 | 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 79 | 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 134 | Line 130 | public class ForkJoinWorkerThread extend
130
131		/**
132		* Maximum work-stealing queue array size.  Must be less than or
133	<	* equal to 1 << 30 to ensure lack of index wraparound.
133	>	* equal to 1 << 28 to ensure lack of index wraparound. (This
134	>	* is less than usual bounds, because we need leftshift by 3
135	>	* to be in int range).
136		*/
137	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30;
137	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
138
139		/**
140	<	* Generator of seeds for per-thread random numbers.
140	>	* The pool this thread works in. Accessed directly by ForkJoinTask.
141		*/
142	<	private static final Random randomSeedGenerator = new Random();
142	>	final ForkJoinPool pool;
143
144		/**
145		* The work-stealing queue array. Size must be a power of two.
146	+	* Initialized when thread starts, to improve memory locality.
147		*/
148		private ForkJoinTask<?>[] queue;
149
#	Line 163 | Line 162 | public class ForkJoinWorkerThread extend
162		private volatile int base;
163
164		/**
165	<	* The pool this thread works in.
166	<	*/
167	<	final ForkJoinPool pool;
168	<
170	<	/**
171	<	* Index of this worker in pool array. Set once by pool before
172	<	* running, and accessed directly by pool during cleanup etc
165	>	* Activity status. When true, this worker is considered active.
166	>	* Must be false upon construction. It must be true when executing
167	>	* tasks, and BEFORE stealing a task. It must be false before
168	>	* calling pool.sync.
169		*/
170	<	int poolIndex;
170	>	private boolean active;
171
172		/**
173		* Run state of this worker. Supports simple versions of the usual
#	Line 179 | Line 175 | public class ForkJoinWorkerThread extend
175		*/
176		private volatile int runState;
177
182	–	// Runstate values. Order matters
183	–	private static final int RUNNING     = 0;
184	–	private static final int SHUTDOWN    = 1;
185	–	private static final int TERMINATING = 2;
186	–	private static final int TERMINATED  = 3;
187	–
178		/**
179	<	* Activity status. When true, this worker is considered active.
180	<	* Must be false upon construction. It must be true when executing
191	<	* tasks, and BEFORE stealing a task. It must be false before
192	<	* blocking on the Pool Barrier.
179	>	* Seed for random number generator for choosing steal victims.
180	>	* Uses Marsaglia xorshift. Must be nonzero upon initialization.
181		*/
182	<	private boolean active;
182	>	private int seed;
183
184		/**
185		* Number of steals, transferred to pool when idle
#	Line 199 | Line 187 | public class ForkJoinWorkerThread extend
187		private int stealCount;
188
189		/**
190	<	* Seed for random number generator for choosing steal victims
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	<	// public access methods
219	>	// Public access methods
220
221		/**
222	<	* Returns the pool hosting the current task execution.
222	>	* Returns the pool hosting this thread.
223	>	*
224		* @return the pool
225		*/
226	<	public static ForkJoinPool getPool() {
227	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pool;
226	>	public ForkJoinPool getPool() {
227	>	return pool;
228		}
229
230		/**
231	<	* Returns the index number of the current worker thread in its
232	<	* pool.  The returned value ranges from zero to the maximum
233	<	* number of threads (minus one) that have ever been created in
234	<	* the pool.  This method may be useful for applications that
235	<	* track status or collect results on a per-worker basis.
236	<	* @return the index number.
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	>	public int getPoolIndex() {
240	>	return poolIndex;
241	>	}
242	>
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	<	public static int getPoolIndex() {
250	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex;
249	>	void setAsyncMode(boolean async) {
250	>	locallyFifo = async;
251		}
252
253	<	//  Access methods used by Pool
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	<	* Get and clear steal count for accumulation by pool.  Called
269	<	* only when known to be idle (in pool.sync and termination).
268	>	* Transitions to at least the given state.
