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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.7 by dl, Thu Jul 16 15:32:34 2009 UTC vs.
Revision 1.29 by jsr166, Thu Aug 6 15:13:54 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
8	>
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.atomic.*;
11	<	import java.util.concurrent.locks.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
10	>
11	>	import java.util.Collection;
12
13		/**
14		* A thread managed by a {@link ForkJoinPool}.  This class is
15		* subclassable solely for the sake of adding functionality -- there
16	<	* are no overridable methods dealing with scheduling or
17	<	* execution. However, you can override initialization and termination
18	<	* methods surrounding the main task processing loop.  If you do
19	<	* create such a subclass, you will also need to supply a custom
20	<	* ForkJoinWorkerThreadFactory to use it in a ForkJoinPool.
16	>	* are no overridable methods dealing with scheduling or execution.
17	>	* However, you can override initialization and termination methods
18	>	* surrounding the main task processing loop.  If you do create such a
19	>	* subclass, you will also need to supply a custom {@link
20	>	* ForkJoinPool.ForkJoinWorkerThreadFactory} to use it in a {@code
21	>	* ForkJoinPool}.
22		*
23	+	* @since 1.7
24	+	* @author Doug Lea
25		*/
26		public class ForkJoinWorkerThread extends Thread {
27		/*
#	Line 44 | Line 45 | public class ForkJoinWorkerThread extend
45		* of tasks. To accomplish this, we shift the CAS arbitrating pop
46		* vs deq (steal) from being on the indices ("base" and "sp") to
47		* the slots themselves (mainly via method "casSlotNull()"). So,
48	<	* both a successful pop and deq mainly entail CAS'ing a nonnull
48	>	* both a successful pop and deq mainly entail CAS'ing a non-null
49		* slot to null.  Because we rely on CASes of references, we do
50		* not need tag bits on base or sp.  They are simple ints as used
51		* in any circular array-based queue (see for example ArrayDeque).
#	Line 56 | Line 57 | public class ForkJoinWorkerThread extend
57		* considered individually, is not wait-free. One thief cannot
58		* successfully continue until another in-progress one (or, if
59		* previously empty, a push) completes.  However, in the
60	<	* aggregate, we ensure at least probablistic non-blockingness. If
61	<	* an attempted steal fails, a thief always chooses a different
62	<	* random victim target to try next. So, in order for one thief to
63	<	* progress, it suffices for any in-progress deq or new push on
64	<	* any empty queue to complete. One reason this works well here is
65	<	* that apparently-nonempty often means soon-to-be-stealable,
66	<	* which gives threads a chance to activate if necessary before
67	<	* stealing (see below).
60	>	* aggregate, we ensure at least probabilistic
61	>	* non-blockingness. If an attempted steal fails, a thief always
62	>	* chooses a different random victim target to try next. So, in
63	>	* order for one thief to progress, it suffices for any
64	>	* in-progress deq or new push on any empty queue to complete. One
65	>	* reason this works well here is that apparently-nonempty often
66	>	* means soon-to-be-stealable, which gives threads a chance to
67	>	* activate if necessary before stealing (see below).
68	>	*
69	>	* This approach also enables support for "async mode" where local
70	>	* task processing is in FIFO, not LIFO order; simply by using a
71	>	* version of deq rather than pop when locallyFifo is true (as set
72	>	* by the ForkJoinPool).  This allows use in message-passing
73	>	* frameworks in which tasks are never joined.
74		*
75		* Efficient implementation of this approach currently relies on
76		* an uncomfortable amount of "Unsafe" mechanics. To maintain
#	Line 73 | Line 80 | public class ForkJoinWorkerThread extend
80		* protected by volatile base reads, reads of the queue array and
81		* its slots do not need volatile load semantics, but writes (in
82		* push) require store order and CASes (in pop and deq) require
83	<	* (volatile) CAS semantics. Since these combinations aren't
84	<	* supported using ordinary volatiles, the only way to accomplish
85	<	* these effciently is to use direct Unsafe calls. (Using external
83	>	* (volatile) CAS semantics.  (See "Idempotent work stealing" by
84	>	* Michael, Saraswat, and Vechev, PPoPP 2009
85	>	* http://portal.acm.org/citation.cfm?id=1504186 for an algorithm
86	>	* with similar properties, but without support for nulling
87	>	* slots.)  Since these combinations aren't supported using
88	>	* ordinary volatiles, the only way to accomplish these
89	>	* efficiently is to use direct Unsafe calls. (Using external
90		* AtomicIntegers and AtomicReferenceArrays for the indices and
91		* array is significantly slower because of memory locality and
92	<	* indirection effects.) Further, performance on most platforms is
93	<	* very sensitive to placement and sizing of the (resizable) queue
94	<	* array.  Even though these queues don't usually become all that
95	<	* big, the initial size must be large enough to counteract cache
92	>	* indirection effects.)
