author | chegar |
Thu, 17 Oct 2019 20:54:25 +0100 | |
branch | datagramsocketimpl-branch |
changeset 58679 | 9c3209ff7550 |
parent 58678 | 9cf78a70fa4f |
parent 58385 | 489532b89775 |
permissions | -rw-r--r-- |
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/* |
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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.ArrayList; |
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import java.util.Collection; |
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import java.util.Date; |
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import java.util.concurrent.TimeUnit; |
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import java.util.concurrent.ForkJoinPool; |
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import jdk.internal.misc.Unsafe; |
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/** |
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* Provides a framework for implementing blocking locks and related |
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* synchronizers (semaphores, events, etc) that rely on |
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* first-in-first-out (FIFO) wait queues. This class is designed to |
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* be a useful basis for most kinds of synchronizers that rely on a |
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* single atomic {@code int} 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 {@code int} |
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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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* {@code AbstractQueuedSynchronizer} 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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* {@code AbstractQueuedSynchronizer} 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 {@code AbstractQueuedSynchronizer} 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 {@code readObject} method that restores this to a known |
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* initial state upon deserialization. |
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* |
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* <h2>Usage</h2> |
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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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* {@code final} 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 id="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 {@code tryAcquire} and/or {@code tryAcquireShared} 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 {@code tryAcquire} |
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* to return {@code false} if {@link #hasQueuedPredecessors} (a method |
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* specifically designed to be used by fair synchronizers) returns |
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* {@code true}. 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 {@code tryAcquire} 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 {@code int} 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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* <h2>Usage Examples</h2> |
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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 some instrumentation methods: |
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* |
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* <pre> {@code |
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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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* // Acquires 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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* // Releases 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 (!isHeldExclusively()) |
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* 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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* // Reports whether in locked state |
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* public boolean isLocked() { |
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* return getState() != 0; |
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* } |
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* |
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* public boolean isHeldExclusively() { |
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* // a data race, but safe due to out-of-thin-air guarantees |
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* return getExclusiveOwnerThread() == Thread.currentThread(); |
