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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.124 by jsr166, Mon Feb 20 23:32:24 2012 UTC vs.
Revision 1.137 by dl, Tue Oct 30 14:23:11 2012 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	+
9		import java.util.ArrayList;
10		import java.util.Arrays;
11		import java.util.Collection;
#	Line 41 | 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 used by any ForkJoinTask that
47	>	* is not explicitly submitted to a specified pool. Using the common
48	>	* pool normally reduces resource usage (its threads are slowly
49	>	* reclaimed during periods of non-use, and reinstated upon subsequent
50	>	* use).  The common pool is by default constructed with default
51	>	* parameters, but these may be controlled by setting any or all of
52	>	* the three properties {@code
53	>	* java.util.concurrent.ForkJoinPool.common.{parallelism,
54	>	* threadFactory, exceptionHandler}}.
55	>	*
56	>	* <p>For applications that require separate or custom pools, a {@code
57	>	* ForkJoinPool} may be constructed with a given target parallelism
58	>	* level; by default, equal to the number of available processors. The
59	>	* pool attempts to maintain enough active (or available) threads by
60	>	* dynamically adding, suspending, or resuming internal worker
61	>	* threads, even if some tasks are stalled waiting to join
62	>	* others. However, no such adjustments are guaranteed in the face of
63	>	* blocked IO or other unmanaged synchronization. The nested {@link
64	>	* ManagedBlocker} interface enables extension of the kinds of
65		* synchronization accommodated.
66		*
67		* <p>In addition to execution and lifecycle control methods, this
#	Line 93 | Line 106 | import java.util.concurrent.locks.Condit
106		*  </tr>
107		* </table>
108		*
96	–	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
97	–	* used for all parallel task execution in a program or subsystem.
98	–	* Otherwise, use would not usually outweigh the construction and
99	–	* bookkeeping overhead of creating a large set of threads. For
100	–	* example, a common pool could be used for the {@code SortTasks}
101	–	* illustrated in {@link RecursiveAction}. Because {@code
102	–	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
103	–	* daemon} mode, there is typically no need to explicitly {@link
104	–	* #shutdown} such a pool upon program exit.
105	–	*
106	–	*  <pre> {@code
107	–	* static final ForkJoinPool mainPool = new ForkJoinPool();
108	–	* ...
109	–	* public void sort(long[] array) {
110	–	*   mainPool.invoke(new SortTask(array, 0, array.length));
111	–	* }}</pre>
112	–	*
109		* <p><b>Implementation notes</b>: This implementation restricts the
110		* maximum number of running threads to 32767. Attempts to create
111		* pools with greater than the maximum number result in
#	Line 239 | Line 235 | public class ForkJoinPool extends Abstra
235		* when locked remains available to check consistency.
236		*
237		* Recording WorkQueues.  WorkQueues are recorded in the
238	<	* "workQueues" array that is created upon pool construction and
239	<	* expanded if necessary.  Updates to the array while recording
240	<	* new workers and unrecording terminated ones are protected from
241	<	* each other by a lock but the array is otherwise concurrently
242	<	* readable, and accessed directly.  To simplify index-based
243	<	* operations, the array size is always a power of two, and all
244	<	* readers must tolerate null slots. Shared (submission) queues
245	<	* are at even indices, worker queues at odd indices. Grouping
246	<	* them together in this way simplifies and speeds up task
251	<	* scanning.
238	>	* "workQueues" array that is created upon first use and expanded
239	>	* if necessary.  Updates to the array while recording new workers
240	>	* and unrecording terminated ones are protected from each other
241	>	* by a lock but the array is otherwise concurrently readable, and
242	>	* accessed directly.  To simplify index-based operations, the
243	>	* array size is always a power of two, and all readers must
244	>	* tolerate null slots. Shared (submission) queues are at even
245	>	* indices, worker queues at odd indices. Grouping them together
246	>	* in this way simplifies and speeds up task scanning.
247		*
248		* All worker thread creation is on-demand, triggered by task
249		* submissions, replacement of terminated workers, and/or
#	Line 320 | Line 315 | public class ForkJoinPool extends Abstra
315		*
316		* Trimming workers. To release resources after periods of lack of
317		* use, a worker starting to wait when the pool is quiescent will
318	<	* time out and terminate if the pool has remained quiescent for
319	<	* SHRINK_RATE nanosecs. This will slowly propagate, eventually
320	<	* terminating all workers after long periods of non-use.
318	>	* time out and terminate if the pool has remained quiescent for a
319	>	* given period -- a short period if there are more threads than
320	>	* parallelism, longer as the number of threads decreases. This
321	>	* will slowly propagate, eventually terminating all workers after
322	>	* periods of non-use.
323		*
324		* Shutdown and Termination. A call to shutdownNow atomically sets
325		* a runState bit and then (non-atomically) sets each worker's
#	Line 413 | Line 410 | public class ForkJoinPool extends Abstra
410		* unblocked threads to the point that we know they are available)
411		* leading to more situations requiring more threads, and so
412		* on. This aspect of control can be seen as an (analytically
413	<	* intractible) game with an opponent that may choose the worst
413	>	* intractable) game with an opponent that may choose the worst
414		* (for us) active thread to stall at any time.  We take several
415		* precautions to bound losses (and thus bound gains), mainly in
416		* methods tryCompensate and awaitJoin: (1) We only try
#	Line 504 | Line 501 | public class ForkJoinPool extends Abstra
501		}
502
503		/**
507	–	* A simple non-reentrant lock used for exclusion when managing
508	–	* queues and workers. We use a custom lock so that we can readily
509	–	* probe lock state in constructions that check among alternative
510	–	* actions. The lock is normally only very briefly held, and
511	–	* sometimes treated as a spinlock, but other usages block to
512	–	* reduce overall contention in those cases where locked code
513	–	* bodies perform allocation/resizing.
514	–	*/
515	–	static final class Mutex extends AbstractQueuedSynchronizer {
516	–	public final boolean tryAcquire(int ignore) {
517	–	return compareAndSetState(0, 1);
518	–	}
519	–	public final boolean tryRelease(int ignore) {
520	–	setState(0);
521	–	return true;
522	–	}
523	–	public final void lock() { acquire(0); }
524	–	public final void unlock() { release(0); }
525	–	public final boolean isHeldExclusively() { return getState() == 1; }
526	–	public final Condition newCondition() { return new ConditionObject(); }
527	–	}
528	–
529	–	/**
504		* Class for artificial tasks that are used to replace the target
505		* of local joins if they are removed from an interior queue slot
506		* in WorkQueue.tryRemoveAndExec. We don't need the proxy to
#	Line 629 | Line 603 | public class ForkJoinPool extends Abstra
603		final ForkJoinPool pool;   // the containing pool (may be null)
604		final ForkJoinWorkerThread owner; // owning thread or null if shared
605		volatile Thread parker;    // == owner during call to park; else null
606	<	ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
606	>	volatile ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
607		ForkJoinTask<?> currentSteal; // current non-local task being executed
608		// Heuristic padding to ameliorate unfortunate memory placements
609		Object p00, p01, p02, p03, p04, p05, p06, p07;
#	Line 717 | Line 691 | public class ForkJoinPool extends Abstra
691
692		/**
693		* Takes next task, if one exists, in LIFO order.  Call only
694	<	* by owner in unshared queues. (We do not have a shared
721	<	* version of this method because it is never needed.)
694	>	* by owner in unshared queues.
