1536 lines
57 KiB
Java
1536 lines
57 KiB
Java
/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package dorkbox.util.messagebus.common.adapter;
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import java.util.Random;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.locks.Condition;
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import java.util.concurrent.locks.Lock;
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import java.util.concurrent.locks.ReadWriteLock;
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/**
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* A capability-based lock with three modes for controlling read/write
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* access. The state of a StampedLock consists of a version and mode.
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* Lock acquisition methods return a stamp that represents and
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* controls access with respect to a lock state; "try" versions of
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* these methods may instead return the special value zero to
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* represent failure to acquire access. Lock release and conversion
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* methods require stamps as arguments, and fail if they do not match
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* the state of the lock. The three modes are:
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*
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* <ul>
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*
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* <li><b>Writing.</b> Method {@link #writeLock} possibly blocks
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* waiting for exclusive access, returning a stamp that can be used
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* in method {@link #unlockWrite} to release the lock. Untimed and
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* timed versions of {@code tryWriteLock} are also provided. When
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* the lock is held in write mode, no read locks may be obtained,
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* and all optimistic read validations will fail. </li>
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*
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* <li><b>Reading.</b> Method {@link #readLock} possibly blocks
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* waiting for non-exclusive access, returning a stamp that can be
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* used in method {@link #unlockRead} to release the lock. Untimed
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* and timed versions of {@code tryReadLock} are also provided. </li>
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*
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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 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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* <p>This class also supports methods that conditionally provide
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* conversions across the three modes. For example, method {@link
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* #tryConvertToWriteLock} attempts to "upgrade" a mode, returning
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* a valid write stamp if (1) already in writing mode (2) in reading
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* mode and there are no other readers or (3) in optimistic mode and
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* the lock is available. The forms of these methods are designed to
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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 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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* sooner than) one year of continuous operation. A stamp held without
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* use or validation for longer than this period may fail to validate
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* correctly. StampedLocks are serializable, but always deserialize
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* into initial unlocked state, so they are not useful for remote
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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. 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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* code illustrates some try/catch conventions even though they are
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* not strictly needed here because no exceptions can occur in their
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* bodies.<br>
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*
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* <pre>{@code
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* class Point {
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* private double x, y;
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* private final StampedLock sl = new StampedLock();
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*
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* void move(double deltaX, double deltaY) { // an exclusively locked method
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* long stamp = sl.writeLock();
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* try {
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* x += deltaX;
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* y += deltaY;
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* } finally {
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* sl.unlockWrite(stamp);
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* }
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* }
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*
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* double distanceFromOrigin() { // A read-only method
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* long stamp = sl.tryOptimisticRead();
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* double currentX = x, currentY = y;
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* if (!sl.validate(stamp)) {
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* stamp = sl.readLock();
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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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* sl.unlockRead(stamp);
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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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* // Could instead start with optimistic, not read mode
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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 = 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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* y = newY;
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* break;
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* }
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* else {
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* sl.unlockRead(stamp);
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* stamp = sl.writeLock();
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* }
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* }
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* } finally {
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* sl.unlock(stamp);
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* }
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* }
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* }}</pre>
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*
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* @since 1.8
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* @author Doug Lea
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*/
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public class StampedLock implements java.io.Serializable {
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/*
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* Algorithmic notes:
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*
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* The design employs elements of Sequence locks
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* (as used in linux kernels; see Lameter's
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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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* and Ordered RW locks (see Shirako et al
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* http://dl.acm.org/citation.cfm?id=2312015)
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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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* However, this is offset by a reader count that is non-zero when
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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 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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* 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.) Method release
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* does not (and sometimes cannot) itself wake up cowaiters. This
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* is done by the primary thread, but helped by any other threads
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* with nothing better to do in methods acquireRead and
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* acquireWrite.
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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. 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 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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* to normal volatile reads (of "state"). In the absence of (but
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* continual hope for) explicit JVM support of intrinsics with
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* double-sided reordering prohibition, or corresponding fence
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* intrinsics, we for now uncomfortably rely on the fact that the
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* Unsafe.getXVolatile intrinsic must have this property
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* (syntactic volatile reads do not) for internal purposes anyway,
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* even though it is not documented.
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*
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* The memory layout keeps lock state and queue pointers together
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* (normally on the same cache line). This usually works well for
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* read-mostly loads. In most other cases, the natural tendency of
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* adaptive-spin CLH locks to reduce memory contention lessens
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* motivation to further spread out contended locations, but might
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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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/** 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 enqueuing on acquisition */
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private static final int SPINS = NCPU > 1 ? 1 << 6 : 0;
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/** Maximum number of retries before blocking at head on acquisition */
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private static final int HEAD_SPINS = NCPU > 1 ? 1 << 10 : 0;
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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 << 16 : 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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/** The number of bits to use for reader count before overflowing */
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private static final int LG_READERS = 7;
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// Values for lock state and stamp operations
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private static final long RUNIT = 1L;
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private static final long WBIT = 1L << LG_READERS;
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private static final long RBITS = WBIT - 1L;
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private static final long RFULL = RBITS - 1L;
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private static final long ABITS = RBITS | WBIT;
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private static final long SBITS = ~RBITS; // note overlap with ABITS
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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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// 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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// 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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// 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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private static final ThreadLocal<Random> randomThreadLocal = new ThreadLocal<Random>() {
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@Override
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protected
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Random initialValue() {
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return new Random();
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}
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};
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/** Wait nodes */
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static final class WNode {
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volatile WNode prev;
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volatile WNode next;
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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) { this.mode = m; this.prev = p; }
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}
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/** Head of CLH queue */
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private transient volatile WNode whead;
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/** Tail (last) of CLH queue */
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private transient volatile WNode wtail;
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// views
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transient ReadLockView readLockView;
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transient WriteLockView writeLockView;
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transient ReadWriteLockView readWriteLockView;
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/** Lock sequence/state */
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private transient volatile long state;
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/** extra reader count when state read count saturated */
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private transient int readerOverflow;
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/**
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* Creates a new lock, initially in unlocked state.
