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root/jsr166/jsr166/src/jsr166e/StampedLock.java

Comparing jsr166/src/jsr166e/StampedLock.java (file contents):
Revision 1.7 by dl, Fri Oct 12 23:11:14 2012 UTC vs.
Revision 1.39 by jsr166, Sun Jan 18 20:17:33 2015 UTC

#	Line 6 | Line 6
6
7		package jsr166e;
8
9	–	import java.util.concurrent.ThreadLocalRandom;
9		import java.util.concurrent.TimeUnit;
10	+	import java.util.concurrent.locks.Lock;
11	+	import java.util.concurrent.locks.Condition;
12	+	import java.util.concurrent.locks.ReadWriteLock;
13	+	import java.util.concurrent.locks.LockSupport;
14
15		/**
16		* A capability-based lock with three modes for controlling read/write
17	<	* access.  The state of a StampedLock consists of a version and
18	<	* mode. Lock acquisition methods return a stamp that represents and
17	>	* access.  The state of a StampedLock consists of a version and mode.
18	>	* Lock acquisition methods return a stamp that represents and
19		* controls access with respect to a lock state; "try" versions of
20		* these methods may instead return the special value zero to
21		* represent failure to acquire access. Lock release and conversion
#	Line 36 | Line 39 | import java.util.concurrent.TimeUnit;
39		*  <li><b>Optimistic Reading.</b> Method {@link #tryOptimisticRead}
40		*   returns a non-zero stamp only if the lock is not currently held
41		*   in write mode. Method {@link #validate} returns true if the lock
42	<	*   has not since been acquired in write mode. This mode can be
43	<	*   thought of as an extremely weak version of a read-lock, that can
44	<	*   be broken by a writer at any time.  The use of optimistic mode
45	<	*   for short read-only code segments often reduces contention and
46	<	*   improves throughput.  However, its use is inherently fragile.
47	<	*   Optimistic read sections should only read fields and hold them in
48	<	*   local variables for later use after validation. Fields read while
49	<	*   in optimistic mode may be wildly inconsistent, so usage applies
50	<	*   only when you are familiar enough with data representations to
51	<	*   check consistency and/or repeatedly invoke method {@code
52	<	*   validate()}.  For example, such steps are typically required when
53	<	*   first reading an object or array reference, and then accessing
54	<	*   one of its fields, elements or methods. </li>
42	>	*   has not been acquired in write mode since obtaining a given
43	>	*   stamp.  This mode can be thought of as an extremely weak version
44	>	*   of a read-lock, that can be broken by a writer at any time.  The
45	>	*   use of optimistic mode for short read-only code segments often
46	>	*   reduces contention and improves throughput.  However, its use is
47	>	*   inherently fragile.  Optimistic read sections should only read
48	>	*   fields and hold them in local variables for later use after
49	>	*   validation. Fields read while in optimistic mode may be wildly
50	>	*   inconsistent, so usage applies only when you are familiar enough
51	>	*   with data representations to check consistency and/or repeatedly
52	>	*   invoke method {@code validate()}.  For example, such steps are
53	>	*   typically required when first reading an object or array
54	>	*   reference, and then accessing one of its fields, elements or
55	>	*   methods. </li>
56		*
57		* </ul>
58		*
59		* <p>This class also supports methods that conditionally provide
60		* conversions across the three modes. For example, method {@link
61		* #tryConvertToWriteLock} attempts to "upgrade" a mode, returning
62	<	* valid write stamp if (1) already in writing mode (2) in reading
62	>	* a valid write stamp if (1) already in writing mode (2) in reading
63		* mode and there are no other readers or (3) in optimistic mode and
64		* the lock is available. The forms of these methods are designed to
65		* help reduce some of the code bloat that otherwise occurs in
66		* retry-based designs.
67		*
68	<	* <p>StampedLocks are designed for use in a different (and generally
69	<	* narrower) range of contexts than most other locks: They are not
70	<	* reentrant, so locked bodies should not call other unknown methods
71	<	* that may try to re-acquire locks (although you may pass a stamp to
72	<	* other methods that can use or convert it). Unvalidated optimistic
73	<	* read sections should further not call methods that are not known to
68	>	* <p>StampedLocks are designed for use as internal utilities in the
69	>	* development of thread-safe components. Their use relies on
70	>	* knowledge of the internal properties of the data, objects, and
71	>	* methods they are protecting.  They are not reentrant, so locked
72	>	* bodies should not call other unknown methods that may try to
73	>	* re-acquire locks (although you may pass a stamp to other methods
74	>	* that can use or convert it).  The use of read lock modes relies on
75	>	* the associated code sections being side-effect-free.  Unvalidated
76	>	* optimistic read sections cannot call methods that are not known to
77		* tolerate potential inconsistencies.  Stamps use finite
78		* representations, and are not cryptographically secure (i.e., a
79		* valid stamp may be guessable). Stamp values may recycle after (no
#	Line 77 | Line 84 | import java.util.concurrent.TimeUnit;
84		* locking.
85		*
86		* <p>The scheduling policy of StampedLock does not consistently
87	<	* prefer readers over writers or vice versa.  A zero return from any
88	<	* "try" method for acquiring or converting locks does carry any
89	<	* information about the state of the lock; a subsequent invocation
90	<	* may succeed.
87	>	* prefer readers over writers or vice versa.  All "try" methods are
88	>	* best-effort and do not necessarily conform to any scheduling or
89	>	* fairness policy. A zero return from any "try" method for acquiring
90	>	* or converting locks does not carry any information about the state
91	>	* of the lock; a subsequent invocation may succeed.
92	>	*
93	>	* <p>Because it supports coordinated usage across multiple lock
94	>	* modes, this class does not directly implement the {@link Lock} or
95	>	* {@link ReadWriteLock} interfaces. However, a StampedLock may be
96	>	* viewed {@link #asReadLock()}, {@link #asWriteLock()}, or {@link
97	>	* #asReadWriteLock()} in applications requiring only the associated
98	>	* set of functionality.
99		*
100		* <p><b>Sample Usage.</b> The following illustrates some usage idioms
101		* in a class that maintains simple two-dimensional points. The sample
#	Line 103 | Line 118 | import java.util.concurrent.TimeUnit;
118		*     }
119		*   }
120		*
121	<	*   double distanceFromOriginV1() { // A read-only method
122	<	*     long stamp;
123	<	*     if ((stamp = sl.tryOptimisticRead()) != 0L) { // optimistic
124	<	*       double currentX = x;
125	<	*       double currentY = y;
126	<	*       if (sl.validate(stamp))
127	<	*         return Math.sqrt(currentX * currentX + currentY * currentY);
128	<	*     }
129	<	*     stamp = sl.readLock(); // fall back to read lock
130	<	*     try {
131	<	*       double currentX = x;
117	<	*       double currentY = y;
118	<	*         return Math.sqrt(currentX * currentX + currentY * currentY);
119	<	*     } finally {
120	<	*       sl.unlockRead(stamp);
121	<	*     }
122	<	*   }
123	<	*
124	<	*   double distanceFromOriginV2() { // combines code paths
125	<	*     for (long stamp = sl.tryOptimisticRead(); ; stamp = sl.readLock()) {
126	<	*       double currentX, currentY;
127	<	*       try {
128	<	*         currentX = x;
129	<	*         currentY = y;
130	<	*       } finally {
131	<	*         if (sl.tryConvertToOptimisticRead(stamp) != 0L) // unlock or validate
132	<	*           return Math.sqrt(currentX * currentX + currentY * currentY);
133	<	*       }
121	>	*   double distanceFromOrigin() { // A read-only method
122	>	*     long stamp = sl.tryOptimisticRead();
123	>	*     double currentX = x, currentY = y;
124	>	*     if (!sl.validate(stamp)) {
125	>	*        stamp = sl.readLock();
126	>	*        try {
127	>	*          currentX = x;
128	>	*          currentY = y;
129	>	*        } finally {
130	>	*           sl.unlockRead(stamp);
131	>	*        }
132		*     }
133	+	*     return Math.sqrt(currentX * currentX + currentY * currentY);
134		*   }
135		*
136		*   void moveIfAtOrigin(double newX, double newY) { // upgrade
#	Line 139 | Line 138 | import java.util.concurrent.TimeUnit;
138		*     long stamp = sl.readLock();
139		*     try {
140		*       while (x == 0.0 && y == 0.0) {
141	<	*         long ws = tryConvertToWriteLock(stamp);
141	>	*         long ws = sl.tryConvertToWriteLock(stamp);
142		*         if (ws != 0L) {
143		*           stamp = ws;
144		*           x = newX;
#	Line 152 | Line 151 | import java.util.concurrent.TimeUnit;
151		*         }
152		*       }
153		*     } finally {
154	<	*        sl.unlock(stamp);
154	>	*       sl.unlock(stamp);
155		*     }
156		*   }
157		* }}</pre>
#	Line 169 | Line 168 | public class StampedLock implements java
168		* http://www.lameter.com/gelato2005.pdf
169		* and elsewhere; see
170		* Boehm's http://www.hpl.hp.com/techreports/2012/HPL-2012-68.html)
171	<	* Ordered RW locks (see Shirako et al
171	>	* and Ordered RW locks (see Shirako et al
172		* http://dl.acm.org/citation.cfm?id=2312015)
174	–	* and Phase-Fair locks (see Brandenburg & Anderson, especially
175	–	* http://www.cs.unc.edu/~bbb/diss/).
