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

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.122 by jsr166, Tue Jan 31 01:51:13 2012 UTC vs.
Revision 1.123 by dl, Mon Feb 20 18:20:06 2012 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	–
8		import java.util.ArrayList;
9		import java.util.Arrays;
10		import java.util.Collection;
#	Line 177 | Line 176 | public class ForkJoinPool extends Abstra
176		* If an attempted steal fails, a thief always chooses a different
177		* random victim target to try next. So, in order for one thief to
178		* progress, it suffices for any in-progress poll or new push on
179	<	* any empty queue to complete.
179	>	* any empty queue to complete. (This is why we normally use
180	>	* method pollAt and its variants that try once at the apparent
181	>	* base index, else consider alternative actions, rather than
182	>	* method poll.)
183		*
184		* This approach also enables support of a user mode in which local
185		* task processing is in FIFO, not LIFO order, simply by using
#	Line 207 | Line 209 | public class ForkJoinPool extends Abstra
209		* lock (mainly to protect in the case of resizing) but we use
210		* only a simple spinlock (using bits in field runState), because
211		* submitters encountering a busy queue move on to try or create
212	<	* other queues, so never block.
212	>	* other queues -- they block only when creating and registering
213	>	* new queues.
214		*
215		* Management
216		* ==========
#	Line 233 | Line 236 | public class ForkJoinPool extends Abstra
236		* deregister WorkQueues, as well as to enable shutdown. It is
237		* only modified under a lock (normally briefly held, but
238		* occasionally protecting allocations and resizings) but even
239	<	* 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.
239	>	* when locked remains available to check consistency.
240		*
241		* Recording WorkQueues.  WorkQueues are recorded in the
242		* "workQueues" array that is created upon pool construction and
#	Line 248 | Line 248 | public class ForkJoinPool extends Abstra
248		* readers must tolerate null slots. Shared (submission) queues
249		* are at even indices, worker queues at odd indices. Grouping
250		* them together in this way simplifies and speeds up task
251	<	* 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.
251	>	* scanning.
252		*
253		* All worker thread creation is on-demand, triggered by task
254		* submissions, replacement of terminated workers, and/or
#	Line 385 | Line 380 | public class ForkJoinPool extends Abstra
380		* (http://portal.acm.org/citation.cfm?id=155354). It differs in
381		* that: (1) We only maintain dependency links across workers upon
382		* steals, rather than use per-task bookkeeping.  This sometimes
383	<	* requires a linear scan of workQueues array to locate stealers, but
384	<	* often doesn't because stealers leave hints (that may become
383	>	* requires a linear scan of workQueues array to locate stealers,
384	>	* but often doesn't because stealers leave hints (that may become
385		* stale/wrong) of where to locate them.  A stealHint is only a
386		* hint because a worker might have had multiple steals and the
387		* hint records only one of them (usually the most current).
#	Line 397 | Line 392 | public class ForkJoinPool extends Abstra
392		* which means that we miss links in the chain during long-lived
393		* tasks, GC stalls etc (which is OK since blocking in such cases
394		* is usually a good idea).  (4) We bound the number of attempts
395	<	* to find work (see MAX_HELP_DEPTH) and fall back to suspending
396	<	* the worker and if necessary replacing it with another.
395	>	* to find work (see MAX_HELP) and fall back to suspending the
396	>	* worker and if necessary replacing it with another.
397		*
398		* It is impossible to keep exactly the target parallelism number
399		* of threads running at any given time.  Determining the
400		* existence of conservatively safe helping targets, the
401		* availability of already-created spares, and the apparent need
402		* to create new spares are all racy, so we rely on multiple
403	<	* retries of each.  Currently, in keeping with on-demand
404	<	* signalling policy, we compensate only if blocking would leave
405	<	* less than one active (non-waiting, non-blocked) worker.
406	<	* Additionally, to avoid some false alarms due to GC, lagging
407	<	* counters, system activity, etc, compensated blocking for joins
408	<	* is only attempted after rechecks stabilize in
409	<	* ForkJoinTask.awaitJoin. (Retries are interspersed with
410	<	* Thread.yield, for good citizenship.)
403	>	* retries of each.  Compensation in the apparent absence of
404	>	* helping opportunities is challenging to control on JVMs, where
405	>	* GC and other activities can stall progress of tasks that in
406	>	* turn stall out many other dependent tasks, without us being
407	>	* able to determine whether they will ever require compensation.
408	>	* Even though work-stealing otherwise encounters little
409	>	* degradation in the presence of more threads than cores,
410	>	* aggressively adding new threads in such cases entails risk of
411	>	* unwanted positive feedback control loops in which more threads
412	>	* cause more dependent stalls (as well as delayed progress of
413	>	* unblocked threads to the point that we know they are available)
414	>	* leading to more situations requiring more threads, and so
415	>	* on. This aspect of control can be seen as an (analytically
416	>	* intractible) game with an opponent that may choose the worst
417	>	* (for us) active thread to stall at any time.  We take several
418	>	* precautions to bound losses (and thus bound gains), mainly in
419	>	* methods tryCompensate and awaitJoin: (1) We only try
420	>	* compensation after attempting enough helping steps (measured
421	>	* via counting and timing) that we have already consumed the
422	>	* estimated cost of creating and activating a new thread.  (2) We
423	>	* allow up to 50% of threads to be blocked before initially
424	>	* adding any others, and unless completely saturated, check that
425	>	* some work is available for a new worker before adding. Also, we
426	>	* create up to only 50% more threads until entering a mode that
427	>	* only adds a thread if all others are possibly blocked.  All
428	>	* together, this means that we might be half as fast to react,
429	>	* and create half as many threads as possible in the ideal case,
430	>	* but present vastly fewer anomalies in all other cases compared
431	>	* to both more aggressive and more conservative alternatives.
432		*
433		* Style notes: There is a lot of representation-level coupling
434		* among classes ForkJoinPool, ForkJoinWorkerThread, and
#	Line 449 | Line 465 | public class ForkJoinPool extends Abstra
465		// Static utilities
466
467		/**
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	–	/**
468		* If there is a security manager, makes sure caller has
469		* permission to modify threads.
470		*/
#	Line 592 | Line 595 | public class ForkJoinPool extends Abstra
595		static final class WorkQueue {
596		/**
597		* Capacity of work-stealing queue array upon initialization.
598	<	* Must be a power of two; at least 4, but set larger to
599	<	* reduce cacheline sharing among queues.
598	>	* Must be a power of two; at least 4, but should be larger to
599	>	* reduce or eliminate cacheline sharing among queues.
600	>	* Currently, it is much larger, as a partial workaround for
601	>	* the fact that JVMs often place arrays in locations that
602	>	* share GC bookkeeping (especially cardmarks) such that
603	>	* per-write accesses encounter serious memory contention.
604		*/
605	<	static final int INITIAL_QUEUE_CAPACITY = 1 << 8;
605	>	static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
606
607		/**
608		* Maximum size for queue arrays. Must be a power of two less
#	Line 619 | Line 626 | public class ForkJoinPool extends Abstra
626		volatile int base;         // index of next slot for poll
627		int top;                   // index of next slot for push
628		ForkJoinTask<?>[] array;   // the elements (initially unallocated)
629	+	final ForkJoinPool pool;   // the containing pool (may be null)
630		final ForkJoinWorkerThread owner; // owning thread or null if shared
631		volatile Thread parker;    // == owner during call to park; else null
632		ForkJoinTask<?> currentJoin;  // task being joined in awaitJoin
633		ForkJoinTask<?> currentSteal; // current non-local task being executed
634		// Heuristic padding to ameliorate unfortunate memory placements
635	<	Object p00, p01, p02, p03, p04, p05, p06, p07, p08, p09, p0a;
635	>	Object p00, p01, p02, p03, p04, p05, p06, p07;
636	>	Object p08, p09, p0a, p0b, p0c, p0d, p0e;
637
638	<	WorkQueue(ForkJoinWorkerThread owner, int mode) {
630	<	this.owner = owner;
638	>	WorkQueue(ForkJoinPool pool, ForkJoinWorkerThread owner, int mode) {
639		this.mode = mode;
640	+	this.pool = pool;
641	+	this.owner = owner;
642		// Place indices in the center of array (that is not yet allocated)
643		base = top = INITIAL_QUEUE_CAPACITY >>> 1;
644		}
645
646		/**
647	<	* Returns number of tasks in the queue.