695		*/
696		final ForkJoinTask<?> pop() {
697	<	ForkJoinTask<?> t; int m;
698	<	ForkJoinTask<?>[] a = array;
726	<	if (a != null && (m = a.length - 1) >= 0) {
697	>	ForkJoinTask<?>[] a; ForkJoinTask<?> t; int m;
698	>	if ((a = array) != null && (m = a.length - 1) >= 0) {
699		for (int s; (s = top - 1) - base >= 0;) {
700	<	int j = ((m & s) << ASHIFT) + ABASE;
701	<	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) == null)
700	>	long j = ((m & s) << ASHIFT) + ABASE;
701	>	if ((t = (ForkJoinTask<?>)U.getObject(a, j)) == null)
702		break;
703		if (U.compareAndSwapObject(a, j, t, null)) {
704		top = s;
#	Line 737 | Line 709 | public class ForkJoinPool extends Abstra
709		return null;
710		}
711
712	+	final ForkJoinTask<?> sharedPop() {
713	+	ForkJoinTask<?> task = null;
714	+	if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
715	+	try {
716	+	ForkJoinTask<?>[] a; int m;
717	+	if ((a = array) != null && (m = a.length - 1) >= 0) {
718	+	for (int s; (s = top - 1) - base >= 0;) {
719	+	long j = ((m & s) << ASHIFT) + ABASE;
720	+	ForkJoinTask<?> t =
721	+	(ForkJoinTask<?>)U.getObject(a, j);
722	+	if (t == null)
723	+	break;
724	+	if (U.compareAndSwapObject(a, j, t, null)) {
725	+	top = s;
726	+	task = t;
727	+	break;
728	+	}
729	+	}
730	+	}
731	+	} finally {
732	+	runState = 0;
733	+	}
734	+	}
735	+	return task;
736	+	}
737	+
738	+	/**
739	+	* Version of pop that takes top element only if it
740	+	* its root is the given CountedCompleter.
741	+	*/
742	+	final ForkJoinTask<?> popCC(CountedCompleter<?> root) {
743	+	ForkJoinTask<?>[] a; int m;
744	+	if (root != null && (a = array) != null && (m = a.length - 1) >= 0) {
745	+	for (int s; (s = top - 1) - base >= 0;) {
746	+	long j = ((m & s) << ASHIFT) + ABASE;
747	+	ForkJoinTask<?> t =
748	+	(ForkJoinTask<?>)U.getObject(a, j);
749	+	if (t == null || !(t instanceof CountedCompleter) ||
750	+	((CountedCompleter<?>)t).getRoot() != root)
751	+	break;
752	+	if (U.compareAndSwapObject(a, j, t, null)) {
753	+	top = s;
754	+	return t;
755	+	}
756	+	if (root.status < 0)
757	+	break;
758	+	}
759	+	}
760	+	return null;
761	+	}
762	+
763	+	/**
764	+	* Shared version of popCC
765	+	*/
766	+	final ForkJoinTask<?> sharedPopCC(CountedCompleter<?> root) {
767	+	ForkJoinTask<?> task = null;
768	+	if (root != null &&
769	+	runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
770	+	try {
771	+	ForkJoinTask<?>[] a; int m;
772	+	if ((a = array) != null && (m = a.length - 1) >= 0) {
773	+	for (int s; (s = top - 1) - base >= 0;) {
774	+	long j = ((m & s) << ASHIFT) + ABASE;
775	+	ForkJoinTask<?> t =
776	+	(ForkJoinTask<?>)U.getObject(a, j);
777	+	if (t == null || !(t instanceof CountedCompleter) ||
778	+	((CountedCompleter<?>)t).getRoot() != root)
779	+	break;
780	+	if (U.compareAndSwapObject(a, j, t, null)) {
781	+	top = s;
782	+	task = t;
783	+	break;
784	+	}
785	+	if (root.status < 0)
786	+	break;
787	+	}
788	+	}
789	+	} finally {
790	+	runState = 0;
791	+	}
792	+	}
793	+	return task;
794	+	}
795	+
796		/**
797		* Takes a task in FIFO order if b is base of queue and a task
798		* can be claimed without contention. Specialized versions
#	Line 814 | Line 870 | public class ForkJoinPool extends Abstra
870		}
871
872		/**
873	+	* Version of tryUnpush for shared queues; called by non-FJ
874	+	* submitters after prechecking that task probably exists.
875	+	*/
876	+	final boolean trySharedUnpush(ForkJoinTask<?> t) {
877	+	boolean success = false;
878	+	if (runState == 0 && U.compareAndSwapInt(this, RUNSTATE, 0, 1)) {
879	+	try {
880	+	ForkJoinTask<?>[] a; int s;
881	+	if ((a = array) != null && (s = top) != base &&
882	+	U.compareAndSwapObject
883	+	(a, (((a.length - 1) & --s) << ASHIFT) + ABASE, t, null)) {
884	+	top = s;
885	+	success = true;
886	+	}
887	+	} finally {
888	+	runState = 0;                         // unlock
889	+	}
890	+	}
891	+	return success;
892	+	}
893	+
894	+	/**
895		* Polls the given task only if it is at the current base.
896		*/
897		final boolean pollFor(ForkJoinTask<?> task) {
#	Line 830 | Line 908 | public class ForkJoinPool extends Abstra
908		}
909
910		/**
833	–	* If present, removes from queue and executes the given task, or
834	–	* any other cancelled task. Returns (true) immediately on any CAS
835	–	* or consistency check failure so caller can retry.
836	–	*
837	–	* @return false if no progress can be made
838	–	*/
839	–	final boolean tryRemoveAndExec(ForkJoinTask<?> task) {
840	–	boolean removed = false, empty = true, progress = true;
841	–	ForkJoinTask<?>[] a; int m, s, b, n;
842	–	if ((a = array) != null && (m = a.length - 1) >= 0 &&
843	–	(n = (s = top) - (b = base)) > 0) {
844	–	for (ForkJoinTask<?> t;;) {           // traverse from s to b
845	–	int j = ((--s & m) << ASHIFT) + ABASE;
846	–	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
847	–	if (t == null)                    // inconsistent length
848	–	break;
849	–	else if (t == task) {
850	–	if (s + 1 == top) {           // pop
851	–	if (!U.compareAndSwapObject(a, j, task, null))
852	–	break;
853	–	top = s;
854	–	removed = true;
855	–	}
856	–	else if (base == b)           // replace with proxy
857	–	removed = U.compareAndSwapObject(a, j, task,
858	–	new EmptyTask());
859	–	break;
860	–	}
861	–	else if (t.status >= 0)
862	–	empty = false;
863	–	else if (s + 1 == top) {          // pop and throw away
864	–	if (U.compareAndSwapObject(a, j, t, null))
865	–	top = s;
866	–	break;
867	–	}
868	–	if (--n == 0) {
869	–	if (!empty && base == b)
870	–	progress = false;
871	–	break;
872	–	}
873	–	}
874	–	}
875	–	if (removed)
876	–	task.doExec();
877	–	return progress;
878	–	}
879	–
880	–	/**
911		* Initializes or doubles the capacity of array. Call either
912		* by owner or with lock held -- it is OK for base, but not
913		* top, to move while resizings are in progress.
#	Line 939 | Line 969 | public class ForkJoinPool extends Abstra
969		// Execution methods
970
971		/**
972	<	* Removes and runs tasks until empty, using local mode
943	<	* ordering. Normally called only after checking for apparent
944	<	* non-emptiness.
972	>	* Pops and runs tasks until empty.
973		*/
974	<	final void runLocalTasks() {
975	<	// hoist checks from repeated pop/poll
976	<	ForkJoinTask<?>[] a; int m;
977	<	if ((a = array) != null && (m = a.length - 1) >= 0) {
978	<	if (mode == 0) {
979	<	for (int s; (s = top - 1) - base >= 0;) {
980	<	int j = ((m & s) << ASHIFT) + ABASE;
981	<	ForkJoinTask<?> t =
982	<	(ForkJoinTask<?>)U.getObjectVolatile(a, j);
983	<	if (t != null) {
984	<	if (U.compareAndSwapObject(a, j, t, null)) {
957	<	top = s;
958	<	t.doExec();
959	<	}
960	<	}
961	<	else
962	<	break;
963	<	}
974	>	private void popAndExecAll() {
975	>	// A bit faster than repeated pop calls
976	>	ForkJoinTask<?>[] a; int m, s; long j; ForkJoinTask<?> t;
977	>	while ((a = array) != null && (m = a.length - 1) >= 0 &&
978	>	(s = top - 1) - base >= 0 &&
979	>	(t = ((ForkJoinTask<?>)
980	>	U.getObject(a, j = ((m & s) << ASHIFT) + ABASE)))
981	>	!= null) {
982	>	if (U.compareAndSwapObject(a, j, t, null)) {
983	>	top = s;
984	>	t.doExec();
985		}
986	<	else {
987	<	for (int b; (b = base) - top < 0;) {
988	<	int j = ((m & b) << ASHIFT) + ABASE;
989	<	ForkJoinTask<?> t =
990	<	(ForkJoinTask<?>)U.getObjectVolatile(a, j);
991	<	if (t != null) {
992	<	if (base == b &&
993	<	U.compareAndSwapObject(a, j, t, null)) {
994	<	base = b + 1;
995	<	t.doExec();
996	<	}
997	<	} else if (base == b) {
998	<	if (b + 1 == top)
986	>	}
987	>	}
988	>
989	>	/**
990	>	* Polls and runs tasks until empty.
