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import java.util.concurrent.ThreadLocalRandom; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.locks.*; |
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/** |
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* A capability-based lock with three modes for controlling read/write |
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* help reduce some of the code bloat that otherwise occurs in |
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* retry-based designs. |
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* |
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* <p>StampedLocks are designed for use in a different (and generally |
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* narrower) range of contexts than most other locks: They are not |
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* reentrant, so locked bodies should not call other unknown methods |
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* that may try to re-acquire locks (although you may pass a stamp to |
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* other methods that can use or convert it). Unvalidated optimistic |
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* read sections should further not call methods that are not known to |
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* <p>StampedLocks are designed for use as internal utilities in the |
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* development of thread-safe components. Their use relies on |
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* knowledge of the internal properties of the data, objects, and |
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* methods they are protecting. They are not reentrant, so locked |
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* bodies should not call other unknown methods that may try to |
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* re-acquire locks (although you may pass a stamp to other methods |
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* that can use or convert it). The use of read lock modes relies on |
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* the associated code sections being side-effect-free. Unvalidated |
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* optimistic read sections cannot call methods that are not known to |
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* tolerate potential inconsistencies. Stamps use finite |
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* representations, and are not cryptographically secure (i.e., a |
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* valid stamp may be guessable). Stamp values may recycle after (no |
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* locking. |
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* |
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* <p>The scheduling policy of StampedLock does not consistently |
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* prefer readers over writers or vice versa. A zero return from any |
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* "try" method for acquiring or converting locks does not carry any |
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* information about the state of the lock; a subsequent invocation |
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* may succeed. |
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* prefer readers over writers or vice versa. All "try" methods are |
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* best-effort and do not necessarily conform to any scheduling or |
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* fairness policy. A zero return from any "try" method for acquiring |
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* or converting locks does not carry any information about the state |
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* of the lock; a subsequent invocation may succeed. |
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* |
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* <p>Because it supports coordinated usage across multiple lock |
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* modes, this class does not directly implement the {@link Lock} or |
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* {@link ReadWriteLock} interfaces. However, a StampedLock may be |
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* viewed {@link #asReadLock()}, {@link #asWriteLock()}, or {@link |
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* #asReadWriteLock()} in applications requiring only the associated |
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* set of functionality. |
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* |
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* <p><b>Sample Usage.</b> The following illustrates some usage idioms |
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* in a class that maintains simple two-dimensional points. The sample |
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* } |
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* |
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* double distanceFromOriginV2() { // combines code paths |
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* double currentX = 0.0, currentY = 0.0; |
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* for (long stamp = sl.tryOptimisticRead(); ; stamp = sl.readLock()) { |
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* double currentX, currentY; |
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* try { |
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* currentX = x; |
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* currentY = y; |
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* } finally { |
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* if (sl.tryConvertToOptimisticRead(stamp) != 0L) // unlock or validate |
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* return Math.sqrt(currentX * currentX + currentY * currentY); |
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* break; |
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* } |
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* } |
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* return Math.sqrt(currentX * currentX + currentY * currentY); |
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* } |
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* |
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* void moveIfAtOrigin(double newX, double newY) { // upgrade |
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* long stamp = sl.readLock(); |
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* try { |
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* while (x == 0.0 && y == 0.0) { |
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* long ws = tryConvertToWriteLock(stamp); |
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* long ws = sl.tryConvertToWriteLock(stamp); |
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* if (ws != 0L) { |
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* stamp = ws; |
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* x = newX; |
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* } |
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* } |
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* } finally { |
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* sl.unlock(stamp); |
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* sl.unlock(stamp); |
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* } |
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* } |
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* }}</pre> |
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* http://www.lameter.com/gelato2005.pdf |
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* and elsewhere; see |
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* Boehm's http://www.hpl.hp.com/techreports/2012/HPL-2012-68.html) |
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* Ordered RW locks (see Shirako et al |
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* and Ordered RW locks (see Shirako et al |
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* http://dl.acm.org/citation.cfm?id=2312015) |
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* and Phase-Fair locks (see Brandenburg & Anderson, especially |
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* http://www.cs.unc.edu/~bbb/diss/). |