647	>	* Returns the approximate number of tasks in the queue.
648		*/
649		final int queueSize() {
650	<	int n = base - top; // non-owner callers must read base first
651	<	return (n >= 0) ? 0 : -n;
650	>	int n = base - top;       // non-owner callers must read base first
651	>	return (n >= 0) ? 0 : -n; // ignore transient negative
652	>	}
653	>
654	>	/**
655	>	* Provides a more accurate estimate of whether this queue has
656	>	* any tasks than does queueSize, by checking whether a
657	>	* near-empty queue has at least one unclaimed task.
658	>	*/
659	>	final boolean isEmpty() {
660	>	ForkJoinTask<?>[] a; int m, s;
661	>	int n = base - (s = top);
662	>	return (n >= 0 ||
663	>	(n == -1 &&
664	>	((a = array) == null ||
665	>	(m = a.length - 1) < 0 ||
666	>	U.getObjectVolatile
667	>	(a, ((m & (s - 1)) << ASHIFT) + ABASE) == null)));
668		}
669
670		/**
671		* Pushes a task. Call only by owner in unshared queues.
672		*
673		* @param task the task. Caller must ensure non-null.
648	–	* @param p if non-null, pool to signal if necessary
674		* @throw RejectedExecutionException if array cannot be resized
675		*/
676	<	final void push(ForkJoinTask<?> task, ForkJoinPool p) {
677	<	ForkJoinTask<?>[] a;
676	>	final void push(ForkJoinTask<?> task) {
677	>	ForkJoinTask<?>[] a; ForkJoinPool p;
678		int s = top, m, n;
679		if ((a = array) != null) {    // ignore if queue removed
680		U.putOrderedObject
681		(a, (((m = a.length - 1) & s) << ASHIFT) + ABASE, task);
682		if ((n = (top = s + 1) - base) <= 2) {
683	<	if (p != null)
683	>	if ((p = pool) != null)
684		p.signalWork();
685		}
686		else if (n >= m)
#	Line 691 | Line 716 | public class ForkJoinPool extends Abstra
716		}
717
718		/**
694	–	* Takes next task, if one exists, in FIFO order.
695	–	*/
696	–	final ForkJoinTask<?> poll() {
697	–	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
698	–	while ((b = base) - top < 0 && (a = array) != null) {
699	–	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
700	–	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
701	–	base == b &&
702	–	U.compareAndSwapObject(a, j, t, null)) {
703	–	base = b + 1;
704	–	return t;
705	–	}
706	–	}
707	–	return null;
708	–	}
709	–
710	–	/**
719		* Takes next task, if one exists, in LIFO order.  Call only
720		* by owner in unshared queues. (We do not have a shared
721		* version of this method because it is never needed.)
#	Line 730 | Line 738 | public class ForkJoinPool extends Abstra
738		}
739
740		/**
741	+	* Takes a task in FIFO order if b is base of queue and a task
742	+	* can be claimed without contention. Specialized versions
743	+	* appear in ForkJoinPool methods scan and tryHelpStealer.
744	+	*/
745	+	final ForkJoinTask<?> pollAt(int b) {
746	+	ForkJoinTask<?> t; ForkJoinTask<?>[] a;
747	+	if ((a = array) != null) {
748	+	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
749	+	if ((t = (ForkJoinTask<?>)U.getObjectVolatile(a, j)) != null &&
750	+	base == b &&
751	+	U.compareAndSwapObject(a, j, t, null)) {
752	+	base = b + 1;
753	+	return t;
754	+	}
755	+	}
756	+	return null;
757	+	}
758	+
759	+	/**
760	+	* Takes next task, if one exists, in FIFO order.
761	+	*/
762	+	final ForkJoinTask<?> poll() {
763	+	ForkJoinTask<?>[] a; int b; ForkJoinTask<?> t;
764	+	while ((b = base) - top < 0 && (a = array) != null) {
765	+	int j = (((a.length - 1) & b) << ASHIFT) + ABASE;
766	+	t = (ForkJoinTask<?>)U.getObjectVolatile(a, j);
767	+	if (t != null) {
768	+	if (base == b &&
769	+	U.compareAndSwapObject(a, j, t, null)) {
770	+	base = b + 1;
771	+	return t;
772	+	}
773	+	}
774	+	else if (base == b) {
775	+	if (b + 1 == top)
776	+	break;
777	+	Thread.yield(); // wait for lagging update
778	+	}
779	+	}
780	+	return null;
781	+	}
782	+
783	+	/**
784		* Takes next task, if one exists, in order specified by mode.
785		*/
786		final ForkJoinTask<?> nextLocalTask() {
#	Line 749 | Line 800 | public class ForkJoinPool extends Abstra
800		}
801
802		/**
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	–	/**
803		* Pops the given task only if it is at the current top.
804		*/
805		final boolean tryUnpush(ForkJoinTask<?> t) {
#	Line 892 | Line 926 | public class ForkJoinPool extends Abstra
926		* Computes next value for random probes.  Scans don't require
927		* a very high quality generator, but also not a crummy one.
928		* Marsaglia xor-shift is cheap and works well enough.  Note:
929	<	* This is manually inlined in several usages in ForkJoinPool
930	<	* to avoid writes inside busy scan loops.
929	>	* This is manually inlined in its usages in ForkJoinPool to
930	>	* avoid writes inside busy scan loops.
931		*/
932		final int nextSeed() {
933		int r = seed;
#	Line 906 | Line 940 | public class ForkJoinPool extends Abstra
940
941		/**
942		* Removes and runs tasks until empty, using local mode
943	<	* ordering.
943	>	* ordering. Normally called only after checking for apparent
944	>	* non-emptiness.
945		*/
946		final void runLocalTasks() {
947	<	if (base - top < 0) {
948	<	for (ForkJoinTask<?> t; (t = nextLocalTask()) != null; )
949	<	t.doExec();
947	>	// hoist checks from repeated pop/poll
948	>	ForkJoinTask<?>[] a; int m;
949	>	if ((a = array) != null && (m = a.length - 1) >= 0) {
950	>	if (mode == 0) {
951	>	for (int s; (s = top - 1) - base >= 0;) {
952	>	int j = ((m & s) << ASHIFT) + ABASE;
953	>	ForkJoinTask<?> t =
954	>	(ForkJoinTask<?>)U.getObjectVolatile(a, j);
955	>	if (t != null) {
956	>	if (U.compareAndSwapObject(a, j, t, null)) {
957	>	top = s;
958	>	t.doExec();
959	>	}
960	>	}
961	>	else
962	>	break;
963	>	}
964	>	}
965	>	else {
966	>	for (int b; (b = base) - top < 0;) {
967	>	int j = ((m & b) << ASHIFT) + ABASE;
968	>	ForkJoinTask<?> t =
969	>	(ForkJoinTask<?>)U.getObjectVolatile(a, j);
970	>	if (t != null) {
971	>	if (base == b &&
972	>	U.compareAndSwapObject(a, j, t, null)) {
973	>	base = b + 1;
974	>	t.doExec();
975	>	}
976	>	} else if (base == b) {
977	>	if (b + 1 == top)
978	>	break;
979	>	Thread.yield(); // wait for lagging update
980	>	}
981	>	}
982	>	}
983		}
984		}
985
#	Line 926 | Line 994 | public class ForkJoinPool extends Abstra
994		if (t != null) {
995		currentSteal = t;
996		t.doExec();
997	<	runLocalTasks();
997	>	if (top != base)        // conservative guard
998	>	runLocalTasks();
999		++nsteals;
1000		currentSteal = null;
1001		}
1002	<	else if (runState < 0)            // terminating
1002	>	else if (runState < 0)      // terminating
1003		alive = false;
1004		return alive;
1005		}
#	Line 1005 | Line 1074 | public class ForkJoinPool extends Abstra
1074		* submission queues in method doSubmit. In the future, this may
1075		* also incorporate a means to implement different task rejection
1076		* and resubmission policies.
