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jeremybenn |
/*
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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/licenses/publicdomain
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*/
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package java.util.concurrent.locks;
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import java.util.*;
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import java.util.concurrent.*;
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import java.util.concurrent.atomic.*;
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import sun.misc.Unsafe;
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/**
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* Provides a framework for implementing blocking locks and related
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* synchronizers (semaphores, events, etc) that rely on
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* first-in-first-out (FIFO) wait queues. This class is designed to
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* be a useful basis for most kinds of synchronizers that rely on a
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* single atomic <tt>int</tt> value to represent state. Subclasses
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* must define the protected methods that change this state, and which
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* define what that state means in terms of this object being acquired
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* or released. Given these, the other methods in this class carry
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* out all queuing and blocking mechanics. Subclasses can maintain
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* other state fields, but only the atomically updated <tt>int</tt>
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* value manipulated using methods {@link #getState}, {@link
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* #setState} and {@link #compareAndSetState} is tracked with respect
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* to synchronization.
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*
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* <p>Subclasses should be defined as non-public internal helper
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* classes that are used to implement the synchronization properties
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* of their enclosing class. Class
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* <tt>AbstractQueuedSynchronizer</tt> does not implement any
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* synchronization interface. Instead it defines methods such as
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* {@link #acquireInterruptibly} that can be invoked as
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* appropriate by concrete locks and related synchronizers to
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* implement their public methods.
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*
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* <p>This class supports either or both a default <em>exclusive</em>
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* mode and a <em>shared</em> mode. When acquired in exclusive mode,
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* attempted acquires by other threads cannot succeed. Shared mode
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* acquires by multiple threads may (but need not) succeed. This class
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* does not "understand" these differences except in the
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* mechanical sense that when a shared mode acquire succeeds, the next
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* waiting thread (if one exists) must also determine whether it can
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* acquire as well. Threads waiting in the different modes share the
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* same FIFO queue. Usually, implementation subclasses support only
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* one of these modes, but both can come into play for example in a
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* {@link ReadWriteLock}. Subclasses that support only exclusive or
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* only shared modes need not define the methods supporting the unused mode.
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*
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* <p>This class defines a nested {@link ConditionObject} class that
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* can be used as a {@link Condition} implementation by subclasses
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* supporting exclusive mode for which method {@link
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* #isHeldExclusively} reports whether synchronization is exclusively
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* held with respect to the current thread, method {@link #release}
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* invoked with the current {@link #getState} value fully releases
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* this object, and {@link #acquire}, given this saved state value,
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* eventually restores this object to its previous acquired state. No
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* <tt>AbstractQueuedSynchronizer</tt> method otherwise creates such a
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* condition, so if this constraint cannot be met, do not use it. The
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* behavior of {@link ConditionObject} depends of course on the
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* semantics of its synchronizer implementation.
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*
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* <p>This class provides inspection, instrumentation, and monitoring
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* methods for the internal queue, as well as similar methods for
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* condition objects. These can be exported as desired into classes
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* using an <tt>AbstractQueuedSynchronizer</tt> for their
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* synchronization mechanics.
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*
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* <p>Serialization of this class stores only the underlying atomic
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* integer maintaining state, so deserialized objects have empty
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* thread queues. Typical subclasses requiring serializability will
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* define a <tt>readObject</tt> method that restores this to a known
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* initial state upon deserialization.
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*
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* <h3>Usage</h3>
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*
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* <p>To use this class as the basis of a synchronizer, redefine the
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* following methods, as applicable, by inspecting and/or modifying
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* the synchronization state using {@link #getState}, {@link
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* #setState} and/or {@link #compareAndSetState}:
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*
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* <ul>
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* <li> {@link #tryAcquire}
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* <li> {@link #tryRelease}
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* <li> {@link #tryAcquireShared}
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* <li> {@link #tryReleaseShared}
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* <li> {@link #isHeldExclusively}
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*</ul>
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*
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* Each of these methods by default throws {@link
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* UnsupportedOperationException}. Implementations of these methods
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* must be internally thread-safe, and should in general be short and
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* not block. Defining these methods is the <em>only</em> supported
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* means of using this class. All other methods are declared
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* <tt>final</tt> because they cannot be independently varied.
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*
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* <p>You may also find the inherited methods from {@link
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* AbstractOwnableSynchronizer} useful to keep track of the thread
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* owning an exclusive synchronizer. You are encouraged to use them
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* -- this enables monitoring and diagnostic tools to assist users in
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* determining which threads hold locks.
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*
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* <p>Even though this class is based on an internal FIFO queue, it
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* does not automatically enforce FIFO acquisition policies. The core
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* of exclusive synchronization takes the form:
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*
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* <pre>
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* Acquire:
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* while (!tryAcquire(arg)) {
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* <em>enqueue thread if it is not already queued</em>;
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* <em>possibly block current thread</em>;
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* }
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*
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* Release:
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* if (tryRelease(arg))
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* <em>unblock the first queued thread</em>;
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* </pre>
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*
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* (Shared mode is similar but may involve cascading signals.)
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*
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* <p>Because checks in acquire are invoked before enqueuing, a newly
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* acquiring thread may <em>barge</em> ahead of others that are
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* blocked and queued. However, you can, if desired, define
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* <tt>tryAcquire</tt> and/or <tt>tryAcquireShared</tt> to disable
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* barging by internally invoking one or more of the inspection
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* methods. In particular, a strict FIFO lock can define
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* <tt>tryAcquire</tt> to immediately return <tt>false</tt> if {@link
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* #getFirstQueuedThread} does not return the current thread. A
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* normally preferable non-strict fair version can immediately return
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* <tt>false</tt> only if {@link #hasQueuedThreads} returns
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* <tt>true</tt> and <tt>getFirstQueuedThread</tt> is not the current
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* thread; or equivalently, that <tt>getFirstQueuedThread</tt> is both
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* non-null and not the current thread. Further variations are
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* possible.
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*
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* <p>Throughput and scalability are generally highest for the
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* default barging (also known as <em>greedy</em>,
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* <em>renouncement</em>, and <em>convoy-avoidance</em>) strategy.
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* While this is not guaranteed to be fair or starvation-free, earlier
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* queued threads are allowed to recontend before later queued
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* threads, and each recontention has an unbiased chance to succeed
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* against incoming threads. Also, while acquires do not
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* "spin" in the usual sense, they may perform multiple
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* invocations of <tt>tryAcquire</tt> interspersed with other
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* computations before blocking. This gives most of the benefits of
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* spins when exclusive synchronization is only briefly held, without
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* most of the liabilities when it isn't. If so desired, you can
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* augment this by preceding calls to acquire methods with
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* "fast-path" checks, possibly prechecking {@link #hasContended}
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* and/or {@link #hasQueuedThreads} to only do so if the synchronizer
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* is likely not to be contended.
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*
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* <p>This class provides an efficient and scalable basis for
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* synchronization in part by specializing its range of use to
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* synchronizers that can rely on <tt>int</tt> state, acquire, and
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* release parameters, and an internal FIFO wait queue. When this does
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* not suffice, you can build synchronizers from a lower level using
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* {@link java.util.concurrent.atomic atomic} classes, your own custom
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* {@link java.util.Queue} classes, and {@link LockSupport} blocking
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* support.
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*
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* <h3>Usage Examples</h3>
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*
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* <p>Here is a non-reentrant mutual exclusion lock class that uses
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* the value zero to represent the unlocked state, and one to
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* represent the locked state. While a non-reentrant lock
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* does not strictly require recording of the current owner
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* thread, this class does so anyway to make usage easier to monitor.
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* It also supports conditions and exposes
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* one of the instrumentation methods:
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*
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* <pre>
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* class Mutex implements Lock, java.io.Serializable {
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*
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* // Our internal helper class
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* private static class Sync extends AbstractQueuedSynchronizer {
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* // Report whether in locked state
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* protected boolean isHeldExclusively() {
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* return getState() == 1;
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* }
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*
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* // Acquire the lock if state is zero
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* public boolean tryAcquire(int acquires) {
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* assert acquires == 1; // Otherwise unused
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* if (compareAndSetState(0, 1)) {
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* setExclusiveOwnerThread(Thread.currentThread());
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* return true;
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* }
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* return false;
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* }
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*
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* // Release the lock by setting state to zero
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* protected boolean tryRelease(int releases) {
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* assert releases == 1; // Otherwise unused
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* if (getState() == 0) throw new IllegalMonitorStateException();
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* setExclusiveOwnerThread(null);
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* setState(0);
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* return true;
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* }
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*
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* // Provide a Condition
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* Condition newCondition() { return new ConditionObject(); }
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*
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* // Deserialize properly
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* private void readObject(ObjectInputStream s)
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* throws IOException, ClassNotFoundException {
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* s.defaultReadObject();
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* setState(0); // reset to unlocked state
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* }
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* }
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*
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* // The sync object does all the hard work. We just forward to it.
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* private final Sync sync = new Sync();
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*
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* public void lock() { sync.acquire(1); }
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* public boolean tryLock() { return sync.tryAcquire(1); }
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* public void unlock() { sync.release(1); }
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* public Condition newCondition() { return sync.newCondition(); }
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* public boolean isLocked() { return sync.isHeldExclusively(); }
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* public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }
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* public void lockInterruptibly() throws InterruptedException {
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* sync.acquireInterruptibly(1);
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* }
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* public boolean tryLock(long timeout, TimeUnit unit)
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* throws InterruptedException {
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* return sync.tryAcquireNanos(1, unit.toNanos(timeout));
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* }
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* }
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* </pre>
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*
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* <p>Here is a latch class that is like a {@link CountDownLatch}
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* except that it only requires a single <tt>signal</tt> to
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* fire. Because a latch is non-exclusive, it uses the <tt>shared</tt>
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* acquire and release methods.
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*
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* <pre>
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* class BooleanLatch {
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*
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* private static class Sync extends AbstractQueuedSynchronizer {
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* boolean isSignalled() { return getState() != 0; }
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*
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* protected int tryAcquireShared(int ignore) {
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* return isSignalled()? 1 : -1;
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* }
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*
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* protected boolean tryReleaseShared(int ignore) {
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* setState(1);
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* return true;
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* }
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* }
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*
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* private final Sync sync = new Sync();
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* public boolean isSignalled() { return sync.isSignalled(); }
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* public void signal() { sync.releaseShared(1); }
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* public void await() throws InterruptedException {
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* sync.acquireSharedInterruptibly(1);
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* }
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* }
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* </pre>
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*
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* @since 1.5
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* @author Doug Lea
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*/
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public abstract class AbstractQueuedSynchronizer
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extends AbstractOwnableSynchronizer
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implements java.io.Serializable {
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private static final long serialVersionUID = 7373984972572414691L;
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/**
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* Creates a new <tt>AbstractQueuedSynchronizer</tt> instance
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* with initial synchronization state of zero.
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*/
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protected AbstractQueuedSynchronizer() { }
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/**
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* Wait queue node class.
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*
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* <p>The wait queue is a variant of a "CLH" (Craig, Landin, and
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* Hagersten) lock queue. CLH locks are normally used for
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* spinlocks. We instead use them for blocking synchronizers, but
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* use the same basic tactic of holding some of the control
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* information about a thread in the predecessor of its node. A
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* "status" field in each node keeps track of whether a thread
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* should block. A node is signalled when its predecessor
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* releases. Each node of the queue otherwise serves as a
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* specific-notification-style monitor holding a single waiting
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* thread. The status field does NOT control whether threads are
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* granted locks etc though. A thread may try to acquire if it is
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* first in the queue. But being first does not guarantee success;
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* it only gives the right to contend. So the currently released
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* contender thread may need to rewait.
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*
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* <p>To enqueue into a CLH lock, you atomically splice it in as new
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* tail. To dequeue, you just set the head field.
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* <pre>
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* +------+ prev +-----+ +-----+
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* head | | <---- | | <---- | | tail
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* +------+ +-----+ +-----+
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* </pre>
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*
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* <p>Insertion into a CLH queue requires only a single atomic
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* operation on "tail", so there is a simple atomic point of
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* demarcation from unqueued to queued. Similarly, dequeing
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* involves only updating the "head". However, it takes a bit
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* more work for nodes to determine who their successors are,
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* in part to deal with possible cancellation due to timeouts
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* and interrupts.
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*
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* <p>The "prev" links (not used in original CLH locks), are mainly
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* needed to handle cancellation. If a node is cancelled, its
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* successor is (normally) relinked to a non-cancelled
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* predecessor. For explanation of similar mechanics in the case
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* of spin locks, see the papers by Scott and Scherer at
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* http://www.cs.rochester.edu/u/scott/synchronization/
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*
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* <p>We also use "next" links to implement blocking mechanics.
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* The thread id for each node is kept in its own node, so a
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* predecessor signals the next node to wake up by traversing
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* next link to determine which thread it is. Determination of
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* successor must avoid races with newly queued nodes to set
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* the "next" fields of their predecessors. This is solved
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* when necessary by checking backwards from the atomically
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* updated "tail" when a node's successor appears to be null.
