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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.4 by dl, Wed Jan 7 20:51:36 2009 UTC vs.
Revision 1.25 by jsr166, Sat Aug 1 21:17:11 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
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.
16	>	* are no overridable methods dealing with scheduling or execution.
17	>	* However, you can override initialization and termination methods
18	>	* surrounding the main task processing loop.  If you do create such a
19	>	* subclass, you will also need to supply a custom {@link
20	>	* ForkJoinWorkerThreadFactory} to use it in a {@code ForkJoinPool}.
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 69 | Line 65 | public class ForkJoinWorkerThread extend
65		* which gives threads a chance to activate if necessary before
66		* stealing (see below).
67		*
68	+	* This approach also enables support for "async mode" where local
69	+	* task processing is in FIFO, not LIFO order; simply by using a
70	+	* version of deq rather than pop when locallyFifo is true (as set
71	+	* by the ForkJoinPool).  This allows use in message-passing
72	+	* frameworks in which tasks are never joined.
73	+	*
74		* Efficient implementation of this approach currently relies on
75		* an uncomfortable amount of "Unsafe" mechanics. To maintain
76		* correct orderings, reads and writes of variable base require
#	Line 79 | Line 81 | public class ForkJoinWorkerThread extend
81		* push) require store order and CASes (in pop and deq) require
82		* (volatile) CAS semantics. Since these combinations aren't
83		* supported using ordinary volatiles, the only way to accomplish
84	<	* these effciently is to use direct Unsafe calls. (Using external
84	>	* these efficiently is to use direct Unsafe calls. (Using external
85		* AtomicIntegers and AtomicReferenceArrays for the indices and
86		* array is significantly slower because of memory locality and
87		* indirection effects.) Further, performance on most platforms is
#	Line 134 | Line 136 | public class ForkJoinWorkerThread extend
136
137		/**
138		* Maximum work-stealing queue array size.  Must be less than or
139	<	* equal to 1 << 30 to ensure lack of index wraparound.
139	>	* equal to 1 << 28 to ensure lack of index wraparound. (This
140	>	* is less than usual bounds, because we need leftshift by 3
141	>	* to be in int range).
142		*/
143	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30;
143	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
144
145		/**
146	<	* Generator of seeds for per-thread random numbers.
146	>	* The pool this thread works in. Accessed directly by ForkJoinTask.
147		*/
148	<	private static final Random randomSeedGenerator = new Random();
148	>	final ForkJoinPool pool;
149
150		/**
151		* The work-stealing queue array. Size must be a power of two.
152	+	* Initialized when thread starts, to improve memory locality.
153		*/
154		private ForkJoinTask<?>[] queue;
155
#	Line 163 | Line 168 | public class ForkJoinWorkerThread extend
168		private volatile int base;
169
170		/**
171	<	* The pool this thread works in.
172	<	*/
173	<	final ForkJoinPool pool;
174	<
170	<	/**
171	<	* Index of this worker in pool array. Set once by pool before
172	<	* running, and accessed directly by pool during cleanup etc
171	>	* Activity status. When true, this worker is considered active.
172	>	* Must be false upon construction. It must be true when executing
173	>	* tasks, and BEFORE stealing a task. It must be false before
174	>	* calling pool.sync.
175		*/
176	<	int poolIndex;
176	>	private boolean active;
177
178		/**
179		* Run state of this worker. Supports simple versions of the usual
#	Line 179 | Line 181 | public class ForkJoinWorkerThread extend
181		*/
182		private volatile int runState;
183
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	–
184		/**
185	<	* Activity status. When true, this worker is considered active.
186	<	* 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.
185	>	* Seed for random number generator for choosing steal victims.
186	>	* Uses Marsaglia xorshift. Must be nonzero upon initialization.
187		*/
188	<	private boolean active;
188	>	private int seed;
189
190		/**
191		* Number of steals, transferred to pool when idle
#	Line 199 | Line 193 | public class ForkJoinWorkerThread extend
193		private int stealCount;
194
195		/**
196	<	* Seed for random number generator for choosing steal victims
196	>	* Index of this worker in pool array. Set once by pool before
197	>	* running, and accessed directly by pool during cleanup etc.
198		*/
199	<	private int randomVictimSeed;
199	>	int poolIndex;
200
201		/**
202	<	* Seed for embedded Jurandom
202	>	* The last barrier event waited for. Accessed in pool callback
203	>	* methods, but only by current thread.