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* } |
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* |
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* // Provides a Condition |
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* public Condition newCondition() { |
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* return new ConditionObject(); |
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* } |
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* |
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* // Deserializes 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.isLocked(); } |
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* public boolean isHeldByCurrentThread() { |
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* return sync.isHeldExclusively(); |
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* } |
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* public boolean hasQueuedThreads() { |
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* return sync.hasQueuedThreads(); |
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* } |
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* public void lockInterruptibly() throws InterruptedException { |
262 |
* 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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* }}</pre> |
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* |
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* <p>Here is a latch class that is like a |
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* {@link java.util.concurrent.CountDownLatch CountDownLatch} |
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* except that it only requires a single {@code signal} to |
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* fire. Because a latch is non-exclusive, it uses the {@code shared} |
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* acquire and release methods. |
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* |
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* <pre> {@code |
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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; |
2 | 284 |
* } |
285 |
* |
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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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* }}</pre> |
2 | 299 |
* |
300 |
* @since 1.5 |
|
301 |
* @author Doug Lea |
|
302 |
*/ |
|
303 |
public abstract class AbstractQueuedSynchronizer |
|
304 |
extends AbstractOwnableSynchronizer |
|
305 |
implements java.io.Serializable { |
|
306 |
||
307 |
private static final long serialVersionUID = 7373984972572414691L; |
|
308 |
||
309 |
/** |
|
18576 | 310 |
* Creates a new {@code AbstractQueuedSynchronizer} instance |
2 | 311 |
* with initial synchronization state of zero. |
312 |
*/ |
|
313 |
protected AbstractQueuedSynchronizer() { } |
|
314 |
||
58134 | 315 |
/* |
316 |
* Overview. |
|
2 | 317 |
* |
58134 | 318 |
* The wait queue is a variant of a "CLH" (Craig, Landin, and |
2 | 319 |
* Hagersten) lock queue. CLH locks are normally used for |
58134 | 320 |
* spinlocks. We instead use them for blocking synchronizers by |
321 |
* including explicit ("prev" and "next") links plus a "status" |
|
322 |
* field that allow nodes to signal successors when releasing |
|
323 |
* locks, and handle cancellation due to interrupts and timeouts. |
|
324 |
* The status field includes bits that track whether a thread |
|
325 |
* needs a signal (using LockSupport.unpark). Despite these |
|
326 |
* additions, we maintain most CLH locality properties. |
|
327 |
* |
|
328 |
* To enqueue into a CLH lock, you atomically splice it in as new |
|
329 |
* tail. To dequeue, you set the head field, so the next eligible |
|
330 |
* waiter becomes first. |
|
2 | 331 |
* |
58134 | 332 |
* +------+ prev +-------+ +------+ |
333 |
* | head | <---- | first | <---- | tail | |
|
334 |
* +------+ +-------+ +------+ |
|
335 |
* |
|
336 |
* Insertion into a CLH queue requires only a single atomic |
|
337 |
* operation on "tail", so there is a simple point of demarcation |
|
338 |
* from unqueued to queued. The "next" link of the predecessor is |
|
339 |
* set by the enqueuing thread after successful CAS. Even though |
|
340 |
* non-atomic, this suffices to ensure that any blocked thread is |
|
341 |
* signalled by a predecessor when eligible (although in the case |
|
342 |
* of cancellation, possibly with the assistance of a signal in |
|
343 |
* method cleanQueue). Signalling is based in part on a |
|
344 |
* Dekker-like scheme in which the to-be waiting thread indicates |
|
345 |
