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

Comparing jsr166/src/jsr166y/ForkJoinWorkerThread.java (file contents):
Revision 1.53 by dl, Sun Oct 24 19:37:26 2010 UTC vs.
Revision 1.71 by dl, Wed Nov 14 17:20:38 2012 UTC

#	Line 1 | Line 1
1		/*
2		* Written by Doug Lea with assistance from members of JCP JSR-166
3		* Expert Group and released to the public domain, as explained at
4	<	* http://creativecommons.org/licenses/publicdomain
4	>	* http://creativecommons.org/publicdomain/zero/1.0/
5		*/
6
7		package jsr166y;
8
9	–	import java.util.Random;
10	–	import java.util.Collection;
11	–	import java.util.concurrent.locks.LockSupport;
12	–	import java.util.concurrent.RejectedExecutionException;
13	–
9		/**
10	<	* A thread managed by a {@link ForkJoinPool}.  This class is
11	<	* subclassable solely for the sake of adding functionality -- there
12	<	* are no overridable methods dealing with scheduling or execution.
13	<	* However, you can override initialization and termination methods
14	<	* surrounding the main task processing loop.  If you do create such a
15	<	* subclass, you will also need to supply a custom {@link
16	<	* ForkJoinPool.ForkJoinWorkerThreadFactory} to use it in a {@code
17	<	* ForkJoinPool}.
10	>	* A thread managed by a {@link ForkJoinPool}, which executes
11	>	* {@link ForkJoinTask}s.
12	>	* This class is subclassable solely for the sake of adding
13	>	* functionality -- there are no overridable methods dealing with
14	>	* scheduling or execution.  However, you can override initialization
15	>	* and termination methods surrounding the main task processing loop.
16	>	* If you do create such a subclass, you will also need to supply a
17	>	* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
18	>	* in a {@code ForkJoinPool}.
19		*
20		* @since 1.7
21		* @author Doug Lea
22		*/
23		public class ForkJoinWorkerThread extends Thread {
24		/*
29	–	* Overview:
30	–	*
25		* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
26	<	* ForkJoinTasks. This class includes bookkeeping in support of
27	<	* worker activation, suspension, and lifecycle control described
34	<	* in more detail in the internal documentation of class
35	<	* ForkJoinPool. And as described further below, this class also
36	<	* includes special-cased support for some ForkJoinTask
37	<	* methods. But the main mechanics involve work-stealing:
38	<	*
39	<	* Work-stealing queues are special forms of Deques that support
40	<	* only three of the four possible end-operations -- push, pop,
41	<	* and deq (aka steal), under the further constraints that push
42	<	* and pop are called only from the owning thread, while deq may
43	<	* be called from other threads.  (If you are unfamiliar with
44	<	* them, you probably want to read Herlihy and Shavit's book "The
45	<	* Art of Multiprocessor programming", chapter 16 describing these
46	<	* in more detail before proceeding.)  The main work-stealing
47	<	* queue design is roughly similar to those in the papers "Dynamic
48	<	* Circular Work-Stealing Deque" by Chase and Lev, SPAA 2005
49	<	* (http://research.sun.com/scalable/pubs/index.html) and
50	<	* "Idempotent work stealing" by Michael, Saraswat, and Vechev,
51	<	* PPoPP 2009 (http://portal.acm.org/citation.cfm?id=1504186).
52	<	* The main differences ultimately stem from gc requirements that
53	<	* we null out taken slots as soon as we can, to maintain as small
54	<	* a footprint as possible even in programs generating huge
55	<	* numbers of tasks. To accomplish this, we shift the CAS
56	<	* arbitrating pop vs deq (steal) from being on the indices
57	<	* ("base" and "sp") to the slots themselves (mainly via method
58	<	* "casSlotNull()"). So, both a successful pop and deq mainly
59	<	* entail a CAS of a slot from non-null to null.  Because we rely
60	<	* on CASes of references, we do not need tag bits on base or sp.
61	<	* They are simple ints as used in any circular array-based queue
62	<	* (see for example ArrayDeque).  Updates to the indices must
63	<	* still be ordered in a way that guarantees that sp == base means
64	<	* the queue is empty, but otherwise may err on the side of
65	<	* possibly making the queue appear nonempty when a push, pop, or
66	<	* deq have not fully committed. Note that this means that the deq
67	<	* operation, considered individually, is not wait-free. One thief
68	<	* cannot successfully continue until another in-progress one (or,
69	<	* if previously empty, a push) completes.  However, in the
70	<	* aggregate, we ensure at least probabilistic non-blockingness.
71	<	* If an attempted steal fails, a thief always chooses a different
72	<	* random victim target to try next. So, in order for one thief to
73	<	* progress, it suffices for any in-progress deq or new push on
74	<	* any empty queue to complete. One reason this works well here is
75	<	* that apparently-nonempty often means soon-to-be-stealable,
76	<	* which gives threads a chance to set activation status if
77	<	* necessary before stealing.
78	<	*
79	<	* This approach also enables support for "async mode" where local
80	<	* task processing is in FIFO, not LIFO order; simply by using a
81	<	* version of deq rather than pop when locallyFifo is true (as set
82	<	* by the ForkJoinPool).  This allows use in message-passing
83	<	* frameworks in which tasks are never joined.
84	<	*
85	<	* When a worker would otherwise be blocked waiting to join a
86	<	* task, it first tries a form of linear helping: Each worker
87	<	* records (in field currentSteal) the most recent task it stole
88	<	* from some other worker. Plus, it records (in field currentJoin)
89	<	* the task it is currently actively joining. Method joinTask uses
90	<	* these markers to try to find a worker to help (i.e., steal back
91	<	* a task from and execute it) that could hasten completion of the
92	<	* actively joined task. In essence, the joiner executes a task
93	<	* that would be on its own local deque had the to-be-joined task
94	<	* not been stolen. This may be seen as a conservative variant of
95	<	* the approach in Wagner & Calder "Leapfrogging: a portable
96	<	* technique for implementing efficient futures" SIGPLAN Notices,
97	<	* 1993 (http://portal.acm.org/citation.cfm?id=155354). It differs
98	<	* in that: (1) We only maintain dependency links across workers
99	<	* upon steals, rather than use per-task bookkeeping.  This may
100	<	* require a linear scan of workers array to locate stealers, but
101	<	* usually doesn't because stealers leave hints (that may become
102	<	* stale/wrong) of where to locate them. This isolates cost to
103	<	* when it is needed, rather than adding to per-task overhead.