93	>	*
94	>	* Further, performance on most platforms is very sensitive to
95	>	* placement and sizing of the (resizable) queue array.  Even
96	>	* though these queues don't usually become all that big, the
97	>	* initial size must be large enough to counteract cache
98		* contention effects across multiple queues (especially in the
99		* presence of GC cardmarking). Also, to improve thread-locality,
100		* queues are currently initialized immediately after the thread
#	Line 98 | Line 111 | public class ForkJoinWorkerThread extend
111		* counter (activeCount) held by the pool. It uses an algorithm
112		* similar to that in Herlihy and Shavit section 17.6 to cause
113		* threads to eventually block when all threads declare they are
114	<	* inactive. (See variable "scans".)  For this to work, threads
115	<	* must be declared active when executing tasks, and before
116	<	* stealing a task. They must be inactive before blocking on the
117	<	* Pool Barrier (awaiting a new submission or other Pool
118	<	* event). In between, there is some free play which we take
119	<	* advantage of to avoid contention and rapid flickering of the
120	<	* global activeCount: If inactive, we activate only if a victim
121	<	* queue appears to be nonempty (see above).  Similarly, a thread
122	<	* tries to inactivate only after a full scan of other threads.
123	<	* The net effect is that contention on activeCount is rarely a
124	<	* measurable performance issue. (There are also a few other cases
125	<	* where we scan for work rather than retry/block upon
113	<	* contention.)
114	>	* inactive. For this to work, threads must be declared active
115	>	* when executing tasks, and before stealing a task. They must be
116	>	* inactive before blocking on the Pool Barrier (awaiting a new
117	>	* submission or other Pool event). In between, there is some free
118	>	* play which we take advantage of to avoid contention and rapid
119	>	* flickering of the global activeCount: If inactive, we activate
120	>	* only if a victim queue appears to be nonempty (see above).
121	>	* Similarly, a thread tries to inactivate only after a full scan
122	>	* of other threads.  The net effect is that contention on
123	>	* activeCount is rarely a measurable performance issue. (There
124	>	* are also a few other cases where we scan for work rather than
125	>	* retry/block upon contention.)
126		*
127		* 3. Selection control. We maintain policy of always choosing to
128		* run local tasks rather than stealing, and always trying to
#	Line 137 | Line 149 | public class ForkJoinWorkerThread extend
149		private static final int MAXIMUM_QUEUE_CAPACITY = 1 << 28;
150
151		/**
152	<	* The pool this thread works in. Accessed directly by ForkJoinTask
152	>	* The pool this thread works in. Accessed directly by ForkJoinTask.
153		*/
154		final ForkJoinPool pool;
155
#	Line 165 | Line 177 | public class ForkJoinWorkerThread extend
177		* Activity status. When true, this worker is considered active.
178		* Must be false upon construction. It must be true when executing
179		* tasks, and BEFORE stealing a task. It must be false before
180	<	* calling pool.sync
180	>	* calling pool.sync.
181		*/
182		private boolean active;
183
#	Line 188 | Line 200 | public class ForkJoinWorkerThread extend
200
201		/**
202		* Index of this worker in pool array. Set once by pool before
203	<	* running, and accessed directly by pool during cleanup etc
203	>	* running, and accessed directly by pool during cleanup etc.
204		*/
205		int poolIndex;
206
#	Line 205 | Line 217 | public class ForkJoinWorkerThread extend
217
218		/**
219		* Creates a ForkJoinWorkerThread operating in the given pool.