991	>	*/
992	>	private void pollAndExecAll() {
993	>	for (ForkJoinTask<?> t; (t = poll()) != null;)
994	>	t.doExec();
995	>	}
996	>
997	>	/**
998	>	* If present, removes from queue and executes the given task, or
999	>	* any other cancelled task. Returns (true) immediately on any CAS
1000	>	* or consistency check failure so caller can retry.
1001	>	*
1002	>	* @return 0 if no progress can be made, else positive
1003	>	* (this unusual convention simplifies use with tryHelpStealer.)
1004	>	*/
1005	>	final int tryRemoveAndExec(ForkJoinTask<?> task) {
1006	>	int stat = 1;
1007	>	boolean removed = false, empty = true;
1008	>	ForkJoinTask<?>[] a; int m, s, b, n;
1009	>	if ((a = array) != null && (m = a.length - 1) >= 0 &&
1010	>	(n = (s = top) - (b = base)) > 0) {
1011	>	for (ForkJoinTask<?> t;;) {           // traverse from s to b
1012	>	int j = ((--s & m) << ASHIFT) + ABASE;
1013	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
1014	>	if (t == null)                    // inconsistent length
1015	>	break;
1016	>	else if (t == task) {
1017	>	if (s + 1 == top) {           // pop
1018	>	if (!U.compareAndSwapObject(a, j, task, null))
1019		break;
1020	<	Thread.yield(); // wait for lagging update
1020	>	top = s;
1021	>	removed = true;
1022		}
1023	+	else if (base == b)           // replace with proxy
1024	+	removed = U.compareAndSwapObject(a, j, task,
1025	+	new EmptyTask());
1026	+	break;
1027	+	}
1028	+	else if (t.status >= 0)
1029	+	empty = false;
1030	+	else if (s + 1 == top) {          // pop and throw away
1031	+	if (U.compareAndSwapObject(a, j, t, null))
1032	+	top = s;
1033	+	break;
1034	+	}
1035	+	if (--n == 0) {
1036	+	if (!empty && base == b)
1037	+	stat = 0;
1038	+	break;
1039		}
1040		}
1041		}
1042	+	if (removed)
1043	+	task.doExec();
1044	+	return stat;
1045		}
1046
1047		/**
1048		* Executes a top-level task and any local tasks remaining
1049		* after execution.
989	–	*
990	–	* @return true unless terminating
1050		*/
1051	<	final boolean runTask(ForkJoinTask<?> t) {
993	<	boolean alive = true;
1051	>	final void runTask(ForkJoinTask<?> t) {
1052		if (t != null) {
1053		currentSteal = t;
1054		t.doExec();
1055	<	if (top != base)        // conservative guard
1056	<	runLocalTasks();
1055	>	if (top != base) {       // process remaining local tasks
1056	>	if (mode == 0)
1057	>	popAndExecAll();
1058	>	else
1059	>	pollAndExecAll();
1060	>	}
1061		++nsteals;
1062		currentSteal = null;
1063		}
1002	–	else if (runState < 0)      // terminating
1003	–	alive = false;
1004	–	return alive;
1064		}
1065
1066		/**
#	Line 1106 | Line 1165 | public class ForkJoinPool extends Abstra
1165		public static final ForkJoinWorkerThreadFactory
1166		defaultForkJoinWorkerThreadFactory;
1167
1168	+
1169	+	/** Property prefix for constructing common pool */
1170	+	private static final String propPrefix =
1171	+	"java.util.concurrent.ForkJoinPool.common.";
1172	+
1173	+	/**
1174	+	* Common (static) pool. Non-null for public use unless a static
1175	+	* construction exception, but internal usages must null-check on
1176	+	* use.
1177	+	*/
1178	+	static final ForkJoinPool commonPool;
1179	+
1180	+	/**
1181	+	* Common pool parallelism. Must equal commonPool.parallelism.
1182	+	*/
1183	+	static final int commonPoolParallelism;
1184	+
1185		/**
1186		* Generator for assigning sequence numbers as pool names.
1187		*/
#	Line 1124 | Line 1200 | public class ForkJoinPool extends Abstra
1200		private static final RuntimePermission modifyThreadPermission;
1201
1202		/**
1203	<	* Per-thread submission bookeeping. Shared across all pools
1203	>	* Per-thread submission bookkeeping. Shared across all pools
1204		* to reduce ThreadLocal pollution and because random motion
1205		* to avoid contention in one pool is likely to hold for others.
1206		*/
#	Line 1133 | Line 1209 | public class ForkJoinPool extends Abstra
1209		// static constants
1210
1211		/**
1212	<	* The wakeup interval (in nanoseconds) for a worker waiting for a
1213	<	* task when the pool is quiescent to instead try to shrink the
1214	<	* number of workers.  The exact value does not matter too
1139	<	* much. It must be short enough to release resources during
1140	<	* sustained periods of idleness, but not so short that threads
1141	<	* are continually re-created.
1212	>	* Initial timeout value (in nanoseconds) for the thread triggering
1213	>	* quiescence to park waiting for new work. On timeout, the thread
1214	>	* will instead try to shrink the number of workers.
1215		*/
1216	<	private static final long SHRINK_RATE =
1144	<	4L * 1000L * 1000L * 1000L; // 4 seconds
1216	>	private static final long IDLE_TIMEOUT      = 1000L * 1000L * 1000L; // 1sec
1217
1218		/**
1219	<	* The timeout value for attempted shrinkage, includes
1148	<	* some slop to cope with system timer imprecision.
1219	>	* Timeout value when there are more threads than parallelism level
1220		*/
1221	<	private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
1221	>	private static final long FAST_IDLE_TIMEOUT =  100L * 1000L * 1000L;
1222
1223		/**
1224		* The maximum stolen->joining link depth allowed in method
#	Line 1160 | Line 1231 | public class ForkJoinPool extends Abstra
1231		* traversal parameters at the expense of sometimes blocking when
1232		* we could be helping.
1233		*/
1234	<	private static final int MAX_HELP = 32;
1234	>	private static final int MAX_HELP = 64;
1235
1236		/**
1237		* Secondary time-based bound (in nanosecs) for helping attempts
#	Line 1170 | Line 1241 | public class ForkJoinPool extends Abstra
1241		* value should roughly approximate the time required to create
1242		* and/or activate a worker thread.
1243		*/
1244	<	private static final long COMPENSATION_DELAY = 100L * 1000L; // 0.1 millisec
1244	>	private static final long COMPENSATION_DELAY = 1L << 18; // ~0.25 millisec
1245
1246		/**
1247		* Increment for seed generators. See class ThreadLocal for
#	Line 1267 | Line 1338 | public class ForkJoinPool extends Abstra
1338		* empirically works OK on current JVMs.
1339		*/
1340
1341	+	volatile long stealCount;                  // collects worker counts
1342		volatile long ctl;                         // main pool control
1343		final int parallelism;                     // parallelism level
1344		final int localMode;                       // per-worker scheduling mode
1345	+	volatile int nextWorkerNumber;             // to create worker name string
1346		final int submitMask;                      // submit queue index bound
1347		int nextSeed;                              // for initializing worker seeds
1348	+	volatile int mainLock;                     // spinlock for array updates
1349		volatile int runState;                     // shutdown status and seq
1350		WorkQueue[] workQueues;                    // main registry
1277	–	final Mutex lock;                          // for registration
1278	–	final Condition termination;               // for awaitTermination
1351		final ForkJoinWorkerThreadFactory factory; // factory for new workers
1352		final Thread.UncaughtExceptionHandler ueh; // per-worker UEH
1281	–	final AtomicLong stealCount;               // collect counts when terminated
1282	–	final AtomicInteger nextWorkerNumber;      // to create worker name string
1353		final String workerNamePrefix;             // to create worker name string
1354
1355	+	/*
1356	+	* Mechanics for main lock protecting worker array updates.  Uses
1357	+	* the same strategy as ConcurrentHashMap bins -- a spinLock for
1358	+	* normal cases, but falling back to builtin lock when (rarely)
1359	+	* needed.  See internal ConcurrentHashMap documentation for
1360	+	* explanation.
