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

Comparing jsr166/src/jsr166e/StampedLock.java (file contents):
Revision 1.22 by jsr166, Wed Oct 17 00:02:47 2012 UTC vs.
Revision 1.34 by jsr166, Mon Jan 28 17:23:04 2013 UTC

#	Line 8 | Line 8 | package jsr166e;
8
9		import java.util.concurrent.ThreadLocalRandom;
10		import java.util.concurrent.TimeUnit;
11	+	import java.util.concurrent.locks.Lock;
12	+	import java.util.concurrent.locks.Condition;
13	+	import java.util.concurrent.locks.ReadWriteLock;
14	+	import java.util.concurrent.locks.LockSupport;
15
16		/**
17		* A capability-based lock with three modes for controlling read/write
#	Line 36 | Line 40 | import java.util.concurrent.TimeUnit;
40		*  <li><b>Optimistic Reading.</b> Method {@link #tryOptimisticRead}
41		*   returns a non-zero stamp only if the lock is not currently held
42		*   in write mode. Method {@link #validate} returns true if the lock
43	<	*   has not since been acquired in write mode. This mode can be
44	<	*   thought of as an extremely weak version of a read-lock, that can
45	<	*   be broken by a writer at any time.  The use of optimistic mode
46	<	*   for short read-only code segments often reduces contention and
47	<	*   improves throughput.  However, its use is inherently fragile.
48	<	*   Optimistic read sections should only read fields and hold them in
49	<	*   local variables for later use after validation. Fields read while
50	<	*   in optimistic mode may be wildly inconsistent, so usage applies
51	<	*   only when you are familiar enough with data representations to
52	<	*   check consistency and/or repeatedly invoke method {@code
53	<	*   validate()}.  For example, such steps are typically required when
54	<	*   first reading an object or array reference, and then accessing
55	<	*   one of its fields, elements or methods. </li>
43	>	*   has not been acquired in write mode since obtaining a given
44	>	*   stamp.  This mode can be thought of as an extremely weak version
45	>	*   of a read-lock, that can be broken by a writer at any time.  The
46	>	*   use of optimistic mode for short read-only code segments often
47	>	*   reduces contention and improves throughput.  However, its use is
48	>	*   inherently fragile.  Optimistic read sections should only read
49	>	*   fields and hold them in local variables for later use after
50	>	*   validation. Fields read while in optimistic mode may be wildly
51	>	*   inconsistent, so usage applies only when you are familiar enough
52	>	*   with data representations to check consistency and/or repeatedly
53	>	*   invoke method {@code validate()}.  For example, such steps are
54	>	*   typically required when first reading an object or array
55	>	*   reference, and then accessing one of its fields, elements or
56	>	*   methods. </li>
57		*
58		* </ul>
59		*
#	Line 80 | Line 85 | import java.util.concurrent.TimeUnit;
85		* locking.
86		*
87		* <p>The scheduling policy of StampedLock does not consistently
88	<	* prefer readers over writers or vice versa.  A zero return from any
89	<	* "try" method for acquiring or converting locks does not carry any
90	<	* information about the state of the lock; a subsequent invocation
91	<	* may succeed.
88	>	* prefer readers over writers or vice versa.  All "try" methods are
89	>	* best-effort and do not necessarily conform to any scheduling or
90	>	* fairness policy. A zero return from any "try" method for acquiring
91	>	* or converting locks does not carry any information about the state
92	>	* of the lock; a subsequent invocation may succeed.
93	>	*
94	>	* <p>Because it supports coordinated usage across multiple lock
95	>	* modes, this class does not directly implement the {@link Lock} or
96	>	* {@link ReadWriteLock} interfaces. However, a StampedLock may be
97	>	* viewed {@link #asReadLock()}, {@link #asWriteLock()}, or {@link
98	>	* #asReadWriteLock()} in applications requiring only the associated
99	>	* set of functionality.
100		*
101		* <p><b>Sample Usage.</b> The following illustrates some usage idioms
102		* in a class that maintains simple two-dimensional points. The sample
#	Line 156 | Line 169 | import java.util.concurrent.TimeUnit;
169		*         }
170		*       }
171		*     } finally {
172	<	*        sl.unlock(stamp);
172	>	*       sl.unlock(stamp);
173		*     }
174		*   }
175		* }}</pre>
#	Line 173 | Line 186 | public class StampedLock implements java
186		* http://www.lameter.com/gelato2005.pdf
187		* and elsewhere; see
188		* Boehm's http://www.hpl.hp.com/techreports/2012/HPL-2012-68.html)
189	<	* Ordered RW locks (see Shirako et al
189	>	* and Ordered RW locks (see Shirako et al
190		* http://dl.acm.org/citation.cfm?id=2312015)
178	–	* and Phase-Fair locks (see Brandenburg & Anderson, especially
179	–	* http://www.cs.unc.edu/~bbb/diss/).
191		*
192		* Conceptually, the primary state of the lock includes a sequence
193		* number that is odd when write-locked and even otherwise.
#	Line 189 | Line 200 | public class StampedLock implements java
200		* reader count value (RBITS) as a spinlock protecting overflow
201		* updates.
202		*
203	<	* Waiting readers and writers use different queues. The writer
204	<	* queue is a modified form of CLH lock.  (For discussion of CLH,
205	<	* see the internal documentation of AbstractQueuedSynchronizer.)
206	<	* The reader "queue" is a form of Treiber stack, that supports
207	<	* simpler/faster operations because order within a queue doesn't
208	<	* matter and all are signalled at once.  However the sequence of
209	<	* threads within the queue vs the current stamp does matter (see
210	<	* Shirako et al) so each carries its incoming stamp value.
211	<	* Waiting writers never need to track sequence values, so they
212	<	* don't.
213	<	*
214	<	* These queue mechanics hardwire the scheduling policy.  Ignoring
215	<	* trylocks, cancellation, and spinning, they implement Phase-Fair
216	<	* preferences:
217	<	*   1. Unlocked writers prefer to signal waiting readers
218	<	*   2. Fully unlocked readers prefer to signal waiting writers
208	<	*   3. When read-locked and a waiting writer exists, the writer
209	<	*      is preferred to incoming readers
203	>	* Waiters use a modified form of CLH lock used in
204	>	* AbstractQueuedSynchronizer (see its internal documentation for
205	>	* a fuller account), where each node is tagged (field mode) as
206	>	* either a reader or writer. Sets of waiting readers are grouped
207	>	* (linked) under a common node (field cowait) so act as a single
208	>	* node with respect to most CLH mechanics.  By virtue of the
209	>	* queue structure, wait nodes need not actually carry sequence
210	>	* numbers; we know each is greater than its predecessor.  This
211	>	* simplifies the scheduling policy to a mainly-FIFO scheme that
212	>	* incorporates elements of Phase-Fair locks (see Brandenburg &
213	>	* Anderson, especially http://www.cs.unc.edu/~bbb/diss/).  In
214	>	* particular, we use the phase-fair anti-barging rule: If an
215	>	* incoming reader arrives while read lock is held but there is a
216	>	* queued writer, this incoming reader is queued.  (This rule is
217	>	* responsible for some of the complexity of method acquireRead,
218	>	* but without it, the lock becomes highly unfair.)
219		*
220		* These rules apply to threads actually queued. All tryLock forms
221		* opportunistically try to acquire locks regardless of preference
222	<	* rules, and so may "barge" their way in.  Additionally, initial
223	<	* phases of the await* methods (invoked from readLock() and
224	<	* writeLock()) use controlled spins that have similar effect.