220	+	*
221		* @param pool the pool this thread works in
222		* @throws NullPointerException if pool is null
223		*/
#	Line 218 | Line 231 | public class ForkJoinWorkerThread extend
231		// Public access methods
232
233		/**
234	<	* Returns the pool hosting this thread
234	>	* Returns the pool hosting this thread.
235	>	*
236		* @return the pool
237		*/
238		public ForkJoinPool getPool() {
#	Line 231 | Line 245 | public class ForkJoinWorkerThread extend
245		* threads (minus one) that have ever been created in the pool.
246		* This method may be useful for applications that track status or
247		* collect results per-worker rather than per-task.
248	<	* @return the index number.
248	>	*
249	>	* @return the index number
250		*/
251		public int getPoolIndex() {
252		return poolIndex;
#	Line 239 | Line 254 | public class ForkJoinWorkerThread extend
254
255		/**
256		* Establishes local first-in-first-out scheduling mode for forked
257	<	* tasks that are never joined.
257	>	* tasks that are never joined.
258	>	*
259		* @param async if true, use locally FIFO scheduling
260		*/
261		void setAsyncMode(boolean async) {
#	Line 261 | Line 277 | public class ForkJoinWorkerThread extend
277		final boolean shutdownNow()   { return transitionRunStateTo(TERMINATING); }
278
279		/**
280	<	* Transition to at least the given state. Return true if not
281	<	* already at least given state.
280	>	* Transitions to at least the given state.
281	>	*
282	>	* @return {@code true} if not already at least at given state
283		*/
284		private boolean transitionRunStateTo(int state) {
285		for (;;) {
286		int s = runState;
287		if (s >= state)
288		return false;
289	<	if (_unsafe.compareAndSwapInt(this, runStateOffset, s, state))
289	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, state))
290		return true;
291		}
292		}
293
294		/**
295	<	* Try to set status to active; fail on contention
295	>	* Tries to set status to active; fails on contention.
296		*/
297		private boolean tryActivate() {
298		if (!active) {
#	Line 287 | Line 304 | public class ForkJoinWorkerThread extend
304		}
305
306		/**
307	<	* Try to set status to active; fail on contention
307	>	* Tries to set status to inactive; fails on contention.
308		*/
309		private boolean tryInactivate() {
310		if (active) {
#	Line 299 | Line 316 | public class ForkJoinWorkerThread extend
316		}
317
318		/**
319	<	* Computes next value for random victim probe. Scans don't
319	>	* Computes next value for random victim probe.  Scans don't
320		* require a very high quality generator, but also not a crummy
321	<	* one. Marsaglia xor-shift is cheap and works well.
321	>	* one.  Marsaglia xor-shift is cheap and works well.
322		*/
323		private static int xorShift(int r) {
324	<	r ^= r << 1;
325	<	r ^= r >>> 3;
326	<	r ^= r << 10;
310	<	return r;
324	>	r ^= (r << 13);
325	>	r ^= (r >>> 17);
326	>	return r ^ (r << 5);
327		}
328
329		// Lifecycle methods
#	Line 331 | Line 347 | public class ForkJoinWorkerThread extend
347		}
348
349		/**
350	<	* Execute tasks until shut down.
350	>	* Executes tasks until shut down.
351		*/
352		private void mainLoop() {
353		while (!isShutdown()) {
#	Line 363 | Line 379 | public class ForkJoinWorkerThread extend
379		}
380
381		/**
382	<	* Perform cleanup associated with termination of this worker
382	>	* Performs cleanup associated with termination of this worker
383		* thread.  If you override this method, you must invoke
384	<	* super.onTermination at the end of the overridden method.
384	>	* {@code super.onTermination} at the end of the overridden method.
385		*
386		* @param exception the exception causing this thread to abort due
387	<	* to an unrecoverable error, or null if completed normally.