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*/
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public StampedLock() {
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this.state = ORIGIN;
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}
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/**
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* Exclusively acquires the lock, blocking if necessary
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* until available.
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*
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* @return a stamp that can be used to unlock or convert mode
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*/
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public long writeLock() {
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long s, next; // bypass acquireWrite in fully unlocked case only
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return ((s = this.state) & ABITS) == 0L &&
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U.compareAndSwapLong(this, STATE, s, next = s + WBIT) ?
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next : acquireWrite(false, 0L);
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}
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/**
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* Exclusively acquires the lock if it is immediately available.
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*
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* @return a stamp that can be used to unlock or convert mode,
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* or zero if the lock is not available
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*/
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public long tryWriteLock() {
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long s, next;
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return ((s = this.state) & ABITS) == 0L &&
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U.compareAndSwapLong(this, STATE, s, next = s + WBIT) ?
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next : 0L;
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}
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/**
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* Exclusively acquires the lock if it is available within the
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* given time and the current thread has not been interrupted.
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* Behavior under timeout and interruption matches that specified
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* for method {@link Lock#tryLock(long,TimeUnit)}.
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*
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* @param time the maximum time to wait for the lock
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* @param unit the time unit of the {@code time} argument
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* @return a stamp that can be used to unlock or convert mode,
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* or zero if the lock is not available
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* @throws InterruptedException if the current thread is interrupted
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* before acquiring the lock
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*/
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public long tryWriteLock(long time, TimeUnit unit)
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throws InterruptedException {
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long nanos = unit.toNanos(time);
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if (!Thread.interrupted()) {
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long next, deadline;
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if ((next = tryWriteLock()) != 0L) {
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return next;
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}
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if (nanos <= 0L) {
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return 0L;
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}
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if ((deadline = System.nanoTime() + nanos) == 0L) {
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deadline = 1L;
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}
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if ((next = acquireWrite(true, deadline)) != INTERRUPTED) {
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return next;
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}
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}
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throw new InterruptedException();
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}
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/**
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* Exclusively acquires the lock, blocking if necessary
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* until available or the current thread is interrupted.
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* Behavior under interruption matches that specified
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* for method {@link Lock#lockInterruptibly()}.
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*
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* @return a stamp that can be used to unlock or convert mode
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* @throws InterruptedException if the current thread is interrupted
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* before acquiring the lock
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*/
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public long writeLockInterruptibly() throws InterruptedException {
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long next;
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if (!Thread.interrupted() &&
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(next = acquireWrite(true, 0L)) != INTERRUPTED) {
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return next;
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}
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throw new InterruptedException();
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}
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/**
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* Non-exclusively acquires the lock, blocking if necessary
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* until available.
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*
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* @return a stamp that can be used to unlock or convert mode
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*/
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public long readLock() {
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long s = this.state, next; // bypass acquireRead on common uncontended case
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return this.whead == this.wtail && (s & ABITS) < RFULL &&
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U.compareAndSwapLong(this, STATE, s, next = s + RUNIT) ?
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next : acquireRead(false, 0L);
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}
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/**
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* Non-exclusively acquires the lock if it is immediately available.
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*
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* @return a stamp that can be used to unlock or convert mode,
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* or zero if the lock is not available
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*/
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public long tryReadLock() {
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for (;;) {
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long s, m, next;
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if ((m = (s = this.state) & ABITS) == WBIT) {
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return 0L;
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} else if (m < RFULL) {
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if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) {
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return next;
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}
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}
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else if ((next = tryIncReaderOverflow(s)) != 0L) {
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return next;
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}
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}
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}
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/**
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* Non-exclusively acquires the lock if it is available within the
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* given time and the current thread has not been interrupted.
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* Behavior under timeout and interruption matches that specified
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* for method {@link Lock#tryLock(long,TimeUnit)}.
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*
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* @param time the maximum time to wait for the lock
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* @param unit the time unit of the {@code time} argument
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* @return a stamp that can be used to unlock or convert mode,
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* or zero if the lock is not available
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* @throws InterruptedException if the current thread is interrupted
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* before acquiring the lock
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*/
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public long tryReadLock(long time, TimeUnit unit)
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throws InterruptedException {
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long s, m, next, deadline;
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long nanos = unit.toNanos(time);
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if (!Thread.interrupted()) {
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if ((m = (s = this.state) & ABITS) != WBIT) {
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if (m < RFULL) {
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if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) {
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return next;
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}
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}
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else if ((next = tryIncReaderOverflow(s)) != 0L) {
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return next;
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}
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}
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if (nanos <= 0L) {
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return 0L;
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}
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if ((deadline = System.nanoTime() + nanos) == 0L) {
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deadline = 1L;
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}
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if ((next = acquireRead(true, deadline)) != INTERRUPTED) {
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return next;
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}
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}
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throw new InterruptedException();
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}
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/**
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* Non-exclusively acquires the lock, blocking if necessary
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* until available or the current thread is interrupted.