173		*
174		* Conceptually, the primary state of the lock includes a sequence
175		* number that is odd when write-locked and even otherwise.
#	Line 180 | Line 177 | public class StampedLock implements java
177		* read-locked.  The read count is ignored when validating
178		* "optimistic" seqlock-reader-style stamps.  Because we must use
179		* a small finite number of bits (currently 7) for readers, a
180	<	* supplementary reader overflow word is used when then number of
180	>	* supplementary reader overflow word is used when the number of
181		* readers exceeds the count field. We do this by treating the max
182		* reader count value (RBITS) as a spinlock protecting overflow
183		* updates.
184		*
185	<	* Waiting readers and writers use different queues. The writer
186	<	* queue is a modified form of CLH lock.  (For discussion of CLH,
187	<	* see the internal documentation of AbstractQueuedSynchronizer.)
188	<	* The reader "queue" is a form of Treiber stack, that supports
189	<	* simpler/faster operations because order within a queue doesn't
190	<	* matter and all are signalled at once.  However the sequence of
191	<	* threads within the queue vs the current stamp does matter (see
192	<	* Shirako et al) so each carries its incoming stamp value.
193	<	* Waiting writers never need to track sequence values, so they
194	<	* don't.
195	<	*
196	<	* These queue mechanics hardwire the scheduling policy.  Ignoring
197	<	* trylocks, cancellation, and spinning, they implement Phase-Fair
198	<	* preferences:
199	<	*   1. Unlocked writers prefer to signal waiting readers
200	<	*   2. Fully unlocked readers prefer to signal waiting writers
201	<	*   3. When read-locked and a waiting writer exists, the writer
202	<	*      is preferred to incoming readers
185	>	* Waiters use a modified form of CLH lock used in
186	>	* AbstractQueuedSynchronizer (see its internal documentation for
187	>	* a fuller account), where each node is tagged (field mode) as
188	>	* either a reader or writer. Sets of waiting readers are grouped
189	>	* (linked) under a common node (field cowait) so act as a single
190	>	* node with respect to most CLH mechanics.  By virtue of the
191	>	* queue structure, wait nodes need not actually carry sequence
192	>	* numbers; we know each is greater than its predecessor.  This
193	>	* simplifies the scheduling policy to a mainly-FIFO scheme that
194	>	* incorporates elements of Phase-Fair locks (see Brandenburg &
195	>	* Anderson, especially http://www.cs.unc.edu/~bbb/diss/).  In
196	>	* particular, we use the phase-fair anti-barging rule: If an
197	>	* incoming reader arrives while read lock is held but there is a
198	>	* queued writer, this incoming reader is queued.  (This rule is
199	>	* responsible for some of the complexity of method acquireRead,
200	>	* but without it, the lock becomes highly unfair.) Method release
201	>	* does not (and sometimes cannot) itself wake up cowaiters. This
202	>	* is done by the primary thread, but helped by any other threads
203	>	* with nothing better to do in methods acquireRead and
204	>	* acquireWrite.
205		*
206		* These rules apply to threads actually queued. All tryLock forms
207		* opportunistically try to acquire locks regardless of preference
208	<	* rules, and so may "barge" their way in.  Additionally, initial
209	<	* phases of the await* methods (invoked from readLock() and
210	<	* writeLock()) use controlled spins that have similar effect.
211	<	* Phase-fair preferences may also be broken on cancellations due
212	<	* to timeouts and interrupts.  Rule #3 (incoming readers when a
213	<	* waiting writer) is approximated with varying precision in
214	<	* different contexts -- some checks do not account for
215	<	* in-progress spins/signals, and others do not account for
216	<	* cancellations.
208	>	* rules, and so may "barge" their way in.  Randomized spinning is
209	>	* used in the acquire methods to reduce (increasingly expensive)
210	>	* context switching while also avoiding sustained memory
211	>	* thrashing among many threads.  We limit spins to the head of
212	>	* queue. A thread spin-waits up to SPINS times (where each
213	>	* iteration decreases spin count with 50% probability) before
214	>	* blocking. If, upon wakening it fails to obtain lock, and is
215	>	* still (or becomes) the first waiting thread (which indicates
216	>	* that some other thread barged and obtained lock), it escalates
217	>	* spins (up to MAX_HEAD_SPINS) to reduce the likelihood of
218	>	* continually losing to barging threads.
219	>	*
220	>	* Nearly all of these mechanics are carried out in methods
221	>	* acquireWrite and acquireRead, that, as typical of such code,
222	>	* sprawl out because actions and retries rely on consistent sets
223	>	* of locally cached reads.
224		*
225		* As noted in Boehm's paper (above), sequence validation (mainly
226		* method validate()) requires stricter ordering rules than apply
#	Line 234 | Line 240 | public class StampedLock implements java
240		* be subject to future improvements.
241		*/
242
243	+	private static final long serialVersionUID = -6001602636862214147L;
244	+
245		/** Number of processors, for spin control */
246		private static final int NCPU = Runtime.getRuntime().availableProcessors();
247
248	<	/** Maximum number of retries before blocking on acquisition */
249	<	private static final int SPINS = (NCPU > 1) ? 1 << 6 : 1;
248	>	/** Maximum number of retries before enqueuing on acquisition */
249	>	private static final int SPINS = (NCPU > 1) ? 1 << 6 : 0;
250	>
251	>	/** Maximum number of retries before blocking at head on acquisition */
252	>	private static final int HEAD_SPINS = (NCPU > 1) ? 1 << 10 : 0;
253
254		/** Maximum number of retries before re-blocking */
255	<	private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 1;
255	>	private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 16 : 0;
256
257		/** The period for yielding when waiting for overflow spinlock */
258		private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1
259
260		/** The number of bits to use for reader count before overflowing */
261	<	private static final int  LG_READERS = 7;
261	>	private static final int LG_READERS = 7;
262
263		// Values for lock state and stamp operations
264		private static final long RUNIT = 1L;
#	Line 260 | Line 271 | public class StampedLock implements java
271		// Initial value for lock state; avoid failure value zero
272		private static final long ORIGIN = WBIT << 1;
273
274	<	// Special value from cancelled await methods so caller can throw IE
274	>	// Special value from cancelled acquire methods so caller can throw IE
275		private static final long INTERRUPTED = 1L;
276
277	<	// Values for writer status; order matters
277	>	// Values for node status; order matters
278		private static final int WAITING   = -1;
279		private static final int CANCELLED =  1;
280
281	<	/** Wait nodes for readers */
282	<	static final class RNode {
283	<	final long seq;         // stamp value upon enqueue
273	<	volatile Thread waiter; // null if no longer waiting
274	<	volatile RNode next;
275	<	RNode(long s, Thread w) { seq = s; waiter = w; }
276	<	}
281	>	// Modes for nodes (int not boolean to allow arithmetic)
282	>	private static final int RMODE = 0;
283	>	private static final int WMODE = 1;
284
285	<	/** Wait nodes for writers */
285	>	/** Wait nodes */
286		static final class WNode {
280	–	volatile int status;   // 0, WAITING, or CANCELLED
287		volatile WNode prev;
288		volatile WNode next;
289	<	volatile Thread thread;
290	<	WNode(Thread t, WNode p) { thread = t; prev = p; }
289	>	volatile WNode cowait;    // list of linked readers
290	>	volatile Thread thread;   // non-null while possibly parked
291	>	volatile int status;      // 0, WAITING, or CANCELLED
292	>	final int mode;           // RMODE or WMODE
293	>	WNode(int m, WNode p) { mode = m; prev = p; }
294		}
295
296	<	/** Head of writer CLH queue */
296	>	/** Head of CLH queue */
297		private transient volatile WNode whead;
298	<	/** Tail (last) of writer CLH queue */
298	>	/** Tail (last) of CLH queue */
299		private transient volatile WNode wtail;
300	<	/** Head of read queue  */
301	<	private transient volatile RNode rhead;
302	<	/** The state of the lock -- high bits hold sequence, low bits read count */
300	>
301	>	// views
302	>	transient ReadLockView readLockView;
303	>	transient WriteLockView writeLockView;
304	>	transient ReadWriteLockView readWriteLockView;
305	>
306	>	/** Lock sequence/state */
307		private transient volatile long state;
308		/** extra reader count when state read count saturated */
309		private transient int readerOverflow;
310
311		/**
312	<	* Creates a new lock initially in unlocked state.
312	>	* Creates a new lock, initially in unlocked state.
313		*/
314		public StampedLock() {
315		state = ORIGIN;
#	Line 309 | Line 322 | public class StampedLock implements java
322		* @return a stamp that can be used to unlock or convert mode
323		*/
324		public long writeLock() {
325	<	long s, next;
326	<	if (((s = state) & ABITS) == 0L &&
327	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
328	<	return next;
316	<	return awaitWrite(false, 0L);
325	>	long s, next;  // bypass acquireWrite in fully unlocked case only
326	>	return ((((s = state) & ABITS) == 0L &&
327	>	U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ?