387	>	* to an unrecoverable error, or {@code null} if completed normally
388		*/
389		protected void onTermination(Throwable exception) {
390		// Execute remaining local tasks unless aborting or terminating
391	<	while (exception == null &&  !pool.isTerminating() && base != sp) {
391	>	while (exception == null && pool.isProcessingTasks() && base != sp) {
392		try {
393		ForkJoinTask<?> t = popTask();
394		if (t != null)
395		t.quietlyExec();
396	<	} catch(Throwable ex) {
396	>	} catch (Throwable ex) {
397		exception = ex;
398		}
399		}
400		// Cancel other tasks, transition status, notify pool, and
401		// propagate exception to uncaught exception handler
402		try {
403	<	do;while (!tryInactivate()); // ensure inactive
403	>	do {} while (!tryInactivate()); // ensure inactive
404		cancelTasks();
405		runState = TERMINATED;
406		pool.workerTerminated(this);
#	Line 400 | Line 416 | public class ForkJoinWorkerThread extend
416		// Intrinsics-based support for queue operations.
417
418		/**
419	<	* Add in store-order the given task at given slot of q to
420	<	* null. Caller must ensure q is nonnull and index is in range.
419	>	* Adds in store-order the given task at given slot of q to null.
420	>	* Caller must ensure q is non-null and index is in range.
421		*/
422		private static void setSlot(ForkJoinTask<?>[] q, int i,
423	<	ForkJoinTask<?> t){
424	<	_unsafe.putOrderedObject(q, (i << qShift) + qBase, t);
423	>	ForkJoinTask<?> t) {
424	>	UNSAFE.putOrderedObject(q, (i << qShift) + qBase, t);
425		}
426
427		/**
428	<	* CAS given slot of q to null. Caller must ensure q is nonnull
428	>	* CAS given slot of q to null. Caller must ensure q is non-null
429		* and index is in range.
430		*/
431		private static boolean casSlotNull(ForkJoinTask<?>[] q, int i,
432		ForkJoinTask<?> t) {
433	<	return _unsafe.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
433	>	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
434		}
435
436		/**
437		* Sets sp in store-order.
438		*/
439		private void storeSp(int s) {
440	<	_unsafe.putOrderedInt(this, spOffset, s);
440	>	UNSAFE.putOrderedInt(this, spOffset, s);
441		}
442
443		// Main queue methods
444
445		/**
446		* Pushes a task. Called only by current thread.
447	<	* @param t the task. Caller must ensure nonnull
447	>	*
448	>	* @param t the task. Caller must ensure non-null.
449		*/
450		final void pushTask(ForkJoinTask<?> t) {
451		ForkJoinTask<?>[] q = queue;
#	Line 445 | Line 462 | public class ForkJoinWorkerThread extend
462		/**
463		* Tries to take a task from the base of the queue, failing if
464		* either empty or contended.
465	<	* @return a task, or null if none or contended.
465	>	*
466	>	* @return a task, or null if none or contended
467		*/
468		final ForkJoinTask<?> deqTask() {
469		ForkJoinTask<?> t;
#	Line 463 | Line 481 | public class ForkJoinWorkerThread extend
481		}
482
483		/**
484	+	* Tries to take a task from the base of own queue, activating if
485	+	* necessary, failing only if empty. Called only by current thread.
486	+	*
487	+	* @return a task, or null if none
488	+	*/
489	+	final ForkJoinTask<?> locallyDeqTask() {
490	+	int b;
491	+	while (sp != (b = base)) {
492	+	if (tryActivate()) {
493	+	ForkJoinTask<?>[] q = queue;
494	+	int i = (q.length - 1) & b;
495	+	ForkJoinTask<?> t = q[i];
496	+	if (t != null && casSlotNull(q, i, t)) {
497	+	base = b + 1;
498	+	return t;
499	+	}
500	+	}
501	+	}
502	+	return null;
503	+	}
504	+
505	+	/**
506		* Returns a popped task, or null if empty. Ensures active status
507	<	* if nonnull. Called only by current thread.
507	>	* if non-null. Called only by current thread.
508		*/
509		final ForkJoinTask<?> popTask() {
510		int s = sp;
#	Line 487 | Line 527 | public class ForkJoinWorkerThread extend
527		* Specialized version of popTask to pop only if
528		* topmost element is the given task. Called only
529		* by current thread while active.
530	<	* @param t the task. Caller must ensure nonnull
530	>	*
531	>	* @param t the task. Caller must ensure non-null.
