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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 1.27 by dl, Mon Aug 3 13:01:15 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
24	<	* 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	>	* ForkJoinPool.ForkJoinWorkerThreadFactory} to use it in a {@code
21	>	* ForkJoinPool}.
22	>	*
23	>	* @since 1.7
24	>	* @author Doug Lea
25		*/
26		public class ForkJoinWorkerThread extends Thread {
27		/*
#	Line 48 | Line 45 | public class ForkJoinWorkerThread extend
45		* of tasks. To accomplish this, we shift the CAS arbitrating pop
46		* vs deq (steal) from being on the indices ("base" and "sp") to
47		* the slots themselves (mainly via method "casSlotNull()"). So,
48	<	* both a successful pop and deq mainly entail CAS'ing a nonnull
48	>	* both a successful pop and deq mainly entail CAS'ing a non-null
49		* slot to null.  Because we rely on CASes of references, we do
50		* not need tag bits on base or sp.  They are simple ints as used
51		* in any circular array-based queue (see for example ArrayDeque).
#	Line 60 | Line 57 | public class ForkJoinWorkerThread extend
57		* considered individually, is not wait-free. One thief cannot
58		* successfully continue until another in-progress one (or, if
59		* previously empty, a push) completes.  However, in the
60	<	* aggregate, we ensure at least probablistic non-blockingness. If
60	>	* aggregate, we ensure at least probabilistic non-blockingness. If
61		* an attempted steal fails, a thief always chooses a different
62		* random victim target to try next. So, in order for one thief to
63		* progress, it suffices for any in-progress deq or new push on
#	Line 69 | Line 66 | public class ForkJoinWorkerThread extend
66		* which gives threads a chance to activate if necessary before
67		* stealing (see below).
68		*
69	+	* This approach also enables support for "async mode" where local
70	+	* task processing is in FIFO, not LIFO order; simply by using a
71	+	* version of deq rather than pop when locallyFifo is true (as set
72	+	* by the ForkJoinPool).  This allows use in message-passing
73	+	* frameworks in which tasks are never joined.
74	+	*
75		* Efficient implementation of this approach currently relies on
76		* an uncomfortable amount of "Unsafe" mechanics. To maintain
77		* correct orderings, reads and writes of variable base require
#	Line 79 | Line 82 | public class ForkJoinWorkerThread extend
82		* push) require store order and CASes (in pop and deq) require
83		* (volatile) CAS semantics. Since these combinations aren't
84		* supported using ordinary volatiles, the only way to accomplish
85	<	* these effciently is to use direct Unsafe calls. (Using external
85	>	* these efficiently is to use direct Unsafe calls. (Using external
86		* AtomicIntegers and AtomicReferenceArrays for the indices and
87		* array is significantly slower because of memory locality and
88		* indirection effects.) Further, performance on most platforms is
#	Line 134 | Line 137 | public class ForkJoinWorkerThread extend
137
138		/**
139		* Maximum work-stealing queue array size.  Must be less than or
140	<	* equal to 1 << 30 to ensure lack of index wraparound.
140	>	* equal to 1 << 28 to ensure lack of index wraparound. (This
141	>	* is less than usual bounds, because we need leftshift by 3
142	>	* to be in int range).
143		*/
144	<	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 30;
144	>	private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
145
146		/**
147	<	* Generator of seeds for per-thread random numbers.
147	>	* The pool this thread works in. Accessed directly by ForkJoinTask.
148		*/
149	<	private static final Random randomSeedGenerator = new Random();
149	>	final ForkJoinPool pool;
150
151		/**
152		* The work-stealing queue array. Size must be a power of two.
153	+	* Initialized when thread starts, to improve memory locality.
154		*/
155		private ForkJoinTask<?>[] queue;
156
#	Line 163 | Line 169 | public class ForkJoinWorkerThread extend
169		private volatile int base;
170
171		/**
172	<	* The pool this thread works in.
173	<	*/
174	<	final ForkJoinPool pool;
175	<
170	<	/**
171	<	* Index of this worker in pool array. Set once by pool before
172	<	* running, and accessed directly by pool during cleanup etc
172	>	* Activity status. When true, this worker is considered active.
173	>	* Must be false upon construction. It must be true when executing
174	>	* tasks, and BEFORE stealing a task. It must be false before
175	>	* calling pool.sync.