269	>	*
270	>	* @return {@code true} if not already at least at given state
271		*/
272	<	final int getAndClearStealCount() {
273	<	int sc = stealCount;
274	<	stealCount = 0;
275	<	return sc;
272	>	private boolean transitionRunStateTo(int state) {
273	>	for (;;) {
274	>	int s = runState;
275	>	if (s >= state)
276	>	return false;
277	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
278	>	return true;
279	>	}
280		}
281
282		/**
283	<	* Returns estimate of the number of tasks in the queue, without
263	<	* correcting for transient negative values
283	>	* Tries to set status to active; fails on contention.
284		*/
285	<	final int getRawQueueSize() {
286	<	return sp - base;
285	>	private boolean tryActivate() {
286	>	if (!active) {
287	>	if (!pool.tryIncrementActiveCount())
288	>	return false;
289	>	active = true;
290	>	}
291	>	return true;
292		}
293
294	<	// Intrinsics-based support for queue operations.
295	<	// Currently these three (setSp, setSlot, casSlotNull) are
296	<	// usually manually inlined to improve performance
294	>	/**
295	>	* Tries to set status to inactive; fails on contention.
296	>	*/
297	>	private boolean tryInactivate() {
298	>	if (active) {
299	>	if (!pool.tryDecrementActiveCount())
300	>	return false;
301	>	active = false;
302	>	}
303	>	return true;
304	>	}
305
306		/**
307	<	* Sets sp in store-order.
307	>	* Computes next value for random victim probe.  Scans don't
308	>	* require a very high quality generator, but also not a crummy
309	>	* one.  Marsaglia xor-shift is cheap and works well.
310	>	*/
311	>	private static int xorShift(int r) {
312	>	r ^= r << 1;
313	>	r ^= r >>> 3;
314	>	r ^= r << 10;
315	>	return r;
316	>	}
317	>
318	>	// Lifecycle methods
319	>
320	>	/**
321	>	* This method is required to be public, but should never be
322	>	* called explicitly. It performs the main run loop to execute
323	>	* ForkJoinTasks.
324		*/
325	<	private void setSp(int s) {
326	<	_unsafe.putOrderedInt(this, spOffset, s);
325	>	public void run() {
326	>	Throwable exception = null;
327	>	try {
328	>	onStart();
329	>	pool.sync(this); // await first pool event
330	>	mainLoop();
331	>	} catch (Throwable ex) {
332	>	exception = ex;
333	>	} finally {
334	>	onTermination(exception);
335	>	}
336	>	}
337	>
338	>	/**
339	>	* Executes tasks until shut down.
340	>	*/
341	>	private void mainLoop() {
342	>	while (!isShutdown()) {
343	>	ForkJoinTask<?> t = pollTask();
344	>	if (t != null || (t = pollSubmission()) != null)
345	>	t.quietlyExec();
346	>	else if (tryInactivate())
347	>	pool.sync(this);
348	>	}
349	>	}
350	>
351	>	/**
352	>	* Initializes internal state after construction but before
353	>	* processing any tasks. If you override this method, you must
354	>	* invoke super.onStart() at the beginning of the method.
355	>	* Initialization requires care: Most fields must have legal
356	>	* default values, to ensure that attempted accesses from other
357	>	* threads work correctly even before this thread starts
358	>	* processing tasks.
359	>	*/
360	>	protected void onStart() {
361	>	// Allocate while starting to improve chances of thread-local
362	>	// isolation
363	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
364	>	// Initial value of seed need not be especially random but
365	>	// should differ across workers and must be nonzero
366	>	int p = poolIndex + 1;
367	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
368		}
369
370		/**
371	<	* Add in store-order the given task at given slot of q to
372	<	* null. Caller must ensure q is nonnull and index is in range.
371	>	* Performs cleanup associated with termination of this worker
372	>	* thread.  If you override this method, you must invoke
373	>	* {@code super.onTermination} at the end of the overridden method.