204		*/
205	<	private long juRandomSeed;
205	>	long lastEventCount;
206
207		/**
208	<	* The last barrier event waited for
208	>	* True if use local fifo, not default lifo, for local polling
209		*/
210	<	private long eventCount;
210	>	private boolean locallyFifo;
211
212		/**
213		* Creates a ForkJoinWorkerThread operating in the given pool.
214	+	*
215		* @param pool the pool this thread works in
216		* @throws NullPointerException if pool is null
217		*/
218		protected ForkJoinWorkerThread(ForkJoinPool pool) {
219		if (pool == null) throw new NullPointerException();
220		this.pool = pool;
221	<	// remaining initialization deferred to onStart
221	>	// Note: poolIndex is set by pool during construction
222	>	// Remaining initialization is deferred to onStart
223		}
224
225	<	// public access methods
225	>	// Public access methods
226
227		/**
228	<	* Returns the pool hosting this thread
228	>	* Returns the pool hosting this thread.
229	>	*
230		* @return the pool
231		*/
232		public ForkJoinPool getPool() {
#	Line 239 | Line 238 | public class ForkJoinWorkerThread extend
238		* returned value ranges from zero to the maximum number of
239		* threads (minus one) that have ever been created in the pool.
240		* This method may be useful for applications that track status or
241	<	* collect results on a per-worker basis.
242	<	* @return the index number.
241	>	* collect results per-worker rather than per-task.
242	>	*
243	>	* @return the index number
244		*/
245		public int getPoolIndex() {
246		return poolIndex;
247		}
248
249	<	//  Access methods used by Pool
249	>	/**
250	>	* Establishes local first-in-first-out scheduling mode for forked
251	>	* tasks that are never joined.
252	>	*
253	>	* @param async if true, use locally FIFO scheduling
254	>	*/
255	>	void setAsyncMode(boolean async) {
256	>	locallyFifo = async;
257	>	}
258	>
259	>	// Runstate management
260	>
261	>	// Runstate values. Order matters
262	>	private static final int RUNNING     = 0;
263	>	private static final int SHUTDOWN    = 1;
264	>	private static final int TERMINATING = 2;
265	>	private static final int TERMINATED  = 3;
266	>
267	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
268	>	final boolean isTerminating() { return runState >= TERMINATING;  }
269	>	final boolean isTerminated()  { return runState == TERMINATED; }
270	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
271	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
272
273		/**
274	<	* Get and clear steal count for accumulation by pool.  Called
275	<	* only when known to be idle (in pool.sync and termination).
274	>	* Transitions to at least the given state.
275	>	*
276	>	* @return {@code true} if not already at least at given state
277		*/
278	<	final int getAndClearStealCount() {
279	<	int sc = stealCount;
280	<	stealCount = 0;
281	<	return sc;
278	>	private boolean transitionRunStateTo(int state) {
279	>	for (;;) {
280	>	int s = runState;
281	>	if (s >= state)
282	>	return false;
283	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
284	>	return true;
285	>	}
286		}
287
288		/**
289	<	* Returns estimate of the number of tasks in the queue, without
263	<	* correcting for transient negative values
289	>	* Tries to set status to active; fails on contention.
290		*/
291	<	final int getRawQueueSize() {
292	<	return sp - base;
291	>	private boolean tryActivate() {
292	>	if (!active) {
293	>	if (!pool.tryIncrementActiveCount())
294	>	return false;
295	>	active = true;
296	>	}
297	>	return true;
298		}
299
300	<	// Intrinsics-based support for queue operations.
301	<	// Currently these three (setSp, setSlot, casSlotNull) are
302	<	// usually manually inlined to improve performance
300	>	/**
301	>	* Tries to set status to inactive; fails on contention.
302	>	*/
303	>	private boolean tryInactivate() {
304	>	if (active) {
305	>	if (!pool.tryDecrementActiveCount())
306	>	return false;
307	>	active = false;
308	>	}
309	>	return true;
310	>	}
311
312		/**
313	<	* Sets sp in store-order.
313	>	* Computes next value for random victim probe.  Scans don't
314	>	* require a very high quality generator, but also not a crummy
315	>	* one.  Marsaglia xor-shift is cheap and works well.