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* Behavior under interruption matches that specified
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* for method {@link Lock#lockInterruptibly()}.
|
|
*
|
|
* @return a stamp that can be used to unlock or convert mode
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
* before acquiring the lock
|
|
*/
|
|
public long readLockInterruptibly() throws InterruptedException {
|
|
long next;
|
|
if (!Thread.interrupted() &&
|
|
(next = acquireRead(true, 0L)) != INTERRUPTED) {
|
|
return next;
|
|
}
|
|
throw new InterruptedException();
|
|
}
|
|
|
|
/**
|
|
* Returns a stamp that can later be validated, or zero
|
|
* if exclusively locked.
|
|
*
|
|
* @return a stamp, or zero if exclusively locked
|
|
*/
|
|
public long tryOptimisticRead() {
|
|
long s;
|
|
return ((s = this.state) & WBIT) == 0L ? s & SBITS : 0L;
|
|
}
|
|
|
|
/**
|
|
* Returns true if the lock has not been exclusively acquired
|
|
* since issuance of the given stamp. Always returns false if the
|
|
* stamp is zero. Always returns true if the stamp represents a
|
|
* currently held lock. Invoking this method with a value not
|
|
* obtained from {@link #tryOptimisticRead} or a locking method
|
|
* for this lock has no defined effect or result.
|
|
*
|
|
* @param stamp a stamp
|
|
* @return {@code true} if the lock has not been exclusively acquired
|
|
* since issuance of the given stamp; else false
|
|
*/
|
|
public boolean validate(long stamp) {
|
|
// See above about current use of getLongVolatile here
|
|
return (stamp & SBITS) == (U.getLongVolatile(this, STATE) & SBITS);
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp, releases the
|
|
* exclusive lock.
|
|
*
|
|
* @param stamp a stamp returned by a write-lock operation
|
|
* @throws IllegalMonitorStateException if the stamp does
|
|
* not match the current state of this lock
|
|
*/
|
|
public void unlockWrite(long stamp) {
|
|
WNode h;
|
|
if (this.state != stamp || (stamp & WBIT) == 0L) {
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
this.state = (stamp += WBIT) == 0L ? ORIGIN : stamp;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp, releases the
|
|
* non-exclusive lock.
|
|
*
|
|
* @param stamp a stamp returned by a read-lock operation
|
|
* @throws IllegalMonitorStateException if the stamp does
|
|
* not match the current state of this lock
|
|
*/
|
|
public void unlockRead(long stamp) {
|
|
long s, m; WNode h;
|
|
for (;;) {
|
|
if (((s = this.state) & SBITS) != (stamp & SBITS) ||
|
|
(stamp & ABITS) == 0L || (m = s & ABITS) == 0L || m == WBIT) {
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
|
|
if (m == RUNIT && (h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
else if (tryDecReaderOverflow(s) != 0L) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp, releases the
|
|
* corresponding mode of the lock.
|
|
*
|
|
* @param stamp a stamp returned by a lock operation
|
|
* @throws IllegalMonitorStateException if the stamp does
|
|
* not match the current state of this lock
|
|
*/
|
|
public void unlock(long stamp) {
|
|
long a = stamp & ABITS, m, s; WNode h;
|
|
while (((s = this.state) & SBITS) == (stamp & SBITS)) {
|
|
if ((m = s & ABITS) == 0L) {
|
|
break;
|
|
} else if (m == WBIT) {
|
|
if (a != m) {
|
|
break;
|
|
}
|
|
this.state = (s += WBIT) == 0L ? ORIGIN : s;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return;
|
|
}
|
|
else if (a == 0L || a >= WBIT) {
|
|
break;
|
|
} else if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
|
|
if (m == RUNIT && (h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return;
|
|
}
|
|
}
|
|
else if (tryDecReaderOverflow(s) != 0L) {
|
|
return;
|
|
}
|
|
}
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp, performs one of
|
|
* the following actions. If the stamp represents holding a write
|
|
* lock, returns it. Or, if a read lock, if the write lock is
|
|
* available, releases the read lock and returns a write stamp.
|
|
* Or, if an optimistic read, returns a write stamp only if
|
|
* immediately available. This method returns zero in all other
|
|
* cases.
|
|
*
|
|
* @param stamp a stamp
|
|
* @return a valid write stamp, or zero on failure
|
|
*/
|
|
public long tryConvertToWriteLock(long stamp) {
|
|
long a = stamp & ABITS, m, s, next;
|
|
while (((s = this.state) & SBITS) == (stamp & SBITS)) {
|
|
if ((m = s & ABITS) == 0L) {
|
|
if (a != 0L) {
|
|
break;
|
|
}
|
|
if (U.compareAndSwapLong(this, STATE, s, next = s + WBIT)) {
|
|
return next;
|
|
}
|
|
}
|
|
else if (m == WBIT) {
|
|
if (a != m) {
|
|
break;
|
|
}
|
|
return stamp;
|
|
}
|
|
else if (m == RUNIT && a != 0L) {
|
|
if (U.compareAndSwapLong(this, STATE, s,
|
|
next = s - RUNIT + WBIT)) {
|
|
return next;
|
|
}
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
return 0L;
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp, performs one of
|
|
* the following actions. If the stamp represents holding a write
|
|
* lock, releases it and obtains a read lock. Or, if a read lock,
|
|
* returns it. Or, if an optimistic read, acquires a read lock and
|
|
* returns a read stamp only if immediately available. This method
|
|
* returns zero in all other cases.
|
|
*
|
|
* @param stamp a stamp
|
|
* @return a valid read stamp, or zero on failure
|
|
*/
|
|
public long tryConvertToReadLock(long stamp) {
|
|
long a = stamp & ABITS, m, s, next; WNode h;
|
|
while (((s = this.state) & SBITS) == (stamp & SBITS)) {
|
|
if ((m = s & ABITS) == 0L) {
|
|
if (a != 0L) {
|
|
break;
|
|
} else if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, next = s + RUNIT)) {
|
|
return next;
|
|
}
|
|
}
|
|
else if ((next = tryIncReaderOverflow(s)) != 0L) {
|
|
return next;
|
|
}
|
|
}
|
|
else if (m == WBIT) {
|
|
if (a != m) {
|
|
break;
|
|
}
|
|
this.state = next = s + WBIT + RUNIT;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return next;
|
|
}
|
|
else if (a != 0L && a < WBIT) {
|
|
return stamp;
|
|
} else {
|
|
break;
|
|
}
|
|
}
|
|
return 0L;
|
|
}
|
|
|
|
/**
|
|
* If the lock state matches the given stamp then, if the stamp
|
|
* represents holding a lock, releases it and returns an
|
|
* observation stamp. Or, if an optimistic read, returns it if
|
|
* validated. This method returns zero in all other cases, and so
|
|
* may be useful as a form of "tryUnlock".