328	>	next : acquireWrite(false, 0L));
329		}
330
331		/**
332		* Exclusively acquires the lock if it is immediately available.
333		*
334		* @return a stamp that can be used to unlock or convert mode,
335	<	* or zero if the lock is not available.
335	>	* or zero if the lock is not available
336		*/
337		public long tryWriteLock() {
338		long s, next;
339	<	if (((s = state) & ABITS) == 0L &&
340	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
341	<	return next;
330	<	return 0L;
339	>	return ((((s = state) & ABITS) == 0L &&
340	>	U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ?
341	>	next : 0L);
342		}
343
344		/**
345		* Exclusively acquires the lock if it is available within the
346		* given time and the current thread has not been interrupted.
347	+	* Behavior under timeout and interruption matches that specified
348	+	* for method {@link Lock#tryLock(long,TimeUnit)}.
349		*
350	+	* @param time the maximum time to wait for the lock
351	+	* @param unit the time unit of the {@code time} argument
352		* @return a stamp that can be used to unlock or convert mode,
353		* or zero if the lock is not available
354		* @throws InterruptedException if the current thread is interrupted
#	Line 343 | Line 358 | public class StampedLock implements java
358		throws InterruptedException {
359		long nanos = unit.toNanos(time);
360		if (!Thread.interrupted()) {
361	<	long s, next, deadline;
362	<	if (((s = state) & ABITS) == 0L &&
348	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
361	>	long next, deadline;
362	>	if ((next = tryWriteLock()) != 0L)
363		return next;
364		if (nanos <= 0L)
365		return 0L;
366		if ((deadline = System.nanoTime() + nanos) == 0L)
367		deadline = 1L;
368	<	if ((next = awaitWrite(true, deadline)) != INTERRUPTED)
368	>	if ((next = acquireWrite(true, deadline)) != INTERRUPTED)
369		return next;
370		}
371		throw new InterruptedException();
#	Line 360 | Line 374 | public class StampedLock implements java
374		/**
375		* Exclusively acquires the lock, blocking if necessary
376		* until available or the current thread is interrupted.
377	+	* Behavior under interruption matches that specified
378	+	* for method {@link Lock#lockInterruptibly()}.
379		*
380		* @return a stamp that can be used to unlock or convert mode
381		* @throws InterruptedException if the current thread is interrupted
382		* before acquiring the lock
383		*/
384		public long writeLockInterruptibly() throws InterruptedException {
385	<	if (!Thread.interrupted()) {
386	<	long s, next;
387	<	if (((s = state) & ABITS) == 0L &&
388	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
373	<	return next;
374	<	if ((next = awaitWrite(true, 0L)) != INTERRUPTED)
375	<	return next;
376	<	}
385	>	long next;
386	>	if (!Thread.interrupted() &&
387	>	(next = acquireWrite(true, 0L)) != INTERRUPTED)
388	>	return next;
389		throw new InterruptedException();
390		}
391
#	Line 384 | Line 396 | public class StampedLock implements java
396		* @return a stamp that can be used to unlock or convert mode
397		*/
398		public long readLock() {
399	<	for (;;) {
400	<	long s, m, next;
401	<	if ((m = (s = state) & ABITS) == 0L ||
402	<	(m < WBIT && whead == wtail)) {
391	<	if (m < RFULL) {
392	<	if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
393	<	return next;
394	<	}
395	<	else if ((next = tryIncReaderOverflow(s)) != 0L)
396	<	return next;
397	<	}
398	<	else
399	<	return awaitRead(s, false, 0L);
400	<	}
399	>	long s = state, next;  // bypass acquireRead on common uncontended case
400	>	return ((whead == wtail && (s & ABITS) < RFULL &&
401	>	U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) ?
402	>	next : acquireRead(false, 0L));
403		}
404
405		/**
#	Line 423 | Line 425 | public class StampedLock implements java
425		/**
426		* Non-exclusively acquires the lock if it is available within the
427		* given time and the current thread has not been interrupted.
428	+	* Behavior under timeout and interruption matches that specified
429	+	* for method {@link Lock#tryLock(long,TimeUnit)}.
430		*
431	+	* @param time the maximum time to wait for the lock
432	+	* @param unit the time unit of the {@code time} argument
433		* @return a stamp that can be used to unlock or convert mode,
434		* or zero if the lock is not available
435		* @throws InterruptedException if the current thread is interrupted
#	Line 431 | Line 437 | public class StampedLock implements java
437		*/
438		public long tryReadLock(long time, TimeUnit unit)
439		throws InterruptedException {
440	+	long s, m, next, deadline;
441		long nanos = unit.toNanos(time);
442		if (!Thread.interrupted()) {
443	<	for (;;) {
444	<	long s, m, next, deadline;
438	<	if ((m = (s = state) & ABITS) == WBIT ||
439	<	(m != 0L && whead != wtail)) {
440	<	if (nanos <= 0L)
441	<	return 0L;
442	<	if ((deadline = System.nanoTime() + nanos) == 0L)
443	<	deadline = 1L;
444	<	if ((next = awaitRead(s, true, deadline)) != INTERRUPTED)
445	<	return next;
446	<	break;
447	<	}
448	<	else if (m < RFULL) {
443	>	if ((m = (s = state) & ABITS) != WBIT) {
444	>	if (m < RFULL) {
445		if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
446		return next;
447		}
448		else if ((next = tryIncReaderOverflow(s)) != 0L)
449		return next;
450		}
451	+	if (nanos <= 0L)
452	+	return 0L;
453	+	if ((deadline = System.nanoTime() + nanos) == 0L)
454	+	deadline = 1L;
455	+	if ((next = acquireRead(true, deadline)) != INTERRUPTED)
456	+	return next;
457		}
458		throw new InterruptedException();
459		}
#	Line 459 | Line 461 | public class StampedLock implements java
461		/**
462		* Non-exclusively acquires the lock, blocking if necessary
463		* until available or the current thread is interrupted.
464	+	* Behavior under interruption matches that specified
465	+	* for method {@link Lock#lockInterruptibly()}.
466		*
467		* @return a stamp that can be used to unlock or convert mode
468		* @throws InterruptedException if the current thread is interrupted
469		* before acquiring the lock
470		*/
471		public long readLockInterruptibly() throws InterruptedException {
472	<	if (!Thread.interrupted()) {
473	<	for (;;) {
474	<	long s, next, m;
475	<	if ((m = (s = state) & ABITS) == WBIT ||
472	<	(m != 0L && whead != wtail)) {
473	<	if ((next = awaitRead(s, true, 0L)) != INTERRUPTED)
474	<	return next;
475	<	break;
476	<	}
477	<	else if (m < RFULL) {
478	<	if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
479	<	return next;
480	<	}
481	<	else if ((next = tryIncReaderOverflow(s)) != 0L)
482	<	return next;
483	<	}
484	<	}
472	>	long next;
473	>	if (!Thread.interrupted() &&
474	>	(next = acquireRead(true, 0L)) != INTERRUPTED)
475	>	return next;
476		throw new InterruptedException();
477		}
478
#	Line 497 | Line 488 | public class StampedLock implements java
488		}
489
490		/**
491	<	* Returns true if the lock has not been exclusively held since
492	<	* issuance of the given stamp. Always returns false if the stamp
493	<	* is zero. Always returns true if the stamp represents a
494	<	* currently held lock.
491	>	* Returns true if the lock has not been exclusively acquired
492	>	* since issuance of the given stamp. Always returns false if the
493	>	* stamp is zero. Always returns true if the stamp represents a
494	>	* currently held lock. Invoking this method with a value not
495	>	* obtained from {@link #tryOptimisticRead} or a locking method
496	>	* for this lock has no defined effect or result.
497		*
498	<	* @return true if the lock has not been exclusively held since
499	<	* issuance of the given stamp; else false
498	>	* @param stamp a stamp
499	>	* @return {@code true} if the lock has not been exclusively acquired
500	>	* since issuance of the given stamp; else false
501		*/
502		public boolean validate(long stamp) {
503	+	// See above about current use of getLongVolatile here
504		return (stamp & SBITS) == (U.getLongVolatile(this, STATE) & SBITS);
505		}
506
#	Line 518 | Line 513 | public class StampedLock implements java
513		* not match the current state of this lock
514		*/
515		public void unlockWrite(long stamp) {
516	+	WNode h;
517		if (state != stamp || (stamp & WBIT) == 0L)
518		throw new IllegalMonitorStateException();
519		state = (stamp += WBIT) == 0L ? ORIGIN : stamp;
520	<	readerPrefSignal();
520	>	if ((h = whead) != null && h.status != 0)
521	>	release(h);
522		}
523
524		/**
525	<	* If the lock state matches the given stamp, releases
525	>	* If the lock state matches the given stamp, releases the
526		* non-exclusive lock.