1077	+	*
1078	+	* Seeds for submitters and workers/workQueues work in basically
1079	+	* the same way but are initialized and updated using slightly
1080	+	* different mechanics. Both are initialized using the same
1081	+	* approach as in class ThreadLocal, where successive values are
1082	+	* unlikely to collide with previous values. This is done during
1083	+	* registration for workers, but requires a separate AtomicInteger
1084	+	* for submitters. Seeds are then randomly modified upon
1085	+	* collisions using xorshifts, which requires a non-zero seed.
1086		*/
1087		static final class Submitter {
1088		int seed;
1089	<	Submitter() { seed = hashId(Thread.currentThread().getId()); }
1089	>	Submitter() {
1090	>	int s = nextSubmitterSeed.getAndAdd(SEED_INCREMENT);
1091	>	seed = (s == 0) ? 1 : s; // ensure non-zero
1092	>	}
1093		}
1094
1095		/** ThreadLocal class for Submitters */
#	Line 1031 | Line 1112 | public class ForkJoinPool extends Abstra
1112		private static final AtomicInteger poolNumberGenerator;
1113
1114		/**
1115	+	* Generator for initial hashes/seeds for submitters. Accessed by
1116	+	* Submitter class constructor.
1117	+	*/
1118	+	static final AtomicInteger nextSubmitterSeed;
1119	+
1120	+	/**
1121		* Permission required for callers of methods that may start or
1122		* kill threads.
1123		*/
#	Line 1063 | Line 1150 | public class ForkJoinPool extends Abstra
1150		private static final long SHRINK_TIMEOUT = SHRINK_RATE - (SHRINK_RATE / 10);
1151
1152		/**
1153	<	* The maximum stolen->joining link depth allowed in tryHelpStealer.
1154	<	* Depths for legitimate chains are unbounded, but we use a fixed
1155	<	* constant to avoid (otherwise unchecked) cycles and to bound
1156	<	* staleness of traversal parameters at the expense of sometimes
1157	<	* blocking when we could be helping.
1153	>	* The maximum stolen->joining link depth allowed in method
1154	>	* tryHelpStealer.  Must be a power of two. This value also
1155	>	* controls the maximum number of times to try to help join a task
1156	>	* without any apparent progress or change in pool state before
1157	>	* giving up and blocking (see awaitJoin).  Depths for legitimate
1158	>	* chains are unbounded, but we use a fixed constant to avoid
1159	>	* (otherwise unchecked) cycles and to bound staleness of
1160	>	* traversal parameters at the expense of sometimes blocking when
1161	>	* we could be helping.
1162	>	*/
1163	>	private static final int MAX_HELP = 32;
1164	>
1165	>	/**
1166	>	* Secondary time-based bound (in nanosecs) for helping attempts
1167	>	* before trying compensated blocking in awaitJoin. Used in
1168	>	* conjunction with MAX_HELP to reduce variance due to different
1169	>	* polling rates associated with different helping options. The
1170	>	* value should roughly approximate the time required to create
1171	>	* and/or activate a worker thread.
1172	>	*/
1173	>	private static final long COMPENSATION_DELAY = 100L * 1000L; // 0.1 millisec
1174	>
1175	>	/**
1176	>	* Increment for seed generators. See class ThreadLocal for
1177	>	* explanation.
1178		*/
1179	<	private static final int MAX_HELP_DEPTH = 16;
1179	>	private static final int SEED_INCREMENT = 0x61c88647;
1180
1181		/**
1182		* Bits and masks for control variables
#	Line 1101 | Line 1208 | public class ForkJoinPool extends Abstra
1208		*
1209		* Field runState is an int packed with:
1210		* SHUTDOWN: true if shutdown is enabled (1 bit)
1211	<	* SEQ:  a sequence number updated upon (de)registering workers (15 bits)
1212	<	* MASK: mask (power of 2 - 1) covering all registered poolIndexes (16 bits)
1211	>	* SEQ:  a sequence number updated upon (de)registering workers (30 bits)
1212	>	* INIT: set true after workQueues array construction (1 bit)
1213		*
1214	<	* The combination of mask and sequence number enables simple
1215	<	* consistency checks: Staleness of read-only operations on the
1216	<	* 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.
1214	>	* The sequence number enables simple consistency checks:
1215	>	* Staleness of read-only operations on the workQueues array can
1216	>	* be checked by comparing runState before vs after the reads.
1217		*/
1218
1219		// bit positions/shifts for fields
#	Line 1119 | Line 1223 | public class ForkJoinPool extends Abstra
1223		private static final int  EC_SHIFT   = 16;
1224
1225		// bounds
1122	–	private static final int  POOL_MAX   = 0x7fff;  // max #workers - 1
1226		private static final int  SMASK      = 0xffff;  // short bits
1227	+	private static final int  MAX_CAP    = 0x7fff;  // max #workers - 1
1228		private static final int  SQMASK     = 0xfffe;  // even short bits
1229		private static final int  SHORT_SIGN = 1 << 15;
1230		private static final int  INT_SIGN   = 1 << 31;
#	Line 1148 | Line 1252 | public class ForkJoinPool extends Abstra
1252
1253		// runState bits
1254		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;
1255
1256		// access mode for WorkQueue
1257		static final int LIFO_QUEUE          =  0;
#	Line 1168 | Line 1270 | public class ForkJoinPool extends Abstra
1270		volatile long ctl;                         // main pool control
1271		final int parallelism;                     // parallelism level
1272		final int localMode;                       // per-worker scheduling mode
1273	<	int growHints;                             // for expanding indices/ranges
1274	<	volatile int runState;                     // shutdown status, seq, and mask
1273	>	final int submitMask;                      // submit queue index bound
1274	>	int nextSeed;                              // for initializing worker seeds
1275	>	volatile int runState;                     // shutdown status and seq
1276		WorkQueue[] workQueues;                    // main registry
1277		final Mutex lock;                          // for registration
1278		final Condition termination;               // for awaitTermination
#	Line 1179 | Line 1282 | public class ForkJoinPool extends Abstra
1282		final AtomicInteger nextWorkerNumber;      // to create worker name string
1283		final String workerNamePrefix;             // to create worker name string
1284
1285	<	//  Creating, registering, deregistering and running workers
1285	>	//  Creating, registering, and deregistering workers
1286
1287		/**
1288		* Tries to create and start a worker
#	Line 1210 | Line 1313 | public class ForkJoinPool extends Abstra
1313		}
1314
1315		/**
1316	<	* Callback from ForkJoinWorkerThread constructor to establish and
1317	<	* record its WorkQueue.
1316	>	* Callback from ForkJoinWorkerThread constructor to establish its
1317	>	* poolIndex and record its WorkQueue. To avoid scanning bias due
1318	>	* to packing entries in front of the workQueues array, we treat
1319	>	* the array as a simple power-of-two hash table using per-thread
1320	>	* seed as hash, expanding as needed.
