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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.120 by jsr166, Tue Jan 31 01:32:25 2012 UTC vs.
Revision 1.135 by dl, Sun Oct 28 22:36:01 2012 UTC

#	Line 42 | Line 42 | import java.util.concurrent.locks.Condit
42		* ForkJoinPool}s may also be appropriate for use with event-style
43		* tasks that are never joined.
44		*
45	<	* <p>A {@code ForkJoinPool} is constructed with a given target
46	<	* parallelism level; by default, equal to the number of available
47	<	* processors. The pool attempts to maintain enough active (or
48	<	* available) threads by dynamically adding, suspending, or resuming
49	<	* internal worker threads, even if some tasks are stalled waiting to
50	<	* join others. However, no such adjustments are guaranteed in the
51	<	* face of blocked IO or other unmanaged synchronization. The nested
52	<	* {@link ManagedBlocker} interface enables extension of the kinds of
45	>	* <p>A static {@link #commonPool} is available and appropriate for
46	>	* most applications. The common pool is constructed upon first
47	>	* access, or upon usage by any ForkJoinTask that is not explictly
48	>	* submitted to a specified pool. Using the common pool normally
49	>	* reduces resource usage (its threads are slowly reclaimed during
50	>	* periods of non-use, and reinstated upon subsequent use).  The
51	>	* common pool is by default constructed with default parameters, but
52	>	* these may be controlled by setting any or all of the three
53	>	* properties {@code
54	>	* java.util.concurrent.ForkJoinPool.common.{parallelism,
55	>	* threadFactory, exceptionHandler}}.
56	>	*
57	>	* <p>For applications that require separate or custom pools, a {@code
58	>	* ForkJoinPool} may be constructed with a given target parallelism
59	>	* level; by default, equal to the number of available processors. The
60	>	* pool attempts to maintain enough active (or available) threads by
61	>	* dynamically adding, suspending, or resuming internal worker
62	>	* threads, even if some tasks are stalled waiting to join
63	>	* others. However, no such adjustments are guaranteed in the face of
64	>	* blocked IO or other unmanaged synchronization. The nested {@link
65	>	* ManagedBlocker} interface enables extension of the kinds of
66		* synchronization accommodated.
67		*
68		* <p>In addition to execution and lifecycle control methods, this
#	Line 94 | Line 107 | import java.util.concurrent.locks.Condit
107		*  </tr>
108		* </table>
109		*
97	–	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
98	–	* used for all parallel task execution in a program or subsystem.
99	–	* Otherwise, use would not usually outweigh the construction and
100	–	* bookkeeping overhead of creating a large set of threads. For
101	–	* example, a common pool could be used for the {@code SortTasks}
102	–	* illustrated in {@link RecursiveAction}. Because {@code
103	–	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
104	–	* daemon} mode, there is typically no need to explicitly {@link
105	–	* #shutdown} such a pool upon program exit.
106	–	*
107	–	*  <pre> {@code
108	–	* static final ForkJoinPool mainPool = new ForkJoinPool();
109	–	* ...
110	–	* public void sort(long[] array) {
111	–	*   mainPool.invoke(new SortTask(array, 0, array.length));
112	–	* }}</pre>
113	–	*
110		* <p><b>Implementation notes</b>: This implementation restricts the
111		* maximum number of running threads to 32767. Attempts to create
112		* pools with greater than the maximum number result in
#	Line 177 | Line 173 | public class ForkJoinPool extends Abstra
173		* If an attempted steal fails, a thief always chooses a different
174		* random victim target to try next. So, in order for one thief to
175		* progress, it suffices for any in-progress poll or new push on
176	<	* any empty queue to complete.
176	>	* any empty queue to complete. (This is why we normally use
177	>	* method pollAt and its variants that try once at the apparent
178	>	* base index, else consider alternative actions, rather than
179	>	* method poll.)
180		*
181		* This approach also enables support of a user mode in which local
182		* task processing is in FIFO, not LIFO order, simply by using
#	Line 207 | Line 206 | public class ForkJoinPool extends Abstra
206		* lock (mainly to protect in the case of resizing) but we use
207		* only a simple spinlock (using bits in field runState), because
208		* submitters encountering a busy queue move on to try or create
209	<	* other queues, so never block.
209	>	* other queues -- they block only when creating and registering
210	>	* new queues.
211		*
212		* Management
213		* ==========
#	Line 233 | Line 233 | public class ForkJoinPool extends Abstra
233		* deregister WorkQueues, as well as to enable shutdown. It is
234		* only modified under a lock (normally briefly held, but
235		* occasionally protecting allocations and resizings) but even
236	<	* when locked remains available to check consistency. An
237	<	* auxiliary field "growHints", also only modified under lock,
238	<	* contains a candidate index for the next WorkQueue and
239	<	* a mask for submission queue indices.
236	>	* when locked remains available to check consistency.
237		*
238		* Recording WorkQueues.  WorkQueues are recorded in the
239		* "workQueues" array that is created upon pool construction and
#	Line 248 | Line 245 | public class ForkJoinPool extends Abstra
245		* readers must tolerate null slots. Shared (submission) queues
246		* are at even indices, worker queues at odd indices. Grouping
247		* them together in this way simplifies and speeds up task
248	<	* scanning. To avoid flailing during start-up, the array is
252	<	* presized to hold twice #parallelism workers (which is unlikely
253	<	* to need further resizing during execution). But to avoid
254	<	* dealing with so many null slots, variable runState includes a
255	<	* mask for the nearest power of two that contains all currently
256	<	* used indices.
248	>	* scanning.
249		*
250		* All worker thread creation is on-demand, triggered by task
251		* submissions, replacement of terminated workers, and/or
#	Line 325 | Line 317 | public class ForkJoinPool extends Abstra
317		*
318		* Trimming workers. To release resources after periods of lack of
319		* use, a worker starting to wait when the pool is quiescent will
320	<	* time out and terminate if the pool has remained quiescent for
321	<	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
322	<	* terminating all workers after long periods of non-use.
320	>	* time out and terminate if the pool has remained quiescent for a
321	>	* given period -- a short period if there are more threads than
322	>	* parallelism, longer as the number of threads decreases. This
323	>	* will slowly propagate, eventually terminating all workers after
324	>	* periods of non-use.
325		*
326		* Shutdown and Termination. A call to shutdownNow atomically sets
327		* a runState bit and then (non-atomically) sets each worker's
#	Line 385 | Line 379 | public class ForkJoinPool extends Abstra
379		* (http://portal.acm.org/citation.cfm?id=155354). It differs in
380		* that: (1) We only maintain dependency links across workers upon
381		* steals, rather than use per-task bookkeeping.  This sometimes
382	<	* requires a linear scan of workQueues array to locate stealers, but
383	<	* often doesn't because stealers leave hints (that may become
382	>	* requires a linear scan of workQueues array to locate stealers,
383	>	* but often doesn't because stealers leave hints (that may become
384		* stale/wrong) of where to locate them.  A stealHint is only a
385		* hint because a worker might have had multiple steals and the
386		* hint records only one of them (usually the most current).
#	Line 397 | Line 391 | public class ForkJoinPool extends Abstra
391		* which means that we miss links in the chain during long-lived
392		* tasks, GC stalls etc (which is OK since blocking in such cases
393		* is usually a good idea).  (4) We bound the number of attempts
394	<	* to find work (see MAX_HELP_DEPTH) and fall back to suspending
395	<	* the worker and if necessary replacing it with another.
394	>	* to find work (see MAX_HELP) and fall back to suspending the
395	>	* worker and if necessary replacing it with another.
396		*
397		* It is impossible to keep exactly the target parallelism number
398		* of threads running at any given time.  Determining the
399		* existence of conservatively safe helping targets, the
400		* availability of already-created spares, and the apparent need
401		* to create new spares are all racy, so we rely on multiple
402	<	* retries of each.  Currently, in keeping with on-demand
403	<	* signalling policy, we compensate only if blocking would leave
404	<	* less than one active (non-waiting, non-blocked) worker.
405	<	* Additionally, to avoid some false alarms due to GC, lagging
406	<	* counters, system activity, etc, compensated blocking for joins
407	<	* is only attempted after rechecks stabilize in
408	<	* ForkJoinTask.awaitJoin. (Retries are interspersed with
409	<	* Thread.yield, for good citizenship.)
402	>	* retries of each.  Compensation in the apparent absence of
403	>	* helping opportunities is challenging to control on JVMs, where
404	>	* GC and other activities can stall progress of tasks that in
405	>	* turn stall out many other dependent tasks, without us being
406	>	* able to determine whether they will ever require compensation.
407	>	* Even though work-stealing otherwise encounters little
408	>	* degradation in the presence of more threads than cores,
409	>	* aggressively adding new threads in such cases entails risk of
410	>	* unwanted positive feedback control loops in which more threads
411	>	* cause more dependent stalls (as well as delayed progress of
412	>	* unblocked threads to the point that we know they are available)
413	>	* leading to more situations requiring more threads, and so
414	>	* on. This aspect of control can be seen as an (analytically
415	>	* intractable) game with an opponent that may choose the worst
416	>	* (for us) active thread to stall at any time.  We take several
417	>	* precautions to bound losses (and thus bound gains), mainly in
418	>	* methods tryCompensate and awaitJoin: (1) We only try
419	>	* compensation after attempting enough helping steps (measured
420	>	* via counting and timing) that we have already consumed the
421	>	* estimated cost of creating and activating a new thread.  (2) We
422	>	* allow up to 50% of threads to be blocked before initially
423	>	* adding any others, and unless completely saturated, check that
424	>	* some work is available for a new worker before adding. Also, we
425	>	* create up to only 50% more threads until entering a mode that
426	>	* only adds a thread if all others are possibly blocked.  All
427	>	* together, this means that we might be half as fast to react,
428	>	* and create half as many threads as possible in the ideal case,
429	>	* but present vastly fewer anomalies in all other cases compared
430	>	* to both more aggressive and more conservative alternatives.
431		*
432		* Style notes: There is a lot of representation-level coupling
433		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 449 | Line 464 | public class ForkJoinPool extends Abstra
464		// Static utilities
465
466		/**
452	–	* Computes an initial hash code (also serving as a non-zero
453	–	* random seed) for a thread id. This method is expected to
454	–	* provide higher-quality hash codes than using method hashCode().
455	–	*/
456	–	static final int hashId(long id) {
457	–	int h = (int)id ^ (int)(id >>> 32); // Use MurmurHash of thread id
458	–	h ^= h >>> 16; h *= 0x85ebca6b;
459	–	h ^= h >>> 13; h *= 0xc2b2ae35;
460	–	h ^= h >>> 16;
461	–	return (h == 0)? 1 : h; // ensure nonzero
462	–	}
463	–
464	–	/**
467		* If there is a security manager, makes sure caller has
468		* permission to modify threads.
469		*/
#	Line 592 | Line 594 | public class ForkJoinPool extends Abstra
594		static final class WorkQueue {
595		/**
596		* Capacity of work-stealing queue array upon initialization.