527		*
528		* @param stamp a stamp returned by a read-lock operation
#	Line 533 | Line 530 | public class StampedLock implements java
530		* not match the current state of this lock
531		*/
532		public void unlockRead(long stamp) {
533	<	long s, m;
534	<	if ((stamp & RBITS) != 0L) {
535	<	while (((s = state) & SBITS) == (stamp & SBITS)) {
536	<	if ((m = s & ABITS) == 0L)
533	>	long s, m; WNode h;
534	>	for (;;) {
535	>	if (((s = state) & SBITS) != (stamp & SBITS) ||
536	>	(stamp & ABITS) == 0L || (m = s & ABITS) == 0L || m == WBIT)
537	>	throw new IllegalMonitorStateException();
538	>	if (m < RFULL) {
539	>	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
540	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
541	>	release(h);
542		break;
541	–	else if (m < RFULL) {
542	–	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
543	–	if (m == RUNIT)
544	–	writerPrefSignal();
545	–	return;
546	–	}
543		}
548	–	else if (m >= WBIT)
549	–	break;
550	–	else if (tryDecReaderOverflow(s) != 0L)
551	–	return;
544		}
545	+	else if (tryDecReaderOverflow(s) != 0L)
546	+	break;
547		}
554	–	throw new IllegalMonitorStateException();
548		}
549
550		/**
#	Line 563 | Line 556 | public class StampedLock implements java
556		* not match the current state of this lock
557		*/
558		public void unlock(long stamp) {
559	<	long a = stamp & ABITS, m, s;
559	>	long a = stamp & ABITS, m, s; WNode h;
560		while (((s = state) & SBITS) == (stamp & SBITS)) {
561		if ((m = s & ABITS) == 0L)
562		break;
#	Line 571 | Line 564 | public class StampedLock implements java
564		if (a != m)
565		break;
566		state = (s += WBIT) == 0L ? ORIGIN : s;
567	<	readerPrefSignal();
567	>	if ((h = whead) != null && h.status != 0)
568	>	release(h);
569		return;
570		}
571		else if (a == 0L || a >= WBIT)
572		break;
573		else if (m < RFULL) {
574		if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
575	<	if (m == RUNIT)
576	<	writerPrefSignal();
575	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
576	>	release(h);
577		return;
578		}
579		}
#	Line 590 | Line 584 | public class StampedLock implements java
584		}
585
586		/**
587	<	* If the lock state matches the given stamp then performs one of
587	>	* If the lock state matches the given stamp, performs one of
588		* the following actions. If the stamp represents holding a write
589	<	* lock, returns it. Or, if a read lock, if the write lock is
590	<	* available, releases the read and returns a write stamp. Or, if
591	<	* an optimistic read, returns a write stamp only if immediately
592	<	* available. This method returns zero in all other cases.
589	>	* lock, returns it.  Or, if a read lock, if the write lock is
590	>	* available, releases the read lock and returns a write stamp.
591	>	* Or, if an optimistic read, returns a write stamp only if
592	>	* immediately available. This method returns zero in all other
593	>	* cases.
594		*
595		* @param stamp a stamp
596		* @return a valid write stamp, or zero on failure
#	Line 614 | Line 609 | public class StampedLock implements java
609		break;
610		return stamp;
611		}
612	<	else if (m == RUNIT && a != 0L && a < WBIT) {
612	>	else if (m == RUNIT && a != 0L) {
613		if (U.compareAndSwapLong(this, STATE, s,
614		next = s - RUNIT + WBIT))
615		return next;
#	Line 626 | Line 621 | public class StampedLock implements java
621		}
622
623		/**
624	<	* If the lock state matches the given stamp then performs one of
624	>	* If the lock state matches the given stamp, performs one of
625		* the following actions. If the stamp represents holding a write
626		* lock, releases it and obtains a read lock.  Or, if a read lock,
627		* returns it. Or, if an optimistic read, acquires a read lock and
#	Line 637 | Line 632 | public class StampedLock implements java
632		* @return a valid read stamp, or zero on failure
633		*/
634		public long tryConvertToReadLock(long stamp) {
635	<	long a = stamp & ABITS, m, s, next;
635	>	long a = stamp & ABITS, m, s, next; WNode h;
636		while (((s = state) & SBITS) == (stamp & SBITS)) {
637		if ((m = s & ABITS) == 0L) {
638		if (a != 0L)
#	Line 652 | Line 647 | public class StampedLock implements java
647		else if (m == WBIT) {
648		if (a != m)
649		break;
650	<	next = state = s + (WBIT + RUNIT);
651	<	readerPrefSignal();
650	>	state = next = s + (WBIT + RUNIT);
651	>	if ((h = whead) != null && h.status != 0)
652	>	release(h);
653		return next;
654		}
655		else if (a != 0L && a < WBIT)
#	Line 675 | Line 671 | public class StampedLock implements java
671		* @return a valid optimistic read stamp, or zero on failure
672		*/
673		public long tryConvertToOptimisticRead(long stamp) {
674	<	long a = stamp & ABITS, m, s, next;
675	<	while (((s = U.getLongVolatile(this, STATE)) &
676	<	SBITS) == (stamp & SBITS)) {
674	>	long a = stamp & ABITS, m, s, next; WNode h;
675	>	for (;;) {
676	>	s = U.getLongVolatile(this, STATE); // see above
677	>	if (((s = state) & SBITS) != (stamp & SBITS))
678	>	break;
679		if ((m = s & ABITS) == 0L) {
680		if (a != 0L)
681		break;
#	Line 686 | Line 684 | public class StampedLock implements java
684		else if (m == WBIT) {
685		if (a != m)
686		break;
687	<	next = state = (s += WBIT) == 0L ? ORIGIN : s;
688	<	readerPrefSignal();
687	>	state = next = (s += WBIT) == 0L ? ORIGIN : s;
688	>	if ((h = whead) != null && h.status != 0)
689	>	release(h);
690		return next;
691		}
692		else if (a == 0L || a >= WBIT)
693		break;
694		else if (m < RFULL) {
695		if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) {
696	<	if (m == RUNIT)
697	<	writerPrefSignal();
696	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
697	>	release(h);
698		return next & SBITS;
699		}
700		}
#	Line 710 | Line 709 | public class StampedLock implements java
709		* stamp value. This method may be useful for recovery after
710		* errors.
711		*
712	<	* @return true if the lock was held, else false
712	>	* @return {@code true} if the lock was held, else false
713		*/
714		public boolean tryUnlockWrite() {
715	<	long s;
715	>	long s; WNode h;
716		if (((s = state) & WBIT) != 0L) {
717		state = (s += WBIT) == 0L ? ORIGIN : s;
718	<	readerPrefSignal();
718	>	if ((h = whead) != null && h.status != 0)
719	>	release(h);
720		return true;
721		}
722		return false;
#	Line 727 | Line 727 | public class StampedLock implements java
727		* requiring a stamp value. This method may be useful for recovery
728		* after errors.
729		*
730	<	* @return true if the read lock was held, else false
730	>	* @return {@code true} if the read lock was held, else false
731		*/
732		public boolean tryUnlockRead() {
733	<	long s, m;
733	>	long s, m; WNode h;
734		while ((m = (s = state) & ABITS) != 0L && m < WBIT) {
735		if (m < RFULL) {
736		if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
737	<	if (m == RUNIT)
738	<	writerPrefSignal();
737	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
738	>	release(h);
739		return true;
740		}
741		}
#	Line 745 | Line 745 | public class StampedLock implements java
745		return false;
746		}
747
748	+	// status monitoring methods
749	+
750	+	/**
751	+	* Returns combined state-held and overflow read count for given
752	+	* state s.
753	+	*/
754	+	private int getReadLockCount(long s) {
755	+	long readers;
756	+	if ((readers = s & RBITS) >= RFULL)
757	+	readers = RFULL + readerOverflow;
758	+	return (int) readers;
759	+	}
760	+
761		/**
762	<	* Returns true if the lock is currently held exclusively.
762	>	* Returns {@code true} if the lock is currently held exclusively.
763		*
764	<	* @return true if the lock is currently held exclusively
764	>	* @return {@code true} if the lock is currently held exclusively
765		*/
766		public boolean isWriteLocked() {
767		return (state & WBIT) != 0L;
768		}
769
770		/**
771	<	* Returns true if the lock is currently held non-exclusively.
771	>	* Returns {@code true} if the lock is currently held non-exclusively.
772		*
773	<	* @return true if the lock is currently held non-exclusively
773	>	* @return {@code true} if the lock is currently held non-exclusively
774		*/
775		public boolean isReadLocked() {
776	<	long m;
777	<	return (m = state & ABITS) > 0L && m < WBIT;
776	>	return (state & RBITS) != 0L;
777	>	}
778	>
779	>	/**
780	>	* Queries the number of read locks held for this lock. This
781	>	* method is designed for use in monitoring system state, not for
782	>	* synchronization control.
783	>	* @return the number of read locks held
784	>	*/
785	>	public int getReadLockCount() {
786	>	return getReadLockCount(state);
787	>	}
788	>
789	>	/**
790	>	* Returns a string identifying this lock, as well as its lock
791	>	* state.  The state, in brackets, includes the String {@code
792	>	* "Unlocked"} or the String {@code "Write-locked"} or the String
793	>	* {@code "Read-locks:"} followed by the current number of
794	>	* read-locks held.