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* (Or, said differently, the next-links are an optimization
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|
|
* so that we don't usually need a backward scan.)
|
327 |
|
|
*
|
328 |
|
|
* <p>Cancellation introduces some conservatism to the basic
|
329 |
|
|
* algorithms. Since we must poll for cancellation of other
|
330 |
|
|
* nodes, we can miss noticing whether a cancelled node is
|
331 |
|
|
* ahead or behind us. This is dealt with by always unparking
|
332 |
|
|
* successors upon cancellation, allowing them to stabilize on
|
333 |
|
|
* a new predecessor.
|
334 |
|
|
*
|
335 |
|
|
* <p>CLH queues need a dummy header node to get started. But
|
336 |
|
|
* we don't create them on construction, because it would be wasted
|
337 |
|
|
* effort if there is never contention. Instead, the node
|
338 |
|
|
* is constructed and head and tail pointers are set upon first
|
339 |
|
|
* contention.
|
340 |
|
|
*
|
341 |
|
|
* <p>Threads waiting on Conditions use the same nodes, but
|
342 |
|
|
* use an additional link. Conditions only need to link nodes
|
343 |
|
|
* in simple (non-concurrent) linked queues because they are
|
344 |
|
|
* only accessed when exclusively held. Upon await, a node is
|
345 |
|
|
* inserted into a condition queue. Upon signal, the node is
|
346 |
|
|
* transferred to the main queue. A special value of status
|
347 |
|
|
* field is used to mark which queue a node is on.
|
348 |
|
|
*
|
349 |
|
|
* <p>Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill
|
350 |
|
|
* Scherer and Michael Scott, along with members of JSR-166
|
351 |
|
|
* expert group, for helpful ideas, discussions, and critiques
|
352 |
|
|
* on the design of this class.
|
353 |
|
|
*/
|
354 |
|
|
static final class Node {
|
355 |
|
|
/** waitStatus value to indicate thread has cancelled */
|
356 |
|
|
static final int CANCELLED = 1;
|
357 |
|
|
/** waitStatus value to indicate successor's thread needs unparking */
|
358 |
|
|
static final int SIGNAL = -1;
|
359 |
|
|
/** waitStatus value to indicate thread is waiting on condition */
|
360 |
|
|
static final int CONDITION = -2;
|
361 |
|
|
/** Marker to indicate a node is waiting in shared mode */
|
362 |
|
|
static final Node SHARED = new Node();
|
363 |
|
|
/** Marker to indicate a node is waiting in exclusive mode */
|
364 |
|
|
static final Node EXCLUSIVE = null;
|
365 |
|
|
|
366 |
|
|
/**
|
367 |
|
|
* Status field, taking on only the values:
|
368 |
|
|
* SIGNAL: The successor of this node is (or will soon be)
|
369 |
|
|
* blocked (via park), so the current node must
|
370 |
|
|
* unpark its successor when it releases or
|
371 |
|
|
* cancels. To avoid races, acquire methods must
|
372 |
|
|
* first indicate they need a signal,
|
373 |
|
|
* then retry the atomic acquire, and then,
|
374 |
|
|
* on failure, block.
|
375 |
|
|
* CANCELLED: This node is cancelled due to timeout or interrupt.
|
376 |
|
|
* Nodes never leave this state. In particular,
|
377 |
|
|
* a thread with cancelled node never again blocks.
|
378 |
|
|
* CONDITION: This node is currently on a condition queue.
|
379 |
|
|
* It will not be used as a sync queue node until
|
380 |
|
|
* transferred. (Use of this value here
|
381 |
|
|
* has nothing to do with the other uses
|
382 |
|
|
* of the field, but simplifies mechanics.)
|
383 |
|
|
* 0: None of the above
|
384 |
|
|
*
|
385 |
|
|
* The values are arranged numerically to simplify use.
|
386 |
|
|
* Non-negative values mean that a node doesn't need to
|
387 |
|
|
* signal. So, most code doesn't need to check for particular
|
388 |
|
|
* values, just for sign.
|
389 |
|
|
*
|
390 |
|
|
* The field is initialized to 0 for normal sync nodes, and
|
391 |
|
|
* CONDITION for condition nodes. It is modified only using
|
392 |
|
|
* CAS.
|
393 |
|
|
*/
|
394 |
|
|
volatile int waitStatus;
|
395 |
|
|
|
396 |
|
|
/**
|
397 |
|
|
* Link to predecessor node that current node/thread relies on
|
398 |
|
|
* for checking waitStatus. Assigned during enqueing, and nulled
|
399 |
|
|
* out (for sake of GC) only upon dequeuing. Also, upon
|
400 |
|
|
* cancellation of a predecessor, we short-circuit while
|
401 |
|
|
* finding a non-cancelled one, which will always exist
|
402 |
|
|
* because the head node is never cancelled: A node becomes
|
403 |
|
|
* head only as a result of successful acquire. A
|
404 |
|
|
* cancelled thread never succeeds in acquiring, and a thread only
|
405 |
|
|
* cancels itself, not any other node.
|
406 |
|
|
*/
|
407 |
|
|
volatile Node prev;
|
408 |
|
|
|
409 |
|
|
/**
|
410 |
|
|
* Link to the successor node that the current node/thread
|
411 |
|
|
* unparks upon release. Assigned once during enqueuing, and
|
412 |
|
|
* nulled out (for sake of GC) when no longer needed. Upon
|
413 |
|
|
* cancellation, we cannot adjust this field, but can notice
|
414 |
|
|
* status and bypass the node if cancelled. The enq operation
|
415 |
|
|
* does not assign next field of a predecessor until after
|
416 |
|
|
* attachment, so seeing a null next field does not
|
417 |
|
|
* necessarily mean that node is at end of queue. However, if
|
418 |
|
|
* a next field appears to be null, we can scan prev's from
|
419 |
|
|
* the tail to double-check.
|
420 |
|
|
*/
|
421 |
|
|
volatile Node next;
|
422 |
|
|
|
423 |
|
|
/**
|
424 |
|
|
* The thread that enqueued this node. Initialized on
|
425 |
|
|
* construction and nulled out after use.
|
426 |
|
|
*/
|
427 |
|
|
volatile Thread thread;
|
428 |
|
|
|
429 |
|
|
/**
|
430 |
|
|
* Link to next node waiting on condition, or the special
|
431 |
|
|
* value SHARED. Because condition queues are accessed only
|
432 |
|
|
* when holding in exclusive mode, we just need a simple
|
433 |
|
|
* linked queue to hold nodes while they are waiting on
|
434 |
|
|
* conditions. They are then transferred to the queue to
|
435 |
|
|
* re-acquire. And because conditions can only be exclusive,
|
436 |
|
|
* we save a field by using special value to indicate shared
|
437 |
|
|
* mode.
|
438 |
|
|
*/
|
439 |
|
|
Node nextWaiter;
|
440 |
|
|
|
441 |
|
|
/**
|
442 |
|
|
* Returns true if node is waiting in shared mode
|
443 |
|
|
*/
|
444 |
|
|
final boolean isShared() {
|
445 |
|
|
return nextWaiter == SHARED;
|
446 |
|
|
}
|
447 |
|
|
|
448 |
|
|
/**
|
449 |
|
|
* Returns previous node, or throws NullPointerException if
|
450 |
|
|
* null. Use when predecessor cannot be null.
|
451 |
|
|
* @return the predecessor of this node
|
452 |
|
|
*/
|
453 |
|
|
final Node predecessor() throws NullPointerException {
|
454 |
|
|
Node p = prev;
|
455 |
|
|
if (p == null)
|
456 |
|
|
throw new NullPointerException();
|
457 |
|
|
else
|
458 |
|
|
return p;
|
459 |
|
|
}
|
460 |
|
|
|
461 |
|
|
Node() { // Used to establish initial head or SHARED marker
|
462 |
|
|
}
|
463 |
|
|
|
464 |
|
|
Node(Thread thread, Node mode) { // Used by addWaiter
|
465 |
|
|
this.nextWaiter = mode;
|
466 |
|
|
this.thread = thread;
|
467 |
|
|
}
|
468 |
|
|
|
469 |
|
|
Node(Thread thread, int waitStatus) { // Used by Condition
|
470 |
|
|
this.waitStatus = waitStatus;
|
471 |
|
|
this.thread = thread;
|
472 |
|
|
}
|
473 |
|
|
}
|
474 |
|
|
|
475 |
|
|
/**
|
476 |
|
|
* Head of the wait queue, lazily initialized. Except for
|
477 |
|
|
* initialization, it is modified only via method setHead. Note:
|
478 |
|
|
* If head exists, its waitStatus is guaranteed not to be
|
479 |
|
|
* CANCELLED.
|
480 |
|
|
*/
|
481 |
|
|
private transient volatile Node head;
|
482 |
|
|
|
483 |
|
|
/**
|
484 |
|
|
* Tail of the wait queue, lazily initialized. Modified only via
|
485 |
|
|
* method enq to add new wait node.
|
486 |
|
|
*/
|
487 |
|
|
private transient volatile Node tail;
|
488 |
|
|
|
489 |
|
|
/**
|
490 |
|
|
* The synchronization state.
|
491 |
|
|
*/
|
492 |
|
|
private volatile int state;
|
493 |
|
|
|
494 |
|
|
/**
|
495 |
|
|
* Returns the current value of synchronization state.
|
496 |
|
|
* This operation has memory semantics of a <tt>volatile</tt> read.
|
497 |
|
|
* @return current state value
|
498 |
|
|
*/
|
499 |
|
|
protected final int getState() {
|
500 |
|
|
return state;
|
501 |
|
|
}
|
502 |
|
|
|
503 |
|
|
/**
|
504 |
|
|
* Sets the value of synchronization state.
|
505 |
|
|
* This operation has memory semantics of a <tt>volatile</tt> write.
|
506 |
|
|
* @param newState the new state value
|
507 |
|
|
*/
|
508 |
|
|
protected final void setState(int newState) {
|
509 |
|
|
state = newState;
|
510 |
|
|
}
|
511 |
|
|
|
512 |
|
|
/**
|
513 |
|
|
* Atomically sets synchronization state to the given updated
|
514 |
|
|
* value if the current state value equals the expected value.
|
515 |
|
|
* This operation has memory semantics of a <tt>volatile</tt> read
|
516 |
|
|
* and write.
|
517 |
|
|
*
|
518 |
|
|
* @param expect the expected value
|
519 |
|
|
* @param update the new value
|
520 |
|
|
* @return true if successful. False return indicates that the actual
|
521 |
|
|
* value was not equal to the expected value.
|
522 |
|
|
*/
|
523 |
|
|
protected final boolean compareAndSetState(int expect, int update) {
|
524 |
|
|
// See below for intrinsics setup to support this
|
525 |
|
|
return unsafe.compareAndSwapInt(this, stateOffset, expect, update);
|
526 |
|
|
}
|
527 |
|
|
|
528 |
|
|
// Queuing utilities
|
529 |
|
|
|
530 |
|
|
/**
|
531 |
|
|
* The number of nanoseconds for which it is faster to spin
|
532 |
|
|
* rather than to use timed park. A rough estimate suffices
|
533 |
|
|
* to improve responsiveness with very short timeouts.
|
534 |
|
|
*/
|
535 |
|
|
static final long spinForTimeoutThreshold = 1000L;
|
536 |
|
|
|
537 |
|
|
/**
|
538 |
|
|
* Inserts node into queue, initializing if necessary. See picture above.
|
539 |
|
|
* @param node the node to insert
|
540 |
|
|
* @return node's predecessor
|
541 |
|
|
*/
|
542 |
|
|
private Node enq(final Node node) {
|
543 |
|
|
for (;;) {
|
544 |
|
|
Node t = tail;
|
545 |
|
|
if (t == null) { // Must initialize
|
546 |
|
|
Node h = new Node(); // Dummy header
|
547 |
|
|
h.next = node;
|
548 |
|
|
node.prev = h;
|
549 |
|
|
if (compareAndSetHead(h)) {
|
550 |
|
|
tail = node;
|
551 |
|
|
return h;
|
552 |
|
|
}
|
553 |
|
|
}
|
554 |
|
|
else {
|
555 |
|
|
node.prev = t;
|
556 |
|
|
if (compareAndSetTail(t, node)) {
|
557 |
|
|
t.next = node;
|
558 |
|
|
return t;
|
559 |
|
|
}
|
560 |
|
|
}
|
561 |
|
|
}
|
562 |
|
|
}
|
563 |
|
|
|
564 |
|
|
/**
|
565 |
|
|
* Creates and enqueues node for given thread and mode.
|
566 |
|
|
*
|
567 |
|
|
* @param current the thread
|
568 |
|
|
* @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared
|
569 |
|
|
* @return the new node
|
570 |
|
|
*/
|
571 |
|
|
private Node addWaiter(Node mode) {
|
572 |
|
|
Node node = new Node(Thread.currentThread(), mode);
|
573 |
|
|
// Try the fast path of enq; backup to full enq on failure
|
574 |
|
|
Node pred = tail;
|
575 |
|
|
if (pred != null) {
|
576 |
|
|
node.prev = pred;
|
577 |
|
|
if (compareAndSetTail(pred, node)) {
|
578 |
|
|
pred.next = node;
|
579 |
|
|
return node;
|
580 |
|
|
}
|
581 |
|
|
}
|
582 |
|
|
enq(node);
|
583 |
|
|
return node;
|
584 |
|
|
}
|
585 |
|
|
|
586 |
|
|
/**
|
587 |
|
|
* Sets head of queue to be node, thus dequeuing. Called only by
|
588 |
|
|
* acquire methods. Also nulls out unused fields for sake of GC
|
589 |
|
|
* and to suppress unnecessary signals and traversals.
|
590 |
|
|
*
|
591 |
|
|
* @param node the node
|
592 |
|
|
*/
|
593 |
|
|
private void setHead(Node node) {
|
594 |
|
|
head = node;
|
595 |
|
|
node.thread = null;
|
596 |
|
|
node.prev = null;
|
597 |
|
|
}
|
598 |
|
|
|
599 |
|
|
/**
|
600 |
|
|
* Wakes up node's successor, if one exists.
|
601 |
|
|
*
|
602 |
|
|
* @param node the node
|
603 |
|
|
*/
|
604 |
|
|
private void unparkSuccessor(Node node) {
|
605 |
|
|
/*
|
606 |
|
|
* Try to clear status in anticipation of signalling. It is
|
607 |
|
|
* OK if this fails or if status is changed by waiting thread.