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* |
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* Conceptually, the primary state of the lock includes a sequence |
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* number that is odd when write-locked and even otherwise. |
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* read-locked. The read count is ignored when validating |
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* "optimistic" seqlock-reader-style stamps. Because we must use |
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* a small finite number of bits (currently 7) for readers, a |
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* supplementary reader overflow word is used when then number of |
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* supplementary reader overflow word is used when the number of |
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* readers exceeds the count field. We do this by treating the max |
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* reader count value (RBITS) as a spinlock protecting overflow |
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* updates. |
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* |
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* Waiting readers and writers use different queues. The writer |
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* queue is a modified form of CLH lock. (For discussion of CLH, |
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* see the internal documentation of AbstractQueuedSynchronizer.) |
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* The reader "queue" is a form of Treiber stack, that supports |
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* simpler/faster operations because order within a queue doesn't |
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* matter and all are signalled at once. However the sequence of |
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* threads within the queue vs the current stamp does matter (see |
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* Shirako et al) so each carries its incoming stamp value. |
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* Waiting writers never need to track sequence values, so they |
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* don't. |
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* |
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* These queue mechanics hardwire the scheduling policy. Ignoring |
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* trylocks, cancellation, and spinning, they implement Phase-Fair |
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* preferences: |
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* 1. Unlocked writers prefer to signal waiting readers |
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* 2. Fully unlocked readers prefer to signal waiting writers |
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* 3. When read-locked and a waiting writer exists, the writer |
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* is preferred to incoming readers |
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* Waiters use a modified form of CLH lock used in |
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* AbstractQueuedSynchronizer (see its internal documentation for |
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* a fuller account), where each node it tagged (field mode) as |
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* either a reader or writer. Sets of waiting readers are grouped |
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* (linked) under a common node (field cowait) so act as a single |
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* node with respect to most CLH mechanics. By virtue of its |
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* structure, wait nodes need not actually carry sequence numbers; |
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* we know each is >= its predecessor. These queue mechanics |
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* simplify the scheduling policy to a mainly-FIFO scheme that |
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* incorporates elements of Phase-Fair locks (see Brandenburg & |
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* Anderson, especially http://www.cs.unc.edu/~bbb/diss/). In |
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* particular, we use the phase-fair anti-barging rule: If an |
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* incoming reader arrives while read lock is held but there is a |
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* queued writer, this incoming reader is queued. (This rule is |
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* responsible for some of the complexity of method acquireRead, |
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* but without it, the lock becomes highly unfair.) |
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* |
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* These rules apply to threads actually queued. All tryLock forms |
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* opportunistically try to acquire locks regardless of preference |
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* rules, and so may "barge" their way in. Additionally, initial |
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* phases of the await* methods (invoked from readLock() and |
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* writeLock()) use controlled spins that have similar effect. |
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* Phase-fair preferences may also be broken on cancellations due |
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* to timeouts and interrupts. Rule #3 (incoming readers when a |
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* waiting writer) is approximated with varying precision in |
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* different contexts -- some checks do not account for |
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* in-progress spins/signals, and others do not account for |
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* cancellations. |
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* |
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* Controlled, randomized spinning is used in the two await |
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* methods to reduce (increasingly expensive) context switching |
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* while also avoiding sustained memory thrashing among many |
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* threads. Both await methods use a similar spin strategy: If |
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* the associated queue appears to be empty, then the thread |
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* spin-waits up to SPINS times (where each iteration decreases |
225 |
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* spin count with 50% probablility) before enqueing, and then, if |
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* it is the first thread to be enqueued, spins again up to SPINS |
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* times before blocking. If, upon wakening it fails to obtain |
228 |
< |
* lock, and is still (or becomes) the first waiting thread (which |
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* indicates that some other thread barged and obtained lock), it |
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* escalates spins (up to MAX_HEAD_SPINS) to reduce the likelihood |
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* of continually losing to barging threads. |
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* rules, and so may "barge" their way in. Randomized spinning is |
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* used in the acquire methods to reduce (increasingly expensive) |
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* context switching while also avoiding sustained memory |
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* thrashing among many threads. We limit spins to the head of |
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* queue. A thread spin-waits up to SPINS times (where each |
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* iteration decreases spin count with 50% probability) before |