|
|
*
|
|
* @param stamp a stamp
|
|
* @return a valid optimistic read stamp, or zero on failure
|
|
*/
|
|
public long tryConvertToOptimisticRead(long stamp) {
|
|
long a = stamp & ABITS, m, s, next; WNode h;
|
|
for (;;) {
|
|
s = U.getLongVolatile(this, STATE); // see above
|
|
if (((s = this.state) & SBITS) != (stamp & SBITS)) {
|
|
break;
|
|
}
|
|
if ((m = s & ABITS) == 0L) {
|
|
if (a != 0L) {
|
|
break;
|
|
}
|
|
return s;
|
|
}
|
|
else if (m == WBIT) {
|
|
if (a != m) {
|
|
break;
|
|
}
|
|
this.state = next = (s += WBIT) == 0L ? ORIGIN : s;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return next;
|
|
}
|
|
else if (a == 0L || a >= WBIT) {
|
|
break;
|
|
} else if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, next = s - RUNIT)) {
|
|
if (m == RUNIT && (h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return next & SBITS;
|
|
}
|
|
}
|
|
else if ((next = tryDecReaderOverflow(s)) != 0L) {
|
|
return next & SBITS;
|
|
}
|
|
}
|
|
return 0L;
|
|
}
|
|
|
|
/**
|
|
* Releases the write lock if it is held, without requiring a
|
|
* stamp value. This method may be useful for recovery after
|
|
* errors.
|
|
*
|
|
* @return {@code true} if the lock was held, else false
|
|
*/
|
|
public boolean tryUnlockWrite() {
|
|
long s; WNode h;
|
|
if (((s = this.state) & WBIT) != 0L) {
|
|
this.state = (s += WBIT) == 0L ? ORIGIN : s;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Releases one hold of the read lock if it is held, without
|
|
* requiring a stamp value. This method may be useful for recovery
|
|
* after errors.
|
|
*
|
|
* @return {@code true} if the read lock was held, else false
|
|
*/
|
|
public boolean tryUnlockRead() {
|
|
long s, m; WNode h;
|
|
while ((m = (s = this.state) & ABITS) != 0L && m < WBIT) {
|
|
if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
|
|
if (m == RUNIT && (h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
return true;
|
|
}
|
|
}
|
|
else if (tryDecReaderOverflow(s) != 0L) {
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// status monitoring methods
|
|
|
|
/**
|
|
* Returns combined state-held and overflow read count for given
|
|
* state s.
|
|
*/
|
|
private int getReadLockCount(long s) {
|
|
long readers;
|
|
if ((readers = s & RBITS) >= RFULL) {
|
|
readers = RFULL + this.readerOverflow;
|
|
}
|
|
return (int) readers;
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if the lock is currently held exclusively.
|
|
*
|
|
* @return {@code true} if the lock is currently held exclusively
|
|
*/
|
|
public boolean isWriteLocked() {
|
|
return (this.state & WBIT) != 0L;
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if the lock is currently held non-exclusively.
|
|
*
|
|
* @return {@code true} if the lock is currently held non-exclusively
|
|
*/
|
|
public boolean isReadLocked() {
|
|
return (this.state & RBITS) != 0L;
|
|
}
|
|
|
|
/**
|
|
* Queries the number of read locks held for this lock. This
|
|
* method is designed for use in monitoring system state, not for
|
|
* synchronization control.
|
|
* @return the number of read locks held
|
|
*/
|
|
public int getReadLockCount() {
|
|
return getReadLockCount(this.state);
|
|
}
|
|
|
|
/**
|
|
* Returns a string identifying this lock, as well as its lock
|
|
* state. The state, in brackets, includes the String {@code
|
|
* "Unlocked"} or the String {@code "Write-locked"} or the String
|
|
* {@code "Read-locks:"} followed by the current number of
|
|
* read-locks held.
|
|
*
|
|
* @return a string identifying this lock, as well as its lock state
|
|
*/
|
|
@Override
|
|
public String toString() {
|
|
long s = this.state;
|
|
return super.toString() +
|
|
((s & ABITS) == 0L ? "[Unlocked]" :
|
|
(s & WBIT) != 0L ? "[Write-locked]" :
|
|
"[Read-locks:" + getReadLockCount(s) + "]");
|
|
}
|
|
|
|
// views
|
|
|
|
/**
|
|
* Returns a plain {@link Lock} view of this StampedLock in which
|
|
* the {@link Lock#lock} method is mapped to {@link #readLock},
|
|
* and similarly for other methods. The returned Lock does not
|
|
* support a {@link Condition}; method {@link
|
|
* Lock#newCondition()} throws {@code
|
|
* UnsupportedOperationException}.
|
|
*
|
|
* @return the lock
|
|
*/
|
|
public Lock asReadLock() {
|
|
ReadLockView v;
|
|
return (v = this.readLockView) != null ? v :
|
|
(this.readLockView = new ReadLockView());
|
|
}
|
|
|
|
/**
|
|
* Returns a plain {@link Lock} view of this StampedLock in which
|
|
* the {@link Lock#lock} method is mapped to {@link #writeLock},
|
|
* and similarly for other methods. The returned Lock does not
|
|
* support a {@link Condition}; method {@link
|
|
* Lock#newCondition()} throws {@code
|
|
* UnsupportedOperationException}.