795	>	*
796	>	* @return a string identifying this lock, as well as its lock state
797	>	*/
798	>	public String toString() {
799	>	long s = state;
800	>	return super.toString() +
801	>	((s & ABITS) == 0L ? "[Unlocked]" :
802	>	(s & WBIT) != 0L ? "[Write-locked]" :
803	>	"[Read-locks:" + getReadLockCount(s) + "]");
804	>	}
805	>
806	>	// views
807	>
808	>	/**
809	>	* Returns a plain {@link Lock} view of this StampedLock in which
810	>	* the {@link Lock#lock} method is mapped to {@link #readLock},
811	>	* and similarly for other methods. The returned Lock does not
812	>	* support a {@link Condition}; method {@link
813	>	* Lock#newCondition()} throws {@code
814	>	* UnsupportedOperationException}.
815	>	*
816	>	* @return the lock
817	>	*/
818	>	public Lock asReadLock() {
819	>	ReadLockView v;
820	>	return ((v = readLockView) != null ? v :
821	>	(readLockView = new ReadLockView()));
822	>	}
823	>
824	>	/**
825	>	* Returns a plain {@link Lock} view of this StampedLock in which
826	>	* the {@link Lock#lock} method is mapped to {@link #writeLock},
827	>	* and similarly for other methods. The returned Lock does not
828	>	* support a {@link Condition}; method {@link
829	>	* Lock#newCondition()} throws {@code
830	>	* UnsupportedOperationException}.
831	>	*
832	>	* @return the lock
833	>	*/
834	>	public Lock asWriteLock() {
835	>	WriteLockView v;
836	>	return ((v = writeLockView) != null ? v :
837	>	(writeLockView = new WriteLockView()));
838	>	}
839	>
840	>	/**
841	>	* Returns a {@link ReadWriteLock} view of this StampedLock in
842	>	* which the {@link ReadWriteLock#readLock()} method is mapped to
843	>	* {@link #asReadLock()}, and {@link ReadWriteLock#writeLock()} to
844	>	* {@link #asWriteLock()}.
845	>	*
846	>	* @return the lock
847	>	*/
848	>	public ReadWriteLock asReadWriteLock() {
849	>	ReadWriteLockView v;
850	>	return ((v = readWriteLockView) != null ? v :
851	>	(readWriteLockView = new ReadWriteLockView()));
852	>	}
853	>
854	>	// view classes
855	>
856	>	final class ReadLockView implements Lock {
857	>	public void lock() { readLock(); }
858	>	public void lockInterruptibly() throws InterruptedException {
859	>	readLockInterruptibly();
860	>	}
861	>	public boolean tryLock() { return tryReadLock() != 0L; }
862	>	public boolean tryLock(long time, TimeUnit unit)
863	>	throws InterruptedException {
864	>	return tryReadLock(time, unit) != 0L;
865	>	}
866	>	public void unlock() { unstampedUnlockRead(); }
867	>	public Condition newCondition() {
868	>	throw new UnsupportedOperationException();
869	>	}
870	>	}
871	>
872	>	final class WriteLockView implements Lock {
873	>	public void lock() { writeLock(); }
874	>	public void lockInterruptibly() throws InterruptedException {
875	>	writeLockInterruptibly();
876	>	}
877	>	public boolean tryLock() { return tryWriteLock() != 0L; }
878	>	public boolean tryLock(long time, TimeUnit unit)
879	>	throws InterruptedException {
880	>	return tryWriteLock(time, unit) != 0L;
881	>	}
882	>	public void unlock() { unstampedUnlockWrite(); }
883	>	public Condition newCondition() {
884	>	throw new UnsupportedOperationException();
885	>	}
886	>	}
887	>
888	>	final class ReadWriteLockView implements ReadWriteLock {
889	>	public Lock readLock() { return asReadLock(); }
890	>	public Lock writeLock() { return asWriteLock(); }
891	>	}
892	>
893	>	// Unlock methods without stamp argument checks for view classes.
894	>	// Needed because view-class lock methods throw away stamps.
895	>
896	>	final void unstampedUnlockWrite() {
897	>	WNode h; long s;
898	>	if (((s = state) & WBIT) == 0L)
899	>	throw new IllegalMonitorStateException();
900	>	state = (s += WBIT) == 0L ? ORIGIN : s;
901	>	if ((h = whead) != null && h.status != 0)
902	>	release(h);
903	>	}
904	>
905	>	final void unstampedUnlockRead() {
906	>	for (;;) {
907	>	long s, m; WNode h;
908	>	if ((m = (s = state) & ABITS) == 0L || m >= WBIT)
909	>	throw new IllegalMonitorStateException();
910	>	else if (m < RFULL) {
911	>	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
912	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
913	>	release(h);
914	>	break;
915	>	}
916	>	}
917	>	else if (tryDecReaderOverflow(s) != 0L)
918	>	break;
919	>	}
920		}
921
922		private void readObject(java.io.ObjectInputStream s)
#	Line 777 | Line 932 | public class StampedLock implements java
932		* access bits value to RBITS, indicating hold of spinlock,
933		* then updating, then releasing.
934		*
935	<	* @param stamp, assumed that (stamp & ABITS) >= RFULL
935	>	* @param s a reader overflow stamp: (s & ABITS) >= RFULL
936		* @return new stamp on success, else zero
937		*/
938		private long tryIncReaderOverflow(long s) {
939	+	// assert (s & ABITS) >= RFULL;
940		if ((s & ABITS) == RFULL) {
941		if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) {
942		++readerOverflow;
#	Line 797 | Line 953 | public class StampedLock implements java
953		/**
954		* Tries to decrement readerOverflow.
955		*
956	<	* @param stamp, assumed that (stamp & ABITS) >= RFULL
956	>	* @param s a reader overflow stamp: (s & ABITS) >= RFULL
957		* @return new stamp on success, else zero
958		*/
959		private long tryDecReaderOverflow(long s) {
960	+	// assert (s & ABITS) >= RFULL;
961		if ((s & ABITS) == RFULL) {
962		if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) {
963		int r; long next;
#	Line 820 | Line 977 | public class StampedLock implements java
977		return 0L;
978		}
979
980	<	/*
981	<	* The two versions of signal implement the phase-fair policy.
982	<	* They include almost the same code, but repacked in different
983	<	* ways.  Integrating the policy with the mechanics eliminates
984	<	* state rechecks that would be needed with separate reader and
985	<	* writer signal methods.  Both methods assume that they are
986	<	* called when the lock is last known to be available, and
987	<	* continue until the lock is unavailable, or at least one thread
988	<	* is signalled, or there are no more waiting threads.  Signalling
989	<	* a reader entails popping (CASing) from rhead and unparking
990	<	* unless the thread already cancelled (indicated by a null waiter
834	<	* field). Signalling a writer requires finding the first node,
835	<	* i.e., the successor of whead. This is normally just head.next,
836	<	* but may require traversal from wtail if next pointers are
837	<	* lagging. These methods may fail to wake up an acquiring thread
838	<	* when one or more have been cancelled, but the cancel methods
839	<	* themselves provide extra safeguards to ensure liveness.
840	<	*/
841	<
842	<	private void readerPrefSignal() {
843	<	boolean readers = false;
844	<	RNode p; WNode h, q; long s; Thread w;
845	<	while ((p = rhead) != null) {
846	<	if (((s = state) & WBIT) != 0L)
847	<	return;
848	<	if (p.seq == (s & SBITS))
849	<	break;
850	<	readers = true;
851	<	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
852	<	(w = p.waiter) != null &&
853	<	U.compareAndSwapObject(p, WAITER, w, null))
854	<	U.unpark(w);
855	<	}
856	<	if (!readers && (state & ABITS) == 0L &&
857	<	(h = whead) != null && h.status != 0) {
858	<	U.compareAndSwapInt(h, STATUS, WAITING, 0);
859	<	if ((q = h.next) == null || q.status == CANCELLED) {
860	<	q = null;
861	<	for (WNode t = wtail; t != null && t != h; t = t.prev)
862	<	if (t.status <= 0)
863	<	q = t;
864	<	}
865	<	if (q != null && (w = q.thread) != null)
866	<	U.unpark(w);
867	<	}
868	<	}
869	<
870	<	private void writerPrefSignal() {
871	<	RNode p; WNode h, q; long s; Thread w;
872	<	if ((h = whead) != null && h.status != 0) {
873	<	U.compareAndSwapInt(h, STATUS, WAITING, 0);
980	>	/**
981	>	* Wakes up the successor of h (normally whead). This is normally
982	>	* just h.next, but may require traversal from wtail if next
983	>	* pointers are lagging. This may fail to wake up an acquiring
984	>	* thread when one or more have been cancelled, but the cancel
985	>	* methods themselves provide extra safeguards to ensure liveness.
