2300 lines
89 KiB
Java
2300 lines
89 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package 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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/**
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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><a name="barging">Because checks in acquire are invoked before
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* enqueuing, a newly acquiring thread may <em>barge</em> ahead of
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* others that are blocked and queued. However, you can, if desired,
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* define <tt>tryAcquire</tt> and/or <tt>tryAcquireShared</tt> to
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* disable barging by internally invoking one or more of the inspection
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* methods, thereby providing a <em>fair</em> FIFO acquisition order.
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* In particular, most fair synchronizers can define <tt>tryAcquire</tt>
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* to return <tt>false</tt> if {@link #hasQueuedPredecessors} (a method
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* specifically designed to be used by fair synchronizers) returns
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* <tt>true</tt>. Other variations are 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.)
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*
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* <p>Cancellation introduces some conservatism to the basic
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* algorithms. Since we must poll for cancellation of other
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* nodes, we can miss noticing whether a cancelled node is
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* ahead or behind us. This is dealt with by always unparking
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* successors upon cancellation, allowing them to stabilize on
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* a new predecessor, unless we can identify an uncancelled
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* predecessor who will carry this responsibility.
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*
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* <p>CLH queues need a dummy header node to get started. But
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* we don't create them on construction, because it would be wasted
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* effort if there is never contention. Instead, the node
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* is constructed and head and tail pointers are set upon first
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* contention.
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*
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* <p>Threads waiting on Conditions use the same nodes, but
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* use an additional link. Conditions only need to link nodes
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* in simple (non-concurrent) linked queues because they are
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* only accessed when exclusively held. Upon await, a node is
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* inserted into a condition queue. Upon signal, the node is
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* transferred to the main queue. A special value of status
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* field is used to mark which queue a node is on.
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*
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* <p>Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill
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* Scherer and Michael Scott, along with members of JSR-166
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* expert group, for helpful ideas, discussions, and critiques
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* on the design of this class.
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*/
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static final class Node {
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static final AtomicReferenceFieldUpdater<Node, Node> nextUpdater = AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "next");
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/** Marker to indicate a node is waiting in shared mode */
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static final Node SHARED = new Node();
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/** Marker to indicate a node is waiting in exclusive mode */
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static final Node EXCLUSIVE = null;
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/** waitStatus value to indicate thread has cancelled */
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static final int CANCELLED = 1;
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/** waitStatus value to indicate successor's thread needs unparking */
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static final int SIGNAL = -1;
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/** waitStatus value to indicate thread is waiting on condition */
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static final int CONDITION = -2;
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/**
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* waitStatus value to indicate the next acquireShared should
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* unconditionally propagate
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*/
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static final int PROPAGATE = -3;
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/**
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* Status field, taking on only the values:
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* SIGNAL: The successor of this node is (or will soon be)
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* blocked (via park), so the current node must
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* unpark its successor when it releases or
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* cancels. To avoid races, acquire methods must
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* first indicate they need a signal,
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* then retry the atomic acquire, and then,
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* on failure, block.
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* CANCELLED: This node is cancelled due to timeout or interrupt.
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* Nodes never leave this state. In particular,
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* a thread with cancelled node never again blocks.
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* CONDITION: This node is currently on a condition queue.
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* It will not be used as a sync queue node
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* until transferred, at which time the status
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* will be set to 0. (Use of this value here has
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* nothing to do with the other uses of the
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* field, but simplifies mechanics.)
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* PROPAGATE: A releaseShared should be propagated to other
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* nodes. This is set (for head node only) in
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* doReleaseShared to ensure propagation
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* continues, even if other operations have
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* since intervened.
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* 0: None of the above
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*
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* The values are arranged numerically to simplify use.
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* Non-negative values mean that a node doesn't need to
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* signal. So, most code doesn't need to check for particular
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* values, just for sign.
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*
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* The field is initialized to 0 for normal sync nodes, and
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* CONDITION for condition nodes. It is modified using CAS
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* (or when possible, unconditional volatile writes).
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*/
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volatile int waitStatus;
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|
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/**
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* Link to predecessor node that current node/thread relies on
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* for checking waitStatus. Assigned during enqueing, and nulled
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* out (for sake of GC) only upon dequeuing. Also, upon
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* cancellation of a predecessor, we short-circuit while
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* finding a non-cancelled one, which will always exist
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* because the head node is never cancelled: A node becomes
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* head only as a result of successful acquire. A
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* cancelled thread never succeeds in acquiring, and a thread only
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* cancels itself, not any other node.
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*/
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volatile Node prev;
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|
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/**
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* Link to the successor node that the current node/thread
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* unparks upon release. Assigned during enqueuing, adjusted
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* when bypassing cancelled predecessors, and nulled out (for
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* sake of GC) when dequeued. The enq operation does not
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* assign next field of a predecessor until after attachment,
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* so seeing a null next field does not necessarily mean that
|
|
* node is at end of queue. However, if a next field appears
|
|
* to be null, we can scan prev's from the tail to
|
|
* double-check. The next field of cancelled nodes is set to
|
|
* point to the node itself instead of null, to make life
|
|
* easier for isOnSyncQueue.
|
|
*/
|
|
volatile Node next;
|
|
|
|
/**
|
|
* The thread that enqueued this node. Initialized on
|
|
* construction and nulled out after use.
|
|
*/
|
|
volatile Thread thread;
|
|
|
|
/**
|
|
* Link to next node waiting on condition, or the special
|
|
* value SHARED. Because condition queues are accessed only
|
|
* when holding in exclusive mode, we just need a simple
|
|
* linked queue to hold nodes while they are waiting on
|
|
* conditions. They are then transferred to the queue to
|
|
* re-acquire. And because conditions can only be exclusive,
|
|
* we save a field by using special value to indicate shared
|
|
* mode.
|
|
*/
|
|
Node nextWaiter;
|
|
|
|
/**
|
|
* Returns true if node is waiting in shared mode
|
|
*/
|
|
final boolean isShared() {
|
|
return nextWaiter == SHARED;
|
|
}
|
|
|
|
/**
|
|
* Returns previous node, or throws NullPointerException if null.
|
|
* Use when predecessor cannot be null. The null check could
|
|
* be elided, but is present to help the VM.
|
|
*
|
|
* @return the predecessor of this node
|
|
*/
|
|
final Node predecessor() throws NullPointerException {
|
|
Node p = prev;
|
|
if (p == null)
|
|
throw new NullPointerException();
|
|
else
|
|
return p;
|
|
}
|
|
|
|
Node() { // Used to establish initial head or SHARED marker
|
|
}
|
|
|
|
Node(Thread thread, Node mode) { // Used by addWaiter
|
|
this.nextWaiter = mode;
|
|
this.thread = thread;
|
|
}
|
|
|
|
Node(Thread thread, int waitStatus) { // Used by Condition
|
|
this.waitStatus = waitStatus;
|
|
this.thread = thread;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Head of the wait queue, lazily initialized. Except for
|
|
* initialization, it is modified only via method setHead. Note:
|
|
* If head exists, its waitStatus is guaranteed not to be
|
|
* CANCELLED.
|
|
*/
|
|
private transient volatile Node head;
|
|
|
|
/**
|
|
* Tail of the wait queue, lazily initialized. Modified only via
|
|
* method enq to add new wait node.
|
|
*/
|
|
private transient volatile Node tail;
|
|
|
|
/**
|
|
* The synchronization state.
|
|
*/
|
|
private volatile int state;
|
|
|
|
/**
|
|
* Returns the current value of synchronization state.
|
|
* This operation has memory semantics of a <tt>volatile</tt> read.
|
|
* @return current state value
|
|
*/
|
|
protected final int getState() {
|
|
return state;
|
|
}
|
|
|
|
/**
|
|
* Sets the value of synchronization state.