316	>	*/
317	>	private static int xorShift(int r) {
318	>	r ^= (r << 13);
319	>	r ^= (r >>> 17);
320	>	return r ^ (r << 5);
321	>	}
322	>
323	>	// Lifecycle methods
324	>
325	>	/**
326	>	* This method is required to be public, but should never be
327	>	* called explicitly. It performs the main run loop to execute
328	>	* ForkJoinTasks.
329	>	*/
330	>	public void run() {
331	>	Throwable exception = null;
332	>	try {
333	>	onStart();
334	>	pool.sync(this); // await first pool event
335	>	mainLoop();
336	>	} catch (Throwable ex) {
337	>	exception = ex;
338	>	} finally {
339	>	onTermination(exception);
340	>	}
341	>	}
342	>
343	>	/**
344	>	* Executes tasks until shut down.
345		*/
346	<	private void setSp(int s) {
347	<	_unsafe.putOrderedInt(this, spOffset, s);
346	>	private void mainLoop() {
347	>	while (!isShutdown()) {
348	>	ForkJoinTask<?> t = pollTask();
349	>	if (t != null || (t = pollSubmission()) != null)
350	>	t.quietlyExec();
351	>	else if (tryInactivate())
352	>	pool.sync(this);
353	>	}
354		}
355
356		/**
357	<	* Add in store-order the given task at given slot of q to
358	<	* null. Caller must ensure q is nonnull and index is in range.
357	>	* Initializes internal state after construction but before
358	>	* processing any tasks. If you override this method, you must
359	>	* invoke super.onStart() at the beginning of the method.
360	>	* Initialization requires care: Most fields must have legal
361	>	* default values, to ensure that attempted accesses from other
362	>	* threads work correctly even before this thread starts
363	>	* processing tasks.
364	>	*/
365	>	protected void onStart() {
366	>	// Allocate while starting to improve chances of thread-local
367	>	// isolation
368	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
369	>	// Initial value of seed need not be especially random but
370	>	// should differ across workers and must be nonzero
371	>	int p = poolIndex + 1;
372	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
373	>	}
374	>
375	>	/**
376	>	* Performs cleanup associated with termination of this worker
377	>	* thread.  If you override this method, you must invoke
378	>	* {@code super.onTermination} at the end of the overridden method.
379	>	*
380	>	* @param exception the exception causing this thread to abort due
381	>	* to an unrecoverable error, or {@code null} if completed normally
382	>	*/
383	>	protected void onTermination(Throwable exception) {
384	>	// Execute remaining local tasks unless aborting or terminating
385	>	while (exception == null &&  !pool.isTerminating() && base != sp) {
386	>	try {
387	>	ForkJoinTask<?> t = popTask();
388	>	if (t != null)
389	>	t.quietlyExec();
390	>	} catch (Throwable ex) {
391	>	exception = ex;
392	>	}
393	>	}
394	>	// Cancel other tasks, transition status, notify pool, and
395	>	// propagate exception to uncaught exception handler
396	>	try {
397	>	do {} while (!tryInactivate()); // ensure inactive
398	>	cancelTasks();
399	>	runState = TERMINATED;
400	>	pool.workerTerminated(this);
401	>	} catch (Throwable ex) {        // Shouldn't ever happen
402	>	if (exception == null)      // but if so, at least rethrown
403	>	exception = ex;
404	>	} finally {
405	>	if (exception != null)
406	>	ForkJoinTask.rethrowException(exception);
407	>	}
408	>	}
409	>
410	>	// Intrinsics-based support for queue operations.
411	>
412	>	/**
413	>	* Adds in store-order the given task at given slot of q to null.
414	>	* Caller must ensure q is non-null and index is in range.
415		*/
416		private static void setSlot(ForkJoinTask<?>[] q, int i,
417	<	ForkJoinTask<?> t){
418	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
417	>	ForkJoinTask<?> t) {
418	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
419		}
420
421		/**
422	<	* CAS given slot of q to null. Caller must ensure q is nonnull
422	>	* CAS given slot of q to null. Caller must ensure q is non-null
423		* and index is in range.
424		*/
425		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
426		ForkJoinTask<?> t) {
427	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
427	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
428	>	}
429	>
430	>	/**
431	>	* Sets sp in store-order.
432	>	*/
433	>	private void storeSp(int s) {
434	>	UNSAFE.putOrderedInt(this, spOffset, s);
435		}
436
437		// Main queue methods
438
439		/**
440		* Pushes a task. Called only by current thread.