|
608 |
|
|
*/
|
609 |
|
|
compareAndSetWaitStatus(node, Node.SIGNAL, 0);
|
610 |
|
|
|
611 |
|
|
/*
|
612 |
|
|
* Thread to unpark is held in successor, which is normally
|
613 |
|
|
* just the next node. But if cancelled or apparently null,
|
614 |
|
|
* traverse backwards from tail to find the actual
|
615 |
|
|
* non-cancelled successor.
|
616 |
|
|
*/
|
617 |
|
|
Node s = node.next;
|
618 |
|
|
if (s == null || s.waitStatus > 0) {
|
619 |
|
|
s = null;
|
620 |
|
|
for (Node t = tail; t != null && t != node; t = t.prev)
|
621 |
|
|
if (t.waitStatus <= 0)
|
622 |
|
|
s = t;
|
623 |
|
|
}
|
624 |
|
|
if (s != null)
|
625 |
|
|
LockSupport.unpark(s.thread);
|
626 |
|
|
}
|
627 |
|
|
|
628 |
|
|
/**
|
629 |
|
|
* Sets head of queue, and checks if successor may be waiting
|
630 |
|
|
* in shared mode, if so propagating if propagate > 0.
|
631 |
|
|
*
|
632 |
|
|
* @param pred the node holding waitStatus for node
|
633 |
|
|
* @param node the node
|
634 |
|
|
* @param propagate the return value from a tryAcquireShared
|
635 |
|
|
*/
|
636 |
|
|
private void setHeadAndPropagate(Node node, int propagate) {
|
637 |
|
|
setHead(node);
|
638 |
|
|
if (propagate > 0 && node.waitStatus != 0) {
|
639 |
|
|
/*
|
640 |
|
|
* Don't bother fully figuring out successor. If it
|
641 |
|
|
* looks null, call unparkSuccessor anyway to be safe.
|
642 |
|
|
*/
|
643 |
|
|
Node s = node.next;
|
644 |
|
|
if (s == null || s.isShared())
|
645 |
|
|
unparkSuccessor(node);
|
646 |
|
|
}
|
647 |
|
|
}
|
648 |
|
|
|
649 |
|
|
// Utilities for various versions of acquire
|
650 |
|
|
|
651 |
|
|
/**
|
652 |
|
|
* Cancels an ongoing attempt to acquire.
|
653 |
|
|
*
|
654 |
|
|
* @param node the node
|
655 |
|
|
*/
|
656 |
|
|
private void cancelAcquire(Node node) {
|
657 |
|
|
if (node != null) { // Ignore if node doesn't exist
|
658 |
|
|
node.thread = null;
|
659 |
|
|
// Can use unconditional write instead of CAS here
|
660 |
|
|
node.waitStatus = Node.CANCELLED;
|
661 |
|
|
unparkSuccessor(node);
|
662 |
|
|
}
|
663 |
|
|
}
|
664 |
|
|
|
665 |
|
|
/**
|
666 |
|
|
* Checks and updates status for a node that failed to acquire.
|
667 |
|
|
* Returns true if thread should block. This is the main signal
|
668 |
|
|
* control in all acquire loops. Requires that pred == node.prev
|
669 |
|
|
*
|
670 |
|
|
* @param pred node's predecessor holding status
|
671 |
|
|
* @param node the node
|
672 |
|
|
* @return {@code true} if thread should block
|
673 |
|
|
*/
|
674 |
|
|
private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
|
675 |
|
|
int s = pred.waitStatus;
|
676 |
|
|
if (s < 0)
|
677 |
|
|
/*
|
678 |
|
|
* This node has already set status asking a release
|
679 |
|
|
* to signal it, so it can safely park
|
680 |
|
|
*/
|
681 |
|
|
return true;
|
682 |
|
|
if (s > 0)
|
683 |
|
|
/*
|
684 |
|
|
* Predecessor was cancelled. Move up to its predecessor
|
685 |
|
|
* and indicate retry.
|
686 |
|
|
*/
|
687 |
|
|
node.prev = pred.prev;
|
688 |
|
|
else
|
689 |
|
|
/*
|
690 |
|
|
* Indicate that we need a signal, but don't park yet. Caller
|
691 |
|
|
* will need to retry to make sure it cannot acquire before
|
692 |
|
|
* parking.
|
693 |
|
|
*/
|
694 |
|
|
compareAndSetWaitStatus(pred, 0, Node.SIGNAL);
|
695 |
|
|
return false;
|
696 |
|
|
}
|
697 |
|
|
|
698 |
|
|
/**
|
699 |
|
|
* Convenience method to interrupt current thread.
|
700 |
|
|
*/
|
701 |
|
|
private static void selfInterrupt() {
|
702 |
|
|
Thread.currentThread().interrupt();
|
703 |
|
|
}
|
704 |
|
|
|
705 |
|
|
/**
|
706 |
|
|
* Convenience method to park and then check if interrupted
|
707 |
|
|
*
|
708 |
|
|
* @return {@code true} if interrupted
|
709 |
|
|
*/
|
710 |
|
|
private final boolean parkAndCheckInterrupt() {
|
711 |
|
|
LockSupport.park(this);
|
712 |
|
|
return Thread.interrupted();
|
713 |
|
|
}
|
714 |
|
|
|
715 |
|
|
/*
|
716 |
|
|
* Various flavors of acquire, varying in exclusive/shared and
|
717 |
|
|
* control modes. Each is mostly the same, but annoyingly
|
718 |
|
|
* different. Only a little bit of factoring is possible due to
|
719 |
|
|
* interactions of exception mechanics (including ensuring that we
|
720 |
|
|
* cancel if tryAcquire throws exception) and other control, at
|
721 |
|
|
* least not without hurting performance too much.
|
722 |
|
|
*/
|
723 |
|
|
|
724 |
|
|
/**
|
725 |
|
|
* Acquires in exclusive uninterruptible mode for thread already in
|
726 |
|
|
* queue. Used by condition wait methods as well as acquire.
|
727 |
|
|
*
|
728 |
|
|
* @param node the node
|
729 |
|
|
* @param arg the acquire argument
|
730 |
|
|
* @return {@code true} if interrupted while waiting
|
731 |
|
|
*/
|
732 |
|
|
final boolean acquireQueued(final Node node, int arg) {
|
733 |
|
|
try {
|
734 |
|
|
boolean interrupted = false;
|
735 |
|
|
for (;;) {
|
736 |
|
|
final Node p = node.predecessor();
|
737 |
|
|
if (p == head && tryAcquire(arg)) {
|
738 |
|
|
setHead(node);
|
739 |
|
|
p.next = null; // help GC
|
740 |
|
|
return interrupted;
|
741 |
|
|
}
|
742 |
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
743 |
|
|
parkAndCheckInterrupt())
|
744 |
|
|
interrupted = true;
|
745 |
|
|
}
|
746 |
|
|
} catch (RuntimeException ex) {
|
747 |
|
|
cancelAcquire(node);
|
748 |
|
|
throw ex;
|
749 |
|
|
}
|
750 |
|
|
}
|
751 |
|
|
|
752 |
|
|
/**
|
753 |
|
|
* Acquires in exclusive interruptible mode.
|
754 |
|
|
* @param arg the acquire argument
|
755 |
|
|
*/
|
756 |
|
|
private void doAcquireInterruptibly(int arg)
|
757 |
|
|
throws InterruptedException {
|
758 |
|
|
final Node node = addWaiter(Node.EXCLUSIVE);
|
759 |
|
|
try {
|
760 |
|
|
for (;;) {
|
761 |
|
|
final Node p = node.predecessor();
|
762 |
|
|
if (p == head && tryAcquire(arg)) {
|
763 |
|
|
setHead(node);
|
764 |
|
|
p.next = null; // help GC
|
765 |
|
|
return;
|
766 |
|
|
}
|
767 |
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
768 |
|
|
parkAndCheckInterrupt())
|
769 |
|
|
break;
|
770 |
|
|
}
|
771 |
|
|
} catch (RuntimeException ex) {
|
772 |
|
|
cancelAcquire(node);
|
773 |
|
|
throw ex;
|
774 |
|
|
}
|
775 |
|
|
// Arrive here only if interrupted
|
776 |
|
|
cancelAcquire(node);
|
777 |
|
|
throw new InterruptedException();
|
778 |
|
|
}
|
779 |
|
|
|
780 |
|
|
/**
|
781 |
|
|
* Acquires in exclusive timed mode.
|
782 |
|
|
*
|
783 |
|
|
* @param arg the acquire argument
|
784 |
|
|
* @param nanosTimeout max wait time
|
785 |
|
|
* @return {@code true} if acquired
|
786 |
|
|
*/
|
787 |
|
|
private boolean doAcquireNanos(int arg, long nanosTimeout)
|
788 |
|
|
throws InterruptedException {
|
789 |
|
|
long lastTime = System.nanoTime();
|
790 |
|
|
final Node node = addWaiter(Node.EXCLUSIVE);
|
791 |
|
|
try {
|
792 |
|
|
for (;;) {
|
793 |
|
|
final Node p = node.predecessor();
|
794 |
|
|
if (p == head && tryAcquire(arg)) {
|
795 |
|
|
setHead(node);
|
796 |
|
|
p.next = null; // help GC
|
797 |
|
|
return true;
|
798 |
|
|
}
|
799 |
|
|
if (nanosTimeout <= 0) {
|
800 |
|
|
cancelAcquire(node);
|
801 |
|
|
return false;
|
802 |
|
|
}
|
803 |
|
|
if (nanosTimeout > spinForTimeoutThreshold &&
|
804 |
|
|
shouldParkAfterFailedAcquire(p, node))
|
805 |
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
806 |
|
|
long now = System.nanoTime();
|
807 |
|
|
nanosTimeout -= now - lastTime;
|
808 |
|
|
lastTime = now;
|
809 |
|
|
if (Thread.interrupted())
|
810 |
|
|
break;
|
811 |
|
|
}
|
812 |
|
|
} catch (RuntimeException ex) {
|
813 |
|
|
cancelAcquire(node);
|
814 |
|
|
throw ex;
|
815 |
|
|
}
|
816 |
|
|
// Arrive here only if interrupted
|
817 |
|
|
cancelAcquire(node);
|
818 |
|
|
throw new InterruptedException();
|
819 |
|
|
}
|
820 |
|
|
|
821 |
|
|
/**
|
822 |
|
|
* Acquires in shared uninterruptible mode.
|
823 |
|
|
* @param arg the acquire argument
|
824 |
|
|
*/
|
825 |
|
|
private void doAcquireShared(int arg) {
|
826 |
|
|
final Node node = addWaiter(Node.SHARED);
|
827 |
|
|
try {
|
828 |
|
|
boolean interrupted = false;
|
829 |
|
|
for (;;) {
|
830 |
|
|
final Node p = node.predecessor();
|
831 |
|
|
if (p == head) {
|
832 |
|
|
int r = tryAcquireShared(arg);
|
833 |
|
|
if (r >= 0) {
|
834 |
|
|
setHeadAndPropagate(node, r);
|
835 |
|
|
p.next = null; // help GC
|
836 |
|
|
if (interrupted)
|
837 |
|
|
selfInterrupt();
|
838 |
|
|
return;
|
839 |
|
|
}
|
840 |
|
|
}
|
841 |
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
842 |
|
|
parkAndCheckInterrupt())
|
843 |
|
|
interrupted = true;
|
844 |
|
|
}
|
845 |
|
|
} catch (RuntimeException ex) {
|
846 |
|
|
cancelAcquire(node);
|
847 |
|
|
throw ex;
|
848 |
|
|
}
|
849 |
|
|
}
|
850 |
|
|
|
851 |
|
|
/**
|
852 |
|
|
* Acquires in shared interruptible mode.
|
853 |
|
|
* @param arg the acquire argument
|
854 |
|
|
*/
|
855 |
|
|
private void doAcquireSharedInterruptibly(int arg)
|
856 |
|
|
throws InterruptedException {
|
857 |
|
|
final Node node = addWaiter(Node.SHARED);
|
858 |
|
|
try {
|
859 |
|
|
for (;;) {
|
860 |
|
|
final Node p = node.predecessor();
|
861 |
|
|
if (p == head) {
|
862 |
|
|
int r = tryAcquireShared(arg);
|
863 |
|
|
if (r >= 0) {
|
864 |
|
|
setHeadAndPropagate(node, r);
|
865 |
|
|
p.next = null; // help GC
|
866 |
|
|
return;
|
867 |
|
|
}
|
868 |
|
|
}
|
869 |
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
870 |
|
|
parkAndCheckInterrupt())
|
871 |
|
|
break;
|
872 |
|
|
}
|
873 |
|
|
} catch (RuntimeException ex) {
|
874 |
|
|
cancelAcquire(node);
|
875 |
|
|
throw ex;
|
876 |
|
|
}
|
877 |
|
|
// Arrive here only if interrupted
|
878 |
|
|
cancelAcquire(node);
|
879 |
|
|
throw new InterruptedException();
|
880 |
|
|
}
|
881 |
|
|
|
882 |
|
|
/**
|
883 |
|
|
* Acquires in shared timed mode.