597	<	* Must be a power of two; at least 4, but set larger to
598	<	* reduce cacheline sharing among queues.
597	>	* Must be a power of two; at least 4, but should be larger to
598	>	* reduce or eliminate cacheline sharing among queues.
599	>	* Currently, it is much larger, as a partial workaround for
600	>	* the fact that JVMs often place arrays in locations that
601	>	* share GC bookkeeping (especially cardmarks) such that
602	>	* per-write accesses encounter serious memory contention.
603		*/
604	<	static final int INITIAL_QUEUE_CAPACITY = 1 << 8;
604	>	static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
605
606		/**
607		* Maximum size for queue arrays. Must be a power of two less
#	Line 619 | Line 625 | public class ForkJoinPool extends Abstra
625		volatile int base;         // index of next slot for poll
626		int top;                   // index of next slot for push
627		ForkJoinTask<?>[] array;   // the elements (initially unallocated)
628	+	final ForkJoinPool pool;   // the containing pool (may be null)
629		final ForkJoinWorkerThread owner; // owning thread or null if shared
630		volatile Thread parker;    // == owner during call to park; else null
631	<	ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
631	>	volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
632		ForkJoinTask<?> currentSteal; // current non-local task being executed
633		// Heuristic padding to ameliorate unfortunate memory placements
634	<	Object p00, p01, p02, p03, p04, p05, p06, p07, p08, p09, p0a;
634	>	Object p00, p01, p02, p03, p04, p05, p06, p07;
635	>	Object p08, p09, p0a, p0b, p0c, p0d, p0e;
636
637	<	WorkQueue(ForkJoinWorkerThread owner, int mode) {
630	<	this.owner = owner;
637	>	WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
638		this.mode = mode;
639	+	this.pool = pool;
640	+	this.owner = owner;
641		// Place indices in the center of array (that is not yet allocated)
642		base = top = INITIAL_QUEUE_CAPACITY >>> 1;
643		}
644
645		/**
646	<	* Returns number of tasks in the queue.
646	>	* Returns the approximate number of tasks in the queue.
647		*/
648		final int queueSize() {
649	<	int n = base - top; // non-owner callers must read base first
650	<	return (n >= 0) ? 0 : -n;
649	>	int n = base - top;       // non-owner callers must read base first
650	>	return (n >= 0) ? 0 : -n; // ignore transient negative
651	>	}
652	>
653	>	/**
654	>	* Provides a more accurate estimate of whether this queue has
655	>	* any tasks than does queueSize, by checking whether a
656	>	* near-empty queue has at least one unclaimed task.
657	>	*/
658	>	final boolean isEmpty() {
659	>	ForkJoinTask<?>[] a; int m, s;
660	>	int n = base - (s = top);
661	>	return (n >= 0 ||
662	>	(n == -1 &&
663	>	((a = array) == null ||
664	>	(m = a.length - 1) < 0 ||
665	>	U.getObjectVolatile
666	>	(a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
667		}
668
669		/**
670		* Pushes a task. Call only by owner in unshared queues.
671		*
672		* @param task the task. Caller must ensure non-null.
648	–	* @param p if non-null, pool to signal if necessary
673		* @throw RejectedExecutionException if array cannot be resized
674		*/
675	<	final void push(ForkJoinTask<?> task, ForkJoinPool p) {
676	<	ForkJoinTask<?>[] a;
675	>	final void push(ForkJoinTask<?> task) {
676	>	ForkJoinTask<?>[] a; ForkJoinPool p;
677		int s = top, m, n;
678		if ((a = array) != null) {    // ignore if queue removed
679		U.putOrderedObject
680		(a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
681		if ((n = (top = s + 1) - base) <= 2) {
682	<	if (p != null)
682	>	if ((p = pool) != null)
683		p.signalWork();
684		}
685		else if (n >= m)
#	Line 691 | Line 715 | public class ForkJoinPool extends Abstra
715		}
716
717		/**
718	<	* Takes next task, if one exists, in FIFO order.
718	>	* Takes next task, if one exists, in LIFO order.  Call only
719	>	* by owner in unshared queues. (We do not have a shared
720	>	* version of this method because it is never needed.)
721		*/
722	<	final ForkJoinTask<?> poll() {
723	<	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
724	<	while ((b = base) - top < 0 && (a = array) != null) {
722	>	final ForkJoinTask<?> pop() {
723	>	ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
724	>	if ((a = array) != null && (m = a.length - 1) >= 0) {
725	>	for (int s; (s = top - 1) - base >= 0;) {
726	>	long j = ((m & s) << ASHIFT) + ABASE;
727	>	if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
728	>	break;
729	>	if (U.compareAndSwapObject(a, j, t, null)) {
730	>	top = s;
731	>	return t;
732	>	}
733	>	}
734	>	}
735	>	return null;
736	>	}
737	>
738	>	/**
739	>	* Takes a task in FIFO order if b is base of queue and a task
740	>	* can be claimed without contention. Specialized versions
741	>	* appear in ForkJoinPool methods scan and tryHelpStealer.
742	>	*/
743	>	final ForkJoinTask<?> pollAt(int b) {
744	>	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
745	>	if ((a = array) != null) {
746		int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
747		if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
748		base == b &&
#	Line 708 | Line 755 | public class ForkJoinPool extends Abstra
755		}
756
757		/**
758	<	* Takes next task, if one exists, in LIFO order.  Call only
712	<	* by owner in unshared queues. (We do not have a shared
713	<	* version of this method because it is never needed.)
758	>	* Takes next task, if one exists, in FIFO order.
759		*/
760	<	final ForkJoinTask<?> pop() {
761	<	ForkJoinTask<?> t; int m;
762	<	ForkJoinTask<?>[] a = array;
763	<	if (a != null && (m = a.length - 1) >= 0) {
764	<	for (int s; (s = top - 1) - base >= 0;) {
765	<	int j = ((m & s) << ASHIFT) + ABASE;
766	<	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) == null)
767	<	break;
768	<	if (U.compareAndSwapObject(a, j, t, null)) {
724	<	top = s;
760	>	final ForkJoinTask<?> poll() {
761	>	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
762	>	while ((b = base) - top < 0 && (a = array) != null) {
763	>	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
764	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
765	>	if (t != null) {
766	>	if (base == b &&
767	>	U.compareAndSwapObject(a, j, t, null)) {
768	>	base = b + 1;
769		return t;
770		}
771		}
772	+	else if (base == b) {
773	+	if (b + 1 == top)
774	+	break;
775	+	Thread.yield(); // wait for lagging update
776	+	}
777		}
778		return null;
779		}
#	Line 749 | Line 798 | public class ForkJoinPool extends Abstra
798		}
799
800		/**
752	–	* Returns task at index b if b is current base of queue.
753	–	*/
754	–	final ForkJoinTask<?> pollAt(int b) {
755	–	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
756	–	if ((a = array) != null) {
757	–	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
758	–	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
759	–	base == b &&
760	–	U.compareAndSwapObject(a, j, t, null)) {
761	–	base = b + 1;
762	–	return t;
763	–	}
764	–	}
765	–	return null;
766	–	}
767	–
768	–	/**
801		* Pops the given task only if it is at the current top.
802		*/
803		final boolean tryUnpush(ForkJoinTask<?> t) {
#	Line 780 | Line 812 | public class ForkJoinPool extends Abstra
812		}
813
814		/**
815	+	* Version of tryUnpush for shared queues; called by non-FJ
816	+	* submitters. Conservatively fails to unpush if all workers
817	+	* are active unless there are multiple tasks in queue.
818	+	*/
819	+	final boolean trySharedUnpush(ForkJoinTask<?> task, ForkJoinPool p) {
820	+	boolean success = false;
821	+	if (task != null && top != base && runState == 0 &&
822	+	U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
823	+	try {
824	+	ForkJoinTask<?>[] a; int n, s;
825	+	if ((a = array) != null && (n = (s = top) - base) > 0 &&
826	+	(n > 1 || p == null || (int)(p.ctl >> AC_SHIFT) < 0)) {
827	+	int j = (((a.length - 1) & --s) << ASHIFT) + ABASE;
828	+	if (U.getObjectVolatile(a, j) == task &&
829	+	U.compareAndSwapObject(a, j, task, null)) {
830	+	top = s;
831	+	success = true;
832	+	}
833	+	}
834	+	} finally {
835	+	runState = 0;                         // unlock
836	+	}
837	+	}
838	+	return success;
839	+	}
840	+
841	+	/**
842		* Polls the given task only if it is at the current base.
843		*/
844		final boolean pollFor(ForkJoinTask<?> task) {
#	Line 796 | Line 855 | public class ForkJoinPool extends Abstra
855		}
856
857		/**
799	–	* If present, removes from queue and executes the given task, or
800	–	* any other cancelled task. Returns (true) immediately on any CAS
801	–	* or consistency check failure so caller can retry.
802	–	*
803	–	* @return false if no progress can be made
804	–	*/
805	–	final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
806	–	boolean removed = false, empty = true, progress = true;
807	–	ForkJoinTask<?>[] a; int m, s, b, n;
808	–	if ((a = array) != null && (m = a.length - 1) >= 0 &&
809	–	(n = (s = top) - (b = base)) > 0) {
810	–	for (ForkJoinTask<?> t;;) {           // traverse from s to b
811	–	int j = ((--s & m) << ASHIFT) + ABASE;
812	–	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
813	–	if (t == null)                    // inconsistent length
814	–	break;
815	–	else if (t == task) {
816	–	if (s + 1 == top) {           // pop
817	–	if (!U.compareAndSwapObject(a, j, task, null))
818	–	break;
819	–	top = s;
820	–	removed = true;
821	–	}
822	–	else if (base == b)           // replace with proxy
823	–	removed = U.compareAndSwapObject(a, j, task,
824	–	new EmptyTask());
825	–	break;
826	–	}
827	–	else if (t.status >= 0)
828	–	empty = false;
829	–	else if (s + 1 == top) {          // pop and throw away
830	–	if (U.compareAndSwapObject(a, j, t, null))
831	–	top = s;
832	–	break;
833	–	}
834	–	if (--n == 0) {
835	–	if (!empty && base == b)
836	–	progress = false;
837	–	break;
838	–	}
839	–	}
840	–	}
841	–	if (removed)
842	–	task.doExec();
843	–	return progress;
844	–	}
845	–
846	–	/**
858		* Initializes or doubles the capacity of array. Call either
859		* by owner or with lock held -- it is OK for base, but not
860		* top, to move while resizings are in progress.
#	Line 892 | Line 903 | public class ForkJoinPool extends Abstra
903		* Computes next value for random probes.  Scans don't require
904		* a very high quality generator, but also not a crummy one.
905		* Marsaglia xor-shift is cheap and works well enough.  Note:
906	<	* This is manually inlined in several usages in ForkJoinPool
907	<	* to avoid writes inside busy scan loops.
906	>	* This is manually inlined in its usages in ForkJoinPool to
907	>	* avoid writes inside busy scan loops.