* WAITING status, then retries acquiring, and then rechecks |
|
346 |
* status before blocking. The signaller atomically clears WAITING |
|
347 |
* status when unparking. |
|
2 | 348 |
* |
58134 | 349 |
* Dequeuing on acquire involves detaching (nulling) a node's |
350 |
* "prev" node and then updating the "head". Other threads check |
|
351 |
* if a node is or was dequeued by checking "prev" rather than |
|
352 |
* head. We enforce the nulling then setting order by spin-waiting |
|
353 |
* if necessary. Because of this, the lock algorithm is not itself |
|
354 |
* strictly "lock-free" because an acquiring thread may need to |
|
355 |
* wait for a previous acquire to make progress. When used with |
|
356 |
* exclusive locks, such progress is required anyway. However |
|
357 |
* Shared mode may (uncommonly) require a spin-wait before |
|
358 |
* setting head field to ensure proper propagation. (Historical |
|
359 |
* note: This allows some simplifications and efficiencies |
|
360 |
* compared to previous versions of this class.) |
|
2 | 361 |
* |
58134 | 362 |
* A node's predecessor can change due to cancellation while it is |
363 |
* waiting, until the node is first in queue, at which point it |
|
364 |
* cannot change. The acquire methods cope with this by rechecking |
|
365 |
* "prev" before waiting. The prev and next fields are modified |
|
366 |
* only via CAS by cancelled nodes in method cleanQueue. The |
|
367 |
* unsplice strategy is reminiscent of Michael-Scott queues in |
|
368 |
* that after a successful CAS to prev field, other threads help |
|
369 |
* fix next fields. Because cancellation often occurs in bunches |
|
370 |
* that complicate decisions about necessary signals, each call to |
|
371 |
* cleanQueue traverses the queue until a clean sweep. Nodes that |
|
372 |
* become relinked as first are unconditionally unparked |
|
373 |
* (sometimes unnecessarily, but those cases are not worth |
|
374 |
* avoiding). |
|
2 | 375 |
* |
58134 | 376 |
* A thread may try to acquire if it is first (frontmost) in the |
377 |
* queue, and sometimes before. Being first does not guarantee |
|
378 |
* success; it only gives the right to contend. We balance |
|
379 |
* throughput, overhead, and fairness by allowing incoming threads |
|
380 |
* to "barge" and acquire the synchronizer while in the process of |
|
381 |
* enqueuing, in which case an awakened first thread may need to |
|
382 |
* rewait. To counteract possible repeated unlucky rewaits, we |
|
383 |
* exponentially increase retries (up to 256) to acquire each time |
|
384 |
* a thread is unparked. Except in this case, AQS locks do not |
|
385 |
* spin; they instead interleave attempts to acquire with |
|
386 |
* bookkeeping steps. (Users who want spinlocks can use |
|
387 |
* tryAcquire.) |
|
2 | 388 |
* |
58134 | 389 |
* To improve garbage collectibility, fields of nodes not yet on |
390 |
* list are null. (It is not rare to create and then throw away a |
|
391 |
* node without using it.) Fields of nodes coming off the list are |
|
392 |
* nulled out as soon as possible. This accentuates the challenge |
|
393 |
* of externally determining the first waiting thread (as in |
|
394 |
* method getFirstQueuedThread). This sometimes requires the |
|
395 |
* fallback of traversing backwards from the atomically updated |
|
396 |
* "tail" when fields appear null. (This is never needed in the |
|
397 |
* process of signalling though.) |
|
398 |
* |
|
399 |
* CLH queues need a dummy header node to get started. But |
|
2 | 400 |
* we don't create them on construction, because it would be wasted |
401 |
* effort if there is never contention. Instead, the node |
|
402 |
* is constructed and head and tail pointers are set upon first |
|
403 |
* contention. |
|
404 |
* |
|
58134 | 405 |
* Shared mode operations differ from Exclusive in that an acquire |
406 |
* signals the next waiter to try to acquire if it is also |
|
407 |
* Shared. The tryAcquireShared API allows users to indicate the |
|
408 |
* degree of propagation, but in most applications, it is more |
|
409 |
* efficient to ignore this, allowing the successor to try |
|
410 |
* acquiring in any case. |
|
411 |
* |
|
412 |
* Threads waiting on Conditions use nodes with an additional |
|
413 |
* link to maintain the (FIFO) list of conditions. Conditions only |
|
414 |
* need to link nodes in simple (non-concurrent) linked queues |
|
415 |
* because they are only accessed when exclusively held. Upon |
|
416 |
* await, a node is inserted into a condition queue. Upon signal, |
|
417 |
* the node is enqueued on the main queue. A special status field |
|
418 |
* value is used to track and atomically trigger this. |
|
2 | 419 |
* |
58134 | 420 |