225	<	* Phase-fair preferences may also be broken on cancellations due
226	<	* to timeouts and interrupts.  Rule #3 (incoming readers when a
227	<	* waiting writer) is approximated with varying precision in
228	<	* different contexts -- some checks do not account for
229	<	* in-progress spins/signals, and others do not account for
230	<	* cancellations.
231	<	*
232	<	* Controlled, randomized spinning is used in the two await
233	<	* methods to reduce (increasingly expensive) context switching
234	<	* while also avoiding sustained memory thrashing among many
235	<	* threads.  Both await methods use a similar spin strategy: If
236	<	* the associated queue appears to be empty, then the thread
237	<	* spin-waits up to SPINS times (where each iteration decreases
229	<	* spin count with 50% probability) before enqueing, and then, if
230	<	* it is the first thread to be enqueued, spins again up to SPINS
231	<	* times before blocking. If, upon wakening it fails to obtain
232	<	* lock, and is still (or becomes) the first waiting thread (which
233	<	* indicates that some other thread barged and obtained lock), it
234	<	* escalates spins (up to MAX_HEAD_SPINS) to reduce the likelihood
235	<	* of continually losing to barging threads.
222	>	* rules, and so may "barge" their way in.  Randomized spinning is
223	>	* used in the acquire methods to reduce (increasingly expensive)
224	>	* context switching while also avoiding sustained memory
225	>	* thrashing among many threads.  We limit spins to the head of
226	>	* queue. A thread spin-waits up to SPINS times (where each
227	>	* iteration decreases spin count with 50% probability) before
228	>	* blocking. If, upon wakening it fails to obtain lock, and is
229	>	* still (or becomes) the first waiting thread (which indicates
230	>	* that some other thread barged and obtained lock), it escalates
231	>	* spins (up to MAX_HEAD_SPINS) to reduce the likelihood of
232	>	* continually losing to barging threads.
233	>	*
234	>	* Nearly all of these mechanics are carried out in methods
235	>	* acquireWrite and acquireRead, that, as typical of such code,
236	>	* sprawl out because actions and retries rely on consistent sets
237	>	* of locally cached reads.
238		*
239		* As noted in Boehm's paper (above), sequence validation (mainly
240		* method validate()) requires stricter ordering rules than apply
#	Line 252 | Line 254 | public class StampedLock implements java
254		* be subject to future improvements.
255		*/
256
257	+	private static final long serialVersionUID = -6001602636862214147L;
258	+
259		/** Number of processors, for spin control */
260		private static final int NCPU = Runtime.getRuntime().availableProcessors();
261
262		/** Maximum number of retries before blocking on acquisition */
263	<	private static final int SPINS = (NCPU > 1) ? 1 << 6 : 1;
263	>	private static final int SPINS = (NCPU > 1) ? 1 << 6 : 0;
264
265		/** Maximum number of retries before re-blocking */
266	<	private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 1;
266	>	private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 0;
267
268		/** The period for yielding when waiting for overflow spinlock */
269		private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1
#	Line 278 | Line 282 | public class StampedLock implements java
282		// Initial value for lock state; avoid failure value zero
283		private static final long ORIGIN = WBIT << 1;
284
285	<	// Special value from cancelled await methods so caller can throw IE
285	>	// Special value from cancelled acquire methods so caller can throw IE
286		private static final long INTERRUPTED = 1L;
287
288	<	// Values for writer status; order matters
288	>	// Values for node status; order matters
289		private static final int WAITING   = -1;
290		private static final int CANCELLED =  1;
291
292	<	/** Wait nodes for readers */
293	<	static final class RNode {
294	<	final long seq;         // stamp value upon enqueue
291	<	volatile Thread waiter; // null if no longer waiting
292	<	volatile RNode next;
293	<	RNode(long s, Thread w) { seq = s; waiter = w; }
294	<	}
292	>	// Modes for nodes (int not boolean to allow arithmetic)
293	>	private static final int RMODE = 0;
294	>	private static final int WMODE = 1;
295
296	<	/** Wait nodes for writers */
296	>	/** Wait nodes */
297		static final class WNode {
298	–	volatile int status;   // 0, WAITING, or CANCELLED
298		volatile WNode prev;
299		volatile WNode next;
300	<	volatile Thread thread;
301	<	WNode(Thread t, WNode p) { thread = t; prev = p; }
300	>	volatile WNode cowait;    // list of linked readers
301	>	volatile Thread thread;   // non-null while possibly parked
302	>	volatile int status;      // 0, WAITING, or CANCELLED
303	>	final int mode;           // RMODE or WMODE
304	>	WNode(int m, WNode p) { mode = m; prev = p; }
305		}
306
307	<	/** Head of writer CLH queue */
307	>	/** Head of CLH queue */
308		private transient volatile WNode whead;
309	<	/** Tail (last) of writer CLH queue */
309	>	/** Tail (last) of CLH queue */
310		private transient volatile WNode wtail;
311	<	/** Head of read queue  */
312	<	private transient volatile RNode rhead;
313	<	/** The state of the lock -- high bits hold sequence, low bits read count */
311	>
312	>	// views
313	>	transient ReadLockView readLockView;
314	>	transient WriteLockView writeLockView;
315	>	transient ReadWriteLockView readWriteLockView;
316	>
317	>	/** Lock sequence/state */
318		private transient volatile long state;
319		/** extra reader count when state read count saturated */
320		private transient int readerOverflow;
#	Line 327 | Line 333 | public class StampedLock implements java
333		* @return a stamp that can be used to unlock or convert mode
334		*/
335		public long writeLock() {
336	<	long s, next;
337	<	if (((s = state) & ABITS) == 0L &&
338	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
339	<	return next;
334	<	return awaitWrite(false, 0L);
336	>	long s, next;  // bypass acquireWrite in fully unlocked case only
337	>	return ((((s = state) & ABITS) == 0L &&
338	>	U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ?
339	>	next : acquireWrite(false, 0L));
340		}
341
342		/**
#	Line 342 | Line 347 | public class StampedLock implements java
347		*/
348		public long tryWriteLock() {
349		long s, next;
350	<	if (((s = state) & ABITS) == 0L &&
351	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
352	<	return next;
348	<	return 0L;
350	>	return ((((s = state) & ABITS) == 0L &&
351	>	U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ?
352	>	next : 0L);
353		}
354
355		/**
356		* Exclusively acquires the lock if it is available within the
357		* given time and the current thread has not been interrupted.
358	+	* Behavior under timeout and interruption matches that specified
359	+	* for method {@link Lock#tryLock(long,TimeUnit)}.
360		*
361		* @return a stamp that can be used to unlock or convert mode,
362		* or zero if the lock is not available
#	Line 361 | Line 367 | public class StampedLock implements java
367		throws InterruptedException {
368		long nanos = unit.toNanos(time);
369		if (!Thread.interrupted()) {
370	<	long s, next, deadline;
371	<	if (((s = state) & ABITS) == 0L &&
366	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
370	>	long next, deadline;
371	>	if ((next = tryWriteLock()) != 0L)
372		return next;
373		if (nanos <= 0L)
374		return 0L;
375		if ((deadline = System.nanoTime() + nanos) == 0L)
376		deadline = 1L;
377	<	if ((next = awaitWrite(true, deadline)) != INTERRUPTED)
377	>	if ((next = acquireWrite(true, deadline)) != INTERRUPTED)
378		return next;
379		}
380		throw new InterruptedException();
#	Line 378 | Line 383 | public class StampedLock implements java
383		/**
384		* Exclusively acquires the lock, blocking if necessary
385		* until available or the current thread is interrupted.