|
|
*
|
|
* @return the lock
|
|
*/
|
|
public Lock asWriteLock() {
|
|
WriteLockView v;
|
|
return (v = this.writeLockView) != null ? v :
|
|
(this.writeLockView = new WriteLockView());
|
|
}
|
|
|
|
/**
|
|
* Returns a {@link ReadWriteLock} view of this StampedLock in
|
|
* which the {@link ReadWriteLock#readLock()} method is mapped to
|
|
* {@link #asReadLock()}, and {@link ReadWriteLock#writeLock()} to
|
|
* {@link #asWriteLock()}.
|
|
*
|
|
* @return the lock
|
|
*/
|
|
public ReadWriteLock asReadWriteLock() {
|
|
ReadWriteLockView v;
|
|
return (v = this.readWriteLockView) != null ? v :
|
|
(this.readWriteLockView = new ReadWriteLockView());
|
|
}
|
|
|
|
// view classes
|
|
|
|
final class ReadLockView implements Lock {
|
|
@Override
|
|
public void lock() { readLock(); }
|
|
@Override
|
|
public void lockInterruptibly() throws InterruptedException {
|
|
readLockInterruptibly();
|
|
}
|
|
@Override
|
|
public boolean tryLock() { return tryReadLock() != 0L; }
|
|
@Override
|
|
public boolean tryLock(long time, TimeUnit unit)
|
|
throws InterruptedException {
|
|
return tryReadLock(time, unit) != 0L;
|
|
}
|
|
@Override
|
|
public void unlock() { unstampedUnlockRead(); }
|
|
@Override
|
|
public Condition newCondition() {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
}
|
|
|
|
final class WriteLockView implements Lock {
|
|
@Override
|
|
public void lock() { writeLock(); }
|
|
@Override
|
|
public void lockInterruptibly() throws InterruptedException {
|
|
writeLockInterruptibly();
|
|
}
|
|
@Override
|
|
public boolean tryLock() { return tryWriteLock() != 0L; }
|
|
@Override
|
|
public boolean tryLock(long time, TimeUnit unit)
|
|
throws InterruptedException {
|
|
return tryWriteLock(time, unit) != 0L;
|
|
}
|
|
@Override
|
|
public void unlock() { unstampedUnlockWrite(); }
|
|
@Override
|
|
public Condition newCondition() {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
}
|
|
|
|
final class ReadWriteLockView implements ReadWriteLock {
|
|
@Override
|
|
public Lock readLock() { return asReadLock(); }
|
|
@Override
|
|
public Lock writeLock() { return asWriteLock(); }
|
|
}
|
|
|
|
// Unlock methods without stamp argument checks for view classes.
|
|
// Needed because view-class lock methods throw away stamps.
|
|
|
|
final void unstampedUnlockWrite() {
|
|
WNode h; long s;
|
|
if (((s = this.state) & WBIT) == 0L) {
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
this.state = (s += WBIT) == 0L ? ORIGIN : s;
|
|
if ((h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
}
|
|
|
|
final void unstampedUnlockRead() {
|
|
for (;;) {
|
|
long s, m; WNode h;
|
|
if ((m = (s = this.state) & ABITS) == 0L || m >= WBIT) {
|
|
throw new IllegalMonitorStateException();
|
|
} else if (m < RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s - RUNIT)) {
|
|
if (m == RUNIT && (h = this.whead) != null && h.status != 0) {
|
|
release(h);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
else if (tryDecReaderOverflow(s) != 0L) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
private void readObject(java.io.ObjectInputStream s)
|
|
throws java.io.IOException, ClassNotFoundException {
|
|
s.defaultReadObject();
|
|
this.state = ORIGIN; // reset to unlocked state
|
|
}
|
|
|
|
// internals
|
|
|
|
/**
|
|
* Tries to increment readerOverflow by first setting state
|
|
* access bits value to RBITS, indicating hold of spinlock,
|
|
* then updating, then releasing.
|
|
*
|
|
* @param s a reader overflow stamp: (s & ABITS) >= RFULL
|
|
* @return new stamp on success, else zero
|
|
*/
|
|
private long tryIncReaderOverflow(long s) {
|
|
// assert (s & ABITS) >= RFULL;
|
|
if ((s & ABITS) == RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) {
|
|
++this.readerOverflow;
|
|
this.state = s;
|
|
return s;
|
|
}
|
|
}
|
|
else if ((randomThreadLocal.get().nextInt() &
|
|
OVERFLOW_YIELD_RATE) == 0) {
|
|
Thread.yield();
|
|
}
|
|
return 0L;
|
|
}
|
|
|
|
/**
|
|
* Tries to decrement readerOverflow.
|
|
*
|
|
* @param s a reader overflow stamp: (s & ABITS) >= RFULL
|
|
* @return new stamp on success, else zero
|
|
*/
|
|
private long tryDecReaderOverflow(long s) {
|
|
// assert (s & ABITS) >= RFULL;
|
|
if ((s & ABITS) == RFULL) {
|
|
if (U.compareAndSwapLong(this, STATE, s, s | RBITS)) {
|
|
int r; long next;
|
|
if ((r = this.readerOverflow) > 0) {
|
|
this.readerOverflow = r - 1;
|
|
next = s;
|
|
} else {
|
|
next = s - RUNIT;
|
|
}
|
|
this.state = next;
|
|
return next;
|
|
}
|
|
}
|
|
else if ((randomThreadLocal.get().nextInt() &
|
|
OVERFLOW_YIELD_RATE) == 0) {
|
|
Thread.yield();
|
|
}
|
|
return 0L;
|
|
}
|
|
|
|
/**
|
|
* Wakes up the successor of h (normally whead). This is normally
|
|
* just h.next, but may require traversal from wtail if next
|
|
* pointers are lagging. This may fail to wake up an acquiring
|
|
* thread when one or more have been cancelled, but the cancel
|
|
* methods themselves provide extra safeguards to ensure liveness.