1361	+	*/
1362	+
1363	+	static final int LOCK_WAITING = 2; // bit to indicate need for signal
1364	+	static final int MAX_LOCK_SPINS = 1 << 8;
1365	+
1366	+	private void tryAwaitMainLock() {
1367	+	int spins = MAX_LOCK_SPINS, r = 0, h;
1368	+	while (((h = mainLock) & 1) != 0) {
1369	+	if (r == 0)
1370	+	r = ThreadLocalRandom.current().nextInt(); // randomize spins
1371	+	else if (spins >= 0) {
1372	+	r ^= r << 1; r ^= r >>> 3; r ^= r << 10; // xorshift
1373	+	if (r >= 0)
1374	+	--spins;
1375	+	}
1376	+	else if (U.compareAndSwapInt(this, MAINLOCK, h, h | LOCK_WAITING)) {
1377	+	synchronized (this) {
1378	+	if ((mainLock & LOCK_WAITING) != 0) {
1379	+	try {
1380	+	wait();
1381	+	} catch (InterruptedException ie) {
1382	+	Thread.currentThread().interrupt();
1383	+	}
1384	+	}
1385	+	else
1386	+	notifyAll(); // possibly won race vs signaller
1387	+	}
1388	+	break;
1389	+	}
1390	+	}
1391	+	}
1392	+
1393		//  Creating, registering, and deregistering workers
1394
1395		/**
#	Line 1308 | Line 1416 | public class ForkJoinPool extends Abstra
1416		* ForkJoinWorkerThread.
1417		*/
1418		final String nextWorkerName() {
1419	<	return workerNamePrefix.concat
1420	<	(Integer.toString(nextWorkerNumber.addAndGet(1)));
1419	>	int n;
1420	>	do {} while(!U.compareAndSwapInt(this, NEXTWORKERNUMBER,
1421	>	n = nextWorkerNumber, ++n));
1422	>	return workerNamePrefix.concat(Integer.toString(n));
1423		}
1424
1425		/**
#	Line 1322 | Line 1432 | public class ForkJoinPool extends Abstra
1432		* @param w the worker's queue
1433		*/
1434		final void registerWorker(WorkQueue w) {
1435	<	Mutex lock = this.lock;
1436	<	lock.lock();
1435	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1436	>	tryAwaitMainLock();
1437		try {
1438	<	WorkQueue[] ws = workQueues;
1439	<	if (w != null && ws != null) {          // skip on shutdown/failure
1440	<	int rs, n;
1441	<	while ((n = ws.length) <            // ensure can hold total
1442	<	(parallelism + (short)(ctl >>> TC_SHIFT) << 1))
1333	<	workQueues = ws = Arrays.copyOf(ws, n << 1);
1334	<	int m = n - 1;
1438	>	WorkQueue[] ws;
1439	>	if ((ws = workQueues) == null)
1440	>	ws = workQueues = new WorkQueue[submitMask + 1];
1441	>	if (w != null) {
1442	>	int rs, n =  ws.length, m = n - 1;
1443		int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
1444		w.seed = (s == 0) ? 1 : s;          // ensure non-zero seed
1445		int r = (s << 1) | 1;               // use odd-numbered indices
1446	<	while (ws[r &= m] != null)          // step by approx half size
1447	<	r += ((n >>> 1) & SQMASK) + 2;
1446	>	if (ws[r &= m] != null) {           // collision
1447	>	int probes = 0;                 // step by approx half size
1448	>	int step = (n <= 4) ? 2 : ((n >>> 1) & SQMASK) + 2;
1449	>	while (ws[r = (r + step) & m] != null) {
1450	>	if (++probes >= n) {
1451	>	workQueues = ws = Arrays.copyOf(ws, n <<= 1);
1452	>	m = n - 1;
1453	>	probes = 0;
1454	>	}
1455	>	}
1456	>	}
1457		w.eventCount = w.poolIndex = r;     // establish before recording
1458		ws[r] = w;                          // also update seq
1459		runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
1460		}
1461		} finally {
1462	<	lock.unlock();
1462	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1463	>	mainLock = 0;
1464	>	synchronized (this) { notifyAll(); };
1465	>	}
1466		}
1467	+
1468		}
1469
1470		/**
#	Line 1356 | Line 1477 | public class ForkJoinPool extends Abstra
1477		* @param ex the exception causing failure, or null if none
1478		*/
1479		final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1359	–	Mutex lock = this.lock;
1480		WorkQueue w = null;
1481		if (wt != null && (w = wt.workQueue) != null) {
1482		w.runState = -1;                // ensure runState is set
1483	<	stealCount.getAndAdd(w.totalSteals + w.nsteals);
1483	>	long steals = w.totalSteals + w.nsteals, sc;
1484	>	do {} while(!U.compareAndSwapLong(this, STEALCOUNT,
1485	>	sc = stealCount, sc + steals));
1486		int idx = w.poolIndex;
1487	<	lock.lock();
1488	<	try {                           // remove record from array
1487	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1488	>	tryAwaitMainLock();
1489	>	try {
1490		WorkQueue[] ws = workQueues;
1491		if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
1492		ws[idx] = null;
1493		} finally {
1494	<	lock.unlock();
1494	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1495	>	mainLock = 0;
1496	>	synchronized (this) { notifyAll(); };
1497	>	}
1498		}
1499		}
1500
#	Line 1390 | Line 1516 | public class ForkJoinPool extends Abstra
1516		U.throwException(ex);
1517		}
1518
1393	–
1519		// Submissions
1520
1521		/**
#	Line 1399 | Line 1524 | public class ForkJoinPool extends Abstra
1524		* range). If no queue exists at the index, one is created.  If
1525		* the queue is busy, another index is randomly chosen. The
1526		* submitMask bounds the effective number of queues to the
1527	<	* (nearest poswer of two for) parallelism level.
1527	>	* (nearest power of two for) parallelism level.
1528		*
1529		* @param task the task. Caller must ensure non-null.
1530		*/
#	Line 1408 | Line 1533 | public class ForkJoinPool extends Abstra
1533		for (int r = s.seed, m = submitMask;;) {
1534		WorkQueue[] ws; WorkQueue q;
1535		int k = r & m & SQMASK;          // use only even indices
1536	<	if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
1536	>	if (runState < 0)
1537		throw new RejectedExecutionException(); // shutting down
1538	+	else if ((ws = workQueues) == null || ws.length <= k) {
1539	+	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1540	+	tryAwaitMainLock();
1541	+	try {
1542	+	if (workQueues == null)
1543	+	workQueues = new WorkQueue[submitMask + 1];
1544	+	} finally {
1545	+	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1546	+	mainLock = 0;
1547	+	synchronized (this) { notifyAll(); };
1548	+	}
1549	+	}
1550	+	}
1551		else if ((q = ws[k]) == null) {  // create new queue
1552		WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
1553	<	Mutex lock = this.lock;      // construct outside lock
1554	<	lock.lock();
1555	<	try {                        // recheck under lock
1553	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
1554	>	tryAwaitMainLock();
1555	>	try {
1556		int rs = runState;       // to update seq
1557		if (ws == workQueues && ws[k] == null) {
1558		ws[k] = nq;
1559		runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
1560		}
1561		} finally {
1562	<	lock.unlock();
1562	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
1563	>	mainLock = 0;
1564	>	synchronized (this) { notifyAll(); };
1565	>	}
1566		}
1567		}
1568		else if (q.trySharedPush(task)) {
#	Line 1438 | Line 1579 | public class ForkJoinPool extends Abstra
1579		}
1580		}
1581
1582	+	/**
1583	+	* Submits the given (non-null) task to the common pool, if possible.
1584	+	*/
1585	+	static void submitToCommonPool(ForkJoinTask<?> task) {
1586	+	ForkJoinPool p;
1587	+	if ((p = commonPool) == null)
1588	+	throw new RejectedExecutionException("Common Pool Unavailable");
1589	+	p.doSubmit(task);
1590	+	}
1591	+
1592	+	/**
1593	+	* Returns true if caller is (or may be) submitter to the common
1594	+	* pool, and not all workers are active, and there appear to be
1595	+	* tasks in the associated submission queue.