908		*/
909		final int nextSeed() {
910		int r = seed;
#	Line 905 | Line 916 | public class ForkJoinPool extends Abstra
916		// Execution methods
917
918		/**
919	<	* Removes and runs tasks until empty, using local mode
909	<	* ordering.
919	>	* Pops and runs tasks until empty.
920		*/
921	<	final void runLocalTasks() {
922	<	if (base - top < 0) {
923	<	for (ForkJoinTask<?> t; (t = nextLocalTask()) != null; )
921	>	private void popAndExecAll() {
922	>	// A bit faster than repeated pop calls
923	>	ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
924	>	while ((a = array) != null && (m = a.length - 1) >= 0 &&
925	>	(s = top - 1) - base >= 0 &&
926	>	(t = ((ForkJoinTask<?>)
927	>	U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
928	>	!= null) {
929	>	if (U.compareAndSwapObject(a, j, t, null)) {
930	>	top = s;
931		t.doExec();
932	+	}
933	+	}
934	+	}
935	+
936	+	/**
937	+	* Polls and runs tasks until empty.
938	+	*/
939	+	private void pollAndExecAll() {
940	+	for (ForkJoinTask<?> t; (t = poll()) != null;)
941	+	t.doExec();
942	+	}
943	+
944	+	/**
945	+	* If present, removes from queue and executes the given task, or
946	+	* any other cancelled task. Returns (true) immediately on any CAS
947	+	* or consistency check failure so caller can retry.
948	+	*
949	+	* @return 0 if no progress can be made, else positive
950	+	* (this unusual convention simplifies use with tryHelpStealer.)
951	+	*/
952	+	final int tryRemoveAndExec(ForkJoinTask<?> task) {
953	+	int stat = 1;
954	+	boolean removed = false, empty = true;
955	+	ForkJoinTask<?>[] a; int m, s, b, n;
956	+	if ((a = array) != null && (m = a.length - 1) >= 0 &&
957	+	(n = (s = top) - (b = base)) > 0) {
958	+	for (ForkJoinTask<?> t;;) {           // traverse from s to b
959	+	int j = ((--s & m) << ASHIFT) + ABASE;
960	+	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
961	+	if (t == null)                    // inconsistent length
962	+	break;
963	+	else if (t == task) {
964	+	if (s + 1 == top) {           // pop
965	+	if (!U.compareAndSwapObject(a, j, task, null))
966	+	break;
967	+	top = s;
968	+	removed = true;
969	+	}
970	+	else if (base == b)           // replace with proxy
971	+	removed = U.compareAndSwapObject(a, j, task,
972	+	new EmptyTask());
973	+	break;
974	+	}
975	+	else if (t.status >= 0)
976	+	empty = false;
977	+	else if (s + 1 == top) {          // pop and throw away
978	+	if (U.compareAndSwapObject(a, j, t, null))
979	+	top = s;
980	+	break;
981	+	}
982	+	if (--n == 0) {
983	+	if (!empty && base == b)
984	+	stat = 0;
985	+	break;
986	+	}
987	+	}
988		}
989	+	if (removed)
990	+	task.doExec();
991	+	return stat;
992		}
993
994		/**
995		* Executes a top-level task and any local tasks remaining
996		* after execution.
921	–	*
922	–	* @return true unless terminating
997		*/
998	<	final boolean runTask(ForkJoinTask<?> t) {
925	<	boolean alive = true;
998	>	final void runTask(ForkJoinTask<?> t) {
999		if (t != null) {
1000		currentSteal = t;
1001		t.doExec();
1002	<	runLocalTasks();
1002	>	if (top != base) {       // process remaining local tasks
1003	>	if (mode == 0)
1004	>	popAndExecAll();
1005	>	else
1006	>	pollAndExecAll();
1007	>	}
1008		++nsteals;
1009		currentSteal = null;
1010		}
933	–	else if (runState < 0)            // terminating
934	–	alive = false;
935	–	return alive;
1011		}
1012
1013		/**
#	Line 1005 | Line 1080 | public class ForkJoinPool extends Abstra
1080		* submission queues in method doSubmit. In the future, this may
1081		* also incorporate a means to implement different task rejection
1082		* and resubmission policies.
1083	+	*
1084	+	* Seeds for submitters and workers/workQueues work in basically
1085	+	* the same way but are initialized and updated using slightly
1086	+	* different mechanics. Both are initialized using the same
1087	+	* approach as in class ThreadLocal, where successive values are
1088	+	* unlikely to collide with previous values. This is done during
1089	+	* registration for workers, but requires a separate AtomicInteger
1090	+	* for submitters. Seeds are then randomly modified upon
1091	+	* collisions using xorshifts, which requires a non-zero seed.
1092		*/
1093		static final class Submitter {
1094		int seed;
1095	<	Submitter() { seed = hashId(Thread.currentThread().getId()); }
1095	>	Submitter() {
1096	>	int s = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
1097	>	seed = (s == 0) ? 1 : s; // ensure non-zero
1098	>	}
1099		}
1100
1101		/** ThreadLocal class for Submitters */
#	Line 1031 | Line 1118 | public class ForkJoinPool extends Abstra
1118		private static final AtomicInteger poolNumberGenerator;
1119
1120		/**
1121	+	* Generator for initial hashes/seeds for submitters. Accessed by
1122	+	* Submitter class constructor.
1123	+	*/
1124	+	static final AtomicInteger nextSubmitterSeed;
1125	+
1126	+	/**
1127		* Permission required for callers of methods that may start or
1128		* kill threads.
1129		*/
1130		private static final RuntimePermission modifyThreadPermission;
1131
1132		/**
1133	<	* Per-thread submission bookeeping. Shared across all pools
1133	>	* Per-thread submission bookkeeping. Shared across all pools
1134		* to reduce ThreadLocal pollution and because random motion
1135		* to avoid contention in one pool is likely to hold for others.
1136		*/
1137		private static final ThreadSubmitter submitters;
1138
1139	+	/** Common default pool */
1140	+	static volatile ForkJoinPool commonPool;
1141	+
1142	+	// commonPool construction parameters
1143	+	private static final String propPrefix =
1144	+	"java.util.concurrent.ForkJoinPool.common.";
1145	+	private static final Thread.UncaughtExceptionHandler commonPoolUEH;
1146	+	private static final ForkJoinWorkerThreadFactory commonPoolFactory;
1147	+	static final int commonPoolParallelism;
1148	+
1149	+	/** Static initialization lock */
1150	+	private static final Mutex initializationLock;
1151	+
1152		// static constants
1153
1154		/**
1155	<	* The wakeup interval (in nanoseconds) for a worker waiting for a
1156	<	* task when the pool is quiescent to instead try to shrink the
1157	<	* number of workers.  The exact value does not matter too
1158	<	* much. It must be short enough to release resources during
1159	<	* sustained periods of idleness, but not so short that threads
1160	<	* are continually re-created.
1155	>	* Initial timeout value (in nanoseconds) for the tread triggering
1156	>	* quiescence to park waiting for new work. On timeout, the thread
1157	>	* will instead try to shrink the number of workers.
1158	>	*/
1159	>	private static final long IDLE_TIMEOUT      = 1000L * 1000L * 1000L; // 1sec
1160	>
1161	>	/**
1162	>	* Timeout value when there are more threads than parallelism level
1163	>	*/
1164	>	private static final long FAST_IDLE_TIMEOUT =  100L * 1000L * 1000L;
1165	>
1166	>	/**
1167	>	* The maximum stolen->joining link depth allowed in method
1168	>	* tryHelpStealer.  Must be a power of two. This value also
1169	>	* controls the maximum number of times to try to help join a task
1170	>	* without any apparent progress or change in pool state before
1171	>	* giving up and blocking (see awaitJoin).  Depths for legitimate
1172	>	* chains are unbounded, but we use a fixed constant to avoid
1173	>	* (otherwise unchecked) cycles and to bound staleness of
1174	>	* traversal parameters at the expense of sometimes blocking when
1175	>	* we could be helping.
1176		*/
1177	<	private static final long SHRINK_RATE =
1057	<	4L * 1000L * 1000L * 1000L; // 4 seconds
1177	>	private static final int MAX_HELP = 64;
1178
1179		/**
1180	<	* The timeout value for attempted shrinkage, includes
1181	<	* some slop to cope with system timer imprecision.
1180	>	* Secondary time-based bound (in nanosecs) for helping attempts
1181	>	* before trying compensated blocking in awaitJoin. Used in
1182	>	* conjunction with MAX_HELP to reduce variance due to different
1183	>	* polling rates associated with different helping options. The
1184	>	* value should roughly approximate the time required to create
1185	>	* and/or activate a worker thread.
1186		*/
1187	<	private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
1187	>	private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
1188
1189		/**
1190	<	* The maximum stolen->joining link depth allowed in tryHelpStealer.
1191	<	* Depths for legitimate chains are unbounded, but we use a fixed
1068	<	* constant to avoid (otherwise unchecked) cycles and to bound
1069	<	* staleness of traversal parameters at the expense of sometimes
1070	<	* blocking when we could be helping.
1190	>	* Increment for seed generators. See class ThreadLocal for
1191	>	* explanation.
1192		*/
1193	<	private static final int MAX_HELP_DEPTH = 16;
1193	>	private static final int SEED_INCREMENT = 0x61c88647;
1194
1195		/**
1196		* Bits and masks for control variables
#	Line 1101 | Line 1222 | public class ForkJoinPool extends Abstra
1222		*
1223		* Field runState is an int packed with:
1224		* SHUTDOWN: true if shutdown is enabled (1 bit)
1225	<	* SEQ:  a sequence number updated upon (de)registering workers (15 bits)
1226	<	* MASK: mask (power of 2 - 1) covering all registered poolIndexes (16 bits)
1225	>	* SEQ:  a sequence number updated upon (de)registering workers (30 bits)
1226	>	* INIT: set true after workQueues array construction (1 bit)
1227		*
1228	<	* The combination of mask and sequence number enables simple
1229	<	* consistency checks: Staleness of read-only operations on the
1230	<	* workQueues array can be checked by comparing runState before vs
1110	<	* after the reads. The low 16 bits (i.e, anding with SMASK) hold
1111	<	* the smallest power of two covering all indices, minus
1112	<	* one.
1228	>	* The sequence number enables simple consistency checks:
1229	>	* Staleness of read-only operations on the workQueues array can
1230	>	* be checked by comparing runState before vs after the reads.