1321		*
1322	<	* @param wt the worker thread
1322	>	* @param w the worker's queue
1323		*/
1324	<	final void registerWorker(ForkJoinWorkerThread wt) {
1219	<	WorkQueue w = wt.workQueue;
1324	>	final void registerWorker(WorkQueue w) {
1325		Mutex lock = this.lock;
1326		lock.lock();
1327		try {
1223	–	int g = growHints, k = g & SMASK;
1328		WorkQueue[] ws = workQueues;
1329	<	if (ws != null) {                       // ignore on shutdown
1330	<	int n = ws.length;
1331	<	if ((k & 1) == 0 || k >= n || ws[k] != null) {
1332	<	for (k = 1; k < n && ws[k] != null; k += 2)
1333	<	;                           // workers are at odd indices
1334	<	if (k >= n)                     // resize
1335	<	workQueues = ws = Arrays.copyOf(ws, n << 1);
1336	<	}
1337	<	w.eventCount = w.poolIndex = k;     // establish before recording
1338	<	ws[k] = w;
1339	<	growHints = (g & ~SMASK) | ((k + 2) & SMASK);
1340	<	int rs = runState;
1341	<	int m = rs & SMASK;                 // recalculate runState mask
1342	<	if (k > m)
1239	<	m = (m << 1) + 1;
1240	<	runState = (rs & SHUTDOWN) | ((rs + RS_SEQ) & RS_SEQ_MASK) | m;
1329	>	if (w != null && ws != null) {          // skip on shutdown/failure
1330	>	int rs, n;
1331	>	while ((n = ws.length) <            // ensure can hold total
1332	>	(parallelism + (short)(ctl >>> TC_SHIFT) << 1))
1333	>	workQueues = ws = Arrays.copyOf(ws, n << 1);
1334	>	int m = n - 1;
1335	>	int s = nextSeed += SEED_INCREMENT; // rarely-colliding sequence
1336	>	w.seed = (s == 0) ? 1 : s;          // ensure non-zero seed
1337	>	int r = (s << 1) | 1;               // use odd-numbered indices
1338	>	while (ws[r &= m] != null)          // step by approx half size
1339	>	r += ((n >>> 1) & SQMASK) + 2;
1340	>	w.eventCount = w.poolIndex = r;     // establish before recording
1341	>	ws[r] = w;                          // also update seq
1342	>	runState = ((rs = runState) & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN);
1343		}
1344		} finally {
1345		lock.unlock();
#	Line 1254 | Line 1356 | public class ForkJoinPool extends Abstra
1356		* @param ex the exception causing failure, or null if none
1357		*/
1358		final void deregisterWorker(ForkJoinWorkerThread wt, Throwable ex) {
1359	+	Mutex lock = this.lock;
1360		WorkQueue w = null;
1361		if (wt != null && (w = wt.workQueue) != null) {
1362		w.runState = -1;                // ensure runState is set
1363		stealCount.getAndAdd(w.totalSteals + w.nsteals);
1364		int idx = w.poolIndex;
1262	–	Mutex lock = this.lock;
1365		lock.lock();
1366		try {                           // remove record from array
1367		WorkQueue[] ws = workQueues;
1368	<	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w) {
1368	>	if (ws != null && idx >= 0 && idx < ws.length && ws[idx] == w)
1369		ws[idx] = null;
1268	–	growHints = (growHints & ~SMASK) | idx;
1269	–	}
1370		} finally {
1371		lock.unlock();
1372		}
#	Line 1290 | Line 1390 | public class ForkJoinPool extends Abstra
1390		U.throwException(ex);
1391		}
1392
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	–	}
1393
1394		// Submissions
1395
1396		/**
1397		* Unless shutting down, adds the given task to a submission queue
1398		* at submitter's current queue index (modulo submission
1399	<	* range). If no queue exists at the index, one is created unless
1400	<	* pool lock is busy.  If the queue and/or lock are busy, another
1401	<	* index is randomly chosen. The mask in growHints controls the
1402	<	* effective index range of queues considered. The mask is
1403	<	* expanded, up to the current workerQueue mask, upon any detected
1404	<	* contention but otherwise remains small to avoid needlessly
1316	<	* creating queues when there is no contention.
1399	>	* range). If no queue exists at the index, one is created.  If
1400	>	* the queue is busy, another index is randomly chosen. The
1401	>	* submitMask bounds the effective number of queues to the
1402	>	* (nearest poswer of two for) parallelism level.
1403	>	*
1404	>	* @param task the task. Caller must ensure non-null.
1405		*/
1406		private void doSubmit(ForkJoinTask<?> task) {
1319	–	if (task == null)
1320	–	throw new NullPointerException();
1407		Submitter s = submitters.get();
1408	<	for (int r = s.seed, m = growHints >>> 16;;) {
1409	<	WorkQueue[] ws; WorkQueue q; Mutex lk;
1408	>	for (int r = s.seed, m = submitMask;;) {
1409	>	WorkQueue[] ws; WorkQueue q;
1410		int k = r & m & SQMASK;          // use only even indices
1411		if (runState < 0 || (ws = workQueues) == null || ws.length <= k)
1412		throw new RejectedExecutionException(); // shutting down
1413	<	if ((q = ws[k]) == null && (lk = lock).tryAcquire(0)) {
1414	<	try {                        // try to create new queue
1415	<	if (ws == workQueues && (q = ws[k]) == null) {
1416	<	int rs;              // update runState seq
1417	<	ws[k] = q = new WorkQueue(null, SHARED_QUEUE);
1418	<	runState = (((rs = runState) & SHUTDOWN) |
1419	<	((rs + RS_SEQ) & ~SHUTDOWN));
1413	>	else if ((q = ws[k]) == null) {  // create new queue
1414	>	WorkQueue nq = new WorkQueue(this, null, SHARED_QUEUE);
1415	>	Mutex lock = this.lock;      // construct outside lock
1416	>	lock.lock();
1417	>	try {                        // recheck under lock
1418	>	int rs = runState;       // to update seq
1419	>	if (ws == workQueues && ws[k] == null) {
1420	>	ws[k] = nq;
1421	>	runState = ((rs & SHUTDOWN) | ((rs + 2) & ~SHUTDOWN));
1422		}
1423		} finally {
1424	<	lk.unlock();
1424	>	lock.unlock();
1425		}
1426		}
1427	<	if (q != null) {
1428	<	if (q.trySharedPush(task)) {
1429	<	signalWork();
1430	<	return;
1431	<	}
1432	<	else if (m < parallelism - 1 && m < (runState & SMASK)) {
1433	<	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
1427	>	else if (q.trySharedPush(task)) {
1428	>	signalWork();
1429	>	return;
1430	>	}
1431	>	else if (m > 1) {                // move to a different index
1432	>	r ^= r << 13;                // same xorshift as WorkQueues
1433	>	r ^= r >>> 17;
1434		s.seed = r ^= r << 5;
1435		}
1436	+	else
1437	+	Thread.yield();              // yield if no alternatives
1438		}
1439		}
1440
#	Line 1405 | Line 1483 | public class ForkJoinPool extends Abstra
1483		}
1484		}
1485
1486	+
1487	+	// Scanning for tasks
1488	+
1489		/**
1490	<	* 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
1490	>	* Top-level runloop for workers, called by ForkJoinWorkerThread.run.
1491		*/
1492	<	final boolean tryCompensate() {
1493	<	WorkQueue w; Thread p;
1494	<	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;
1492	>	final void runWorker(WorkQueue w) {
1493	>	w.growArray(false);         // initialize queue array in this thread
1494	>	do {} while (w.runTask(scan(w)));
1495		}
1496
1449	–	// Scanning for tasks
1450	–
1497		/**
1498		* Scans for and, if found, returns one task, else possibly
1499		* inactivates the worker. This method operates on single reads of
1500	<	* volatile state and is designed to be re-invoked continuously in
1501	<	* part because it returns upon detecting inconsistencies,
1500	>	* volatile state and is designed to be re-invoked continuously,
1501	>	* in part because it returns upon detecting inconsistencies,
1502		* contention, or state changes that indicate possible success on
1503		* re-invocation.
1504		*
1505	<	* The scan searches for tasks across queues, randomly selecting
1506	<	* the first #queues probes, favoring steals over submissions
1507	<	* (by exploiting even/odd indexing), and then performing a
1508	<	* circular sweep of all queues.  The scan terminates upon either
1509	<	* finding a non-empty queue, or completing a full sweep. If the
1510	<	* worker is not inactivated, it takes and returns a task from
1511	<	* this queue.  On failure to find a task, we take one of the
1512	<	* following actions, after which the caller will retry calling
1467	<	* this method unless terminated.
1505	>	* The scan searches for tasks across a random permutation of
1506	>	* queues (starting at a random index and stepping by a random
1507	>	* relative prime, checking each at least once).  The scan
1508	>	* terminates upon either finding a non-empty queue, or completing
1509	>	* the sweep. If the worker is not inactivated, it takes and
1510	>	* returns a task from this queue.  On failure to find a task, we
1511	>	* take one of the following actions, after which the caller will
1512	>	* retry calling this method unless terminated.
1513		*
1514		* * If pool is terminating, terminate the worker.
1515		*
#	Line 1475 | Line 1520 | public class ForkJoinPool extends Abstra
1520		* another worker, but with same net effect. Releasing in other
1521		* cases as well ensures that we have enough workers running.
1522		*
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	–	*
1523		* * If not already enqueued, try to inactivate and enqueue the
1524	<	* worker on wait queue.