104	<	* (2) It is "shallow", ignoring nesting and potentially cyclic
105	<	* mutual steals.  (3) It is intentionally racy: field currentJoin
106	<	* is updated only while actively joining, which means that we
107	<	* miss links in the chain during long-lived tasks, GC stalls etc
108	<	* (which is OK since blocking in such cases is usually a good
109	<	* idea).  (4) We bound the number of attempts to find work (see
110	<	* MAX_HELP_DEPTH) and fall back to suspending the worker and if
111	<	* necessary replacing it with a spare (see
112	<	* ForkJoinPool.awaitJoin).
113	<	*
114	<	* Efficient implementation of these algorithms currently relies
115	<	* on an uncomfortable amount of "Unsafe" mechanics. To maintain
116	<	* correct orderings, reads and writes of variable base require
117	<	* volatile ordering.  Variable sp does not require volatile
118	<	* writes but still needs store-ordering, which we accomplish by
119	<	* pre-incrementing sp before filling the slot with an ordered
120	<	* store.  (Pre-incrementing also enables backouts used in
121	<	* joinTask.)  Because they are protected by volatile base reads,
122	<	* reads of the queue array and its slots by other threads do not
123	<	* need volatile load semantics, but writes (in push) require
124	<	* store order and CASes (in pop and deq) require (volatile) CAS
125	<	* semantics.  (Michael, Saraswat, and Vechev's algorithm has
126	<	* similar properties, but without support for nulling slots.)
127	<	* Since these combinations aren't supported using ordinary
128	<	* volatiles, the only way to accomplish these efficiently is to
129	<	* use direct Unsafe calls. (Using external AtomicIntegers and
130	<	* AtomicReferenceArrays for the indices and array is
131	<	* significantly slower because of memory locality and indirection
132	<	* effects.)
133	<	*
134	<	* Further, performance on most platforms is very sensitive to
135	<	* placement and sizing of the (resizable) queue array.  Even
136	<	* though these queues don't usually become all that big, the
137	<	* initial size must be large enough to counteract cache
138	<	* contention effects across multiple queues (especially in the
139	<	* presence of GC cardmarking). Also, to improve thread-locality,
140	<	* queues are initialized after starting.  All together, these
141	<	* low-level implementation choices produce as much as a factor of
142	<	* 4 performance improvement compared to naive implementations,
143	<	* and enable the processing of billions of tasks per second,
144	<	* sometimes at the expense of ugliness.
145	<	*/
146	<
147	<	/**
148	<	* Generator for initial random seeds for random victim
149	<	* selection. This is used only to create initial seeds. Random
150	<	* steals use a cheaper xorshift generator per steal attempt. We
151	<	* expect only rare contention on seedGenerator, so just use a
152	<	* plain Random.
153	<	*/
154	<	private static final Random seedGenerator = new Random();
155	<
156	<	/**
157	<	* The maximum stolen->joining link depth allowed in helpJoinTask.
158	<	* Depths for legitimate chains are unbounded, but we use a fixed
159	<	* constant to avoid (otherwise unchecked) cycles and bound
160	<	* staleness of traversal parameters at the expense of sometimes
161	<	* blocking when we could be helping.
162	<	*/
163	<	private static final int MAX_HELP_DEPTH = 8;
164	<
165	<	/**
166	<	* Capacity of work-stealing queue array upon initialization.
167	<	* Must be a power of two. Initial size must be at least 4, but is
168	<	* padded to minimize cache effects.
169	<	*/
170	<	private static final int INITIAL_QUEUE_CAPACITY = 1 << 13;
171	<
172	<	/**
173	<	* Maximum work-stealing queue array size.  Must be less than or
174	<	* equal to 1 << (31 - width of array entry) to ensure lack of
175	<	* index wraparound. The value is set in the static block
176	<	* at the end of this file after obtaining width.
177	<	*/
178	<	private static final int MAXIMUM_QUEUE_CAPACITY;
179	<
180	<	/**
181	<	* The pool this thread works in. Accessed directly by ForkJoinTask.
182	<	*/
183	<	final ForkJoinPool pool;
184	<
185	<	/**
186	<	* The work-stealing queue array. Size must be a power of two.
187	<	* Initialized in onStart, to improve memory locality.
188	<	*/
189	<	private ForkJoinTask<?>[] queue;
190	<
191	<	/**
192	<	* Index (mod queue.length) of least valid queue slot, which is
193	<	* always the next position to steal from if nonempty.
194	<	*/
195	<	private volatile int base;
196	<
197	<	/**
198	<	* Index (mod queue.length) of next queue slot to push to or pop
199	<	* from. It is written only by owner thread, and accessed by other
200	<	* threads only after reading (volatile) base.  Both sp and base
201	<	* are allowed to wrap around on overflow, but (sp - base) still
202	<	* estimates size.
203	<	*/
204	<	private int sp;
205	<
206	<	/**
207	<	* The index of most recent stealer, used as a hint to avoid
208	<	* traversal in method helpJoinTask. This is only a hint because a
209	<	* worker might have had multiple steals and this only holds one
210	<	* of them (usually the most current). Declared non-volatile,
211	<	* relying on other prevailing sync to keep reasonably current.
212	<	*/
213	<	private int stealHint;
214	<
215	<	/**
216	<	* Run state of this worker. In addition to the usual run levels,
217	<	* tracks if this worker is suspended as a spare, and if it was
218	<	* killed (trimmed) while suspended. However, "active" status is
219	<	* maintained separately and modified only in conjunction with
220	<	* CASes of the pool's runState (which are currently sadly
221	<	* manually inlined for performance.)  Accessed directly by pool
222	<	* to simplify checks for normal (zero) status.
223	<	*/
224	<	volatile int runState;
225	<
226	<	private static final int TERMINATING = 0x01;
227	<	private static final int TERMINATED  = 0x02;
228	<	private static final int SUSPENDED   = 0x04; // inactive spare
229	<	private static final int TRIMMED     = 0x08; // killed while suspended
230	<
231	<	/**
232	<	* Number of steals. Directly accessed (and reset) by
233	<	* pool.tryAccumulateStealCount when idle.
234	<	*/
235	<	int stealCount;
236	<
237	<	/**
238	<	* Seed for random number generator for choosing steal victims.
239	<	* Uses Marsaglia xorshift. Must be initialized as nonzero.