* Accesses to fields head, tail, and state use full Volatile |
421 |
* mode, along with CAS. Node fields status, prev and next also do |
|
422 |
* so while threads may be signallable, but sometimes use weaker |
|
423 |
* modes otherwise. Accesses to field "waiter" (the thread to be |
|
424 |
* signalled) are always sandwiched between other atomic accesses |
|
425 |
* so are used in Plain mode. We use jdk.internal Unsafe versions |
|
426 |
* of atomic access methods rather than VarHandles to avoid |
|
427 |
* potential VM bootstrap issues. |
|
428 |
* |
|
429 |
* Most of the above is performed by primary internal method |
|
430 |
* acquire, that is invoked in some way by all exported acquire |
|
431 |
* methods. (It is usually easy for compilers to optimize |
|
432 |
* call-site specializations when heavily used.) |
|
433 |
* |
|
434 |
* There are several arbitrary decisions about when and how to |
|
435 |
* check interrupts in both acquire and await before and/or after |
|
436 |
* blocking. The decisions are less arbitrary in implementation |
|
437 |
* updates because some users appear to rely on original behaviors |
|
438 |
* in ways that are racy and so (rarely) wrong in general but hard |
|
439 |
* to justify changing. |
|
440 |
* |
|
441 |
* Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill |
|
2 | 442 |
* Scherer and Michael Scott, along with members of JSR-166 |
443 |
* expert group, for helpful ideas, discussions, and critiques |
|
444 |
* on the design of this class. |
|
445 |
*/ |
|
58134 | 446 |
|
447 |
// Node status bits, also used as argument and return values |
|
448 |
static final int WAITING = 1; // must be 1 |
|
449 |
static final int CANCELLED = 0x80000000; // must be negative |
|
450 |
static final int COND = 2; // in a condition wait |
|
2 | 451 |
|
58134 | 452 |
/** CLH Nodes */ |
453 |
abstract static class Node { |
|
454 |
volatile Node prev; // initially attached via casTail |
|
455 |
volatile Node next; // visibly nonnull when signallable |
|
456 |
Thread waiter; // visibly nonnull when enqueued |
|
457 |
volatile int status; // written by owner, atomic bit ops by others |
|
2 | 458 |
|
58134 | 459 |
// methods for atomic operations |
460 |
final boolean casPrev(Node c, Node v) { // for cleanQueue |
|
461 |
return U.weakCompareAndSetReference(this, PREV, c, v); |
|
462 |
} |
|
463 |
final boolean casNext(Node c, Node v) { // for cleanQueue |
|
464 |
return U.weakCompareAndSetReference(this, NEXT, c, v); |
|
465 |
} |
|
466 |
final int getAndUnsetStatus(int v) { // for signalling |
|
467 |
return U.getAndBitwiseAndInt(this, STATUS, ~v); |
|
468 |
} |
|
469 |
final void setPrevRelaxed(Node p) { // for off-queue assignment |
|
470 |
U.putReference(this, PREV, p); |
|
471 |
} |
|
472 |
final void setStatusRelaxed(int s) { // for off-queue assignment |
|
473 |
U.putInt(this, STATUS, s); |
|
474 |
} |
|
475 |
final void clearStatus() { // for reducing unneeded signals |
|
476 |
U.putIntOpaque(this, STATUS, 0); |
|
477 |
} |
|
2 | 478 |
|
58134 | 479 |
private static final long STATUS |
480 |
= U.objectFieldOffset(Node.class, "status"); |
|
481 |
private static final long NEXT |
|
482 |
= U.objectFieldOffset(Node.class, "next"); |
|
483 |
private static final long PREV |
|
484 |
= U.objectFieldOffset(Node.class, "prev"); |
|
485 |
} |
|
2 | 486 |
|
58134 | 487 |
// Concrete classes tagged by type |
488 |
static final class ExclusiveNode extends Node { } |
|
489 |
static final class SharedNode extends Node { } |
|
490 |
||
491 |
static final class ConditionNode extends Node |
|
492 |
implements ForkJoinPool.ManagedBlocker { |
|
493 |
ConditionNode nextWaiter; // link to next waiting node |
|
2 | 494 |
|
495 |
/** |
|
58134 | 496 |
* Allows Conditions to be used in ForkJoinPools without |
497 |
* risking fixed pool exhaustion. This is usable only for |
|
498 |
* untimed Condition waits, not timed versions. |
|
2 | 499 |
*/ |
58134 | 500 |
public final boolean isReleasable() { |
501 |
return status <= 1 || Thread.currentThread().isInterrupted(); |
|
2 | 502 |
} |
503 |
||
58134 | 504 |
public final boolean block() { |
58385
489532b89775
8231032: ThreadMXBean locking tests fail after JSR 166 refresh
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58134
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|
505 |
while (!isReleasable()) LockSupport.park(); |
58134 | 506 |
return true; |
2 | 507 |
} |
508 |
} |
|
509 |
||
510 |
/** |
|
58134 | 511 |
* Head of the wait queue, lazily initialized. |
2 | 512 |
*/ |
513 |
private transient volatile Node head; |
|
514 |
||
515 |
/** |
|
58134 | 516 |
* Tail of the wait queue. After initialization, modified only via casTail. |
2 | 517 |
*/ |
518 |