1524	>	* worker on wait queue. Or, if inactivating has caused the pool
1525	>	* to be quiescent, relay to idleAwaitWork to check for
1526	>	* termination and possibly shrink pool.
1527	>	*
1528	>	* * If already inactive, and the caller has run a task since the
1529	>	* last empty scan, return (to allow rescan) unless others are
1530	>	* also inactivated.  Field WorkQueue.rescans counts down on each
1531	>	* scan to ensure eventual inactivation and blocking.
1532		*
1533	<	* * If already enqueued and none of the above apply, either park
1534	<	* 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.
1533	>	* * If already enqueued and none of the above apply, park
1534	>	* awaiting signal,
1535		*
1536		* @param w the worker (via its WorkQueue)
1537		* @return a task or null of none found
1538		*/
1539		private final ForkJoinTask<?> scan(WorkQueue w) {
1540	<	boolean swept = false;               // true after full empty scan
1541	<	WorkQueue[] ws;                      // volatile read order matters
1542	<	int r = w.seed, ec = w.eventCount;   // ec is negative if inactive
1543	<	int rs = runState, m = rs & SMASK;
1544	<	if ((ws = workQueues) != null && ws.length > m) { // consistency check
1545	<	for (int k = 0, j = -1 - m; ; ++j) {
1546	<	WorkQueue q; int b;
1547	<	if (j < 0) {                 // random probes while j negative
1548	<	r ^= r << 13; r ^= r >>> 17; k = (r ^= r << 5) | (j & 1);
1549	<	}                            // worker (not submit) for odd j
1550	<	else                         // cyclic scan when j >= 0
1551	<	k += 7;                  // step 7 reduces array packing bias
1552	<	if ((q = ws[k & m]) != null && (b = q.base) - q.top < 0) {
1553	<	ForkJoinTask<?> t = (ec >= 0) ? q.pollAt(b) : null;
1554	<	w.seed = r;              // save seed for next scan
1510	<	if (t != null)
1540	>	WorkQueue[] ws;                       // first update random seed
1541	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1542	>	int rs = runState, m;                 // volatile read order matters
1543	>	if ((ws = workQueues) != null && (m = ws.length - 1) > 0) {
1544	>	int ec = w.eventCount;            // ec is negative if inactive
1545	>	int step = (r >>> 16) | 1;        // relative prime
1546	>	for (int j = (m + 1) << 2; ; r += step) {
1547	>	WorkQueue q; ForkJoinTask<?> t; ForkJoinTask<?>[] a; int b;
1548	>	if ((q = ws[r & m]) != null && (b = q.base) - q.top < 0 &&
1549	>	(a = q.array) != null) {  // probably nonempty
1550	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1551	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1552	>	if (q.base == b && ec >= 0 && t != null &&
1553	>	U.compareAndSwapObject(a, i, t, null)) {
1554	>	q.base = b + 1;       // specialization of pollAt
1555		return t;
1556	<	break;
1556	>	}
1557	>	else if ((t != null || b + 1 != q.top) &&
1558	>	(ec < 0 || j <= m)) {
1559	>	rs = 0;               // mark scan as imcomplete
1560	>	break;                // caller can retry after release
1561	>	}
1562		}
1563	<	else if (j - m > m) {
1515	<	if (rs == runState)      // staleness check
1516	<	swept = true;
1563	>	if (--j < 0)
1564		break;
1518	–	}
1565		}
1520	–
1521	–	// Decode ctl on empty scan
1566		long c = ctl; int e = (int)c, a = (int)(c >> AC_SHIFT), nr, ns;
1567	<	if (e < 0)                       // pool is terminating
1568	<	w.runState = -1;
1569	<	else if (!swept) {               // try to release a waiter
1570	<	WorkQueue v; Thread p;
1571	<	if (e > 0 && a < 0 && (v = ws[e & m]) != null &&
1572	<	v.eventCount == (e | INT_SIGN)) {
1567	>	if (e < 0)                        // decode ctl on empty scan
1568	>	w.runState = -1;              // pool is terminating
1569	>	else if (rs == 0 || rs != runState) { // incomplete scan
1570	>	WorkQueue v; Thread p;        // try to release a waiter
1571	>	if (e > 0 && a < 0 && w.eventCount == ec &&
1572	>	(v = ws[e & m]) != null && v.eventCount == (e | INT_SIGN)) {
1573		long nc = ((long)(v.nextWait & E_MASK) |
1574		((c + AC_UNIT) & (AC_MASK|TC_MASK)));
1575	<	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1575	>	if (ctl == c && U.compareAndSwapLong(this, CTL, c, nc)) {
1576		v.eventCount = (e + E_SEQ) & E_MASK;
1577		if ((p = v.parker) != null)
1578		U.unpark(p);
1579		}
1580		}
1581		}
1582	<	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
1582	>	else if (ec >= 0) {               // try to enqueue/inactivate
1583		long nc = (long)ec | ((c - AC_UNIT) & (AC_MASK|TC_MASK));
1584		w.nextWait = e;
1585	<	w.eventCount = ec | INT_SIGN;// mark as inactive
1586	<	if (!U.compareAndSwapLong(this, CTL, c, nc))
1587	<	w.eventCount = ec;       // unmark on CAS failure
1588	<	else if ((ns = w.nsteals) != 0) {
1589	<	w.nsteals = 0;           // set rescans if ran task
1590	<	w.rescans = a + parallelism;
1591	<	w.totalSteals += ns;
1585	>	w.eventCount = ec | INT_SIGN; // mark as inactive
1586	>	if (ctl != c || !U.compareAndSwapLong(this, CTL, c, nc))
1587	>	w.eventCount = ec;        // unmark on CAS failure
1588	>	else {
1589	>	if ((ns = w.nsteals) != 0) {
1590	>	w.nsteals = 0;        // set rescans if ran task
1591	>	w.rescans = (a > 0)? 0 : a + parallelism;
1592	>	w.totalSteals += ns;
1593	>	}
1594	>	if (a == 1 - parallelism) // quiescent
1595	>	idleAwaitWork(w, nc, c);
1596		}
1597		}
1598	<	else {                           // already queued
1599	<	if (parallelism == -a)
1600	<	idleAwaitWork(w);        // quiescent
1601	<	if (w.eventCount == ec) {
1602	<	Thread.interrupted();    // clear status
1603	<	ForkJoinWorkerThread wt = w.owner;
1598	>	else if (w.eventCount < 0) {      // already queued
1599	>	if ((nr = w.rescans) > 0) {   // continue rescanning
1600	>	int ac = a + parallelism;
1601	>	if (((w.rescans = (ac < nr) ? ac : nr - 1) & 3) == 0)
1602	>	Thread.yield();       // yield before block
1603	>	}
1604	>	else {
1605	>	Thread.interrupted();     // clear status
1606	>	Thread wt = Thread.currentThread();
1607		U.putObject(wt, PARKBLOCKER, this);
1608	<	w.parker = wt;           // emulate LockSupport.park
1609	<	if (w.eventCount == ec)  // recheck
1610	<	U.park(false, 0L);   // block
1608	>	w.parker = wt;            // emulate LockSupport.park
1609	>	if (w.eventCount < 0)     // recheck
1610	>	U.park(false, 0L);
1611		w.parker = null;
1612		U.putObject(wt, PARKBLOCKER, null);
1613		}
#	Line 1572 | Line 1617 | public class ForkJoinPool extends Abstra
1617		}
1618
1619		/**
1620	<	* If inactivating worker w has caused pool to become quiescent,
1621	<	* checks for pool termination, and, so long as this is not the
1622	<	* only worker, waits for event for up to SHRINK_RATE nanosecs.
1623	<	* On timeout, if ctl has not changed, terminates the worker,
1624	<	* which will in turn wake up another worker to possibly repeat
1625	<	* this process.
1620	>	* If inactivating worker w has caused the pool to become
1621	>	* quiescent, checks for pool termination, and, so long as this is
1622	>	* not the only worker, waits for event for up to SHRINK_RATE
1623	>	* nanosecs.  On timeout, if ctl has not changed, terminates the
1624	>	* worker, which will in turn wake up another worker to possibly
1625	>	* repeat this process.