986	>	*/
987	>	private void release(WNode h) {
988	>	if (h != null) {
989	>	WNode q; Thread w;
990	>	U.compareAndSwapInt(h, WSTATUS, WAITING, 0);
991		if ((q = h.next) == null || q.status == CANCELLED) {
875	–	q = null;
992		for (WNode t = wtail; t != null && t != h; t = t.prev)
993		if (t.status <= 0)
994		q = t;
#	Line 880 | Line 996 | public class StampedLock implements java
996		if (q != null && (w = q.thread) != null)
997		U.unpark(w);
998		}
883	–	else {
884	–	while ((p = rhead) != null && ((s = state) & WBIT) == 0L &&
885	–	p.seq != (s & SBITS)) {
886	–	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
887	–	(w = p.waiter) != null &&
888	–	U.compareAndSwapObject(p, WAITER, w, null))
889	–	U.unpark(w);
890	–	}
891	–	}
999		}
1000
1001		/**
1002	<	* RNG for local spins. The first call from await{Read,Write}
896	<	* produces a thread-local value. Unless zero, subsequent calls
897	<	* use an xorShift to further reduce memory traffic.  Both await
898	<	* methods use a similar spin strategy: If associated queue
899	<	* appears to be empty, then the thread spin-waits up to SPINS
900	<	* times before enqueing, and then, if the first thread to be
901	<	* enqueued, spins again up to SPINS times before blocking. If,
902	<	* upon wakening it fails to obtain lock, and is still (or
903	<	* becomes) the first waiting thread (which indicates that some
904	<	* other thread barged and obtained lock), it escalates spins (up
905	<	* to MAX_HEAD_SPINS) to reduce the likelihood of continually
906	<	* losing to barging threads.
907	<	*/
908	<	private static int nextRandom(int r) {
909	<	if (r == 0)
910	<	return ThreadLocalRandom.current().nextInt();
911	<	r ^= r << 1; // xorshift
912	<	r ^= r >>> 3;
913	<	r ^= r << 10;
914	<	return r;
915	<	}
916	<
917	<	/**
918	<	* Possibly spins trying to obtain write lock, then enqueues and
919	<	* blocks while not head of write queue or cannot acquire lock,
920	<	* possibly spinning when at head; cancelling on timeout or
921	<	* interrupt.
1002	>	* See above for explanation.
1003		*
1004		* @param interruptible true if should check interrupts and if so
1005		* return INTERRUPTED
1006		* @param deadline if nonzero, the System.nanoTime value to timeout
1007		* at (and return zero)
1008	+	* @return next state, or INTERRUPTED
1009		*/
1010	<	private long awaitWrite(boolean interruptible, long deadline) {
1011	<	WNode node = null;
1012	<	for (int r = 0, spins = -1;;) {
1013	<	WNode p; long s, next;
1014	<	if (((s = state) & ABITS) == 0L) {
1015	<	if (U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
1016	<	return next;
1010	>	private long acquireWrite(boolean interruptible, long deadline) {
1011	>	WNode node = null, p;
1012	>	for (int spins = -1;;) { // spin while enqueuing
1013	>	long m, s, ns;
1014	>	if ((m = (s = state) & ABITS) == 0L) {
1015	>	if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT))
1016	>	return ns;
1017		}
1018		else if (spins < 0)
1019	<	spins = whead == wtail ? SPINS : 0;
1019	>	spins = (m == WBIT && wtail == whead) ? SPINS : 0;
1020		else if (spins > 0) {
1021	<	if ((r = nextRandom(r)) >= 0)
1021	>	if (ThreadLocalRandom.current().nextInt() >= 0)
1022		--spins;
1023		}
1024		else if ((p = wtail) == null) { // initialize queue
1025	<	if (U.compareAndSwapObject(this, WHEAD, null,
1026	<	new WNode(null, null)))
1027	<	wtail = whead;
1025	>	WNode hd = new WNode(WMODE, null);
1026	>	if (U.compareAndSwapObject(this, WHEAD, null, hd))
1027	>	wtail = hd;
1028		}
1029		else if (node == null)
1030	<	node = new WNode(Thread.currentThread(), p);
1030	>	node = new WNode(WMODE, p);
1031		else if (node.prev != p)
1032		node.prev = p;
1033		else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
1034		p.next = node;
1035	<	for (int headSpins = SPINS;;) {
1036	<	WNode np; int ps;
1037	<	if ((np = node.prev) != p && np != null)
1038	<	(p = np).next = node; // stale
1039	<	if (p == whead) {
1040	<	for (int k = headSpins;;) {
1041	<	if (((s = state) & ABITS) == 0L) {
1042	<	if (U.compareAndSwapLong(this, STATE,
1043	<	s, next = s + WBIT)) {
1044	<	whead = node;
1045	<	node.thread = null;
1046	<	node.prev = null;
1047	<	return next;
1048	<	}
1049	<	break;
1050	<	}
1051	<	if ((r = nextRandom(r)) >= 0 && --k <= 0)
1052	<	break;
1053	<	}
972	<	if (headSpins < MAX_HEAD_SPINS)
973	<	headSpins <<= 1;
974	<	}
975	<	if ((ps = p.status) == 0)
976	<	U.compareAndSwapInt(p, STATUS, 0, WAITING);
977	<	else if (ps == CANCELLED)
978	<	node.prev = p.prev;
979	<	else {
980	<	long time; // 0 argument to park means no timeout
981	<	if (deadline == 0L)
982	<	time = 0L;
983	<	else if ((time = deadline - System.nanoTime()) <= 0L)
984	<	return cancelWriter(node, false);
985	<	if (node.prev == p && p.status == WAITING &&
986	<	(p != whead || (state & WBIT) != 0L)) { // recheck
987	<	U.park(false, time);
988	<	if (interruptible && Thread.interrupted())
989	<	return cancelWriter(node, true);
1035	>	break;
1036	>	}
1037	>	}
1038	>
1039	>	for (int spins = -1;;) {
1040	>	WNode h, np, pp; int ps;
1041	>	if ((h = whead) == p) {
1042	>	if (spins < 0)
1043	>	spins = HEAD_SPINS;
1044	>	else if (spins < MAX_HEAD_SPINS)
1045	>	spins <<= 1;
1046	>	for (int k = spins;;) { // spin at head
1047	>	long s, ns;
1048	>	if (((s = state) & ABITS) == 0L) {
1049	>	if (U.compareAndSwapLong(this, STATE, s,
1050	>	ns = s + WBIT)) {
1051	>	whead = node;
1052	>	node.prev = null;
1053	>	return ns;
1054		}
1055		}
1056	+	else if (ThreadLocalRandom.current().nextInt() >= 0 &&
1057	+	--k <= 0)
1058	+	break;
1059		}
1060		}
1061	<	}
1062	<	}
1063	<
1064	<	/**
1065	<	* If node non-null, forces cancel status and unsplices from queue
1066	<	* if possible. This is a streamlined variant of cancellation
1067	<	* methods in AbstractQueuedSynchronizer that includes a detailed
1068	<	* explanation.
1069	<	*/
1070	<	private long cancelWriter(WNode node, boolean interrupted) {
1071	<	WNode pred;
1072	<	if (node != null && (pred = node.prev) != null) {
1073	<	WNode pp;
1074	<	node.thread = null;
1075	<	while (pred.status == CANCELLED && (pp = pred.prev) != null)
1076	<	pred = node.prev = pp;
1077	<	WNode predNext = pred.next;
1078	<	node.status = CANCELLED;
1079	<	if (predNext != null) {
1080	<	Thread w = null;
1081	<	WNode succ = node.next;
1082	<	while (succ != null && succ.status == CANCELLED)
1083	<	succ = succ.next;
1084	<	if (succ != null)
1085	<	w = succ.thread;
1086	<	else if (node == wtail)
1087	<	U.compareAndSwapObject(this, WTAIL, node, pred);
1088	<	U.compareAndSwapObject(pred, WNEXT, predNext, succ);
1089	<	if (w != null)
1090	<	U.unpark(w);
1061	>	else if (h != null) { // help release stale waiters
1062	>	WNode c; Thread w;
1063	>	while ((c = h.cowait) != null) {
1064	>	if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
1065	>	(w = c.thread) != null)
1066	>	U.unpark(w);
1067	>	}
1068	>	}
1069	>	if (whead == h) {
1070	>	if ((np = node.prev) != p) {
1071	>	if (np != null)
1072	>	(p = np).next = node;   // stale
1073	>	}
1074	>	else if ((ps = p.status) == 0)
1075	>	U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
1076	>	else if (ps == CANCELLED) {
1077	>	if ((pp = p.prev) != null) {
1078	>	node.prev = pp;
1079	>	pp.next = node;
1080	>	}
1081	>	}
1082	>	else {
1083	>	long time; // 0 argument to park means no timeout
1084	>	if (deadline == 0L)
1085	>	time = 0L;
1086	>	else if ((time = deadline - System.nanoTime()) <= 0L)
1087	>	return cancelWaiter(node, node, false);
1088	>	Thread wt = Thread.currentThread();
1089	>	U.putObject(wt, PARKBLOCKER, this);
1090	>	node.thread = wt;
1091	>	if (p.status < 0 && (p != h || (state & ABITS) != 0L) &&
1092	>	whead == h && node.prev == p)
1093	>	U.park(false, time);  // emulate LockSupport.park
1094	>	node.thread = null;
1095	>	U.putObject(wt, PARKBLOCKER, null);
1096	>	if (interruptible && Thread.interrupted())
1097	>	return cancelWaiter(node, node, true);
1098	>	}
1099		}
1100		}
1026	–	writerPrefSignal();
1027	–	return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L;
1101		}
1102
1103		/**
1104	<	* Waits for read lock or timeout or interrupt. The form of
1105	<	* awaitRead differs from awaitWrite mainly because it must
1106	<	* restart (with a new wait node) if the thread was unqueued and
1107	<	* unparked but could not the obtain lock.  We also need to help
1108	<	* with preference rules by not trying to acquire the lock before
1109	<	* enqueuing if there is a known waiting writer, but also helping
1110	<	* to release those threads that are still queued from the last
1111	<	* release.