|
884 |
|
|
*
|
885 |
|
|
* @param arg the acquire argument
|
886 |
|
|
* @param nanosTimeout max wait time
|
887 |
|
|
* @return {@code true} if acquired
|
888 |
|
|
*/
|
889 |
|
|
private boolean doAcquireSharedNanos(int arg, long nanosTimeout)
|
890 |
|
|
throws InterruptedException {
|
891 |
|
|
|
892 |
|
|
long lastTime = System.nanoTime();
|
893 |
|
|
final Node node = addWaiter(Node.SHARED);
|
894 |
|
|
try {
|
895 |
|
|
for (;;) {
|
896 |
|
|
final Node p = node.predecessor();
|
897 |
|
|
if (p == head) {
|
898 |
|
|
int r = tryAcquireShared(arg);
|
899 |
|
|
if (r >= 0) {
|
900 |
|
|
setHeadAndPropagate(node, r);
|
901 |
|
|
p.next = null; // help GC
|
902 |
|
|
return true;
|
903 |
|
|
}
|
904 |
|
|
}
|
905 |
|
|
if (nanosTimeout <= 0) {
|
906 |
|
|
cancelAcquire(node);
|
907 |
|
|
return false;
|
908 |
|
|
}
|
909 |
|
|
if (nanosTimeout > spinForTimeoutThreshold &&
|
910 |
|
|
shouldParkAfterFailedAcquire(p, node))
|
911 |
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
912 |
|
|
long now = System.nanoTime();
|
913 |
|
|
nanosTimeout -= now - lastTime;
|
914 |
|
|
lastTime = now;
|
915 |
|
|
if (Thread.interrupted())
|
916 |
|
|
break;
|
917 |
|
|
}
|
918 |
|
|
} catch (RuntimeException ex) {
|
919 |
|
|
cancelAcquire(node);
|
920 |
|
|
throw ex;
|
921 |
|
|
}
|
922 |
|
|
// Arrive here only if interrupted
|
923 |
|
|
cancelAcquire(node);
|
924 |
|
|
throw new InterruptedException();
|
925 |
|
|
}
|
926 |
|
|
|
927 |
|
|
// Main exported methods
|
928 |
|
|
|
929 |
|
|
/**
|
930 |
|
|
* Attempts to acquire in exclusive mode. This method should query
|
931 |
|
|
* if the state of the object permits it to be acquired in the
|
932 |
|
|
* exclusive mode, and if so to acquire it.
|
933 |
|
|
*
|
934 |
|
|
* <p>This method is always invoked by the thread performing
|
935 |
|
|
* acquire. If this method reports failure, the acquire method
|
936 |
|
|
* may queue the thread, if it is not already queued, until it is
|
937 |
|
|
* signalled by a release from some other thread. This can be used
|
938 |
|
|
* to implement method {@link Lock#tryLock()}.
|
939 |
|
|
*
|
940 |
|
|
* <p>The default
|
941 |
|
|
* implementation throws {@link UnsupportedOperationException}.
|
942 |
|
|
*
|
943 |
|
|
* @param arg the acquire argument. This value is always the one
|
944 |
|
|
* passed to an acquire method, or is the value saved on entry
|
945 |
|
|
* to a condition wait. The value is otherwise uninterpreted
|
946 |
|
|
* and can represent anything you like.
|
947 |
|
|
* @return {@code true} if successful. Upon success, this object has
|
948 |
|
|
* been acquired.
|
949 |
|
|
* @throws IllegalMonitorStateException if acquiring would place this
|
950 |
|
|
* synchronizer in an illegal state. This exception must be
|
951 |
|
|
* thrown in a consistent fashion for synchronization to work
|
952 |
|
|
* correctly.
|
953 |
|
|
* @throws UnsupportedOperationException if exclusive mode is not supported
|
954 |
|
|
*/
|
955 |
|
|
protected boolean tryAcquire(int arg) {
|
956 |
|
|
throw new UnsupportedOperationException();
|
957 |
|
|
}
|
958 |
|
|
|
959 |
|
|
/**
|
960 |
|
|
* Attempts to set the state to reflect a release in exclusive
|
961 |
|
|
* mode.
|
962 |
|
|
*
|
963 |
|
|
* <p>This method is always invoked by the thread performing release.
|
964 |
|
|
*
|
965 |
|
|
* <p>The default implementation throws
|
966 |
|
|
* {@link UnsupportedOperationException}.
|
967 |
|
|
*
|
968 |
|
|
* @param arg the release argument. This value is always the one
|
969 |
|
|
* passed to a release method, or the current state value upon
|
970 |
|
|
* entry to a condition wait. The value is otherwise
|
971 |
|
|
* uninterpreted and can represent anything you like.
|
972 |
|
|
* @return {@code true} if this object is now in a fully released
|
973 |
|
|
* state, so that any waiting threads may attempt to acquire;
|
974 |
|
|
* and {@code false} otherwise.
|
975 |
|
|
* @throws IllegalMonitorStateException if releasing would place this
|
976 |
|
|
* synchronizer in an illegal state. This exception must be
|
977 |
|
|
* thrown in a consistent fashion for synchronization to work
|
978 |
|
|
* correctly.
|
979 |
|
|
* @throws UnsupportedOperationException if exclusive mode is not supported
|
980 |
|
|
*/
|
981 |
|
|
protected boolean tryRelease(int arg) {
|
982 |
|
|
throw new UnsupportedOperationException();
|
983 |
|
|
}
|
984 |
|
|
|
985 |
|
|
/**
|
986 |
|
|
* Attempts to acquire in shared mode. This method should query if
|
987 |
|
|
* the state of the object permits it to be acquired in the shared
|
988 |
|
|
* mode, and if so to acquire it.
|
989 |
|
|
*
|
990 |
|
|
* <p>This method is always invoked by the thread performing
|
991 |
|
|
* acquire. If this method reports failure, the acquire method
|
992 |
|
|
* may queue the thread, if it is not already queued, until it is
|
993 |
|
|
* signalled by a release from some other thread.
|
994 |
|
|
*
|
995 |
|
|
* <p>The default implementation throws {@link
|
996 |
|
|
* UnsupportedOperationException}.
|
997 |
|
|
*
|
998 |
|
|
* @param arg the acquire argument. This value is always the one
|
999 |
|
|
* passed to an acquire method, or is the value saved on entry
|
1000 |
|
|
* to a condition wait. The value is otherwise uninterpreted
|
1001 |
|
|
* and can represent anything you like.
|
1002 |
|
|
* @return a negative value on failure; zero if acquisition in shared
|
1003 |
|
|
* mode succeeded but no subsequent shared-mode acquire can
|
1004 |
|
|
* succeed; and a positive value if acquisition in shared
|
1005 |
|
|
* mode succeeded and subsequent shared-mode acquires might
|
1006 |
|
|
* also succeed, in which case a subsequent waiting thread
|
1007 |
|
|
* must check availability. (Support for three different
|
1008 |
|
|
* return values enables this method to be used in contexts
|
1009 |
|
|
* where acquires only sometimes act exclusively.) Upon
|
1010 |
|
|
* success, this object has been acquired.
|
1011 |
|
|
* @throws IllegalMonitorStateException if acquiring would place this
|
1012 |
|
|
* synchronizer in an illegal state. This exception must be
|
1013 |
|
|
* thrown in a consistent fashion for synchronization to work
|
1014 |
|
|
* correctly.
|
1015 |
|
|
* @throws UnsupportedOperationException if shared mode is not supported
|
1016 |
|
|
*/
|
1017 |
|
|
protected int tryAcquireShared(int arg) {
|
1018 |
|
|
throw new UnsupportedOperationException();
|
1019 |
|
|
}
|
1020 |
|
|
|
1021 |
|
|
/**
|
1022 |
|
|
* Attempts to set the state to reflect a release in shared mode.
|
1023 |
|
|
*
|
1024 |
|
|
* <p>This method is always invoked by the thread performing release.
|
1025 |
|
|
*
|
1026 |
|
|
* <p>The default implementation throws
|
1027 |
|
|
* {@link UnsupportedOperationException}.
|
1028 |
|
|
*
|
1029 |
|
|
* @param arg the release argument. This value is always the one
|
1030 |
|
|
* passed to a release method, or the current state value upon
|
1031 |
|
|
* entry to a condition wait. The value is otherwise
|
1032 |
|
|
* uninterpreted and can represent anything you like.
|
1033 |
|
|
* @return {@code true} if this release of shared mode may permit a
|
1034 |
|
|
* waiting acquire (shared or exclusive) to succeed; and
|
1035 |
|
|
* {@code false} otherwise
|
1036 |
|
|
* @throws IllegalMonitorStateException if releasing would place this
|
1037 |
|
|
* synchronizer in an illegal state. This exception must be
|
1038 |
|
|
* thrown in a consistent fashion for synchronization to work
|
1039 |
|
|
* correctly.
|
1040 |
|
|
* @throws UnsupportedOperationException if shared mode is not supported
|
1041 |
|
|
*/
|
1042 |
|
|
protected boolean tryReleaseShared(int arg) {
|
1043 |
|
|
throw new UnsupportedOperationException();
|
1044 |
|
|
}
|
1045 |
|
|
|
1046 |
|
|
/**
|
1047 |
|
|
* Returns {@code true} if synchronization is held exclusively with
|
1048 |
|
|
* respect to the current (calling) thread. This method is invoked
|
1049 |
|
|
* upon each call to a non-waiting {@link ConditionObject} method.
|
1050 |
|
|
* (Waiting methods instead invoke {@link #release}.)
|
1051 |
|
|
*
|
1052 |
|
|
* <p>The default implementation throws {@link
|
1053 |
|
|
* UnsupportedOperationException}. This method is invoked
|
1054 |
|
|
* internally only within {@link ConditionObject} methods, so need
|
1055 |
|
|
* not be defined if conditions are not used.
|
1056 |
|
|
*
|
1057 |
|
|
* @return {@code true} if synchronization is held exclusively;
|
1058 |
|
|
* {@code false} otherwise
|
1059 |
|
|
* @throws UnsupportedOperationException if conditions are not supported
|
1060 |
|
|
*/
|
1061 |
|
|
protected boolean isHeldExclusively() {
|
1062 |
|
|
throw new UnsupportedOperationException();
|
1063 |
|
|
}
|
1064 |
|
|
|
1065 |
|
|
/**
|
1066 |
|
|
* Acquires in exclusive mode, ignoring interrupts. Implemented
|
1067 |
|
|
* by invoking at least once {@link #tryAcquire},
|
1068 |
|
|
* returning on success. Otherwise the thread is queued, possibly
|
1069 |
|
|
* repeatedly blocking and unblocking, invoking {@link
|
1070 |
|
|
* #tryAcquire} until success. This method can be used
|
1071 |
|
|
* to implement method {@link Lock#lock}.
|
1072 |
|
|
*
|
1073 |
|
|
* @param arg the acquire argument. This value is conveyed to
|
1074 |
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
1075 |
|
|
* can represent anything you like.
|
1076 |
|
|
*/
|
1077 |
|
|
public final void acquire(int arg) {
|
1078 |
|
|
if (!tryAcquire(arg) &&
|
1079 |
|
|
acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
|
1080 |
|
|
selfInterrupt();
|
1081 |
|
|
}
|
1082 |
|
|
|
1083 |
|
|
/**
|
1084 |
|
|
* Acquires in exclusive mode, aborting if interrupted.
|
1085 |
|
|
* Implemented by first checking interrupt status, then invoking
|
1086 |
|
|
* at least once {@link #tryAcquire}, returning on
|
1087 |
|
|
* success. Otherwise the thread is queued, possibly repeatedly
|
1088 |
|
|
* blocking and unblocking, invoking {@link #tryAcquire}
|
1089 |
|
|
* until success or the thread is interrupted. This method can be
|
1090 |
|
|
* used to implement method {@link Lock#lockInterruptibly}.
|
1091 |
|
|
*
|
1092 |
|
|
* @param arg the acquire argument. This value is conveyed to
|
1093 |
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
1094 |
|
|
* can represent anything you like.
|
1095 |
|
|
* @throws InterruptedException if the current thread is interrupted
|
1096 |
|
|
*/
|
1097 |
|
|
public final void acquireInterruptibly(int arg) throws InterruptedException {
|
1098 |
|
|
if (Thread.interrupted())
|
1099 |
|
|
throw new InterruptedException();
|
1100 |
|
|
if (!tryAcquire(arg))
|
1101 |
|
|
doAcquireInterruptibly(arg);
|
1102 |
|
|
}
|
1103 |
|
|
|
1104 |
|
|
/**
|
1105 |
|
|
* Attempts to acquire in exclusive mode, aborting if interrupted,
|
1106 |
|
|
* and failing if the given timeout elapses. Implemented by first
|
1107 |
|
|
* checking interrupt status, then invoking at least once {@link
|
1108 |
|
|
* #tryAcquire}, returning on success. Otherwise, the thread is
|
1109 |
|
|
* queued, possibly repeatedly blocking and unblocking, invoking
|
1110 |
|
|
* {@link #tryAcquire} until success or the thread is interrupted
|
1111 |
|
|
* or the timeout elapses. This method can be used to implement
|
1112 |
|
|
* method {@link Lock#tryLock(long, TimeUnit)}.
|
1113 |
|
|
*
|
1114 |
|
|
* @param arg the acquire argument. This value is conveyed to
|
1115 |
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
1116 |
|
|
* can represent anything you like.
|
1117 |
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
1118 |
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
1119 |
|
|
* @throws InterruptedException if the current thread is interrupted
|
1120 |
|
|
*/
|
1121 |
|
|
public final boolean tryAcquireNanos(int arg, long nanosTimeout) throws InterruptedException {
|
1122 |
|
|
if (Thread.interrupted())
|
1123 |
|
|
throw new InterruptedException();
|
1124 |
|
|
return tryAcquire(arg) ||
|
1125 |
|
|
doAcquireNanos(arg, nanosTimeout);
|
1126 |
|
|
}
|
1127 |
|
|
|
1128 |
|
|
/**
|
1129 |
|
|
* Releases in exclusive mode. Implemented by unblocking one or
|
1130 |
|
|
* more threads if {@link #tryRelease} returns true.