240	<	*/
241	<	private int seed;
242	<
243	<	/**
244	<	* Activity status. When true, this worker is considered active.
245	<	* Accessed directly by pool.  Must be false upon construction.
246	<	*/
247	<	boolean active;
248	<
249	<	/**
250	<	* True if use local fifo, not default lifo, for local polling.
251	<	* Shadows value from ForkJoinPool.
252	<	*/
253	<	private final boolean locallyFifo;
254	<
255	<	/**
256	<	* Index of this worker in pool array. Set once by pool before
257	<	* running, and accessed directly by pool to locate this worker in
258	<	* its workers array.
259	<	*/
260	<	int poolIndex;
261	<
262	<	/**
263	<	* The last pool event waited for. Accessed only by pool in
264	<	* callback methods invoked within this thread.
265	<	*/
266	<	int lastEventCount;
267	<
268	<	/**
269	<	* Encoded index and event count of next event waiter. Accessed
270	<	* only by ForkJoinPool for managing event waiters.
271	<	*/
272	<	volatile long nextWaiter;
273	<
274	<	/**
275	<	* Number of times this thread suspended as spare. Accessed only
276	<	* by pool.
277	<	*/
278	<	int spareCount;
279	<
280	<	/**
281	<	* Encoded index and count of next spare waiter. Accessed only
282	<	* by ForkJoinPool for managing spares.
26	>	* ForkJoinTasks. For explanation, see the internal documentation
27	>	* of class ForkJoinPool.
28		*/
284	–	volatile int nextSpare;
29
30	<	/**
31	<	* The task currently being joined, set only when actively trying
288	<	* to help other stealers in helpJoinTask. Written only by this
289	<	* thread, but read by others.
290	<	*/
291	<	private volatile ForkJoinTask<?> currentJoin;
30	>	final ForkJoinPool.WorkQueue workQueue; // Work-stealing mechanics
31	>	final ForkJoinPool pool;                // the pool this thread works in
32
33		/**
34	<	* The task most recently stolen from another worker (or
35	<	* submission queue).  Written only by this thread, but read by
36	<	* others.
34	>	* An initial name for a newly constructed worker, used until
35	>	* onStart can establish a useful name. This removes need to
36	>	* establish a name from worker startup path.
37		*/
38	<	private volatile ForkJoinTask<?> currentSteal;
38	>	static final String provisionalName = "aForkJoinWorkerThread";
39
40		/**
41		* Creates a ForkJoinWorkerThread operating in the given pool.
#	Line 304 | Line 44 | public class ForkJoinWorkerThread extend
44		* @throws NullPointerException if pool is null
45		*/
46		protected ForkJoinWorkerThread(ForkJoinPool pool) {
47	<	this.pool = pool;
48	<	this.locallyFifo = pool.locallyFifo;
309	<	setDaemon(true);
310	<	// To avoid exposing construction details to subclasses,
311	<	// remaining initialization is in start() and onStart()
312	<	}
313	<
314	<	/**
315	<	* Performs additional initialization and starts this thread.
316	<	*/
317	<	final void start(int poolIndex, UncaughtExceptionHandler ueh) {
318	<	this.poolIndex = poolIndex;
47	>	super(provisionalName); // bootstrap name
48	>	Thread.UncaughtExceptionHandler ueh = pool.ueh;
49		if (ueh != null)
50		setUncaughtExceptionHandler(ueh);
51	<	start();
51	>	setDaemon(true);
52	>	this.pool = pool;
53	>	pool.registerWorker(this.workQueue = new ForkJoinPool.WorkQueue
54	>	(pool, this, pool.localMode));
55		}
56
324	–	// Public/protected methods
325	–
57		/**
58		* Returns the pool hosting this thread.
59		*
#	Line 342 | Line 73 | public class ForkJoinWorkerThread extend
73		* @return the index number
74		*/
75		public int getPoolIndex() {
76	<	return poolIndex;
76	>	return workQueue.poolIndex;
77		}
78
79		/**
80		* Initializes internal state after construction but before
81		* processing any tasks. If you override this method, you must
82	<	* invoke @code{super.onStart()} at the beginning of the method.
82	>	* invoke {@code super.onStart()} at the beginning of the method.
83		* Initialization requires care: Most fields must have legal
84		* default values, to ensure that attempted accesses from other
85		* threads work correctly even before this thread starts
86		* processing tasks.
87		*/
88		protected void onStart() {
89	<	int rs = seedGenerator.nextInt();
90	<	seed = rs == 0? 1 : rs; // seed must be nonzero
91	<
92	<	// Allocate name string and arrays in this thread
362	<	String pid = Integer.toString(pool.getPoolNumber());
363	<	String wid = Integer.toString(poolIndex);
364	<	setName("ForkJoinPool-" + pid + "-worker-" + wid);
365	<
366	<	queue = new ForkJoinTask<?>[INITIAL_QUEUE_CAPACITY];
89	>	String pref; // replace bootstrap name
90	>	if (provisionalName.equals(getName()) &&
91	>	(pref = pool.workerNamePrefix) != null)
92	>	setName(pref.concat(Long.toString(getId())));
93		}
94
95		/**
#	Line 375 | Line 101 | public class ForkJoinWorkerThread extend
101		* to an unrecoverable error, or {@code null} if completed normally
102		*/
103		protected void onTermination(Throwable exception) {
378	–	try {
379	–	ForkJoinPool p = pool;
380	–	if (active) {
381	–	int a; // inline p.tryDecrementActiveCount
382	–	active = false;
383	–	do {} while (!UNSAFE.compareAndSwapInt
384	–	(p, poolRunStateOffset, a = p.runState, a - 1));
385	–	}
386	–	cancelTasks();
387	–	setTerminated();
388	–	p.workerTerminated(this);
389	–	} catch (Throwable ex) {        // Shouldn't ever happen
390	–	if (exception == null)      // but if so, at least rethrown
391	–	exception = ex;
392	–	} finally {
393	–	if (exception != null)
394	–	UNSAFE.throwException(exception);
395	–	}
104		}
105
106		/**
107		* This method is required to be public, but should never be
108		* called explicitly. It performs the main run loop to execute
109	<	* ForkJoinTasks.
109	>	* {@link ForkJoinTask}s.
110		*/
111		public void run() {
112		Throwable exception = null;
113		try {
114		onStart();
115	<	mainLoop();
115	>	pool.runWorker(workQueue);
116		} catch (Throwable ex) {
117		exception = ex;
118		} finally {
411	–	onTermination(exception);
412	–	}
413	–	}
414	–
415	–	// helpers for run()
416	–
417	–	/**
418	–	* Finds and executes tasks, and checks status while running.