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* blocking. If, upon wakening it fails to obtain lock, and is |
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* still (or becomes) the first waiting thread (which indicates |
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* that some other thread barged and obtained lock), it escalates |
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* spins (up to MAX_HEAD_SPINS) to reduce the likelihood of |
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* continually losing to barging threads. |
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* |
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* Nearly all of these mechanics are carried out in methods |
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* acquireWrite and acquireRead, that, as typical of such code, |
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* sprawl out because actions and retries rely on consitent sets |
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* of locally cahced reads. |
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* |
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* As noted in Boehm's paper (above), sequence validation (mainly |
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* method validate()) requires stricter ordering rules than apply |
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* be subject to future improvements. |
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*/ |
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private static final long serialVersionUID = -6001602636862214147L; |
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|
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/** Number of processors, for spin control */ |
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private static final int NCPU = Runtime.getRuntime().availableProcessors(); |
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/** Maximum number of retries before blocking on acquisition */ |
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< |
private static final int SPINS = (NCPU > 1) ? 1 << 6 : 1; |
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> |
private static final int SPINS = (NCPU > 1) ? 1 << 6 : 0; |
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|
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/** Maximum number of retries before re-blocking */ |
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private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 1; |
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> |
private static final int MAX_HEAD_SPINS = (NCPU > 1) ? 1 << 12 : 0; |
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|
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/** The period for yielding when waiting for overflow spinlock */ |
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private static final int OVERFLOW_YIELD_RATE = 7; // must be power 2 - 1 |
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|
267 |
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/** The number of bits to use for reader count before overflowing */ |
268 |
< |
private static final int LG_READERS = 7; |
268 |
> |
private static final int LG_READERS = 7; |
269 |
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|
270 |
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// Values for lock state and stamp operations |
271 |
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private static final long RUNIT = 1L; |
278 |
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// Initial value for lock state; avoid failure value zero |
279 |
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private static final long ORIGIN = WBIT << 1; |
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|
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< |
// Special value from cancelled await methods so caller can throw IE |
281 |
> |
// Special value from cancelled acquire methods so caller can throw IE |
282 |
|
private static final long INTERRUPTED = 1L; |
283 |
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|
284 |
< |
// Values for writer status; order matters |
284 |
> |
// Values for node status; order matters |
285 |
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private static final int WAITING = -1; |
286 |
|
private static final int CANCELLED = 1; |
287 |
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|
288 |
< |
/** Wait nodes for readers */ |
289 |
< |
static final class RNode { |
290 |
< |
final long seq; // stamp value upon enqueue |
287 |
< |
volatile Thread waiter; // null if no longer waiting |
288 |
< |
volatile RNode next; |
289 |
< |
RNode(long s, Thread w) { seq = s; waiter = w; } |
290 |
< |
} |
288 |
> |
// Modes for nodes (int not boolean to allow arithmetic) |
289 |
> |
private static final int RMODE = 0; |
290 |
> |
private static final int WMODE = 1; |
291 |
|
|
292 |
< |
/** Wait nodes for writers */ |
292 |
> |
/** Wait nodes */ |
293 |
|
static final class WNode { |
294 |
– |
volatile int status; // 0, WAITING, or CANCELLED |
294 |
|
volatile WNode prev; |
295 |
|
volatile WNode next; |
296 |
< |
volatile Thread thread; |
297 |
< |
WNode(Thread t, WNode p) { thread = t; prev = p; } |
296 |
> |
volatile WNode cowait; // list of linked readers |
297 |
> |
volatile Thread thread; // non-null while possibly parked |
298 |
> |
volatile int status; // 0, WAITING, or CANCELLED |
299 |
> |
final int mode; // RMODE or WMODE |
300 |
> |
WNode(int m, WNode p) { mode = m; prev = p; } |
301 |
|
} |
302 |
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|
303 |
< |
/** Head of writer CLH queue */ |
303 |
> |
/** Head of CLH queue */ |
304 |
|
private transient volatile WNode whead; |
305 |
< |
/** Tail (last) of writer CLH queue */ |
305 |
> |
/** Tail (last) of CLH queue */ |
306 |
|
private transient volatile WNode wtail; |
307 |
< |
/** Head of read queue */ |
308 |
< |
private transient volatile RNode rhead; |
309 |
< |
/** The state of the lock -- high bits hold sequence, low bits read count */ |
307 |
> |
|
308 |
> |
// views |
309 |
> |
transient ReadLockView readLockView; |
310 |
> |
transient WriteLockView writeLockView; |
311 |
> |
transient ReadWriteLockView readWriteLockView; |
312 |
> |
|
313 |
> |
/** Lock sequence/state */ |
314 |
|
private transient volatile long state; |
315 |
|
/** extra reader count when state read count saturated */ |
316 |
|
private transient int readerOverflow; |
317 |
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|
318 |
|
/** |
319 |
< |
* Creates a new lock initially in unlocked state. |
319 |
> |
* Creates a new lock, initially in unlocked state. |
320 |
|
*/ |
321 |
|
public StampedLock() { |
322 |
|
state = ORIGIN; |
329 |
|
* @return a stamp that can be used to unlock or convert mode |
330 |
|
*/ |
331 |
|
public long writeLock() { |
332 |
< |
long s, next; |
333 |
< |
if (((s = state) & ABITS) == 0L && |
334 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
335 |
< |
return next; |
330 |
< |
return awaitWrite(false, 0L); |
332 |
> |
long s, next; // bypass acquireWrite in fully onlocked case only |
333 |
> |
return ((((s = state) & ABITS) == 0L && |
334 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ? |
335 |
> |
next : acquireWrite(false, 0L)); |
336 |
|
} |
337 |
|
|
338 |
|
/** |
339 |
|
* Exclusively acquires the lock if it is immediately available. |
340 |
|
* |
341 |
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* @return a stamp that can be used to unlock or convert mode, |
342 |
< |
* or zero if the lock is not available. |
342 |
> |
* or zero if the lock is not available |
343 |
|
*/ |
344 |
|
public long tryWriteLock() { |
345 |
|
long s, next; |
346 |
< |
if (((s = state) & ABITS) == 0L && |
347 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
348 |
< |
return next; |
344 |
< |
return 0L; |
346 |
> |
return ((((s = state) & ABITS) == 0L && |
347 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) ? |
348 |
> |
next : 0L); |
349 |
|
} |
350 |
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|
351 |
|
/** |
352 |
|
* Exclusively acquires the lock if it is available within the |
353 |
|
* given time and the current thread has not been interrupted. |
354 |
+ |
* Behavior under timeout and interruption matches that specified |
355 |
+ |
* for method {@link Lock#tryLock(long,TimeUnit)}. |
356 |
|
* |
357 |
|
* @return a stamp that can be used to unlock or convert mode, |
358 |
|
* or zero if the lock is not available |
363 |
|
throws InterruptedException { |
364 |
|
long nanos = unit.toNanos(time); |
365 |
|
if (!Thread.interrupted()) { |
366 |
< |