|
|
* This operation has memory semantics of a <tt>volatile</tt> write.
|
|
* @param newState the new state value
|
|
*/
|
|
protected final void setState(int newState) {
|
|
state = newState;
|
|
}
|
|
|
|
/**
|
|
* Atomically sets synchronization state to the given updated
|
|
* value if the current state value equals the expected value.
|
|
* This operation has memory semantics of a <tt>volatile</tt> read
|
|
* and write.
|
|
*
|
|
* @param expect the expected value
|
|
* @param update the new value
|
|
* @return true if successful. False return indicates that the actual
|
|
* value was not equal to the expected value.
|
|
*/
|
|
protected final native boolean compareAndSetState(int expect, int update); // implemented in map.xml
|
|
|
|
// Queuing utilities
|
|
|
|
/**
|
|
* The number of nanoseconds for which it is faster to spin
|
|
* rather than to use timed park. A rough estimate suffices
|
|
* to improve responsiveness with very short timeouts.
|
|
*/
|
|
static final long spinForTimeoutThreshold = 1000L;
|
|
|
|
/**
|
|
* Inserts node into queue, initializing if necessary. See picture above.
|
|
* @param node the node to insert
|
|
* @return node's predecessor
|
|
*/
|
|
private Node enq(final Node node) {
|
|
for (;;) {
|
|
Node t = tail;
|
|
if (t == null) { // Must initialize
|
|
if (compareAndSetHead(new Node()))
|
|
tail = head;
|
|
} else {
|
|
node.prev = t;
|
|
if (compareAndSetTail(t, node)) {
|
|
t.next = node;
|
|
return t;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Creates and enqueues node for current thread and given mode.
|
|
*
|
|
* @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared
|
|
* @return the new node
|
|
*/
|
|
private Node addWaiter(Node mode) {
|
|
Node node = new Node(Thread.currentThread(), mode);
|
|
// Try the fast path of enq; backup to full enq on failure
|
|
Node pred = tail;
|
|
if (pred != null) {
|
|
node.prev = pred;
|
|
if (compareAndSetTail(pred, node)) {
|
|
pred.next = node;
|
|
return node;
|
|
}
|
|
}
|
|
enq(node);
|
|
return node;
|
|
}
|
|
|
|
/**
|
|
* Sets head of queue to be node, thus dequeuing. Called only by
|
|
* acquire methods. Also nulls out unused fields for sake of GC
|
|
* and to suppress unnecessary signals and traversals.
|
|
*
|
|
* @param node the node
|
|
*/
|
|
private void setHead(Node node) {
|
|
head = node;
|
|
node.thread = null;
|
|
node.prev = null;
|
|
}
|
|
|
|
/**
|
|
* Wakes up node's successor, if one exists.
|
|
*
|
|
* @param node the node
|
|
*/
|
|
private void unparkSuccessor(Node node) {
|
|
/*
|
|
* If status is negative (i.e., possibly needing signal) try
|
|
* to clear in anticipation of signalling. It is OK if this
|
|
* fails or if status is changed by waiting thread.
|
|
*/
|
|
int ws = node.waitStatus;
|
|
if (ws < 0)
|
|
compareAndSetWaitStatus(node, ws, 0);
|
|
|
|
/*
|
|
* Thread to unpark is held in successor, which is normally
|
|
* just the next node. But if cancelled or apparently null,
|
|
* traverse backwards from tail to find the actual
|
|
* non-cancelled successor.
|
|
*/
|
|
Node s = node.next;
|
|
if (s == null || s.waitStatus > 0) {
|
|
s = null;
|
|
for (Node t = tail; t != null && t != node; t = t.prev)
|
|
if (t.waitStatus <= 0)
|
|
s = t;
|
|
}
|
|
if (s != null)
|
|
LockSupport.unpark(s.thread);
|
|
}
|
|
|
|
/**
|
|
* Release action for shared mode -- signal successor and ensure
|
|
* propagation. (Note: For exclusive mode, release just amounts
|
|
* to calling unparkSuccessor of head if it needs signal.)
|
|
*/
|
|
private void doReleaseShared() {
|
|
/*
|
|
* Ensure that a release propagates, even if there are other
|
|
* in-progress acquires/releases. This proceeds in the usual
|
|
* way of trying to unparkSuccessor of head if it needs
|
|
* signal. But if it does not, status is set to PROPAGATE to
|
|
* ensure that upon release, propagation continues.
|
|
* Additionally, we must loop in case a new node is added
|
|
* while we are doing this. Also, unlike other uses of
|
|
* unparkSuccessor, we need to know if CAS to reset status
|
|
* fails, if so rechecking.
|
|
*/
|
|
for (;;) {
|
|
Node h = head;
|
|
if (h != null && h != tail) {
|
|
int ws = h.waitStatus;
|
|
if (ws == Node.SIGNAL) {
|
|
if (!compareAndSetWaitStatus(h, Node.SIGNAL, 0))
|
|
continue; // loop to recheck cases
|
|
unparkSuccessor(h);
|
|
}
|
|
else if (ws == 0 &&
|
|
!compareAndSetWaitStatus(h, 0, Node.PROPAGATE))
|
|
continue; // loop on failed CAS
|
|
}
|
|
if (h == head) // loop if head changed
|
|
break;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Sets head of queue, and checks if successor may be waiting
|
|
* in shared mode, if so propagating if either propagate > 0 or
|
|
* PROPAGATE status was set.
|
|
*
|
|
* @param node the node
|
|
* @param propagate the return value from a tryAcquireShared
|
|
*/
|
|
private void setHeadAndPropagate(Node node, int propagate) {
|
|
Node h = head; // Record old head for check below
|
|
setHead(node);
|
|
/*
|
|
* Try to signal next queued node if:
|
|
* Propagation was indicated by caller,
|
|
* or was recorded (as h.waitStatus) by a previous operation
|
|
* (note: this uses sign-check of waitStatus because
|
|
* PROPAGATE status may transition to SIGNAL.)
|
|
* and
|
|
* The next node is waiting in shared mode,
|
|
* or we don't know, because it appears null
|
|
*
|
|
* The conservatism in both of these checks may cause
|
|
* unnecessary wake-ups, but only when there are multiple
|
|
* racing acquires/releases, so most need signals now or soon
|
|
* anyway.
|
|
*/
|
|
if (propagate > 0 || h == null || h.waitStatus < 0) {
|
|
Node s = node.next;
|
|
if (s == null || s.isShared())
|
|
doReleaseShared();
|
|
}
|
|
}
|
|
|
|
// Utilities for various versions of acquire
|
|
|
|
/**
|
|
* Cancels an ongoing attempt to acquire.
|
|
*
|
|
* @param node the node
|
|
*/
|
|
private void cancelAcquire(Node node) {
|
|
// Ignore if node doesn't exist
|
|
if (node == null)
|
|
return;
|
|
|
|
node.thread = null;
|
|
|
|
// Skip cancelled predecessors
|
|
Node pred = node.prev;
|
|
while (pred.waitStatus > 0)
|
|
node.prev = pred = pred.prev;
|
|
|
|
// predNext is the apparent node to unsplice. CASes below will
|
|
// fail if not, in which case, we lost race vs another cancel
|
|
// or signal, so no further action is necessary.
|
|
Node predNext = pred.next;
|
|
|
|
// Can use unconditional write instead of CAS here.
|
|
// After this atomic step, other Nodes can skip past us.
|
|
// Before, we are free of interference from other threads.
|
|
node.waitStatus = Node.CANCELLED;
|
|
|
|
// If we are the tail, remove ourselves.