1596	+	*/
1597	+	static boolean canHelpCommonPool() {
1598	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
1599	+	int k = submitters.get().seed & SQMASK;
1600	+	return ((p = commonPool) != null &&
1601	+	(int)(p.ctl >> AC_SHIFT) < 0 &&
1602	+	(ws = p.workQueues) != null &&
1603	+	ws.length > (k &= p.submitMask) &&
1604	+	(q = ws[k]) != null &&
1605	+	q.top - q.base > 0);
1606	+	}
1607	+
1608	+	/**
1609	+	* Returns true if the given task was submitted to common pool
1610	+	* and has not yet commenced execution, and is available for
1611	+	* removal according to execution policies; if so removing the
1612	+	* submission from the pool.
1613	+	*
1614	+	* @param task the task
1615	+	* @return true if successful
1616	+	*/
1617	+	static boolean tryUnsubmitFromCommonPool(ForkJoinTask<?> task) {
1618	+	// Peek, looking for task and eligibility before
1619	+	// using trySharedUnpush to actually take it under lock
1620	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
1621	+	ForkJoinTask<?>[] a; int s;
1622	+	int k = submitters.get().seed & SQMASK;
1623	+	return ((p = commonPool) != null &&
1624	+	(int)(p.ctl >> AC_SHIFT) < 0 &&
1625	+	(ws = p.workQueues) != null &&
1626	+	ws.length > (k &= p.submitMask) &&
1627	+	(q = ws[k]) != null &&
1628	+	(a = q.array) != null &&
1629	+	(s = q.top - 1) - q.base >= 0 &&
1630	+	s >= 0 && s < a.length &&
1631	+	a[s] == task &&
1632	+	q.trySharedUnpush(task));
1633	+	}
1634	+
1635	+	/**
1636	+	* Tries to pop a task from common pool with given root
1637	+	*/
1638	+	static ForkJoinTask<?> popCCFromCommonPool(CountedCompleter<?> root) {
1639	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
1640	+	ForkJoinTask<?> t;
1641	+	int k = submitters.get().seed & SQMASK;
1642	+	if (root != null &&
1643	+	(p = commonPool) != null &&
1644	+	(int)(p.ctl >> AC_SHIFT) < 0 &&
1645	+	(ws = p.workQueues) != null &&
1646	+	ws.length > (k &= p.submitMask) &&
1647	+	(q = ws[k]) != null && q.top - q.base > 0 &&
1648	+	root.status < 0 &&
1649	+	(t = q.sharedPopCC(root)) != null)
1650	+	return t;
1651	+	return null;
1652	+	}
1653	+
1654	+
1655		// Maintaining ctl counts
1656
1657		/**
#	Line 1449 | Line 1663 | public class ForkJoinPool extends Abstra
1663		}
1664
1665		/**
1666	<	* Tries to activate or create a worker if too few are active.
1666	>	* Tries to create one or activate one or more workers if too few are active.
1667		*/
1668		final void signalWork() {
1669		long c; int u;
#	Line 1483 | Line 1697 | public class ForkJoinPool extends Abstra
1697		}
1698		}
1699
1486	–
1700		// Scanning for tasks
1701
1702		/**
#	Line 1491 | Line 1704 | public class ForkJoinPool extends Abstra
1704		*/
1705		final void runWorker(WorkQueue w) {
1706		w.growArray(false);         // initialize queue array in this thread
1707	<	do {} while (w.runTask(scan(w)));
1707	>	do { w.runTask(scan(w)); } while (w.runState >= 0);
1708		}
1709
1710		/**
#	Line 1534 | Line 1747 | public class ForkJoinPool extends Abstra
1747		* awaiting signal,
1748		*
1749		* @param w the worker (via its WorkQueue)
1750	<	* @return a task or null of none found
1750	>	* @return a task or null if none found
1751		*/
1752		private final ForkJoinTask<?> scan(WorkQueue w) {
1753		WorkQueue[] ws;                       // first update random seed
#	Line 1551 | Line 1764 | public class ForkJoinPool extends Abstra
1764		t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1765		if (q.base == b && ec >= 0 && t != null &&
1766		U.compareAndSwapObject(a, i, t, null)) {
1767	<	q.base = b + 1;       // specialization of pollAt
1767	>	if (q.top - (q.base = b + 1) > 0)
1768	>	signalWork();    // help pushes signal
1769		return t;
1770		}
1771	<	else if ((t != null || b + 1 != q.top) &&
1558	<	(ec < 0 || j <= m)) {
1771	>	else if (ec < 0 || j <= m) {
1772		rs = 0;               // mark scan as imcomplete
1773		break;                // caller can retry after release
1774		}
#	Line 1563 | Line 1776 | public class ForkJoinPool extends Abstra
1776		if (--j < 0)
1777		break;
1778		}
1779	+
1780		long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
1781		if (e < 0)                        // decode ctl on empty scan
1782		w.runState = -1;              // pool is terminating
#	Line 1596 | Line 1810 | public class ForkJoinPool extends Abstra
1810		}
1811		}
1812		else if (w.eventCount < 0) {      // already queued
1813	<	if ((nr = w.rescans) > 0) {   // continue rescanning
1814	<	int ac = a + parallelism;
1815	<	if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0)
1816	<	Thread.yield();       // yield before block
1603	<	}
1604	<	else {
1813	>	int ac = a + parallelism;
1814	>	if ((nr = w.rescans) > 0)     // continue rescanning
1815	>	w.rescans = (ac < nr) ? ac : nr - 1;
1816	>	else if (((w.seed >>> 16) & ac) == 0) { // randomize park
1817		Thread.interrupted();     // clear status
1818		Thread wt = Thread.currentThread();
1819		U.putObject(wt, PARKBLOCKER, this);
#	Line 1619 | Line 1831 | public class ForkJoinPool extends Abstra
1831		/**
1832		* If inactivating worker w has caused the pool to become
1833		* quiescent, checks for pool termination, and, so long as this is
1834	<	* not the only worker, waits for event for up to SHRINK_RATE
1835	<	* nanosecs.  On timeout, if ctl has not changed, terminates the
1834	>	* not the only worker, waits for event for up to a given
1835	>	* duration.  On timeout, if ctl has not changed, terminates the
1836		* worker, which will in turn wake up another worker to possibly
1837		* repeat this process.
1838		*
#	Line 1630 | Line 1842 | public class ForkJoinPool extends Abstra
1842		*/
1843		private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
1844		if (w.eventCount < 0 && !tryTerminate(false, false) &&
1845	<	(int)prevCtl != 0 && ctl == currentCtl) {
1845	>	(int)prevCtl != 0 && !hasQueuedSubmissions() && ctl == currentCtl) {
1846	>	int dc = -(short)(currentCtl >>> TC_SHIFT);
1847	>	long parkTime = dc < 0 ? FAST_IDLE_TIMEOUT: (dc + 1) * IDLE_TIMEOUT;
1848	>	long deadline = System.nanoTime() + parkTime - 100000L; // 1ms slop
1849		Thread wt = Thread.currentThread();
1635	–	Thread.yield();            // yield before block
1850		while (ctl == currentCtl) {
1637	–	long startTime = System.nanoTime();
1851		Thread.interrupted();  // timed variant of version in scan()
1852		U.putObject(wt, PARKBLOCKER, this);
1853		w.parker = wt;
1854		if (ctl == currentCtl)
1855	<	U.park(false, SHRINK_RATE);
1855	>	U.park(false, parkTime);
1856		w.parker = null;
1857		U.putObject(wt, PARKBLOCKER, null);
1858		if (ctl != currentCtl)
1859		break;
1860	<	if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
1860	>	if (deadline - System.nanoTime() <= 0L &&
1861		U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
1862		w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
1863		w.runState = -1;   // shrink
#	Line 1665 | Line 1878 | public class ForkJoinPool extends Abstra
1878		* leaves hints in workers to speed up subsequent calls. The
1879		* implementation is very branchy to cope with potential
1880		* inconsistencies or loops encountering chains that are stale,
1881	<	* unknown, or so long that they are likely cyclic.  All of these
1669	<	* cases are dealt with by just retrying by caller.
1881	>	* unknown, or so long that they are likely cyclic.