1231		*/
1232
1233		// bit positions/shifts for fields
#	Line 1119 | Line 1237 | public class ForkJoinPool extends Abstra
1237		private static final int  EC_SHIFT   = 16;
1238
1239		// bounds
1122	–	private static final int  POOL_MAX   = 0x7fff;  // max #workers - 1
1240		private static final int  SMASK      = 0xffff;  // short bits
1241	+	private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
1242		private static final int  SQMASK     = 0xfffe;  // even short bits
1243		private static final int  SHORT_SIGN = 1 << 15;
1244		private static final int  INT_SIGN   = 1 << 31;
#	Line 1148 | Line 1266 | public class ForkJoinPool extends Abstra
1266
1267		// runState bits
1268		private static final int SHUTDOWN    = 1 << 31;
1151	–	private static final int RS_SEQ      = 1 << 16;
1152	–	private static final int RS_SEQ_MASK = 0x7fff0000;
1269
1270		// access mode for WorkQueue
1271		static final int LIFO_QUEUE          =  0;
#	Line 1168 | Line 1284 | public class ForkJoinPool extends Abstra
1284		volatile long ctl;                         // main pool control
1285		final int parallelism;                     // parallelism level
1286		final int localMode;                       // per-worker scheduling mode
1287	<	int growHints;                             // for expanding indices/ranges
1288	<	volatile int runState;                     // shutdown status, seq, and mask
1287	>	final int submitMask;                      // submit queue index bound
1288	>	int nextSeed;                              // for initializing worker seeds
1289	>	volatile int runState;                     // shutdown status and seq
1290		WorkQueue[] workQueues;                    // main registry
1291		final Mutex lock;                          // for registration
1292		final Condition termination;               // for awaitTermination
#	Line 1177 | Line 1294 | public class ForkJoinPool extends Abstra
1294		final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
1295		final AtomicLong stealCount;               // collect counts when terminated
1296		final AtomicInteger nextWorkerNumber;      // to create worker name string
1297	<	final String workerNamePrefix;             // to create worker name string
1297	>	String workerNamePrefix;                   // to create worker name string
1298
1299	<	//  Creating, registering, deregistering and running workers
1299	>	//  Creating, registering, and deregistering workers
1300
1301		/**
1302		* Tries to create and start a worker
#	Line 1210 | Line 1327 | public class ForkJoinPool extends Abstra
1327		}
1328
1329		/**
1330	<	* Callback from ForkJoinWorkerThread constructor to establish and
1331	<	* record its WorkQueue.
1330	>	* Callback from ForkJoinWorkerThread constructor to establish its
1331	>	* poolIndex and record its WorkQueue. To avoid scanning bias due
1332	>	* to packing entries in front of the workQueues array, we treat
1333	>	* the array as a simple power-of-two hash table using per-thread
1334	>	* seed as hash, expanding as needed.
1335		*
1336	<	* @param wt the worker thread
1336	>	* @param w the worker's queue
1337		*/
1338	<	final void registerWorker(ForkJoinWorkerThread wt) {
1219	<	WorkQueue w = wt.workQueue;
1338	>	final void registerWorker(WorkQueue w) {
1339		Mutex lock = this.lock;
1340		lock.lock();
1341		try {
1223	–	int g = growHints, k = g & SMASK;
1342		WorkQueue[] ws = workQueues;
1343	<	if (ws != null) {                       // ignore on shutdown
1344	<	int n = ws.length;
1345	<	if ((k & 1) == 0 || k >= n || ws[k] != null) {
1346	<	for (k = 1; k < n && ws[k] != null; k += 2)
1347	<	;                           // workers are at odd indices
1348	<	if (k >= n)                     // resize
1349	<	workQueues = ws = Arrays.copyOf(ws, n << 1);
1350	<	}
1351	<	w.eventCount = w.poolIndex = k;     // establish before recording
1352	<	ws[k] = w;
1353	<	growHints = (g & ~SMASK) | ((k + 2) & SMASK);
1354	<	int rs = runState;
1355	<	int m = rs & SMASK;                 // recalculate runState mask
1356	<	if (k > m)
1357	<	m = (m << 1) + 1;
1358	<	runState = (rs & SHUTDOWN) | ((rs + RS_SEQ) & RS_SEQ_MASK) | m;
1343	>	if (w != null && ws != null) {          // skip on shutdown/failure
1344	>	int rs, n = ws.length, m = n - 1;
1345	>	int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
1346	>	w.seed = (s == 0) ? 1 : s;          // ensure non-zero seed
1347	>	int r = (s << 1) | 1;               // use odd-numbered indices
1348	>	if (ws[r &= m] != null) {           // collision
1349	>	int probes = 0;                 // step by approx half size
1350	>	int step = (n <= 4) ? 2 : ((n >>> 1) & SQMASK) + 2;
1351	>	while (ws[r = (r + step) & m] != null) {
1352	>	if (++probes >= n) {
1353	>	workQueues = ws = Arrays.copyOf(ws, n <<= 1);
1354	>	m = n - 1;
1355	>	probes = 0;
1356	>	}
1357	>	}
1358	>	}
1359	>	w.eventCount = w.poolIndex = r;     // establish before recording
1360	>	ws[r] = w;                          // also update seq
1361	>	runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
1362		}
1363		} finally {
1364		lock.unlock();
#	Line 1254 | Line 1375 | public class ForkJoinPool extends Abstra
1375		* @param ex the exception causing failure, or null if none
1376		*/
1377		final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1378	+	Mutex lock = this.lock;
1379		WorkQueue w = null;
1380		if (wt != null && (w = wt.workQueue) != null) {
1381		w.runState = -1;                // ensure runState is set
1382		stealCount.getAndAdd(w.totalSteals + w.nsteals);
1383		int idx = w.poolIndex;
1262	–	Mutex lock = this.lock;
1384		lock.lock();
1385		try {                           // remove record from array
1386		WorkQueue[] ws = workQueues;
1387	<	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w) {
1387	>	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
1388		ws[idx] = null;
1268	–	growHints = (growHints & ~SMASK) | idx;
1269	–	}
1389		} finally {
1390		lock.unlock();
1391		}
#	Line 1290 | Line 1409 | public class ForkJoinPool extends Abstra
1409		U.throwException(ex);
1410		}
1411
1293	–	/**
1294	–	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1295	–	*/
1296	–	final void runWorker(ForkJoinWorkerThread wt) {
1297	–	// Initialize queue array and seed in this thread
1298	–	WorkQueue w = wt.workQueue;
1299	–	w.growArray(false);
1300	–	w.seed = hashId(Thread.currentThread().getId());
1301	–
1302	–	do {} while (w.runTask(scan(w)));
1303	–	}
1304	–
1412		// Submissions
1413
1414		/**
1415		* Unless shutting down, adds the given task to a submission queue
1416		* at submitter's current queue index (modulo submission
1417	<	* range). If no queue exists at the index, one is created unless
1418	<	* pool lock is busy.  If the queue and/or lock are busy, another
1419	<	* index is randomly chosen. The mask in growHints controls the
1420	<	* effective index range of queues considered. The mask is
1421	<	* expanded, up to the current workerQueue mask, upon any detected
1422	<	* contention but otherwise remains small to avoid needlessly
1316	<	* creating queues when there is no contention.
1417	>	* range). If no queue exists at the index, one is created.  If
1418	>	* the queue is busy, another index is randomly chosen. The
1419	>	* submitMask bounds the effective number of queues to the
1420	>	* (nearest power of two for) parallelism level.
1421	>	*
1422	>	* @param task the task. Caller must ensure non-null.
1423		*/
1424		private void doSubmit(ForkJoinTask<?> task) {
1319	–	if (task == null)
1320	–	throw new NullPointerException();
1425		Submitter s = submitters.get();
1426	<	for (int r = s.seed, m = growHints >>> 16;;) {
1427	<	WorkQueue[] ws; WorkQueue q; Mutex lk;
1426	>	for (int r = s.seed, m = submitMask;;) {
1427	>	WorkQueue[] ws; WorkQueue q;
1428		int k = r & m & SQMASK;          // use only even indices
1429		if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
1430		throw new RejectedExecutionException(); // shutting down
1431	<	if ((q = ws[k]) == null && (lk = lock).tryAcquire(0)) {
1432	<	try {                        // try to create new queue
1433	<	if (ws == workQueues && (q = ws[k]) == null) {
1434	<	int rs;              // update runState seq
1435	<	ws[k] = q = new WorkQueue(null, SHARED_QUEUE);
1436	<	runState = (((rs = runState) & SHUTDOWN) |
1437	<	((rs + RS_SEQ) & ~SHUTDOWN));
1431	>	else if ((q = ws[k]) == null) {  // create new queue
1432	>	WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
1433	>	Mutex lock = this.lock;      // construct outside lock
1434	>	lock.lock();
1435	>	try {                        // recheck under lock
1436	>	int rs = runState;       // to update seq
1437	>	if (ws == workQueues && ws[k] == null) {
1438	>	ws[k] = nq;
1439	>	runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
1440		}
1441		} finally {
1442	<	lk.unlock();
1442	>	lock.unlock();
1443		}
1444		}
1445	<	if (q != null) {
1446	<	if (q.trySharedPush(task)) {
1447	<	signalWork();
1448	<	return;
1449	<	}
1450	<	else if (m < parallelism - 1 && m < (runState & SMASK)) {
1451	<	Mutex lock = this.lock;
1346	<	lock.lock();             // block until lock free
1347	<	int g = growHints;
1348	<	if (g >>> 16 == m)       // expand range
1349	<	growHints = (((m << 1) + 1) << 16) | (g & SMASK);
1350	<	lock.unlock();           // no need for try/finally
1351	<	}
1352	<	else if ((r & m) == 0)
1353	<	Thread.yield();          // occasionally yield if busy
1354	<	}
1355	<	if (m == (m = growHints >>> 16)) {
1356	<	r ^= r << 13;                // update seed unless new range
1357	<	r ^= r >>> 17;               // same xorshift as WorkQueues
1445	>	else if (q.trySharedPush(task)) {
1446	>	signalWork();
1447	>	return;
1448	>	}
1449	>	else if (m > 1) {                // move to a different index
1450	>	r ^= r << 13;                // same xorshift as WorkQueues
1451	>	r ^= r >>> 17;
1452		s.seed = r ^= r << 5;
1453		}
1454	+	else
1455	+	Thread.yield();              // yield if no alternatives
1456		}
1457		}
1458
1459	+	/**
1460	+	* Submits the given (non-null) task to the common pool, if possible.
1461	+	*/
1462	+	static void submitToCommonPool(ForkJoinTask<?> task) {
1463	+	ForkJoinPool p;
1464	+	if ((p = commonPool) == null)
1465	+	p = ensureCommonPool();
1466	+	p.doSubmit(task);
1467	+	}
1468	+
1469	+	/**
1470	+	* Returns true if the given task was submitted to common pool
1471	+	* and has not yet commenced execution, and is available for
1472	+	* removal according to execution policies; if so removing the
1473	+	* submission from the pool.
1474	+	*
1475	+	* @param task the task
1476	+	* @return true if successful
1477	+	*/
1478	+	static boolean tryUnsubmitFromCommonPool(ForkJoinTask<?> task) {
1479	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
1480	+	int k = submitters.get().seed & SQMASK;
1481	+	return ((p = commonPool) != null &&
1482	+	(ws = p.workQueues) != null &&
1483	+	ws.length > (k &= p.submitMask) &&
1484	+	(q = ws[k]) != null &&
1485	+	q.trySharedUnpush(task, p));
1486	+	}
1487	+
1488		// Maintaining ctl counts
1489
1490		/**
#	Line 1371 | Line 1496 | public class ForkJoinPool extends Abstra
1496		}
1497
1498		/**
1499	<	* Tries to activate or create a worker if too few are active.
