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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.Lock; |
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import java.util.concurrent.locks.Condition; |
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import java.util.concurrent.locks.ReadWriteLock; |
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import java.util.concurrent.locks.LockSupport; |
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/** |
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* A capability-based lock with three modes for controlling read/write |
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* <li><b>Optimistic Reading.</b> Method {@link #tryOptimisticRead} |
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* returns a non-zero stamp only if the lock is not currently held |
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* in write mode. Method {@link #validate} returns true if the lock |
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* has not since been acquired in write mode. This mode can be |
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* thought of as an extremely weak version of a read-lock, that can |
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* be broken by a writer at any time. The use of optimistic mode |
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* for short read-only code segments often reduces contention and |
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* improves throughput. However, its use is inherently fragile. |
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* Optimistic read sections should only read fields and hold them in |
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* local variables for later use after validation. Fields read while |
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* in optimistic mode may be wildly inconsistent, so usage applies |
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* only when you are familiar enough with data representations to |
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* check consistency and/or repeatedly invoke method {@code |
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* validate()}. For example, such steps are typically required when |
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* first reading an object or array reference, and then accessing |
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* one of its fields, elements or methods. </li> |
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* has not been acquired in write mode since obtaining a given |
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* stamp. This mode can be thought of as an extremely weak version |
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* of a read-lock, that can be broken by a writer at any time. The |
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* use of optimistic mode for short read-only code segments often |
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* reduces contention and improves throughput. However, its use is |
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* inherently fragile. Optimistic read sections should only read |
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* fields and hold them in local variables for later use after |
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* validation. Fields read while in optimistic mode may be wildly |
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* inconsistent, so usage applies only when you are familiar enough |
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* with data representations to check consistency and/or repeatedly |
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* invoke method {@code validate()}. For example, such steps are |
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* typically required when first reading an object or array |
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* reference, and then accessing one of its fields, elements or |
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* methods. </li> |
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* |
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* </ul> |
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* |
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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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* 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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* 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 is 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 the |
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* queue structure, wait nodes need not actually carry sequence |
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* numbers; we know each is greater than its predecessor. This |
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* simplifies 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 |
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* spin count with 50% probability) 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 |
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* 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 |
227 |
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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 consistent sets |
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* of locally cached 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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/** 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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// Initial value for lock state; avoid failure value zero |
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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 |
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// Special value from cancelled acquire methods so caller can throw IE |
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private static final long INTERRUPTED = 1L; |
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|
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// Values for writer status; order matters |
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// Values for node status; order matters |
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private static final int WAITING = -1; |
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private static final int CANCELLED = 1; |
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|
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/** Wait nodes for readers */ |
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static final class RNode { |
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final long seq; // stamp value upon enqueue |
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volatile Thread waiter; // null if no longer waiting |
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volatile RNode next; |
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RNode(long s, Thread w) { seq = s; waiter = w; } |
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} |
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// Modes for nodes (int not boolean to allow arithmetic) |
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private static final int RMODE = 0; |
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private static final int WMODE = 1; |
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|
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/** Wait nodes for writers */ |
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/** Wait nodes */ |
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static final class WNode { |
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volatile int status; // 0, WAITING, or CANCELLED |
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volatile WNode prev; |
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volatile WNode next; |
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volatile Thread thread; |
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WNode(Thread t, WNode p) { thread = t; prev = p; } |
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> |
volatile WNode cowait; // list of linked readers |
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> |
volatile Thread thread; // non-null while possibly parked |
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> |
volatile int status; // 0, WAITING, or CANCELLED |
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> |
final int mode; // RMODE or WMODE |
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> |
WNode(int m, WNode p) { mode = m; prev = p; } |
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} |
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|
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< |
/** Head of writer CLH queue */ |
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> |
/** Head of CLH queue */ |
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private transient volatile WNode whead; |
309 |
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/** Tail (last) of writer CLH queue */ |
309 |
> |
/** Tail (last) of CLH queue */ |
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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 |
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private transient volatile long state; |
319 |
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/** extra reader count when state read count saturated */ |
320 |
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private transient int readerOverflow; |
333 |
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* @return a stamp that can be used to unlock or convert mode |
334 |
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*/ |
335 |
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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 |
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|
342 |
|
/** |
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 |
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|
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 |
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(); |
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 |
|
|
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 |
|
/** |
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 |
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 |
|
} |
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 |
|
|
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 |
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 |
|
/** |
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 |
|
/** |
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; |
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 |
|
} |
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. |
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 |
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) |
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) |
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; |
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 |
|
} |
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; |
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 |
|
} |
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 |
|
/** |
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 & ABITS) != 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); |
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 |
|
} |