1626		*
1627		* @param w the calling worker
1628	+	* @param currentCtl the ctl value triggering possible quiescence
1629	+	* @param prevCtl the ctl value to restore if thread is terminated
1630		*/
1631	<	private void idleAwaitWork(WorkQueue w) {
1632	<	long c; int nw, ec;
1633	<	if (!tryTerminate(false, false) &&
1634	<	(int)((c = ctl) >> AC_SHIFT) + parallelism == 0 &&
1635	<	(ec = w.eventCount) == ((int)c | INT_SIGN) &&
1636	<	(nw = w.nextWait) != 0) {
1590	<	long nc = ((long)(nw & E_MASK) | // ctl to restore on timeout
1591	<	((c + AC_UNIT) & AC_MASK) | (c & TC_MASK));
1592	<	ForkJoinWorkerThread wt = w.owner;
1593	<	while (ctl == c) {
1631	>	private void idleAwaitWork(WorkQueue w, long currentCtl, long prevCtl) {
1632	>	if (w.eventCount < 0 && !tryTerminate(false, false) &&
1633	>	(int)prevCtl != 0 && ctl == currentCtl) {
1634	>	Thread wt = Thread.currentThread();
1635	>	Thread.yield();            // yield before block
1636	>	while (ctl == currentCtl) {
1637		long startTime = System.nanoTime();
1638		Thread.interrupted();  // timed variant of version in scan()
1639		U.putObject(wt, PARKBLOCKER, this);
1640		w.parker = wt;
1641	<	if (ctl == c)
1641	>	if (ctl == currentCtl)
1642		U.park(false, SHRINK_RATE);
1643		w.parker = null;
1644		U.putObject(wt, PARKBLOCKER, null);
1645	<	if (ctl != c)
1645	>	if (ctl != currentCtl)
1646		break;
1647		if (System.nanoTime() - startTime >= SHRINK_TIMEOUT &&
1648	<	U.compareAndSwapLong(this, CTL, c, nc)) {
1649	<	w.eventCount = (ec + E_SEQ) | E_MASK;
1650	<	w.runState = -1;          // shrink
1648	>	U.compareAndSwapLong(this, CTL, currentCtl, prevCtl)) {
1649	>	w.eventCount = (w.eventCount + E_SEQ) | E_MASK;
1650	>	w.runState = -1;   // shrink
1651		break;
1652		}
1653		}
#	Line 1622 | Line 1665 | public class ForkJoinPool extends Abstra
1665		* leaves hints in workers to speed up subsequent calls. The
1666		* implementation is very branchy to cope with potential
1667		* inconsistencies or loops encountering chains that are stale,
1668	<	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
1669	<	* of these cases are dealt with by just retrying by caller.
1668	>	* unknown, or so long that they are likely cyclic.  All of these
1669	>	* cases are dealt with by just retrying by caller.
1670		*
1671		* @param joiner the joining worker
1672		* @param task the task to join
1673		* @return true if found or ran a task (and so is immediately retryable)
1674		*/
1675	<	final boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1676	<	ForkJoinTask<?> subtask;    // current target
1675	>	private boolean tryHelpStealer(WorkQueue joiner, ForkJoinTask<?> task) {
1676	>	WorkQueue[] ws;
1677	>	int m, depth = MAX_HELP;                // remaining chain depth
1678		boolean progress = false;
1679	<	int depth = 0;              // current chain depth
1680	<	int m = runState & SMASK;
1681	<	WorkQueue[] ws = workQueues;
1682	<
1683	<	if (ws != null && ws.length > m && (subtask = task).status >= 0) {
1684	<	outer:for (WorkQueue j = joiner;;) {
1641	<	// Try to find the stealer of subtask, by first using hint
1642	<	WorkQueue stealer = null;
1643	<	WorkQueue v = ws[j.stealHint & m];
1679	>	if ((ws = workQueues) != null && (m = ws.length - 1) > 0 &&
1680	>	task.status >= 0) {
1681	>	ForkJoinTask<?> subtask = task;     // current target
1682	>	outer: for (WorkQueue j = joiner;;) {
1683	>	WorkQueue stealer = null;       // find stealer of subtask
1684	>	WorkQueue v = ws[j.stealHint & m]; // try hint
1685		if (v != null && v.currentSteal == subtask)
1686		stealer = v;
1687	<	else {
1687	>	else {                          // scan
1688		for (int i = 1; i <= m; i += 2) {
1689	<	if ((v = ws[i]) != null && v.currentSteal == subtask) {
1689	>	if ((v = ws[i]) != null && v.currentSteal == subtask &&
1690	>	v != joiner) {
1691		stealer = v;
1692	<	j.stealHint = i; // save hint
1692	>	j.stealHint = i;    // save hint
1693		break;
1694		}
1695		}
#	Line 1655 | Line 1697 | public class ForkJoinPool extends Abstra
1697		break;
1698		}
1699
1700	<	for (WorkQueue q = stealer;;) { // Try to help stealer
1701	<	ForkJoinTask<?> t; int b;
1700	>	for (WorkQueue q = stealer;;) { // try to help stealer
1701	>	ForkJoinTask[] a; ForkJoinTask<?> t; int b;
1702		if (task.status < 0)
1703		break outer;
1704	<	if ((b = q.base) - q.top < 0) {
1704	>	if ((b = q.base) - q.top < 0 && (a = q.array) != null) {
1705		progress = true;
1706	<	if (subtask.status < 0)
1707	<	break outer;               // stale
1708	<	if ((t = q.pollAt(b)) != null) {
1709	<	stealer.stealHint = joiner.poolIndex;
1706	>	int i = (((a.length - 1) & b) << ASHIFT) + ABASE;
1707	>	t = (ForkJoinTask<?>)U.getObjectVolatile(a, i);
1708	>	if (subtask.status < 0) // must recheck before taking
1709	>	break outer;
1710	>	if (t != null &&
1711	>	q.base == b &&
1712	>	U.compareAndSwapObject(a, i, t, null)) {
1713	>	q.base = b + 1;
1714		joiner.runSubtask(t);
1715		}
1716	+	else if (q.base == b)
1717	+	break outer;        // possibly stalled
1718		}
1719	<	else { // empty - try to descend to find stealer's stealer
1719	>	else {                      // descend
1720		ForkJoinTask<?> next = stealer.currentJoin;
1721	<	if (++depth == MAX_HELP_DEPTH || subtask.status < 0 ||
1721	>	if (--depth <= 0 || subtask.status < 0 ||
1722		next == null || next == subtask)
1723	<	break outer;  // max depth, stale, dead-end, cyclic
1723	>	break outer;        // stale, dead-end, or cyclic
1724		subtask = next;
1725		j = stealer;
1726		break;
#	Line 1689 | Line 1737 | public class ForkJoinPool extends Abstra
1737		* @param joiner the joining worker
1738		* @param task the task
1739		*/
1740	<	final void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1740	>	private void tryPollForAndExec(WorkQueue joiner, ForkJoinTask<?> task) {
1741		WorkQueue[] ws;
1742	<	int m = runState & SMASK;
1743	<	if ((ws = workQueues) != null && ws.length > m) {
1696	<	for (int j = 1; j <= m && task.status >= 0; j += 2) {
1742	>	if ((ws = workQueues) != null) {
1743	>	for (int j = 1; j < ws.length && task.status >= 0; j += 2) {
1744		WorkQueue q = ws[j];
1745		if (q != null && q.pollFor(task)) {
1746		joiner.runSubtask(task);
#	Line 1704 | Line 1751 | public class ForkJoinPool extends Abstra
1751		}
1752
1753		/**
1754	<	* Returns a non-empty steal queue, if one is found during a random,
1755	<	* then cyclic scan, else null.  This method must be retried by
1756	<	* caller if, by the time it tries to use the queue, it is empty.
1754	>	* Tries to decrement active count (sometimes implicitly) and
1755	>	* possibly release or create a compensating worker in preparation
1756	>	* for blocking. Fails on contention or termination. Otherwise,
1757	>	* adds a new thread if no idle workers are available and either
1758	>	* pool would become completely starved or: (at least half
1759	>	* starved, and fewer than 50% spares exist, and there is at least
1760	>	* one task apparently available). Even though the availablity
1761	>	* check requires a full scan, it is worthwhile in reducing false
1762	>	* alarms.