441	<	* @param t the task. Caller must ensure nonnull
441	>	*
442	>	* @param t the task. Caller must ensure non-null.
443		*/
444		final void pushTask(ForkJoinTask<?> t) {
445		ForkJoinTask<?>[] q = queue;
446		int mask = q.length - 1;
447		int s = sp;
448	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
449	<	_unsafe.putOrderedInt(this, spOffset, ++s);
448	>	setSlot(q, s & mask, t);
449	>	storeSp(++s);
450		if ((s -= base) == 1)
451	<	pool.signalNonEmptyWorkerQueue();
451	>	pool.signalWork();
452		else if (s >= mask)
453		growQueue();
454		}
#	Line 316 | Line 456 | public class ForkJoinWorkerThread extend
456		/**
457		* Tries to take a task from the base of the queue, failing if
458		* either empty or contended.
459	<	* @return a task, or null if none or contended.
459	>	*
460	>	* @return a task, or null if none or contended
461		*/
462	<	private ForkJoinTask<?> deqTask() {
322	<	ForkJoinTask<?>[] q;
462	>	final ForkJoinTask<?> deqTask() {
463		ForkJoinTask<?> t;
464	+	ForkJoinTask<?>[] q;
465		int i;
466		int b;
467		if (sp != (b = base) &&
468		(q = queue) != null && // must read q after b
469		(t = q[i = (q.length - 1) & b]) != null &&
470	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
470	>	casSlotNull(q, i, t)) {
471		base = b + 1;
472		return t;
473		}
#	Line 334 | Line 475 | public class ForkJoinWorkerThread extend
475		}
476
477		/**
478	<	* Returns a popped task, or null if empty.  Called only by
479	<	* current thread.
478	>	* Tries to take a task from the base of own queue, activating if
479	>	* necessary, failing only if empty. Called only by current thread.
480	>	*
481	>	* @return a task, or null if none
482	>	*/
483	>	final ForkJoinTask<?> locallyDeqTask() {
484	>	int b;
485	>	while (sp != (b = base)) {
486	>	if (tryActivate()) {
487	>	ForkJoinTask<?>[] q = queue;
488	>	int i = (q.length - 1) & b;
489	>	ForkJoinTask<?> t = q[i];
490	>	if (t != null && casSlotNull(q, i, t)) {
491	>	base = b + 1;
492	>	return t;
493	>	}
494	>	}
495	>	}
496	>	return null;
497	>	}
498	>
499	>	/**
500	>	* Returns a popped task, or null if empty. Ensures active status
501	>	* if non-null. Called only by current thread.
502		*/
503		final ForkJoinTask<?> popTask() {
341	–	ForkJoinTask<?> t;
342	–	int i;
343	–	ForkJoinTask<?>[] q = queue;
344	–	int mask = q.length - 1;
504		int s = sp;
505	<	if (s != base &&
506	<	(t = q[i = (s - 1) & mask]) != null &&
507	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
508	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
509	<	return t;
505	>	while (s != base) {
506	>	if (tryActivate()) {
507	>	ForkJoinTask<?>[] q = queue;
508	>	int mask = q.length - 1;
509	>	int i = (s - 1) & mask;
510	>	ForkJoinTask<?> t = q[i];
511	>	if (t == null || !casSlotNull(q, i, t))
512	>	break;
513	>	storeSp(s - 1);
514	>	return t;
515	>	}
516		}
517		return null;
518		}
#	Line 355 | Line 520 | public class ForkJoinWorkerThread extend
520		/**
521		* Specialized version of popTask to pop only if
522		* topmost element is the given task. Called only
523	<	* by current thread.
524	<	* @param t the task. Caller must ensure nonnull
523	>	* by current thread while active.
524	>	*
525	>	* @param t the task. Caller must ensure non-null.
526		*/
527		final boolean unpushTask(ForkJoinTask<?> t) {
528		ForkJoinTask<?>[] q = queue;
529		int mask = q.length - 1;
530		int s = sp - 1;
531	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
532	<	t, null)) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
531	>	if (casSlotNull(q, s & mask, t)) {
532	>	storeSp(s);
533		return true;
534		}
535		return false;
536		}
537
538		/**
539	<	* Returns next task to pop.