374	>	*
375	>	* @param exception the exception causing this thread to abort due
376	>	* to an unrecoverable error, or {@code null} if completed normally
377	>	*/
378	>	protected void onTermination(Throwable exception) {
379	>	// Execute remaining local tasks unless aborting or terminating
380	>	while (exception == null &&  !pool.isTerminating() && base != sp) {
381	>	try {
382	>	ForkJoinTask<?> t = popTask();
383	>	if (t != null)
384	>	t.quietlyExec();
385	>	} catch (Throwable ex) {
386	>	exception = ex;
387	>	}
388	>	}
389	>	// Cancel other tasks, transition status, notify pool, and
390	>	// propagate exception to uncaught exception handler
391	>	try {
392	>	do {} while (!tryInactivate()); // ensure inactive
393	>	cancelTasks();
394	>	runState = TERMINATED;
395	>	pool.workerTerminated(this);
396	>	} catch (Throwable ex) {        // Shouldn't ever happen
397	>	if (exception == null)      // but if so, at least rethrown
398	>	exception = ex;
399	>	} finally {
400	>	if (exception != null)
401	>	ForkJoinTask.rethrowException(exception);
402	>	}
403	>	}
404	>
405	>	// Intrinsics-based support for queue operations.
406	>
407	>	/**
408	>	* Adds in store-order the given task at given slot of q to null.
409	>	* Caller must ensure q is non-null and index is in range.
410		*/
411		private static void setSlot(ForkJoinTask<?>[] q, int i,
412	<	ForkJoinTask<?> t){
413	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
412	>	ForkJoinTask<?> t) {
413	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
414		}
415
416		/**
417	<	* CAS given slot of q to null. Caller must ensure q is nonnull
417	>	* CAS given slot of q to null. Caller must ensure q is non-null
418		* and index is in range.
419		*/
420		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
421		ForkJoinTask<?> t) {
422	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
422	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
423	>	}
424	>
425	>	/**
426	>	* Sets sp in store-order.
427	>	*/
428	>	private void storeSp(int s) {
429	>	UNSAFE.putOrderedInt(this, spOffset, s);
430		}
431
432		// Main queue methods
433
434		/**
435		* Pushes a task. Called only by current thread.
436	<	* @param t the task. Caller must ensure nonnull
436	>	*
437	>	* @param t the task. Caller must ensure non-null.
438		*/
439		final void pushTask(ForkJoinTask<?> t) {
440		ForkJoinTask<?>[] q = queue;
441		int mask = q.length - 1;
442		int s = sp;
443	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
444	<	_unsafe.putOrderedInt(this, spOffset, ++s);
443	>	setSlot(q, s & mask, t);
444	>	storeSp(++s);
445		if ((s -= base) == 1)
446	<	pool.signalNonEmptyWorkerQueue();
446	>	pool.signalWork();
447		else if (s >= mask)
448		growQueue();
449		}
#	Line 316 | Line 451 | public class ForkJoinWorkerThread extend
451		/**
452		* Tries to take a task from the base of the queue, failing if
453		* either empty or contended.
454	<	* @return a task, or null if none or contended.
454	>	*
455	>	* @return a task, or null if none or contended
456		*/
457	<	private ForkJoinTask<?> deqTask() {
322	<	ForkJoinTask<?>[] q;
457	>	final ForkJoinTask<?> deqTask() {
458		ForkJoinTask<?> t;
459	+	ForkJoinTask<?>[] q;
460		int i;
461		int b;
462		if (sp != (b = base) &&
463		(q = queue) != null && // must read q after b
464		(t = q[i = (q.length - 1) & b]) != null &&
465	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
465	>	casSlotNull(q, i, t)) {
466		base = b + 1;
467		return t;
468		}
#	Line 334 | Line 470 | public class ForkJoinWorkerThread extend
470		}
471
472		/**
473	<	* Returns a popped task, or null if empty.  Called only by
474	<	* current thread.
473	>	* Returns a popped task, or null if empty. Ensures active status
474	>	* if non-null. Called only by current thread.
475		*/
476		final ForkJoinTask<?> popTask() {
341	–	ForkJoinTask<?> t;
342	–	int i;
343	–	ForkJoinTask<?>[] q = queue;
344	–	int mask = q.length - 1;
477		int s = sp;
478	<	if (s != base &&
479	<	(t = q[i = (s - 1) & mask]) != null &&
480	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
481	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
482	<	return t;
478	>	while (s != base) {
479	>	if (tryActivate()) {
480	>	ForkJoinTask<?>[] q = queue;
481	>	int mask = q.length - 1;
482	>	int i = (s - 1) & mask;
483	>	ForkJoinTask<?> t = q[i];
484	>	if (t == null || !casSlotNull(q, i, t))
485	>	break;
486	>	storeSp(s - 1);
487	>	return t;
488	>	}
489		}
490		return null;
491		}
#	Line 355 | Line 493 | public class ForkJoinWorkerThread extend
493		/**
494		* Specialized version of popTask to pop only if
495		* topmost element is the given task. Called only
496	<	* by current thread.