176		*/
177	<	int poolIndex;
177	>	private boolean active;
178
179		/**
180		* Run state of this worker. Supports simple versions of the usual
#	Line 179 | Line 182 | public class ForkJoinWorkerThread extend
182		*/
183		private volatile int runState;
184
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	–
185		/**
186	<	* Activity status. When true, this worker is considered active.
187	<	* 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.
186	>	* Seed for random number generator for choosing steal victims.
187	>	* Uses Marsaglia xorshift. Must be nonzero upon initialization.
188		*/
189	<	private boolean active;
189	>	private int seed;
190
191		/**
192		* Number of steals, transferred to pool when idle
#	Line 199 | Line 194 | public class ForkJoinWorkerThread extend
194		private int stealCount;
195
196		/**
197	<	* Seed for random number generator for choosing steal victims
197	>	* Index of this worker in pool array. Set once by pool before
198	>	* running, and accessed directly by pool during cleanup etc.
199		*/
200	<	private int randomVictimSeed;
200	>	int poolIndex;
201
202		/**
203	<	* Seed for embedded Jurandom
203	>	* The last barrier event waited for. Accessed in pool callback
204	>	* methods, but only by current thread.
205		*/
206	<	private long juRandomSeed;
206	>	long lastEventCount;
207
208		/**
209	<	* The last barrier event waited for
209	>	* True if use local fifo, not default lifo, for local polling
210		*/
211	<	private long eventCount;
211	>	private boolean locallyFifo;
212
213		/**
214		* Creates a ForkJoinWorkerThread operating in the given pool.
215	+	*
216		* @param pool the pool this thread works in
217		* @throws NullPointerException if pool is null
218		*/
219		protected ForkJoinWorkerThread(ForkJoinPool pool) {
220		if (pool == null) throw new NullPointerException();
221		this.pool = pool;
222	<	// remaining initialization deferred to onStart
222	>	// Note: poolIndex is set by pool during construction
223	>	// Remaining initialization is deferred to onStart
224		}
225
226	<	// public access methods
226	>	// Public access methods
227
228		/**
229	<	* Returns the pool hosting the current task execution.
229	>	* Returns the pool hosting this thread.
230	>	*
231		* @return the pool
232		*/
233	<	public static ForkJoinPool getPool() {
234	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).pool;
233	>	public ForkJoinPool getPool() {
234	>	return pool;
235	>	}
236	>
237	>	/**
238	>	* Returns the index number of this thread in its pool.  The
239	>	* returned value ranges from zero to the maximum number of
240	>	* threads (minus one) that have ever been created in the pool.
241	>	* This method may be useful for applications that track status or
242	>	* collect results per-worker rather than per-task.
243	>	*
244	>	* @return the index number
245	>	*/
246	>	public int getPoolIndex() {
247	>	return poolIndex;
248		}
249
250		/**
251	<	* Returns the index number of the current worker thread in its
252	<	* pool.  The returned value ranges from zero to the maximum
253	<	* number of threads (minus one) that have ever been created in
254	<	* the pool.  This method may be useful for applications that
255	<	* track status or collect results on a per-worker basis.
256	<	* @return the index number.
251	>	* Establishes local first-in-first-out scheduling mode for forked
252	>	* tasks that are never joined.
253	>	*
254	>	* @param async if true, use locally FIFO scheduling
255	>	*/
256	>	void setAsyncMode(boolean async) {
257	>	locallyFifo = async;
258	>	}
259	>
260	>	// Runstate management
261	>
262	>	// Runstate values. Order matters
263	>	private static final int RUNNING     = 0;
264	>	private static final int SHUTDOWN    = 1;
265	>	private static final int TERMINATING = 2;
266	>	private static final int TERMINATED  = 3;
267	>
268	>	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
269	>	final boolean isTerminating() { return runState >= TERMINATING;  }
270	>	final boolean isTerminated()  { return runState == TERMINATED; }
271	>	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
272	>	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
273	>
274	>	/**
275	>	* Transitions to at least the given state.
276	>	*
277	>	* @return {@code true} if not already at least at given state
278		*/
279	<	public static int getPoolIndex() {
280	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).poolIndex;
279	>	private boolean transitionRunStateTo(int state) {
280	>	for (;;) {
281	>	int s = runState;
282	>	if (s >= state)
283	>	return false;
284	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
285	>	return true;
286	>	}
287		}
288
289	<	//  Access methods used by Pool
289	>	/**
290	>	* Tries to set status to active; fails on contention.