1112	<	*/
1113	<	private long awaitRead(long stamp, boolean interruptible, long deadline) {
1114	<	long seq = stamp & SBITS;
1115	<	RNode node = null;
1116	<	boolean queued = false;
1117	<	for (int r = 0, headSpins = SPINS, spins = -1;;) {
1118	<	long s, m, next; RNode p; WNode wh; Thread w;
1119	<	if ((m = (s = state) & ABITS) != WBIT &&
1120	<	((s & SBITS) != seq || (wh = whead) == null ||
1121	<	wh.status == 0)) {
1122	<	if (m < RFULL ?
1123	<	U.compareAndSwapLong(this, STATE, s, next = s + RUNIT) :
1124	<	(next = tryIncReaderOverflow(s)) != 0L) {
1125	<	if (node != null && (w = node.waiter) != null)
1126	<	U.compareAndSwapObject(node, WAITER, w, null);
1127	<	if ((p = rhead) != null && (s & SBITS) != p.seq &&
1128	<	U.compareAndSwapObject(this, RHEAD, p, p.next) &&
1129	<	(w = p.waiter) != null &&
1130	<	U.compareAndSwapObject(p, WAITER, w, null))
1131	<	U.unpark(w); // help signal other waiters
1132	<	return next;
1104	>	* See above for explanation.
1105	>	*
1106	>	* @param interruptible true if should check interrupts and if so
1107	>	* return INTERRUPTED
1108	>	* @param deadline if nonzero, the System.nanoTime value to timeout
1109	>	* at (and return zero)
1110	>	* @return next state, or INTERRUPTED
1111	>	*/
1112	>	private long acquireRead(boolean interruptible, long deadline) {
1113	>	WNode node = null, p;
1114	>	for (int spins = -1;;) {
1115	>	WNode h;
1116	>	if ((h = whead) == (p = wtail)) {
1117	>	for (long m, s, ns;;) {
1118	>	if ((m = (s = state) & ABITS) < RFULL ?
1119	>	U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) :
1120	>	(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L))
1121	>	return ns;
1122	>	else if (m >= WBIT) {
1123	>	if (spins > 0) {
1124	>	if (ThreadLocalRandom.current().nextInt() >= 0)
1125	>	--spins;
1126	>	}
1127	>	else {
1128	>	if (spins == 0) {
1129	>	WNode nh = whead, np = wtail;
1130	>	if ((nh == h && np == p) || (h = nh) != (p = np))
1131	>	break;
1132	>	}
1133	>	spins = SPINS;
1134	>	}
1135	>	}
1136		}
1137		}
1138	<	else if (m != WBIT && (p = rhead) != null &&
1139	<	(s & SBITS) != p.seq) { // help release old readers
1140	<	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
1141	<	(w = p.waiter) != null &&
1066	<	U.compareAndSwapObject(p, WAITER, w, null))
1067	<	U.unpark(w);
1068	<	}
1069	<	else if (queued && node != null && node.waiter == null) {
1070	<	node = null;    // restart
1071	<	queued = false;
1072	<	spins = -1;
1073	<	}
1074	<	else if (spins < 0) {
1075	<	if (rhead != node)
1076	<	spins = 0;
1077	<	else if ((spins = headSpins) < MAX_HEAD_SPINS && node != null)
1078	<	headSpins <<= 1;
1079	<	}
1080	<	else if (spins > 0) {
1081	<	if ((r = nextRandom(r)) >= 0)
1082	<	--spins;
1138	>	if (p == null) { // initialize queue
1139	>	WNode hd = new WNode(WMODE, null);
1140	>	if (U.compareAndSwapObject(this, WHEAD, null, hd))
1141	>	wtail = hd;
1142		}
1143		else if (node == null)
1144	<	node = new RNode(seq, Thread.currentThread());
1145	<	else if (!queued) {
1146	<	if (queued = U.compareAndSwapObject(this, RHEAD,
1147	<	node.next = rhead, node))
1148	<	spins = -1;
1144	>	node = new WNode(RMODE, p);
1145	>	else if (h == p || p.mode != RMODE) {
1146	>	if (node.prev != p)
1147	>	node.prev = p;
1148	>	else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
1149	>	p.next = node;
1150	>	break;
1151	>	}
1152		}
1153	+	else if (!U.compareAndSwapObject(p, WCOWAIT,
1154	+	node.cowait = p.cowait, node))
1155	+	node.cowait = null;
1156		else {
1157	<	long time;
1158	<	if (deadline == 0L)
1159	<	time = 0L;
1160	<	else if ((time = deadline - System.nanoTime()) <= 0L)
1161	<	return cancelReader(node, false);
1162	<	if ((state & WBIT) != 0L && node.waiter != null) { // recheck
1163	<	U.park(false, time);
1164	<	if (interruptible && Thread.interrupted())
1165	<	return cancelReader(node, true);
1157	>	for (;;) {
1158	>	WNode pp, c; Thread w;
1159	>	if ((h = whead) != null && (c = h.cowait) != null &&
1160	>	U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
1161	>	(w = c.thread) != null) // help release
1162	>	U.unpark(w);
1163	>	if (h == (pp = p.prev) || h == p || pp == null) {
1164	>	long m, s, ns;
1165	>	do {
1166	>	if ((m = (s = state) & ABITS) < RFULL ?
1167	>	U.compareAndSwapLong(this, STATE, s,
1168	>	ns = s + RUNIT) :
1169	>	(m < WBIT &&
1170	>	(ns = tryIncReaderOverflow(s)) != 0L))
1171	>	return ns;
1172	>	} while (m < WBIT);
1173	>	}
1174	>	if (whead == h && p.prev == pp) {
1175	>	long time;
1176	>	if (pp == null || h == p || p.status > 0) {
1177	>	node = null; // throw away
1178	>	break;
1179	>	}
1180	>	if (deadline == 0L)
1181	>	time = 0L;
1182	>	else if ((time = deadline - System.nanoTime()) <= 0L)
1183	>	return cancelWaiter(node, p, false);
1184	>	Thread wt = Thread.currentThread();
1185	>	U.putObject(wt, PARKBLOCKER, this);
1186	>	node.thread = wt;
1187	>	if ((h != pp || (state & ABITS) == WBIT) &&
1188	>	whead == h && p.prev == pp)
1189	>	U.park(false, time);
1190	>	node.thread = null;
1191	>	U.putObject(wt, PARKBLOCKER, null);
1192	>	if (interruptible && Thread.interrupted())
1193	>	return cancelWaiter(node, p, true);
1194	>	}
1195		}
1196		}
1197		}
1104	–	}
1198
1199	<	/**
1200	<	* If node non-null, forces cancel status and unsplices from queue
1201	<	* if possible, by traversing entire queue looking for cancelled
1202	<	* nodes.
1203	<	*/
1204	<	private long cancelReader(RNode node, boolean interrupted) {
1205	<	Thread w;
1206	<	if (node != null && (w = node.waiter) != null &&
1207	<	U.compareAndSwapObject(node, WAITER, w, null)) {
1208	<	for (RNode pred = null, p = rhead; p != null;) {
1209	<	RNode q = p.next;
1210	<	if (p.waiter == null) {
1211	<	if (pred == null) {
1212	<	U.compareAndSwapObject(this, RHEAD, p, q);
1213	<	p = rhead;
1199	>	for (int spins = -1;;) {
1200	>	WNode h, np, pp; int ps;
1201	>	if ((h = whead) == p) {
1202	>	if (spins < 0)
1203	>	spins = HEAD_SPINS;
1204	>	else if (spins < MAX_HEAD_SPINS)
1205	>	spins <<= 1;
1206	>	for (int k = spins;;) { // spin at head
1207	>	long m, s, ns;
1208	>	if ((m = (s = state) & ABITS) < RFULL ?