497	<	* @param t the task. Caller must ensure nonnull
496	>	* by current thread while active.
497	>	*
498	>	* @param t the task. Caller must ensure non-null.
499		*/
500		final boolean unpushTask(ForkJoinTask<?> t) {
501		ForkJoinTask<?>[] q = queue;
502		int mask = q.length - 1;
503		int s = sp - 1;
504	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
505	<	t, null)) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
504	>	if (casSlotNull(q, s & mask, t)) {
505	>	storeSp(s);
506		return true;
507		}
508		return false;
509		}
510
511		/**
512	<	* Returns next task to pop.
512	>	* Returns next task.
513		*/
514		final ForkJoinTask<?> peekTask() {
515		ForkJoinTask<?>[] q = queue;
516	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
516	>	if (q == null)
517	>	return null;
518	>	int mask = q.length - 1;
519	>	int i = locallyFifo ? base : (sp - 1);
520	>	return q[i & mask];
521		}
522
523		/**
#	Line 402 | Line 544 | public class ForkJoinWorkerThread extend
544		t = null;
545		setSlot(newQ, b & newMask, t);
546		} while (++b != bf);
547	<	pool.signalIdleWorkers(false);
547	>	pool.signalWork();
548		}
549
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	–
550		/**
551	<	* Transition to at least the given state. Return true if not
552	<	* already at least given state.
553	<	*/
554	<	private boolean transitionRunStateTo(int state) {
555	<	for (;;) {
556	<	int s = runState;
557	<	if (s >= state)
558	<	return false;
559	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
560	<	return true;
561	<	}
562	<	}
563	<
564	<	/**
565	<	* Ensure status is active and if necessary adjust pool active count
566	<	*/
433	<	final void activate() {
434	<	if (!active) {
435	<	active = true;
436	<	pool.incrementActiveCount();
437	<	}
438	<	}
439	<
440	<	/**
441	<	* Ensure status is inactive and if necessary adjust pool active count
551	>	* Tries to steal a task from another worker. Starts at a random
552	>	* index of workers array, and probes workers until finding one
553	>	* with non-empty queue or finding that all are empty.  It
554	>	* randomly selects the first n probes. If these are empty, it
555	>	* resorts to a full circular traversal, which is necessary to
556	>	* accurately set active status by caller. Also restarts if pool
557	>	* events occurred since last scan, which forces refresh of
558	>	* workers array, in case barrier was associated with resize.
559	>	*
560	>	* This method must be both fast and quiet -- usually avoiding
561	>	* memory accesses that could disrupt cache sharing etc other than
562	>	* those needed to check for and take tasks. This accounts for,
563	>	* among other things, updating random seed in place without
564	>	* storing it until exit.
565	>	*
566	>	* @return a task, or null if none found
567		*/
568	<	final void inactivate() {
569	<	if (active) {
570	<	active = false;
571	<	pool.decrementActiveCount();
572	<	}
568	>	private ForkJoinTask<?> scan() {
569	>	ForkJoinTask<?> t = null;
570	>	int r = seed;                    // extract once to keep scan quiet
571	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
572	>	int mask;                        // must be power 2 minus 1 and > 0
573	>	outer:do {
574	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
575	>	int idx = r;
576	>	int probes = ~mask;      // use random index while negative
577	>	for (;;) {
578	>	r = xorShift(r);     // update random seed
579	>	ForkJoinWorkerThread v = ws[mask & idx];
580	>	if (v == null || v.sp == v.base) {
581	>	if (probes <= mask)
582	>	idx = (probes++ < 0) ? r : (idx + 1);
583	>	else
584	>	break;
585	>	}
586	>	else if (!tryActivate() || (t = v.deqTask()) == null)
587	>	continue outer;  // restart on contention
588	>	else
589	>	break outer;
590	>	}
591	>	}
592	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
593	>	seed = r;
594	>	return t;
595		}
596
450	–	// Lifecycle methods
451	–
597		/**
598	<	* Initializes internal state after construction but before
599	<	* processing any tasks. If you override this method, you must
600	<	* 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.