|
|
if (node == tail && compareAndSetTail(node, pred)) {
|
|
compareAndSetNext(pred, predNext, null);
|
|
} else {
|
|
// If successor needs signal, try to set pred's next-link
|
|
// so it will get one. Otherwise wake it up to propagate.
|
|
int ws;
|
|
if (pred != head &&
|
|
((ws = pred.waitStatus) == Node.SIGNAL ||
|
|
(ws <= 0 && compareAndSetWaitStatus(pred, ws, Node.SIGNAL))) &&
|
|
pred.thread != null) {
|
|
Node next = node.next;
|
|
if (next != null && next.waitStatus <= 0)
|
|
compareAndSetNext(pred, predNext, next);
|
|
} else {
|
|
unparkSuccessor(node);
|
|
}
|
|
|
|
node.next = node; // help GC
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Checks and updates status for a node that failed to acquire.
|
|
* Returns true if thread should block. This is the main signal
|
|
* control in all acquire loops. Requires that pred == node.prev
|
|
*
|
|
* @param pred node's predecessor holding status
|
|
* @param node the node
|
|
* @return {@code true} if thread should block
|
|
*/
|
|
private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
|
|
int ws = pred.waitStatus;
|
|
if (ws == Node.SIGNAL)
|
|
/*
|
|
* This node has already set status asking a release
|
|
* to signal it, so it can safely park.
|
|
*/
|
|
return true;
|
|
if (ws > 0) {
|
|
/*
|
|
* Predecessor was cancelled. Skip over predecessors and
|
|
* indicate retry.
|
|
*/
|
|
do {
|
|
node.prev = pred = pred.prev;
|
|
} while (pred.waitStatus > 0);
|
|
pred.next = node;
|
|
} else {
|
|
/*
|
|
* waitStatus must be 0 or PROPAGATE. Indicate that we
|
|
* need a signal, but don't park yet. Caller will need to
|
|
* retry to make sure it cannot acquire before parking.
|
|
*/
|
|
compareAndSetWaitStatus(pred, ws, Node.SIGNAL);
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Convenience method to interrupt current thread.
|
|
*/
|
|
private static void selfInterrupt() {
|
|
Thread.currentThread().interrupt();
|
|
}
|
|
|
|
/**
|
|
* Convenience method to park and then check if interrupted
|
|
*
|
|
* @return {@code true} if interrupted
|
|
*/
|
|
private final boolean parkAndCheckInterrupt() {
|
|
LockSupport.park(this);
|
|
return Thread.interrupted();
|
|
}
|
|
|
|
/*
|
|
* Various flavors of acquire, varying in exclusive/shared and
|
|
* control modes. Each is mostly the same, but annoyingly
|
|
* different. Only a little bit of factoring is possible due to
|
|
* interactions of exception mechanics (including ensuring that we
|
|
* cancel if tryAcquire throws exception) and other control, at
|
|
* least not without hurting performance too much.
|
|
*/
|
|
|
|
/**
|
|
* Acquires in exclusive uninterruptible mode for thread already in
|
|
* queue. Used by condition wait methods as well as acquire.
|
|
*
|
|
* @param node the node
|
|
* @param arg the acquire argument
|
|
* @return {@code true} if interrupted while waiting
|
|
*/
|
|
final boolean acquireQueued(final Node node, int arg) {
|
|
boolean failed = true;
|
|
try {
|
|
boolean interrupted = false;
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head && tryAcquire(arg)) {
|
|
setHead(node);
|
|
p.next = null; // help GC
|
|
failed = false;
|
|
return interrupted;
|
|
}
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
parkAndCheckInterrupt())
|
|
interrupted = true;
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive interruptible mode.
|
|
* @param arg the acquire argument
|
|
*/
|
|
private void doAcquireInterruptibly(int arg)
|
|
throws InterruptedException {
|
|
final Node node = addWaiter(Node.EXCLUSIVE);
|
|
boolean failed = true;
|
|
try {
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head && tryAcquire(arg)) {
|
|
setHead(node);
|
|
p.next = null; // help GC
|
|
failed = false;
|
|
return;
|
|
}
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
parkAndCheckInterrupt())
|
|
throw new InterruptedException();
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive timed mode.
|
|
*
|
|
* @param arg the acquire argument
|
|
* @param nanosTimeout max wait time
|
|
* @return {@code true} if acquired
|
|
*/
|
|
private boolean doAcquireNanos(int arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
long lastTime = System.nanoTime();
|
|
final Node node = addWaiter(Node.EXCLUSIVE);
|
|
boolean failed = true;
|
|
try {
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head && tryAcquire(arg)) {
|
|
setHead(node);
|
|
p.next = null; // help GC
|
|
failed = false;
|
|
return true;
|
|
}
|
|
if (nanosTimeout <= 0)
|
|
return false;
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
nanosTimeout > spinForTimeoutThreshold)
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
|
long now = System.nanoTime();
|
|
nanosTimeout -= now - lastTime;
|
|
lastTime = now;
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared uninterruptible mode.
|
|
* @param arg the acquire argument
|
|
*/
|
|
private void doAcquireShared(int arg) {
|
|
final Node node = addWaiter(Node.SHARED);
|
|
boolean failed = true;
|
|
try {
|
|
boolean interrupted = false;
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head) {
|
|
int r = tryAcquireShared(arg);
|
|
if (r >= 0) {
|
|
setHeadAndPropagate(node, r);
|
|
p.next = null; // help GC
|
|
if (interrupted)
|
|
selfInterrupt();
|
|
failed = false;
|
|
return;
|
|
}
|
|
}
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
parkAndCheckInterrupt())
|
|
interrupted = true;
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared interruptible mode.
|
|
* @param arg the acquire argument
|
|
*/
|
|
private void doAcquireSharedInterruptibly(int arg)
|
|
throws InterruptedException {
|
|
final Node node = addWaiter(Node.SHARED);
|
|
boolean failed = true;
|
|
try {
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head) {
|
|
int r = tryAcquireShared(arg);
|
|
if (r >= 0) {
|
|
setHeadAndPropagate(node, r);
|
|
p.next = null; // help GC
|
|
failed = false;
|
|
return;
|
|
}
|
|
}
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
parkAndCheckInterrupt())
|
|
throw new InterruptedException();
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared timed mode.
|
|
*
|
|
* @param arg the acquire argument
|
|
* @param nanosTimeout max wait time
|
|
* @return {@code true} if acquired
|
|
*/
|
|
private boolean doAcquireSharedNanos(int arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
|
|
long lastTime = System.nanoTime();
|
|
final Node node = addWaiter(Node.SHARED);
|
|
boolean failed = true;
|
|
try {
|
|
for (;;) {
|
|
final Node p = node.predecessor();
|
|
if (p == head) {
|
|
int r = tryAcquireShared(arg);
|
|
if (r >= 0) {
|
|
setHeadAndPropagate(node, r);
|
|
p.next = null; // help GC
|
|
failed = false;
|
|
return true;
|
|
}
|
|
}
|
|
if (nanosTimeout <= 0)
|
|
return false;
|
|
if (shouldParkAfterFailedAcquire(p, node) &&
|
|
nanosTimeout > spinForTimeoutThreshold)
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
|
long now = System.nanoTime();
|
|
nanosTimeout -= now - lastTime;
|
|
lastTime = now;
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
cancelAcquire(node);
|
|
}
|
|
}
|
|
|
|
// Main exported methods
|
|
|
|
/**
|
|
* Attempts to acquire in exclusive mode. This method should query
|
|
* if the state of the object permits it to be acquired in the
|
|
* exclusive mode, and if so to acquire it.