419	–	*/
420	–	private void mainLoop() {
421	–	boolean ran = false; // true if ran a task on last step
422	–	ForkJoinPool p = pool;
423	–	for (;;) {
424	–	p.preStep(this, ran);
425	–	if (runState != 0)
426	–	break;
427	–	ran = tryExecSteal() || tryExecSubmission();
428	–	}
429	–	}
430	–
431	–	/**
432	–	* Tries to steal a task and execute it.
433	–	*
434	–	* @return true if ran a task
435	–	*/
436	–	private boolean tryExecSteal() {
437	–	ForkJoinTask<?> t;
438	–	if ((t = scan()) != null) {
439	–	t.quietlyExec();
440	–	UNSAFE.putOrderedObject(this, currentStealOffset, null);
441	–	if (sp != base)
442	–	execLocalTasks();
443	–	return true;
444	–	}
445	–	return false;
446	–	}
447	–
448	–	/**
449	–	* If a submission exists, try to activate and run it.
450	–	*
451	–	* @return true if ran a task
452	–	*/
453	–	private boolean tryExecSubmission() {
454	–	ForkJoinPool p = pool;
455	–	// This loop is needed in case attempt to activate fails, in
456	–	// which case we only retry if there still appears to be a
457	–	// submission.
458	–	while (p.hasQueuedSubmissions()) {
459	–	ForkJoinTask<?> t; int a;
460	–	if (active || // inline p.tryIncrementActiveCount
461	–	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
462	–	a = p.runState, a + 1))) {
463	–	if ((t = p.pollSubmission()) != null) {
464	–	UNSAFE.putOrderedObject(this, currentStealOffset, t);
465	–	t.quietlyExec();
466	–	UNSAFE.putOrderedObject(this, currentStealOffset, null);
467	–	if (sp != base)
468	–	execLocalTasks();
469	–	return true;
470	–	}
471	–	}
472	–	}
473	–	return false;
474	–	}
475	–
476	–	/**
477	–	* Runs local tasks until queue is empty or shut down.  Call only
478	–	* while active.
479	–	*/
480	–	private void execLocalTasks() {
481	–	while (runState == 0) {
482	–	ForkJoinTask<?> t = locallyFifo ? locallyDeqTask() : popTask();
483	–	if (t != null)
484	–	t.quietlyExec();
485	–	else if (sp == base)
486	–	break;
487	–	}
488	–	}
489	–
490	–	/*
491	–	* Intrinsics-based atomic writes for queue slots. These are
492	–	* basically the same as methods in AtomicReferenceArray, but
493	–	* specialized for (1) ForkJoinTask elements (2) requirement that
494	–	* nullness and bounds checks have already been performed by
495	–	* callers and (3) effective offsets are known not to overflow
496	–	* from int to long (because of MAXIMUM_QUEUE_CAPACITY). We don't
497	–	* need corresponding version for reads: plain array reads are OK
498	–	* because they are protected by other volatile reads and are
499	–	* confirmed by CASes.
500	–	*
501	–	* Most uses don't actually call these methods, but instead contain
502	–	* inlined forms that enable more predictable optimization.  We
503	–	* don't define the version of write used in pushTask at all, but
504	–	* instead inline there a store-fenced array slot write.
505	–	*/
506	–
507	–	/**
508	–	* CASes slot i of array q from t to null. Caller must ensure q is
509	–	* non-null and index is in range.
510	–	*/
511	–	private static final boolean casSlotNull(ForkJoinTask<?>[] q, int i,
512	–	ForkJoinTask<?> t) {
513	–	return UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null);
514	–	}
515	–
516	–	/**
517	–	* Performs a volatile write of the given task at given slot of
518	–	* array q.  Caller must ensure q is non-null and index is in
519	–	* range. This method is used only during resets and backouts.
520	–	*/
521	–	private static final void writeSlot(ForkJoinTask<?>[] q, int i,
522	–	ForkJoinTask<?> t) {
523	–	UNSAFE.putObjectVolatile(q, (i << qShift) + qBase, t);
524	–	}
525	–
526	–	// queue methods
527	–
528	–	/**
529	–	* Pushes a task. Call only from this thread.
530	–	*
531	–	* @param t the task. Caller must ensure non-null.
532	–	*/
533	–	final void pushTask(ForkJoinTask<?> t) {
534	–	ForkJoinTask<?>[] q = queue;
535	–	int mask = q.length - 1; // implicit assert q != null
536	–	int s = sp++;            // ok to increment sp before slot write
537	–	UNSAFE.putOrderedObject(q, ((s & mask) << qShift) + qBase, t);
538	–	if ((s -= base) == 0)
539	–	pool.signalWork();   // was empty
540	–	else if (s == mask)
541	–	growQueue();         // is full
542	–	}
543	–
544	–	/**
545	–	* Tries to take a task from the base of the queue, failing if
546	–	* empty or contended. Note: Specializations of this code appear
547	–	* in locallyDeqTask and elsewhere.
548	–	*
549	–	* @return a task, or null if none or contended
550	–	*/
551	–	final ForkJoinTask<?> deqTask() {
552	–	ForkJoinTask<?> t;
553	–	ForkJoinTask<?>[] q;
554	–	int b, i;
555	–	if (sp != (b = base) &&
556	–	(q = queue) != null && // must read q after b
557	–	(t = q[i = (q.length - 1) & b]) != null && base == b &&
558	–	UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase, t, null)) {
559	–	base = b + 1;
560	–	return t;
561	–	}
562	–	return null;
563	–	}
564	–
565	–	/**
566	–	* Tries to take a task from the base of own queue. Assumes active
567	–	* status.  Called only by this thread.
568	–	*
569	–	* @return a task, or null if none
570	–	*/
571	–	final ForkJoinTask<?> locallyDeqTask() {
572	–	ForkJoinTask<?>[] q = queue;
573	–	if (q != null) {
574	–	ForkJoinTask<?> t;
575	–	int b, i;
576	–	while (sp != (b = base)) {
577	–	if ((t = q[i = (q.length - 1) & b]) != null && base == b &&
578	–	UNSAFE.compareAndSwapObject(q, (i << qShift) + qBase,
579	–	t, null)) {
580	–	base = b + 1;
581	–	return t;
582	–	}
583	–	}
584	–	}
585	–	return null;
586	–	}
587	–
588	–	/**
589	–	* Returns a popped task, or null if empty. Assumes active status.