598	>	* Gets and removes a local or stolen task.
599	>	*
600	>	* @return a task, if available
601		*/
602	<	protected void onStart() {
603	<	juRandomSeed = randomSeedGenerator.nextLong();
604	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
605	<	if (queue == null)
606	<	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	<	}
602	>	final ForkJoinTask<?> pollTask() {
603	>	ForkJoinTask<?> t = locallyFifo ? deqTask() : popTask();
604	>	if (t == null && (t = scan()) != null)
605	>	++stealCount;
606	>	return t;
607		}
608
609		/**
610	<	* 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.
610	>	* Gets a local task.
611		*
612	<	* @param exception the exception causing this thread to abort due
480	<	* to an unrecoverable error, or null if completed normally.
612	>	* @return a task, if available
613		*/
614	<	protected void onTermination(Throwable exception) {
615	<	try {
484	<	clearLocalTasks();
485	<	inactivate();
486	<	cancelTasks();
487	<	} finally {
488	<	terminate(exception);
489	<	}
614	>	final ForkJoinTask<?> pollLocalTask() {
615	>	return locallyFifo ? deqTask() : popTask();
616		}
617
618		/**
619	<	* Notify pool of termination and, if exception is nonnull,
620	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
619	>	* Returns a pool submission, if one exists, activating first.
620	>	*
621	>	* @return a submission, if available
622		*/
623	<	private void terminate(Throwable exception) {
624	<	transitionRunStateTo(TERMINATED);
625	<	try {
626	<	pool.workerTerminated(this);
627	<	} finally {
628	<	if (exception != null)
502	<	ForkJoinTask.rethrowException(exception);
623	>	private ForkJoinTask<?> pollSubmission() {
624	>	ForkJoinPool p = pool;
625	>	while (p.hasQueuedSubmissions()) {
626	>	ForkJoinTask<?> t;
627	>	if (tryActivate() && (t = p.pollSubmission()) != null)
628	>	return t;
629		}
630	+	return null;
631		}
632
633	<	/**
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	<	}
633	>	// Methods accessed only by Pool
634
635		/**
636		* Removes and cancels all tasks in queue.  Can be called from any
637		* thread.
638		*/
639		final void cancelTasks() {
640	<	while (base != sp) {
641	<	ForkJoinTask<?> t = deqTask();
642	<	if (t != null)
527	<	t.cancelIgnoreExceptions();
528	<	}
529	<	}
530	<
531	<	/**
532	<	* This method is required to be public, but should never be
533	<	* called explicitly. It performs the main run loop to execute
534	<	* ForkJoinTasks.
535	<	*/
536	<	public void run() {
537	<	Throwable exception = null;
538	<	try {
539	<	onStart();
540	<	while (!isShutdown())
541	<	step();
542	<	} catch (Throwable ex) {
543	<	exception = ex;
544	<	} finally {
545	<	onTermination(exception);
546	<	}
640	>	ForkJoinTask<?> t;
641	>	while (base != sp && (t = deqTask()) != null)
642	>	t.cancelIgnoringExceptions();
643		}
644
645		/**
646	<	* Main top-level action.
646	>	* Drains tasks to given collection c.
647	>	*
648	>	* @return the number of tasks drained
649		*/
650	<	private void step() {
651	<	ForkJoinTask<?> t = sp != base? popTask() : null;
652	<	if (t != null || (t = scan(null, true)) != null) {
653	<	activate();
654	<	t.quietlyExec();
655	<	}
558	<	else {
559	<	inactivate();
560	<	eventCount = pool.sync(this, eventCount);
650	>	final int drainTasksTo(Collection<ForkJoinTask<?>> c) {
651	>	int n = 0;
652	>	ForkJoinTask<?> t;
653	>	while (base != sp && (t = deqTask()) != null) {
654	>	c.add(t);
655	>	++n;
656		}
657	+	return n;
658		}
659
564	–	// scanning for and stealing tasks
565	–
660		/**
661	<	* Computes next value for random victim probe. Scans don't
662	<	* require a very high quality generator, but also not a crummy
569	<	* one. Marsaglia xor-shift is cheap and works well.