1499	>	* Tries to create one or activate one or more workers if too few are active.
1500		*/
1501		final void signalWork() {
1502		long c; int u;
#	Line 1405 | Line 1530 | public class ForkJoinPool extends Abstra
1530		}
1531		}
1532
1533	+	// Scanning for tasks
1534	+
1535		/**
1536	<	* Tries to decrement active count (sometimes implicitly) and
1410	<	* possibly release or create a compensating worker in preparation
1411	<	* for blocking. Fails on contention or termination.
1412	<	*
1413	<	* @return true if the caller can block, else should recheck and retry
1536	>	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1537		*/
1538	<	final boolean tryCompensate() {
1539	<	WorkQueue w; Thread p;
1540	<	int pc = parallelism, e, u, ac, tc, i;
1418	<	long c = ctl;
1419	<	WorkQueue[] ws = workQueues;
1420	<	if ((e = (int)c) >= 0) {
1421	<	if ((ac = ((u = (int)(c >>> 32)) >> UAC_SHIFT)) <= 0 &&
1422	<	e != 0 && ws != null && (i = e & SMASK) < ws.length &&
1423	<	(w = ws[i]) != null) {
1424	<	long nc = (long)(w.nextWait & E_MASK) | (c & (AC_MASK|TC_MASK));
1425	<	if (w.eventCount == (e | INT_SIGN) &&
1426	<	U.compareAndSwapLong(this, CTL, c, nc)) {
1427	<	w.eventCount = (e + E_SEQ) & E_MASK;
1428	<	if ((p = w.parker) != null)
1429	<	U.unpark(p);
1430	<	return true;             // release an idle worker
1431	<	}
1432	<	}
1433	<	else if ((tc = (short)(u >>> UTC_SHIFT)) >= 0 && ac + pc > 1) {
1434	<	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1435	<	if (U.compareAndSwapLong(this, CTL, c, nc))
1436	<	return true;             // no compensation needed
1437	<	}
1438	<	else if (tc + pc < POOL_MAX) {
1439	<	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1440	<	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1441	<	addWorker();
1442	<	return true;             // create replacement
1443	<	}
1444	<	}
1445	<	}
1446	<	return false;
1538	>	final void runWorker(WorkQueue w) {
1539	>	w.growArray(false);         // initialize queue array in this thread
1540	>	do { w.runTask(scan(w)); } while (w.runState >= 0);
1541		}
1542
1449	–	// Scanning for tasks
1450	–
1543		/**
1544		* Scans for and, if found, returns one task, else possibly
1545		* inactivates the worker. This method operates on single reads of
1546	<	* volatile state and is designed to be re-invoked continuously in
1547	<	* part because it returns upon detecting inconsistencies,
1546	>	* volatile state and is designed to be re-invoked continuously,
1547	>	* in part because it returns upon detecting inconsistencies,
1548		* contention, or state changes that indicate possible success on
1549		* re-invocation.
1550		*
1551	<	* The scan searches for tasks across queues, randomly selecting
1552	<	* the first #queues probes, favoring steals over submissions
1553	<	* (by exploiting even/odd indexing), and then performing a
1554	<	* circular sweep of all queues.  The scan terminates upon either
1555	<	* finding a non-empty queue, or completing a full sweep. If the
1556	<	* worker is not inactivated, it takes and returns a task from
1557	<	* this queue.  On failure to find a task, we take one of the
1558	<	* following actions, after which the caller will retry calling
1467	<	* this method unless terminated.
1551	>	* The scan searches for tasks across a random permutation of
1552	>	* queues (starting at a random index and stepping by a random
1553	>	* relative prime, checking each at least once).  The scan
1554	>	* terminates upon either finding a non-empty queue, or completing
1555	>	* the sweep. If the worker is not inactivated, it takes and
1556	>	* returns a task from this queue.  On failure to find a task, we
1557	>	* take one of the following actions, after which the caller will
1558	>	* retry calling this method unless terminated.
1559		*
1560		* * If pool is terminating, terminate the worker.
1561		*
#	Line 1475 | Line 1566 | public class ForkJoinPool extends Abstra
1566		* another worker, but with same net effect. Releasing in other
1567		* cases as well ensures that we have enough workers running.
1568		*
1478	–	* * If the caller has run a task since the last empty scan,
1479	–	* return (to allow rescan) if other workers are not also yet
1480	–	* enqueued.  Field WorkQueue.rescans counts down on each scan to
1481	–	* ensure eventual inactivation and blocking.
1482	–	*
1569		* * If not already enqueued, try to inactivate and enqueue the
1570	<	* worker on wait queue.
1570	>	* worker on wait queue. Or, if inactivating has caused the pool
1571	>	* to be quiescent, relay to idleAwaitWork to check for
1572	>	* termination and possibly shrink pool.
1573	>	*
1574	>	* * If already inactive, and the caller has run a task since the
1575	>	* last empty scan, return (to allow rescan) unless others are
1576	>	* also inactivated.  Field WorkQueue.rescans counts down on each
1577	>	* scan to ensure eventual inactivation and blocking.
1578		*
1579	<	* * If already enqueued and none of the above apply, either park
1580	<	* awaiting signal, or if this is the most recent waiter and pool
1488	<	* is quiescent, relay to idleAwaitWork to check for termination
1489	<	* and possibly shrink pool.
1579	>	* * If already enqueued and none of the above apply, park
1580	>	* awaiting signal,
1581		*
1582		* @param w the worker (via its WorkQueue)
1583	<	* @return a task or null of none found
1583	>	* @return a task or null if none found
1584		*/
1585		private final ForkJoinTask<?> scan(WorkQueue w) {
1586	<	boolean swept = false;               // true after full empty scan
1587	<	WorkQueue[] ws;                      // volatile read order matters
1588	<	int r = w.seed, ec = w.eventCount;   // ec is negative if inactive
1589	<	int rs = runState, m = rs & SMASK;
1590	<	if ((ws = workQueues) != null && ws.length > m) { // consistency check
1591	<	for (int k = 0, j = -1 - m; ; ++j) {
1592	<	WorkQueue q; int b;
1593	<	if (j < 0) {                 // random probes while j negative
1594	<	r ^= r << 13; r ^= r >>> 17; k = (r ^= r << 5) | (j & 1);
1595	<	}                            // worker (not submit) for odd j
1596	<	else                         // cyclic scan when j >= 0
1597	<	k += 7;                  // step 7 reduces array packing bias
1598	<	if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
1599	<	ForkJoinTask<?> t = (ec >= 0) ? q.pollAt(b) : null;
1600	<	w.seed = r;              // save seed for next scan
1601	<	if (t != null)
1586	>	WorkQueue[] ws;                       // first update random seed
1587	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1588	>	int rs = runState, m;                 // volatile read order matters
1589	>	if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
1590	>	int ec = w.eventCount;            // ec is negative if inactive
1591	>	int step = (r >>> 16) | 1;        // relative prime
1592	>	for (int j = (m + 1) << 2; ; r += step) {
1593	>	WorkQueue q; ForkJoinTask<?> t; ForkJoinTask<?>[] a; int b;
1594	>	if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
1595	>	(a = q.array) != null) {  // probably nonempty
1596	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1597	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1598	>	if (q.base == b && ec >= 0 && t != null &&
1599	>	U.compareAndSwapObject(a, i, t, null)) {
1600	>	if (q.top - (q.base = b + 1) > 0)
1601	>	signalWork();    // help pushes signal
1602		return t;
1603	<	break;
1603	>	}
1604	>	else if (ec < 0 || j <= m) {
1605	>	rs = 0;               // mark scan as imcomplete
1606	>	break;                // caller can retry after release
1607	>	}
1608		}
1609	<	else if (j - m > m) {
1515	<	if (rs == runState)      // staleness check
1516	<	swept = true;
1609	>	if (--j < 0)
1610		break;
1518	–	}
1611		}
1612
1521	–	// Decode ctl on empty scan
1613		long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
1614	<	if (e < 0)                       // pool is terminating
1615	<	w.runState = -1;
1616	<	else if (!swept) {               // try to release a waiter
1617	<	WorkQueue v; Thread p;
1618	<	if (e > 0 && a < 0 && (v = ws[e & m]) != null &&
1619	<	v.eventCount == (e | INT_SIGN)) {
1614	>	if (e < 0)                        // decode ctl on empty scan
1615	>	w.runState = -1;              // pool is terminating
1616	>	else if (rs == 0 || rs != runState) { // incomplete scan
1617	>	WorkQueue v; Thread p;        // try to release a waiter
1618	>	if (e > 0 && a < 0 && w.eventCount == ec &&
1619	>	(v = ws[e & m]) != null && v.eventCount == (e | INT_SIGN)) {
1620		long nc = ((long)(v.nextWait & E_MASK) |
1621		((c + AC_UNIT) & (AC_MASK|TC_MASK)));
1622	<	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1622	>	if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
1623		v.eventCount = (e + E_SEQ) & E_MASK;
1624		if ((p = v.parker) != null)
1625		U.unpark(p);
1626		}
1627		}
1628		}
1629	<	else if ((nr = w.rescans) > 0) { // continue rescanning
1539	<	int ac = a + parallelism;
1540	<	if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0 &&
1541	<	w.eventCount == ec)
1542	<	Thread.yield();          // occasionally yield
1543	<	}
1544	<	else if (ec >= 0) {              // try to enqueue
1629	>	else if (ec >= 0) {               // try to enqueue/inactivate
1630		long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
1631		w.nextWait = e;
1632	<	w.eventCount = ec | INT_SIGN;// mark as inactive
1633	<	if (!U.compareAndSwapLong(this, CTL, c, nc))
1634	<	w.eventCount = ec;       // unmark on CAS failure
1635	<	else if ((ns = w.nsteals) != 0) {
1636	<	w.nsteals = 0;           // set rescans if ran task
1637	<	w.rescans = a + parallelism;
1638	<	w.totalSteals += ns;
1632	>	w.eventCount = ec | INT_SIGN; // mark as inactive
1633	>	if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
1634	>	w.eventCount = ec;        // unmark on CAS failure
1635	>	else {
1636	>	if ((ns = w.nsteals) != 0) {
1637	>	w.nsteals = 0;        // set rescans if ran task
1638	>	w.rescans = (a > 0) ? 0 : a + parallelism;
1639	>	w.totalSteals += ns;
1640	>	}
1641	>	if (a == 1 - parallelism) // quiescent
1642	>	idleAwaitWork(w, nc, c);
1643		}
1644		}
1645	<	else{                            // already queued
1646	<	if (parallelism == -a)
1647	<	idleAwaitWork(w);        // quiescent
1648	<	if (w.eventCount == ec) {
1649	<	Thread.interrupted();    // clear status
1650	<	ForkJoinWorkerThread wt = w.owner;
1645	>	else if (w.eventCount < 0) {      // already queued
1646	>	int ac = a + parallelism;
1647	>	if ((nr = w.rescans) > 0)     // continue rescanning
1648	>	w.rescans = (ac < nr) ? ac : nr - 1;
1649	>	else if (((w.seed >>> 16) & ac) == 0) { // randomize park
1650	>	Thread.interrupted();     // clear status
1651	>	Thread wt = Thread.currentThread();
1652		U.putObject(wt, PARKBLOCKER, this);
1653	<	w.parker = wt;           // emulate LockSupport.park
1654	<	if (w.eventCount == ec)  // recheck
1655	<	U.park(false, 0L);   // block
1653	>	w.parker = wt;            // emulate LockSupport.park
1654	>	if (w.eventCount < 0)     // recheck
1655	>	U.park(false, 0L);
1656		w.parker = null;
1657		U.putObject(wt, PARKBLOCKER, null);
1658		}
#	Line 1572 | Line 1662 | public class ForkJoinPool extends Abstra
1662		}
1663
1664		/**
1665	<	* If inactivating worker w has caused pool to become quiescent,
1666	<	* checks for pool termination, and, so long as this is not the
1667	<	* only worker, waits for event for up to SHRINK_RATE nanosecs.