private transient volatile Node tail; |
|
519 |
||
520 |
/** |
|
521 |
* The synchronization state. |
|
522 |
*/ |
|
523 |
private volatile int state; |
|
524 |
||
525 |
/** |
|
526 |
* Returns the current value of synchronization state. |
|
18576 | 527 |
* This operation has memory semantics of a {@code volatile} read. |
2 | 528 |
* @return current state value |
529 |
*/ |
|
530 |
protected final int getState() { |
|
531 |
return state; |
|
532 |
} |
|
533 |
||
534 |
/** |
|
535 |
* Sets the value of synchronization state. |
|
18576 | 536 |
* This operation has memory semantics of a {@code volatile} write. |
2 | 537 |
* @param newState the new state value |
538 |
*/ |
|
539 |
protected final void setState(int newState) { |
|
540 |
state = newState; |
|
541 |
} |
|
542 |
||
543 |
/** |
|
544 |
* Atomically sets synchronization state to the given updated |
|
545 |
* value if the current state value equals the expected value. |
|
18576 | 546 |
* This operation has memory semantics of a {@code volatile} read |
2 | 547 |
* and write. |
548 |
* |
|
549 |
* @param expect the expected value |
|
550 |
* @param update the new value |
|
18576 | 551 |
* @return {@code true} if successful. False return indicates that the actual |
2 | 552 |
* value was not equal to the expected value. |
553 |
*/ |
|
554 |
protected final boolean compareAndSetState(int expect, int update) { |
|
58134 | 555 |
return U.compareAndSetInt(this, STATE, expect, update); |
2 | 556 |
} |
557 |
||
558 |
// Queuing utilities |
|
559 |
||
58134 | 560 |
private boolean casTail(Node c, Node v) { |
561 |
return U.compareAndSetReference(this, TAIL, c, v); |
|
562 |
} |
|
563 |
||
564 |
/** tries once to CAS a new dummy node for head */ |
|
565 |
private void tryInitializeHead() { |
|
566 |
Node h = new ExclusiveNode(); |
|
567 |
if (U.compareAndSetReference(this, HEAD, null, h)) |
|
568 |
tail = h; |
|
569 |
} |
|
2 | 570 |
|
571 |
/** |
|
58134 | 572 |
* Enqueues the node unless null. (Currently used only for |
573 |
* ConditionNodes; other cases are interleaved with acquires.) |
|
2 | 574 |
*/ |
58134 | 575 |
final void enqueue(Node node) { |
576 |
if (node != null) { |
|
577 |
for (;;) { |
|
578 |
Node t = tail; |
|
579 |
node.setPrevRelaxed(t); // avoid unnecessary fence |
|
580 |
if (t == null) // initialize |
|
581 |
tryInitializeHead(); |
|
582 |
else if (casTail(t, node)) { |
|
583 |
t.next = node; |
|
584 |
if (t.status < 0) // wake up to clean link |
|
585 |
LockSupport.unpark(node.waiter); |
|
586 |
break; |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
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|
587 |
} |
2 | 588 |
} |
589 |
} |
|
590 |
} |
|
591 |
||
58134 | 592 |
/** Returns true if node is found in traversal from tail */ |
593 |
final boolean isEnqueued(Node node) { |
|
594 |
for (Node t = tail; t != null; t = t.prev) |
|
595 |
if (t == node) |
|
596 |
return true; |
|
597 |
return false; |
|
598 |
} |
|
599 |
||
2 | 600 |
/** |
58134 | 601 |
* Wakes up the successor of given node, if one exists, and unsets its |
602 |
* WAITING status to avoid park race. This may fail to wake up an |
|
603 |
* eligible thread when one or more have been cancelled, but |
|
604 |
* cancelAcquire ensures liveness. |
|
605 |
*/ |
|
606 |
private static void signalNext(Node h) { |
|
607 |
Node s; |
|
608 |
if (h != null && (s = h.next) != null && s.status != 0) { |
|
609 |
s.getAndUnsetStatus(WAITING); |
|
610 |
LockSupport.unpark(s.waiter); |
|
611 |
} |
|
612 |
} |
|
613 |
||
614 |
/** Wakes up the given node if in shared mode */ |
|
615 |
private static void signalNextIfShared(Node h) { |
|
616 |
Node s; |
|
617 |
if (h != null && (s = h.next) != null && |
|
618 |
(s instanceof SharedNode) && s.status != 0) { |
|
619 |
s.getAndUnsetStatus(WAITING); |
|
620 |
LockSupport.unpark(s.waiter); |
|
621 |
} |
|
622 |
} |
|
623 |
||
624 |
/** |
|
625 |
* Main acquire method, invoked by all exported acquire methods. |
|
2 | 626 |
* |
58134 | 627 |
* @param node null unless a reacquiring Condition |
628 |
* @param arg the acquire argument |
|
629 |
* @param shared true if shared mode else exclusive |
|
630 |
* @param interruptible if abort and return negative on interrupt |
|
631 |
* @param timed if true use timed waits |
|
632 |
* @param time if timed, the System.nanoTime value to timeout |
|
633 |
* @return positive if acquired, 0 if timed out, negative if interrupted |
|
2 | 634 |
*/ |
58134 | 635 |
final int acquire(Node node, int arg, boolean shared, |
636 |
boolean interruptible, boolean timed, long time) { |
|
637 |
Thread current = Thread.currentThread(); |
|
638 |
byte spins = 0, postSpins = 0; // retries upon unpark of first thread |
|
639 |