long s, next, deadline; |
367 |
< |
if (((s = state) & ABITS) == 0L && |
362 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
366 |
> |
long next, deadline; |
367 |
> |
if ((next = tryWriteLock()) != 0) |
368 |
|
return next; |
369 |
|
if (nanos <= 0L) |
370 |
|
return 0L; |
371 |
|
if ((deadline = System.nanoTime() + nanos) == 0L) |
372 |
|
deadline = 1L; |
373 |
< |
if ((next = awaitWrite(true, deadline)) != INTERRUPTED) |
373 |
> |
if ((next = acquireWrite(true, deadline)) != INTERRUPTED) |
374 |
|
return next; |
375 |
|
} |
376 |
|
throw new InterruptedException(); |
379 |
|
/** |
380 |
|
* Exclusively acquires the lock, blocking if necessary |
381 |
|
* until available or the current thread is interrupted. |
382 |
+ |
* Behavior under interruption matches that specified |
383 |
+ |
* for method {@link Lock#lockInterruptibly()}. |
384 |
|
* |
385 |
|
* @return a stamp that can be used to unlock or convert mode |
386 |
|
* @throws InterruptedException if the current thread is interrupted |
387 |
|
* before acquiring the lock |
388 |
|
*/ |
389 |
|
public long writeLockInterruptibly() throws InterruptedException { |
390 |
< |
if (!Thread.interrupted()) { |
391 |
< |
long s, next; |
392 |
< |
if (((s = state) & ABITS) == 0L && |
393 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
387 |
< |
return next; |
388 |
< |
if ((next = awaitWrite(true, 0L)) != INTERRUPTED) |
389 |
< |
return next; |
390 |
< |
} |
390 |
> |
long next; |
391 |
> |
if (!Thread.interrupted() && |
392 |
> |
(next = acquireWrite(true, 0L)) != INTERRUPTED) |
393 |
> |
return next; |
394 |
|
throw new InterruptedException(); |
395 |
|
} |
396 |
|
|
401 |
|
* @return a stamp that can be used to unlock or convert mode |
402 |
|
*/ |
403 |
|
public long readLock() { |
404 |
< |
for (;;) { |
405 |
< |
long s, m, next; |
406 |
< |
if ((m = (s = state) & ABITS) == 0L || |
407 |
< |
(m < WBIT && whead == wtail)) { |
405 |
< |
if (m < RFULL) { |
406 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
407 |
< |
return next; |
408 |
< |
} |
409 |
< |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
410 |
< |
return next; |
411 |
< |
} |
412 |
< |
else |
413 |
< |
return awaitRead(s, false, 0L); |
414 |
< |
} |
404 |
> |
long s, next; // bypass acquireRead on fully onlocked case only |
405 |
> |
return ((((s = state) & ABITS) == 0L && |
406 |
> |
U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) ? |
407 |
> |
next : acquireRead(false, 0L)); |
408 |
|
} |
409 |
|
|
410 |
|
/** |
430 |
|
/** |
431 |
|
* Non-exclusively acquires the lock if it is available within the |
432 |
|
* given time and the current thread has not been interrupted. |
433 |
+ |
* Behavior under timeout and interruption matches that specified |
434 |
+ |
* for method {@link Lock#tryLock(long,TimeUnit)}. |
435 |
|
* |
436 |
|
* @return a stamp that can be used to unlock or convert mode, |
437 |
|
* or zero if the lock is not available |
440 |
|
*/ |
441 |
|
public long tryReadLock(long time, TimeUnit unit) |
442 |
|
throws InterruptedException { |
443 |
+ |
long next, deadline; |
444 |
|
long nanos = unit.toNanos(time); |
445 |
|
if (!Thread.interrupted()) { |
446 |
< |
for (;;) { |
447 |
< |
long s, m, next, deadline; |
448 |
< |
if ((m = (s = state) & ABITS) == WBIT || |
449 |
< |
(m != 0L && whead != wtail)) { |
450 |
< |
if (nanos <= 0L) |
451 |
< |
return 0L; |
452 |
< |
if ((deadline = System.nanoTime() + nanos) == 0L) |
453 |
< |
deadline = 1L; |
458 |
< |
if ((next = awaitRead(s, true, deadline)) != INTERRUPTED) |
459 |
< |
return next; |
460 |
< |
break; |
461 |
< |
} |
462 |
< |
else if (m < RFULL) { |
463 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
464 |
< |
return next; |
465 |
< |
} |
466 |
< |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
467 |
< |
return next; |
468 |
< |
} |
446 |
> |
if ((next = tryReadLock()) != 0) |
447 |
> |
return next; |
448 |
> |
if (nanos <= 0L) |
449 |
> |
return 0L; |
450 |
> |
if ((deadline = System.nanoTime() + nanos) == 0L) |
451 |
> |
deadline = 1L; |
452 |
> |
if ((next = acquireRead(true, deadline)) != INTERRUPTED) |
453 |
> |
return next; |
454 |
|
} |
455 |
|
throw new InterruptedException(); |
456 |
|
} |
458 |
|
/** |
459 |
|
* Non-exclusively acquires the lock, blocking if necessary |
460 |
|
* until available or the current thread is interrupted. |
461 |
+ |
* Behavior under interruption matches that specified |
462 |
+ |
* for method {@link Lock#lockInterruptibly()}. |
463 |
|
* |
464 |
|
* @return a stamp that can be used to unlock or convert mode |
465 |
|
* @throws InterruptedException if the current thread is interrupted |
466 |
|
* before acquiring the lock |
467 |
|
*/ |
468 |
|
public long readLockInterruptibly() throws InterruptedException { |
469 |
< |
if (!Thread.interrupted()) { |
470 |
< |
for (;;) { |
471 |
< |
long s, next, m; |
472 |
< |
if ((m = (s = state) & ABITS) == WBIT || |
486 |
< |
(m != 0L && whead != wtail)) { |
487 |
< |
if ((next = awaitRead(s, true, 0L)) != INTERRUPTED) |
488 |
< |
return next; |
489 |
< |
break; |
490 |
< |
} |
491 |
< |
else if (m < RFULL) { |
492 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) |
493 |
< |
return next; |
494 |
< |
} |
495 |
< |
else if ((next = tryIncReaderOverflow(s)) != 0L) |
496 |
< |
return next; |
497 |
< |
} |
498 |
< |
} |
469 |
> |
long next; |
470 |
> |
if (!Thread.interrupted() && |
471 |
> |
(next = acquireRead(true, 0L)) != INTERRUPTED) |
472 |
> |
return next; |
473 |
|
throw new InterruptedException(); |
474 |
|
} |
475 |
|
|
485 |
|
} |
486 |
|
|
487 |
|
/** |
488 |
< |
* Returns true if the lock has not been exclusively held since |
489 |
< |
* issuance of the given stamp. Always returns false if the stamp |
490 |
< |
* is zero. Always returns true if the stamp represents a |
488 |
> |
* Returns true if the lock has not been exclusively acquired |
489 |
> |
* since issuance of the given stamp. Always returns false if the |
490 |
> |
* stamp is zero. Always returns true if the stamp represents a |
491 |
|
* currently held lock. |
492 |
|
* |
493 |
< |
* @return true if the lock has not been exclusively held since |
494 |
< |
* issuance of the given stamp; else false |
493 |
> |
* @return true if the lock has not been exclusively acquired |
494 |
> |
* since issuance of the given stamp; else false |
495 |
|
*/ |
496 |
|
public boolean validate(long stamp) { |
497 |
+ |
// See above about current use of getLongVolatile here |
498 |
|
return (stamp & SBITS) == (U.getLongVolatile(this, STATE) & SBITS); |
499 |
|
} |
500 |
|
|
507 |
|
* not match the current state of this lock |
508 |
|
*/ |
509 |
|
public void unlockWrite(long stamp) { |
510 |
+ |
WNode h; |
511 |
|
if (state != stamp || (stamp & WBIT) == 0L) |
512 |
|
throw new IllegalMonitorStateException(); |
513 |
|
state = (stamp += WBIT) == 0L ? ORIGIN : stamp; |
514 |
< |
readerPrefSignal(); |
514 |
> |
if ((h = whead) != null && h.status != 0) |
515 |
> |
release(h); |
516 |
|
} |
517 |
|
|
518 |
|
/** |
519 |
< |
* If the lock state matches the given stamp, releases |
519 |
> |
* If the lock state matches the given stamp, releases the |
520 |
|
* non-exclusive lock. |
521 |
|
* |
522 |
|
* @param stamp a stamp returned by a read-lock operation |
524 |
|
* not match the current state of this lock |
525 |
|
*/ |
526 |
|
public void unlockRead(long stamp) { |
527 |
< |
long s, m; |
527 |
> |
long s, m; WNode h; |
528 |
|
if ((stamp & RBITS) != 0L) { |
529 |
|
while (((s = state) & SBITS) == (stamp & SBITS)) { |
530 |
|
if ((m = s & ABITS) == 0L) |
531 |
|
break; |
532 |
|
else if (m < RFULL) { |
533 |
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
534 |
< |
if (m == RUNIT) |
535 |
< |
writerPrefSignal(); |
534 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
535 |
> |
release(h); |
536 |
|
return; |
537 |
|
} |
538 |
|
} |
554 |
|
* not match the current state of this lock |
555 |
|
*/ |
556 |
|
public void unlock(long stamp) { |
557 |
< |
long a = stamp & ABITS, m, s; |
557 |
> |
long a = stamp & ABITS, m, s; WNode h; |
558 |
|
while (((s = state) & SBITS) == (stamp & SBITS)) { |
559 |
|
if ((m = s & ABITS) == 0L) |
560 |
|
break; |
562 |
|
if (a != m) |
563 |
|
break; |
564 |
|
state = (s += WBIT) == 0L ? ORIGIN : s; |
565 |
< |
readerPrefSignal(); |
565 |
> |
if ((h = whead) != null && h.status != 0) |
566 |
> |
release(h); |
567 |
|
return; |
568 |
|
} |
569 |
|
else if (a == 0L || a >= WBIT) |
570 |
|
break; |
571 |
|
else if (m < RFULL) { |
572 |
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
573 |
< |
if (m == RUNIT) |
574 |
< |
writerPrefSignal(); |
573 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