291	>	*/
292	>	private boolean tryActivate() {
293	>	if (!active) {
294	>	if (!pool.tryIncrementActiveCount())
295	>	return false;
296	>	active = true;
297	>	}
298	>	return true;
299	>	}
300
301		/**
302	<	* Get and clear steal count for accumulation by pool.  Called
253	<	* only when known to be idle (in pool.sync and termination).
302	>	* Tries to set status to inactive; fails on contention.
303		*/
304	<	final int getAndClearStealCount() {
305	<	int sc = stealCount;
306	<	stealCount = 0;
307	<	return sc;
304	>	private boolean tryInactivate() {
305	>	if (active) {
306	>	if (!pool.tryDecrementActiveCount())
307	>	return false;
308	>	active = false;
309	>	}
310	>	return true;
311		}
312
313		/**
314	<	* Returns estimate of the number of tasks in the queue, without
315	<	* correcting for transient negative values
314	>	* Computes next value for random victim probe.  Scans don't
315	>	* require a very high quality generator, but also not a crummy
316	>	* one.  Marsaglia xor-shift is cheap and works well.
317		*/
318	<	final int getRawQueueSize() {
319	<	return sp - base;
318	>	private static int xorShift(int r) {
319	>	r ^= (r << 13);
320	>	r ^= (r >>> 17);
321	>	return r ^ (r << 5);
322		}
323
324	<	// Intrinsics-based support for queue operations.
270	<	// Currently these three (setSp, setSlot, casSlotNull) are
271	<	// usually manually inlined to improve performance
324	>	// Lifecycle methods
325
326		/**
327	<	* Sets sp in store-order.
327	>	* This method is required to be public, but should never be
328	>	* called explicitly. It performs the main run loop to execute
329	>	* ForkJoinTasks.
330	>	*/
331	>	public void run() {
332	>	Throwable exception = null;
333	>	try {
334	>	onStart();
335	>	pool.sync(this); // await first pool event
336	>	mainLoop();
337	>	} catch (Throwable ex) {
338	>	exception = ex;
339	>	} finally {
340	>	onTermination(exception);
341	>	}
342	>	}
343	>
344	>	/**
345	>	* Executes tasks until shut down.
346	>	*/
347	>	private void mainLoop() {
348	>	while (!isShutdown()) {
349	>	ForkJoinTask<?> t = pollTask();
350	>	if (t != null || (t = pollSubmission()) != null)
351	>	t.quietlyExec();
352	>	else if (tryInactivate())
353	>	pool.sync(this);
354	>	}
355	>	}
356	>
357	>	/**
358	>	* Initializes internal state after construction but before
359	>	* processing any tasks. If you override this method, you must
360	>	* invoke super.onStart() at the beginning of the method.
361	>	* Initialization requires care: Most fields must have legal
362	>	* default values, to ensure that attempted accesses from other
363	>	* threads work correctly even before this thread starts
364	>	* processing tasks.
365		*/
366	<	private void setSp(int s) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
366	>	protected void onStart() {
367	>	// Allocate while starting to improve chances of thread-local
368	>	// isolation
369	>	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
370	>	// Initial value of seed need not be especially random but
371	>	// should differ across workers and must be nonzero
372	>	int p = poolIndex + 1;
373	>	seed = p + (p << 8) + (p << 16) + (p << 24); // spread bits
374	>	}
375	>
376	>	/**
377	>	* Performs cleanup associated with termination of this worker
378	>	* thread.  If you override this method, you must invoke
379	>	* {@code super.onTermination} at the end of the overridden method.
380	>	*
381	>	* @param exception the exception causing this thread to abort due
382	>	* to an unrecoverable error, or {@code null} if completed normally
383	>	*/
384	>	protected void onTermination(Throwable exception) {
385	>	// Execute remaining local tasks unless aborting or terminating
386	>	while (exception == null && pool.isProcessingTasks() && base != sp) {
387	>	try {
388	>	ForkJoinTask<?> t = popTask();
389	>	if (t != null)
390	>	t.quietlyExec();
391	>	} catch (Throwable ex) {
392	>	exception = ex;
393	>	}
394	>	}
395	>	// Cancel other tasks, transition status, notify pool, and
396	>	// propagate exception to uncaught exception handler
397	>	try {
398	>	do {} while (!tryInactivate()); // ensure inactive
399	>	cancelTasks();
400	>	runState = TERMINATED;
401	>	pool.workerTerminated(this);
402	>	} catch (Throwable ex) {        // Shouldn't ever happen
403	>	if (exception == null)      // but if so, at least rethrown
404	>	exception = ex;
405	>	} finally {
406	>	if (exception != null)
407	>	ForkJoinTask.rethrowException(exception);
408	>	}
409		}
410
411	+	// Intrinsics-based support for queue operations.