570	<	*
571	<	* This is currently unused, and manually inlined
661	>	* Gets and clears steal count for accumulation by pool.  Called
662	>	* only when known to be idle (in pool.sync and termination).
663		*/
664	<	private static int xorShift(int r) {
665	<	r ^= r << 1;
666	<	r ^= r >>> 3;
667	<	r ^= r << 10;
577	<	return r;
664	>	final int getAndClearStealCount() {
665	>	int sc = stealCount;
666	>	stealCount = 0;
667	>	return sc;
668		}
669
670		/**
671	<	* Tries to steal a task from another worker and/or, if enabled,
672	<	* 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.
671	>	* Returns {@code true} if at least one worker in the given array
672	>	* appears to have at least one queued task.
673		*
674	<	* 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
674	>	* @param ws array of workers
675		*/
676	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
677	<	boolean checkSubmissions) {
678	<	ForkJoinPool p = pool;
679	<	if (p == null)                    // Never null, but avoids
680	<	return null;                  //   implicit nullchecks below
681	<	int r = randomVictimSeed;         // extract once to keep scan quiet
682	<	restart:                          // outer loop refreshes ws array
683	<	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;
676	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
677	>	if (ws != null) {
678	>	int len = ws.length;
679	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
680	>	for (int i = 0; i < len; ++i) {
681	>	ForkJoinWorkerThread w = ws[i];
682	>	if (w != null && w.sp != w.base)
683	>	return true;
684		}
685		}
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	–	}
686		}
687	<	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;
666	<	}
667	<	}
668	<
669	<	// Support for ForkJoinTask methods
670	<
671	<	/**
672	<	* Implements ForkJoinTask.helpJoin
673	<	*/
674	<	final int helpJoinTask(ForkJoinTask<?> joinMe) {
675	<	ForkJoinTask<?> t = null;
676	<	int s;
677	<	while ((s = joinMe.status) >= 0) {
678	<	if (t == null) {
679	<	if ((t = scan(joinMe, false)) == null)  // block if no work
680	<	return joinMe.awaitDone(this, false);
681	<	// else recheck status before exec
682	<	}
683	<	else {
684	<	t.quietlyExec();
685	<	t = null;
686	<	}
687	<	}
688	<	if (t != null) // unsteal
689	<	pushTask(t);
690	<	return s;
691	<	}
692	<
693	<	/**
694	<	* Pops or steals a task
695	<	* @return task, or null if none available
696	<	*/
697	<	final ForkJoinTask<?> getLocalOrStolenTask() {
698	<	ForkJoinTask<?> t = popTask();
699	<	return t != null? t : scan(null, false);
687	>	return false;
688		}
689
690	<	/**
703	<	* Runs tasks until pool isQuiescent
704	<	*/
705	<	final void helpQuiescePool() {
706	<	for (;;) {
707	<	ForkJoinTask<?> t = getLocalOrStolenTask();
708	<	if (t != null) {
709	<	activate();
710	<	t.quietlyExec();
711	<	}
712	<	else {
713	<	inactivate();
714	<	if (pool.isQuiescent()) {
715	<	activate(); // re-activate on exit
716	<	break;
717	<	}
718	<	}
719	<	}
720	<	}
690	>	// Support methods for ForkJoinTask
691
692		/**
693		* Returns an estimate of the number of tasks in the queue.
694		*/
695		final int getQueueSize() {
696	<	int b = base;
697	<	int n = sp - b;
728	<	return n <= 0? 0 : n; // suppress momentarily negative values
696	>	// suppress momentarily negative values
697	>	return Math.max(0, sp - base);
698		}
699
700		/**
#	Line 733 | Line 702 | public class ForkJoinWorkerThread extend
702		* function of number of idle workers.