574 |
> |
release(h); |
575 |
|
return; |
576 |
|
} |
577 |
|
} |
582 |
|
} |
583 |
|
|
584 |
|
/** |
585 |
< |
* If the lock state matches the given stamp then performs one of |
585 |
> |
* If the lock state matches the given stamp, performs one of |
586 |
|
* the following actions. If the stamp represents holding a write |
587 |
< |
* lock, returns it. Or, if a read lock, if the write lock is |
588 |
< |
* available, releases the read and returns a write stamp. Or, if |
589 |
< |
* an optimistic read, returns a write stamp only if immediately |
590 |
< |
* available. This method returns zero in all other cases. |
587 |
> |
* lock, returns it. Or, if a read lock, if the write lock is |
588 |
> |
* available, releases the read lock and returns a write stamp. |
589 |
> |
* Or, if an optimistic read, returns a write stamp only if |
590 |
> |
* immediately available. This method returns zero in all other |
591 |
> |
* cases. |
592 |
|
* |
593 |
|
* @param stamp a stamp |
594 |
|
* @return a valid write stamp, or zero on failure |
607 |
|
break; |
608 |
|
return stamp; |
609 |
|
} |
610 |
< |
else if (m == RUNIT && a != 0L && a < WBIT) { |
610 |
> |
else if (m == RUNIT && a != 0L) { |
611 |
|
if (U.compareAndSwapLong(this, STATE, s, |
612 |
|
next = s - RUNIT + WBIT)) |
613 |
|
return next; |
619 |
|
} |
620 |
|
|
621 |
|
/** |
622 |
< |
* If the lock state matches the given stamp then performs one of |
622 |
> |
* If the lock state matches the given stamp, performs one of |
623 |
|
* the following actions. If the stamp represents holding a write |
624 |
|
* lock, releases it and obtains a read lock. Or, if a read lock, |
625 |
|
* returns it. Or, if an optimistic read, acquires a read lock and |
630 |
|
* @return a valid read stamp, or zero on failure |
631 |
|
*/ |
632 |
|
public long tryConvertToReadLock(long stamp) { |
633 |
< |
long a = stamp & ABITS, m, s, next; |
633 |
> |
long a = stamp & ABITS, m, s, next; WNode h; |
634 |
|
while (((s = state) & SBITS) == (stamp & SBITS)) { |
635 |
|
if ((m = s & ABITS) == 0L) { |
636 |
|
if (a != 0L) |
645 |
|
else if (m == WBIT) { |
646 |
|
if (a != m) |
647 |
|
break; |
648 |
< |
next = state = s + (WBIT + RUNIT); |
649 |
< |
readerPrefSignal(); |
648 |
> |
state = next = s + (WBIT + RUNIT); |
649 |
> |
if ((h = whead) != null && h.status != 0) |
650 |
> |
release(h); |
651 |
|
return next; |
652 |
|
} |
653 |
|
else if (a != 0L && a < WBIT) |
669 |
|
* @return a valid optimistic read stamp, or zero on failure |
670 |
|
*/ |
671 |
|
public long tryConvertToOptimisticRead(long stamp) { |
672 |
< |
long a = stamp & ABITS, m, s, next; |
673 |
< |
while (((s = U.getLongVolatile(this, STATE)) & |
674 |
< |
SBITS) == (stamp & SBITS)) { |
672 |
> |
long a = stamp & ABITS, m, s, next; WNode h; |
673 |
> |
for (;;) { |
674 |
> |
s = U.getLongVolatile(this, STATE); // see above |
675 |
> |
if ((s & SBITS) != (stamp & SBITS)) |
676 |
> |
break; |
677 |
|
if ((m = s & ABITS) == 0L) { |
678 |
|
if (a != 0L) |
679 |
|
break; |
682 |
|
else if (m == WBIT) { |
683 |
|
if (a != m) |
684 |
|
break; |
685 |
< |
next = state = (s += WBIT) == 0L ? ORIGIN : s; |
686 |
< |
readerPrefSignal(); |
685 |
> |
state = next = (s += WBIT) == 0L ? ORIGIN : s; |
686 |
> |
if ((h = whead) != null && h.status != 0) |
687 |
> |
release(h); |
688 |
|
return next; |
689 |
|
} |
690 |
|
else if (a == 0L || a >= WBIT) |
691 |
|
break; |
692 |
|
else if (m < RFULL) { |
693 |
|
if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) { |
694 |
< |
if (m == RUNIT) |
695 |
< |
writerPrefSignal(); |
694 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
695 |
> |
release(h); |
696 |
|
return next & SBITS; |
697 |
|
} |
698 |
|
} |
710 |
|
* @return true if the lock was held, else false |
711 |
|
*/ |
712 |
|
public boolean tryUnlockWrite() { |
713 |
< |
long s; |
713 |
> |
long s; WNode h; |
714 |
|
if (((s = state) & WBIT) != 0L) { |
715 |
|
state = (s += WBIT) == 0L ? ORIGIN : s; |
716 |
< |
readerPrefSignal(); |
716 |
> |
if ((h = whead) != null && h.status != 0) |
717 |
> |
release(h); |
718 |
|
return true; |
719 |
|
} |
720 |
|
return false; |
728 |
|
* @return true if the read lock was held, else false |
729 |
|
*/ |
730 |
|
public boolean tryUnlockRead() { |
731 |
< |
long s, m; |
731 |
> |
long s, m; WNode h; |
732 |
|
while ((m = (s = state) & ABITS) != 0L && m < WBIT) { |
733 |
|
if (m < RFULL) { |
734 |
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) { |
735 |
< |
if (m == RUNIT) |
736 |
< |
writerPrefSignal(); |
735 |
> |
if (m == RUNIT && (h = whead) != null && h.status != 0) |
736 |
> |
release(h); |
737 |
|
return true; |
738 |
|
} |
739 |
|
} |
758 |
|
* @return true if the lock is currently held non-exclusively |
759 |
|
*/ |
760 |
|
public boolean isReadLocked() { |
761 |
< |
long m; |
778 |
< |
return (m = state & ABITS) > 0L && m < WBIT; |
761 |
> |
return (state & RBITS) != 0L; |
762 |
|
} |
763 |
|
|
764 |
|
private void readObject(java.io.ObjectInputStream s) |
767 |
|
state = ORIGIN; // reset to unlocked state |
768 |
|
} |
769 |
|
|
770 |
+ |
/** |
771 |
+ |
* Returns a plain {@link Lock} view of this StampedLock in which |
772 |
+ |
* the {@link Lock#lock} method is mapped to {@link #readLock}, |
773 |
+ |
* and similarly for other methods. The returned Lock does not |
774 |
+ |
* support a {@link Condition}; method {@link |
775 |
+ |
* Lock#newCondition()} throws {@code |
776 |
+ |
* UnsupportedOperationException}. |
777 |
+ |
* |
778 |
+ |
* @return the lock |
779 |
+ |
*/ |
780 |
+ |
public Lock asReadLock() { |
781 |
+ |
ReadLockView v; |
782 |
+ |
return ((v = readLockView) != null ? v : |
783 |
+ |
(readLockView = new ReadLockView())); |
784 |
+ |
} |
785 |
+ |
|
786 |
+ |
/** |
787 |
+ |
* Returns a plain {@link Lock} view of this StampedLock in which |
788 |
+ |
* the {@link Lock#lock} method is mapped to {@link #writeLock}, |
789 |
+ |
* and similarly for other methods. The returned Lock does not |
790 |
+ |
* support a {@link Condition}; method {@link |
791 |
+ |
* Lock#newCondition()} throws {@code |
792 |
+ |
* UnsupportedOperationException}. |
793 |
+ |
* |
794 |
+ |
* @return the lock |
795 |
+ |
*/ |
796 |
+ |
public Lock asWriteLock() { |
797 |
+ |
WriteLockView v; |
798 |
+ |
return ((v = writeLockView) != null ? v : |
799 |
+ |
(writeLockView = new WriteLockView())); |
800 |
+ |
} |
801 |
+ |
|
802 |
+ |
/** |
803 |
+ |
* Returns a {@link ReadWriteLock} view of this StampedLock in |
804 |
+ |
* which the {@link ReadWriteLock#readLock()} method is mapped to |
805 |
+ |
* {@link #asReadLock()}, and {@link ReadWriteLock#writeLock()} to |
806 |
+ |
* {@link #asWriteLock()}. |
807 |
+ |
* |
808 |
+ |
* @return the lock |
809 |
+ |
*/ |
810 |
+ |
public ReadWriteLock asReadWriteLock() { |
811 |
+ |
ReadWriteLockView v; |
812 |
+ |
return ((v = readWriteLockView) != null ? v : |
813 |
+ |
(readWriteLockView = new ReadWriteLockView())); |
814 |
+ |
} |
815 |
+ |
|
816 |
+ |
// view classes |
817 |
+ |
|
818 |
+ |
final class ReadLockView implements Lock { |
819 |
+ |
public void lock() { readLock(); } |
820 |
+ |
public void lockInterruptibly() throws InterruptedException { |
821 |
+ |
readLockInterruptibly(); |
822 |
+ |
} |
823 |
+ |
public boolean tryLock() { return tryReadLock() != 0L; } |
824 |
+ |
public boolean tryLock(long time, TimeUnit unit) |
825 |
+ |
throws InterruptedException { |
826 |
+ |
return tryReadLock(time, unit) != 0L; |
827 |
+ |
} |
828 |
+ |
// note that we give up ability to check mode so just use current state |
829 |
+ |
public void unlock() { unlockRead(state); } |
830 |
+ |
public Condition newCondition() { |
831 |
+ |
throw new UnsupportedOperationException(); |
832 |
+ |
} |
833 |
+ |
} |
834 |
+ |
|
835 |
+ |
final class WriteLockView implements Lock { |
836 |
+ |
public void lock() { writeLock(); } |
837 |
+ |
public void lockInterruptibly() throws InterruptedException { |
838 |
+ |
writeLockInterruptibly(); |
839 |
+ |
} |
840 |
+ |
public boolean tryLock() { return tryWriteLock() != 0L; } |
841 |
+ |
public boolean tryLock(long time, TimeUnit unit) |
842 |
+ |
throws InterruptedException { |
843 |
+ |
return tryWriteLock(time, unit) != 0L; |
844 |
+ |
} |
845 |
+ |
public void unlock() { unlockWrite(state); } |
846 |
+ |
public Condition newCondition() { |
847 |
+ |
throw new UnsupportedOperationException(); |
848 |
+ |
} |
849 |
+ |
} |
850 |
+ |
|
851 |
+ |
final class ReadWriteLockView implements ReadWriteLock { |
852 |
+ |
public Lock readLock() { return asReadLock(); } |
853 |
+ |
public Lock writeLock() { return asWriteLock(); } |
854 |
+ |
} |
855 |
+ |
|
856 |
|
// internals |