590	–	* Called only by this thread.
591	–	*/
592	–	private ForkJoinTask<?> popTask() {
593	–	ForkJoinTask<?>[] q = queue;
594	–	if (q != null) {
595	–	int s;
596	–	while ((s = sp) != base) {
597	–	int i = (q.length - 1) & --s;
598	–	long u = (i << qShift) + qBase; // raw offset
599	–	ForkJoinTask<?> t = q[i];
600	–	if (t == null)   // lost to stealer
601	–	break;
602	–	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
603	–	sp = s; // putOrderedInt may encourage more timely write
604	–	// UNSAFE.putOrderedInt(this, spOffset, s);
605	–	return t;
606	–	}
607	–	}
608	–	}
609	–	return null;
610	–	}
611	–
612	–	/**
613	–	* Specialized version of popTask to pop only if topmost element
614	–	* is the given task. Called only by this thread while active.
615	–	*
616	–	* @param t the task. Caller must ensure non-null.
617	–	*/
618	–	final boolean unpushTask(ForkJoinTask<?> t) {
619	–	int s;
620	–	ForkJoinTask<?>[] q = queue;
621	–	if ((s = sp) != base && q != null &&
622	–	UNSAFE.compareAndSwapObject
623	–	(q, (((q.length - 1) & --s) << qShift) + qBase, t, null)) {
624	–	sp = s; // putOrderedInt may encourage more timely write
625	–	// UNSAFE.putOrderedInt(this, spOffset, s);
626	–	return true;
627	–	}
628	–	return false;
629	–	}
630	–
631	–	/**
632	–	* Returns next task, or null if empty or contended.
633	–	*/
634	–	final ForkJoinTask<?> peekTask() {
635	–	ForkJoinTask<?>[] q = queue;
636	–	if (q == null)
637	–	return null;
638	–	int mask = q.length - 1;
639	–	int i = locallyFifo ? base : (sp - 1);
640	–	return q[i & mask];
641	–	}
642	–
643	–	/**
644	–	* Doubles queue array size. Transfers elements by emulating
645	–	* steals (deqs) from old array and placing, oldest first, into
646	–	* new array.
647	–	*/
648	–	private void growQueue() {
649	–	ForkJoinTask<?>[] oldQ = queue;
650	–	int oldSize = oldQ.length;
651	–	int newSize = oldSize << 1;
652	–	if (newSize > MAXIMUM_QUEUE_CAPACITY)
653	–	throw new RejectedExecutionException("Queue capacity exceeded");
654	–	ForkJoinTask<?>[] newQ = queue = new ForkJoinTask<?>[newSize];
655	–
656	–	int b = base;
657	–	int bf = b + oldSize;
658	–	int oldMask = oldSize - 1;
659	–	int newMask = newSize - 1;
660	–	do {
661	–	int oldIndex = b & oldMask;
662	–	ForkJoinTask<?> t = oldQ[oldIndex];
663	–	if (t != null && !casSlotNull(oldQ, oldIndex, t))
664	–	t = null;
665	–	writeSlot(newQ, b & newMask, t);
666	–	} while (++b != bf);
667	–	pool.signalWork();
668	–	}
669	–
670	–	/**
671	–	* Computes next value for random victim probe in scan().  Scans
672	–	* don't require a very high quality generator, but also not a
673	–	* crummy one.  Marsaglia xor-shift is cheap and works well enough.
674	–	* Note: This is manually inlined in scan().
675	–	*/
676	–	private static final int xorShift(int r) {
677	–	r ^= r << 13;
678	–	r ^= r >>> 17;
679	–	return r ^ (r << 5);
680	–	}
681	–
682	–	/**
683	–	* Tries to steal a task from another worker. Starts at a random
684	–	* index of workers array, and probes workers until finding one
685	–	* with non-empty queue or finding that all are empty.  It
686	–	* randomly selects the first n probes. If these are empty, it
687	–	* resorts to a circular sweep, which is necessary to accurately
688	–	* set active status. (The circular sweep uses steps of
689	–	* approximately half the array size plus 1, to avoid bias
690	–	* stemming from leftmost packing of the array in ForkJoinPool.)
691	–	*
692	–	* This method must be both fast and quiet -- usually avoiding
693	–	* memory accesses that could disrupt cache sharing etc other than
694	–	* those needed to check for and take tasks (or to activate if not
695	–	* already active). This accounts for, among other things,
696	–	* updating random seed in place without storing it until exit.
697	–	*
698	–	* @return a task, or null if none found
699	–	*/
700	–	private ForkJoinTask<?> scan() {
701	–	ForkJoinPool p = pool;
702	–	ForkJoinWorkerThread[] ws;        // worker array
703	–	int n;                            // upper bound of #workers
704	–	if ((ws = p.workers) != null && (n = ws.length) > 1) {
705	–	boolean canSteal = active;    // shadow active status
706	–	int r = seed;                 // extract seed once
707	–	int mask = n - 1;
708	–	int j = -n;                   // loop counter
709	–	int k = r;                    // worker index, random if j < 0
710	–	for (;;) {
711	–	ForkJoinWorkerThread v = ws[k & mask];
712	–	r ^= r << 13; r ^= r >>> 17; r ^= r << 5; // inline xorshift
713	–	ForkJoinTask<?>[] q; ForkJoinTask<?> t; int b, a;
714	–	if (v != null && (b = v.base) != v.sp &&
715	–	(q = v.queue) != null) {
716	–	int i = (q.length - 1) & b;
717	–	long u = (i << qShift) + qBase; // raw offset
718	–	int pid = poolIndex;
719	–	if ((t = q[i]) != null) {
720	–	if (!canSteal &&  // inline p.tryIncrementActiveCount
721	–	UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
722	–	a = p.runState, a + 1))
723	–	canSteal = active = true;
724	–	if (canSteal && v.base == b++ &&
725	–	UNSAFE.compareAndSwapObject(q, u, t, null)) {
726	–	v.base = b;
727	–	v.stealHint = pid;
728	–	UNSAFE.putOrderedObject(this,
729	–	currentStealOffset, t);
730	–	seed = r;
731	–	++stealCount;
732	–	return t;
733	–	}
734	–	}
735	–	j = -n;
736	–	k = r;                // restart on contention
737	–	}
738	–	else if (++j <= 0)
739	–	k = r;
740	–	else if (j <= n)
741	–	k += (n >>> 1) | 1;
742	–	else
743	–	break;
744	–	}
745	–	}
746	–	return null;
747	–	}
748	–
749	–	// Run State management
750	–
751	–	// status check methods used mainly by ForkJoinPool
752	–	final boolean isRunning()    { return runState == 0; }
753	–	final boolean isTerminated() { return (runState & TERMINATED) != 0; }
754	–	final boolean isSuspended()  { return (runState & SUSPENDED) != 0; }
755	–	final boolean isTrimmed()    { return (runState & TRIMMED) != 0; }
756	–
757	–	final boolean isTerminating() {
758	–	if ((runState & TERMINATING) != 0)
759	–	return true;
760	–	if (pool.isAtLeastTerminating()) { // propagate pool state
761	–	shutdown();
762	–	return true;
763	–	}
764	–	return false;
765	–	}
766	–
767	–	/**
768	–	* Sets state to TERMINATING. Does NOT unpark or interrupt
769	–	* to wake up if currently blocked. Callers must do so if desired.