|
|
*
|
|
* <p>This method is always invoked by the thread performing
|
|
* acquire. If this method reports failure, the acquire method
|
|
* may queue the thread, if it is not already queued, until it is
|
|
* signalled by a release from some other thread. This can be used
|
|
* to implement method {@link Lock#tryLock()}.
|
|
*
|
|
* <p>The default
|
|
* implementation throws {@link UnsupportedOperationException}.
|
|
*
|
|
* @param arg the acquire argument. This value is always the one
|
|
* passed to an acquire method, or is the value saved on entry
|
|
* to a condition wait. The value is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @return {@code true} if successful. Upon success, this object has
|
|
* been acquired.
|
|
* @throws IllegalMonitorStateException if acquiring would place this
|
|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
|
|
* @throws UnsupportedOperationException if exclusive mode is not supported
|
|
*/
|
|
protected boolean tryAcquire(int arg) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Attempts to set the state to reflect a release in exclusive
|
|
* mode.
|
|
*
|
|
* <p>This method is always invoked by the thread performing release.
|
|
*
|
|
* <p>The default implementation throws
|
|
* {@link UnsupportedOperationException}.
|
|
*
|
|
* @param arg the release argument. This value is always the one
|
|
* passed to a release method, or the current state value upon
|
|
* entry to a condition wait. The value is otherwise
|
|
* uninterpreted and can represent anything you like.
|
|
* @return {@code true} if this object is now in a fully released
|
|
* state, so that any waiting threads may attempt to acquire;
|
|
* and {@code false} otherwise.
|
|
* @throws IllegalMonitorStateException if releasing would place this
|
|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
|
|
* @throws UnsupportedOperationException if exclusive mode is not supported
|
|
*/
|
|
protected boolean tryRelease(int arg) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire in shared mode. This method should query if
|
|
* the state of the object permits it to be acquired in the shared
|
|
* mode, and if so to acquire it.
|
|
*
|
|
* <p>This method is always invoked by the thread performing
|
|
* acquire. If this method reports failure, the acquire method
|
|
* may queue the thread, if it is not already queued, until it is
|
|
* signalled by a release from some other thread.
|
|
*
|
|
* <p>The default implementation throws {@link
|
|
* UnsupportedOperationException}.
|
|
*
|
|
* @param arg the acquire argument. This value is always the one
|
|
* passed to an acquire method, or is the value saved on entry
|
|
* to a condition wait. The value is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @return a negative value on failure; zero if acquisition in shared
|
|
* mode succeeded but no subsequent shared-mode acquire can
|
|
* succeed; and a positive value if acquisition in shared
|
|
* mode succeeded and subsequent shared-mode acquires might
|
|
* also succeed, in which case a subsequent waiting thread
|
|
* must check availability. (Support for three different
|
|
* return values enables this method to be used in contexts
|
|
* where acquires only sometimes act exclusively.) Upon
|
|
* success, this object has been acquired.
|
|
* @throws IllegalMonitorStateException if acquiring would place this
|
|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
|
|
* @throws UnsupportedOperationException if shared mode is not supported
|
|
*/
|
|
protected int tryAcquireShared(int arg) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Attempts to set the state to reflect a release in shared mode.
|
|
*
|
|
* <p>This method is always invoked by the thread performing release.
|
|
*
|
|
* <p>The default implementation throws
|
|
* {@link UnsupportedOperationException}.
|
|
*
|
|
* @param arg the release argument. This value is always the one
|
|
* passed to a release method, or the current state value upon
|
|
* entry to a condition wait. The value is otherwise
|
|
* uninterpreted and can represent anything you like.
|
|
* @return {@code true} if this release of shared mode may permit a
|
|
* waiting acquire (shared or exclusive) to succeed; and
|
|
* {@code false} otherwise
|
|
* @throws IllegalMonitorStateException if releasing would place this
|
|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
|
|
* @throws UnsupportedOperationException if shared mode is not supported
|
|
*/
|
|
protected boolean tryReleaseShared(int arg) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if synchronization is held exclusively with
|
|
* respect to the current (calling) thread. This method is invoked
|
|
* upon each call to a non-waiting {@link ConditionObject} method.
|
|
* (Waiting methods instead invoke {@link #release}.)
|
|
*
|
|
* <p>The default implementation throws {@link
|
|
* UnsupportedOperationException}. This method is invoked
|
|
* internally only within {@link ConditionObject} methods, so need
|
|
* not be defined if conditions are not used.
|
|
*
|
|
* @return {@code true} if synchronization is held exclusively;
|
|
* {@code false} otherwise
|
|
* @throws UnsupportedOperationException if conditions are not supported
|
|
*/
|
|
protected boolean isHeldExclusively() {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive mode, ignoring interrupts. Implemented
|
|
* by invoking at least once {@link #tryAcquire},
|
|
* returning on success. Otherwise the thread is queued, possibly
|
|
* repeatedly blocking and unblocking, invoking {@link
|
|
* #tryAcquire} until success. This method can be used
|
|
* to implement method {@link Lock#lock}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
*/
|
|
public final void acquire(int arg) {
|
|
if (!tryAcquire(arg) &&
|
|
acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
|
|
selfInterrupt();
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive mode, aborting if interrupted.
|
|
* Implemented by first checking interrupt status, then invoking
|
|
* at least once {@link #tryAcquire}, returning on
|
|
* success. Otherwise the thread is queued, possibly repeatedly
|
|
* blocking and unblocking, invoking {@link #tryAcquire}
|
|
* until success or the thread is interrupted. This method can be
|
|
* used to implement method {@link Lock#lockInterruptibly}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final void acquireInterruptibly(int arg)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
if (!tryAcquire(arg))
|
|
doAcquireInterruptibly(arg);
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire in exclusive mode, aborting if interrupted,
|
|
* and failing if the given timeout elapses. Implemented by first
|
|
* checking interrupt status, then invoking at least once {@link
|
|
* #tryAcquire}, returning on success. Otherwise, the thread is
|
|
* queued, possibly repeatedly blocking and unblocking, invoking
|
|
* {@link #tryAcquire} until success or the thread is interrupted
|
|
* or the timeout elapses. This method can be used to implement
|
|
* method {@link Lock#tryLock(long, TimeUnit)}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final boolean tryAcquireNanos(int arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
return tryAcquire(arg) ||
|
|
doAcquireNanos(arg, nanosTimeout);
|
|
}
|
|
|
|
/**
|
|
* Releases in exclusive mode. Implemented by unblocking one or
|
|
* more threads if {@link #tryRelease} returns true.
|
|
* This method can be used to implement method {@link Lock#unlock}.
|
|
*
|
|
* @param arg the release argument. This value is conveyed to
|
|
* {@link #tryRelease} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @return the value returned from {@link #tryRelease}
|
|
*/
|
|
public final boolean release(int arg) {
|
|
if (tryRelease(arg)) {
|
|
Node h = head;
|
|
if (h != null && h.waitStatus != 0)
|
|
unparkSuccessor(h);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared mode, ignoring interrupts. Implemented by
|
|
* first invoking at least once {@link #tryAcquireShared},
|
|
* returning on success. Otherwise the thread is queued, possibly
|
|
* repeatedly blocking and unblocking, invoking {@link
|
|
* #tryAcquireShared} until success.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
*/
|
|
public final void acquireShared(int arg) {
|
|
if (tryAcquireShared(arg) < 0)
|
|
doAcquireShared(arg);
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared mode, aborting if interrupted. Implemented
|
|
* by first checking interrupt status, then invoking at least once
|
|
* {@link #tryAcquireShared}, returning on success. Otherwise the
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
|
* is interrupted.
|
|
* @param arg the acquire argument
|
|
* This value is conveyed to {@link #tryAcquireShared} but is
|
|
* otherwise uninterpreted and can represent anything
|
|
* you like.