|
|
*/
|
|
private void release(WNode h) {
|
|
if (h != null) {
|
|
WNode q; Thread w;
|
|
U.compareAndSwapInt(h, WSTATUS, WAITING, 0);
|
|
if ((q = h.next) == null || q.status == CANCELLED) {
|
|
for (WNode t = this.wtail; t != null && t != h; t = t.prev) {
|
|
if (t.status <= 0) {
|
|
q = t;
|
|
}
|
|
}
|
|
}
|
|
if (q != null && (w = q.thread) != null) {
|
|
U.unpark(w);
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* See above for explanation.
|
|
*
|
|
* @param interruptible true if should check interrupts and if so
|
|
* return INTERRUPTED
|
|
* @param deadline if nonzero, the System.nanoTime value to timeout
|
|
* at (and return zero)
|
|
* @return next state, or INTERRUPTED
|
|
*/
|
|
private long acquireWrite(boolean interruptible, long deadline) {
|
|
WNode node = null, p;
|
|
for (int spins = -1;;) { // spin while enqueuing
|
|
long m, s, ns;
|
|
if ((m = (s = this.state) & ABITS) == 0L) {
|
|
if (U.compareAndSwapLong(this, STATE, s, ns = s + WBIT)) {
|
|
return ns;
|
|
}
|
|
}
|
|
else if (spins < 0) {
|
|
spins = m == WBIT && this.wtail == this.whead ? SPINS : 0;
|
|
} else if (spins > 0) {
|
|
if (randomThreadLocal.get().nextInt() >= 0) {
|
|
--spins;
|
|
}
|
|
}
|
|
else if ((p = this.wtail) == null) { // initialize queue
|
|
WNode hd = new WNode(WMODE, null);
|
|
if (U.compareAndSwapObject(this, WHEAD, null, hd)) {
|
|
this.wtail = hd;
|
|
}
|
|
}
|
|
else if (node == null) {
|
|
node = new WNode(WMODE, p);
|
|
} else if (node.prev != p) {
|
|
node.prev = p;
|
|
} else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
|
|
p.next = node;
|
|
break;
|
|
}
|
|
}
|
|
|
|
for (int spins = -1;;) {
|
|
WNode h, np, pp; int ps;
|
|
if ((h = this.whead) == p) {
|
|
if (spins < 0) {
|
|
spins = HEAD_SPINS;
|
|
} else if (spins < MAX_HEAD_SPINS) {
|
|
spins <<= 1;
|
|
}
|
|
for (int k = spins;;) { // spin at head
|
|
long s, ns;
|
|
if (((s = this.state) & ABITS) == 0L) {
|
|
if (U.compareAndSwapLong(this, STATE, s,
|
|
ns = s + WBIT)) {
|
|
this.whead = node;
|
|
node.prev = null;
|
|
return ns;
|
|
}
|
|
}
|
|
else if (randomThreadLocal.get().nextInt() >= 0 &&
|
|
--k <= 0) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
else if (h != null) { // help release stale waiters
|
|
WNode c; Thread w;
|
|
while ((c = h.cowait) != null) {
|
|
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
|
|
(w = c.thread) != null) {
|
|
U.unpark(w);
|
|
}
|
|
}
|
|
}
|
|
if (this.whead == h) {
|
|
if ((np = node.prev) != p) {
|
|
if (np != null)
|
|
{
|
|
(p = np).next = node; // stale
|
|
}
|
|
}
|
|
else if ((ps = p.status) == 0) {
|
|
U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
|
|
} else if (ps == CANCELLED) {
|
|
if ((pp = p.prev) != null) {
|
|
node.prev = pp;
|
|
pp.next = node;
|
|
}
|
|
}
|
|
else {
|
|
long time; // 0 argument to park means no timeout
|
|
if (deadline == 0L) {
|
|
time = 0L;
|
|
} else if ((time = deadline - System.nanoTime()) <= 0L) {
|
|
return cancelWaiter(node, node, false);
|
|
}
|
|
Thread wt = Thread.currentThread();
|
|
U.putObject(wt, PARKBLOCKER, this);
|
|
node.thread = wt;
|
|
if (p.status < 0 && (p != h || (this.state & ABITS) != 0L) &&
|
|
this.whead == h && node.prev == p)
|
|
{
|
|
U.park(false, time); // emulate LockSupport.park
|
|
}
|
|
node.thread = null;
|
|
U.putObject(wt, PARKBLOCKER, null);
|
|
if (interruptible && Thread.interrupted()) {
|
|
return cancelWaiter(node, node, true);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* See above for explanation.
|
|
*
|
|
* @param interruptible true if should check interrupts and if so
|
|
* return INTERRUPTED
|
|
* @param deadline if nonzero, the System.nanoTime value to timeout
|
|
* at (and return zero)
|
|
* @return next state, or INTERRUPTED
|
|
*/
|
|
private long acquireRead(boolean interruptible, long deadline) {
|
|
WNode node = null, p;
|
|
for (int spins = -1;;) {
|
|
WNode h;
|
|
if ((h = this.whead) == (p = this.wtail)) {
|
|
for (long m, s, ns;;) {
|
|
if ((m = (s = this.state) & ABITS) < RFULL ?