770	–	*/
771	–	final void shutdown() {
772	–	for (;;) {
773	–	int s = runState;
774	–	if ((s & (TERMINATING|TERMINATED)) != 0)
775	–	break;
776	–	if ((s & SUSPENDED) != 0) { // kill and wakeup if suspended
777	–	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
778	–	(s & ~SUSPENDED) |
779	–	(TRIMMED|TERMINATING)))
780	–	break;
781	–	}
782	–	else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
783	–	s | TERMINATING))
784	–	break;
785	–	}
786	–	}
787	–
788	–	/**
789	–	* Sets state to TERMINATED. Called only by onTermination().
790	–	*/
791	–	private void setTerminated() {
792	–	int s;
793	–	do {} while (!UNSAFE.compareAndSwapInt(this, runStateOffset,
794	–	s = runState,
795	–	s | (TERMINATING|TERMINATED)));
796	–	}
797	–
798	–	/**
799	–	* If suspended, tries to set status to unsuspended.
800	–	* Does NOT wake up if blocked.
801	–	*
802	–	* @return true if successful
803	–	*/
804	–	final boolean tryUnsuspend() {
805	–	int s;
806	–	while (((s = runState) & SUSPENDED) != 0) {
807	–	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
808	–	s & ~SUSPENDED))
809	–	return true;
810	–	}
811	–	return false;
812	–	}
813	–
814	–	/**
815	–	* Sets suspended status and blocks as spare until resumed
816	–	* or shutdown.
817	–	*/
818	–	final void suspendAsSpare() {
819	–	for (;;) {                  // set suspended unless terminating
820	–	int s = runState;
821	–	if ((s & TERMINATING) != 0) { // must kill
822	–	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
823	–	s | (TRIMMED | TERMINATING)))
824	–	return;
825	–	}
826	–	else if (UNSAFE.compareAndSwapInt(this, runStateOffset, s,
827	–	s | SUSPENDED))
828	–	break;
829	–	}
830	–	ForkJoinPool p = pool;
831	–	p.pushSpare(this);
832	–	while ((runState & SUSPENDED) != 0) {
833	–	if (p.tryAccumulateStealCount(this)) {
834	–	interrupted();          // clear/ignore interrupts
835	–	if ((runState & SUSPENDED) == 0)
836	–	break;
837	–	LockSupport.park(this);
838	–	}
839	–	}
840	–	}
841	–
842	–	// Misc support methods for ForkJoinPool
843	–
844	–	/**
845	–	* Returns an estimate of the number of tasks in the queue.  Also
846	–	* used by ForkJoinTask.
847	–	*/
848	–	final int getQueueSize() {
849	–	int n; // external calls must read base first
850	–	return (n = -base + sp) <= 0 ? 0 : n;
851	–	}
852	–
853	–	/**
854	–	* Removes and cancels all tasks in queue.  Can be called from any
855	–	* thread.
856	–	*/
857	–	final void cancelTasks() {
858	–	ForkJoinTask<?> cj = currentJoin; // try to cancel ongoing tasks
859	–	if (cj != null) {
860	–	currentJoin = null;
861	–	cj.cancelIgnoringExceptions();
862	–	try {
863	–	this.interrupt(); // awaken wait
864	–	} catch (SecurityException ignore) {
865	–	}
866	–	}
867	–	ForkJoinTask<?> cs = currentSteal;
868	–	if (cs != null) {
869	–	currentSteal = null;
870	–	cs.cancelIgnoringExceptions();
871	–	}
872	–	while (base != sp) {
873	–	ForkJoinTask<?> t = deqTask();
874	–	if (t != null)
875	–	t.cancelIgnoringExceptions();
876	–	}
877	–	}
878	–
879	–	/**
880	–	* Drains tasks to given collection c.
881	–	*
882	–	* @return the number of tasks drained
883	–	*/
884	–	final int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
885	–	int n = 0;
886	–	while (base != sp) {
887	–	ForkJoinTask<?> t = deqTask();
888	–	if (t != null) {
889	–	c.add(t);
890	–	++n;
891	–	}
892	–	}
893	–	return n;
894	–	}
895	–
896	–	// Support methods for ForkJoinTask
897	–
898	–	/**
899	–	* Gets and removes a local task.
900	–	*
901	–	* @return a task, if available
902	–	*/
903	–	final ForkJoinTask<?> pollLocalTask() {
904	–	ForkJoinPool p = pool;
905	–	while (sp != base) {
906	–	int a; // inline p.tryIncrementActiveCount
907	–	if (active ||
908	–	(active = UNSAFE.compareAndSwapInt(p, poolRunStateOffset,
909	–	a = p.runState, a + 1)))
910	–	return locallyFifo ? locallyDeqTask() : popTask();
911	–	}
912	–	return null;
913	–	}
914	–
915	–	/**
916	–	* Gets and removes a local or stolen task.
917	–	*
918	–	* @return a task, if available
919	–	*/
920	–	final ForkJoinTask<?> pollTask() {
921	–	ForkJoinTask<?> t = pollLocalTask();
922	–	if (t == null) {
923	–	t = scan();
924	–	// cannot retain/track/help steal
925	–	UNSAFE.putOrderedObject(this, currentStealOffset, null);
926	–	}
927	–	return t;
928	–	}
929	–
930	–	/**
931	–	* Possibly runs some tasks and/or blocks, until task is done.