412	+
413		/**
414	<	* Add in store-order the given task at given slot of q to
415	<	* null. Caller must ensure q is nonnull and index is in range.
414	>	* Adds in store-order the given task at given slot of q to null.
415	>	* Caller must ensure q is non-null and index is in range.
416		*/
417		private static void setSlot(ForkJoinTask<?>[] q, int i,
418	<	ForkJoinTask<?> t){
419	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
418	>	ForkJoinTask<?> t) {
419	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
420		}
421
422		/**
423	<	* CAS given slot of q to null. Caller must ensure q is nonnull
423	>	* CAS given slot of q to null. Caller must ensure q is non-null
424		* and index is in range.
425		*/
426		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
427		ForkJoinTask<?> t) {
428	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
428	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
429	>	}
430	>
431	>	/**
432	>	* Sets sp in store-order.
433	>	*/
434	>	private void storeSp(int s) {
435	>	UNSAFE.putOrderedInt(this, spOffset, s);
436		}
437
438		// Main queue methods
439
440		/**
441		* Pushes a task. Called only by current thread.
442	<	* @param t the task. Caller must ensure nonnull
442	>	*
443	>	* @param t the task. Caller must ensure non-null.
444		*/
445		final void pushTask(ForkJoinTask<?> t) {
446		ForkJoinTask<?>[] q = queue;
447		int mask = q.length - 1;
448		int s = sp;
449	<	_unsafe.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
450	<	_unsafe.putOrderedInt(this, spOffset, ++s);
449	>	setSlot(q, s & mask, t);
450	>	storeSp(++s);
451		if ((s -= base) == 1)
452	<	pool.signalNonEmptyWorkerQueue();
452	>	pool.signalWork();
453		else if (s >= mask)
454		growQueue();
455		}
#	Line 316 | Line 457 | public class ForkJoinWorkerThread extend
457		/**
458		* Tries to take a task from the base of the queue, failing if
459		* either empty or contended.
460	<	* @return a task, or null if none or contended.
460	>	*
461	>	* @return a task, or null if none or contended
462		*/
463	<	private ForkJoinTask<?> deqTask() {
322	<	ForkJoinTask<?>[] q;
463	>	final ForkJoinTask<?> deqTask() {
464		ForkJoinTask<?> t;
465	+	ForkJoinTask<?>[] q;
466		int i;
467		int b;
468		if (sp != (b = base) &&
469		(q = queue) != null && // must read q after b
470		(t = q[i = (q.length - 1) & b]) != null &&
471	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
471	>	casSlotNull(q, i, t)) {
472		base = b + 1;
473		return t;
474		}
#	Line 334 | Line 476 | public class ForkJoinWorkerThread extend
476		}
477
478		/**
479	<	* Returns a popped task, or null if empty.  Called only by
480	<	* current thread.
479	>	* Tries to take a task from the base of own queue, activating if
480	>	* necessary, failing only if empty. Called only by current thread.
481	>	*
482	>	* @return a task, or null if none
483	>	*/
484	>	final ForkJoinTask<?> locallyDeqTask() {
485	>	int b;
486	>	while (sp != (b = base)) {
487	>	if (tryActivate()) {
488	>	ForkJoinTask<?>[] q = queue;
489	>	int i = (q.length - 1) & b;
490	>	ForkJoinTask<?> t = q[i];
491	>	if (t != null && casSlotNull(q, i, t)) {
492	>	base = b + 1;
493	>	return t;
494	>	}
495	>	}
496	>	}
497	>	return null;
498	>	}
499	>
500	>	/**
501	>	* Returns a popped task, or null if empty. Ensures active status
502	>	* if non-null. Called only by current thread.