|
|
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) :
|
|
m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L) {
|
|
return ns;
|
|
} else if (m >= WBIT) {
|
|
if (spins > 0) {
|
|
if (randomThreadLocal.get().nextInt() >= 0) {
|
|
--spins;
|
|
}
|
|
}
|
|
else {
|
|
if (spins == 0) {
|
|
WNode nh = this.whead, np = this.wtail;
|
|
if (nh == h && np == p || (h = nh) != (p = np)) {
|
|
break;
|
|
}
|
|
}
|
|
spins = SPINS;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
if (p == null) { // initialize queue
|
|
WNode hd = new WNode(WMODE, null);
|
|
if (U.compareAndSwapObject(this, WHEAD, null, hd)) {
|
|
this.wtail = hd;
|
|
}
|
|
}
|
|
else if (node == null) {
|
|
node = new WNode(RMODE, p);
|
|
} else if (h == p || p.mode != RMODE) {
|
|
if (node.prev != p) {
|
|
node.prev = p;
|
|
} else if (U.compareAndSwapObject(this, WTAIL, p, node)) {
|
|
p.next = node;
|
|
break;
|
|
}
|
|
}
|
|
else if (!U.compareAndSwapObject(p, WCOWAIT,
|
|
node.cowait = p.cowait, node)) {
|
|
node.cowait = null;
|
|
} else {
|
|
for (;;) {
|
|
WNode pp, c; Thread w;
|
|
if ((h = this.whead) != null && (c = h.cowait) != null &&
|
|
U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
|
|
(w = c.thread) != null) {
|
|
U.unpark(w);
|
|
}
|
|
if (h == (pp = p.prev) || h == p || pp == null) {
|
|
long m, s, ns;
|
|
do {
|
|
if ((m = (s = this.state) & ABITS) < RFULL ?
|
|
U.compareAndSwapLong(this, STATE, s,
|
|
ns = s + RUNIT) :
|
|
m < WBIT &&
|
|
(ns = tryIncReaderOverflow(s)) != 0L) {
|
|
return ns;
|
|
}
|
|
} while (m < WBIT);
|
|
}
|
|
if (this.whead == h && p.prev == pp) {
|
|
long time;
|
|
if (pp == null || h == p || p.status > 0) {
|
|
node = null; // throw away
|
|
break;
|
|
}
|
|
if (deadline == 0L) {
|
|
time = 0L;
|
|
} else if ((time = deadline - System.nanoTime()) <= 0L) {
|
|
return cancelWaiter(node, p, false);
|
|
}
|
|
Thread wt = Thread.currentThread();
|
|
U.putObject(wt, PARKBLOCKER, this);
|
|
node.thread = wt;
|
|
if ((h != pp || (this.state & ABITS) == WBIT) &&
|
|
this.whead == h && p.prev == pp) {
|
|
U.park(false, time);
|
|
}
|
|
node.thread = null;
|
|
U.putObject(wt, PARKBLOCKER, null);
|
|
if (interruptible && Thread.interrupted()) {
|
|
return cancelWaiter(node, p, true);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
for (int spins = -1;;) {
|
|
WNode h, np, pp; int ps;
|
|
if ((h = this.whead) == p) {
|
|
if (spins < 0) {
|
|
spins = HEAD_SPINS;
|
|
} else if (spins < MAX_HEAD_SPINS) {
|
|
spins <<= 1;
|
|
}
|
|
for (int k = spins;;) { // spin at head
|
|
long m, s, ns;
|
|
if ((m = (s = this.state) & ABITS) < RFULL ?
|
|
U.compareAndSwapLong(this, STATE, s, ns = s + RUNIT) :
|
|
m < WBIT && (ns = tryIncReaderOverflow(s)) != 0L) {
|
|
WNode c; Thread w;
|
|
this.whead = node;
|
|
node.prev = null;
|
|
while ((c = node.cowait) != null) {
|
|
if (U.compareAndSwapObject(node, WCOWAIT,
|
|
c, c.cowait) &&
|
|
(w = c.thread) != null) {
|
|
U.unpark(w);
|
|
}
|
|
}
|
|
return ns;
|
|
}
|
|
else if (m >= WBIT &&
|
|
randomThreadLocal.get().nextInt() >= 0 && --k <= 0) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
else if (h != null) {
|
|
WNode c; Thread w;
|
|
while ((c = h.cowait) != null) {
|
|
if (U.compareAndSwapObject(h, WCOWAIT, c, c.cowait) &&
|
|
(w = c.thread) != null) {
|
|
U.unpark(w);
|
|
}
|
|
}
|
|
}
|
|
if (this.whead == h) {
|
|
if ((np = node.prev) != p) {
|
|
if (np != null)
|
|
{
|
|
(p = np).next = node; // stale
|
|
}
|
|
}
|
|
else if ((ps = p.status) == 0) {
|
|
U.compareAndSwapInt(p, WSTATUS, 0, WAITING);
|
|
} else if (ps == CANCELLED) {
|
|
if ((pp = p.prev) != null) {
|
|
node.prev = pp;
|
|
pp.next = node;
|
|
}
|
|
}
|
|
else {
|
|
long time;
|
|
if (deadline == 0L) {
|
|
time = 0L;
|
|
} else if ((time = deadline - System.nanoTime()) <= 0L) {
|
|
return cancelWaiter(node, node, false);
|
|
}
|
|
Thread wt = Thread.currentThread();
|
|
U.putObject(wt, PARKBLOCKER, this);
|
|
node.thread = wt;
|
|
if (p.status < 0 &&
|
|
(p != h || (this.state & ABITS) == WBIT) &&
|
|
this.whead == h && node.prev == p) {
|
|
U.park(false, time);
|
|
}
|
|
node.thread = null;
|
|
U.putObject(wt, PARKBLOCKER, null);
|
|
if (interruptible && Thread.interrupted()) {
|
|
return cancelWaiter(node, node, true);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* If node non-null, forces cancel status and unsplices it from
|
|
* queue if possible and wakes up any cowaiters (of the node, or
|
|
* group, as applicable), and in any case helps release current
|
|
* first waiter if lock is free. (Calling with null arguments
|
|
* serves as a conditional form of release, which is not currently
|
|
* needed but may be needed under possible future cancellation
|
|
* policies). This is a variant of cancellation methods in
|
|
* AbstractQueuedSynchronizer (see its detailed explanation in AQS
|
|
* internal documentation).