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final void acquireSharedInterruptibly(int arg)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
if (tryAcquireShared(arg) < 0)
|
|
doAcquireSharedInterruptibly(arg);
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire in shared mode, aborting if interrupted, and
|
|
* failing if the given timeout elapses. Implemented by first
|
|
* checking interrupt status, then invoking at least once {@link
|
|
* #tryAcquireShared}, returning on success. Otherwise, the
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
|
* is interrupted or the timeout elapses.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
return tryAcquireShared(arg) >= 0 ||
|
|
doAcquireSharedNanos(arg, nanosTimeout);
|
|
}
|
|
|
|
/**
|
|
* Releases in shared mode. Implemented by unblocking one or more
|
|
* threads if {@link #tryReleaseShared} returns true.
|
|
*
|
|
* @param arg the release argument. This value is conveyed to
|
|
* {@link #tryReleaseShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @return the value returned from {@link #tryReleaseShared}
|
|
*/
|
|
public final boolean releaseShared(int arg) {
|
|
if (tryReleaseShared(arg)) {
|
|
doReleaseShared();
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// Queue inspection methods
|
|
|
|
/**
|
|
* Queries whether any threads are waiting to acquire. Note that
|
|
* because cancellations due to interrupts and timeouts may occur
|
|
* at any time, a {@code true} return does not guarantee that any
|
|
* other thread will ever acquire.
|
|
*
|
|
* <p>In this implementation, this operation returns in
|
|
* constant time.
|
|
*
|
|
* @return {@code true} if there may be other threads waiting to acquire
|
|
*/
|
|
public final boolean hasQueuedThreads() {
|
|
return head != tail;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads have ever contended to acquire this
|
|
* synchronizer; that is if an acquire method has ever blocked.
|
|
*
|
|
* <p>In this implementation, this operation returns in
|
|
* constant time.
|
|
*
|
|
* @return {@code true} if there has ever been contention
|
|
*/
|
|
public final boolean hasContended() {
|
|
return head != null;
|
|
}
|
|
|
|
/**
|
|
* Returns the first (longest-waiting) thread in the queue, or
|
|
* {@code null} if no threads are currently queued.
|
|
*
|
|
* <p>In this implementation, this operation normally returns in
|
|
* constant time, but may iterate upon contention if other threads are
|
|
* concurrently modifying the queue.
|
|
*
|
|
* @return the first (longest-waiting) thread in the queue, or
|
|
* {@code null} if no threads are currently queued
|
|
*/
|
|
public final Thread getFirstQueuedThread() {
|
|
// handle only fast path, else relay
|
|
return (head == tail) ? null : fullGetFirstQueuedThread();
|
|
}
|
|
|
|
/**
|
|
* Version of getFirstQueuedThread called when fastpath fails
|
|
*/
|
|
private Thread fullGetFirstQueuedThread() {
|
|
/*
|
|
* The first node is normally head.next. Try to get its
|
|
* thread field, ensuring consistent reads: If thread
|
|
* field is nulled out or s.prev is no longer head, then
|
|
* some other thread(s) concurrently performed setHead in
|
|
* between some of our reads. We try this twice before
|
|
* resorting to traversal.
|
|
*/
|
|
Node h, s;
|
|
Thread st;
|
|
if (((h = head) != null && (s = h.next) != null &&
|
|
s.prev == head && (st = s.thread) != null) ||
|
|
((h = head) != null && (s = h.next) != null &&
|
|
s.prev == head && (st = s.thread) != null))
|
|
return st;
|
|
|
|
/*
|
|
* Head's next field might not have been set yet, or may have
|
|
* been unset after setHead. So we must check to see if tail
|
|
* is actually first node. If not, we continue on, safely
|
|
* traversing from tail back to head to find first,
|
|
* guaranteeing termination.
|
|
*/
|
|
|
|
Node t = tail;
|
|
Thread firstThread = null;
|
|
while (t != null && t != head) {
|
|
Thread tt = t.thread;
|
|
if (tt != null)
|
|
firstThread = tt;
|
|
t = t.prev;
|
|
}
|
|
return firstThread;
|
|
}
|
|
|
|
/**
|
|
* Returns true if the given thread is currently queued.
|
|
*
|
|
* <p>This implementation traverses the queue to determine
|
|
* presence of the given thread.
|
|
*
|
|
* @param thread the thread
|
|
* @return {@code true} if the given thread is on the queue
|
|
* @throws NullPointerException if the thread is null
|
|
*/
|
|
public final boolean isQueued(Thread thread) {
|
|
if (thread == null)
|
|
throw new NullPointerException();
|
|
for (Node p = tail; p != null; p = p.prev)
|
|
if (p.thread == thread)
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if the apparent first queued thread, if one
|
|
* exists, is waiting in exclusive mode. If this method returns
|
|
* {@code true}, and the current thread is attempting to acquire in
|
|
* shared mode (that is, this method is invoked from {@link
|
|
* #tryAcquireShared}) then it is guaranteed that the current thread
|
|
* is not the first queued thread. Used only as a heuristic in
|
|
* ReentrantReadWriteLock.
|
|
*/
|
|
final boolean apparentlyFirstQueuedIsExclusive() {
|
|
Node h, s;
|
|
return (h = head) != null &&
|
|
(s = h.next) != null &&
|
|
!s.isShared() &&
|
|
s.thread != null;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads have been waiting to acquire longer
|
|
* than the current thread.
|
|
*
|
|
* <p>An invocation of this method is equivalent to (but may be
|
|
* more efficient than):
|
|
* <pre> {@code
|
|
* getFirstQueuedThread() != Thread.currentThread() &&
|
|
* hasQueuedThreads()}</pre>
|
|
*
|
|
* <p>Note that because cancellations due to interrupts and
|
|
* timeouts may occur at any time, a {@code true} return does not
|
|
* guarantee that some other thread will acquire before the current
|
|
* thread. Likewise, it is possible for another thread to win a
|
|
* race to enqueue after this method has returned {@code false},
|
|
* due to the queue being empty.
|
|
*
|
|
* <p>This method is designed to be used by a fair synchronizer to
|
|
* avoid <a href="AbstractQueuedSynchronizer#barging">barging</a>.
|
|
* Such a synchronizer's {@link #tryAcquire} method should return
|
|
* {@code false}, and its {@link #tryAcquireShared} method should
|
|
* return a negative value, if this method returns {@code true}
|
|
* (unless this is a reentrant acquire). For example, the {@code
|
|
* tryAcquire} method for a fair, reentrant, exclusive mode
|
|
* synchronizer might look like this:
|
|
*
|
|
* <pre> {@code
|
|
* protected boolean tryAcquire(int arg) {
|
|
* if (isHeldExclusively()) {
|
|
* // A reentrant acquire; increment hold count
|
|
* return true;
|
|
* } else if (hasQueuedPredecessors()) {
|
|
* return false;
|
|
* } else {
|
|
* // try to acquire normally
|
|
* }
|
|
* }}</pre>
|
|
*
|
|
* @return {@code true} if there is a queued thread preceding the
|
|
* current thread, and {@code false} if the current thread
|
|
* is at the head of the queue or the queue is empty
|
|
* @since 1.7
|
|
*/
|
|
public final boolean hasQueuedPredecessors() {
|
|
// The correctness of this depends on head being initialized
|
|
// before tail and on head.next being accurate if the current
|
|
// thread is first in queue.
|
|
Node t = tail; // Read fields in reverse initialization order
|
|
Node h = head;
|
|
Node s;
|
|
return h != t &&
|
|
((s = h.next) == null || s.thread != Thread.currentThread());
|
|
}
|
|
|
|
|
|
// Instrumentation and monitoring methods
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting to
|
|
* acquire. The value is only an estimate because the number of
|
|
* threads may change dynamically while this method traverses
|
|
* internal data structures. This method is designed for use in
|
|
* monitoring system state, not for synchronization
|
|
* control.