503		*/
504		final ForkJoinTask<?> popTask() {
341	–	ForkJoinTask<?> t;
342	–	int i;
343	–	ForkJoinTask<?>[] q = queue;
344	–	int mask = q.length - 1;
505		int s = sp;
506	<	if (s != base &&
507	<	(t = q[i = (s - 1) & mask]) != null &&
508	<	_unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
509	<	_unsafe.putOrderedInt(this, spOffset, s - 1);
510	<	return t;
506	>	while (s != base) {
507	>	if (tryActivate()) {
508	>	ForkJoinTask<?>[] q = queue;
509	>	int mask = q.length - 1;
510	>	int i = (s - 1) & mask;
511	>	ForkJoinTask<?> t = q[i];
512	>	if (t == null || !casSlotNull(q, i, t))
513	>	break;
514	>	storeSp(s - 1);
515	>	return t;
516	>	}
517		}
518		return null;
519		}
#	Line 355 | Line 521 | public class ForkJoinWorkerThread extend
521		/**
522		* Specialized version of popTask to pop only if
523		* topmost element is the given task. Called only
524	<	* by current thread.
525	<	* @param t the task. Caller must ensure nonnull
524	>	* by current thread while active.
525	>	*
526	>	* @param t the task. Caller must ensure non-null.
527		*/
528		final boolean unpushTask(ForkJoinTask<?> t) {
529		ForkJoinTask<?>[] q = queue;
530		int mask = q.length - 1;
531		int s = sp - 1;
532	<	if (_unsafe.compareAndSwapObject(q, ((s & mask) << qShift) + qBase,
533	<	t, null)) {
367	<	_unsafe.putOrderedInt(this, spOffset, s);
532	>	if (casSlotNull(q, s & mask, t)) {
533	>	storeSp(s);
534		return true;
535		}
536		return false;
537		}
538
539		/**
540	<	* Returns next task to pop.
540	>	* Returns next task or null if empty or contended
541		*/
542		final ForkJoinTask<?> peekTask() {
543		ForkJoinTask<?>[] q = queue;
544	<	return q == null? null : q[(sp - 1) & (q.length - 1)];
544	>	if (q == null)
545	>	return null;
546	>	int mask = q.length - 1;
547	>	int i = locallyFifo ? base : (sp - 1);
548	>	return q[i & mask];
549		}
550
551		/**
#	Line 402 | Line 572 | public class ForkJoinWorkerThread extend
572		t = null;
573		setSlot(newQ, b & newMask, t);
574		} while (++b != bf);
575	<	pool.signalIdleWorkers(false);
406	<	}
407	<
408	<	// Runstate management
409	<
410	<	final boolean isShutdown()    { return runState >= SHUTDOWN;  }
411	<	final boolean isTerminating() { return runState >= TERMINATING;  }
412	<	final boolean isTerminated()  { return runState == TERMINATED; }
413	<	final boolean shutdown()      { return transitionRunStateTo(SHUTDOWN); }
414	<	final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
415	<
416	<	/**
417	<	* Transition to at least the given state. Return true if not
418	<	* already at least given state.
419	<	*/
420	<	private boolean transitionRunStateTo(int state) {
421	<	for (;;) {
422	<	int s = runState;
423	<	if (s >= state)
424	<	return false;
425	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
426	<	return true;
427	<	}
575	>	pool.signalWork();
576		}
577
578		/**
579	<	* Ensure status is active and if necessary adjust pool active count
580	<	*/
581	<	final void activate() {
582	<	if (!active) {
583	<	active = true;
584	<	pool.incrementActiveCount();
585	<	}
586	<	}
587	<
588	<	/**
589	<	* Ensure status is inactive and if necessary adjust pool active count
579	>	* Tries to steal a task from another worker. Starts at a random
580	>	* index of workers array, and probes workers until finding one
581	>	* with non-empty queue or finding that all are empty.  It
582	>	* randomly selects the first n probes. If these are empty, it
583	>	* resorts to a full circular traversal, which is necessary to
584	>	* accurately set active status by caller. Also restarts if pool
585	>	* events occurred since last scan, which forces refresh of
586	>	* workers array, in case barrier was associated with resize.
587	>	*
588	>	* This method must be both fast and quiet -- usually avoiding
589	>	* memory accesses that could disrupt cache sharing etc other than
590	>	* those needed to check for and take tasks. This accounts for,
591	>	* among other things, updating random seed in place without
592	>	* storing it until exit.