1882		*
1883		* @param joiner the joining worker
1884		* @param task the task to join
1885	<	* @return true if found or ran a task (and so is immediately retryable)
1885	>	* @return 0 if no progress can be made, negative if task
1886	>	* known complete, else positive
1887		*/
1888	<	private boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1889	<	WorkQueue[] ws;
1890	<	int m, depth = MAX_HELP;                // remaining chain depth
1891	<	boolean progress = false;
1892	<	if ((ws = workQueues) != null && (m = ws.length - 1) > 0 &&
1893	<	task.status >= 0) {
1894	<	ForkJoinTask<?> subtask = task;     // current target
1895	<	outer: for (WorkQueue j = joiner;;) {
1896	<	WorkQueue stealer = null;       // find stealer of subtask
1897	<	WorkQueue v = ws[j.stealHint & m]; // try hint
1898	<	if (v != null && v.currentSteal == subtask)
1899	<	stealer = v;
1900	<	else {                          // scan
1901	<	for (int i = 1; i <= m; i += 2) {
1902	<	if ((v = ws[i]) != null && v.currentSteal == subtask &&
1903	<	v != joiner) {
1904	<	stealer = v;
1905	<	j.stealHint = i;    // save hint
1906	<	break;
1888	>	private int tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1889	>	int stat = 0, steps = 0;                    // bound to avoid cycles
1890	>	if (joiner != null && task != null) {       // hoist null checks
1891	>	restart: for (;;) {
1892	>	ForkJoinTask<?> subtask = task;     // current target
1893	>	for (WorkQueue j = joiner, v;;) {   // v is stealer of subtask
1894	>	WorkQueue[] ws; int m, s, h;
1895	>	if ((s = task.status) < 0) {
1896	>	stat = s;
1897	>	break restart;
1898	>	}
1899	>	if ((ws = workQueues) == null || (m = ws.length - 1) <= 0)
1900	>	break restart;              // shutting down
1901	>	if ((v = ws[h = (j.stealHint | 1) & m]) == null ||
1902	>	v.currentSteal != subtask) {
1903	>	for (int origin = h;;) {    // find stealer
1904	>	if (((h = (h + 2) & m) & 15) == 1 &&
1905	>	(subtask.status < 0 || j.currentJoin != subtask))
1906	>	continue restart;   // occasional staleness check
1907	>	if ((v = ws[h]) != null &&
1908	>	v.currentSteal == subtask) {
1909	>	j.stealHint = h;    // save hint
1910	>	break;
1911	>	}
1912	>	if (h == origin)
1913	>	break restart;      // cannot find stealer
1914		}
1915		}
1916	<	if (stealer == null)
1917	<	break;
1918	<	}
1919	<
1920	<	for (WorkQueue q = stealer;;) { // try to help stealer
1921	<	ForkJoinTask[] a; ForkJoinTask<?> t; int b;
1922	<	if (task.status < 0)
1923	<	break outer;
1924	<	if ((b = q.base) - q.top < 0 && (a = q.array) != null) {
1925	<	progress = true;
1926	<	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1927	<	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1928	<	if (subtask.status < 0) // must recheck before taking
1929	<	break outer;
1930	<	if (t != null &&
1931	<	q.base == b &&
1932	<	U.compareAndSwapObject(a, i, t, null)) {
1933	<	q.base = b + 1;
1934	<	joiner.runSubtask(t);
1916	>	for (;;) { // help stealer or descend to its stealer
1917	>	ForkJoinTask[] a;  int b;
1918	>	if (subtask.status < 0)     // surround probes with
1919	>	continue restart;       //   consistency checks
1920	>	if ((b = v.base) - v.top < 0 && (a = v.array) != null) {
1921	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1922	>	ForkJoinTask<?> t =
1923	>	(ForkJoinTask<?>)U.getObjectVolatile(a, i);
1924	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1925	>	v.currentSteal != subtask)
1926	>	continue restart;   // stale
1927	>	stat = 1;               // apparent progress
1928	>	if (t != null && v.base == b &&
1929	>	U.compareAndSwapObject(a, i, t, null)) {
1930	>	v.base = b + 1;     // help stealer
1931	>	joiner.runSubtask(t);
1932	>	}
1933	>	else if (v.base == b && ++steps == MAX_HELP)
1934	>	break restart;      // v apparently stalled
1935	>	}
1936	>	else {                      // empty -- try to descend
1937	>	ForkJoinTask<?> next = v.currentJoin;
1938	>	if (subtask.status < 0 || j.currentJoin != subtask ||
1939	>	v.currentSteal != subtask)
1940	>	continue restart;   // stale
1941	>	else if (next == null || ++steps == MAX_HELP)
1942	>	break restart;      // dead-end or maybe cyclic
1943	>	else {
1944	>	subtask = next;
1945	>	j = v;
1946	>	break;
1947	>	}
1948		}
1716	–	else if (q.base == b)
1717	–	break outer;        // possibly stalled
1718	–	}
1719	–	else {                      // descend
1720	–	ForkJoinTask<?> next = stealer.currentJoin;
1721	–	if (--depth <= 0 || subtask.status < 0 ||
1722	–	next == null || next == subtask)
1723	–	break outer;        // stale, dead-end, or cyclic
1724	–	subtask = next;
1725	–	j = stealer;
1726	–	break;
1949		}
1950		}
1951		}
1952		}
1953	<	return progress;
1953	>	return stat;
1954		}
1955
1956		/**
#	Line 1757 | Line 1979 | public class ForkJoinPool extends Abstra
1979		* adds a new thread if no idle workers are available and either
1980		* pool would become completely starved or: (at least half
1981		* starved, and fewer than 50% spares exist, and there is at least
1982	<	* one task apparently available). Even though the availablity
1982	>	* one task apparently available). Even though the availability
1983		* check requires a full scan, it is worthwhile in reducing false
1984		* alarms.
1985		*
1986	<	* @param task if nonnull, a task being waited for
1987	<	* @param blocker if nonnull, a blocker being waited for
1986	>	* @param task if non-null, a task being waited for
1987	>	* @param blocker if non-null, a blocker being waited for
1988		* @return true if the caller can block, else should recheck and retry
1989		*/
1990		final boolean tryCompensate(ForkJoinTask<?> task, ManagedBlocker blocker) {
#	Line 1821 | Line 2043 | public class ForkJoinPool extends Abstra
2043		}
2044
2045		/**
2046	<	* Helps and/or blocks until the given task is done
2046	>	* Helps and/or blocks until the given task is done.
2047		*
2048		* @param joiner the joining worker
2049		* @param task the task
2050		* @return task status on exit
2051		*/
2052		final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
2053	<	ForkJoinTask<?> prevJoin = joiner.currentJoin;
2054	<	joiner.currentJoin = task;
2055	<	long startTime = 0L;
2056	<	for (int k = 0, s; ; ++k) {
2057	<	if ((joiner.isEmpty() ?                  // try to help
2058	<	!tryHelpStealer(joiner, task) :
2059	<	!joiner.tryRemoveAndExec(task))) {
2060	<	if (k == 0) {
2061	<	startTime = System.nanoTime();
2062	<	tryPollForAndExec(joiner, task); // check uncommon case
2063	<	}
2064	<	else if ((k & (MAX_HELP - 1)) == 0 &&
2065	<	System.nanoTime() - startTime >= COMPENSATION_DELAY &&
2066	<	tryCompensate(task, null)) {
2067	<	if (task.trySetSignal() && task.status >= 0) {
2068	<	synchronized (task) {
2069	<	if (task.status >= 0) {
2070	<	try {                // see ForkJoinTask
2071	<	task.wait();     //  for explanation
2072	<	} catch (InterruptedException ie) {
2053	>	int s;
2054	>	if ((s = task.status) >= 0) {
2055	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
2056	>	joiner.currentJoin = task;
2057	>	long startTime = 0L;
2058	>	for (int k = 0;;) {
2059	>	if ((s = (joiner.isEmpty() ?           // try to help
2060	>	tryHelpStealer(joiner, task) :
2061	>	joiner.tryRemoveAndExec(task))) == 0 &&
2062	>	(s = task.status) >= 0) {
2063	>	if (k == 0) {
2064	>	startTime = System.nanoTime();
2065	>	tryPollForAndExec(joiner, task); // check uncommon case
2066	>	}
2067	>	else if ((k & (MAX_HELP - 1)) == 0 &&
2068	>	System.nanoTime() - startTime >=
2069	>	COMPENSATION_DELAY &&
2070	>	tryCompensate(task, null)) {
2071	>	if (task.trySetSignal()) {
2072	>	synchronized (task) {
2073	>	if (task.status >= 0) {
2074	>	try {                // see ForkJoinTask
2075	>	task.wait();     //  for explanation
2076	>	} catch (InterruptedException ie) {
2077	>	}
2078		}
2079	+	else
2080	+	task.notifyAll();
2081		}
1853	–	else
1854	–	task.notifyAll();
2082		}
2083	+	long c;                          // re-activate
2084	+	do {} while (!U.compareAndSwapLong
2085	+	(this, CTL, c = ctl, c + AC_UNIT));
2086		}
1857	–	long c;                          // re-activate
1858	–	do {} while (!U.compareAndSwapLong
1859	–	(this, CTL, c = ctl, c + AC_UNIT));
2087		}
2088	+	if (s < 0 || (s = task.status) < 0) {
2089	+	joiner.currentJoin = prevJoin;
2090	+	break;
2091	+	}
2092	+	else if ((k++ & (MAX_HELP - 1)) == MAX_HELP >>> 1)
2093	+	Thread.yield();                     // for politeness
2094		}
1862	–	if ((s = task.status) < 0) {
1863	–	joiner.currentJoin = prevJoin;
1864	–	return s;
1865	–	}
1866	–	else if ((k & (MAX_HELP - 1)) == MAX_HELP >>> 1)
1867	–	Thread.yield();                     // for politeness
2095		}
2096	+	return s;
2097		}
2098
2099		/**
#	Line 1882 | Line 2110 | public class ForkJoinPool extends Abstra
2110		while ((s = task.status) >= 0 &&
2111		(joiner.isEmpty() ?