|
|
*
|
|
* @return the estimated number of threads waiting to acquire
|
|
*/
|
|
public final int getQueueLength() {
|
|
int n = 0;
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (p.thread != null)
|
|
++n;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire. Because the actual set of threads may change
|
|
* dynamically while constructing this result, the returned
|
|
* collection is only a best-effort estimate. The elements of the
|
|
* returned collection are in no particular order. This method is
|
|
* designed to facilitate construction of subclasses that provide
|
|
* more extensive monitoring facilities.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
Thread t = p.thread;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire in exclusive mode. This has the same properties
|
|
* as {@link #getQueuedThreads} except that it only returns
|
|
* those threads waiting due to an exclusive acquire.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getExclusiveQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (!p.isShared()) {
|
|
Thread t = p.thread;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire in shared mode. This has the same properties
|
|
* as {@link #getQueuedThreads} except that it only returns
|
|
* those threads waiting due to a shared acquire.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getSharedQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (p.isShared()) {
|
|
Thread t = p.thread;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a string identifying this synchronizer, as well as its state.
|
|
* The state, in brackets, includes the String {@code "State ="}
|
|
* followed by the current value of {@link #getState}, and either
|
|
* {@code "nonempty"} or {@code "empty"} depending on whether the
|
|
* queue is empty.
|
|
*
|
|
* @return a string identifying this synchronizer, as well as its state
|
|
*/
|
|
public String toString() {
|
|
int s = getState();
|
|
String q = hasQueuedThreads() ? "non" : "";
|
|
return super.toString() +
|
|
"[State = " + s + ", " + q + "empty queue]";
|
|
}
|
|
|
|
|
|
// Internal support methods for Conditions
|
|
|
|
/**
|
|
* Returns true if a node, always one that was initially placed on
|
|
* a condition queue, is now waiting to reacquire on sync queue.
|
|
* @param node the node
|
|
* @return true if is reacquiring
|
|
*/
|
|
final boolean isOnSyncQueue(Node node) {
|
|
if (node.waitStatus == Node.CONDITION || node.prev == null)
|
|
return false;
|
|
if (node.next != null) // If has successor, it must be on queue
|
|
return true;
|
|
/*
|
|
* node.prev can be non-null, but not yet on queue because
|
|
* the CAS to place it on queue can fail. So we have to
|
|
* traverse from tail to make sure it actually made it. It
|
|
* will always be near the tail in calls to this method, and
|
|
* unless the CAS failed (which is unlikely), it will be
|
|
* there, so we hardly ever traverse much.
|
|
*/
|
|
return findNodeFromTail(node);
|
|
}
|
|
|
|
/**
|
|
* Returns true if node is on sync queue by searching backwards from tail.
|
|
* Called only when needed by isOnSyncQueue.
|
|
* @return true if present
|
|
*/
|
|
private boolean findNodeFromTail(Node node) {
|
|
Node t = tail;
|
|
for (;;) {
|
|
if (t == node)
|
|
return true;
|
|
if (t == null)
|
|
return false;
|
|
t = t.prev;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Transfers a node from a condition queue onto sync queue.
|
|
* Returns true if successful.
|
|
* @param node the node
|
|
* @return true if successfully transferred (else the node was
|
|
* cancelled before signal).
|
|
*/
|
|
final boolean transferForSignal(Node node) {
|
|
/*
|
|
* If cannot change waitStatus, the node has been cancelled.
|
|
*/
|
|
if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
|
|
return false;
|
|
|
|
/*
|
|
* Splice onto queue and try to set waitStatus of predecessor to
|
|
* indicate that thread is (probably) waiting. If cancelled or
|
|
* attempt to set waitStatus fails, wake up to resync (in which
|
|
* case the waitStatus can be transiently and harmlessly wrong).
|
|
*/
|
|
Node p = enq(node);
|
|
int ws = p.waitStatus;
|
|
if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
|
|
LockSupport.unpark(node.thread);
|
|
return true;
|
|
}
|
|
|
|
/**
|
|
* Transfers node, if necessary, to sync queue after a cancelled
|
|
* wait. Returns true if thread was cancelled before being
|
|
* signalled.
|
|
* @param current the waiting thread
|
|
* @param node its node
|
|
* @return true if cancelled before the node was signalled
|
|
*/
|
|
final boolean transferAfterCancelledWait(Node node) {
|
|
if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
|
|
enq(node);
|
|
return true;
|
|
}
|
|
/*
|
|
* If we lost out to a signal(), then we can't proceed
|
|
* until it finishes its enq(). Cancelling during an
|
|
* incomplete transfer is both rare and transient, so just
|
|
* spin.
|
|
*/
|
|
while (!isOnSyncQueue(node))
|
|
Thread.yield();
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Invokes release with current state value; returns saved state.
|
|
* Cancels node and throws exception on failure.
|
|
* @param node the condition node for this wait
|
|
* @return previous sync state
|
|
*/
|
|
final int fullyRelease(Node node) {
|
|
boolean failed = true;
|
|
try {
|
|
int savedState = getState();
|
|
if (release(savedState)) {
|
|
failed = false;
|
|
return savedState;
|
|
} else {
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
} finally {
|
|
if (failed)
|
|
node.waitStatus = Node.CANCELLED;
|
|
}
|
|
}
|
|
|
|
// Instrumentation methods for conditions
|
|
|
|
/**
|
|
* Queries whether the given ConditionObject
|
|
* uses this synchronizer as its lock.
|
|
*
|
|
* @param condition the condition
|
|
* @return <tt>true</tt> if owned
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final boolean owns(ConditionObject condition) {
|
|
if (condition == null)
|
|
throw new NullPointerException();
|
|
return condition.isOwnedBy(this);
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads are waiting on the given condition
|
|
* associated with this synchronizer. Note that because timeouts
|
|
* and interrupts may occur at any time, a <tt>true</tt> return
|
|
* does not guarantee that a future <tt>signal</tt> will awaken
|
|
* any threads. This method is designed primarily for use in
|
|
* monitoring of the system state.
|
|
*
|
|
* @param condition the condition
|
|
* @return <tt>true</tt> if there are any waiting threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final boolean hasWaiters(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.hasWaiters();
|
|
}
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting on the
|
|
* given condition associated with this synchronizer. Note that
|
|
* because timeouts and interrupts may occur at any time, the
|
|
* estimate serves only as an upper bound on the actual number of
|
|
* waiters. This method is designed for use in monitoring of the
|
|
* system state, not for synchronization control.
|
|
*
|
|
* @param condition the condition
|
|
* @return the estimated number of waiting threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final int getWaitQueueLength(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.getWaitQueueLength();
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing those threads that may be
|
|
* waiting on the given condition associated with this
|
|
* synchronizer. Because the actual set of threads may change
|
|
* dynamically while constructing this result, the returned
|
|
* collection is only a best-effort estimate. The elements of the
|
|
* returned collection are in no particular order.
|
|
*
|
|
* @param condition the condition
|
|
* @return the collection of threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.getWaitingThreads();
|
|
}
|
|
|
|
/**
|
|
* Condition implementation for a {@link
|
|
* AbstractQueuedSynchronizer} serving as the basis of a {@link
|
|
* Lock} implementation.
|
|
*
|
|
* <p>Method documentation for this class describes mechanics,
|
|
* not behavioral specifications from the point of view of Lock
|
|
* and Condition users. Exported versions of this class will in
|
|
* general need to be accompanied by documentation describing
|
|
* condition semantics that rely on those of the associated
|
|
* <tt>AbstractQueuedSynchronizer</tt>.