|
1131 |
|
|
* This method can be used to implement method {@link Lock#unlock}.
|
1132 |
|
|
*
|
1133 |
|
|
* @param arg the release argument. This value is conveyed to
|
1134 |
|
|
* {@link #tryRelease} but is otherwise uninterpreted and
|
1135 |
|
|
* can represent anything you like.
|
1136 |
|
|
* @return the value returned from {@link #tryRelease}
|
1137 |
|
|
*/
|
1138 |
|
|
public final boolean release(int arg) {
|
1139 |
|
|
if (tryRelease(arg)) {
|
1140 |
|
|
Node h = head;
|
1141 |
|
|
if (h != null && h.waitStatus != 0)
|
1142 |
|
|
unparkSuccessor(h);
|
1143 |
|
|
return true;
|
1144 |
|
|
}
|
1145 |
|
|
return false;
|
1146 |
|
|
}
|
1147 |
|
|
|
1148 |
|
|
/**
|
1149 |
|
|
* Acquires in shared mode, ignoring interrupts. Implemented by
|
1150 |
|
|
* first invoking at least once {@link #tryAcquireShared},
|
1151 |
|
|
* returning on success. Otherwise the thread is queued, possibly
|
1152 |
|
|
* repeatedly blocking and unblocking, invoking {@link
|
1153 |
|
|
* #tryAcquireShared} until success.
|
1154 |
|
|
*
|
1155 |
|
|
* @param arg the acquire argument. This value is conveyed to
|
1156 |
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
1157 |
|
|
* and can represent anything you like.
|
1158 |
|
|
*/
|
1159 |
|
|
public final void acquireShared(int arg) {
|
1160 |
|
|
if (tryAcquireShared(arg) < 0)
|
1161 |
|
|
doAcquireShared(arg);
|
1162 |
|
|
}
|
1163 |
|
|
|
1164 |
|
|
/**
|
1165 |
|
|
* Acquires in shared mode, aborting if interrupted. Implemented
|
1166 |
|
|
* by first checking interrupt status, then invoking at least once
|
1167 |
|
|
* {@link #tryAcquireShared}, returning on success. Otherwise the
|
1168 |
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
1169 |
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
1170 |
|
|
* is interrupted.
|
1171 |
|
|
* @param arg the acquire argument.
|
1172 |
|
|
* This value is conveyed to {@link #tryAcquireShared} but is
|
1173 |
|
|
* otherwise uninterpreted and can represent anything
|
1174 |
|
|
* you like.
|
1175 |
|
|
* @throws InterruptedException if the current thread is interrupted
|
1176 |
|
|
*/
|
1177 |
|
|
public final void acquireSharedInterruptibly(int arg) throws InterruptedException {
|
1178 |
|
|
if (Thread.interrupted())
|
1179 |
|
|
throw new InterruptedException();
|
1180 |
|
|
if (tryAcquireShared(arg) < 0)
|
1181 |
|
|
doAcquireSharedInterruptibly(arg);
|
1182 |
|
|
}
|
1183 |
|
|
|
1184 |
|
|
/**
|
1185 |
|
|
* Attempts to acquire in shared mode, aborting if interrupted, and
|
1186 |
|
|
* failing if the given timeout elapses. Implemented by first
|
1187 |
|
|
* checking interrupt status, then invoking at least once {@link
|
1188 |
|
|
* #tryAcquireShared}, returning on success. Otherwise, the
|
1189 |
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
1190 |
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
1191 |
|
|
* is interrupted or the timeout elapses.
|
1192 |
|
|
*
|
1193 |
|
|
* @param arg the acquire argument. This value is conveyed to
|
1194 |
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
1195 |
|
|
* and can represent anything you like.
|
1196 |
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
1197 |
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
1198 |
|
|
* @throws InterruptedException if the current thread is interrupted
|
1199 |
|
|
*/
|
1200 |
|
|
public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout) throws InterruptedException {
|
1201 |
|
|
if (Thread.interrupted())
|
1202 |
|
|
throw new InterruptedException();
|
1203 |
|
|
return tryAcquireShared(arg) >= 0 ||
|
1204 |
|
|
doAcquireSharedNanos(arg, nanosTimeout);
|
1205 |
|
|
}
|
1206 |
|
|
|
1207 |
|
|
/**
|
1208 |
|
|
* Releases in shared mode. Implemented by unblocking one or more
|
1209 |
|
|
* threads if {@link #tryReleaseShared} returns true.
|
1210 |
|
|
*
|
1211 |
|
|
* @param arg the release argument. This value is conveyed to
|
1212 |
|
|
* {@link #tryReleaseShared} but is otherwise uninterpreted
|
1213 |
|
|
* and can represent anything you like.
|
1214 |
|
|
* @return the value returned from {@link #tryReleaseShared}
|
1215 |
|
|
*/
|
1216 |
|
|
public final boolean releaseShared(int arg) {
|
1217 |
|
|
if (tryReleaseShared(arg)) {
|
1218 |
|
|
Node h = head;
|
1219 |
|
|
if (h != null && h.waitStatus != 0)
|
1220 |
|
|
unparkSuccessor(h);
|
1221 |
|
|
return true;
|
1222 |
|
|
}
|
1223 |
|
|
return false;
|
1224 |
|
|
}
|
1225 |
|
|
|
1226 |
|
|
// Queue inspection methods
|
1227 |
|
|
|
1228 |
|
|
/**
|
1229 |
|
|
* Queries whether any threads are waiting to acquire. Note that
|
1230 |
|
|
* because cancellations due to interrupts and timeouts may occur
|
1231 |
|
|
* at any time, a {@code true} return does not guarantee that any
|
1232 |
|
|
* other thread will ever acquire.
|
1233 |
|
|
*
|
1234 |
|
|
* <p>In this implementation, this operation returns in
|
1235 |
|
|
* constant time.
|
1236 |
|
|
*
|
1237 |
|
|
* @return {@code true} if there may be other threads waiting to acquire
|
1238 |
|
|
*/
|
1239 |
|
|
public final boolean hasQueuedThreads() {
|
1240 |
|
|
return head != tail;
|
1241 |
|
|
}
|
1242 |
|
|
|
1243 |
|
|
/**
|
1244 |
|
|
* Queries whether any threads have ever contended to acquire this
|
1245 |
|
|
* synchronizer; that is if an acquire method has ever blocked.
|
1246 |
|
|
*
|
1247 |
|
|
* <p>In this implementation, this operation returns in
|
1248 |
|
|
* constant time.
|
1249 |
|
|
*
|
1250 |
|
|
* @return {@code true} if there has ever been contention
|
1251 |
|
|
*/
|
1252 |
|
|
public final boolean hasContended() {
|
1253 |
|
|
return head != null;
|
1254 |
|
|
}
|
1255 |
|
|
|
1256 |
|
|
/**
|
1257 |
|
|
* Returns the first (longest-waiting) thread in the queue, or
|
1258 |
|
|
* {@code null} if no threads are currently queued.
|
1259 |
|
|
*
|
1260 |
|
|
* <p>In this implementation, this operation normally returns in
|
1261 |
|
|
* constant time, but may iterate upon contention if other threads are
|
1262 |
|
|
* concurrently modifying the queue.
|
1263 |
|
|
*
|
1264 |
|
|
* @return the first (longest-waiting) thread in the queue, or
|
1265 |
|
|
* {@code null} if no threads are currently queued
|
1266 |
|
|
*/
|
1267 |
|
|
public final Thread getFirstQueuedThread() {
|
1268 |
|
|
// handle only fast path, else relay
|
1269 |
|
|
return (head == tail)? null : fullGetFirstQueuedThread();
|
1270 |
|
|
}
|
1271 |
|
|
|
1272 |
|
|
/**
|
1273 |
|
|
* Version of getFirstQueuedThread called when fastpath fails
|
1274 |
|
|
*/
|
1275 |
|
|
private Thread fullGetFirstQueuedThread() {
|
1276 |
|
|
/*
|
1277 |
|
|
* The first node is normally h.next. Try to get its
|
1278 |
|
|
* thread field, ensuring consistent reads: If thread
|
1279 |
|
|
* field is nulled out or s.prev is no longer head, then
|
1280 |
|
|
* some other thread(s) concurrently performed setHead in
|
1281 |
|
|
* between some of our reads. We try this twice before
|
1282 |
|
|
* resorting to traversal.
|
1283 |
|
|
*/
|
1284 |
|
|
Node h, s;
|
1285 |
|
|
Thread st;
|
1286 |
|
|
if (((h = head) != null && (s = h.next) != null &&
|
1287 |
|
|
s.prev == head && (st = s.thread) != null) ||
|
1288 |
|
|
((h = head) != null && (s = h.next) != null &&
|
1289 |
|
|
s.prev == head && (st = s.thread) != null))
|
1290 |
|
|
return st;
|
1291 |
|
|
|
1292 |
|
|
/*
|
1293 |
|
|
* Head's next field might not have been set yet, or may have
|
1294 |
|
|
* been unset after setHead. So we must check to see if tail
|
1295 |
|
|
* is actually first node. If not, we continue on, safely
|
1296 |
|
|
* traversing from tail back to head to find first,
|
1297 |
|
|
* guaranteeing termination.
|
1298 |
|
|
*/
|
1299 |
|
|
|
1300 |
|
|
Node t = tail;
|
1301 |
|
|
Thread firstThread = null;
|
1302 |
|
|
while (t != null && t != head) {
|
1303 |
|
|
Thread tt = t.thread;
|
1304 |
|
|
if (tt != null)
|
1305 |
|
|
firstThread = tt;
|
1306 |
|
|
t = t.prev;
|
1307 |
|
|
}
|
1308 |
|
|
return firstThread;
|
1309 |
|
|
}
|
1310 |
|
|
|
1311 |
|
|
/**
|
1312 |
|
|
* Returns true if the given thread is currently queued.
|
1313 |
|
|
*
|
1314 |
|
|
* <p>This implementation traverses the queue to determine
|
1315 |
|
|
* presence of the given thread.
|
1316 |
|
|
*
|
1317 |
|
|
* @param thread the thread
|
1318 |
|
|
* @return {@code true} if the given thread is on the queue
|
1319 |
|
|
* @throws NullPointerException if the thread is null
|
1320 |
|
|
*/
|
1321 |
|
|
public final boolean isQueued(Thread thread) {
|
1322 |
|
|
if (thread == null)
|
1323 |
|
|
throw new NullPointerException();
|
1324 |
|
|
for (Node p = tail; p != null; p = p.prev)
|
1325 |
|
|
if (p.thread == thread)
|
1326 |
|
|
return true;
|
1327 |
|
|
return false;
|
1328 |
|
|
}
|
1329 |
|
|
|
1330 |
|
|
/**
|
1331 |
|
|
* Return {@code true} if the apparent first queued thread, if one
|
1332 |
|
|
* exists, is not waiting in exclusive mode. Used only as a heuristic
|
1333 |
|
|
* in ReentrantReadWriteLock.
|
1334 |
|
|
*/
|
1335 |
|
|
final boolean apparentlyFirstQueuedIsExclusive() {
|
1336 |
|
|
Node h, s;
|
1337 |
|
|
return ((h = head) != null && (s = h.next) != null &&
|
1338 |
|
|
s.nextWaiter != Node.SHARED);
|
1339 |
|
|
}
|
1340 |
|
|
|
1341 |
|
|
/**
|
1342 |
|
|
* Return {@code true} if the queue is empty or if the given thread
|
1343 |
|
|
* is at the head of the queue. This is reliable only if
|
1344 |
|
|
* <tt>current</tt> is actually Thread.currentThread() of caller.
|
1345 |
|
|
*/
|
1346 |
|
|
final boolean isFirst(Thread current) {
|
1347 |
|
|
Node h, s;
|
1348 |
|
|
return ((h = head) == null ||
|
1349 |
|
|
((s = h.next) != null && s.thread == current) ||
|
1350 |
|
|
fullIsFirst(current));
|
1351 |
|
|
}
|
1352 |
|
|
|
1353 |
|
|
final boolean fullIsFirst(Thread current) {
|
1354 |
|
|
// same idea as fullGetFirstQueuedThread
|
1355 |
|
|
Node h, s;
|
1356 |
|
|
Thread firstThread = null;
|
1357 |
|
|
if (((h = head) != null && (s = h.next) != null &&
|
1358 |
|
|
s.prev == head && (firstThread = s.thread) != null))
|
1359 |
|
|
return firstThread == current;
|
1360 |
|
|
Node t = tail;
|
1361 |
|
|
while (t != null && t != head) {
|
1362 |
|
|
Thread tt = t.thread;
|
1363 |
|
|
if (tt != null)
|
1364 |
|
|
firstThread = tt;
|
1365 |
|
|
t = t.prev;
|
1366 |
|
|
}
|
1367 |
|
|
return firstThread == current || firstThread == null;
|
1368 |
|
|
}
|
1369 |
|
|
|
1370 |
|
|
|
1371 |
|
|
// Instrumentation and monitoring methods
|
1372 |
|
|
|
1373 |
|
|
/**
|
1374 |
|
|
* Returns an estimate of the number of threads waiting to
|
1375 |
|
|
* acquire. The value is only an estimate because the number of
|
1376 |
|
|
* threads may change dynamically while this method traverses
|
1377 |
|
|
* internal data structures. This method is designed for use in
|
1378 |
|
|
* monitoring system state, not for synchronization
|
1379 |
|
|
* control.