386	+	* Behavior under interruption matches that specified
387	+	* for method {@link Lock#lockInterruptibly()}.
388		*
389		* @return a stamp that can be used to unlock or convert mode
390		* @throws InterruptedException if the current thread is interrupted
391		* before acquiring the lock
392		*/
393		public long writeLockInterruptibly() throws InterruptedException {
394	<	if (!Thread.interrupted()) {
395	<	long s, next;
396	<	if (((s = state) & ABITS) == 0L &&
397	<	U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
391	<	return next;
392	<	if ((next = awaitWrite(true, 0L)) != INTERRUPTED)
393	<	return next;
394	<	}
394	>	long next;
395	>	if (!Thread.interrupted() &&
396	>	(next = acquireWrite(true, 0L)) != INTERRUPTED)
397	>	return next;
398		throw new InterruptedException();
399		}
400
#	Line 402 | Line 405 | public class StampedLock implements java
405		* @return a stamp that can be used to unlock or convert mode
406		*/
407		public long readLock() {
408	<	for (;;) {
409	<	long s, m, next;
410	<	if ((m = (s = state) & ABITS) == 0L ||
411	<	(m < WBIT && whead == wtail)) {
409	<	if (m < RFULL) {
410	<	if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
411	<	return next;
412	<	}
413	<	else if ((next = tryIncReaderOverflow(s)) != 0L)
414	<	return next;
415	<	}
416	<	else
417	<	return awaitRead(s, false, 0L);
418	<	}
408	>	long s, next;  // bypass acquireRead on fully unlocked case only
409	>	return ((((s = state) & ABITS) == 0L &&
410	>	U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) ?
411	>	next : acquireRead(false, 0L));
412		}
413
414		/**
#	Line 441 | Line 434 | public class StampedLock implements java
434		/**
435		* Non-exclusively acquires the lock if it is available within the
436		* given time and the current thread has not been interrupted.
437	+	* Behavior under timeout and interruption matches that specified
438	+	* for method {@link Lock#tryLock(long,TimeUnit)}.
439		*
440		* @return a stamp that can be used to unlock or convert mode,
441		* or zero if the lock is not available
#	Line 449 | Line 444 | public class StampedLock implements java
444		*/
445		public long tryReadLock(long time, TimeUnit unit)
446		throws InterruptedException {
447	+	long s, m, next, deadline;
448		long nanos = unit.toNanos(time);
449		if (!Thread.interrupted()) {
450	<	for (;;) {
451	<	long s, m, next, deadline;
456	<	if ((m = (s = state) & ABITS) == WBIT ||
457	<	(m != 0L && whead != wtail)) {
458	<	if (nanos <= 0L)
459	<	return 0L;
460	<	if ((deadline = System.nanoTime() + nanos) == 0L)
461	<	deadline = 1L;
462	<	if ((next = awaitRead(s, true, deadline)) != INTERRUPTED)
463	<	return next;
464	<	break;
465	<	}
466	<	else if (m < RFULL) {
450	>	if ((m = (s = state) & ABITS) != WBIT) {
451	>	if (m < RFULL) {
452		if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
453		return next;
454		}
455		else if ((next = tryIncReaderOverflow(s)) != 0L)
456		return next;
457		}
458	+	if (nanos <= 0L)
459	+	return 0L;
460	+	if ((deadline = System.nanoTime() + nanos) == 0L)
461	+	deadline = 1L;
462	+	if ((next = acquireRead(true, deadline)) != INTERRUPTED)
463	+	return next;
464		}
465		throw new InterruptedException();
466		}
#	Line 477 | Line 468 | public class StampedLock implements java
468		/**
469		* Non-exclusively acquires the lock, blocking if necessary
470		* until available or the current thread is interrupted.
471	+	* Behavior under interruption matches that specified
472	+	* for method {@link Lock#lockInterruptibly()}.
473		*
474		* @return a stamp that can be used to unlock or convert mode
475		* @throws InterruptedException if the current thread is interrupted
476		* before acquiring the lock
477		*/
478		public long readLockInterruptibly() throws InterruptedException {
479	<	if (!Thread.interrupted()) {
480	<	for (;;) {
481	<	long s, next, m;
482	<	if ((m = (s = state) & ABITS) == WBIT ||
490	<	(m != 0L && whead != wtail)) {
491	<	if ((next = awaitRead(s, true, 0L)) != INTERRUPTED)
492	<	return next;
493	<	break;
494	<	}
495	<	else if (m < RFULL) {
496	<	if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT))
497	<	return next;
498	<	}
499	<	else if ((next = tryIncReaderOverflow(s)) != 0L)
500	<	return next;
501	<	}
502	<	}
479	>	long next;
480	>	if (!Thread.interrupted() &&
481	>	(next = acquireRead(true, 0L)) != INTERRUPTED)
482	>	return next;
483		throw new InterruptedException();
484		}
485
#	Line 518 | Line 498 | public class StampedLock implements java
498		* Returns true if the lock has not been exclusively acquired
499		* since issuance of the given stamp. Always returns false if the
500		* stamp is zero. Always returns true if the stamp represents a
501	<	* currently held lock.
501	>	* currently held lock. Invoking this method with a value not
502	>	* obtained from {@link #tryOptimisticRead} or a locking method
503	>	* for this lock has no defined effect or result.
504		*
505		* @return true if the lock has not been exclusively acquired
506		* since issuance of the given stamp; else false
#	Line 537 | Line 519 | public class StampedLock implements java
519		* not match the current state of this lock
520		*/
521		public void unlockWrite(long stamp) {
522	+	WNode h;
523		if (state != stamp || (stamp & WBIT) == 0L)
524		throw new IllegalMonitorStateException();
525		state = (stamp += WBIT) == 0L ? ORIGIN : stamp;
526	<	readerPrefSignal();
526	>	if ((h = whead) != null && h.status != 0)
527	>	release(h);
528		}
529
530		/**
#	Line 552 | Line 536 | public class StampedLock implements java
536		* not match the current state of this lock
537		*/
538		public void unlockRead(long stamp) {
539	<	long s, m;
540	<	if ((stamp & RBITS) != 0L) {
541	<	while (((s = state) & SBITS) == (stamp & SBITS)) {
542	<	if ((m = s & ABITS) == 0L)
539	>	long s, m; WNode h;
540	>	for (;;) {
541	>	if (((s = state) & SBITS) != (stamp & SBITS) ||
542	>	(stamp & ABITS) == 0L || (m = s & ABITS) == 0L || m == WBIT)
543	>	throw new IllegalMonitorStateException();
544	>	if (m < RFULL) {
545	>	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
546	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
547	>	release(h);
548		break;
560	–	else if (m < RFULL) {
561	–	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
562	–	if (m == RUNIT)
563	–	writerPrefSignal();
564	–	return;
565	–	}
549		}
567	–	else if (m >= WBIT)
568	–	break;
569	–	else if (tryDecReaderOverflow(s) != 0L)
570	–	return;
550		}
551	+	else if (tryDecReaderOverflow(s) != 0L)
552	+	break;
553		}
573	–	throw new IllegalMonitorStateException();
554		}
555
556		/**
#	Line 582 | Line 562 | public class StampedLock implements java
562		* not match the current state of this lock
563		*/
564		public void unlock(long stamp) {
565	<	long a = stamp & ABITS, m, s;
565	>	long a = stamp & ABITS, m, s; WNode h;
566		while (((s = state) & SBITS) == (stamp & SBITS)) {
567		if ((m = s & ABITS) == 0L)
568		break;
#	Line 590 | Line 570 | public class StampedLock implements java
570		if (a != m)
571		break;
572		state = (s += WBIT) == 0L ? ORIGIN : s;
573	<	readerPrefSignal();
573	>	if ((h = whead) != null && h.status != 0)
574	>	release(h);
575		return;
576		}
577		else if (a == 0L || a >= WBIT)
578		break;
579		else if (m < RFULL) {
580		if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
581	<	if (m == RUNIT)
582	<	writerPrefSignal();
581	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
582	>	release(h);
583		return;
584		}
585		}
#	Line 609 | Line 590 | public class StampedLock implements java
590		}
591
592		/**
593	<	* If the lock state matches the given stamp then performs one of
593	>	* If the lock state matches the given stamp, performs one of
594		* the following actions. If the stamp represents holding a write
595		* lock, returns it.  Or, if a read lock, if the write lock is
596		* available, releases the read lock and returns a write stamp.