539	>	* Returns next task or null if empty or contended
540		*/
541		final ForkJoinTask<?> peekTask() {
542		ForkJoinTask<?>[] q = queue;
543	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
543	>	if (q == null)
544	>	return null;
545	>	int mask = q.length - 1;
546	>	int i = locallyFifo ? base : (sp - 1);
547	>	return q[i & mask];
548		}
549
550		/**
#	Line 402 | Line 571 | public class ForkJoinWorkerThread extend
571		t = null;
572		setSlot(newQ, b & newMask, t);
573		} while (++b != bf);
574	<	pool.signalIdleWorkers(false);
574	>	pool.signalWork();
575		}
576
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	–
577		/**
578	<	* Transition to at least the given state. Return true if not
579	<	* already at least given state.
580	<	*/
581	<	private boolean transitionRunStateTo(int state) {
582	<	for (;;) {
583	<	int s = runState;
584	<	if (s >= state)
585	<	return false;
586	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
587	<	return true;
588	<	}
589	<	}
590	<
591	<	/**
592	<	* Ensure status is active and if necessary adjust pool active count
593	<	*/
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
578	>	* Tries to steal a task from another worker. Starts at a random
579	>	* index of workers array, and probes workers until finding one
580	>	* with non-empty queue or finding that all are empty.  It
581	>	* randomly selects the first n probes. If these are empty, it
582	>	* resorts to a full circular traversal, which is necessary to
583	>	* accurately set active status by caller. Also restarts if pool
584	>	* events occurred since last scan, which forces refresh of
585	>	* workers array, in case barrier was associated with resize.
586	>	*
587	>	* This method must be both fast and quiet -- usually avoiding
588	>	* memory accesses that could disrupt cache sharing etc other than
589	>	* those needed to check for and take tasks. This accounts for,
590	>	* among other things, updating random seed in place without
591	>	* storing it until exit.
592	>	*
593	>	* @return a task, or null if none found
594		*/
595	<	final void inactivate() {
596	<	if (active) {
597	<	active = false;
598	<	pool.decrementActiveCount();
599	<	}
595	>	private ForkJoinTask<?> scan() {
596	>	ForkJoinTask<?> t = null;
597	>	int r = seed;                    // extract once to keep scan quiet
598	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
599	>	int mask;                        // must be power 2 minus 1 and > 0
600	>	outer:do {
601	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
602	>	int idx = r;
603	>	int probes = ~mask;      // use random index while negative
604	>	for (;;) {
605	>	r = xorShift(r);     // update random seed
606	>	ForkJoinWorkerThread v = ws[mask & idx];
607	>	if (v == null || v.sp == v.base) {
608	>	if (probes <= mask)
609	>	idx = (probes++ < 0) ? r : (idx + 1);
610	>	else
611	>	break;
612	>	}
613	>	else if (!tryActivate() || (t = v.deqTask()) == null)
614	>	continue outer;  // restart on contention
615	>	else
616	>	break outer;
617	>	}
618	>	}
619	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
620	>	seed = r;
621	>	return t;
622		}
623
450	–	// Lifecycle methods
451	–
624		/**
625	<	* Initializes internal state after construction but before
626	<	* processing any tasks. If you override this method, you must
627	<	* 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.
625	>	* Gets and removes a local or stolen task.
626	>	*
627	>	* @return a task, if available
628		*/
629	<	protected void onStart() {
630	<	juRandomSeed = randomSeedGenerator.nextLong();
631	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
632	<	if (queue == null)
633	<	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	<	}
629	>	final ForkJoinTask<?> pollTask() {
630	>	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
631	>	if (t == null && (t = scan()) != null)
632	>	++stealCount;
633	>	return t;
634		}
635
636		/**
637	<	* 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.
637	>	* Gets a local task.
638		*
639	<	* @param exception the exception causing this thread to abort due
480	<	* to an unrecoverable error, or null if completed normally.
639	>	* @return a task, if available
640		*/
641	<	protected void onTermination(Throwable exception) {
642	<	try {
484	<	clearLocalTasks();
485	<	inactivate();
486	<	cancelTasks();
487	<	} finally {
488	<	terminate(exception);
489	<	}
641	>	final ForkJoinTask<?> pollLocalTask() {
642	>	return locallyFifo ? locallyDeqTask() : popTask();
643		}
644
645		/**
646	<	* Notify pool of termination and, if exception is nonnull,
647	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
646	>	* Returns a pool submission, if one exists, activating first.