703		*/
704		final int getEstimatedSurplusTaskCount() {
705	+	// The halving approximates weighting idle vs non-idle workers
706		return (sp - base) - (pool.getIdleThreadCount() >>> 1);
707		}
708
739	–	// Per-worker exported random numbers
740	–
741	–	// Same constants as java.util.Random
742	–	final static long JURandomMultiplier = 0x5DEECE66DL;
743	–	final static long JURandomAddend = 0xBL;
744	–	final static long JURandomMask = (1L << 48) - 1;
745	–
746	–	private final int nextJURandom(int bits) {
747	–	long next = (juRandomSeed * JURandomMultiplier + JURandomAddend) &
748	–	JURandomMask;
749	–	juRandomSeed = next;
750	–	return (int)(next >>> (48 - bits));
751	–	}
752	–
753	–	private final int nextJURandomInt(int n) {
754	–	if (n <= 0)
755	–	throw new IllegalArgumentException("n must be positive");
756	–	int bits = nextJURandom(31);
757	–	if ((n & -n) == n)
758	–	return (int)((n * (long)bits) >> 31);
759	–
760	–	for (;;) {
761	–	int val = bits % n;
762	–	if (bits - val + (n-1) >= 0)
763	–	return val;
764	–	bits = nextJURandom(31);
765	–	}
766	–	}
767	–
768	–	private final long nextJURandomLong() {
769	–	return ((long)(nextJURandom(32)) << 32) + nextJURandom(32);
770	–	}
771	–
772	–	private final long nextJURandomLong(long n) {
773	–	if (n <= 0)
774	–	throw new IllegalArgumentException("n must be positive");
775	–	long offset = 0;
776	–	while (n >= Integer.MAX_VALUE) { // randomly pick half range
777	–	int bits = nextJURandom(2); // 2nd bit for odd vs even split
778	–	long half = n >>> 1;
779	–	long nextn = ((bits & 2) == 0)? half : n - half;
780	–	if ((bits & 1) == 0)
781	–	offset += n - nextn;
782	–	n = nextn;
783	–	}
784	–	return offset + nextJURandomInt((int)n);
785	–	}
786	–
787	–	private final double nextJURandomDouble() {
788	–	return (((long)(nextJURandom(26)) << 27) + nextJURandom(27))
789	–	/ (double)(1L << 53);
790	–	}
791	–
709		/**
710	<	* Returns a random integer using a per-worker random
794	<	* number generator with the same properties as
795	<	* {@link java.util.Random#nextInt}
796	<	* @return the next pseudorandom, uniformly distributed {@code int}
797	<	*         value from this worker's random number generator's sequence
710	>	* Scans, returning early if joinMe done.
711		*/
712	<	public static int nextRandomInt() {
713	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
714	<	nextJURandom(32);
712	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
713	>	ForkJoinTask<?> t = pollTask();
714	>	if (t != null && joinMe.status < 0 && sp == base) {
715	>	pushTask(t); // unsteal if done and this task would be stealable
716	>	t = null;
717	>	}
718	>	return t;
719		}
720
721		/**
722	<	* Returns a random integer using a per-worker random
806	<	* number generator with the same properties as
807	<	* {@link java.util.Random#nextInt(int)}
808	<	* @param n the bound on the random number to be returned.  Must be
809	<	*        positive.
810	<	* @return the next pseudorandom, uniformly distributed {@code int}
811	<	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
812	<	*         from this worker's random number generator's sequence
813	<	* @throws IllegalArgumentException if n is not positive
722	>	* Runs tasks until {@code pool.isQuiescent()}.