#	Line 646 | Line 627 | public class StampedLock implements java
627		}
628
629		/**
630	<	* If the lock state matches the given stamp then performs one of
630	>	* If the lock state matches the given stamp, performs one of
631		* the following actions. If the stamp represents holding a write
632		* lock, releases it and obtains a read lock.  Or, if a read lock,
633		* returns it. Or, if an optimistic read, acquires a read lock and
#	Line 657 | Line 638 | public class StampedLock implements java
638		* @return a valid read stamp, or zero on failure
639		*/
640		public long tryConvertToReadLock(long stamp) {
641	<	long a = stamp & ABITS, m, s, next;
641	>	long a = stamp & ABITS, m, s, next; WNode h;
642		while (((s = state) & SBITS) == (stamp & SBITS)) {
643		if ((m = s & ABITS) == 0L) {
644		if (a != 0L)
#	Line 673 | Line 654 | public class StampedLock implements java
654		if (a != m)
655		break;
656		state = next = s + (WBIT + RUNIT);
657	<	readerPrefSignal();
657	>	if ((h = whead) != null && h.status != 0)
658	>	release(h);
659		return next;
660		}
661		else if (a != 0L && a < WBIT)
#	Line 695 | Line 677 | public class StampedLock implements java
677		* @return a valid optimistic read stamp, or zero on failure
678		*/
679		public long tryConvertToOptimisticRead(long stamp) {
680	<	long a = stamp & ABITS, m, s, next;
681	<	while (((s = U.getLongVolatile(this, STATE)) &
682	<	SBITS) == (stamp & SBITS)) {
680	>	long a = stamp & ABITS, m, s, next; WNode h;
681	>	for (;;) {
682	>	s = U.getLongVolatile(this, STATE); // see above
683	>	if ((s & SBITS) != (stamp & SBITS))
684	>	break;
685		if ((m = s & ABITS) == 0L) {
686		if (a != 0L)
687		break;
#	Line 707 | Line 691 | public class StampedLock implements java
691		if (a != m)
692		break;
693		state = next = (s += WBIT) == 0L ? ORIGIN : s;
694	<	readerPrefSignal();
694	>	if ((h = whead) != null && h.status != 0)
695	>	release(h);
696		return next;
697		}
698		else if (a == 0L || a >= WBIT)
699		break;
700		else if (m < RFULL) {
701		if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) {
702	<	if (m == RUNIT)
703	<	writerPrefSignal();
702	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
703	>	release(h);
704		return next & SBITS;
705		}
706		}
#	Line 733 | Line 718 | public class StampedLock implements java
718		* @return true if the lock was held, else false
719		*/
720		public boolean tryUnlockWrite() {
721	<	long s;
721	>	long s; WNode h;
722		if (((s = state) & WBIT) != 0L) {
723		state = (s += WBIT) == 0L ? ORIGIN : s;
724	<	readerPrefSignal();
724	>	if ((h = whead) != null && h.status != 0)
725	>	release(h);
726		return true;
727		}
728		return false;
#	Line 750 | Line 736 | public class StampedLock implements java
736		* @return true if the read lock was held, else false
737		*/
738		public boolean tryUnlockRead() {
739	<	long s, m;
739	>	long s, m; WNode h;
740		while ((m = (s = state) & ABITS) != 0L && m < WBIT) {
741		if (m < RFULL) {
742		if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
743	<	if (m == RUNIT)
744	<	writerPrefSignal();
743	>	if (m == RUNIT && (h = whead) != null && h.status != 0)
744	>	release(h);
745		return true;
746		}
747		}
#	Line 789 | Line 775 | public class StampedLock implements java
775		state = ORIGIN; // reset to unlocked state
776		}
777
778	+	/**
779	+	* Returns a plain {@link Lock} view of this StampedLock in which
780	+	* the {@link Lock#lock} method is mapped to {@link #readLock},
781	+	* and similarly for other methods. The returned Lock does not
782	+	* support a {@link Condition}; method {@link
783	+	* Lock#newCondition()} throws {@code
784	+	* UnsupportedOperationException}.
785	+	*
786	+	* @return the lock
787	+	*/
788	+	public Lock asReadLock() {
789	+	ReadLockView v;
790	+	return ((v = readLockView) != null ? v :
791	+	(readLockView = new ReadLockView()));
792	+	}
793	+
794	+	/**
795	+	* Returns a plain {@link Lock} view of this StampedLock in which
796	+	* the {@link Lock#lock} method is mapped to {@link #writeLock},
797	+	* and similarly for other methods. The returned Lock does not
798	+	* support a {@link Condition}; method {@link
799	+	* Lock#newCondition()} throws {@code
800	+	* UnsupportedOperationException}.
801	+	*
802	+	* @return the lock
803	+	*/
804	+	public Lock asWriteLock() {
805	+	WriteLockView v;
806	+	return ((v = writeLockView) != null ? v :
807	+	(writeLockView = new WriteLockView()));
808	+	}
809	+
810	+	/**
811	+	* Returns a {@link ReadWriteLock} view of this StampedLock in
812	+	* which the {@link ReadWriteLock#readLock()} method is mapped to
813	+	* {@link #asReadLock()}, and {@link ReadWriteLock#writeLock()} to
814	+	* {@link #asWriteLock()}.
815	+	*
816	+	* @return the lock
817	+	*/
818	+	public ReadWriteLock asReadWriteLock() {
819	+	ReadWriteLockView v;
820	+	return ((v = readWriteLockView) != null ? v :
821	+	(readWriteLockView = new ReadWriteLockView()));
822	+	}
823	+
824	+	// view classes
825	+
826	+	final class ReadLockView implements Lock {
827	+	public void lock() { readLock(); }
828	+	public void lockInterruptibly() throws InterruptedException {
829	+	readLockInterruptibly();
830	+	}
831	+	public boolean tryLock() { return tryReadLock() != 0L; }
832	+	public boolean tryLock(long time, TimeUnit unit)
833	+	throws InterruptedException {
834	+	return tryReadLock(time, unit) != 0L;
835	+	}
836	+	public void unlock() { unstampedUnlockRead(); }
837	+	public Condition newCondition() {
838	+	throw new UnsupportedOperationException();
839	+	}
840	+	}
841	+
842	+	final class WriteLockView implements Lock {
843	+	public void lock() { writeLock(); }
844	+	public void lockInterruptibly() throws InterruptedException {
845	+	writeLockInterruptibly();
846	+	}
847	+	public boolean tryLock() { return tryWriteLock() != 0L; }
848	+	public boolean tryLock(long time, TimeUnit unit)
849	+	throws InterruptedException {
850	+	return tryWriteLock(time, unit) != 0L;
851	+	}
852	+	public void unlock() { unstampedUnlockWrite(); }
853	+	public Condition newCondition() {
854	+	throw new UnsupportedOperationException();
855	+	}
856	+	}
857	+
858	+	final class ReadWriteLockView implements ReadWriteLock {
859	+	public Lock readLock() { return asReadLock(); }
860	+	public Lock writeLock() { return asWriteLock(); }
861	+	}
862	+
863	+	// Unlock methods without stamp argument checks for view classes.