857 |
|
|
858 |
|
/** |
860 |
|
* access bits value to RBITS, indicating hold of spinlock, |
861 |
|
* then updating, then releasing. |
862 |
|
* |
863 |
< |
* @param stamp, assumed that (stamp & ABITS) >= RFULL |
863 |
> |
* @param s, assumed that (s & ABITS) >= RFULL |
864 |
|
* @return new stamp on success, else zero |
865 |
|
*/ |
866 |
|
private long tryIncReaderOverflow(long s) { |
880 |
|
/** |
881 |
|
* Tries to decrement readerOverflow. |
882 |
|
* |
883 |
< |
* @param stamp, assumed that (stamp & ABITS) >= RFULL |
883 |
> |
* @param s, assumed that (s & ABITS) >= RFULL |
884 |
|
* @return new stamp on success, else zero |
885 |
|
*/ |
886 |
|
private long tryDecReaderOverflow(long s) { |
904 |
|
} |
905 |
|
|
906 |
|
/* |
907 |
< |
* The two versions of signal implement the phase-fair policy. |
908 |
< |
* They include almost the same code, but repacked in different |
909 |
< |
* ways. Integrating the policy with the mechanics eliminates |
910 |
< |
* state rechecks that would be needed with separate reader and |
911 |
< |
* writer signal methods. Both methods assume that they are |
912 |
< |
* called when the lock is last known to be available, and |
913 |
< |
* continue until the lock is unavailable, or at least one thread |
914 |
< |
* is signalled, or there are no more waiting threads. Signalling |
915 |
< |
* a reader entails popping (CASing) from rhead and unparking |
916 |
< |
* unless the thread already cancelled (indicated by a null waiter |
848 |
< |
* field). Signalling a writer requires finding the first node, |
849 |
< |
* i.e., the successor of whead. This is normally just head.next, |
850 |
< |
* but may require traversal from wtail if next pointers are |
851 |
< |
* lagging. These methods may fail to wake up an acquiring thread |
852 |
< |
* when one or more have been cancelled, but the cancel methods |
853 |
< |
* themselves provide extra safeguards to ensure liveness. |
854 |
< |
*/ |
855 |
< |
|
856 |
< |
private void readerPrefSignal() { |
857 |
< |
boolean readers = false; |
858 |
< |
RNode p; WNode h, q; long s; Thread w; |
859 |
< |
while ((p = rhead) != null) { |
860 |
< |
if (((s = state) & WBIT) != 0L) |
861 |
< |
return; |
862 |
< |
if (p.seq == (s & SBITS)) |
863 |
< |
break; |
864 |
< |
readers = true; |
865 |
< |
if (U.compareAndSwapObject(this, RHEAD, p, p.next) && |
866 |
< |
(w = p.waiter) != null && |
867 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
868 |
< |
U.unpark(w); |
869 |
< |
} |
870 |
< |
if (!readers && (state & ABITS) == 0L && |
871 |
< |
(h = whead) != null && h.status != 0) { |
872 |
< |
U.compareAndSwapInt(h, STATUS, WAITING, 0); |
907 |
> |
* Wakes up the successor of h (normally whead). This is normally |
908 |
> |
* just h.next, but may require traversal from wtail if next |
909 |
> |
* pointers are lagging. This may fail to wake up an acquiring |
910 |
> |
* thread when one or more have been cancelled, but the cancel |
911 |
> |
* methods themselves provide extra safeguards to ensure liveness. |
912 |
> |
*/ |
913 |
> |
private void release(WNode h) { |
914 |
> |
if (h != null) { |
915 |
> |
WNode q; Thread w; |
916 |
> |
U.compareAndSwapInt(h, WSTATUS, WAITING, 0); |
917 |
|
if ((q = h.next) == null || q.status == CANCELLED) { |
874 |
– |
q = null; |
918 |
|
for (WNode t = wtail; t != null && t != h; t = t.prev) |
919 |
|
if (t.status <= 0) |
920 |
|
q = t; |
921 |
|
} |
922 |
< |
if (q != null && (w = q.thread) != null) |
923 |
< |
U.unpark(w); |
924 |
< |
} |
925 |
< |
} |
926 |
< |
|
927 |
< |
private void writerPrefSignal() { |
928 |
< |
RNode p; WNode h, q; long s; Thread w; |
929 |
< |
if ((h = whead) != null && h.status != 0) { |
930 |
< |
U.compareAndSwapInt(h, STATUS, WAITING, 0); |
931 |
< |
if ((q = h.next) == null || q.status == CANCELLED) { |
889 |
< |
q = null; |
890 |
< |
for (WNode t = wtail; t != null && t != h; t = t.prev) |
891 |
< |
if (t.status <= 0) |
892 |
< |
q = t; |
893 |
< |
} |
894 |
< |
if (q != null && (w = q.thread) != null) |
895 |
< |
U.unpark(w); |
896 |
< |
} |
897 |
< |
else { |
898 |
< |
while ((p = rhead) != null && ((s = state) & WBIT) == 0L && |
899 |
< |
p.seq != (s & SBITS)) { |
900 |
< |
if (U.compareAndSwapObject(this, RHEAD, p, p.next) && |
901 |
< |
(w = p.waiter) != null && |
902 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
903 |
< |
U.unpark(w); |
922 |
> |
if (q != null) { |
923 |
> |
for (WNode r = q;;) { // release co-waiters too |
924 |
> |
if ((w = r.thread) != null) { |
925 |
> |
r.thread = null; |
926 |
> |
U.unpark(w); |
927 |
> |
} |
928 |
> |
if ((r = q.cowait) == null) |
929 |
> |
break; |
930 |
> |
U.compareAndSwapObject(q, WCOWAIT, r, r.cowait); |
931 |
> |
} |
932 |
|
} |
933 |
|
} |
934 |
|
} |
935 |
|
|
936 |
|
/** |
937 |
< |
* RNG for local spins. The first call from await{Read,Write} |
910 |
< |
* produces a thread-local value. Unless zero, subsequent calls |
911 |
< |
* use an xorShift to further reduce memory traffic. |
912 |
< |
*/ |
913 |
< |
private static int nextRandom(int r) { |
914 |
< |
if (r == 0) |
915 |
< |
return ThreadLocalRandom.current().nextInt(); |
916 |
< |
r ^= r << 1; // xorshift |
917 |
< |
r ^= r >>> 3; |
918 |
< |
r ^= r << 10; |
919 |
< |
return r; |
920 |
< |
} |
921 |
< |
|
922 |
< |
/** |
923 |
< |
* Possibly spins trying to obtain write lock, then enqueues and |
924 |
< |
* blocks while not head of write queue or cannot acquire lock, |
925 |
< |
* possibly spinning when at head; cancelling on timeout or |
926 |
< |
* interrupt. |
937 |
> |
* See above for explanation. |
938 |
|
* |
939 |
|
* @param interruptible true if should check interrupts and if so |
940 |
|
* return INTERRUPTED |
941 |
|
* @param deadline if nonzero, the System.nanoTime value to timeout |
942 |
|
* at (and return zero) |
943 |
+ |
* @return next state, or INTERRUPTED |
944 |
|
*/ |
945 |
< |
private long awaitWrite(boolean interruptible, long deadline) { |
946 |
< |
WNode node = null; |
947 |
< |
for (int r = 0, spins = -1;;) { |
948 |
< |
WNode p; long s, next; |
945 |
> |
private long acquireWrite(boolean interruptible, long deadline) { |
946 |
> |
WNode node = null, p; |
947 |
> |
for (int spins = -1;;) { // spin while enqueuing |
948 |
> |
long s, ns; |
949 |
|
if (((s = state) & ABITS) == 0L) { |
950 |
< |
if (U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) |
951 |
< |
return next; |
950 |
> |
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) |
951 |
> |
return ns; |
952 |
|
} |
941 |
– |
else if (spins < 0) |
942 |
– |
spins = whead == wtail ? SPINS : 0; |
953 |
|
else if (spins > 0) { |
954 |
< |
if ((r = nextRandom(r)) >= 0) |
954 |
> |
if (ThreadLocalRandom.current().nextInt() >= 0) |
955 |
|
--spins; |
956 |
|
} |
957 |
|
else if ((p = wtail) == null) { // initialize queue |
958 |
< |
if (U.compareAndSwapObject(this, WHEAD, null, |
959 |
< |
new WNode(null, null))) |
960 |
< |
wtail = whead; |
958 |
> |
WNode h = new WNode(WMODE, null); |
959 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
960 |
> |
wtail = h; |
961 |
|
} |
962 |
+ |
else if (spins < 0) |
963 |
+ |
spins = (p == whead) ? SPINS : 0; |
964 |
|
else if (node == null) |
965 |
< |
node = new WNode(Thread.currentThread(), p); |
965 |
> |
node = new WNode(WMODE, p); |
966 |
|
else if (node.prev != p) |
967 |
|
node.prev = p; |
968 |
|
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
969 |
|
p.next = node; |
970 |
< |
for (int headSpins = SPINS;;) { |
971 |
< |
WNode np; int ps; |
972 |
< |
if ((np = node.prev) != p && np != null && |
973 |
< |
(p = np).next != node) |
974 |
< |
p.next = node; // stale |
975 |
< |
if (p == whead) { |
976 |
< |
for (int k = headSpins;;) { |
977 |
< |
if (((s = state) & ABITS) == 0L) { |
978 |
< |
if (U.compareAndSwapLong(this, STATE, |
979 |
< |
s, next = s + WBIT)) { |
980 |
< |
whead = node; |
981 |
< |
node.thread = null; |
982 |
< |
node.prev = null; |
983 |
< |
return next; |
984 |
< |
} |
985 |
< |
break; |
970 |
> |
break; |
971 |
> |
} |
972 |
> |
} |
973 |
> |
|
974 |
> |
for (int spins = SPINS;;) { |
975 |
> |
WNode np, pp; int ps; long s, ns; Thread w; |
976 |
> |
while ((np = node.prev) != p && np != null) |
977 |
> |
(p = np).next = node; // stale |
978 |
> |
if (whead == p) { |
979 |
> |
for (int k = spins;;) { // spin at head |
980 |
> |
if (((s = state) & ABITS) == 0L && |
981 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) { |
982 |
> |
whead = node; |
983 |
> |
node.prev = null; |
984 |
> |
return ns; |
985 |
> |
} |
986 |
> |
else if (ThreadLocalRandom.current().nextInt() >= 0 && |
987 |
> |
--k <= 0) |
988 |
> |
break; |
989 |
> |
} |
990 |
> |
if (spins < MAX_HEAD_SPINS) |