|
1380 |
|
|
*
|
1381 |
|
|
* @return the estimated number of threads waiting to acquire
|
1382 |
|
|
*/
|
1383 |
|
|
public final int getQueueLength() {
|
1384 |
|
|
int n = 0;
|
1385 |
|
|
for (Node p = tail; p != null; p = p.prev) {
|
1386 |
|
|
if (p.thread != null)
|
1387 |
|
|
++n;
|
1388 |
|
|
}
|
1389 |
|
|
return n;
|
1390 |
|
|
}
|
1391 |
|
|
|
1392 |
|
|
/**
|
1393 |
|
|
* Returns a collection containing threads that may be waiting to
|
1394 |
|
|
* acquire. Because the actual set of threads may change
|
1395 |
|
|
* dynamically while constructing this result, the returned
|
1396 |
|
|
* collection is only a best-effort estimate. The elements of the
|
1397 |
|
|
* returned collection are in no particular order. This method is
|
1398 |
|
|
* designed to facilitate construction of subclasses that provide
|
1399 |
|
|
* more extensive monitoring facilities.
|
1400 |
|
|
*
|
1401 |
|
|
* @return the collection of threads
|
1402 |
|
|
*/
|
1403 |
|
|
public final Collection<Thread> getQueuedThreads() {
|
1404 |
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
1405 |
|
|
for (Node p = tail; p != null; p = p.prev) {
|
1406 |
|
|
Thread t = p.thread;
|
1407 |
|
|
if (t != null)
|
1408 |
|
|
list.add(t);
|
1409 |
|
|
}
|
1410 |
|
|
return list;
|
1411 |
|
|
}
|
1412 |
|
|
|
1413 |
|
|
/**
|
1414 |
|
|
* Returns a collection containing threads that may be waiting to
|
1415 |
|
|
* acquire in exclusive mode. This has the same properties
|
1416 |
|
|
* as {@link #getQueuedThreads} except that it only returns
|
1417 |
|
|
* those threads waiting due to an exclusive acquire.
|
1418 |
|
|
*
|
1419 |
|
|
* @return the collection of threads
|
1420 |
|
|
*/
|
1421 |
|
|
public final Collection<Thread> getExclusiveQueuedThreads() {
|
1422 |
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
1423 |
|
|
for (Node p = tail; p != null; p = p.prev) {
|
1424 |
|
|
if (!p.isShared()) {
|
1425 |
|
|
Thread t = p.thread;
|
1426 |
|
|
if (t != null)
|
1427 |
|
|
list.add(t);
|
1428 |
|
|
}
|
1429 |
|
|
}
|
1430 |
|
|
return list;
|
1431 |
|
|
}
|
1432 |
|
|
|
1433 |
|
|
/**
|
1434 |
|
|
* Returns a collection containing threads that may be waiting to
|
1435 |
|
|
* acquire in shared mode. This has the same properties
|
1436 |
|
|
* as {@link #getQueuedThreads} except that it only returns
|
1437 |
|
|
* those threads waiting due to a shared acquire.
|
1438 |
|
|
*
|
1439 |
|
|
* @return the collection of threads
|
1440 |
|
|
*/
|
1441 |
|
|
public final Collection<Thread> getSharedQueuedThreads() {
|
1442 |
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
1443 |
|
|
for (Node p = tail; p != null; p = p.prev) {
|
1444 |
|
|
if (p.isShared()) {
|
1445 |
|
|
Thread t = p.thread;
|
1446 |
|
|
if (t != null)
|
1447 |
|
|
list.add(t);
|
1448 |
|
|
}
|
1449 |
|
|
}
|
1450 |
|
|
return list;
|
1451 |
|
|
}
|
1452 |
|
|
|
1453 |
|
|
/**
|
1454 |
|
|
* Returns a string identifying this synchronizer, as well as its state.
|
1455 |
|
|
* The state, in brackets, includes the String {@code "State ="}
|
1456 |
|
|
* followed by the current value of {@link #getState}, and either
|
1457 |
|
|
* {@code "nonempty"} or {@code "empty"} depending on whether the
|
1458 |
|
|
* queue is empty.
|
1459 |
|
|
*
|
1460 |
|
|
* @return a string identifying this synchronizer, as well as its state
|
1461 |
|
|
*/
|
1462 |
|
|
public String toString() {
|
1463 |
|
|
int s = getState();
|
1464 |
|
|
String q = hasQueuedThreads()? "non" : "";
|
1465 |
|
|
return super.toString() +
|
1466 |
|
|
"[State = " + s + ", " + q + "empty queue]";
|
1467 |
|
|
}
|
1468 |
|
|
|
1469 |
|
|
|
1470 |
|
|
// Internal support methods for Conditions
|
1471 |
|
|
|
1472 |
|
|
/**
|
1473 |
|
|
* Returns true if a node, always one that was initially placed on
|
1474 |
|
|
* a condition queue, is now waiting to reacquire on sync queue.
|
1475 |
|
|
* @param node the node
|
1476 |
|
|
* @return true if is reacquiring
|
1477 |
|
|
*/
|
1478 |
|
|
final boolean isOnSyncQueue(Node node) {
|
1479 |
|
|
if (node.waitStatus == Node.CONDITION || node.prev == null)
|
1480 |
|
|
return false;
|
1481 |
|
|
if (node.next != null) // If has successor, it must be on queue
|
1482 |
|
|
return true;
|
1483 |
|
|
/*
|
1484 |
|
|
* node.prev can be non-null, but not yet on queue because
|
1485 |
|
|
* the CAS to place it on queue can fail. So we have to
|
1486 |
|
|
* traverse from tail to make sure it actually made it. It
|
1487 |
|
|
* will always be near the tail in calls to this method, and
|
1488 |
|
|
* unless the CAS failed (which is unlikely), it will be
|
1489 |
|
|
* there, so we hardly ever traverse much.
|
1490 |
|
|
*/
|
1491 |
|
|
return findNodeFromTail(node);
|
1492 |
|
|
}
|
1493 |
|
|
|
1494 |
|
|
/**
|
1495 |
|
|
* Returns true if node is on sync queue by searching backwards from tail.
|
1496 |
|
|
* Called only when needed by isOnSyncQueue.
|
1497 |
|
|
* @return true if present
|
1498 |
|
|
*/
|
1499 |
|
|
private boolean findNodeFromTail(Node node) {
|
1500 |
|
|
Node t = tail;
|
1501 |
|
|
for (;;) {
|
1502 |
|
|
if (t == node)
|
1503 |
|
|
return true;
|
1504 |
|
|
if (t == null)
|
1505 |
|
|
return false;
|
1506 |
|
|
t = t.prev;
|
1507 |
|
|
}
|
1508 |
|
|
}
|
1509 |
|
|
|
1510 |
|
|
/**
|
1511 |
|
|
* Transfers a node from a condition queue onto sync queue.
|
1512 |
|
|
* Returns true if successful.
|
1513 |
|
|
* @param node the node
|
1514 |
|
|
* @return true if successfully transferred (else the node was
|
1515 |
|
|
* cancelled before signal).
|
1516 |
|
|
*/
|
1517 |
|
|
final boolean transferForSignal(Node node) {
|
1518 |
|
|
/*
|
1519 |
|
|
* If cannot change waitStatus, the node has been cancelled.
|
1520 |
|
|
*/
|
1521 |
|
|
if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
|
1522 |
|
|
return false;
|
1523 |
|
|
|
1524 |
|
|
/*
|
1525 |
|
|
* Splice onto queue and try to set waitStatus of predecessor to
|
1526 |
|
|
* indicate that thread is (probably) waiting. If cancelled or
|
1527 |
|
|
* attempt to set waitStatus fails, wake up to resync (in which
|
1528 |
|
|
* case the waitStatus can be transiently and harmlessly wrong).
|
1529 |
|
|
*/
|
1530 |
|
|
Node p = enq(node);
|
1531 |
|
|
int c = p.waitStatus;
|
1532 |
|
|
if (c > 0 || !compareAndSetWaitStatus(p, c, Node.SIGNAL))
|
1533 |
|
|
LockSupport.unpark(node.thread);
|
1534 |
|
|
return true;
|
1535 |
|
|
}
|
1536 |
|
|
|
1537 |
|
|
/**
|
1538 |
|
|
* Transfers node, if necessary, to sync queue after a cancelled
|
1539 |
|
|
* wait. Returns true if thread was cancelled before being
|
1540 |
|
|
* signalled.
|
1541 |
|
|
* @param current the waiting thread
|
1542 |
|
|
* @param node its node
|
1543 |
|
|
* @return true if cancelled before the node was signalled.
|
1544 |
|
|
*/
|
1545 |
|
|
final boolean transferAfterCancelledWait(Node node) {
|
1546 |
|
|
if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
|
1547 |
|
|
enq(node);
|
1548 |
|
|
return true;
|
1549 |
|
|
}
|
1550 |
|
|
/*
|
1551 |
|
|
* If we lost out to a signal(), then we can't proceed
|
1552 |
|
|
* until it finishes its enq(). Cancelling during an
|
1553 |
|
|
* incomplete transfer is both rare and transient, so just
|
1554 |
|
|
* spin.
|
1555 |
|
|
*/
|
1556 |
|
|
while (!isOnSyncQueue(node))
|
1557 |
|
|
Thread.yield();
|
1558 |
|
|
return false;
|
1559 |
|
|
}
|
1560 |
|
|
|
1561 |
|
|
/**
|
1562 |
|
|
* Invokes release with current state value; returns saved state.
|
1563 |
|
|
* Cancels node and throws exception on failure.
|
1564 |
|
|
* @param node the condition node for this wait
|
1565 |
|
|
* @return previous sync state
|
1566 |
|
|
*/
|
1567 |
|
|
final int fullyRelease(Node node) {
|
1568 |
|
|
try {
|
1569 |
|
|
int savedState = getState();
|
1570 |
|
|
if (release(savedState))
|
1571 |
|
|
return savedState;
|
1572 |
|
|
} catch (RuntimeException ex) {
|
1573 |
|
|
node.waitStatus = Node.CANCELLED;
|
1574 |
|
|
throw ex;
|
1575 |
|
|
}
|
1576 |
|
|
// reach here if release fails
|
1577 |
|
|
node.waitStatus = Node.CANCELLED;
|
1578 |
|
|
throw new IllegalMonitorStateException();
|
1579 |
|
|
}
|
1580 |
|
|
|
1581 |
|
|
// Instrumentation methods for conditions
|
1582 |
|
|
|
1583 |
|
|
/**
|
1584 |
|
|
* Queries whether the given ConditionObject
|
1585 |
|
|
* uses this synchronizer as its lock.
|
1586 |
|
|
*
|
1587 |
|
|
* @param condition the condition
|
1588 |
|
|
* @return <tt>true</tt> if owned
|
1589 |
|
|
* @throws NullPointerException if the condition is null
|
1590 |
|
|
*/
|
1591 |
|
|
public final boolean owns(ConditionObject condition) {
|
1592 |
|
|
if (condition == null)
|
1593 |
|
|
throw new NullPointerException();
|
1594 |
|
|
return condition.isOwnedBy(this);
|
1595 |
|
|
}
|
1596 |
|
|
|
1597 |
|
|
/**
|
1598 |
|
|
* Queries whether any threads are waiting on the given condition
|
1599 |
|
|
* associated with this synchronizer. Note that because timeouts
|
1600 |
|
|
* and interrupts may occur at any time, a <tt>true</tt> return
|
1601 |
|
|
* does not guarantee that a future <tt>signal</tt> will awaken
|
1602 |
|
|
* any threads. This method is designed primarily for use in
|
1603 |
|
|
* monitoring of the system state.
|
1604 |
|
|
*
|
1605 |
|
|
* @param condition the condition
|
1606 |
|
|
* @return <tt>true</tt> if there are any waiting threads
|
1607 |
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
1608 |
|
|
* is not held
|
1609 |
|
|
* @throws IllegalArgumentException if the given condition is
|
1610 |
|
|
* not associated with this synchronizer
|
1611 |
|
|
* @throws NullPointerException if the condition is null
|
1612 |
|
|
*/
|
1613 |
|
|
public final boolean hasWaiters(ConditionObject condition) {
|
1614 |
|
|
if (!owns(condition))
|
1615 |
|
|
throw new IllegalArgumentException("Not owner");
|
1616 |
|
|
return condition.hasWaiters();
|
1617 |
|
|
}
|
1618 |
|
|
|
1619 |
|
|
/**
|
1620 |
|
|
* Returns an estimate of the number of threads waiting on the
|
1621 |
|
|
* given condition associated with this synchronizer. Note that
|
1622 |
|
|
* because timeouts and interrupts may occur at any time, the
|
1623 |
|
|
* estimate serves only as an upper bound on the actual number of
|
1624 |
|
|
* waiters. This method is designed for use in monitoring of the
|
1625 |
|
|
* system state, not for synchronization control.
|
1626 |
|
|
*
|
1627 |
|
|
* @param condition the condition
|
1628 |
|
|
* @return the estimated number of waiting threads
|
1629 |
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
1630 |
|
|
* is not held
|
1631 |
|
|
* @throws IllegalArgumentException if the given condition is
|
1632 |
|
|
* not associated with this synchronizer
|
1633 |
|
|
* @throws NullPointerException if the condition is null
|
1634 |
|
|
*/
|
1635 |
|
|
public final int getWaitQueueLength(ConditionObject condition) {
|
1636 |
|
|
if (!owns(condition))
|
1637 |
|
|
throw new IllegalArgumentException("Not owner");
|
1638 |
|
|
return condition.getWaitQueueLength();
|
1639 |
|
|
}
|
1640 |
|
|
|
1641 |
|
|
/**
|
1642 |
|
|
* Returns a collection containing those threads that may be
|
1643 |
|
|
* waiting on the given condition associated with this
|
1644 |
|
|
* synchronizer. Because the actual set of threads may change
|
1645 |
|
|
* dynamically while constructing this result, the returned
|
1646 |
|
|
* collection is only a best-effort estimate. The elements of the
|
1647 |
|
|
* returned collection are in no particular order.