593	>	*
594	>	* @return a task, or null if none found
595		*/
596	<	final void inactivate() {
597	<	if (active) {
598	<	active = false;
599	<	pool.decrementActiveCount();
600	<	}
596	>	private ForkJoinTask<?> scan() {
597	>	ForkJoinTask<?> t = null;
598	>	int r = seed;                    // extract once to keep scan quiet
599	>	ForkJoinWorkerThread[] ws;       // refreshed on outer loop
600	>	int mask;                        // must be power 2 minus 1 and > 0
601	>	outer:do {
602	>	if ((ws = pool.workers) != null && (mask = ws.length - 1) > 0) {
603	>	int idx = r;
604	>	int probes = ~mask;      // use random index while negative
605	>	for (;;) {
606	>	r = xorShift(r);     // update random seed
607	>	ForkJoinWorkerThread v = ws[mask & idx];
608	>	if (v == null || v.sp == v.base) {
609	>	if (probes <= mask)
610	>	idx = (probes++ < 0) ? r : (idx + 1);
611	>	else
612	>	break;
613	>	}
614	>	else if (!tryActivate() || (t = v.deqTask()) == null)
615	>	continue outer;  // restart on contention
616	>	else
617	>	break outer;
618	>	}
619	>	}
620	>	} while (pool.hasNewSyncEvent(this)); // retry on pool events
621	>	seed = r;
622	>	return t;
623		}
624
450	–	// Lifecycle methods
451	–
625		/**
626	<	* Initializes internal state after construction but before
627	<	* processing any tasks. If you override this method, you must
628	<	* 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.
626	>	* Gets and removes a local or stolen task.
627	>	*
628	>	* @return a task, if available
629		*/
630	<	protected void onStart() {
631	<	juRandomSeed = randomSeedGenerator.nextLong();
632	<	do;while((randomVictimSeed = nextRandomInt()) == 0); // must be nonzero
633	<	if (queue == null)
634	<	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	<	}
630	>	final ForkJoinTask<?> pollTask() {
631	>	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
632	>	if (t == null && (t = scan()) != null)
633	>	++stealCount;
634	>	return t;
635		}
636
637		/**
638	<	* 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.
638	>	* Gets a local task.
639		*
640	<	* @param exception the exception causing this thread to abort due
480	<	* to an unrecoverable error, or null if completed normally.
640	>	* @return a task, if available
641		*/
642	<	protected void onTermination(Throwable exception) {
643	<	try {
484	<	clearLocalTasks();
485	<	inactivate();
486	<	cancelTasks();
487	<	} finally {
488	<	terminate(exception);
489	<	}
642	>	final ForkJoinTask<?> pollLocalTask() {
643	>	return locallyFifo ? locallyDeqTask() : popTask();
644		}
645
646		/**
647	<	* Notify pool of termination and, if exception is nonnull,
648	<	* rethrow it to trigger this thread's uncaughtExceptionHandler
647	>	* Returns a pool submission, if one exists, activating first.
648	>	*
649	>	* @return a submission, if available
650		*/
651	<	private void terminate(Throwable exception) {
652	<	transitionRunStateTo(TERMINATED);
653	<	try {
654	<	pool.workerTerminated(this);
655	<	} finally {
656	<	if (exception != null)
502	<	ForkJoinTask.rethrowException(exception);
651	>	private ForkJoinTask<?> pollSubmission() {
652	>	ForkJoinPool p = pool;
653	>	while (p.hasQueuedSubmissions()) {
654	>	ForkJoinTask<?> t;
655	>	if (tryActivate() && (t = p.pollSubmission()) != null)
656	>	return t;
657		}
658	+	return null;
659		}
660
661	<	/**
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	<	}
661	>	// Methods accessed only by Pool
662
663		/**
664		* Removes and cancels all tasks in queue.  Can be called from any
665		* thread.
666		*/
667		final void cancelTasks() {
668	<	while (base != sp) {
669	<	ForkJoinTask<?> t = deqTask();
670	<	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	<	}
668	>	ForkJoinTask<?> t;
669	>	while (base != sp && (t = deqTask()) != null)
670	>	t.cancelIgnoringExceptions();
671		}
672
673		/**
674	<	* Main top-level action.