1668	<	* On timeout, if ctl has not changed, terminates the worker,
1669	<	* which will in turn wake up another worker to possibly repeat
1670	<	* this process.
1665	>	* If inactivating worker w has caused the pool to become
1666	>	* quiescent, checks for pool termination, and, so long as this is
1667	>	* not the only worker, waits for event for up to a given
1668	>	* duration.  On timeout, if ctl has not changed, terminates the
1669	>	* worker, which will in turn wake up another worker to possibly
1670	>	* repeat this process.
1671		*
1672		* @param w the calling worker
1673	+	* @param currentCtl the ctl value triggering possible quiescence
1674	+	* @param prevCtl the ctl value to restore if thread is terminated
1675		*/
1676	<	private void idleAwaitWork(WorkQueue w) {
1677	<	long c; int nw, ec;
1678	<	if (!tryTerminate(false, false) &&
1679	<	(int)((c = ctl) >> AC_SHIFT) + parallelism == 0 &&
1680	<	(ec = w.eventCount) == ((int)c | INT_SIGN) &&
1681	<	(nw = w.nextWait) != 0) {
1682	<	long nc = ((long)(nw & E_MASK) | // ctl to restore on timeout
1683	<	((c + AC_UNIT) & AC_MASK) | (c & TC_MASK));
1592	<	ForkJoinWorkerThread wt = w.owner;
1593	<	while (ctl == c) {
1594	<	long startTime = System.nanoTime();
1676	>	private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
1677	>	if (w.eventCount < 0 && !tryTerminate(false, false) &&
1678	>	(int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
1679	>	int dc = -(short)(currentCtl >>> TC_SHIFT);
1680	>	long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
1681	>	long deadline = System.nanoTime() + parkTime - 100000L; // 1ms slop
1682	>	Thread wt = Thread.currentThread();
1683	>	while (ctl == currentCtl) {
1684		Thread.interrupted();  // timed variant of version in scan()
1685		U.putObject(wt, PARKBLOCKER, this);
1686		w.parker = wt;
1687	<	if (ctl == c)
1688	<	U.park(false, SHRINK_RATE);
1687	>	if (ctl == currentCtl)
1688	>	U.park(false, parkTime);
1689		w.parker = null;
1690		U.putObject(wt, PARKBLOCKER, null);
1691	<	if (ctl != c)
1691	>	if (ctl != currentCtl)
1692		break;
1693	<	if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
1694	<	U.compareAndSwapLong(this, CTL, c, nc)) {
1695	<	w.eventCount = (ec + E_SEQ) | E_MASK;
1696	<	w.runState = -1;          // shrink
1693	>	if (deadline - System.nanoTime() <= 0L &&
1694	>	U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
1695	>	w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
1696	>	w.runState = -1;   // shrink
1697		break;
1698		}
1699		}
#	Line 1622 | Line 1711 | public class ForkJoinPool extends Abstra
1711		* leaves hints in workers to speed up subsequent calls. The
1712		* implementation is very branchy to cope with potential
1713		* inconsistencies or loops encountering chains that are stale,
1714	<	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
1626	<	* of these cases are dealt with by just retrying by caller.
1714	>	* unknown, or so long that they are likely cyclic.
1715		*
1716		* @param joiner the joining worker
1717		* @param task the task to join
1718	<	* @return true if found or ran a task (and so is immediately retryable)
1718	>	* @return 0 if no progress can be made, negative if task
1719	>	* known complete, else positive
1720		*/
1721	<	final boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1722	<	ForkJoinTask<?> subtask;    // current target
1723	<	boolean progress = false;
1724	<	int depth = 0;              // current chain depth
1725	<	int m = runState & SMASK;
1726	<	WorkQueue[] ws = workQueues;
1727	<
1728	<	if (ws != null && ws.length > m && (subtask = task).status >= 0) {
1729	<	outer:for (WorkQueue j = joiner;;) {
1730	<	// Try to find the stealer of subtask, by first using hint
1642	<	WorkQueue stealer = null;
1643	<	WorkQueue v = ws[j.stealHint & m];
1644	<	if (v != null && v.currentSteal == subtask)
1645	<	stealer = v;
1646	<	else {
1647	<	for (int i = 1; i <= m; i += 2) {
1648	<	if ((v = ws[i]) != null && v.currentSteal == subtask) {
1649	<	stealer = v;
1650	<	j.stealHint = i; // save hint
1651	<	break;
1652	<	}
1721	>	private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1722	>	int stat = 0, steps = 0;                    // bound to avoid cycles
1723	>	if (joiner != null && task != null) {       // hoist null checks
1724	>	restart: for (;;) {
1725	>	ForkJoinTask<?> subtask = task;     // current target
1726	>	for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
1727	>	WorkQueue[] ws; int m, s, h;
1728	>	if ((s = task.status) < 0) {
1729	>	stat = s;
1730	>	break restart;
1731		}
1732	<	if (stealer == null)
1733	<	break;
1734	<	}
1735	<
1736	<	for (WorkQueue q = stealer;;) { // Try to help stealer
1737	<	ForkJoinTask<?> t; int b;
1738	<	if (task.status < 0)
1739	<	break outer;
1740	<	if ((b = q.base) - q.top < 0) {
1741	<	progress = true;
1742	<	if (subtask.status < 0)
1743	<	break outer;               // stale
1744	<	if ((t = q.pollAt(b)) != null) {
1745	<	stealer.stealHint = joiner.poolIndex;
1746	<	joiner.runSubtask(t);
1732	>	if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
1733	>	break restart;              // shutting down
1734	>	if ((v = ws[h = (j.stealHint | 1) & m]) == null ||
1735	>	v.currentSteal != subtask) {
1736	>	for (int origin = h;;) {    // find stealer
1737	>	if (((h = (h + 2) & m) & 15) == 1 &&
1738	>	(subtask.status < 0 || j.currentJoin != subtask))
1739	>	continue restart;   // occasional staleness check
1740	>	if ((v = ws[h]) != null &&
1741	>	v.currentSteal == subtask) {
1742	>	j.stealHint = h;    // save hint
1743	>	break;
1744	>	}
1745	>	if (h == origin)
1746	>	break restart;      // cannot find stealer
1747		}
1748		}
1749	<	else { // empty - try to descend to find stealer's stealer
1750	<	ForkJoinTask<?> next = stealer.currentJoin;
1751	<	if (++depth == MAX_HELP_DEPTH || subtask.status < 0 ||
1752	<	next == null || next == subtask)
1753	<	break outer;  // max depth, stale, dead-end, cyclic
1754	<	subtask = next;
1755	<	j = stealer;
1756	<	break;
1749	>	for (;;) { // help stealer or descend to its stealer
1750	>	ForkJoinTask[] a;  int b;
1751	>	if (subtask.status < 0)     // surround probes with
1752	>	continue restart;       //   consistency checks
1753	>	if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
1754	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1755	>	ForkJoinTask<?> t =
1756	>	(ForkJoinTask<?>)U.getObjectVolatile(a, i);
1757	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1758	>	v.currentSteal != subtask)
1759	>	continue restart;   // stale
1760	>	stat = 1;               // apparent progress
1761	>	if (t != null && v.base == b &&
1762	>	U.compareAndSwapObject(a, i, t, null)) {
1763	>	v.base = b + 1;     // help stealer
1764	>	joiner.runSubtask(t);
1765	>	}
1766	>	else if (v.base == b && ++steps == MAX_HELP)
1767	>	break restart;      // v apparently stalled
1768	>	}
1769	>	else {                      // empty -- try to descend
1770	>	ForkJoinTask<?> next = v.currentJoin;
1771	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1772	>	v.currentSteal != subtask)
1773	>	continue restart;   // stale
1774	>	else if (next == null || ++steps == MAX_HELP)
1775	>	break restart;      // dead-end or maybe cyclic
1776	>	else {
1777	>	subtask = next;
1778	>	j = v;
1779	>	break;
1780	>	}
1781	>	}
1782		}
1783		}
1784		}
1785		}
1786	<	return progress;
1786	>	return stat;
1787		}
1788
1789		/**
#	Line 1689 | Line 1792 | public class ForkJoinPool extends Abstra
1792		* @param joiner the joining worker
1793		* @param task the task
1794		*/
1795	<	final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1795	>	private void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1796		WorkQueue[] ws;
1797	<	int m = runState & SMASK;
1798	<	if ((ws = workQueues) != null && ws.length > m) {
1696	<	for (int j = 1; j <= m && task.status >= 0; j += 2) {
1797	>	if ((ws = workQueues) != null) {
1798	>	for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
1799		WorkQueue q = ws[j];
1800		if (q != null && q.pollFor(task)) {
1801		joiner.runSubtask(task);
#	Line 1704 | Line 1806 | public class ForkJoinPool extends Abstra
1806		}
1807
1808		/**
1809	<	* Returns a non-empty steal queue, if one is found during a random,
1810	<	* then cyclic scan, else null.  This method must be retried by
1811	<	* caller if, by the time it tries to use the queue, it is empty.
1809	>	* Tries to decrement active count (sometimes implicitly) and
1810	>	* possibly release or create a compensating worker in preparation
1811	>	* for blocking. Fails on contention or termination. Otherwise,
1812	>	* adds a new thread if no idle workers are available and either
1813	>	* pool would become completely starved or: (at least half
1814	>	* starved, and fewer than 50% spares exist, and there is at least
1815	>	* one task apparently available). Even though the availability
1816	>	* check requires a full scan, it is worthwhile in reducing false
1817	>	* alarms.