647	>	*
648	>	* @return a submission, if available
649		*/
650	<	private void terminate(Throwable exception) {
651	<	transitionRunStateTo(TERMINATED);
652	<	try {
653	<	pool.workerTerminated(this);
654	<	} finally {
655	<	if (exception != null)
502	<	ForkJoinTask.rethrowException(exception);
650	>	private ForkJoinTask<?> pollSubmission() {
651	>	ForkJoinPool p = pool;
652	>	while (p.hasQueuedSubmissions()) {
653	>	ForkJoinTask<?> t;
654	>	if (tryActivate() && (t = p.pollSubmission()) != null)
655	>	return t;
656		}
657	+	return null;
658		}
659
660	<	/**
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	<	}
660	>	// Methods accessed only by Pool
661
662		/**
663		* Removes and cancels all tasks in queue.  Can be called from any
664		* thread.
665		*/
666		final void cancelTasks() {
667	<	while (base != sp) {
668	<	ForkJoinTask<?> t = deqTask();
669	<	if (t != null)
527	<	t.cancelIgnoringExceptions();
528	<	}
529	<	}
530	<
531	<	/**
532	<	* This method is required to be public, but should never be
533	<	* called explicitly. It performs the main run loop to execute
534	<	* ForkJoinTasks.
535	<	*/
536	<	public void run() {
537	<	Throwable exception = null;
538	<	try {
539	<	onStart();
540	<	while (!isShutdown())
541	<	step();
542	<	} catch (Throwable ex) {
543	<	exception = ex;
544	<	} finally {
545	<	onTermination(exception);
546	<	}
667	>	ForkJoinTask<?> t;
668	>	while (base != sp && (t = deqTask()) != null)
669	>	t.cancelIgnoringExceptions();
670		}
671
672		/**
673	<	* Main top-level action.
673	>	* Drains tasks to given collection c.
674	>	*
675	>	* @return the number of tasks drained
676		*/
677	<	private void step() {
678	<	ForkJoinTask<?> t = sp != base? popTask() : null;
679	<	if (t != null || (t = scan(null, true)) != null) {
680	<	activate();
681	<	t.quietlyExec();
682	<	}
558	<	else {
559	<	inactivate();
560	<	eventCount = pool.sync(this, eventCount);
677	>	final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
678	>	int n = 0;
679	>	ForkJoinTask<?> t;
680	>	while (base != sp && (t = deqTask()) != null) {
681	>	c.add(t);
682	>	++n;
683		}
684	+	return n;
685		}
686
564	–	// scanning for and stealing tasks
565	–
687		/**
688	<	* Computes next value for random victim probe. Scans don't
689	<	* 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
688	>	* Gets and clears steal count for accumulation by pool.  Called
689	>	* only when known to be idle (in pool.sync and termination).
690		*/
691	<	private static int xorShift(int r) {
692	<	r ^= r << 1;
693	<	r ^= r >>> 3;
694	<	r ^= r << 10;
577	<	return r;
691	>	final int getAndClearStealCount() {
692	>	int sc = stealCount;
693	>	stealCount = 0;
694	>	return sc;
695		}
696
697		/**
698	<	* Tries to steal a task from another worker and/or, if enabled,
699	<	* 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.
698	>	* Returns {@code true} if at least one worker in the given array
699	>	* appears to have at least one queued task.
700		*
701	<	* 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
701	>	* @param ws array of workers
702		*/
703	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
704	<	boolean checkSubmissions) {
705	<	ForkJoinPool p = pool;
706	<	if (p == null)                    // Never null, but avoids
707	<	return null;                  //   implicit nullchecks below
708	<	int r = randomVictimSeed;         // extract once to keep scan quiet
709	<	restart:                          // outer loop refreshes ws array
710	<	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;
703	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
704	>	if (ws != null) {
705	>	int len = ws.length;
706	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
707	>	for (int i = 0; i < len; ++i) {
708	>	ForkJoinWorkerThread w = ws[i];
709	>	if (w != null && w.sp != w.base)
710	>	return true;
711		}
712		}
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	–	}
713		}
714	<	return null;
714	>	return false;
715		}
716
717	+	// Support methods for ForkJoinTask
718	+
719		/**
720	<	* Callback from pool.sync to rescan before blocking.  If a
721	<	* task is found, it is pushed so it can be executed upon return.