864	+	// Needed because view-class lock methods throw away stamps.
865	+
866	+	final void unstampedUnlockWrite() {
867	+	WNode h; long s;
868	+	if (((s = state) & WBIT) == 0L)
869	+	throw new IllegalMonitorStateException();
870	+	state = (s += WBIT) == 0L ? ORIGIN : s;
871	+	if ((h = whead) != null && h.status != 0)
872	+	release(h);
873	+	}
874	+
875	+	final void unstampedUnlockRead() {
876	+	for (;;) {
877	+	long s, m; WNode h;
878	+	if ((m = (s = state) & ABITS) == 0L || m >= WBIT)
879	+	throw new IllegalMonitorStateException();
880	+	else if (m < RFULL) {
881	+	if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
882	+	if (m == RUNIT && (h = whead) != null && h.status != 0)
883	+	release(h);
884	+	break;
885	+	}
886	+	}
887	+	else if (tryDecReaderOverflow(s) != 0L)
888	+	break;
889	+	}
890	+	}
891	+
892		// internals
893
894		/**
#	Line 839 | Line 939 | public class StampedLock implements java
939		return 0L;
940		}
941
942	<	/*
943	<	* The two versions of signal implement the phase-fair policy.
944	<	* They include almost the same code, but repacked in different
945	<	* ways.  Integrating the policy with the mechanics eliminates
946	<	* state rechecks that would be needed with separate reader and
947	<	* writer signal methods.  Both methods assume that they are
948	<	* called when the lock is last known to be available, and
949	<	* continue until the lock is unavailable, or at least one thread
950	<	* is signalled, or there are no more waiting threads.  Signalling
951	<	* a reader entails popping (CASing) from rhead and unparking
952	<	* unless the thread already cancelled (indicated by a null waiter
853	<	* field). Signalling a writer requires finding the first node,
854	<	* i.e., the successor of whead. This is normally just head.next,
855	<	* but may require traversal from wtail if next pointers are
856	<	* lagging. These methods may fail to wake up an acquiring thread
857	<	* when one or more have been cancelled, but the cancel methods
858	<	* themselves provide extra safeguards to ensure liveness.
859	<	*/
860	<
861	<	private void readerPrefSignal() {
862	<	boolean readers = false;
863	<	RNode p; WNode h, q; long s; Thread w;
864	<	while ((p = rhead) != null) {
865	<	if (((s = state) & WBIT) != 0L)
866	<	return;
867	<	if (p.seq == (s & SBITS))
868	<	break;
869	<	readers = true;
870	<	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
871	<	(w = p.waiter) != null &&
872	<	U.compareAndSwapObject(p, WAITER, w, null))
873	<	U.unpark(w);
874	<	}
875	<	if (!readers && (h = whead) != null && h.status != 0 &&
876	<	(state & ABITS) == 0L) {
877	<	U.compareAndSwapInt(h, STATUS, WAITING, 0);
878	<	if ((q = h.next) == null || q.status == CANCELLED) {
879	<	for (WNode t = wtail; t != null && t != h; t = t.prev)
880	<	if (t.status <= 0)
881	<	q = t;
882	<	}
883	<	if (q != null && (w = q.thread) != null)
884	<	U.unpark(w);
885	<	}
886	<	}
887	<
888	<	private void writerPrefSignal() {
889	<	RNode p; WNode h, q; long s; Thread w;
890	<	if ((h = whead) != null && h.status != 0) {
891	<	U.compareAndSwapInt(h, STATUS, WAITING, 0);
942	>	/**
943	>	* Wakes up the successor of h (normally whead). This is normally
944	>	* just h.next, but may require traversal from wtail if next
945	>	* pointers are lagging. This may fail to wake up an acquiring
946	>	* thread when one or more have been cancelled, but the cancel
947	>	* methods themselves provide extra safeguards to ensure liveness.
948	>	*/
949	>	private void release(WNode h) {
950	>	if (h != null) {
951	>	WNode q; Thread w;
952	>	U.compareAndSwapInt(h, WSTATUS, WAITING, 0);
953		if ((q = h.next) == null || q.status == CANCELLED) {
954		for (WNode t = wtail; t != null && t != h; t = t.prev)
955		if (t.status <= 0)
956		q = t;
957		}
958	<	if (q != null && (w = q.thread) != null)
959	<	U.unpark(w);
960	<	}
961	<	else {
962	<	while ((p = rhead) != null && ((s = state) & WBIT) == 0L &&
963	<	p.seq != (s & SBITS)) {
964	<	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
965	<	(w = p.waiter) != null &&
966	<	U.compareAndSwapObject(p, WAITER, w, null))
967	<	U.unpark(w);
958	>	if (q != null) {
959	>	for (WNode r = q;;) {  // release co-waiters too
960	>	if ((w = r.thread) != null) {
961	>	r.thread = null;
962	>	U.unpark(w);
963	>	}
964	>	if ((r = q.cowait) == null)
965	>	break;
966	>	U.compareAndSwapObject(q, WCOWAIT, r, r.cowait);
967	>	}
968		}
969		}
970		}
971
972		/**
973	<	* RNG for local spins. The first call from await{Read,Write}
913	<	* produces a thread-local value. Unless zero, subsequent calls
914	<	* use an xorShift to further reduce memory traffic.
915	<	*/
916	<	private static int nextRandom(int r) {
917	<	if (r == 0)
918	<	return ThreadLocalRandom.current().nextInt();
919	<	r ^= r << 1; // xorshift
920	<	r ^= r >>> 3;
921	<	r ^= r << 10;
922	<	return r;
923	<	}
924	<
925	<	/**
926	<	* Possibly spins trying to obtain write lock, then enqueues and
927	<	* blocks while not head of write queue or cannot acquire lock,
928	<	* possibly spinning when at head; cancelling on timeout or
929	<	* interrupt.
973	>	* See above for explanation.