1763	>	*
1764	>	* @param task if nonnull, a task being waited for
1765	>	* @param blocker if nonnull, a blocker being waited for
1766	>	* @return true if the caller can block, else should recheck and retry
1767	>	*/
1768	>	final boolean tryCompensate(ForkJoinTask<?> task, ManagedBlocker blocker) {
1769	>	int pc = parallelism, e;
1770	>	long c = ctl;
1771	>	WorkQueue[] ws = workQueues;
1772	>	if ((e = (int)c) >= 0 && ws != null) {
1773	>	int u, a, ac, hc;
1774	>	int tc = (short)((u = (int)(c >>> 32)) >>> UTC_SHIFT) + pc;
1775	>	boolean replace = false;
1776	>	if ((a = u >> UAC_SHIFT) <= 0) {
1777	>	if ((ac = a + pc) <= 1)
1778	>	replace = true;
1779	>	else if ((e > 0 || (task != null &&
1780	>	ac <= (hc = pc >>> 1) && tc < pc + hc))) {
1781	>	WorkQueue w;
1782	>	for (int j = 0; j < ws.length; ++j) {
1783	>	if ((w = ws[j]) != null && !w.isEmpty()) {
1784	>	replace = true;
1785	>	break;   // in compensation range and tasks available
1786	>	}
1787	>	}
1788	>	}
1789	>	}
1790	>	if ((task == null || task.status >= 0) && // recheck need to block
1791	>	(blocker == null || !blocker.isReleasable()) && ctl == c) {
1792	>	if (!replace) {          // no compensation
1793	>	long nc = ((c - AC_UNIT) & AC_MASK) | (c & ~AC_MASK);
1794	>	if (U.compareAndSwapLong(this, CTL, c, nc))
1795	>	return true;
1796	>	}
1797	>	else if (e != 0) {       // release an idle worker
1798	>	WorkQueue w; Thread p; int i;
1799	>	if ((i = e & SMASK) < ws.length && (w = ws[i]) != null) {
1800	>	long nc = ((long)(w.nextWait & E_MASK) |
1801	>	(c & (AC_MASK|TC_MASK)));
1802	>	if (w.eventCount == (e | INT_SIGN) &&
1803	>	U.compareAndSwapLong(this, CTL, c, nc)) {
1804	>	w.eventCount = (e + E_SEQ) & E_MASK;
1805	>	if ((p = w.parker) != null)
1806	>	U.unpark(p);
1807	>	return true;
1808	>	}
1809	>	}
1810	>	}
1811	>	else if (tc < MAX_CAP) { // create replacement
1812	>	long nc = ((c + TC_UNIT) & TC_MASK) | (c & ~TC_MASK);
1813	>	if (U.compareAndSwapLong(this, CTL, c, nc)) {
1814	>	addWorker();
1815	>	return true;
1816	>	}
1817	>	}
1818	>	}
1819	>	}
1820	>	return false;
1821	>	}
1822	>
1823	>	/**
1824	>	* Helps and/or blocks until the given task is done
1825	>	*
1826	>	* @param joiner the joining worker
1827	>	* @param task the task
1828	>	* @return task status on exit
1829	>	*/
1830	>	final int awaitJoin(WorkQueue joiner, ForkJoinTask<?> task) {
1831	>	ForkJoinTask<?> prevJoin = joiner.currentJoin;
1832	>	joiner.currentJoin = task;
1833	>	long startTime = 0L;
1834	>	for (int k = 0, s; ; ++k) {
1835	>	if ((joiner.isEmpty() ?                  // try to help
1836	>	!tryHelpStealer(joiner, task) :
1837	>	!joiner.tryRemoveAndExec(task))) {
1838	>	if (k == 0) {
1839	>	startTime = System.nanoTime();
1840	>	tryPollForAndExec(joiner, task); // check uncommon case
1841	>	}
1842	>	else if ((k & (MAX_HELP - 1)) == 0 &&
1843	>	System.nanoTime() - startTime >= COMPENSATION_DELAY &&
1844	>	tryCompensate(task, null)) {
1845	>	if (task.trySetSignal() && task.status >= 0) {
1846	>	synchronized (task) {
1847	>	if (task.status >= 0) {
1848	>	try {                // see ForkJoinTask
1849	>	task.wait();     //  for explanation
1850	>	} catch (InterruptedException ie) {
1851	>	}
1852	>	}
1853	>	else
1854	>	task.notifyAll();
1855	>	}
1856	>	}
1857	>	long c;                          // re-activate
1858	>	do {} while (!U.compareAndSwapLong
1859	>	(this, CTL, c = ctl, c + AC_UNIT));
1860	>	}
1861	>	}
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
1868	>	}
1869	>	}
1870	>
1871	>	/**
1872	>	* Stripped-down variant of awaitJoin used by timed joins. Tries
1873	>	* to help join only while there is continuous progress. (Caller
1874	>	* will then enter a timed wait.)
1875	>	*
1876	>	* @param joiner the joining worker
1877	>	* @param task the task
1878	>	* @return task status on exit
1879	>	*/
1880	>	final int helpJoinOnce(WorkQueue joiner, ForkJoinTask<?> task) {
1881	>	int s;
1882	>	while ((s = task.status) >= 0 &&
1883	>	(joiner.isEmpty() ?
1884	>	tryHelpStealer(joiner, task) :
1885	>	joiner.tryRemoveAndExec(task)))
1886	>	;
1887	>	return s;
1888	>	}
1889	>
1890	>	/**
1891	>	* Returns a (probably) non-empty steal queue, if one is found
1892	>	* during a random, then cyclic scan, else null.  This method must
1893	>	* be retried by caller if, by the time it tries to use the queue,
1894	>	* it is empty.
1895		*/
1896		private WorkQueue findNonEmptyStealQueue(WorkQueue w) {
1897	<	int r = w.seed;    // Same idea as scan(), but ignoring submissions
1897	>	// Similar to loop in scan(), but ignoring submissions
1898	>	int r = w.seed; r ^= r << 13; r ^= r >>> 17; w.seed = r ^= r << 5;
1899	>	int step = (r >>> 16) | 1;
1900		for (WorkQueue[] ws;;) {
1901	<	int m = runState & SMASK;
1902	<	if ((ws = workQueues) == null)
1901	>	int rs = runState, m;
1902	>	if ((ws = workQueues) == null || (m = ws.length - 1) < 1)
1903		return null;
1904	<	if (ws.length > m) {
1905	<	WorkQueue q;
1906	<	for (int k = 0, j = -1 - m;; ++j) {
1907	<	if (j < 0) {
1908	<	r ^= r << 13; r ^= r >>> 17; k = r ^= r << 5;
1909	<	}
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)
1904	>	for (int j = (m + 1) << 2; ; r += step) {
1905	>	WorkQueue q = ws[((r << 1) | 1) & m];
1906	>	if (q != null && !q.isEmpty())
1907	>	return q;
1908	>	else if (--j < 0) {
1909	>	if (runState == rs)
1910		return null;
1911	+	break;
1912		}
1913		}
1914		}
#	Line 1741 | Line 1922 | public class ForkJoinPool extends Abstra
1922		*/
1923		final void helpQuiescePool(WorkQueue w) {
1924		for (boolean active = true;;) {
1925	<	w.runLocalTasks();      // exhaust local queue
1925	>	if (w.base - w.top < 0)
1926	>	w.runLocalTasks();  // exhaust local queue
1927		WorkQueue q = findNonEmptyStealQueue(w);
1928		if (q != null) {
1929	<	ForkJoinTask<?> t;
1929	>	ForkJoinTask<?> t; int b;
1930		if (!active) {      // re-establish active count
1931		long c;
1932		active = true;
1933		do {} while (!U.compareAndSwapLong
1934		(this, CTL, c = ctl, c + AC_UNIT));
1935		}
1936	<	if ((t = q.poll()) != null)
1936	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
1937		w.runSubtask(t);
1938		}
1939		else {
#	Line 1779 | Line 1961 | public class ForkJoinPool extends Abstra
1961		*/
1962		final ForkJoinTask<?> nextTaskFor(WorkQueue w) {
1963		for (ForkJoinTask<?> t;;) {
1964	<	WorkQueue q;
1964	>	WorkQueue q; int b;
1965		if ((t = w.nextLocalTask()) != null)
1966		return t;
1967		if ((q = findNonEmptyStealQueue(w)) == null)
1968		return null;
1969	<	if ((t = q.poll()) != null)
1969	>	if ((b = q.base) - q.top < 0 && (t = q.pollAt(b)) != null)
1970		return t;
1971		}
1972		}
#	Line 1959 | Line 2141 | public class ForkJoinPool extends Abstra
2141		checkPermission();
2142		if (factory == null)
2143		throw new NullPointerException();
2144	<	if (parallelism <= 0 || parallelism > POOL_MAX)
2144	>	if (parallelism <= 0 || parallelism > MAX_CAP)
2145		throw new IllegalArgumentException();
2146		this.parallelism = parallelism;
2147		this.factory = factory;
2148		this.ueh = handler;
2149		this.localMode = asyncMode ? FIFO_QUEUE : LIFO_QUEUE;
1968	–	this.growHints = 1;
2150		long np = (long)(-parallelism); // offset ctl counts
2151		this.ctl = ((np << AC_SHIFT) & AC_MASK) | ((np << TC_SHIFT) & TC_MASK);
2152	<	// initialize workQueues array with room for 2*parallelism if possible
2153	<	int n = parallelism << 1;
2154	<	if (n >= POOL_MAX)
2155	<	n = POOL_MAX;
2156	<	else { // See Hackers Delight, sec 3.2, where n < (1 << 16)
2157	<	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8;
1977	<	}
1978	<	this.workQueues = new WorkQueue[(n + 1) << 1]; // #slots = 2 * #workers
2152	>	// Use nearest power 2 for workQueues size. See Hackers Delight sec 3.2.