723		*/
724	<	public static int nextRandomInt(int n) {
725	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
726	<	nextJURandomInt(n);
724	>	final void helpQuiescePool() {
725	>	for (;;) {
726	>	ForkJoinTask<?> t = pollTask();
727	>	if (t != null)
728	>	t.quietlyExec();
729	>	else if (tryInactivate() && pool.isQuiescent())
730	>	break;
731	>	}
732	>	do {} while (!tryActivate()); // re-activate on exit
733		}
734
735	<	/**
736	<	* Returns a random long using a per-worker random
737	<	* number generator with the same properties as
738	<	* {@link java.util.Random#nextLong}
739	<	* @return the next pseudorandom, uniformly distributed {@code long}
740	<	*         value from this worker's random number generator's sequence
741	<	*/
742	<	public static long nextRandomLong() {
743	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
744	<	nextJURandomLong();
735	>	// Unsafe mechanics
736	>
737	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
738	>	private static final long spOffset =
739	>	objectFieldOffset("sp", ForkJoinWorkerThread.class);
740	>	private static final long runStateOffset =
741	>	objectFieldOffset("runState", ForkJoinWorkerThread.class);
742	>	private static final long qBase;
743	>	private static final int qShift;
744	>
745	>	static {
746	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
747	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
748	>	if ((s & (s-1)) != 0)
749	>	throw new Error("data type scale not a power of two");
750	>	qShift = 31 - Integer.numberOfLeadingZeros(s);
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
758	<	*        positive.
759	<	* @return the next pseudorandom, uniformly distributed {@code int}
760	<	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
761	<	*         from this worker's random number generator's sequence
841	<	* @throws IllegalArgumentException if n is not positive
842	<	*/
843	<	public static long nextRandomLong(long n) {
844	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
845	<	nextJURandomLong(n);
753	>	private static long objectFieldOffset(String field, Class<?> klazz) {
754	>	try {
755	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
756	>	} catch (NoSuchFieldException e) {
757	>	// Convert Exception to corresponding Error
758	>	NoSuchFieldError error = new NoSuchFieldError(field);
759	>	error.initCause(e);
760	>	throw error;
761	>	}
762		}
763
764		/**
765	<	* Returns a random double using a per-worker random
766	<	* number generator with the same properties as
767	<	* {@link java.util.Random#nextDouble}
768	<	* @return the next pseudorandom, uniformly distributed {@code double}
769	<	*         value between {@code 0.0} and {@code 1.0} from this
854	<	*         worker's random number generator's sequence
765	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
766	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
767	>	* into a jdk.
768	>	*
769	>	* @return a sun.misc.Unsafe
770		*/
771	<	public static double nextRandomDouble() {
857	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
858	<	nextJURandomDouble();
859	<	}
860	<
861	<	// Temporary Unsafe mechanics for preliminary release
862	<
863	<	static final Unsafe _unsafe;
864	<	static final long baseOffset;
865	<	static final long spOffset;
866	<	static final long qBase;
867	<	static final int qShift;
868	<	static final long runStateOffset;
869	<	static {
771	>	private static sun.misc.Unsafe getUnsafe() {
772		try {
773	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
774	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
775	<	f.setAccessible(true);
776	<	_unsafe = (Unsafe)f.get(null);
773	>	return sun.misc.Unsafe.getUnsafe();
774	>	} catch (SecurityException se) {
775	>	try {
776	>	return java.security.AccessController.doPrivileged
777	>	(new java.security
778	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
779	>	public sun.misc.Unsafe run() throws Exception {
780	>	java.lang.reflect.Field f = sun.misc
781	>	.Unsafe.class.getDeclaredField("theUnsafe");
782	>	f.setAccessible(true);
783	>	return (sun.misc.Unsafe) f.get(null);
784	>	}});
785	>	} catch (java.security.PrivilegedActionException e) {
786	>	throw new RuntimeException("Could not initialize intrinsics",
787	>	e.getCause());
788		}
876	–	else
877	–	_unsafe = Unsafe.getUnsafe();
878	–	baseOffset = _unsafe.objectFieldOffset
879	–	(ForkJoinWorkerThread.class.getDeclaredField("base"));
880	–	spOffset = _unsafe.objectFieldOffset
881	–	(ForkJoinWorkerThread.class.getDeclaredField("sp"));
882	–	runStateOffset = _unsafe.objectFieldOffset
883	–	(ForkJoinWorkerThread.class.getDeclaredField("runState"));
884	–	qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class);
885	–	int s = _unsafe.arrayIndexScale(ForkJoinTask[].class);
886	–	if ((s & (s-1)) != 0)
887	–	throw new Error("data type scale not a power of two");
888	–	qShift = 31 - Integer.numberOfLeadingZeros(s);
889	–	} catch (Exception e) {
890	–	throw new RuntimeException("Could not initialize intrinsics", e);
789		}
790		}
791		}

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