991 |
> |
spins <<= 1; |
992 |
> |
} |
993 |
> |
if ((ps = p.status) == 0) |
994 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
995 |
> |
else if (ps == CANCELLED) { |
996 |
> |
if ((pp = p.prev) != null) { |
997 |
> |
node.prev = pp; |
998 |
> |
pp.next = node; |
999 |
> |
} |
1000 |
> |
} |
1001 |
> |
else { |
1002 |
> |
long time; // 0 argument to park means no timeout |
1003 |
> |
if (deadline == 0L) |
1004 |
> |
time = 0L; |
1005 |
> |
else if ((time = deadline - System.nanoTime()) <= 0L) |
1006 |
> |
return cancelWaiter(node, null, false); |
1007 |
> |
node.thread = Thread.currentThread(); |
1008 |
> |
if (node.prev == p && p.status == WAITING && // recheck |
1009 |
> |
(p != whead || (state & ABITS) != 0L)) { |
1010 |
> |
U.park(false, time); |
1011 |
> |
if (interruptible && Thread.interrupted()) |
1012 |
> |
return cancelWaiter(node, null, true); |
1013 |
> |
} |
1014 |
> |
node.thread = null; |
1015 |
> |
} |
1016 |
> |
} |
1017 |
> |
} |
1018 |
> |
|
1019 |
> |
/** |
1020 |
> |
* See above for explanation. |
1021 |
> |
* |
1022 |
> |
* @param interruptible true if should check interrupts and if so |
1023 |
> |
* return INTERRUPTED |
1024 |
> |
* @param deadline if nonzero, the System.nanoTime value to timeout |
1025 |
> |
* at (and return zero) |
1026 |
> |
* @return next state, or INTERRUPTED |
1027 |
> |
*/ |
1028 |
> |
private long acquireRead(boolean interruptible, long deadline) { |
1029 |
> |
WNode node = null, group = null, p; |
1030 |
> |
for (int spins = -1;;) { |
1031 |
> |
for (;;) { |
1032 |
> |
long s, m, ns; WNode h, q; Thread w; // anti-barging guard |
1033 |
> |
if (group == null && (h = whead) != null && |
1034 |
> |
(q = h.next) != null && q.mode != RMODE) |
1035 |
> |
break; |
1036 |
> |
if ((m = (s = state) & ABITS) == WBIT) |
1037 |
> |
break; |
1038 |
> |
if (m < RFULL ? |
1039 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) : |
1040 |
> |
(ns = tryIncReaderOverflow(s)) != 0L) { |
1041 |
> |
if (group != null) { // help release others |
1042 |
> |
for (WNode r = group;;) { |
1043 |
> |
if ((w = r.thread) != null) { |
1044 |
> |
r.thread = null; |
1045 |
> |
U.unpark(w); |
1046 |
|
} |
1047 |
< |
if ((r = nextRandom(r)) >= 0 && --k <= 0) |
1047 |
> |
if ((r = group.cowait) == null) |
1048 |
|
break; |
1049 |
+ |
U.compareAndSwapObject(group, WCOWAIT, r, r.cowait); |
1050 |
|
} |
978 |
– |
if (headSpins < MAX_HEAD_SPINS) |
979 |
– |
headSpins <<= 1; |
1051 |
|
} |
1052 |
< |
if ((ps = p.status) == 0) |
1053 |
< |
U.compareAndSwapInt(p, STATUS, 0, WAITING); |
1054 |
< |
else if (ps == CANCELLED) |
1055 |
< |
node.prev = p.prev; |
1056 |
< |
else { |
1057 |
< |
long time; // 0 argument to park means no timeout |
1052 |
> |
return ns; |
1053 |
> |
} |
1054 |
> |
} |
1055 |
> |
if (spins > 0) { |
1056 |
> |
if (ThreadLocalRandom.current().nextInt() >= 0) |
1057 |
> |
--spins; |
1058 |
> |
} |
1059 |
> |
else if ((p = wtail) == null) { |
1060 |
> |
WNode h = new WNode(WMODE, null); |
1061 |
> |
if (U.compareAndSwapObject(this, WHEAD, null, h)) |
1062 |
> |
wtail = h; |
1063 |
> |
} |
1064 |
> |
else if (spins < 0) |
1065 |
> |
spins = (p == whead) ? SPINS : 0; |
1066 |
> |
else if (node == null) |
1067 |
> |
node = new WNode(WMODE, p); |
1068 |
> |
else if (node.prev != p) |
1069 |
> |
node.prev = p; |
1070 |
> |
else if (p.mode == RMODE && p != whead) { |
1071 |
> |
WNode pp = p.prev; // become co-waiter with group p |
1072 |
> |
if (pp != null && p == wtail && |
1073 |
> |
U.compareAndSwapObject(p, WCOWAIT, |
1074 |
> |
node.cowait = p.cowait, node)) { |
1075 |
> |
node.thread = Thread.currentThread(); |
1076 |
> |
for (long time;;) { |
1077 |
|
if (deadline == 0L) |
1078 |
|
time = 0L; |
1079 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1080 |
< |
return cancelWriter(node, false); |
1081 |
< |
if (node.prev == p && p.status == WAITING && |
1082 |
< |
(p != whead || (state & WBIT) != 0L)) { // recheck |
1083 |
< |
U.park(false, time); |
1084 |
< |
if (interruptible && Thread.interrupted()) |
1085 |
< |
return cancelWriter(node, true); |
1080 |
> |
return cancelWaiter(node, p, false); |
1081 |
> |
if (node.thread == null) |
1082 |
> |
break; |
1083 |
> |
if (p.prev != pp || p.status == CANCELLED || |
1084 |
> |
p == whead || p.prev != pp) { |
1085 |
> |
node.thread = null; |
1086 |
> |
break; |
1087 |
|
} |
1088 |
+ |
if (node.thread == null) // must recheck |
1089 |
+ |
break; |
1090 |
+ |
U.park(false, time); |
1091 |
+ |
if (interruptible && Thread.interrupted()) |
1092 |
+ |
return cancelWaiter(node, p, true); |
1093 |
|
} |
1094 |
+ |
group = p; |
1095 |
|
} |
1096 |
+ |
node = null; // throw away |
1097 |
|
} |
1098 |
< |
} |
1099 |
< |
} |
1100 |
< |
|
1003 |
< |
/** |
1004 |
< |
* If node non-null, forces cancel status and unsplices from queue |
1005 |
< |
* if possible. This is a streamlined variant of cancellation |
1006 |
< |
* methods in AbstractQueuedSynchronizer that includes a detailed |
1007 |
< |
* explanation. |
1008 |
< |
*/ |
1009 |
< |
private long cancelWriter(WNode node, boolean interrupted) { |
1010 |
< |
WNode pred; |
1011 |
< |
if (node != null && (pred = node.prev) != null) { |
1012 |
< |
WNode pp; |
1013 |
< |
node.thread = null; |
1014 |
< |
while (pred.status == CANCELLED && (pp = pred.prev) != null) |
1015 |
< |
pred = node.prev = pp; |
1016 |
< |
WNode predNext = pred.next; |
1017 |
< |
node.status = CANCELLED; |
1018 |
< |
if (predNext != null) { |
1019 |
< |
Thread w; |
1020 |
< |
WNode succ = node.next; |
1021 |
< |
if (succ == null || succ.status == CANCELLED) { |
1022 |
< |
succ = null; |
1023 |
< |
for (WNode t = wtail; t != null && t != node; t = t.prev) |
1024 |
< |
if (t.status <= 0) |
1025 |
< |
succ = t; |
1026 |
< |
if (succ == null && node == wtail) |
1027 |
< |
U.compareAndSwapObject(this, WTAIL, node, pred); |
1028 |
< |
} |
1029 |
< |
U.compareAndSwapObject(pred, WNEXT, predNext, succ); |
1030 |
< |
if (succ != null && (w = succ.thread) != null) |
1031 |
< |
U.unpark(w); |
1098 |
> |
else if (U.compareAndSwapObject(this, WTAIL, p, node)) { |
1099 |
> |
p.next = node; |
1100 |
> |
break; |
1101 |
|
} |
1102 |
|
} |
1034 |
– |
writerPrefSignal(); |
1035 |
– |
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1036 |
– |
} |
1103 |
|
|
1104 |
< |
/** |
1105 |
< |
* Waits for read lock or timeout or interrupt. The form of |
1106 |
< |
* awaitRead differs from awaitWrite mainly because it must |
1107 |
< |
* restart (with a new wait node) if the thread was unqueued and |
1108 |
< |
* unparked but could not the obtain lock. We also need to help |
1109 |
< |
* with preference rules by not trying to acquire the lock before |
1110 |
< |
* enqueuing if there is a known waiting writer, but also helping |
1111 |
< |
* to release those threads that are still queued from the last |
1112 |
< |
* release. |
1113 |
< |
*/ |
1114 |
< |
private long awaitRead(long stamp, boolean interruptible, long deadline) { |
1115 |
< |
long seq = stamp & SBITS; |
1116 |
< |
RNode node = null; |
1117 |
< |
boolean queued = false; |
1118 |
< |
for (int r = 0, headSpins = SPINS, spins = -1;;) { |
1119 |
< |
long s, m, next; RNode p; WNode wh; Thread w; |
1120 |
< |
if ((m = (s = state) & ABITS) != WBIT && |
1121 |
< |
((s & SBITS) != seq || (wh = whead) == null || |
1122 |
< |
wh.status == 0)) { |
1123 |
< |
if (m < RFULL ? |
1124 |
< |
U.compareAndSwapLong(this, STATE, s, next = s + RUNIT) : |
1125 |
< |
(next = tryIncReaderOverflow(s)) != 0L) { |
1126 |
< |
if (node != null && (w = node.waiter) != null) |
1127 |
< |
U.compareAndSwapObject(node, WAITER, w, null); |
1128 |
< |
if ((p = rhead) != null && (s & SBITS) != p.seq && |
1129 |
< |
U.compareAndSwapObject(this, RHEAD, p, p.next) && |
1064 |
< |
(w = p.waiter) != null && |
1065 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
1066 |
< |
U.unpark(w); // help signal other waiters |
1067 |
< |
return next; |
1104 |
> |
for (int spins = SPINS;;) { |
1105 |
> |
WNode np, pp, r; int ps; long m, s, ns; Thread w; |
1106 |
> |
while ((np = node.prev) != p && np != null) |
1107 |
> |
(p = np).next = node; |
1108 |
> |
if (whead == p) { |
1109 |
> |
for (int k = spins;;) { |
1110 |
> |
if ((m = (s = state) & ABITS) != WBIT) { |
1111 |
> |
if (m < RFULL ? |
1112 |
> |
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT): |
1113 |
> |
(ns = tryIncReaderOverflow(s)) != 0L) { |
1114 |
> |
whead = node; |
1115 |
> |
node.prev = null; |
1116 |
> |
while ((r = node.cowait) != null) { |
1117 |
> |
if (U.compareAndSwapObject(node, WCOWAIT, |
1118 |
> |
r, r.cowait) && |
1119 |
> |
(w = r.thread) != null) { |
1120 |
> |
r.thread = null; |
1121 |
> |
U.unpark(w); // release co-waiter |