974		*
975		* @param interruptible true if should check interrupts and if so
976		* return INTERRUPTED
977		* @param deadline if nonzero, the System.nanoTime value to timeout
978		* at (and return zero)
979	+	* @return next state, or INTERRUPTED
980		*/
981	<	private long awaitWrite(boolean interruptible, long deadline) {
982	<	WNode node = null;
983	<	for (int r = 0, spins = -1;;) {
984	<	WNode p; long s, next;
981	>	private long acquireWrite(boolean interruptible, long deadline) {
982	>	WNode node = null, p;
983	>	for (int spins = -1;;) { // spin while enqueuing
984	>	long s, ns;
985		if (((s = state) & ABITS) == 0L) {
986	<	if (U.compareAndSwapLong(this, STATE, s, next = s + WBIT))
987	<	return next;
986	>	if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT))
987	>	return ns;
988		}
944	–	else if (spins < 0)
945	–	spins = whead == wtail ? SPINS : 0;
989		else if (spins > 0) {
990	<	if ((r = nextRandom(r)) >= 0)
990	>	if (ThreadLocalRandom.current().nextInt() >= 0)
991		--spins;
992		}
993		else if ((p = wtail) == null) { // initialize queue
994	<	if (U.compareAndSwapObject(this, WHEAD, null,
995	<	new WNode(null, null)))
996	<	wtail = whead;
994	>	WNode h = new WNode(WMODE, null);
995	>	if (U.compareAndSwapObject(this, WHEAD, null, h))
996	>	wtail = h;
997		}
998	+	else if (spins < 0)
999	+	spins = (p == whead) ? SPINS : 0;
1000		else if (node == null)
1001	<	node = new WNode(Thread.currentThread(), p);
1001	>	node = new WNode(WMODE, p);
1002		else if (node.prev != p)
1003		node.prev = p;
1004		else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
1005		p.next = node;
1006	<	for (int headSpins = SPINS;;) {
1007	<	WNode np, pp; int ps;
1008	<	while ((np = node.prev) != p && np != null)
1009	<	(p = np).next = node; // stale
1010	<	if (p == whead) {
1011	<	for (int k = headSpins;;) {
1012	<	if (((s = state) & ABITS) == 0L) {
1013	<	if (U.compareAndSwapLong(this, STATE,
1014	<	s, next = s + WBIT)) {
1015	<	whead = node;
1016	<	node.thread = null;
1017	<	node.prev = null;
1018	<	return next;
1019	<	}
1020	<	break;
976	<	}
977	<	if ((r = nextRandom(r)) >= 0 && --k <= 0)
978	<	break;
979	<	}
980	<	if (headSpins < MAX_HEAD_SPINS)
981	<	headSpins <<= 1;
982	<	}
983	<	if ((ps = p.status) == 0)
984	<	U.compareAndSwapInt(p, STATUS, 0, WAITING);
985	<	else if (ps == CANCELLED) {
986	<	if ((pp = p.prev) != null) {
987	<	node.prev = pp;
988	<	pp.next = node;
1006	>	break;
1007	>	}
1008	>	}
1009	>
1010	>	for (int spins = SPINS;;) {
1011	>	WNode np, pp; int ps; long s, ns; Thread w;
1012	>	while ((np = node.prev) != p && np != null)
1013	>	(p = np).next = node;   // stale
1014	>	if (whead == p) {
1015	>	for (int k = spins;;) { // spin at head
1016	>	if (((s = state) & ABITS) == 0L) {
1017	>	if (U.compareAndSwapLong(this, STATE, s, ns = s+WBIT)) {
1018	>	whead = node;
1019	>	node.prev = null;
1020	>	return ns;
1021		}
1022		}
1023	<	else {
1024	<	long time; // 0 argument to park means no timeout
1025	<	if (deadline == 0L)
1026	<	time = 0L;
1027	<	else if ((time = deadline - System.nanoTime()) <= 0L)
1028	<	return cancelWriter(node, false);
1029	<	if (node.prev == p && p.status == WAITING &&
1030	<	(p != whead || (state & WBIT) != 0L)) // recheck
1031	<	U.park(false, time);
1032	<	if (interruptible && Thread.interrupted())
1033	<	return cancelWriter(node, true);
1034	<	}
1023	>	else if (ThreadLocalRandom.current().nextInt() >= 0 &&
1024	>	--k <= 0)
1025	>	break;
1026	>	}
1027	>	if (spins < MAX_HEAD_SPINS)
1028	>	spins <<= 1;
1029	>	}
1030	>	if ((ps = p.status) == 0)
1031	>	U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
1032	>	else if (ps == CANCELLED) {
1033	>	if ((pp = p.prev) != null) {
1034	>	node.prev = pp;
1035	>	pp.next = node;
1036		}
1037		}
1038	+	else {
1039	+	long time; // 0 argument to park means no timeout
1040	+	if (deadline == 0L)
1041	+	time = 0L;
1042	+	else if ((time = deadline - System.nanoTime()) <= 0L)
1043	+	return cancelWaiter(node, node, false);
1044	+	node.thread = Thread.currentThread();
1045	+	if (node.prev == p && p.status == WAITING && // recheck
1046	+	(p != whead || (state & ABITS) != 0L))
1047	+	U.park(false, time);
1048	+	node.thread = null;
1049	+	if (interruptible && Thread.interrupted())
1050	+	return cancelWaiter(node, node, true);
1051	+	}
1052		}
1053		}
1054
1055		/**
1056	<	* If node non-null, forces cancel status and unsplices from queue
1057	<	* if possible. This is a variant of cancellation methods in
1058	<	* AbstractQueuedSynchronizer (see its detailed explanation in AQS
1059	<	* internal documentation) that more conservatively wakes up other
1060	<	* threads that may have had their links changed, so as to preserve
1061	<	* liveness in the main signalling methods.
1056	>	* See above for explanation.
1057	>	*
1058	>	* @param interruptible true if should check interrupts and if so
1059	>	* return INTERRUPTED
1060	>	* @param deadline if nonzero, the System.nanoTime value to timeout
1061	>	* at (and return zero)
1062	>	* @return next state, or INTERRUPTED
1063		*/
1064	<	private long cancelWriter(WNode node, boolean interrupted) {
1065	<	if (node != null) {
1066	<	node.thread = null;
1067	<	node.status = CANCELLED;
1068	<	for (WNode pred = node.prev; pred != null; ) {
1069	<	WNode succ, pp; Thread w;
1070	<	while ((succ = node.next) == null || succ.status == CANCELLED) {
1071	<	WNode q = null;
1072	<	for (WNode t = wtail; t != null && t != node; t = t.prev)
1073	<	if (t.status != CANCELLED)
1074	<	q = t;
1075	<	if (succ == q ||
1076	<	U.compareAndSwapObject(node, WNEXT, succ, succ = q)) {
1077	<	if (succ == null && node == wtail)
1078	<	U.compareAndSwapObject(this, WTAIL, node, pred);
1079	<	break;
1064	>	private long acquireRead(boolean interruptible, long deadline) {
1065	>	WNode node = null, group = null, p;
1066	>	for (int spins = -1;;) {
1067	>	for (;;) {
1068	>	long s, m, ns; WNode h, q; Thread w; // anti-barging guard
1069	>	if (group == null && (h = whead) != null &&
1070	>	(q = h.next) != null && q.mode != RMODE)
1071	>	break;
1072	>	if ((m = (s = state) & ABITS) < RFULL ?
1073	>	U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) :
1074	>	(m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L)) {
1075	>	if (group != null) {  // help release others
1076	>	for (WNode r = group;;) {
1077	>	if ((w = r.thread) != null) {
1078	>	r.thread = null;
1079	>	U.unpark(w);
1080	>	}
1081	>	if ((r = group.cowait) == null)
1082	>	break;
1083	>	U.compareAndSwapObject(group, WCOWAIT, r, r.cowait);
1084	>	}
1085		}
1086	+	return ns;
1087		}
1088	<	if (pred.next == node)
1035	<	U.compareAndSwapObject(pred, WNEXT, node, succ);
1036	<	if (succ != null && (w = succ.thread) != null)
1037	<	U.unpark(w);
1038	<	if (pred.status != CANCELLED || (pp = pred.prev) == null)
1088	>	if (m >= WBIT)
1089		break;
1040	–	node.prev = pp; // repeat for new pred
1041	–	U.compareAndSwapObject(pp, WNEXT, pred, succ);
1042	–	pred = pp;
1090		}
1091	<	}
1092	<	writerPrefSignal();
1093	<	return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L;
1094	<	}
1095	<
1096	<	/**
1097	<	* Waits for read lock or timeout or interrupt. The form of
1098	<	* awaitRead differs from awaitWrite mainly because it must
1099	<	* restart (with a new wait node) if the thread was unqueued and
1100	<	* unparked but could not the obtain lock.  We also need to help
1101	<	* with preference rules by not trying to acquire the lock before
1102	<	* enqueuing if there is a known waiting writer, but also helping
1103	<	* to release those threads that are still queued from the last
1104	<	* release.