|
|
*
|
|
* <p>This class is Serializable, but all fields are transient,
|
|
* so deserialized conditions have no waiters.
|
|
*/
|
|
public class ConditionObject implements Condition, java.io.Serializable {
|
|
private static final long serialVersionUID = 1173984872572414699L;
|
|
/** First node of condition queue. */
|
|
private transient Node firstWaiter;
|
|
/** Last node of condition queue. */
|
|
private transient Node lastWaiter;
|
|
|
|
/**
|
|
* Creates a new <tt>ConditionObject</tt> instance.
|
|
*/
|
|
public ConditionObject() { }
|
|
|
|
// Internal methods
|
|
|
|
/**
|
|
* Adds a new waiter to wait queue.
|
|
* @return its new wait node
|
|
*/
|
|
private Node addConditionWaiter() {
|
|
Node t = lastWaiter;
|
|
// If lastWaiter is cancelled, clean out.
|
|
if (t != null && t.waitStatus != Node.CONDITION) {
|
|
unlinkCancelledWaiters();
|
|
t = lastWaiter;
|
|
}
|
|
Node node = new Node(Thread.currentThread(), Node.CONDITION);
|
|
if (t == null)
|
|
firstWaiter = node;
|
|
else
|
|
t.nextWaiter = node;
|
|
lastWaiter = node;
|
|
return node;
|
|
}
|
|
|
|
/**
|
|
* Removes and transfers nodes until hit non-cancelled one or
|
|
* null. Split out from signal in part to encourage compilers
|
|
* to inline the case of no waiters.
|
|
* @param first (non-null) the first node on condition queue
|
|
*/
|
|
private void doSignal(Node first) {
|
|
do {
|
|
if ( (firstWaiter = first.nextWaiter) == null)
|
|
lastWaiter = null;
|
|
first.nextWaiter = null;
|
|
} while (!transferForSignal(first) &&
|
|
(first = firstWaiter) != null);
|
|
}
|
|
|
|
/**
|
|
* Removes and transfers all nodes.
|
|
* @param first (non-null) the first node on condition queue
|
|
*/
|
|
private void doSignalAll(Node first) {
|
|
lastWaiter = firstWaiter = null;
|
|
do {
|
|
Node next = first.nextWaiter;
|
|
first.nextWaiter = null;
|
|
transferForSignal(first);
|
|
first = next;
|
|
} while (first != null);
|
|
}
|
|
|
|
/**
|
|
* Unlinks cancelled waiter nodes from condition queue.
|
|
* Called only while holding lock. This is called when
|
|
* cancellation occurred during condition wait, and upon
|
|
* insertion of a new waiter when lastWaiter is seen to have
|
|
* been cancelled. This method is needed to avoid garbage
|
|
* retention in the absence of signals. So even though it may
|
|
* require a full traversal, it comes into play only when
|
|
* timeouts or cancellations occur in the absence of
|
|
* signals. It traverses all nodes rather than stopping at a
|
|
* particular target to unlink all pointers to garbage nodes
|
|
* without requiring many re-traversals during cancellation
|
|
* storms.
|
|
*/
|
|
private void unlinkCancelledWaiters() {
|
|
Node t = firstWaiter;
|
|
Node trail = null;
|
|
while (t != null) {
|
|
Node next = t.nextWaiter;
|
|
if (t.waitStatus != Node.CONDITION) {
|
|
t.nextWaiter = null;
|
|
if (trail == null)
|
|
firstWaiter = next;
|
|
else
|
|
trail.nextWaiter = next;
|
|
if (next == null)
|
|
lastWaiter = trail;
|
|
}
|
|
else
|
|
trail = t;
|
|
t = next;
|
|
}
|
|
}
|
|
|
|
// public methods
|
|
|
|
/**
|
|
* Moves the longest-waiting thread, if one exists, from the
|
|
* wait queue for this condition to the wait queue for the
|
|
* owning lock.
|
|
*
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
public final void signal() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
Node first = firstWaiter;
|
|
if (first != null)
|
|
doSignal(first);
|
|
}
|
|
|
|
/**
|
|
* Moves all threads from the wait queue for this condition to
|
|
* the wait queue for the owning lock.
|
|
*
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
public final void signalAll() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
Node first = firstWaiter;
|
|
if (first != null)
|
|
doSignalAll(first);
|
|
}
|
|
|
|
/**
|
|
* Implements uninterruptible condition wait.
|
|
* <ol>
|
|
* <li> Save lock state returned by {@link #getState}.
|
|
* <li> Invoke {@link #release} with
|
|
* saved state as argument, throwing
|
|
* IllegalMonitorStateException if it fails.
|
|
* <li> Block until signalled.
|
|
* <li> Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* </ol>
|
|
*/
|
|
public final void awaitUninterruptibly() {
|
|
Node node = addConditionWaiter();
|
|
int savedState = fullyRelease(node);
|
|
boolean interrupted = false;
|
|
while (!isOnSyncQueue(node)) {
|
|
LockSupport.park(this);
|
|
if (Thread.interrupted())
|
|
interrupted = true;
|
|
}
|
|
if (acquireQueued(node, savedState) || interrupted)
|
|
selfInterrupt();
|
|
}
|
|
|
|
/*
|
|
* For interruptible waits, we need to track whether to throw
|
|
* InterruptedException, if interrupted while blocked on
|
|
* condition, versus reinterrupt current thread, if
|
|
* interrupted while blocked waiting to re-acquire.
|
|
*/
|
|
|
|
/** Mode meaning to reinterrupt on exit from wait */
|
|
private static final int REINTERRUPT = 1;
|
|
/** Mode meaning to throw InterruptedException on exit from wait */
|
|
private static final int THROW_IE = -1;
|
|
|
|
/**
|
|
* Checks for interrupt, returning THROW_IE if interrupted
|
|
* before signalled, REINTERRUPT if after signalled, or
|
|
* 0 if not interrupted.
|
|
*/
|
|
private int checkInterruptWhileWaiting(Node node) {
|
|
return Thread.interrupted() ?
|
|
(transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
|
|
0;
|
|
}
|
|
|
|
/**
|
|
* Throws InterruptedException, reinterrupts current thread, or
|
|
* does nothing, depending on mode.
|
|
*/
|
|
private void reportInterruptAfterWait(int interruptMode)
|
|
throws InterruptedException {
|
|
if (interruptMode == THROW_IE)
|
|
throw new InterruptedException();
|
|
else if (interruptMode == REINTERRUPT)
|
|
selfInterrupt();
|
|
}
|
|
|
|
/**
|
|
* Implements interruptible condition wait.
|
|
* <ol>
|
|
* <li> If current thread is interrupted, throw InterruptedException.
|
|
* <li> Save lock state returned by {@link #getState}.
|
|
* <li> Invoke {@link #release} with
|
|
* saved state as argument, throwing
|
|
* IllegalMonitorStateException if it fails.
|
|
* <li> Block until signalled or interrupted.
|
|
* <li> Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException.
|
|
* </ol>
|
|
*/
|
|
public final void await() throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
Node node = addConditionWaiter();
|
|
int savedState = fullyRelease(node);
|
|
int interruptMode = 0;
|
|
while (!isOnSyncQueue(node)) {
|
|
LockSupport.park(this);
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
|
break;
|
|
}
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
|
interruptMode = REINTERRUPT;
|
|
if (node.nextWaiter != null) // clean up if cancelled
|
|
unlinkCancelledWaiters();
|
|
if (interruptMode != 0)
|
|
reportInterruptAfterWait(interruptMode);
|
|
}
|
|
|
|
/**
|
|
* Implements timed condition wait.