1818	>	*
1819	>	* @param task if non-null, a task being waited for
1820	>	* @param blocker if non-null, a blocker being waited for
1821	>	* @return true if the caller can block, else should recheck and retry
1822	>	*/
1823	>	final boolean tryCompensate(ForkJoinTask<?> task, ManagedBlocker blocker) {
1824	>	int pc = parallelism, e;
1825	>	long c = ctl;
1826	>	WorkQueue[] ws = workQueues;
1827	>	if ((e = (int)c) >= 0 && ws != null) {
1828	>	int u, a, ac, hc;
1829	>	int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
1830	>	boolean replace = false;
1831	>	if ((a = u >> UAC_SHIFT) <= 0) {
1832	>	if ((ac = a + pc) <= 1)
1833	>	replace = true;
1834	>	else if ((e > 0 || (task != null &&
1835	>	ac <= (hc = pc >>> 1) && tc < pc + hc))) {
1836	>	WorkQueue w;
1837	>	for (int j = 0; j < ws.length; ++j) {
1838	>	if ((w = ws[j]) != null && !w.isEmpty()) {
1839	>	replace = true;
1840	>	break;   // in compensation range and tasks available
1841	>	}
1842	>	}
1843	>	}
1844	>	}
1845	>	if ((task == null || task.status >= 0) && // recheck need to block
1846	>	(blocker == null || !blocker.isReleasable()) && ctl == c) {
1847	>	if (!replace) {          // no compensation
1848	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1849	>	if (U.compareAndSwapLong(this, CTL, c, nc))
1850	>	return true;
1851	>	}
1852	>	else if (e != 0) {       // release an idle worker
1853	>	WorkQueue w; Thread p; int i;
1854	>	if ((i = e & SMASK) < ws.length && (w = ws[i]) != null) {
1855	>	long nc = ((long)(w.nextWait & E_MASK) |
1856	>	(c & (AC_MASK|TC_MASK)));
1857	>	if (w.eventCount == (e | INT_SIGN) &&
1858	>	U.compareAndSwapLong(this, CTL, c, nc)) {
1859	>	w.eventCount = (e + E_SEQ) & E_MASK;
1860	>	if ((p = w.parker) != null)
1861	>	U.unpark(p);
1862	>	return true;
1863	>	}
1864	>	}
1865	>	}
1866	>	else if (tc < MAX_CAP) { // create replacement
1867	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1868	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1869	>	addWorker();
1870	>	return true;
1871	>	}
1872	>	}
1873	>	}
1874	>	}
1875	>	return false;
1876	>	}
1877	>
1878	>	/**
1879	>	* Helps and/or blocks until the given task is done.
1880	>	*
1881	>	* @param joiner the joining worker
1882	>	* @param task the task
1883	>	* @return task status on exit
1884	>	*/
1885	>	final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
1886	>	int s;
1887	>	if ((s = task.status) >= 0) {
1888	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
1889	>	joiner.currentJoin = task;
1890	>	long startTime = 0L;
1891	>	for (int k = 0;;) {
1892	>	if ((s = (joiner.isEmpty() ?           // try to help
1893	>	tryHelpStealer(joiner, task) :
1894	>	joiner.tryRemoveAndExec(task))) == 0 &&
1895	>	(s = task.status) >= 0) {
1896	>	if (k == 0) {
1897	>	startTime = System.nanoTime();
1898	>	tryPollForAndExec(joiner, task); // check uncommon case
1899	>	}
1900	>	else if ((k & (MAX_HELP - 1)) == 0 &&
1901	>	System.nanoTime() - startTime >=
1902	>	COMPENSATION_DELAY &&
1903	>	tryCompensate(task, null)) {
1904	>	if (task.trySetSignal()) {
1905	>	synchronized (task) {
1906	>	if (task.status >= 0) {
1907	>	try {                // see ForkJoinTask
1908	>	task.wait();     //  for explanation
1909	>	} catch (InterruptedException ie) {
1910	>	}
1911	>	}
1912	>	else
1913	>	task.notifyAll();
1914	>	}
1915	>	}
1916	>	long c;                          // re-activate
1917	>	do {} while (!U.compareAndSwapLong
1918	>	(this, CTL, c = ctl, c + AC_UNIT));
1919	>	}
1920	>	}
1921	>	if (s < 0 || (s = task.status) < 0) {
1922	>	joiner.currentJoin = prevJoin;
1923	>	break;
1924	>	}
1925	>	else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
1926	>	Thread.yield();                     // for politeness
1927	>	}
1928	>	}
1929	>	return s;
1930	>	}
1931	>
1932	>	/**
1933	>	* Stripped-down variant of awaitJoin used by timed joins. Tries
1934	>	* to help join only while there is continuous progress. (Caller
1935	>	* will then enter a timed wait.)
1936	>	*
1937	>	* @param joiner the joining worker
1938	>	* @param task the task
1939	>	* @return task status on exit
1940	>	*/
1941	>	final int helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
1942	>	int s;
1943	>	while ((s = task.status) >= 0 &&
1944	>	(joiner.isEmpty() ?
1945	>	tryHelpStealer(joiner, task) :
1946	>	joiner.tryRemoveAndExec(task)) != 0)
1947	>	;
1948	>	return s;
1949	>	}
1950	>
1951	>	/**
1952	>	* Returns a (probably) non-empty steal queue, if one is found
1953	>	* during a random, then cyclic scan, else null.  This method must
1954	>	* be retried by caller if, by the time it tries to use the queue,
1955	>	* it is empty.
1956		*/
1957		private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
1958	<	int r = w.seed;    // Same idea as scan(), but ignoring submissions
1958	>	// Similar to loop in scan(), but ignoring submissions
1959	>	int r;
1960	>	if (w == null) // allow external callers
1961	>	r = ThreadLocalRandom.current().nextInt();
1962	>	else {
1963	>	r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1964	>	}
1965	>	int step = (r >>> 16) | 1;
1966		for (WorkQueue[] ws;;) {
1967	<	int m = runState & SMASK;
1968	<	if ((ws = workQueues) == null)
1967	>	int rs = runState, m;
1968	>	if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
1969		return null;
1970	<	if (ws.length > m) {
1971	<	WorkQueue q;
1972	<	for (int k = 0, j = -1 - m;; ++j) {
1973	<	if (j < 0) {
1974	<	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
1975	<	}
1723	<	else
1724	<	k += 7;
1725	<	if ((q = ws[(k | 1) & m]) != null && q.base - q.top < 0) {
1726	<	w.seed = r;
1727	<	return q;
1728	<	}
1729	<	else if (j - m > m)
1970	>	for (int j = (m + 1) << 2; ; r += step) {
1971	>	WorkQueue q = ws[((r << 1) | 1) & m];
1972	>	if (q != null && !q.isEmpty())
1973	>	return q;
1974	>	else if (--j < 0) {
1975	>	if (runState == rs)
1976		return null;
1977	+	break;
1978		}
1979		}
1980		}
#	Line 1741 | Line 1988 | public class ForkJoinPool extends Abstra
1988		*/
1989		final void helpQuiescePool(WorkQueue w) {
1990		for (boolean active = true;;) {
1991	<	w.runLocalTasks();      // exhaust local queue
1991	>	ForkJoinTask<?> localTask; // exhaust local queue
1992	>	while ((localTask = w.nextLocalTask()) != null)
1993	>	localTask.doExec();
1994		WorkQueue q = findNonEmptyStealQueue(w);
1995		if (q != null) {
1996	<	ForkJoinTask<?> t;
1996	>	ForkJoinTask<?> t; int b;
1997		if (!active) {      // re-establish active count
1998		long c;
1999		active = true;
2000		do {} while (!U.compareAndSwapLong
2001		(this, CTL, c = ctl, c + AC_UNIT));
2002		}
2003	<	if ((t = q.poll()) != null)
2003	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2004		w.runSubtask(t);
2005		}
2006		else {
#	Line 1773 | Line 2022 | public class ForkJoinPool extends Abstra
2022		}
2023
2024		/**
2025	+	* Restricted version of helpQuiescePool for non-FJ callers
2026	+	*/
2027	+	static void externalHelpQuiescePool() {
2028	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue w, q;
2029	+	ForkJoinTask<?> t; int b;
2030	+	int k = submitters.get().seed & SQMASK;
2031	+	if ((p = commonPool) != null &&
2032	+	(ws = p.workQueues) != null &&
2033	+	ws.length > (k &= p.submitMask) &&
2034	+	(w = ws[k]) != null &&
2035	+	(q = p.findNonEmptyStealQueue(w)) != null &&
2036	+	(b = q.base) - q.top < 0 &&
2037	+	(t = q.pollAt(b)) != null)
2038	+	t.doExec();
2039	+	}
2040	+
2041	+	/**
2042		* Gets and removes a local or stolen task for the given worker.
2043		*
2044		* @return a task, if available
2045		*/
2046		final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
2047		for (ForkJoinTask<?> t;;) {
2048	<	WorkQueue q;
2048	>	WorkQueue q; int b;
2049		if ((t = w.nextLocalTask()) != null)
2050		return t;
2051		if ((q = findNonEmptyStealQueue(w)) == null)
2052		return null;
2053	<	if ((t = q.poll()) != null)
2053	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
2054		return t;
2055		}
2056		}
#	Line 1805 | Line 2071 | public class ForkJoinPool extends Abstra
2071		8);
2072		}
2073
2074	+	/**
2075	+	* Returns approximate submission queue length for the given caller
2076	+	*/
2077	+	static int getEstimatedSubmitterQueueLength() {
2078	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
2079	+	int k = submitters.get().seed & SQMASK;
2080	+	return ((p = commonPool) != null &&
2081	+	p.runState >= 0 &&
2082	+	(ws = p.workQueues) != null &&
2083	+	ws.length > (k &= p.submitMask) &&
2084	+	(q = ws[k]) != null) ?