722	<	* @return true if found and pushed a task
723	<	*/
724	<	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	<	}
720	>	* Returns an estimate of the number of tasks in the queue.
721	>	*/
722	>	final int getQueueSize() {
723	>	// suppress momentarily negative values
724	>	return Math.max(0, sp - base);
725		}
726
727	<	// Support for ForkJoinTask methods
727	>	/**
728	>	* Returns an estimate of the number of tasks, offset by a
729	>	* function of number of idle workers.
730	>	*/
731	>	final int getEstimatedSurplusTaskCount() {
732	>	// The halving approximates weighting idle vs non-idle workers
733	>	return (sp - base) - (pool.getIdleThreadCount() >>> 1);
734	>	}
735
736		/**
737	<	* Scan, returning early if joinMe done
737	>	* Scans, returning early if joinMe done.
738		*/
739		final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
740	<	ForkJoinTask<?> t = scan(joinMe, false);
740	>	ForkJoinTask<?> t = pollTask();
741		if (t != null && joinMe.status < 0 && sp == base) {
742		pushTask(t); // unsteal if done and this task would be stealable
743		t = null;
744		}
745		return t;
746		}
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	–	}
747
748		/**
749	<	* Runs tasks until pool isQuiescent
749	>	* Runs tasks until {@code pool.isQuiescent()}.
750		*/
751		final void helpQuiescePool() {
752		for (;;) {
753	<	ForkJoinTask<?> t = pollLocalOrStolenTask();
754	<	if (t != null) {
699	<	activate();
753	>	ForkJoinTask<?> t = pollTask();
754	>	if (t != null)
755		t.quietlyExec();
756	<	}
757	<	else {
703	<	inactivate();
704	<	if (pool.isQuiescent()) {
705	<	activate(); // re-activate on exit
706	<	break;
707	<	}
708	<	}
756	>	else if (tryInactivate() && pool.isQuiescent())
757	>	break;
758		}
759	+	do {} while (!tryActivate()); // re-activate on exit
760		}
761
762	<	/**
713	<	* Returns an estimate of the number of tasks in the queue.
714	<	*/
715	<	final int getQueueSize() {
716	<	int n = sp - base;
717	<	return n <= 0? 0 : n; // suppress momentarily negative values
718	<	}
719	<
720	<	/**
721	<	* Returns an estimate of the number of tasks, offset by a
722	<	* function of number of idle workers.
723	<	*/
724	<	final int getEstimatedSurplusTaskCount() {
725	<	// The halving approximates weighting idle vs non-idle workers
726	<	return (sp - base) - (pool.getIdleThreadCount() >>> 1);
727	<	}
762	>	// Unsafe mechanics
763
764	<	// Per-worker exported random numbers
764	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
765	>	private static final long spOffset =
766	>	objectFieldOffset("sp", ForkJoinWorkerThread.class);
767	>	private static final long runStateOffset =
768	>	objectFieldOffset("runState", ForkJoinWorkerThread.class);
769	>	private static final long qBase;
770	>	private static final int qShift;
771
772	<	// Same constants as java.util.Random
773	<	final static long JURandomMultiplier = 0x5DEECE66DL;
774	<	final static long JURandomAddend = 0xBL;
775	<	final static long JURandomMask = (1L << 48) - 1;
776	<
777	<	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);
772	>	static {
773	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
774	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
775	>	if ((s & (s-1)) != 0)
776	>	throw new Error("data type scale not a power of two");
777	>	qShift = 31 - Integer.numberOfLeadingZeros(s);
778		}
779
780	<	private final long nextJURandomLong(long n) {
781	<	if (n <= 0)
782	<	throw new IllegalArgumentException("n must be positive");
783	<	long offset = 0;
784	<	while (n >= Integer.MAX_VALUE) { // randomly pick half range
785	<	int bits = nextJURandom(2); // 2nd bit for odd vs even split
786	<	long half = n >>> 1;
787	<	long nextn = ((bits & 2) == 0)? half : n - half;
770	<	if ((bits & 1) == 0)
771	<	offset += n - nextn;
772	<	n = nextn;
780	>	private static long objectFieldOffset(String field, Class<?> klazz) {
781	>	try {
782	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
783	>	} catch (NoSuchFieldException e) {
784	>	// Convert Exception to corresponding Error
785	>	NoSuchFieldError error = new NoSuchFieldError(field);
786	>	error.initCause(e);
787	>	throw error;
788		}
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	–
782	–	/**
783	–	* Returns a random integer using a per-worker random
784	–	* number generator with the same properties as
785	–	* {@link java.util.Random#nextInt}
786	–	* @return the next pseudorandom, uniformly distributed {@code int}
787	–	*         value from this worker's random number generator's sequence
788	–	*/
789	–	public static int nextRandomInt() {
790	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
791	–	nextJURandom(32);
792	–	}
793	–
794	–	/**
795	–	* Returns a random integer using a per-worker random
796	–	* number generator with the same properties as
797	–	* {@link java.util.Random#nextInt(int)}
798	–	* @param n the bound on the random number to be returned.  Must be
799	–	*        positive.