|
1648 |
|
|
*
|
1649 |
|
|
* @param condition the condition
|
1650 |
|
|
* @return the collection of threads
|
1651 |
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
1652 |
|
|
* is not held
|
1653 |
|
|
* @throws IllegalArgumentException if the given condition is
|
1654 |
|
|
* not associated with this synchronizer
|
1655 |
|
|
* @throws NullPointerException if the condition is null
|
1656 |
|
|
*/
|
1657 |
|
|
public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
|
1658 |
|
|
if (!owns(condition))
|
1659 |
|
|
throw new IllegalArgumentException("Not owner");
|
1660 |
|
|
return condition.getWaitingThreads();
|
1661 |
|
|
}
|
1662 |
|
|
|
1663 |
|
|
/**
|
1664 |
|
|
* Condition implementation for a {@link
|
1665 |
|
|
* AbstractQueuedSynchronizer} serving as the basis of a {@link
|
1666 |
|
|
* Lock} implementation.
|
1667 |
|
|
*
|
1668 |
|
|
* <p>Method documentation for this class describes mechanics,
|
1669 |
|
|
* not behavioral specifications from the point of view of Lock
|
1670 |
|
|
* and Condition users. Exported versions of this class will in
|
1671 |
|
|
* general need to be accompanied by documentation describing
|
1672 |
|
|
* condition semantics that rely on those of the associated
|
1673 |
|
|
* <tt>AbstractQueuedSynchronizer</tt>.
|
1674 |
|
|
*
|
1675 |
|
|
* <p>This class is Serializable, but all fields are transient,
|
1676 |
|
|
* so deserialized conditions have no waiters.
|
1677 |
|
|
*/
|
1678 |
|
|
public class ConditionObject implements Condition, java.io.Serializable {
|
1679 |
|
|
private static final long serialVersionUID = 1173984872572414699L;
|
1680 |
|
|
/** First node of condition queue. */
|
1681 |
|
|
private transient Node firstWaiter;
|
1682 |
|
|
/** Last node of condition queue. */
|
1683 |
|
|
private transient Node lastWaiter;
|
1684 |
|
|
|
1685 |
|
|
/**
|
1686 |
|
|
* Creates a new <tt>ConditionObject</tt> instance.
|
1687 |
|
|
*/
|
1688 |
|
|
public ConditionObject() { }
|
1689 |
|
|
|
1690 |
|
|
// Internal methods
|
1691 |
|
|
|
1692 |
|
|
/**
|
1693 |
|
|
* Adds a new waiter to wait queue.
|
1694 |
|
|
* @return its new wait node
|
1695 |
|
|
*/
|
1696 |
|
|
private Node addConditionWaiter() {
|
1697 |
|
|
Node node = new Node(Thread.currentThread(), Node.CONDITION);
|
1698 |
|
|
Node t = lastWaiter;
|
1699 |
|
|
if (t == null)
|
1700 |
|
|
firstWaiter = node;
|
1701 |
|
|
else
|
1702 |
|
|
t.nextWaiter = node;
|
1703 |
|
|
lastWaiter = node;
|
1704 |
|
|
return node;
|
1705 |
|
|
}
|
1706 |
|
|
|
1707 |
|
|
/**
|
1708 |
|
|
* Removes and transfers nodes until hit non-cancelled one or
|
1709 |
|
|
* null. Split out from signal in part to encourage compilers
|
1710 |
|
|
* to inline the case of no waiters.
|
1711 |
|
|
* @param first (non-null) the first node on condition queue
|
1712 |
|
|
*/
|
1713 |
|
|
private void doSignal(Node first) {
|
1714 |
|
|
do {
|
1715 |
|
|
if ( (firstWaiter = first.nextWaiter) == null)
|
1716 |
|
|
lastWaiter = null;
|
1717 |
|
|
first.nextWaiter = null;
|
1718 |
|
|
} while (!transferForSignal(first) &&
|
1719 |
|
|
(first = firstWaiter) != null);
|
1720 |
|
|
}
|
1721 |
|
|
|
1722 |
|
|
/**
|
1723 |
|
|
* Removes and transfers all nodes.
|
1724 |
|
|
* @param first (non-null) the first node on condition queue
|
1725 |
|
|
*/
|
1726 |
|
|
private void doSignalAll(Node first) {
|
1727 |
|
|
lastWaiter = firstWaiter = null;
|
1728 |
|
|
do {
|
1729 |
|
|
Node next = first.nextWaiter;
|
1730 |
|
|
first.nextWaiter = null;
|
1731 |
|
|
transferForSignal(first);
|
1732 |
|
|
first = next;
|
1733 |
|
|
} while (first != null);
|
1734 |
|
|
}
|
1735 |
|
|
|
1736 |
|
|
/**
|
1737 |
|
|
* Returns true if given node is on this condition queue.
|
1738 |
|
|
* Call only when holding lock.
|
1739 |
|
|
*/
|
1740 |
|
|
private boolean isOnConditionQueue(Node node) {
|
1741 |
|
|
return node.next != null || node == lastWaiter;
|
1742 |
|
|
}
|
1743 |
|
|
|
1744 |
|
|
/**
|
1745 |
|
|
* Unlinks a cancelled waiter node from condition queue. This
|
1746 |
|
|
* is called when cancellation occurred during condition wait,
|
1747 |
|
|
* not lock wait, and is called only after lock has been
|
1748 |
|
|
* re-acquired by a cancelled waiter and the node is not known
|
1749 |
|
|
* to already have been dequeued. It is needed to avoid
|
1750 |
|
|
* garbage retention in the absence of signals. So even though
|
1751 |
|
|
* it may require a full traversal, it comes into play only
|
1752 |
|
|
* when timeouts or cancellations occur in the absence of
|
1753 |
|
|
* signals.
|
1754 |
|
|
*/
|
1755 |
|
|
private void unlinkCancelledWaiter(Node node) {
|
1756 |
|
|
Node t = firstWaiter;
|
1757 |
|
|
Node trail = null;
|
1758 |
|
|
while (t != null) {
|
1759 |
|
|
if (t == node) {
|
1760 |
|
|
Node next = t.nextWaiter;
|
1761 |
|
|
if (trail == null)
|
1762 |
|
|
firstWaiter = next;
|
1763 |
|
|
else
|
1764 |
|
|
trail.nextWaiter = next;
|
1765 |
|
|
if (lastWaiter == node)
|
1766 |
|
|
lastWaiter = trail;
|
1767 |
|
|
break;
|
1768 |
|
|
}
|
1769 |
|
|
trail = t;
|
1770 |
|
|
t = t.nextWaiter;
|
1771 |
|
|
}
|
1772 |
|
|
}
|
1773 |
|
|
|
1774 |
|
|
// public methods
|
1775 |
|
|
|
1776 |
|
|
/**
|
1777 |
|
|
* Moves the longest-waiting thread, if one exists, from the
|
1778 |
|
|
* wait queue for this condition to the wait queue for the
|
1779 |
|
|
* owning lock.
|
1780 |
|
|
*
|
1781 |
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
1782 |
|
|
* returns {@code false}
|
1783 |
|
|
*/
|
1784 |
|
|
public final void signal() {
|
1785 |
|
|
if (!isHeldExclusively())
|
1786 |
|
|
throw new IllegalMonitorStateException();
|
1787 |
|
|
Node first = firstWaiter;
|
1788 |
|
|
if (first != null)
|
1789 |
|
|
doSignal(first);
|
1790 |
|
|
}
|
1791 |
|
|
|
1792 |
|
|
/**
|
1793 |
|
|
* Moves all threads from the wait queue for this condition to
|
1794 |
|
|
* the wait queue for the owning lock.
|
1795 |
|
|
*
|
1796 |
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
1797 |
|
|
* returns {@code false}
|
1798 |
|
|
*/
|
1799 |
|
|
public final void signalAll() {
|
1800 |
|
|
if (!isHeldExclusively())
|
1801 |
|
|
throw new IllegalMonitorStateException();
|
1802 |
|
|
Node first = firstWaiter;
|
1803 |
|
|
if (first != null)
|
1804 |
|
|
doSignalAll(first);
|
1805 |
|
|
}
|
1806 |
|
|
|
1807 |
|
|
/**
|
1808 |
|
|
* Implements uninterruptible condition wait.
|
1809 |
|
|
* <ol>
|
1810 |
|
|
* <li> Save lock state returned by {@link #getState}
|
1811 |
|
|
* <li> Invoke {@link #release} with
|
1812 |
|
|
* saved state as argument, throwing
|
1813 |
|
|
* IllegalMonitorStateException if it fails.
|
1814 |
|
|
* <li> Block until signalled
|
1815 |
|
|
* <li> Reacquire by invoking specialized version of
|
1816 |
|
|
* {@link #acquire} with saved state as argument.
|
1817 |
|
|
* </ol>
|
1818 |
|
|
*/
|
1819 |
|
|
public final void awaitUninterruptibly() {
|
1820 |
|
|
Node node = addConditionWaiter();
|
1821 |
|
|
int savedState = fullyRelease(node);
|
1822 |
|
|
boolean interrupted = false;
|
1823 |
|
|
while (!isOnSyncQueue(node)) {
|
1824 |
|
|
LockSupport.park(this);
|
1825 |
|
|
if (Thread.interrupted())
|
1826 |
|
|
interrupted = true;
|
1827 |
|
|
}
|
1828 |
|
|
if (acquireQueued(node, savedState) || interrupted)
|
1829 |
|
|
selfInterrupt();
|
1830 |
|
|
}
|
1831 |
|
|
|
1832 |
|
|
/*
|
1833 |
|
|
* For interruptible waits, we need to track whether to throw
|
1834 |
|
|
* InterruptedException, if interrupted while blocked on
|
1835 |
|
|
* condition, versus reinterrupt current thread, if
|
1836 |
|
|
* interrupted while blocked waiting to re-acquire.
|
1837 |
|
|
*/
|
1838 |
|
|
|
1839 |
|
|
/** Mode meaning to reinterrupt on exit from wait */
|
1840 |
|
|
private static final int REINTERRUPT = 1;
|
1841 |
|
|
/** Mode meaning to throw InterruptedException on exit from wait */
|
1842 |
|
|
private static final int THROW_IE = -1;
|
1843 |
|
|
|
1844 |
|
|
/**
|
1845 |
|
|
* Checks for interrupt, returning THROW_IE if interrupted
|
1846 |
|
|
* before signalled, REINTERRUPT if after signalled, or
|
1847 |
|
|
* 0 if not interrupted.
|
1848 |
|
|
*/
|
1849 |
|
|
private int checkInterruptWhileWaiting(Node node) {
|
1850 |
|
|
return (Thread.interrupted()) ?
|
1851 |
|
|
((transferAfterCancelledWait(node))? THROW_IE : REINTERRUPT) :
|
1852 |
|
|
0;
|
1853 |
|
|
}
|
1854 |
|
|
|
1855 |
|
|
/**
|
1856 |
|
|
* Throws InterruptedException, reinterrupts current thread, or
|
1857 |
|
|
* does nothing, depending on mode.
|
1858 |
|
|
*/
|
1859 |
|
|
private void reportInterruptAfterWait(int interruptMode)
|
1860 |
|
|
throws InterruptedException {
|
1861 |
|
|
if (interruptMode == THROW_IE)
|
1862 |
|
|
throw new InterruptedException();
|
1863 |
|
|
else if (interruptMode == REINTERRUPT)
|
1864 |
|
|
selfInterrupt();
|
1865 |
|
|
}
|
1866 |
|
|
|
1867 |
|
|
/**
|
1868 |
|
|
* Implements interruptible condition wait.
|
1869 |
|
|
* <ol>
|
1870 |
|
|
* <li> If current thread is interrupted, throw InterruptedException
|
1871 |
|
|
* <li> Save lock state returned by {@link #getState}
|
1872 |
|
|
* <li> Invoke {@link #release} with
|
1873 |
|
|
* saved state as argument, throwing
|
1874 |
|
|
* IllegalMonitorStateException if it fails.
|
1875 |
|
|
* <li> Block until signalled or interrupted
|
1876 |
|
|
* <li> Reacquire by invoking specialized version of
|
1877 |
|
|
* {@link #acquire} with saved state as argument.
|
1878 |
|
|
* <li> If interrupted while blocked in step 4, throw exception
|
1879 |
|
|
* </ol>
|
1880 |
|
|
*/
|
1881 |
|
|
public final void await() throws InterruptedException {
|
1882 |
|
|
if (Thread.interrupted())
|
1883 |
|
|
throw new InterruptedException();
|
1884 |
|
|
Node node = addConditionWaiter();
|
1885 |
|
|
int savedState = fullyRelease(node);
|
1886 |
|
|
int interruptMode = 0;
|
1887 |
|
|
while (!isOnSyncQueue(node)) {
|
1888 |
|
|
LockSupport.park(this);
|
1889 |
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
1890 |
|
|
break;
|
1891 |
|
|
}
|
1892 |
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
1893 |
|
|
interruptMode = REINTERRUPT;
|
1894 |
|
|
if (isOnConditionQueue(node))
|
1895 |
|
|
unlinkCancelledWaiter(node);
|
1896 |
|
|
if (interruptMode != 0)
|
1897 |
|
|
reportInterruptAfterWait(interruptMode);
|
1898 |
|
|
}
|
1899 |
|
|
|
1900 |
|
|
/**
|
1901 |
|
|
* Implements timed condition wait.