2153	>	int n = parallelism - 1;
2154	>	n |= n >>> 1; n |= n >>> 2; n |= n >>> 4; n |= n >>> 8; n |= n >>> 16;
2155	>	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();
2161	+	int pn = poolNumberGenerator.incrementAndGet();
2162		StringBuilder sb = new StringBuilder("ForkJoinPool-");
2163	<	sb.append(poolNumberGenerator.incrementAndGet());
2163	>	sb.append(Integer.toString(pn));
2164		sb.append("-worker-");
2165		this.workerNamePrefix = sb.toString();
2166	+	lock.lock();
2167	+	this.runState = 1;              // set init flag
2168	+	lock.unlock();
2169		}
2170
2171		// Execution methods
#	Line 2004 | Line 2187 | public class ForkJoinPool extends Abstra
2187		*         scheduled for execution
2188		*/
2189		public <T> T invoke(ForkJoinTask<T> task) {
2190	+	if (task == null)
2191	+	throw new NullPointerException();
2192		doSubmit(task);
2193		return task.join();
2194		}
#	Line 2017 | Line 2202 | public class ForkJoinPool extends Abstra
2202		*         scheduled for execution
2203		*/
2204		public void execute(ForkJoinTask<?> task) {
2205	+	if (task == null)
2206	+	throw new NullPointerException();
2207		doSubmit(task);
2208		}
2209
#	Line 2034 | Line 2221 | public class ForkJoinPool extends Abstra
2221		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2222		job = (ForkJoinTask<?>) task;
2223		else
2224	<	job = ForkJoinTask.adapt(task, null);
2224	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2225		doSubmit(job);
2226		}
2227
#	Line 2048 | Line 2235 | public class ForkJoinPool extends Abstra
2235		*         scheduled for execution
2236		*/
2237		public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
2238	+	if (task == null)
2239	+	throw new NullPointerException();
2240		doSubmit(task);
2241		return task;
2242		}
#	Line 2058 | Line 2247 | public class ForkJoinPool extends Abstra
2247		*         scheduled for execution
2248		*/
2249		public <T> ForkJoinTask<T> submit(Callable<T> task) {
2250	<	if (task == null)
2062	<	throw new NullPointerException();
2063	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
2250	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedCallable<T>(task);
2251		doSubmit(job);
2252		return job;
2253		}
#	Line 2071 | Line 2258 | public class ForkJoinPool extends Abstra
2258		*         scheduled for execution
2259		*/
2260		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
2261	<	if (task == null)
2075	<	throw new NullPointerException();
2076	<	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
2261	>	ForkJoinTask<T> job = new ForkJoinTask.AdaptedRunnable<T>(task, result);
2262		doSubmit(job);
2263		return job;
2264		}
#	Line 2090 | Line 2275 | public class ForkJoinPool extends Abstra
2275		if (task instanceof ForkJoinTask<?>) // avoid re-wrap
2276		job = (ForkJoinTask<?>) task;
2277		else
2278	<	job = ForkJoinTask.adapt(task, null);
2278	>	job = new ForkJoinTask.AdaptedRunnableAction(task);
2279		doSubmit(job);
2280		return job;
2281		}
#	Line 2112 | Line 2297 | public class ForkJoinPool extends Abstra
2297		boolean done = false;
2298		try {
2299		for (Callable<T> t : tasks) {
2300	<	ForkJoinTask<T> f = ForkJoinTask.adapt(t);
2300	>	ForkJoinTask<T> f = new ForkJoinTask.AdaptedCallable<T>(t);
2301		doSubmit(f);
2302		fs.add(f);
2303		}
#	Line 2298 | Line 2483 | public class ForkJoinPool extends Abstra
2483		WorkQueue[] ws; WorkQueue w;
2484		if ((ws = workQueues) != null) {
2485		for (int i = 0; i < ws.length; i += 2) {
2486	<	if ((w = ws[i]) != null && w.queueSize() != 0)
2486	>	if ((w = ws[i]) != null && !w.isEmpty())
2487		return true;
2488		}
2489		}
#	Line 2612 | Line 2797 | public class ForkJoinPool extends Abstra
2797		ForkJoinPool p = ((t instanceof ForkJoinWorkerThread) ?
2798		((ForkJoinWorkerThread)t).pool : null);
2799		while (!blocker.isReleasable()) {
2800	<	if (p == null || p.tryCompensate()) {
2800	>	if (p == null || p.tryCompensate(null, blocker)) {
2801		try {
2802		do {} while (!blocker.isReleasable() && !blocker.block());
2803		} finally {
#	Line 2629 | Line 2814 | public class ForkJoinPool extends Abstra
2814		// implement RunnableFuture.
2815
2816		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
2817	<	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
2817	>	return new ForkJoinTask.AdaptedRunnable<T>(runnable, value);
2818		}
2819
2820		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
2821	<	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
2821	>	return new ForkJoinTask.AdaptedCallable<T>(callable);
2822		}
2823
2824		// Unsafe mechanics
2825		private static final sun.misc.Unsafe U;
2826		private static final long CTL;
2827		private static final long PARKBLOCKER;
2828	+	private static final int ABASE;
2829	+	private static final int ASHIFT;
2830
2831		static {
2832		poolNumberGenerator = new AtomicInteger();
2833	+	nextSubmitterSeed = new AtomicInteger(0x55555555);
2834		modifyThreadPermission = new RuntimePermission("modifyThread");
2835		defaultForkJoinWorkerThreadFactory =
2836		new DefaultForkJoinWorkerThreadFactory();
2837		submitters = new ThreadSubmitter();
2838	+	int s;
2839		try {
2840		U = getUnsafe();
2841		Class<?> k = ForkJoinPool.class;
2842	+	Class<?> ak = ForkJoinTask[].class;
2843		CTL = U.objectFieldOffset
2844		(k.getDeclaredField("ctl"));
2845		Class<?> tk = Thread.class;
2846		PARKBLOCKER = U.objectFieldOffset
2847		(tk.getDeclaredField("parkBlocker"));
2848	+	ABASE = U.arrayBaseOffset(ak);
2849	+	s = U.arrayIndexScale(ak);
2850		} catch (Exception e) {
2851		throw new Error(e);
2852		}
2853	+	if ((s & (s-1)) != 0)
2854	+	throw new Error("data type scale not a power of two");
2855	+	ASHIFT = 31 - Integer.numberOfLeadingZeros(s);
2856		}
2857
2858		/**

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