|
|
*
|
|
* @param node if nonnull, the waiter
|
|
* @param group either node or the group node is cowaiting with
|
|
* @param interrupted if already interrupted
|
|
* @return INTERRUPTED if interrupted or Thread.interrupted, else zero
|
|
*/
|
|
private long cancelWaiter(WNode node, WNode group, boolean interrupted) {
|
|
if (node != null && group != null) {
|
|
Thread w;
|
|
node.status = CANCELLED;
|
|
// unsplice cancelled nodes from group
|
|
for (WNode p = group, q; (q = p.cowait) != null;) {
|
|
if (q.status == CANCELLED) {
|
|
U.compareAndSwapObject(p, WCOWAIT, q, q.cowait);
|
|
p = group; // restart
|
|
} else {
|
|
p = q;
|
|
}
|
|
}
|
|
if (group == node) {
|
|
for (WNode r = group.cowait; r != null; r = r.cowait) {
|
|
if ((w = r.thread) != null)
|
|
{
|
|
U.unpark(w); // wake up uncancelled co-waiters
|
|
}
|
|
}
|
|
for (WNode pred = node.prev; pred != null; ) { // unsplice
|
|
WNode succ, pp; // find valid successor
|
|
while ((succ = node.next) == null ||
|
|
succ.status == CANCELLED) {
|
|
WNode q = null; // find successor the slow way
|
|
for (WNode t = this.wtail; t != null && t != node; t = t.prev)
|
|
{
|
|
if (t.status != CANCELLED)
|
|
{
|
|
q = t; // don't link if succ cancelled
|
|
}
|
|
}
|
|
if (succ == q || // ensure accurate successor
|
|
U.compareAndSwapObject(node, WNEXT,
|
|
succ, succ = q)) {
|
|
if (succ == null && node == this.wtail) {
|
|
U.compareAndSwapObject(this, WTAIL, node, pred);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
if (pred.next == node) {
|
|
U.compareAndSwapObject(pred, WNEXT, node, succ);
|
|
}
|
|
if (succ != null && (w = succ.thread) != null) {
|
|
succ.thread = null;
|
|
U.unpark(w); // wake up succ to observe new pred
|
|
}
|
|
if (pred.status != CANCELLED || (pp = pred.prev) == null) {
|
|
break;
|
|
}
|
|
node.prev = pp; // repeat if new pred wrong/cancelled
|
|
U.compareAndSwapObject(pp, WNEXT, pred, succ);
|
|
pred = pp;
|
|
}
|
|
}
|
|
}
|
|
WNode h; // Possibly release first waiter
|
|
while ((h = this.whead) != null) {
|
|
long s; WNode q; // similar to release() but check eligibility
|
|
if ((q = h.next) == null || q.status == CANCELLED) {
|
|
for (WNode t = this.wtail; t != null && t != h; t = t.prev) {
|
|
if (t.status <= 0) {
|
|
q = t;
|
|
}
|
|
}
|
|
}
|
|
if (h == this.whead) {
|
|
if (q != null && h.status == 0 &&
|
|
((s = this.state) & ABITS) != WBIT && // waiter is eligible
|
|
(s == 0L || q.mode == RMODE)) {
|
|
release(h);
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
return interrupted || Thread.interrupted() ? INTERRUPTED : 0L;
|
|
}
|
|
|
|
// Unsafe mechanics
|
|
private static final sun.misc.Unsafe U;
|
|
private static final long STATE;
|
|
private static final long WHEAD;
|
|
private static final long WTAIL;
|
|
private static final long WNEXT;
|
|
private static final long WSTATUS;
|
|
private static final long WCOWAIT;
|
|
private static final long PARKBLOCKER;
|
|
|
|
static {
|
|
try {
|
|
U = getUnsafe();
|
|
Class<?> k = StampedLock.class;
|
|
Class<?> wk = WNode.class;
|
|
STATE = U.objectFieldOffset
|
|
(k.getDeclaredField("state"));
|
|
WHEAD = U.objectFieldOffset
|
|
(k.getDeclaredField("whead"));
|
|
WTAIL = U.objectFieldOffset
|
|
(k.getDeclaredField("wtail"));
|
|
WSTATUS = U.objectFieldOffset
|
|
(wk.getDeclaredField("status"));
|
|
WNEXT = U.objectFieldOffset
|
|
(wk.getDeclaredField("next"));
|
|
WCOWAIT = U.objectFieldOffset
|
|
(wk.getDeclaredField("cowait"));
|
|
Class<?> tk = Thread.class;
|
|
PARKBLOCKER = U.objectFieldOffset
|
|
(tk.getDeclaredField("parkBlocker"));
|
|
|
|
} catch (Exception e) {
|
|
throw new Error(e);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
|
|
* Replace with a simple call to Unsafe.getUnsafe when integrating
|
|
* into a jdk.
|
|
*
|
|
* @return a sun.misc.Unsafe
|
|
*/
|
|
private static sun.misc.Unsafe getUnsafe() {
|
|
try {
|
|
return sun.misc.Unsafe.getUnsafe();
|
|
} catch (SecurityException tryReflectionInstead) {}
|
|
try {
|
|
return java.security.AccessController.doPrivileged
|
|
(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
|
|
@Override
|
|
public sun.misc.Unsafe run() throws Exception {
|
|
Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
|
|
for (java.lang.reflect.Field f : k.getDeclaredFields()) {
|
|
f.setAccessible(true);
|
|
Object x = f.get(null);
|
|
if (k.isInstance(x)) {
|
|
return k.cast(x);
|
|
}
|
|
}
|
|
throw new NoSuchFieldError("the Unsafe");
|
|
}});
|
|
} catch (java.security.PrivilegedActionException e) {
|
|
throw new RuntimeException("Could not initialize intrinsics",
|
|
e.getCause());
|
|
}
|
|
}
|
|
}
|