|
|
* <ol>
|
|
* <li> If current thread is interrupted, throw InterruptedException.
|
|
* <li> Save lock state returned by {@link #getState}.
|
|
* <li> Invoke {@link #release} with
|
|
* saved state as argument, throwing
|
|
* IllegalMonitorStateException if it fails.
|
|
* <li> Block until signalled, interrupted, or timed out.
|
|
* <li> Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException.
|
|
* </ol>
|
|
*/
|
|
public final long awaitNanos(long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
Node node = addConditionWaiter();
|
|
int savedState = fullyRelease(node);
|
|
long lastTime = System.nanoTime();
|
|
int interruptMode = 0;
|
|
while (!isOnSyncQueue(node)) {
|
|
if (nanosTimeout <= 0L) {
|
|
transferAfterCancelledWait(node);
|
|
break;
|
|
}
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
|
break;
|
|
|
|
long now = System.nanoTime();
|
|
nanosTimeout -= now - lastTime;
|
|
lastTime = now;
|
|
}
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
|
interruptMode = REINTERRUPT;
|
|
if (node.nextWaiter != null)
|
|
unlinkCancelledWaiters();
|
|
if (interruptMode != 0)
|
|
reportInterruptAfterWait(interruptMode);
|
|
return nanosTimeout - (System.nanoTime() - lastTime);
|
|
}
|
|
|
|
/**
|
|
* Implements absolute timed condition wait.
|
|
* <ol>
|
|
* <li> If current thread is interrupted, throw InterruptedException.
|
|
* <li> Save lock state returned by {@link #getState}.
|
|
* <li> Invoke {@link #release} with
|
|
* saved state as argument, throwing
|
|
* IllegalMonitorStateException if it fails.
|
|
* <li> Block until signalled, interrupted, or timed out.
|
|
* <li> Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException.
|
|
* <li> If timed out while blocked in step 4, return false, else true.
|
|
* </ol>
|
|
*/
|
|
public final boolean awaitUntil(Date deadline)
|
|
throws InterruptedException {
|
|
if (deadline == null)
|
|
throw new NullPointerException();
|
|
long abstime = deadline.getTime();
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
Node node = addConditionWaiter();
|
|
int savedState = fullyRelease(node);
|
|
boolean timedout = false;
|
|
int interruptMode = 0;
|
|
while (!isOnSyncQueue(node)) {
|
|
if (System.currentTimeMillis() > abstime) {
|
|
timedout = transferAfterCancelledWait(node);
|
|
break;
|
|
}
|
|
LockSupport.parkUntil(this, abstime);
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
|
break;
|
|
}
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
|
interruptMode = REINTERRUPT;
|
|
if (node.nextWaiter != null)
|
|
unlinkCancelledWaiters();
|
|
if (interruptMode != 0)
|
|
reportInterruptAfterWait(interruptMode);
|
|
return !timedout;
|
|
}
|
|
|
|
/**
|
|
* Implements timed condition wait.
|
|
* <ol>
|
|
* <li> If current thread is interrupted, throw InterruptedException.
|
|
* <li> Save lock state returned by {@link #getState}.
|
|
* <li> Invoke {@link #release} with
|
|
* saved state as argument, throwing
|
|
* IllegalMonitorStateException if it fails.
|
|
* <li> Block until signalled, interrupted, or timed out.
|
|
* <li> Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li> If interrupted while blocked in step 4, throw InterruptedException.
|
|
* <li> If timed out while blocked in step 4, return false, else true.
|
|
* </ol>
|
|
*/
|
|
public final boolean await(long time, TimeUnit unit)
|
|
throws InterruptedException {
|
|
if (unit == null)
|
|
throw new NullPointerException();
|
|
long nanosTimeout = unit.toNanos(time);
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
Node node = addConditionWaiter();
|
|
int savedState = fullyRelease(node);
|
|
long lastTime = System.nanoTime();
|
|
boolean timedout = false;
|
|
int interruptMode = 0;
|
|
while (!isOnSyncQueue(node)) {
|
|
if (nanosTimeout <= 0L) {
|
|
timedout = transferAfterCancelledWait(node);
|
|
break;
|
|
}
|
|
if (nanosTimeout >= spinForTimeoutThreshold)
|
|
LockSupport.parkNanos(this, nanosTimeout);
|
|
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
|
|
break;
|
|
long now = System.nanoTime();
|
|
nanosTimeout -= now - lastTime;
|
|
lastTime = now;
|
|
}
|
|
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
|
|
interruptMode = REINTERRUPT;
|
|
if (node.nextWaiter != null)
|
|
unlinkCancelledWaiters();
|
|
if (interruptMode != 0)
|
|
reportInterruptAfterWait(interruptMode);
|
|
return !timedout;
|
|
}
|
|
|
|
// support for instrumentation
|
|
|
|
/**
|
|
* Returns true if this condition was created by the given
|
|
* synchronization object.
|
|
*
|
|
* @return {@code true} if owned
|
|
*/
|
|
final boolean isOwnedBy(AbstractQueuedSynchronizer sync) {
|
|
return sync == AbstractQueuedSynchronizer.this;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads are waiting on this condition.
|
|
* Implements {@link AbstractQueuedSynchronizer#hasWaiters}.
|
|
*
|
|
* @return {@code true} if there are any waiting threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final boolean hasWaiters() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if (w.waitStatus == Node.CONDITION)
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting on
|
|
* this condition.
|
|
* Implements {@link AbstractQueuedSynchronizer#getWaitQueueLength}.
|
|
*
|
|
* @return the estimated number of waiting threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final int getWaitQueueLength() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
int n = 0;
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if (w.waitStatus == Node.CONDITION)
|
|
++n;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing those threads that may be
|
|
* waiting on this Condition.
|
|
* Implements {@link AbstractQueuedSynchronizer#getWaitingThreads}.
|
|
*
|
|
* @return the collection of threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final Collection<Thread> getWaitingThreads() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
ArrayList<Thread> list = new ArrayList<Thread>();
|
|
for (Node w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if (w.waitStatus == Node.CONDITION) {
|
|
Thread t = w.thread;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* IKVM specific. We use AtomicReferenceFieldUpdater instead of Unsafe primitives.
|
|
*/
|
|
private static final AtomicReferenceFieldUpdater<AbstractQueuedSynchronizer, Node> headUpdater =
|
|
AtomicReferenceFieldUpdater.newUpdater(AbstractQueuedSynchronizer.class, Node.class, "head");
|
|
private static final AtomicReferenceFieldUpdater<AbstractQueuedSynchronizer, Node> tailUpdater =
|
|
AtomicReferenceFieldUpdater.newUpdater(AbstractQueuedSynchronizer.class, Node.class, "tail");
|
|
|
|
/**
|
|
* CAS head field. Used only by enq.
|
|
*/
|
|
private final boolean compareAndSetHead(Node update) {
|
|
return headUpdater.compareAndSet(this, null, update);
|
|
}
|
|
|
|
/**
|
|
* CAS tail field. Used only by enq.
|
|
*/
|
|
private final boolean compareAndSetTail(Node expect, Node update) {
|
|
return tailUpdater.compareAndSet(this, expect, update);
|
|
}
|
|
|
|
/**
|
|
* CAS waitStatus field of a node.
|
|
*/
|
|
private static final native boolean compareAndSetWaitStatus(Node node,
|
|
int expect,
|
|
int update); // implemented in map.xml
|
|
/**
|
|
* CAS next field of a node.
|
|
*/
|
|
private static final boolean compareAndSetNext(Node node,
|
|
Node expect,
|
|
Node update) {
|
|
return Node.nextUpdater.compareAndSet(node, expect, update);
|
|
}
|
|
}
|