2112		tryHelpStealer(joiner, task) :
2113	<	joiner.tryRemoveAndExec(task)))
2113	>	joiner.tryRemoveAndExec(task)) != 0)
2114		;
2115		return s;
2116		}
#	Line 1922 | Line 2150 | public class ForkJoinPool extends Abstra
2150		*/
2151		final void helpQuiescePool(WorkQueue w) {
2152		for (boolean active = true;;) {
2153	<	if (w.base - w.top < 0)
2154	<	w.runLocalTasks();  // exhaust local queue
2153	>	ForkJoinTask<?> localTask; // exhaust local queue
2154	>	while ((localTask = w.nextLocalTask()) != null)
2155	>	localTask.doExec();
2156		WorkQueue q = findNonEmptyStealQueue(w);
2157		if (q != null) {
2158		ForkJoinTask<?> t; int b;
#	Line 1955 | Line 2184 | public class ForkJoinPool extends Abstra
2184		}
2185
2186		/**
2187	+	* Restricted version of helpQuiescePool for non-FJ callers
2188	+	*/
2189	+	static void externalHelpQuiescePool() {
2190	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q, sq;
2191	+	ForkJoinTask<?>[] a; int b;
2192	+	ForkJoinTask<?> t = null;
2193	+	int k = submitters.get().seed & SQMASK;
2194	+	if ((p = commonPool) != null &&
2195	+	(int)(p.ctl >> AC_SHIFT) < 0 &&
2196	+	(ws = p.workQueues) != null &&
2197	+	ws.length > (k &= p.submitMask) &&
2198	+	(q = ws[k]) != null) {
2199	+	while (q.top - q.base > 0) {
2200	+	if ((t = q.sharedPop()) != null)
2201	+	break;
2202	+	}
2203	+	if (t == null && (sq = p.findNonEmptyStealQueue(q)) != null &&
2204	+	(b = sq.base) - sq.top < 0)
2205	+	t = sq.pollAt(b);
2206	+	if (t != null)
2207	+	t.doExec();
2208	+	}
2209	+	}
2210	+
2211	+	/**
2212		* Gets and removes a local or stolen task for the given worker.
2213		*
2214		* @return a task, if available
#	Line 1987 | Line 2241 | public class ForkJoinPool extends Abstra
2241		8);
2242		}
2243
2244	+	/**
2245	+	* Returns approximate submission queue length for the given caller
2246	+	*/
2247	+	static int getEstimatedSubmitterQueueLength() {
2248	+	ForkJoinPool p; WorkQueue[] ws; WorkQueue q;
2249	+	int k = submitters.get().seed & SQMASK;
2250	+	return ((p = commonPool) != null &&
2251	+	p.runState >= 0 &&
2252	+	(ws = p.workQueues) != null &&
2253	+	ws.length > (k &= p.submitMask) &&
2254	+	(q = ws[k]) != null) ?
2255	+	q.queueSize() : 0;
2256	+	}
2257	+
2258		//  Termination
2259
2260		/**
#	Line 2004 | Line 2272 | public class ForkJoinPool extends Abstra
2272		* @return true if now terminating or terminated
2273		*/
2274		private boolean tryTerminate(boolean now, boolean enable) {
2007	–	Mutex lock = this.lock;
2275		for (long c;;) {
2276		if (((c = ctl) & STOP_BIT) != 0) {      // already terminating
2277		if ((short)(c >>> TC_SHIFT) == -parallelism) {
2278	<	lock.lock();                    // don't need try/finally
2279	<	termination.signalAll();        // signal when 0 workers
2280	<	lock.unlock();
2278	>	synchronized(this) {
2279	>	notifyAll();                // signal when 0 workers
2280	>	}
2281		}
2282		return true;
2283		}
2284		if (runState >= 0) {                    // not yet enabled
2285		if (!enable)
2286		return false;
2287	<	lock.lock();
2288	<	runState |= SHUTDOWN;
2289	<	lock.unlock();
2287	>	while (!U.compareAndSwapInt(this, MAINLOCK, 0, 1))
2288	>	tryAwaitMainLock();
2289	>	try {
2290	>	runState |= SHUTDOWN;
2291	>	} finally {
2292	>	if (!U.compareAndSwapInt(this, MAINLOCK, 1, 0)) {
2293	>	mainLock = 0;
2294	>	synchronized (this) { notifyAll(); };
2295	>	}
2296	>	}
2297		}
2298		if (!now) {                             // check if idle & no tasks
2299		if ((int)(c >> AC_SHIFT) != -parallelism ||
#	Line 2152 | Line 2426 | public class ForkJoinPool extends Abstra
2426		// Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
2427		int n = parallelism - 1;
2428		n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
2429	<	int size = (n + 1) << 1;        // #slots = 2*#workers
2156	<	this.submitMask = size - 1;     // room for max # of submit queues
2157	<	this.workQueues = new WorkQueue[size];
2158	<	this.termination = (this.lock = new Mutex()).newCondition();
2159	<	this.stealCount = new AtomicLong();
2160	<	this.nextWorkerNumber = new AtomicInteger();
2429	>	this.submitMask = ((n + 1) << 1) - 1;
2430		int pn = poolNumberGenerator.incrementAndGet();
2431		StringBuilder sb = new StringBuilder("ForkJoinPool-");
2432		sb.append(Integer.toString(pn));
2433		sb.append("-worker-");
2434		this.workerNamePrefix = sb.toString();
2166	–	lock.lock();
2435		this.runState = 1;              // set init flag
2436	<	lock.unlock();
2436	>	}
2437	>
2438	>	/**
2439	>	* Constructor for common pool, suitable only for static initialization.
2440	>	* Basically the same as above, but uses smallest possible initial footprint.
2441	>	*/
2442	>	ForkJoinPool(int parallelism, int submitMask,
2443	>	ForkJoinWorkerThreadFactory factory,
2444	>	Thread.UncaughtExceptionHandler handler) {
2445	>	this.factory = factory;
2446	>	this.ueh = handler;
2447	>	this.submitMask = submitMask;
2448	>	this.parallelism = parallelism;
2449	>	long np = (long)(-parallelism);
2450	>	this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2451	>	this.localMode = LIFO_QUEUE;
2452	>	this.workerNamePrefix = "ForkJoinPool.commonPool-worker-";
2453	>	this.runState = 1;
2454	>	}
2455	>
2456	>	/**
2457	>	* Returns the common pool instance.
2458	>	*
2459	>	* @return the common pool instance
2460	>	*/
2461	>	public static ForkJoinPool commonPool() {
2462	>	ForkJoinPool p;
2463	>	if ((p = commonPool) == null)
2464	>	throw new Error("Common Pool Unavailable");
2465	>	return p;
2466		}
2467
2468		// Execution methods
#	Line 2341 | Line 2638 | public class ForkJoinPool extends Abstra
2638		}
2639
2640		/**
2641	+	* Returns the targeted parallelism level of the common pool.