674	>	* Drains tasks to given collection c.
675	>	*
676	>	* @return the number of tasks drained
677		*/
678	<	private void step() {
679	<	ForkJoinTask<?> t = sp != base? popTask() : null;
680	<	if (t != null || (t = scan(null, true)) != null) {
681	<	activate();
682	<	t.quietlyExec();
683	<	}
558	<	else {
559	<	inactivate();
560	<	eventCount = pool.sync(this, eventCount);
678	>	final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
679	>	int n = 0;
680	>	ForkJoinTask<?> t;
681	>	while (base != sp && (t = deqTask()) != null) {
682	>	c.add(t);
683	>	++n;
684		}
685	+	return n;
686		}
687
564	–	// scanning for and stealing tasks
565	–
688		/**
689	<	* Computes next value for random victim probe. Scans don't
690	<	* 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
689	>	* Gets and clears steal count for accumulation by pool.  Called
690	>	* only when known to be idle (in pool.sync and termination).
691		*/
692	<	private static int xorShift(int r) {
693	<	r ^= r << 1;
694	<	r ^= r >>> 3;
695	<	r ^= r << 10;
577	<	return r;
692	>	final int getAndClearStealCount() {
693	>	int sc = stealCount;
694	>	stealCount = 0;
695	>	return sc;
696		}
697
698		/**
699	<	* Tries to steal a task from another worker and/or, if enabled,
700	<	* 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.
699	>	* Returns {@code true} if at least one worker in the given array
700	>	* appears to have at least one queued task.
701		*
702	<	* 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
702	>	* @param ws array of workers
703		*/
704	<	private ForkJoinTask<?> scan(ForkJoinTask<?> joinMe,
705	<	boolean checkSubmissions) {
706	<	ForkJoinPool p = pool;
707	<	if (p == null)                    // Never null, but avoids
708	<	return null;                  //   implicit nullchecks below
709	<	int r = randomVictimSeed;         // extract once to keep scan quiet
710	<	restart:                          // outer loop refreshes ws array
711	<	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;
704	>	static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
705	>	if (ws != null) {
706	>	int len = ws.length;
707	>	for (int j = 0; j < 2; ++j) { // need two passes for clean sweep
708	>	for (int i = 0; i < len; ++i) {
709	>	ForkJoinWorkerThread w = ws[i];
710	>	if (w != null && w.sp != w.base)
711	>	return true;
712		}
713		}
637	–	if (checkSubmissions && p.hasQueuedSubmissions()) {
638	–	activate();
639	–	ForkJoinTask<?> t = p.pollSubmission();
640	–	if (t != null)
641	–	return t;
642	–	}
643	–	else {
644	–	long ec = eventCount;     // restart on pool event
645	–	if ((eventCount = p.getEventCount()) == ec)
646	–	break;
647	–	}
648	–	}
649	–	return null;
650	–	}
651	–
652	–	/**
653	–	* Callback from pool.sync to rescan before blocking.  If a
654	–	* task is found, it is pushed so it can be executed upon return.
655	–	* @return true if found and pushed a task
656	–	*/
657	–	final boolean prescan() {
658	–	ForkJoinTask<?> t = scan(null, true);
659	–	if (t != null) {
660	–	pushTask(t);
661	–	return true;
662	–	}
663	–	else {
664	–	inactivate();
665	–	return false;
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	–	}
714		}
715	<	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);
715	>	return false;
716		}
717
718	<	/**
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	<	}
718	>	// Support methods for ForkJoinTask
719
720		/**
721		* Returns an estimate of the number of tasks in the queue.
722		*/
723		final int getQueueSize() {
724	<	int b = base;
725	<	int n = sp - b;
728	<	return n <= 0? 0 : n; // suppress momentarily negative values
724	>	// suppress momentarily negative values
725	>	return Math.max(0, sp - base);
726		}
727
728		/**
#	Line 733 | Line 730 | public class ForkJoinWorkerThread extend
730		* function of number of idle workers.
731		*/
732		final int getEstimatedSurplusTaskCount() {
733	+	// The halving approximates weighting idle vs non-idle workers
734		return (sp - base) - (pool.getIdleThreadCount() >>> 1);
735		}
736
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	–
737		/**
738	<	* 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
738	>	* Scans, returning early if joinMe done.