800	–	* @return the next pseudorandom, uniformly distributed {@code int}
801	–	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
802	–	*         from this worker's random number generator's sequence
803	–	* @throws IllegalArgumentException if n is not positive
804	–	*/
805	–	public static int nextRandomInt(int n) {
806	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
807	–	nextJURandomInt(n);
808	–	}
809	–
810	–	/**
811	–	* Returns a random long using a per-worker random
812	–	* number generator with the same properties as
813	–	* {@link java.util.Random#nextLong}
814	–	* @return the next pseudorandom, uniformly distributed {@code long}
815	–	*         value from this worker's random number generator's sequence
816	–	*/
817	–	public static long nextRandomLong() {
818	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
819	–	nextJURandomLong();
820	–	}
821	–
822	–	/**
823	–	* Returns a random integer using a per-worker random
824	–	* number generator with the same properties as
825	–	* {@link java.util.Random#nextInt(int)}
826	–	* @param n the bound on the random number to be returned.  Must be
827	–	*        positive.
828	–	* @return the next pseudorandom, uniformly distributed {@code int}
829	–	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
830	–	*         from this worker's random number generator's sequence
831	–	* @throws IllegalArgumentException if n is not positive
832	–	*/
833	–	public static long nextRandomLong(long n) {
834	–	return ((ForkJoinWorkerThread)(Thread.currentThread())).
835	–	nextJURandomLong(n);
789		}
790
791		/**
792	<	* Returns a random double using a per-worker random
793	<	* number generator with the same properties as
794	<	* {@link java.util.Random#nextDouble}
795	<	* @return the next pseudorandom, uniformly distributed {@code double}
796	<	*         value between {@code 0.0} and {@code 1.0} from this
844	<	*         worker's random number generator's sequence
792	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
793	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
794	>	* into a jdk.
795	>	*
796	>	* @return a sun.misc.Unsafe
797		*/
798	<	public static double nextRandomDouble() {
847	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
848	<	nextJURandomDouble();
849	<	}
850	<
851	<	// Temporary Unsafe mechanics for preliminary release
852	<
853	<	static final Unsafe _unsafe;
854	<	static final long baseOffset;
855	<	static final long spOffset;
856	<	static final long qBase;
857	<	static final int qShift;
858	<	static final long runStateOffset;
859	<	static {
798	>	private static sun.misc.Unsafe getUnsafe() {
799		try {
800	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
801	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
802	<	f.setAccessible(true);
803	<	_unsafe = (Unsafe)f.get(null);
800	>	return sun.misc.Unsafe.getUnsafe();
801	>	} catch (SecurityException se) {
802	>	try {
803	>	return java.security.AccessController.doPrivileged
804	>	(new java.security
805	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
806	>	public sun.misc.Unsafe run() throws Exception {
807	>	java.lang.reflect.Field f = sun.misc
808	>	.Unsafe.class.getDeclaredField("theUnsafe");
809	>	f.setAccessible(true);
810	>	return (sun.misc.Unsafe) f.get(null);
811	>	}});
812	>	} catch (java.security.PrivilegedActionException e) {
813	>	throw new RuntimeException("Could not initialize intrinsics",
814	>	e.getCause());
815		}
866	–	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);
876	–	if ((s & (s-1)) != 0)
877	–	throw new Error("data type scale not a power of two");
878	–	qShift = 31 - Integer.numberOfLeadingZeros(s);
879	–	} catch (Exception e) {
880	–	throw new RuntimeException("Could not initialize intrinsics", e);
816		}
817		}
818		}

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