1209	>	U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) :
1210	>	(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) {
1211	>	WNode c; Thread w;
1212	>	whead = node;
1213	>	node.prev = null;
1214	>	while ((c = node.cowait) != null) {
1215	>	if (U.compareAndSwapObject(node, WCOWAIT,
1216	>	c, c.cowait) &&
1217	>	(w = c.thread) != null)
1218	>	U.unpark(w);
1219	>	}
1220	>	return ns;
1221		}
1222	<	else {
1223	<	U.compareAndSwapObject(pred, RNEXT, p, q);
1224	<	p = pred.next;
1222	>	else if (m >= WBIT &&
1223	>	ThreadLocalRandom.current().nextInt() >= 0 && --k <= 0)
1224	>	break;
1225	>	}
1226	>	}
1227	>	else if (h != null) {
1228	>	WNode c; Thread w;
1229	>	while ((c = h.cowait) != null) {
1230	>	if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
1231	>	(w = c.thread) != null)
1232	>	U.unpark(w);
1233	>	}
1234	>	}
1235	>	if (whead == h) {
1236	>	if ((np = node.prev) != p) {
1237	>	if (np != null)
1238	>	(p = np).next = node;   // stale
1239	>	}
1240	>	else if ((ps = p.status) == 0)
1241	>	U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
1242	>	else if (ps == CANCELLED) {
1243	>	if ((pp = p.prev) != null) {
1244	>	node.prev = pp;
1245	>	pp.next = node;
1246		}
1247		}
1248		else {
1249	<	pred = p;
1249	>	long time;
1250	>	if (deadline == 0L)
1251	>	time = 0L;
1252	>	else if ((time = deadline - System.nanoTime()) <= 0L)
1253	>	return cancelWaiter(node, node, false);
1254	>	Thread wt = Thread.currentThread();
1255	>	U.putObject(wt, PARKBLOCKER, this);
1256	>	node.thread = wt;
1257	>	if (p.status < 0 &&
1258	>	(p != h || (state & ABITS) == WBIT) &&
1259	>	whead == h && node.prev == p)
1260	>	U.park(false, time);
1261	>	node.thread = null;
1262	>	U.putObject(wt, PARKBLOCKER, null);
1263	>	if (interruptible && Thread.interrupted())
1264	>	return cancelWaiter(node, node, true);
1265	>	}
1266	>	}
1267	>	}
1268	>	}
1269	>
1270	>	/**
1271	>	* If node non-null, forces cancel status and unsplices it from
1272	>	* queue if possible and wakes up any cowaiters (of the node, or
1273	>	* group, as applicable), and in any case helps release current
1274	>	* first waiter if lock is free. (Calling with null arguments
1275	>	* serves as a conditional form of release, which is not currently
1276	>	* needed but may be needed under possible future cancellation
1277	>	* policies). This is a variant of cancellation methods in
1278	>	* AbstractQueuedSynchronizer (see its detailed explanation in AQS
1279	>	* internal documentation).
1280	>	*
1281	>	* @param node if nonnull, the waiter
1282	>	* @param group either node or the group node is cowaiting with
1283	>	* @param interrupted if already interrupted
1284	>	* @return INTERRUPTED if interrupted or Thread.interrupted, else zero
1285	>	*/
1286	>	private long cancelWaiter(WNode node, WNode group, boolean interrupted) {
1287	>	if (node != null && group != null) {
1288	>	Thread w;
1289	>	node.status = CANCELLED;
1290	>	// unsplice cancelled nodes from group
1291	>	for (WNode p = group, q; (q = p.cowait) != null;) {
1292	>	if (q.status == CANCELLED) {
1293	>	U.compareAndSwapObject(p, WCOWAIT, q, q.cowait);
1294	>	p = group; // restart
1295	>	}
1296	>	else
1297		p = q;
1298	+	}
1299	+	if (group == node) {
1300	+	for (WNode r = group.cowait; r != null; r = r.cowait) {
1301	+	if ((w = r.thread) != null)
1302	+	U.unpark(w);       // wake up uncancelled co-waiters
1303	+	}
1304	+	for (WNode pred = node.prev; pred != null; ) { // unsplice
1305	+	WNode succ, pp;        // find valid successor
1306	+	while ((succ = node.next) == null ||
1307	+	succ.status == CANCELLED) {
1308	+	WNode q = null;    // find successor the slow way
1309	+	for (WNode t = wtail; t != null && t != node; t = t.prev)
1310	+	if (t.status != CANCELLED)
1311	+	q = t;     // don't link if succ cancelled
1312	+	if (succ == q ||   // ensure accurate successor
1313	+	U.compareAndSwapObject(node, WNEXT,
1314	+	succ, succ = q)) {
1315	+	if (succ == null && node == wtail)
1316	+	U.compareAndSwapObject(this, WTAIL, node, pred);
1317	+	break;
1318	+	}
1319	+	}
1320	+	if (pred.next == node) // unsplice pred link
1321	+	U.compareAndSwapObject(pred, WNEXT, node, succ);
1322	+	if (succ != null && (w = succ.thread) != null) {
1323	+	succ.thread = null;
1324	+	U.unpark(w);       // wake up succ to observe new pred
1325	+	}
1326	+	if (pred.status != CANCELLED || (pp = pred.prev) == null)
1327	+	break;
1328	+	node.prev = pp;        // repeat if new pred wrong/cancelled
1329	+	U.compareAndSwapObject(pp, WNEXT, pred, succ);
1330	+	pred = pp;
1331		}
1332		}
1333		}
1334	<	readerPrefSignal();
1334	>	WNode h; // Possibly release first waiter
1335	>	while ((h = whead) != null) {
1336	>	long s; WNode q; // similar to release() but check eligibility
1337	>	if ((q = h.next) == null || q.status == CANCELLED) {
1338	>	for (WNode t = wtail; t != null && t != h; t = t.prev)
1339	>	if (t.status <= 0)
1340	>	q = t;
1341	>	}
1342	>	if (h == whead) {
1343	>	if (q != null && h.status == 0 &&
1344	>	((s = state) & ABITS) != WBIT && // waiter is eligible
1345	>	(s == 0L || q.mode == RMODE))
1346	>	release(h);
1347	>	break;
1348	>	}
1349	>	}
1350		return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L;
1351		}
1352
1353		// Unsafe mechanics
1354		private static final sun.misc.Unsafe U;
1355		private static final long STATE;
1140	–	private static final long RHEAD;
1356		private static final long WHEAD;
1357		private static final long WTAIL;
1143	–	private static final long RNEXT;
1358		private static final long WNEXT;
1359	<	private static final long WPREV;
1360	<	private static final long WAITER;
1361	<	private static final long STATUS;
1359	>	private static final long WSTATUS;
1360	>	private static final long WCOWAIT;
1361	>	private static final long PARKBLOCKER;
1362
1363		static {
1364		try {
1365		U = getUnsafe();
1366		Class<?> k = StampedLock.class;
1153	–	Class<?> rk = RNode.class;
1367		Class<?> wk = WNode.class;
1368		STATE = U.objectFieldOffset
1369		(k.getDeclaredField("state"));
1157	–	RHEAD = U.objectFieldOffset
1158	–	(k.getDeclaredField("rhead"));
1370		WHEAD = U.objectFieldOffset
1371		(k.getDeclaredField("whead"));
1372		WTAIL = U.objectFieldOffset
1373		(k.getDeclaredField("wtail"));
1374	<	RNEXT = U.objectFieldOffset
1164	<	(rk.getDeclaredField("next"));
1165	<	WAITER = U.objectFieldOffset
1166	<	(rk.getDeclaredField("waiter"));
1167	<	STATUS = U.objectFieldOffset
1374	>	WSTATUS = U.objectFieldOffset
1375		(wk.getDeclaredField("status"));
1376		WNEXT = U.objectFieldOffset
1377		(wk.getDeclaredField("next"));
1378	<	WPREV = U.objectFieldOffset
1379	<	(wk.getDeclaredField("prev"));
1378	>	WCOWAIT = U.objectFieldOffset
1379	>	(wk.getDeclaredField("cowait"));
1380	>	Class<?> tk = Thread.class;
1381	>	PARKBLOCKER = U.objectFieldOffset
1382	>	(tk.getDeclaredField("parkBlocker"));
1383
1384		} catch (Exception e) {
1385		throw new Error(e);
#	Line 1186 | Line 1396 | public class StampedLock implements java
1396		private static sun.misc.Unsafe getUnsafe() {
1397		try {
1398		return sun.misc.Unsafe.getUnsafe();
1399	<	} catch (SecurityException se) {
1400	<	try {
1401	<	return java.security.AccessController.doPrivileged
1402	<	(new java.security
1403	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1404	<	public sun.misc.Unsafe run() throws Exception {
1405	<	java.lang.reflect.Field f = sun.misc
1406	<	.Unsafe.class.getDeclaredField("theUnsafe");
1407	<	f.setAccessible(true);
1408	<	return (sun.misc.Unsafe) f.get(null);
1409	<	}});
1410	<	} catch (java.security.PrivilegedActionException e) {
1411	<	throw new RuntimeException("Could not initialize intrinsics",
1412	<	e.getCause());
1413	<	}
1399	>	} catch (SecurityException tryReflectionInstead) {}
1400	>	try {
1401	>	return java.security.AccessController.doPrivileged
1402	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1403	>	public sun.misc.Unsafe run() throws Exception {
1404	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1405	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1406	>	f.setAccessible(true);
1407	>	Object x = f.get(null);
1408	>	if (k.isInstance(x))
1409	>	return k.cast(x);
1410	>	}
1411	>	throw new NoSuchFieldError("the Unsafe");
1412	>	}});
1413	>	} catch (java.security.PrivilegedActionException e) {
1414	>	throw new RuntimeException("Could not initialize intrinsics",
1415	>	e.getCause());
1416		}
1417		}
1206	–
1418		}

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