739		*/
740	<	public static int nextRandomInt() {
741	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
742	<	nextJURandom(32);
740	>	final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
741	>	ForkJoinTask<?> t = pollTask();
742	>	if (t != null && joinMe.status < 0 && sp == base) {
743	>	pushTask(t); // unsteal if done and this task would be stealable
744	>	t = null;
745	>	}
746	>	return t;
747		}
748
749		/**
750	<	* 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
750	>	* Runs tasks until {@code pool.isQuiescent()}.
751		*/
752	<	public static int nextRandomInt(int n) {
753	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
754	<	nextJURandomInt(n);
752	>	final void helpQuiescePool() {
753	>	for (;;) {
754	>	ForkJoinTask<?> t = pollTask();
755	>	if (t != null)
756	>	t.quietlyExec();
757	>	else if (tryInactivate() && pool.isQuiescent())
758	>	break;
759	>	}
760	>	do {} while (!tryActivate()); // re-activate on exit
761		}
762
763	<	/**
764	<	* Returns a random long using a per-worker random
765	<	* number generator with the same properties as
766	<	* {@link java.util.Random#nextLong}
767	<	* @return the next pseudorandom, uniformly distributed {@code long}
768	<	*         value from this worker's random number generator's sequence
769	<	*/
770	<	public static long nextRandomLong() {
771	<	return ((ForkJoinWorkerThread)(Thread.currentThread())).
772	<	nextJURandomLong();
763	>	// Unsafe mechanics
764	>
765	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
766	>	private static final long spOffset =
767	>	objectFieldOffset("sp", ForkJoinWorkerThread.class);
768	>	private static final long runStateOffset =
769	>	objectFieldOffset("runState", ForkJoinWorkerThread.class);
770	>	private static final long qBase;
771	>	private static final int qShift;
772	>
773	>	static {
774	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
775	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
776	>	if ((s & (s-1)) != 0)
777	>	throw new Error("data type scale not a power of two");
778	>	qShift = 31 - Integer.numberOfLeadingZeros(s);
779		}
780
781	<	/**
782	<	* Returns a random integer using a per-worker random
783	<	* number generator with the same properties as
784	<	* {@link java.util.Random#nextInt(int)}
785	<	* @param n the bound on the random number to be returned.  Must be
786	<	*        positive.
787	<	* @return the next pseudorandom, uniformly distributed {@code int}
788	<	*         value between {@code 0} (inclusive) and {@code n} (exclusive)
789	<	*         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);
781	>	private static long objectFieldOffset(String field, Class<?> klazz) {
782	>	try {
783	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
784	>	} catch (NoSuchFieldException e) {
785	>	// Convert Exception to corresponding Error
786	>	NoSuchFieldError error = new NoSuchFieldError(field);
787	>	error.initCause(e);
788	>	throw error;
789	>	}
790		}
791
792		/**
793	<	* Returns a random double using a per-worker random
794	<	* number generator with the same properties as
795	<	* {@link java.util.Random#nextDouble}
796	<	* @return the next pseudorandom, uniformly distributed {@code double}
797	<	*         value between {@code 0.0} and {@code 1.0} from this
854	<	*         worker's random number generator's sequence
793	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
794	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
795	>	* into a jdk.
796	>	*
797	>	* @return a sun.misc.Unsafe
798		*/
799	<	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 {
799	>	private static sun.misc.Unsafe getUnsafe() {
800		try {
801	<	if (ForkJoinWorkerThread.class.getClassLoader() != null) {
802	<	Field f = Unsafe.class.getDeclaredField("theUnsafe");
803	<	f.setAccessible(true);
804	<	_unsafe = (Unsafe)f.get(null);
801	>	return sun.misc.Unsafe.getUnsafe();
802	>	} catch (SecurityException se) {
803	>	try {
804	>	return java.security.AccessController.doPrivileged
805	>	(new java.security
806	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
807	>	public sun.misc.Unsafe run() throws Exception {
808	>	java.lang.reflect.Field f = sun.misc
809	>	.Unsafe.class.getDeclaredField("theUnsafe");
810	>	f.setAccessible(true);
811	>	return (sun.misc.Unsafe) f.get(null);
812	>	}});
813	>	} catch (java.security.PrivilegedActionException e) {
814	>	throw new RuntimeException("Could not initialize intrinsics",
815	>	e.getCause());
816		}
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);
817		}
818		}
819		}

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