532		*/
533		final boolean unpushTask(ForkJoinTask<?> t) {
534		ForkJoinTask<?>[] q = queue;
#	Line 501 | Line 542 | public class ForkJoinWorkerThread extend
542		}
543
544		/**
545	<	* Returns next task.
545	>	* Returns next task or null if empty or contended
546		*/
547		final ForkJoinTask<?> peekTask() {
548		ForkJoinTask<?>[] q = queue;
549		if (q == null)
550		return null;
551		int mask = q.length - 1;
552	<	int i = locallyFifo? base : (sp - 1);
552	>	int i = locallyFifo ? base : (sp - 1);
553		return q[i & mask];
554		}
555
#	Line 571 | Line 612 | public class ForkJoinWorkerThread extend
612		ForkJoinWorkerThread v = ws[mask & idx];
613		if (v == null || v.sp == v.base) {
614		if (probes <= mask)
615	<	idx = (probes++ < 0)? r : (idx + 1);
615	>	idx = (probes++ < 0) ? r : (idx + 1);
616		else
617		break;
618		}
#	Line 587 | Line 628 | public class ForkJoinWorkerThread extend
628		}
629
630		/**
631	<	* gets and removes a local or stolen a task
631	>	* Gets and removes a local or stolen task.
632	>	*
633		* @return a task, if available
634		*/
635		final ForkJoinTask<?> pollTask() {
636	<	ForkJoinTask<?> t = locallyFifo? deqTask() : popTask();
636	>	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
637		if (t == null && (t = scan()) != null)
638		++stealCount;
639		return t;
640		}
641
642		/**
643	<	* gets a local task
643	>	* Gets a local task.
644	>	*
645		* @return a task, if available
646		*/
647		final ForkJoinTask<?> pollLocalTask() {
648	<	return locallyFifo? deqTask() : popTask();
648	>	return locallyFifo ? locallyDeqTask() : popTask();
649		}
650
651		/**
652		* Returns a pool submission, if one exists, activating first.
653	+	*
654		* @return a submission, if available
655		*/
656		private ForkJoinTask<?> pollSubmission() {
#	Line 632 | Line 676 | public class ForkJoinWorkerThread extend
676		}
677
678		/**
679	<	* Drains tasks to given collection c
679	>	* Drains tasks to given collection c.
680	>	*
681		* @return the number of tasks drained
682		*/
683	<	final int drainTasksTo(Collection<ForkJoinTask<?>> c) {
683	>	final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
684		int n = 0;
685		ForkJoinTask<?> t;
686		while (base != sp && (t = deqTask()) != null) {
#	Line 646 | Line 691 | public class ForkJoinWorkerThread extend
691		}
692
693		/**
694	<	* Get and clear steal count for accumulation by pool.  Called
694	>	* Gets and clears steal count for accumulation by pool.  Called
695		* only when known to be idle (in pool.sync and termination).
696		*/
697		final int getAndClearStealCount() {
#	Line 656 | Line 701 | public class ForkJoinWorkerThread extend
701		}
702
703		/**
704	<	* Returns true if at least one worker in the given array appears
705	<	* to have at least one queued task.
704	>	* Returns {@code true} if at least one worker in the given array
705	>	* appears to have at least one queued task.
706	>	*
707		* @param ws array of workers
708		*/
709		static boolean hasQueuedTasks(ForkJoinWorkerThread[] ws) {
#	Line 680 | Line 726 | public class ForkJoinWorkerThread extend
726		* Returns an estimate of the number of tasks in the queue.
727		*/
728		final int getQueueSize() {
729	<	int n = sp - base;
730	<	return n < 0? 0 : n; // suppress momentarily negative values
729	>	// suppress momentarily negative values
730	>	return Math.max(0, sp - base);
731		}
732
733		/**
#	Line 694 | Line 740 | public class ForkJoinWorkerThread extend
740		}
741
742		/**
743	<	* Scan, returning early if joinMe done
743	>	* Scans, returning early if joinMe done.
744		*/
745		final ForkJoinTask<?> scanWhileJoining(ForkJoinTask<?> joinMe) {
746		ForkJoinTask<?> t = pollTask();
#	Line 706 | Line 752 | public class ForkJoinWorkerThread extend
752		}
753
754		/**
755	<	* Runs tasks until pool isQuiescent
755	>	* Runs tasks until {@code pool.isQuiescent()}.