1122 |
> |
} |
1123 |
> |
} |
1124 |
> |
return ns; |
1125 |
> |
} |
1126 |
> |
} |
1127 |
> |
else if (ThreadLocalRandom.current().nextInt() >= 0 && |
1128 |
> |
--k <= 0) |
1129 |
> |
break; |
1130 |
|
} |
1131 |
+ |
if (spins < MAX_HEAD_SPINS) |
1132 |
+ |
spins <<= 1; |
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) && |
1137 |
< |
(w = p.waiter) != null && |
1138 |
< |
U.compareAndSwapObject(p, WAITER, w, null)) |
1139 |
< |
U.unpark(w); |
1140 |
< |
} |
1077 |
< |
else if (queued && node != null && node.waiter == null) { |
1078 |
< |
node = null; // restart |
1079 |
< |
queued = false; |
1080 |
< |
spins = -1; |
1081 |
< |
} |
1082 |
< |
else if (spins < 0) { |
1083 |
< |
if (rhead != node) |
1084 |
< |
spins = 0; |
1085 |
< |
else if ((spins = headSpins) < MAX_HEAD_SPINS && node != null) |
1086 |
< |
headSpins <<= 1; |
1087 |
< |
} |
1088 |
< |
else if (spins > 0) { |
1089 |
< |
if ((r = nextRandom(r)) >= 0) |
1090 |
< |
--spins; |
1091 |
< |
} |
1092 |
< |
else if (node == null) |
1093 |
< |
node = new RNode(seq, Thread.currentThread()); |
1094 |
< |
else if (!queued) { |
1095 |
< |
if (queued = U.compareAndSwapObject(this, RHEAD, |
1096 |
< |
node.next = rhead, node)) |
1097 |
< |
spins = -1; |
1134 |
> |
if ((ps = p.status) == 0) |
1135 |
> |
U.compareAndSwapInt(p, WSTATUS, 0, WAITING); |
1136 |
> |
else if (ps == CANCELLED) { |
1137 |
> |
if ((pp = p.prev) != null) { |
1138 |
> |
node.prev = pp; |
1139 |
> |
pp.next = node; |
1140 |
> |
} |
1141 |
|
} |
1142 |
|
else { |
1143 |
|
long time; |
1144 |
|
if (deadline == 0L) |
1145 |
|
time = 0L; |
1146 |
|
else if ((time = deadline - System.nanoTime()) <= 0L) |
1147 |
< |
return cancelReader(node, false); |
1148 |
< |
if ((state & WBIT) != 0L && node.waiter != null) { // recheck |
1147 |
> |
return cancelWaiter(node, null, false); |
1148 |
> |
node.thread = Thread.currentThread(); |
1149 |
> |
if (node.prev == p && p.status == WAITING && |
1150 |
> |
(p != whead || (state & ABITS) != WBIT)) { |
1151 |
|
U.park(false, time); |
1152 |
|
if (interruptible && Thread.interrupted()) |
1153 |
< |
return cancelReader(node, true); |
1153 |
> |
return cancelWaiter(node, null, true); |
1154 |
|
} |
1155 |
+ |
node.thread = null; |
1156 |
|
} |
1157 |
|
} |
1158 |
|
} |
1159 |
|
|
1160 |
|
/** |
1161 |
|
* If node non-null, forces cancel status and unsplices from queue |
1162 |
< |
* if possible, by traversing entire queue looking for cancelled |
1163 |
< |
* nodes. |
1162 |
> |
* if possible. This is a variant of cancellation methods in |
1163 |
> |
* AbstractQueuedSynchronizer (see its detailed explanation in AQS |
1164 |
> |
* internal documentation) that more conservatively wakes up other |
1165 |
> |
* threads that may have had their links changed, so as to preserve |
1166 |
> |
* liveness in the main signalling methods. |
1167 |
|
*/ |
1168 |
< |
private long cancelReader(RNode node, boolean interrupted) { |
1169 |
< |
Thread w; |
1170 |
< |
if (node != null && (w = node.waiter) != null && |
1171 |
< |
U.compareAndSwapObject(node, WAITER, w, null)) { |
1172 |
< |
for (RNode pred = null, p = rhead; p != null;) { |
1173 |
< |
RNode q = p.next; |
1174 |
< |
if (p.waiter == null) { |
1175 |
< |
if (pred == null) { |
1176 |
< |
U.compareAndSwapObject(this, RHEAD, p, q); |
1128 |
< |
p = rhead; |
1129 |
< |
} |
1130 |
< |
else { |
1131 |
< |
U.compareAndSwapObject(pred, RNEXT, p, q); |
1132 |
< |
p = pred.next; |
1168 |
> |
private long cancelWaiter(WNode node, WNode group, boolean interrupted) { |
1169 |
> |
if (node != null) { |
1170 |
> |
node.thread = null; |
1171 |
> |
node.status = CANCELLED; |
1172 |
> |
if (group != null) { |
1173 |
> |
for (WNode p = group, q; p != null; p = q) { |
1174 |
> |
if ((q = p.cowait) != null && q.status == CANCELLED) { |
1175 |
> |
U.compareAndSwapObject(p, WCOWAIT, q, q.cowait); |
1176 |
> |
break; |
1177 |
|
} |
1178 |
|
} |
1179 |
< |
else { |
1180 |
< |
pred = p; |
1181 |
< |
p = q; |
1179 |
> |
} |
1180 |
> |
else { |
1181 |
> |
for (WNode pred = node.prev; pred != null; ) { |
1182 |
> |
WNode succ, pp; Thread w; |
1183 |
> |
while ((succ = node.next) == null || |
1184 |
> |
succ.status == CANCELLED) { |
1185 |
> |
WNode q = null; |
1186 |
> |
for (WNode t = wtail; t != null && t != node; t = t.prev) |
1187 |
> |
if (t.status != CANCELLED) |
1188 |
> |
q = t; |
1189 |
> |
if (succ == q || |
1190 |
> |
U.compareAndSwapObject(node, WNEXT, |
1191 |
> |
succ, succ = q)) { |
1192 |
> |
if (succ == null && node == wtail) |
1193 |
> |
U.compareAndSwapObject(this, WTAIL, node, pred); |
1194 |
> |
break; |
1195 |
> |
} |
1196 |
> |
} |
1197 |
> |
if (pred.next == node) |
1198 |
> |
U.compareAndSwapObject(pred, WNEXT, node, succ); |
1199 |
> |
if (succ != null && (w = succ.thread) != null) |
1200 |
> |
U.unpark(w); |
1201 |
> |
if (pred.status != CANCELLED || (pp = pred.prev) == null) |
1202 |
> |
break; |
1203 |
> |
node.prev = pp; // repeat for new pred |
1204 |
> |
U.compareAndSwapObject(pp, WNEXT, pred, succ); |
1205 |
> |
pred = pp; |
1206 |
|
} |
1207 |
|
} |
1208 |
|
} |
1209 |
< |
readerPrefSignal(); |
1209 |
> |
release(whead); |
1210 |
|
return (interrupted || Thread.interrupted()) ? INTERRUPTED : 0L; |
1211 |
|
} |
1212 |
|
|
1213 |
|
// Unsafe mechanics |
1214 |
|
private static final sun.misc.Unsafe U; |
1215 |
|
private static final long STATE; |
1148 |
– |
private static final long RHEAD; |
1216 |
|
private static final long WHEAD; |
1217 |
|
private static final long WTAIL; |
1151 |
– |
private static final long RNEXT; |
1218 |
|
private static final long WNEXT; |
1219 |
< |
private static final long WPREV; |
1220 |
< |
private static final long WAITER; |
1155 |
< |
private static final long STATUS; |
1219 |
> |
private static final long WSTATUS; |
1220 |
> |
private static final long WCOWAIT; |
1221 |
|
|
1222 |
|
static { |
1223 |
|
try { |
1224 |
|
U = getUnsafe(); |
1225 |
|
Class<?> k = StampedLock.class; |
1161 |
– |
Class<?> rk = RNode.class; |
1226 |
|
Class<?> wk = WNode.class; |
1227 |
|
STATE = U.objectFieldOffset |
1228 |
|
(k.getDeclaredField("state")); |
1165 |
– |
RHEAD = U.objectFieldOffset |
1166 |
– |
(k.getDeclaredField("rhead")); |
1229 |
|
WHEAD = U.objectFieldOffset |
1230 |
|
(k.getDeclaredField("whead")); |
1231 |
|
WTAIL = U.objectFieldOffset |
1232 |
|
(k.getDeclaredField("wtail")); |
1233 |
< |
RNEXT = U.objectFieldOffset |
1172 |
< |
(rk.getDeclaredField("next")); |
1173 |
< |
WAITER = U.objectFieldOffset |
1174 |
< |
(rk.getDeclaredField("waiter")); |
1175 |
< |
STATUS = U.objectFieldOffset |
1233 |
> |
WSTATUS = U.objectFieldOffset |
1234 |
|
(wk.getDeclaredField("status")); |
1235 |
|
WNEXT = U.objectFieldOffset |
1236 |
|
(wk.getDeclaredField("next")); |
1237 |
< |
WPREV = U.objectFieldOffset |
1238 |
< |
(wk.getDeclaredField("prev")); |
1237 |
> |
WCOWAIT = U.objectFieldOffset |
1238 |
> |
(wk.getDeclaredField("cowait")); |
1239 |
|
|
1240 |
|
} catch (Exception e) { |
1241 |
|
throw new Error(e); |
1252 |
|
private static sun.misc.Unsafe getUnsafe() { |
1253 |
|
try { |
1254 |
|
return sun.misc.Unsafe.getUnsafe(); |
1255 |
< |
} catch (SecurityException se) { |
1256 |
< |
try { |
1257 |
< |
return java.security.AccessController.doPrivileged |
1258 |
< |
(new java.security |
1259 |
< |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1260 |
< |
public sun.misc.Unsafe run() throws Exception { |
1261 |
< |
java.lang.reflect.Field f = sun.misc |
1262 |
< |
.Unsafe.class.getDeclaredField("theUnsafe"); |
1263 |
< |
f.setAccessible(true); |
1264 |
< |
return (sun.misc.Unsafe) f.get(null); |
1265 |
< |
}}); |
1266 |
< |
} catch (java.security.PrivilegedActionException e) { |
1267 |
< |
throw new RuntimeException("Could not initialize intrinsics", |
1268 |
< |
e.getCause()); |
1269 |
< |
} |
1255 |
> |
} catch (SecurityException tryReflectionInstead) {} |
1256 |
> |
try { |
1257 |
> |
return java.security.AccessController.doPrivileged |
1258 |
> |
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
1259 |
> |
public sun.misc.Unsafe run() throws Exception { |
1260 |
> |
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
1261 |
> |
for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
1262 |
> |
f.setAccessible(true); |
1263 |
> |
Object x = f.get(null); |
1264 |
> |
if (k.isInstance(x)) |
1265 |
> |
return k.cast(x); |
1266 |
> |
} |
1267 |
> |
throw new NoSuchFieldError("the Unsafe"); |
1268 |
> |
}}); |
1269 |
> |
} catch (java.security.PrivilegedActionException e) { |
1270 |
> |
throw new RuntimeException("Could not initialize intrinsics", |
1271 |
> |
e.getCause()); |
1272 |
|
} |
1273 |
|
} |
1214 |
– |
|
1274 |
|
} |