932	–	*
933	–	* @param joinMe the task to join
934	–	* @param timed true if use timed wait
935	–	* @param nanos wait time if timed
936	–	*/
937	–	final void joinTask(ForkJoinTask<?> joinMe, boolean timed, long nanos) {
938	–	// currentJoin only written by this thread; only need ordered store
939	–	ForkJoinTask<?> prevJoin = currentJoin;
940	–	UNSAFE.putOrderedObject(this, currentJoinOffset, joinMe);
941	–	if (isTerminating())                // cancel if shutting down
942	–	joinMe.cancelIgnoringExceptions();
943	–	else {
944	–	if (sp != base)
945	–	localHelpJoinTask(joinMe);
946	–	if (joinMe.status >= 0)
947	–	pool.awaitJoin(joinMe, this, timed, nanos);
948	–	}
949	–	UNSAFE.putOrderedObject(this, currentJoinOffset, prevJoin);
950	–	}
951	–
952	–	/**
953	–	* Run tasks in local queue until given task is done.
954	–	*
955	–	* @param joinMe the task to join
956	–	*/
957	–	private void localHelpJoinTask(ForkJoinTask<?> joinMe) {
958	–	int s;
959	–	ForkJoinTask<?>[] q;
960	–	while (joinMe.status >= 0 && (s = sp) != base && (q = queue) != null) {
961	–	int i = (q.length - 1) & --s;
962	–	long u = (i << qShift) + qBase; // raw offset
963	–	ForkJoinTask<?> t = q[i];
964	–	if (t == null)  // lost to a stealer
965	–	break;
966	–	if (UNSAFE.compareAndSwapObject(q, u, t, null)) {
967	–	/*
968	–	* This recheck (and similarly in helpJoinTask)
969	–	* handles cases where joinMe is independently
970	–	* cancelled or forced even though there is other work
971	–	* available. Back out of the pop by putting t back
972	–	* into slot before we commit by writing sp.
973	–	*/
974	–	if (joinMe.status < 0) {
975	–	UNSAFE.putObjectVolatile(q, u, t);
976	–	break;
977	–	}
978	–	sp = s;
979	–	// UNSAFE.putOrderedInt(this, spOffset, s);
980	–	t.quietlyExec();
981	–	}
982	–	}
983	–	}
984	–
985	–	/**
986	–	* Tries to locate and help perform tasks for a stealer of the
987	–	* given task, or in turn one of its stealers.  Traces
988	–	* currentSteal->currentJoin links looking for a thread working on
989	–	* a descendant of the given task and with a non-empty queue to
990	–	* steal back and execute tasks from.
991	–	*
992	–	* The implementation is very branchy to cope with potential
993	–	* inconsistencies or loops encountering chains that are stale,
994	–	* unknown, or of length greater than MAX_HELP_DEPTH links.  All
995	–	* of these cases are dealt with by just returning back to the
996	–	* caller, who is expected to retry if other join mechanisms also
997	–	* don't work out.
998	–	*
999	–	* @param joinMe the task to join
1000	–	*/
1001	–	final void helpJoinTask(ForkJoinTask<?> joinMe) {
1002	–	ForkJoinWorkerThread[] ws;
1003	–	int n;
1004	–	if (joinMe.status < 0)                // already done
1005	–	return;
1006	–	if ((ws = pool.workers) == null || (n = ws.length) <= 1)
1007	–	return;                           // need at least 2 workers
1008	–
1009	–	ForkJoinTask<?> task = joinMe;        // base of chain
1010	–	ForkJoinWorkerThread thread = this;   // thread with stolen task
1011	–	for (int d = 0; d < MAX_HELP_DEPTH; ++d) { // chain length
1012	–	// Try to find v, the stealer of task, by first using hint
1013	–	ForkJoinWorkerThread v = ws[thread.stealHint & (n - 1)];
1014	–	if (v == null || v.currentSteal != task) {
1015	–	for (int j = 0; ; ++j) {      // search array
1016	–	if (j < n) {
1017	–	ForkJoinTask<?> vs;
1018	–	if ((v = ws[j]) != null &&
1019	–	(vs = v.currentSteal) != null) {
1020	–	if (joinMe.status < 0 || task.status < 0)
1021	–	return;       // stale or done
1022	–	if (vs == task) {
1023	–	thread.stealHint = j;
1024	–	break;        // save hint for next time
1025	–	}
1026	–	}
1027	–	}
1028	–	else
1029	–	return;               // no stealer
1030	–	}
1031	–	}
1032	–	for (;;) { // Try to help v, using specialized form of deqTask
1033	–	if (joinMe.status < 0)
1034	–	return;
1035	–	int b = v.base;
1036	–	ForkJoinTask<?>[] q = v.queue;
1037	–	if (b == v.sp || q == null)
1038	–	break;
1039	–	int i = (q.length - 1) & b;
1040	–	long u = (i << qShift) + qBase;
1041	–	ForkJoinTask<?> t = q[i];
1042	–	int pid = poolIndex;
1043	–	ForkJoinTask<?> ps = currentSteal;
1044	–	if (task.status < 0)
1045	–	return;                   // stale or done
1046	–	if (t != null && v.base == b++ &&
1047	–	UNSAFE.compareAndSwapObject(q, u, t, null)) {
1048	–	if (joinMe.status < 0) {
1049	–	UNSAFE.putObjectVolatile(q, u, t);
1050	–	return;               // back out on cancel
1051	–	}
1052	–	v.base = b;
1053	–	v.stealHint = pid;
1054	–	UNSAFE.putOrderedObject(this, currentStealOffset, t);
1055	–	t.quietlyExec();
1056	–	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1057	–	}
1058	–	}
1059	–	// Try to descend to find v's stealer
1060	–	ForkJoinTask<?> next = v.currentJoin;
1061	–	if (task.status < 0 || next == null || next == task ||
1062	–	joinMe.status < 0)
1063	–	return;
1064	–	task = next;
1065	–	thread = v;
1066	–	}
1067	–	}
1068	–
1069	–	/**
1070	–	* Implements ForkJoinTask.getSurplusQueuedTaskCount().
1071	–	* Returns an estimate of the number of tasks, offset by a
1072	–	* function of number of idle workers.
1073	–	*
1074	–	* This method provides a cheap heuristic guide for task
1075	–	* partitioning when programmers, frameworks, tools, or languages
1076	–	* have little or no idea about task granularity.  In essence by
1077	–	* offering this method, we ask users only about tradeoffs in
1078	–	* overhead vs expected throughput and its variance, rather than
1079	–	* how finely to partition tasks.