|
1902 |
|
|
* <ol>
|
1903 |
|
|
* <li> If current thread is interrupted, throw InterruptedException
|
1904 |
|
|
* <li> Save lock state returned by {@link #getState}
|
1905 |
|
|
* <li> Invoke {@link #release} with
|
1906 |
|
|
* saved state as argument, throwing
|
1907 |
|
|
* IllegalMonitorStateException if it fails.
|
1908 |
|
|
* <li> Block until signalled, interrupted, or timed out
|
1909 |
|
|
* <li> Reacquire by invoking specialized version of
|
1910 |
|
|
* {@link #acquire} with saved state as argument.
|
1911 |
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException
|
1912 |
|
|
* </ol>
|
1913 |
|
|
*/
|
1914 |
|
|
public final long awaitNanos(long nanosTimeout) throws InterruptedException {
|
1915 |
|
|
if (Thread.interrupted())
|
1916 |
|
|
throw new InterruptedException();
|
1917 |
|
|
Node node = addConditionWaiter();
|
1918 |
|
|
int savedState = fullyRelease(node);
|
1919 |
|
|
long lastTime = System.nanoTime();
|
1920 |
|
|
int interruptMode = 0;
|
1921 |
|
|
while (!isOnSyncQueue(node)) {
|
1922 |
|
|
if (nanosTimeout <= 0L) {
|
1923 |
|
|
transferAfterCancelledWait(node);
|
1924 |
|
|
break;
|
1925 |
|
|
}
|
1926 |
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
1927 |
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
1928 |
|
|
break;
|
1929 |
|
|
|
1930 |
|
|
long now = System.nanoTime();
|
1931 |
|
|
nanosTimeout -= now - lastTime;
|
1932 |
|
|
lastTime = now;
|
1933 |
|
|
}
|
1934 |
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
1935 |
|
|
interruptMode = REINTERRUPT;
|
1936 |
|
|
if (isOnConditionQueue(node))
|
1937 |
|
|
unlinkCancelledWaiter(node);
|
1938 |
|
|
if (interruptMode != 0)
|
1939 |
|
|
reportInterruptAfterWait(interruptMode);
|
1940 |
|
|
return nanosTimeout - (System.nanoTime() - lastTime);
|
1941 |
|
|
}
|
1942 |
|
|
|
1943 |
|
|
/**
|
1944 |
|
|
* Implements absolute timed condition wait.
|
1945 |
|
|
* <ol>
|
1946 |
|
|
* <li> If current thread is interrupted, throw InterruptedException
|
1947 |
|
|
* <li> Save lock state returned by {@link #getState}
|
1948 |
|
|
* <li> Invoke {@link #release} with
|
1949 |
|
|
* saved state as argument, throwing
|
1950 |
|
|
* IllegalMonitorStateException if it fails.
|
1951 |
|
|
* <li> Block until signalled, interrupted, or timed out
|
1952 |
|
|
* <li> Reacquire by invoking specialized version of
|
1953 |
|
|
* {@link #acquire} with saved state as argument.
|
1954 |
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException
|
1955 |
|
|
* <li> If timed out while blocked in step 4, return false, else true
|
1956 |
|
|
* </ol>
|
1957 |
|
|
*/
|
1958 |
|
|
public final boolean awaitUntil(Date deadline) throws InterruptedException {
|
1959 |
|
|
if (deadline == null)
|
1960 |
|
|
throw new NullPointerException();
|
1961 |
|
|
long abstime = deadline.getTime();
|
1962 |
|
|
if (Thread.interrupted())
|
1963 |
|
|
throw new InterruptedException();
|
1964 |
|
|
Node node = addConditionWaiter();
|
1965 |
|
|
int savedState = fullyRelease(node);
|
1966 |
|
|
boolean timedout = false;
|
1967 |
|
|
int interruptMode = 0;
|
1968 |
|
|
while (!isOnSyncQueue(node)) {
|
1969 |
|
|
if (System.currentTimeMillis() > abstime) {
|
1970 |
|
|
timedout = transferAfterCancelledWait(node);
|
1971 |
|
|
break;
|
1972 |
|
|
}
|
1973 |
|
|
LockSupport.parkUntil(this, abstime);
|
1974 |
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
1975 |
|
|
break;
|
1976 |
|
|
}
|
1977 |
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
1978 |
|
|
interruptMode = REINTERRUPT;
|
1979 |
|
|
if (isOnConditionQueue(node))
|
1980 |
|
|
unlinkCancelledWaiter(node);
|
1981 |
|
|
if (interruptMode != 0)
|
1982 |
|
|
reportInterruptAfterWait(interruptMode);
|
1983 |
|
|
return !timedout;
|
1984 |
|
|
}
|
1985 |
|
|
|
1986 |
|
|
/**
|
1987 |
|
|
* Implements timed condition wait.
|
1988 |
|
|
* <ol>
|
1989 |
|
|
* <li> If current thread is interrupted, throw InterruptedException
|
1990 |
|
|
* <li> Save lock state returned by {@link #getState}
|
1991 |
|
|
* <li> Invoke {@link #release} with
|
1992 |
|
|
* saved state as argument, throwing
|
1993 |
|
|
* IllegalMonitorStateException if it fails.
|
1994 |
|
|
* <li> Block until signalled, interrupted, or timed out
|
1995 |
|
|
* <li> Reacquire by invoking specialized version of
|
1996 |
|
|
* {@link #acquire} with saved state as argument.
|
1997 |
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException
|
1998 |
|
|
* <li> If timed out while blocked in step 4, return false, else true
|
1999 |
|
|
* </ol>
|
2000 |
|
|
*/
|
2001 |
|
|
public final boolean await(long time, TimeUnit unit) throws InterruptedException {
|
2002 |
|
|
if (unit == null)
|
2003 |
|
|
throw new NullPointerException();
|
2004 |
|
|
long nanosTimeout = unit.toNanos(time);
|
2005 |
|
|
if (Thread.interrupted())
|
2006 |
|
|
throw new InterruptedException();
|
2007 |
|
|
Node node = addConditionWaiter();
|
2008 |
|
|
int savedState = fullyRelease(node);
|
2009 |
|
|
long lastTime = System.nanoTime();
|
2010 |
|
|
boolean timedout = false;
|
2011 |
|
|
int interruptMode = 0;
|
2012 |
|
|
while (!isOnSyncQueue(node)) {
|
2013 |
|
|
if (nanosTimeout <= 0L) {
|
2014 |
|
|
timedout = transferAfterCancelledWait(node);
|
2015 |
|
|
break;
|
2016 |
|
|
}
|
2017 |
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
2018 |
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
2019 |
|
|
break;
|
2020 |
|
|
long now = System.nanoTime();
|
2021 |
|
|
nanosTimeout -= now - lastTime;
|
2022 |
|
|
lastTime = now;
|
2023 |
|
|
}
|
2024 |
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
2025 |
|
|
interruptMode = REINTERRUPT;
|
2026 |
|
|
if (isOnConditionQueue(node))
|
2027 |
|
|
unlinkCancelledWaiter(node);
|
2028 |
|
|
if (interruptMode != 0)
|
2029 |
|
|
reportInterruptAfterWait(interruptMode);
|
2030 |
|
|
return !timedout;
|
2031 |
|
|
}
|
2032 |
|
|
|
2033 |
|
|
// support for instrumentation
|
2034 |
|
|
|
2035 |
|
|
/**
|
2036 |
|
|
* Returns true if this condition was created by the given
|
2037 |
|
|
* synchronization object.
|
2038 |
|
|
*
|
2039 |
|
|
* @return {@code true} if owned
|
2040 |
|
|
*/
|
2041 |
|
|
final boolean isOwnedBy(AbstractQueuedSynchronizer sync) {
|
2042 |
|
|
return sync == AbstractQueuedSynchronizer.this;
|
2043 |
|
|
}
|
2044 |
|
|
|
2045 |
|
|
/**
|
2046 |
|
|
* Queries whether any threads are waiting on this condition.
|
2047 |
|
|
* Implements {@link AbstractQueuedSynchronizer#hasWaiters}.
|
2048 |
|
|
*
|
2049 |
|
|
* @return {@code true} if there are any waiting threads
|
2050 |
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
2051 |
|
|
* returns {@code false}
|
2052 |
|
|
*/
|
2053 |
|
|
protected final boolean hasWaiters() {
|
2054 |
|
|
if (!isHeldExclusively())
|
2055 |
|
|
throw new IllegalMonitorStateException();
|
2056 |
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
2057 |
|
|
if (w.waitStatus == Node.CONDITION)
|
2058 |
|
|
return true;
|
2059 |
|
|
}
|
2060 |
|
|
return false;
|
2061 |
|
|
}
|
2062 |
|
|
|
2063 |
|
|
/**
|
2064 |
|
|
* Returns an estimate of the number of threads waiting on
|
2065 |
|
|
* this condition.
|
2066 |
|
|
* Implements {@link AbstractQueuedSynchronizer#getWaitQueueLength}.
|
2067 |
|
|
*
|
2068 |
|
|
* @return the estimated number of waiting threads
|
2069 |
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
2070 |
|
|
* returns {@code false}
|
2071 |
|
|
*/
|
2072 |
|
|
protected final int getWaitQueueLength() {
|
2073 |
|
|
if (!isHeldExclusively())
|
2074 |
|
|
throw new IllegalMonitorStateException();
|
2075 |
|
|
int n = 0;
|
2076 |
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
2077 |
|
|
if (w.waitStatus == Node.CONDITION)
|
2078 |
|
|
++n;
|
2079 |
|
|
}
|
2080 |
|
|
return n;
|
2081 |
|
|
}
|
2082 |
|
|
|
2083 |
|
|
/**
|
2084 |
|
|
* Returns a collection containing those threads that may be
|
2085 |
|
|
* waiting on this Condition.
|
2086 |
|
|
* Implements {@link AbstractQueuedSynchronizer#getWaitingThreads}.
|
2087 |
|
|
*
|
2088 |
|
|
* @return the collection of threads
|
2089 |
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
2090 |
|
|
* returns {@code false}
|
2091 |
|
|
*/
|
2092 |
|
|
protected final Collection<Thread> getWaitingThreads() {
|
2093 |
|
|
if (!isHeldExclusively())
|
2094 |
|
|
throw new IllegalMonitorStateException();
|
2095 |
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
2096 |
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
2097 |
|
|
if (w.waitStatus == Node.CONDITION) {
|
2098 |
|
|
Thread t = w.thread;
|
2099 |
|
|
if (t != null)
|
2100 |
|
|
list.add(t);
|
2101 |
|
|
}
|
2102 |
|
|
}
|
2103 |
|
|
return list;
|
2104 |
|
|
}
|
2105 |
|
|
}
|
2106 |
|
|
|
2107 |
|
|
/**
|
2108 |
|
|
* Setup to support compareAndSet. We need to natively implement
|
2109 |
|
|
* this here: For the sake of permitting future enhancements, we
|
2110 |
|
|
* cannot explicitly subclass AtomicInteger, which would be
|
2111 |
|
|
* efficient and useful otherwise. So, as the lesser of evils, we
|
2112 |
|
|
* natively implement using hotspot intrinsics API. And while we
|
2113 |
|
|
* are at it, we do the same for other CASable fields (which could
|
2114 |
|
|
* otherwise be done with atomic field updaters).
|
2115 |
|
|
*/
|
2116 |
|
|
private static final Unsafe unsafe = Unsafe.getUnsafe();
|
2117 |
|
|
private static final long stateOffset;
|
2118 |
|
|
private static final long headOffset;
|
2119 |
|
|
private static final long tailOffset;
|
2120 |
|
|
private static final long waitStatusOffset;
|
2121 |
|
|
|
2122 |
|
|
static {
|
2123 |
|
|
try {
|
2124 |
|
|
stateOffset = unsafe.objectFieldOffset
|
2125 |
|
|
(AbstractQueuedSynchronizer.class.getDeclaredField("state"));
|
2126 |
|
|
headOffset = unsafe.objectFieldOffset
|
2127 |
|
|
(AbstractQueuedSynchronizer.class.getDeclaredField("head"));
|
2128 |
|
|
tailOffset = unsafe.objectFieldOffset
|
2129 |
|
|
(AbstractQueuedSynchronizer.class.getDeclaredField("tail"));
|
2130 |
|
|
waitStatusOffset = unsafe.objectFieldOffset
|
2131 |
|
|
(Node.class.getDeclaredField("waitStatus"));
|
2132 |
|
|
|
2133 |
|
|
} catch (Exception ex) { throw new Error(ex); }
|
2134 |
|
|
}
|
2135 |
|
|
|
2136 |
|
|
/**
|
2137 |
|
|
* CAS head field. Used only by enq
|
2138 |
|
|
*/
|
2139 |
|
|
private final boolean compareAndSetHead(Node update) {
|
2140 |
|
|
return unsafe.compareAndSwapObject(this, headOffset, null, update);
|
2141 |
|
|
}
|
2142 |
|
|
|
2143 |
|
|
/**
|
2144 |
|
|
* CAS tail field. Used only by enq
|
2145 |
|
|
*/
|
2146 |
|
|
private final boolean compareAndSetTail(Node expect, Node update) {
|
2147 |
|
|
return unsafe.compareAndSwapObject(this, tailOffset, expect, update);
|
2148 |
|
|
}
|
2149 |
|
|
|
2150 |
|
|
/**
|
2151 |
|
|
* CAS waitStatus field of a node.
|
2152 |
|
|
*/
|
2153 |
|
|
private final static boolean compareAndSetWaitStatus(Node node,
|
2154 |
|
|
int expect,
|
2155 |
|
|
int update) {
|
2156 |
|
|
return unsafe.compareAndSwapInt(node, waitStatusOffset,
|
2157 |
|
|
expect, update);
|
2158 |
|
|
}
|
2159 |
|
|
}
|