2642	+	*
2643	+	* @return the targeted parallelism level of the common pool
2644	+	*/
2645	+	public static int getCommonPoolParallelism() {
2646	+	return commonPoolParallelism;
2647	+	}
2648	+
2649	+	/**
2650		* Returns the number of worker threads that have started but not
2651		* yet terminated.  The result returned by this method may differ
2652		* from {@link #getParallelism} when threads are created to
#	Line 2421 | Line 2727 | public class ForkJoinPool extends Abstra
2727		* @return the number of steals
2728		*/
2729		public long getStealCount() {
2730	<	long count = stealCount.get();
2730	>	long count = stealCount;
2731		WorkQueue[] ws; WorkQueue w;
2732		if ((ws = workQueues) != null) {
2733		for (int i = 1; i < ws.length; i += 2) {
#	Line 2551 | Line 2857 | public class ForkJoinPool extends Abstra
2857		public String toString() {
2858		// Use a single pass through workQueues to collect counts
2859		long qt = 0L, qs = 0L; int rc = 0;
2860	<	long st = stealCount.get();
2860	>	long st = stealCount;
2861		long c = ctl;
2862		WorkQueue[] ws; WorkQueue w;
2863		if ((ws = workQueues) != null) {
#	Line 2592 | Line 2898 | public class ForkJoinPool extends Abstra
2898		}
2899
2900		/**
2901	<	* Initiates an orderly shutdown in which previously submitted
2902	<	* tasks are executed, but no new tasks will be accepted.
2903	<	* Invocation has no additional effect if already shut down.
2904	<	* Tasks that are in the process of being submitted concurrently
2905	<	* during the course of this method may or may not be rejected.
2901	>	* Possibly initiates an orderly shutdown in which previously
2902	>	* submitted tasks are executed, but no new tasks will be
2903	>	* accepted. Invocation has no effect on execution state if this
2904	>	* is the {@link #commonPool}, and no additional effect if
2905	>	* already shut down.  Tasks that are in the process of being
2906	>	* submitted concurrently during the course of this method may or
2907	>	* may not be rejected.
2908		*
2909		* @throws SecurityException if a security manager exists and
2910		*         the caller is not permitted to modify threads
#	Line 2605 | Line 2913 | public class ForkJoinPool extends Abstra
2913		*/
2914		public void shutdown() {
2915		checkPermission();
2916	<	tryTerminate(false, true);
2916	>	if (this != commonPool)
2917	>	tryTerminate(false, true);
2918		}
2919
2920		/**
2921	<	* Attempts to cancel and/or stop all tasks, and reject all
2922	<	* subsequently submitted tasks.  Tasks that are in the process of
2923	<	* being submitted or executed concurrently during the course of
2924	<	* this method may or may not be rejected. This method cancels
2925	<	* both existing and unexecuted tasks, in order to permit
2926	<	* termination in the presence of task dependencies. So the method
2927	<	* always returns an empty list (unlike the case for some other
2928	<	* Executors).
2921	>	* Possibly attempts to cancel and/or stop all tasks, and reject
2922	>	* all subsequently submitted tasks.  Invocation has no effect on
2923	>	* execution state if this is the {@link #commonPool}, and no
2924	>	* additional effect if already shut down. Otherwise, tasks that
2925	>	* are in the process of being submitted or executed concurrently
2926	>	* during the course of this method may or may not be
2927	>	* rejected. This method cancels both existing and unexecuted
2928	>	* tasks, in order to permit termination in the presence of task
2929	>	* dependencies. So the method always returns an empty list
2930	>	* (unlike the case for some other Executors).
2931		*
2932		* @return an empty list
2933		* @throws SecurityException if a security manager exists and
#	Line 2626 | Line 2937 | public class ForkJoinPool extends Abstra
2937		*/
2938		public List<Runnable> shutdownNow() {
2939		checkPermission();
2940	<	tryTerminate(true, true);
2940	>	if (this != commonPool)
2941	>	tryTerminate(true, true);
2942		return Collections.emptyList();
2943		}
2944
#	Line 2683 | Line 2995 | public class ForkJoinPool extends Abstra
2995		public boolean awaitTermination(long timeout, TimeUnit unit)
2996		throws InterruptedException {
2997		long nanos = unit.toNanos(timeout);
2998	<	final Mutex lock = this.lock;
2999	<	lock.lock();
3000	<	try {
3001	<	for (;;) {
3002	<	if (isTerminated())
3003	<	return true;
3004	<	if (nanos <= 0)
3005	<	return false;
3006	<	nanos = termination.awaitNanos(nanos);
2998	>	if (isTerminated())
2999	>	return true;
3000	>	long startTime = System.nanoTime();
3001	>	boolean terminated = false;
3002	>	synchronized(this) {
3003	>	for (long waitTime = nanos, millis = 0L;;) {
3004	>	if (terminated = isTerminated() ||
3005	>	waitTime <= 0L ||
3006	>	(millis = unit.toMillis(waitTime)) <= 0L)
3007	>	break;
3008	>	wait(millis);
3009	>	waitTime = nanos - (System.nanoTime() - startTime);
3010		}
2696	–	} finally {
2697	–	lock.unlock();
3011		}
3012	+	return terminated;
3013		}
3014
3015		/**
#	Line 2827 | Line 3141 | public class ForkJoinPool extends Abstra
3141		private static final long PARKBLOCKER;
3142		private static final int ABASE;
3143		private static final int ASHIFT;
3144	+	private static final long NEXTWORKERNUMBER;
3145	+	private static final long STEALCOUNT;
3146	+	private static final long MAINLOCK;
3147
3148		static {
3149		poolNumberGenerator = new AtomicInteger();
#	Line 2842 | Line 3159 | public class ForkJoinPool extends Abstra
3159		Class<?> ak = ForkJoinTask[].class;
3160		CTL = U.objectFieldOffset
3161		(k.getDeclaredField("ctl"));
3162	+	NEXTWORKERNUMBER = U.objectFieldOffset
3163	+	(k.getDeclaredField("nextWorkerNumber"));
3164	+	STEALCOUNT = U.objectFieldOffset
3165	+	(k.getDeclaredField("stealCount"));
3166	+	MAINLOCK = U.objectFieldOffset
3167	+	(k.getDeclaredField("mainLock"));
3168		Class<?> tk = Thread.class;
3169		PARKBLOCKER = U.objectFieldOffset
3170		(tk.getDeclaredField("parkBlocker"));
3171		ABASE = U.arrayBaseOffset(ak);
3172		s = U.arrayIndexScale(ak);
3173	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
3174		} catch (Exception e) {
3175		throw new Error(e);
3176		}
3177		if ((s & (s-1)) != 0)
3178		throw new Error("data type scale not a power of two");
3179	<	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
3179	>	try { // Establish common pool
3180	>	String pp = System.getProperty(propPrefix + "parallelism");
3181	>	String fp = System.getProperty(propPrefix + "threadFactory");
3182	>	String up = System.getProperty(propPrefix + "exceptionHandler");
3183	>	ForkJoinWorkerThreadFactory fac = (fp == null) ?
3184	>	defaultForkJoinWorkerThreadFactory :
3185	>	((ForkJoinWorkerThreadFactory)ClassLoader.
3186	>	getSystemClassLoader().loadClass(fp).newInstance());
3187	>	Thread.UncaughtExceptionHandler ueh = (up == null)? null :
3188	>	((Thread.UncaughtExceptionHandler)ClassLoader.
3189	>	getSystemClassLoader().loadClass(up).newInstance());
3190	>	int par;
3191	>	if ((pp == null || (par = Integer.parseInt(pp)) <= 0))
3192	>	par = Runtime.getRuntime().availableProcessors();
3193	>	if (par > MAX_CAP)
3194	>	par = MAX_CAP;
3195	>	commonPoolParallelism = par;
3196	>	int n = par - 1; // precompute submit mask
3197	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4;
3198	>	n |= n >>> 8; n |= n >>> 16;
3199	>	int mask = ((n + 1) << 1) - 1;
3200	>	commonPool = new ForkJoinPool(par, mask, fac, ueh);
3201	>	} catch (Exception e) {
3202	>	throw new Error(e);
3203	>	}
3204		}
3205
3206		/**

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