2085	+	q.queueSize() : 0;
2086	+	}
2087	+
2088		//  Termination
2089
2090		/**
#	Line 1959 | Line 2239 | public class ForkJoinPool extends Abstra
2239		checkPermission();
2240		if (factory == null)
2241		throw new NullPointerException();
2242	<	if (parallelism <= 0 || parallelism > POOL_MAX)
2242	>	if (parallelism <= 0 || parallelism > MAX_CAP)
2243		throw new IllegalArgumentException();
2244		this.parallelism = parallelism;
2245		this.factory = factory;
2246		this.ueh = handler;
2247		this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
1968	–	this.growHints = 1;
2248		long np = (long)(-parallelism); // offset ctl counts
2249		this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2250	<	// initialize workQueues array with room for 2*parallelism if possible
2251	<	int n = parallelism << 1;
2252	<	if (n >= POOL_MAX)
2253	<	n = POOL_MAX;
2254	<	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
2255	<	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1977	<	}
1978	<	this.workQueues = new WorkQueue[(n + 1) << 1]; // #slots = 2 * #workers
2250	>	// Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
2251	>	int n = parallelism - 1;
2252	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
2253	>	int size = (n + 1) << 1;        // #slots = 2*#workers
2254	>	this.submitMask = size - 1;     // room for max # of submit queues
2255	>	this.workQueues = new WorkQueue[size];
2256		this.termination = (this.lock = new Mutex()).newCondition();
2257		this.stealCount = new AtomicLong();
2258		this.nextWorkerNumber = new AtomicInteger();
2259	+	int pn = poolNumberGenerator.incrementAndGet();
2260		StringBuilder sb = new StringBuilder("ForkJoinPool-");
2261	<	sb.append(poolNumberGenerator.incrementAndGet());
2261	>	sb.append(Integer.toString(pn));
2262		sb.append("-worker-");
2263		this.workerNamePrefix = sb.toString();
2264	+	lock.lock();
2265	+	this.runState = 1;              // set init flag
2266	+	lock.unlock();
2267	+	}
2268	+
2269	+	/**
2270	+	* Returns the common pool instance
2271	+	*
2272	+	* @return the common pool instance
2273	+	*/
2274	+	public static ForkJoinPool commonPool() {
2275	+	ForkJoinPool p;
2276	+	return (p = commonPool) != null? p : ensureCommonPool();
2277	+	}
2278	+
2279	+	private static ForkJoinPool ensureCommonPool() {
2280	+	ForkJoinPool p;
2281	+	if ((p = commonPool) == null) {
2282	+	final Mutex lock = initializationLock;
2283	+	lock.lock();
2284	+	try {
2285	+	if ((p = commonPool) == null) {
2286	+	p = commonPool = new ForkJoinPool(commonPoolParallelism,
2287	+	commonPoolFactory,
2288	+	commonPoolUEH, false);
2289	+	// use a more informative name string for workers
2290	+	p.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
2291	+	}
2292	+	} finally {
2293	+	lock.unlock();
2294	+	}
2295	+	}
2296	+	return p;
2297		}
2298
2299		// Execution methods
#	Line 2004 | Line 2315 | public class ForkJoinPool extends Abstra
2315		*         scheduled for execution
2316		*/
2317		public <T> T invoke(ForkJoinTask<T> task) {
2318	+	if (task == null)
2319	+	throw new NullPointerException();
2320		doSubmit(task);
2321		return task.join();
2322		}
#	Line 2017 | Line 2330 | public class ForkJoinPool extends Abstra
2330		*         scheduled for execution
2331		*/
2332		public void execute(ForkJoinTask<?> task) {
2333	+	if (task == null)
2334	+	throw new NullPointerException();
2335		doSubmit(task);
2336		}
2337
#	Line 2034 | Line 2349 | public class ForkJoinPool extends Abstra
2349		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2350		job = (ForkJoinTask<?>) task;
2351		else
2352	<	job = ForkJoinTask.adapt(task, null);
2352	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2353		doSubmit(job);
2354		}
2355
#	Line 2048 | Line 2363 | public class ForkJoinPool extends Abstra
2363		*         scheduled for execution
2364		*/
2365		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
2366	+	if (task == null)
2367	+	throw new NullPointerException();
2368		doSubmit(task);
2369		return task;
2370		}
#	Line 2058 | Line 2375 | public class ForkJoinPool extends Abstra
2375		*         scheduled for execution
2376		*/
2377		public <T> ForkJoinTask<T> submit(Callable<T> task) {
2378	<	if (task == null)
2062	<	throw new NullPointerException();
2063	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
2378	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
2379		doSubmit(job);
2380		return job;
2381		}
#	Line 2071 | Line 2386 | public class ForkJoinPool extends Abstra
2386		*         scheduled for execution
2387		*/
2388		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
2389	<	if (task == null)
2075	<	throw new NullPointerException();
2076	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
2389	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
2390		doSubmit(job);
2391		return job;
2392		}
#	Line 2090 | Line 2403 | public class ForkJoinPool extends Abstra
2403		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2404		job = (ForkJoinTask<?>) task;
2405		else
2406	<	job = ForkJoinTask.adapt(task, null);
2406	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2407		doSubmit(job);
2408		return job;
2409		}
#	Line 2112 | Line 2425 | public class ForkJoinPool extends Abstra
2425		boolean done = false;
2426		try {
2427		for (Callable<T> t : tasks) {
2428	<	ForkJoinTask<T> f = ForkJoinTask.adapt(t);
2428	>	ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
2429		doSubmit(f);
2430		fs.add(f);
2431		}
#	Line 2156 | Line 2469 | public class ForkJoinPool extends Abstra
2469		}
2470
2471		/**
2472	+	* Returns the targeted parallelism level of the common pool.
2473	+	*
2474	+	* @return the targeted parallelism level of the common pool
2475	+	*/
2476	+	public static int getCommonPoolParallelism() {
2477	+	return commonPoolParallelism;
2478	+	}
2479	+
2480	+	/**
2481		* Returns the number of worker threads that have started but not
2482		* yet terminated.  The result returned by this method may differ
2483		* from {@link #getParallelism} when threads are created to
#	Line 2298 | Line 2620 | public class ForkJoinPool extends Abstra
2620		WorkQueue[] ws; WorkQueue w;
2621		if ((ws = workQueues) != null) {
2622		for (int i = 0; i < ws.length; i += 2) {
2623	<	if ((w = ws[i]) != null && w.queueSize() != 0)
2623	>	if ((w = ws[i]) != null && !w.isEmpty())
2624		return true;
2625		}
2626		}
#	Line 2407 | Line 2729 | public class ForkJoinPool extends Abstra
2729		}
2730
2731		/**
2732	<	* Initiates an orderly shutdown in which previously submitted
2733	<	* tasks are executed, but no new tasks will be accepted.
2734	<	* Invocation has no additional effect if already shut down.
2735	<	* Tasks that are in the process of being submitted concurrently
2736	<	* during the course of this method may or may not be rejected.
2732	>	* Possibly initiates an orderly shutdown in which previously
2733	>	* submitted tasks are executed, but no new tasks will be
2734	>	* accepted. Invocation has no effect on execution state if this
2735	>	* is the {@link #commonPool}, and no additional effect if
2736	>	* already shut down.  Tasks that are in the process of being
2737	>	* submitted concurrently during the course of this method may or
2738	>	* may not be rejected.
2739		*
2740		* @throws SecurityException if a security manager exists and
2741		*         the caller is not permitted to modify threads
#	Line 2420 | Line 2744 | public class ForkJoinPool extends Abstra
2744		*/
2745		public void shutdown() {
2746		checkPermission();
2747	<	tryTerminate(false, true);
2747	>	if (this != commonPool)
2748	>	tryTerminate(false, true);
2749		}
2750
2751		/**
2752	<	* Attempts to cancel and/or stop all tasks, and reject all
2753	<	* subsequently submitted tasks.  Tasks that are in the process of
2754	<	* being submitted or executed concurrently during the course of
2755	<	* this method may or may not be rejected. This method cancels
2756	<	* both existing and unexecuted tasks, in order to permit
2757	<	* termination in the presence of task dependencies. So the method
2758	<	* always returns an empty list (unlike the case for some other
2759	<	* Executors).
2752	>	* Possibly attempts to cancel and/or stop all tasks, and reject
2753	>	* all subsequently submitted tasks.  Invocation has no effect on
2754	>	* execution state if this is the {@link #commonPool}, and no
2755	>	* additional effect if already shut down. Otherwise, tasks that
2756	>	* are in the process of being submitted or executed concurrently
2757	>	* during the course of this method may or may not be
2758	>	* rejected. This method cancels both existing and unexecuted
2759	>	* tasks, in order to permit termination in the presence of task
2760	>	* dependencies. So the method always returns an empty list
2761	>	* (unlike the case for some other Executors).
2762		*
2763		* @return an empty list
2764		* @throws SecurityException if a security manager exists and
#	Line 2441 | Line 2768 | public class ForkJoinPool extends Abstra
2768		*/
2769		public List<Runnable> shutdownNow() {
2770		checkPermission();
2771	<	tryTerminate(true, true);
2771	>	if (this != commonPool)
2772	>	tryTerminate(true, true);
2773		return Collections.emptyList();
2774		}
2775
#	Line 2612 | Line 2940 | public class ForkJoinPool extends Abstra
2940		ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
2941		((ForkJoinWorkerThread)t).pool : null);
2942		while (!blocker.isReleasable()) {
2943	<	if (p == null || p.tryCompensate()) {
2943	>	if (p == null || p.tryCompensate(null, blocker)) {
2944		try {
2945		do {} while (!blocker.isReleasable() && !blocker.block());
2946		} finally {
#	Line 2629 | Line 2957 | public class ForkJoinPool extends Abstra
2957		// implement RunnableFuture.
2958
2959		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
2960	<	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
2960	>	return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
2961		}
2962
2963		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
2964	<	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
2964	>	return new ForkJoinTask.AdaptedCallable<T>(callable);
2965		}
2966
2967		// Unsafe mechanics
2968		private static final sun.misc.Unsafe U;
2969		private static final long CTL;
2970		private static final long PARKBLOCKER;
2971	+	private static final int ABASE;
2972	+	private static final int ASHIFT;
2973
2974		static {
2975		poolNumberGenerator = new AtomicInteger();
2976	+	nextSubmitterSeed = new AtomicInteger(0x55555555);
2977		modifyThreadPermission = new RuntimePermission("modifyThread");
2978		defaultForkJoinWorkerThreadFactory =
2979		new DefaultForkJoinWorkerThreadFactory();
2980		submitters = new ThreadSubmitter();
2981	+	initializationLock = new Mutex();
2982	+	int s;
2983		try {
2984		U = getUnsafe();
2985		Class<?> k = ForkJoinPool.class;
2986	+	Class<?> ak = ForkJoinTask[].class;
2987		CTL = U.objectFieldOffset
2988		(k.getDeclaredField("ctl"));
2989		Class<?> tk = Thread.class;
2990		PARKBLOCKER = U.objectFieldOffset
2991		(tk.getDeclaredField("parkBlocker"));
2992	+	ABASE = U.arrayBaseOffset(ak);
2993	+	s = U.arrayIndexScale(ak);
2994	+	} catch (Exception e) {
2995	+	throw new Error(e);
2996	+	}
2997	+	if ((s & (s-1)) != 0)
2998	+	throw new Error("data type scale not a power of two");
2999	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
3000	+
3001	+	// Establish configuration for default pool
3002	+	try {
3003	+	String pp = System.getProperty(propPrefix + "parallelism");
3004	+	String fp = System.getProperty(propPrefix + "threadFactory");
3005	+	String up = System.getProperty(propPrefix + "exceptionHandler");
3006	+	int par;
3007	+	if ((pp == null || (par = Integer.parseInt(pp)) <= 0))
3008	+	par = Runtime.getRuntime().availableProcessors();
3009	+	commonPoolParallelism = par;
3010	+	if (fp != null)
3011	+	commonPoolFactory = (ForkJoinWorkerThreadFactory)
3012	+	ClassLoader.getSystemClassLoader().loadClass(fp).newInstance();
3013	+	else
3014	+	commonPoolFactory = defaultForkJoinWorkerThreadFactory;
3015	+	if (up != null)
3016	+	commonPoolUEH = (Thread.UncaughtExceptionHandler)
3017	+	ClassLoader.getSystemClassLoader().loadClass(up).newInstance();
3018	+	else
3019	+	commonPoolUEH = null;
3020		} catch (Exception e) {
3021		throw new Error(e);
3022		}

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