1080	–	*
1081	–	* In a steady state strict (tree-structured) computation, each
1082	–	* thread makes available for stealing enough tasks for other
1083	–	* threads to remain active. Inductively, if all threads play by
1084	–	* the same rules, each thread should make available only a
1085	–	* constant number of tasks.
1086	–	*
1087	–	* The minimum useful constant is just 1. But using a value of 1
1088	–	* would require immediate replenishment upon each steal to
1089	–	* maintain enough tasks, which is infeasible.  Further,
1090	–	* partitionings/granularities of offered tasks should minimize
1091	–	* steal rates, which in general means that threads nearer the top
1092	–	* of computation tree should generate more than those nearer the
1093	–	* bottom. In perfect steady state, each thread is at
1094	–	* approximately the same level of computation tree. However,
1095	–	* producing extra tasks amortizes the uncertainty of progress and
1096	–	* diffusion assumptions.
1097	–	*
1098	–	* So, users will want to use values larger, but not much larger
1099	–	* than 1 to both smooth over transient shortages and hedge
1100	–	* against uneven progress; as traded off against the cost of
1101	–	* extra task overhead. We leave the user to pick a threshold
1102	–	* value to compare with the results of this call to guide
1103	–	* decisions, but recommend values such as 3.
1104	–	*
1105	–	* When all threads are active, it is on average OK to estimate
1106	–	* surplus strictly locally. In steady-state, if one thread is
1107	–	* maintaining say 2 surplus tasks, then so are others. So we can
1108	–	* just use estimated queue length (although note that (sp - base)
1109	–	* can be an overestimate because of stealers lagging increments
1110	–	* of base).  However, this strategy alone leads to serious
1111	–	* mis-estimates in some non-steady-state conditions (ramp-up,
1112	–	* ramp-down, other stalls). We can detect many of these by
1113	–	* further considering the number of "idle" threads, that are
1114	–	* known to have zero queued tasks, so compensate by a factor of
1115	–	* (#idle/#active) threads.
1116	–	*/
1117	–	final int getEstimatedSurplusTaskCount() {
1118	–	return sp - base - pool.idlePerActive();
1119	–	}
1120	–
1121	–	/**
1122	–	* Runs tasks until {@code pool.isQuiescent()}.
1123	–	*/
1124	–	final void helpQuiescePool() {
1125	–	ForkJoinTask<?> ps = currentSteal; // to restore below
1126	–	for (;;) {
1127	–	ForkJoinTask<?> t = pollLocalTask();
1128	–	if (t != null || (t = scan()) != null)
1129	–	t.quietlyExec();
1130	–	else {
1131	–	ForkJoinPool p = pool;
1132	–	int a; // to inline CASes
1133	–	if (active) {
1134	–	if (!UNSAFE.compareAndSwapInt
1135	–	(p, poolRunStateOffset, a = p.runState, a - 1))
1136	–	continue;   // retry later
1137	–	active = false; // inactivate
1138	–	UNSAFE.putOrderedObject(this, currentStealOffset, ps);
1139	–	}
1140	–	if (p.isQuiescent()) {
1141	–	active = true; // re-activate
1142	–	do {} while (!UNSAFE.compareAndSwapInt
1143	–	(p, poolRunStateOffset, a = p.runState, a+1));
1144	–	return;
1145	–	}
1146	–	}
1147	–	}
1148	–	}
1149	–
1150	–	// Unsafe mechanics
1151	–
1152	–	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1153	–	private static final long spOffset =
1154	–	objectFieldOffset("sp", ForkJoinWorkerThread.class);
1155	–	private static final long runStateOffset =
1156	–	objectFieldOffset("runState", ForkJoinWorkerThread.class);
1157	–	private static final long currentJoinOffset =
1158	–	objectFieldOffset("currentJoin", ForkJoinWorkerThread.class);
1159	–	private static final long currentStealOffset =
1160	–	objectFieldOffset("currentSteal", ForkJoinWorkerThread.class);
1161	–	private static final long qBase =
1162	–	UNSAFE.arrayBaseOffset(ForkJoinTask[].class);
1163	–	private static final long poolRunStateOffset = // to inline CAS
1164	–	objectFieldOffset("runState", ForkJoinPool.class);
1165	–
1166	–	private static final int qShift;
1167	–
1168	–	static {
1169	–	int s = UNSAFE.arrayIndexScale(ForkJoinTask[].class);
1170	–	if ((s & (s-1)) != 0)
1171	–	throw new Error("data type scale not a power of two");
1172	–	qShift = 31 - Integer.numberOfLeadingZeros(s);
1173	–	MAXIMUM_QUEUE_CAPACITY = 1 << (31 - qShift);
1174	–	}
1175	–
1176	–	private static long objectFieldOffset(String field, Class<?> klazz) {
1177	–	try {
1178	–	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1179	–	} catch (NoSuchFieldException e) {
1180	–	// Convert Exception to corresponding Error
1181	–	NoSuchFieldError error = new NoSuchFieldError(field);
1182	–	error.initCause(e);
1183	–	throw error;
1184	–	}
1185	–	}
1186	–
1187	–	/**
1188	–	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1189	–	* Replace with a simple call to Unsafe.getUnsafe when integrating
1190	–	* into a jdk.
1191	–	*
1192	–	* @return a sun.misc.Unsafe
1193	–	*/
1194	–	private static sun.misc.Unsafe getUnsafe() {
1195	–	try {
1196	–	return sun.misc.Unsafe.getUnsafe();
1197	–	} catch (SecurityException se) {
119		try {
120	<	return java.security.AccessController.doPrivileged
121	<	(new java.security
122	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
123	<	public sun.misc.Unsafe run() throws Exception {
124	<	java.lang.reflect.Field f = sun.misc
125	<	.Unsafe.class.getDeclaredField("theUnsafe");
1205	<	f.setAccessible(true);
1206	<	return (sun.misc.Unsafe) f.get(null);
1207	<	}});
1208	<	} catch (java.security.PrivilegedActionException e) {
1209	<	throw new RuntimeException("Could not initialize intrinsics",
1210	<	e.getCause());
120	>	onTermination(exception);
121	>	} catch (Throwable ex) {
122	>	if (exception == null)
123	>	exception = ex;
124	>	} finally {
125	>	pool.deregisterWorker(this, exception);
126		}
127		}
128		}

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