1105	<	*/
1106	<	private long awaitRead(long stamp, boolean interruptible, long deadline) {
1107	<	long seq = stamp & SBITS;
1108	<	RNode node = null;
1109	<	boolean queued = false;
1110	<	for (int r = 0, headSpins = SPINS, spins = -1;;) {
1111	<	long s, m, next; RNode p; WNode wh; Thread w;
1112	<	if ((m = (s = state) & ABITS) != WBIT &&
1113	<	((s & SBITS) != seq || (wh = whead) == null ||
1114	<	wh.status == 0)) {
1115	<	if (m < RFULL ?
1116	<	U.compareAndSwapLong(this, STATE, s, next = s + RUNIT) :
1117	<	(next = tryIncReaderOverflow(s)) != 0L) {
1118	<	if (node != null && (w = node.waiter) != null)
1119	<	U.compareAndSwapObject(node, WAITER, w, null);
1120	<	if ((p = rhead) != null && (s & SBITS) != p.seq &&
1121	<	U.compareAndSwapObject(this, RHEAD, p, p.next) &&
1122	<	(w = p.waiter) != null &&
1123	<	U.compareAndSwapObject(p, WAITER, w, null))
1124	<	U.unpark(w); // help signal other waiters
1125	<	return next;
1091	>	if (spins > 0) {
1092	>	if (ThreadLocalRandom.current().nextInt() >= 0)
1093	>	--spins;
1094	>	}
1095	>	else if ((p = wtail) == null) {
1096	>	WNode h = new WNode(WMODE, null);
1097	>	if (U.compareAndSwapObject(this, WHEAD, null, h))
1098	>	wtail = h;
1099	>	}
1100	>	else if (spins < 0)
1101	>	spins = (p == whead) ? SPINS : 0;
1102	>	else if (node == null)
1103	>	node = new WNode(WMODE, p);
1104	>	else if (node.prev != p)
1105	>	node.prev = p;
1106	>	else if (p.mode == RMODE && p != whead) {
1107	>	WNode pp = p.prev;  // become co-waiter with group p
1108	>	if (pp != null && p == wtail &&
1109	>	U.compareAndSwapObject(p, WCOWAIT,
1110	>	node.cowait = p.cowait, node)) {
1111	>	node.thread = Thread.currentThread();
1112	>	for (long time;;) {
1113	>	if (interruptible && Thread.interrupted())
1114	>	return cancelWaiter(node, p, true);
1115	>	if (deadline == 0L)
1116	>	time = 0L;
1117	>	else if ((time = deadline - System.nanoTime()) <= 0L)
1118	>	return cancelWaiter(node, p, false);
1119	>	if (node.thread == null)
1120	>	break;
1121	>	if (p.prev != pp || p.status == CANCELLED ||
1122	>	p == whead || p.prev != pp) {
1123	>	node.thread = null;
1124	>	break;
1125	>	}
1126	>	if (node.thread == null) // must recheck
1127	>	break;
1128	>	U.park(false, time);
1129	>	}
1130	>	group = p;
1131		}
1132	+	node = null; // throw away
1133		}
1134	<	else if (m != WBIT && (p = rhead) != null &&
1135	<	(s & SBITS) != p.seq) { // help release old readers
1136	<	if (U.compareAndSwapObject(this, RHEAD, p, p.next) &&
1084	<	(w = p.waiter) != null &&
1085	<	U.compareAndSwapObject(p, WAITER, w, null))
1086	<	U.unpark(w);
1087	<	}
1088	<	else if (queued && node != null && node.waiter == null) {
1089	<	node = null;    // restart
1090	<	queued = false;
1091	<	spins = -1;
1092	<	}
1093	<	else if (spins < 0) {
1094	<	if (rhead != node)
1095	<	spins = 0;
1096	<	else if ((spins = headSpins) < MAX_HEAD_SPINS && node != null)
1097	<	headSpins <<= 1;
1134	>	else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
1135	>	p.next = node;
1136	>	break;
1137		}
1138	<	else if (spins > 0) {
1139	<	if ((r = nextRandom(r)) >= 0)
1140	<	--spins;
1138	>	}
1139	>
1140	>	for (int spins = SPINS;;) {
1141	>	WNode np, pp, r; int ps; long m, s, ns; Thread w;
1142	>	while ((np = node.prev) != p && np != null)
1143	>	(p = np).next = node;
1144	>	if (whead == p) {
1145	>	for (int k = spins;;) {
1146	>	if ((m = (s = state) & ABITS) != WBIT) {
1147	>	if (m < RFULL ?
1148	>	U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT):
1149	>	(ns = tryIncReaderOverflow(s)) != 0L) {
1150	>	whead = node;
1151	>	node.prev = null;
1152	>	while ((r = node.cowait) != null) {
1153	>	if (U.compareAndSwapObject(node, WCOWAIT,
1154	>	r, r.cowait) &&
1155	>	(w = r.thread) != null) {
1156	>	r.thread = null;
1157	>	U.unpark(w); // release co-waiter
1158	>	}
1159	>	}
1160	>	return ns;
1161	>	}
1162	>	}
1163	>	else if (ThreadLocalRandom.current().nextInt() >= 0 &&
1164	>	--k <= 0)
1165	>	break;
1166	>	}
1167	>	if (spins < MAX_HEAD_SPINS)
1168	>	spins <<= 1;
1169		}
1170	<	else if (node == null)
1171	<	node = new RNode(seq, Thread.currentThread());
1172	<	else if (!queued) {
1173	<	if (queued = U.compareAndSwapObject(this, RHEAD,
1174	<	node.next = rhead, node))
1175	<	spins = -1;
1170	>	if ((ps = p.status) == 0)
1171	>	U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
1172	>	else if (ps == CANCELLED) {
1173	>	if ((pp = p.prev) != null) {
1174	>	node.prev = pp;
1175	>	pp.next = node;
1176	>	}
1177		}
1178		else {
1179		long time;
1180		if (deadline == 0L)
1181		time = 0L;
1182		else if ((time = deadline - System.nanoTime()) <= 0L)
1183	<	return cancelReader(node, false);
1184	<	if ((state & WBIT) != 0L && node.waiter != null) // recheck
1183	>	return cancelWaiter(node, node, false);
1184	>	node.thread = Thread.currentThread();
1185	>	if (node.prev == p && p.status == WAITING &&
1186	>	(p != whead || (state & ABITS) != WBIT))
1187		U.park(false, time);
1188	+	node.thread = null;
1189		if (interruptible && Thread.interrupted())
1190	<	return cancelReader(node, true);
1190	>	return cancelWaiter(node, node, true);
1191		}
1192		}
1193		}
1194
1195		/**
1196	<	* If node non-null, forces cancel status and unsplices from queue
1197	<	* if possible, by traversing entire queue looking for cancelled
1198	<	* nodes.
1199	<	*/
1200	<	private long cancelReader(RNode node, boolean interrupted) {
1201	<	Thread w;
1202	<	if (node != null && (w = node.waiter) != null &&
1203	<	U.compareAndSwapObject(node, WAITER, w, null)) {
1204	<	for (RNode pred = null, p = rhead; p != null;) {
1205	<	RNode q = p.next;
1206	<	if (p.waiter == null) {
1207	<	if (pred == null) {
1208	<	U.compareAndSwapObject(this, RHEAD, p, q);
1209	<	p = rhead;
1210	<	}
1211	<	else {
1212	<	U.compareAndSwapObject(pred, RNEXT, p, q);
1213	<	p = pred.next;
1196	>	* If node non-null, forces cancel status and unsplices it from
1197	>	* queue if possible and wakes up any cowaiters (of the node, or
1198	>	* group, as applicable), and in any case helps release current
1199	>	* first waiter if lock is free. (Calling with null arguments
1200	>	* serves as a conditional form of release, which is not currently
1201	>	* needed but may be needed under possible future cancellation
1202	>	* policies). This is a variant of cancellation methods in
1203	>	* AbstractQueuedSynchronizer (see its detailed explanation in AQS
1204	>	* internal documentation).