756		*/
757		final void helpQuiescePool() {
758		for (;;) {
#	Line 716 | Line 762 | public class ForkJoinWorkerThread extend
762		else if (tryInactivate() && pool.isQuiescent())
763		break;
764		}
765	<	do;while (!tryActivate()); // re-activate on exit
765	>	do {} while (!tryActivate()); // re-activate on exit
766		}
767
768	<	// Temporary Unsafe mechanics for preliminary release
769	<	private static Unsafe getUnsafe() throws Throwable {
768	>	// Unsafe mechanics
769	>
770	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
771	>	private static final long spOffset =
772	>	objectFieldOffset("sp", ForkJoinWorkerThread.class);
773	>	private static final long runStateOffset =
774	>	objectFieldOffset("runState", ForkJoinWorkerThread.class);
775	>	private static final long qBase;
776	>	private static final int qShift;
777	>
778	>	static {
779	>	qBase = UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
780	>	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
781	>	if ((s & (s-1)) != 0)
782	>	throw new Error("data type scale not a power of two");
783	>	qShift = 31 - Integer.numberOfLeadingZeros(s);
784	>	}
785	>
786	>	private static long objectFieldOffset(String field, Class<?> klazz) {
787		try {
788	<	return Unsafe.getUnsafe();
788	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
789	>	} catch (NoSuchFieldException e) {
790	>	// Convert Exception to corresponding Error
791	>	NoSuchFieldError error = new NoSuchFieldError(field);
792	>	error.initCause(e);
793	>	throw error;
794	>	}
795	>	}
796	>
797	>	/**
798	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
799	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
800	>	* into a jdk.
801	>	*
802	>	* @return a sun.misc.Unsafe
803	>	*/
804	>	private static sun.misc.Unsafe getUnsafe() {
805	>	try {
806	>	return sun.misc.Unsafe.getUnsafe();
807		} catch (SecurityException se) {
808		try {
809		return java.security.AccessController.doPrivileged
810	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
811	<	public Unsafe run() throws Exception {
812	<	return getUnsafePrivileged();
810	>	(new java.security
811	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
812	>	public sun.misc.Unsafe run() throws Exception {
813	>	java.lang.reflect.Field f = sun.misc
814	>	.Unsafe.class.getDeclaredField("theUnsafe");
815	>	f.setAccessible(true);
816	>	return (sun.misc.Unsafe) f.get(null);
817		}});
818		} catch (java.security.PrivilegedActionException e) {
819	<	throw e.getCause();
819	>	throw new RuntimeException("Could not initialize intrinsics",
820	>	e.getCause());
821		}
822		}
823		}
738	–
739	–	private static Unsafe getUnsafePrivileged()
740	–	throws NoSuchFieldException, IllegalAccessException {
741	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
742	–	f.setAccessible(true);
743	–	return (Unsafe) f.get(null);
744	–	}
745	–
746	–	private static long fieldOffset(String fieldName)
747	–	throws NoSuchFieldException {
748	–	return _unsafe.objectFieldOffset
749	–	(ForkJoinWorkerThread.class.getDeclaredField(fieldName));
750	–	}
751	–
752	–	static final Unsafe _unsafe;
753	–	static final long baseOffset;
754	–	static final long spOffset;
755	–	static final long runStateOffset;
756	–	static final long qBase;
757	–	static final int qShift;
758	–	static {
759	–	try {
760	–	_unsafe = getUnsafe();
761	–	baseOffset = fieldOffset("base");
762	–	spOffset = fieldOffset("sp");
763	–	runStateOffset = fieldOffset("runState");
764	–	qBase = _unsafe.arrayBaseOffset(ForkJoinTask[].class);
765	–	int s = _unsafe.arrayIndexScale(ForkJoinTask[].class);
766	–	if ((s & (s-1)) != 0)
767	–	throw new Error("data type scale not a power of two");
768	–	qShift = 31 - Integer.numberOfLeadingZeros(s);
769	–	} catch (Throwable e) {
770	–	throw new RuntimeException("Could not initialize intrinsics", e);
771	–	}
772	–	}
824		}

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