1205	>	*
1206	>	* @param node if nonnull, the waiter
1207	>	* @param group, either node or the group node is cowaiting with
1208	>	* @param interrupted if already interrupted
1209	>	* @return INTERRUPTED if interrupted or Thread.interrupted, else zero
1210	>	*/
1211	>	private long cancelWaiter(WNode node, WNode group, boolean interrupted) {
1212	>	if (node != null && group != null) {
1213	>	Thread w;
1214	>	node.status = CANCELLED;
1215	>	node.thread = null;
1216	>	// unsplice cancelled nodes from group
1217	>	for (WNode p = group, q; (q = p.cowait) != null;) {
1218	>	if (q.status == CANCELLED)
1219	>	U.compareAndSwapObject(p, WNEXT, q, q.next);
1220	>	else
1221	>	p = q;
1222	>	}
1223	>	if (group == node) {
1224	>	WNode r; // detach and wake up uncancelled co-waiters
1225	>	while ((r = node.cowait) != null) {
1226	>	if (U.compareAndSwapObject(node, WCOWAIT, r, r.cowait) &&
1227	>	(w = r.thread) != null) {
1228	>	r.thread = null;
1229	>	U.unpark(w);
1230		}
1231		}
1232	<	else {
1233	<	pred = p;
1234	<	p = q;
1232	>	for (WNode pred = node.prev; pred != null; ) { // unsplice
1233	>	WNode succ, pp;        // find valid successor
1234	>	while ((succ = node.next) == null ||
1235	>	succ.status == CANCELLED) {
1236	>	WNode q = null;    // find successor the slow way
1237	>	for (WNode t = wtail; t != null && t != node; t = t.prev)
1238	>	if (t.status != CANCELLED)
1239	>	q = t;     // don't link if succ cancelled
1240	>	if (succ == q ||   // ensure accurate successor
1241	>	U.compareAndSwapObject(node, WNEXT,
1242	>	succ, succ = q)) {
1243	>	if (succ == null && node == wtail)
1244	>	U.compareAndSwapObject(this, WTAIL, node, pred);
1245	>	break;
1246	>	}
1247	>	}
1248	>	if (pred.next == node) // unsplice pred link
1249	>	U.compareAndSwapObject(pred, WNEXT, node, succ);
1250	>	if (succ != null && (w = succ.thread) != null) {
1251	>	succ.thread = null;
1252	>	U.unpark(w);       // wake up succ to observe new pred
1253	>	}
1254	>	if (pred.status != CANCELLED || (pp = pred.prev) == null)
1255	>	break;
1256	>	node.prev = pp;        // repeat if new pred wrong/cancelled
1257	>	U.compareAndSwapObject(pp, WNEXT, pred, succ);
1258	>	pred = pp;
1259		}
1260		}
1261		}
1262	<	readerPrefSignal();
1262	>	WNode h; // Possibly release first waiter
1263	>	while ((h = whead) != null) {
1264	>	long s; WNode q; // similar to release() but check eligibility
1265	>	if ((q = h.next) == null || q.status == CANCELLED) {
1266	>	for (WNode t = wtail; t != null && t != h; t = t.prev)
1267	>	if (t.status <= 0)
1268	>	q = t;
1269	>	}
1270	>	if (h == whead) {
1271	>	if (q != null && h.status == 0 &&
1272	>	((s = state) & ABITS) != WBIT && // waiter is eligible
1273	>	(s == 0L || q.mode == RMODE))
1274	>	release(h);
1275	>	break;
1276	>	}
1277	>	}
1278		return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L;
1279		}
1280
1281		// Unsafe mechanics
1282		private static final sun.misc.Unsafe U;
1283		private static final long STATE;
1158	–	private static final long RHEAD;
1284		private static final long WHEAD;
1285		private static final long WTAIL;
1161	–	private static final long RNEXT;
1286		private static final long WNEXT;
1287	<	private static final long WPREV;
1288	<	private static final long WAITER;
1165	<	private static final long STATUS;
1287	>	private static final long WSTATUS;
1288	>	private static final long WCOWAIT;
1289
1290		static {
1291		try {
1292		U = getUnsafe();
1293		Class<?> k = StampedLock.class;
1171	–	Class<?> rk = RNode.class;
1294		Class<?> wk = WNode.class;
1295		STATE = U.objectFieldOffset
1296		(k.getDeclaredField("state"));
1175	–	RHEAD = U.objectFieldOffset
1176	–	(k.getDeclaredField("rhead"));
1297		WHEAD = U.objectFieldOffset
1298		(k.getDeclaredField("whead"));
1299		WTAIL = U.objectFieldOffset
1300		(k.getDeclaredField("wtail"));
1301	<	RNEXT = U.objectFieldOffset
1182	<	(rk.getDeclaredField("next"));
1183	<	WAITER = U.objectFieldOffset
1184	<	(rk.getDeclaredField("waiter"));
1185	<	STATUS = U.objectFieldOffset
1301	>	WSTATUS = U.objectFieldOffset
1302		(wk.getDeclaredField("status"));
1303		WNEXT = U.objectFieldOffset
1304		(wk.getDeclaredField("next"));
1305	<	WPREV = U.objectFieldOffset
1306	<	(wk.getDeclaredField("prev"));
1305	>	WCOWAIT = U.objectFieldOffset
1306	>	(wk.getDeclaredField("cowait"));
1307
1308		} catch (Exception e) {
1309		throw new Error(e);
#	Line 1204 | Line 1320 | public class StampedLock implements java
1320		private static sun.misc.Unsafe getUnsafe() {
1321		try {
1322		return sun.misc.Unsafe.getUnsafe();
1323	<	} catch (SecurityException se) {
1324	<	try {
1325	<	return java.security.AccessController.doPrivileged
1326	<	(new java.security
1327	<	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1328	<	public sun.misc.Unsafe run() throws Exception {
1329	<	java.lang.reflect.Field f = sun.misc
1330	<	.Unsafe.class.getDeclaredField("theUnsafe");
1331	<	f.setAccessible(true);
1332	<	return (sun.misc.Unsafe) f.get(null);
1333	<	}});
1334	<	} catch (java.security.PrivilegedActionException e) {
1335	<	throw new RuntimeException("Could not initialize intrinsics",
1336	<	e.getCause());
1337	<	}
1323	>	} catch (SecurityException tryReflectionInstead) {}
1324	>	try {
1325	>	return java.security.AccessController.doPrivileged
1326	>	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1327	>	public sun.misc.Unsafe run() throws Exception {
1328	>	Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
1329	>	for (java.lang.reflect.Field f : k.getDeclaredFields()) {
1330	>	f.setAccessible(true);
1331	>	Object x = f.get(null);
1332	>	if (k.isInstance(x))
1333	>	return k.cast(x);
1334	>	}
1335	>	throw new NoSuchFieldError("the Unsafe");
1336	>	}});
1337	>	} catch (java.security.PrivilegedActionException e) {
1338	>	throw new RuntimeException("Could not initialize intrinsics",
1339	>	e.getCause());
1340		}
1341		}
1224	–
1342		}

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