boolean interrupted = false, first = false; |
|
640 |
Node pred = null; // predecessor of node when enqueued |
|
641 |
||
642 |
/* |
|
643 |
* Repeatedly: |
|
644 |
* Check if node now first |
|
645 |
* if so, ensure head stable, else ensure valid predecessor |
|
646 |
* if node is first or not yet enqueued, try acquiring |
|
647 |
* else if node not yet created, create it |
|
648 |
* else if not yet enqueued, try once to enqueue |
|
649 |
* else if woken from park, retry (up to postSpins times) |
|
650 |
* else if WAITING status not set, set and retry |
|
651 |
* else park and clear WAITING status, and check cancellation |
|
652 |
*/ |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
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parents:
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|
653 |
|
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
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changeset
|
654 |
for (;;) { |
58134 | 655 |
if (!first && (pred = (node == null) ? null : node.prev) != null && |
656 |
!(first = (head == pred))) { |
|
657 |
if (pred.status < 0) { |
|
658 |
cleanQueue(); // predecessor cancelled |
|
659 |
continue; |
|
660 |
} else if (pred.prev == null) { |
|
661 |
Thread.onSpinWait(); // ensure serialization |
|
662 |
continue; |
|
663 |
} |
|
664 |
} |
|
665 |
if (first || pred == null) { |
|
666 |
boolean acquired; |
|
667 |
try { |
|
668 |
if (shared) |
|
669 |
acquired = (tryAcquireShared(arg) >= 0); |
|
670 |
else |
|
671 |
acquired = tryAcquire(arg); |
|
672 |
} catch (Throwable ex) { |
|
673 |
cancelAcquire(node, interrupted, false); |
|
674 |
throw ex; |
|
675 |
} |
|
676 |
if (acquired) { |
|
677 |
if (first) { |
|
678 |
node.prev = null; |
|
679 |
head = node; |
|
680 |
pred.next = null; |
|
681 |
node.waiter = null; |
|
682 |
if (shared) |
|
683 |
signalNextIfShared(node); |
|
684 |
if (interrupted) |
|
685 |
current.interrupt(); |
|
686 |
} |
|
687 |
return 1; |
|
32990
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changeset
|
688 |
} |
58134 | 689 |
} |
690 |
if (node == null) { // allocate; retry before enqueue |
|
691 |
if (shared) |
|
692 |
node = new SharedNode(); |
|
693 |
else |
|
694 |
node = new ExclusiveNode(); |
|
695 |
} else if (pred == null) { // try to enqueue |
|
696 |
node.waiter = current; |
|
697 |
Node t = tail; |
|
698 |
node.setPrevRelaxed(t); // avoid unnecessary fence |
|
699 |
if (t == null) |
|
700 |
tryInitializeHead(); |
|
701 |
else if (!casTail(t, node)) |
|
702 |
node.setPrevRelaxed(null); // back out |
|
703 |
else |
|
704 |
t.next = node; |
|
705 |
} else if (first && spins != 0) { |
|
706 |
--spins; // reduce unfairness on rewaits |
|
707 |
Thread.onSpinWait(); |
|
708 |
} else if (node.status == 0) { |
|
709 |
node.status = WAITING; // enable signal and recheck |
|
32990
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|
710 |
} else { |
58134 | 711 |
long nanos; |
712 |
spins = postSpins = (byte)((postSpins << 1) | 1); |
|
713 |
if (!timed) |
|
714 |
LockSupport.park(this); |
|
715 |
else if ((nanos = time - System.nanoTime()) > 0L) |
|
716 |
LockSupport.parkNanos(this, nanos); |
|
717 |
else |
|
718 |
break; |
|
719 |
node.clearStatus(); |
|
720 |
if ((interrupted |= Thread.interrupted()) && interruptible) |
|
721 |
break; |
|
722 |
} |
|
723 |
} |
|
724 |
return cancelAcquire(node, interrupted, interruptible); |
|
725 |
} |
|
726 |
||
727 |
/** |
|
728 |
* Possibly repeatedly traverses from tail, unsplicing cancelled |
|
729 |
* nodes until none are found. Unparks nodes that may have been |
|
730 |
* relinked to be next eligible acquirer. |
|
731 |
*/ |
|
732 |
private void cleanQueue() { |
|
733 |
for (;;) { // restart point |
|
734 |
for (Node q = tail, s = null, p, n;;) { // (p, q, s) triples |
|
735 |
if (q == null || (p = q.prev) == null) |
|
736 |
return; // end of list |
|
737 |
if (s == null ? tail != q : (s.prev != q || s.status < 0)) |
|
738 |
break; // inconsistent |
|
739 |
if (q.status < 0) { // cancelled |
|
740 |
if ((s == null ? casTail(q, p) : s.casPrev(q, p)) && |
|
741 |
q.prev == p) { |
|
742 |
p.casNext(q, s); // OK if fails |
|
743 |
if (p.prev == null) |
|
744 |
signalNext(p); |
|
745 |
} |
|
746 |
break; |
|
747 |
} |
|
748 |
if ((n = p.next) != q) { // help finish |
|
749 |
if (n != null && q.prev == p) { |
|
750 |
p.casNext(n, q); |
|
751 |
if (p.prev == null) |
|
752 |
signalNext(p); |
|
753 |
} |
|
754 |
break; |
|
755 |
} |
|
756 |
s = q; |
|
757 |
q = q.prev; |
|
2 | 758 |
} |
759 |
} |
|
760 |
} |
|
761 |
||
762 |
/** |
|
763 |
* Cancels an ongoing attempt to acquire. |
|
764 |
* |
|
58134 | 765 |
* @param node the node (may be null if cancelled before enqueuing) |
766 |
* @param interrupted true if thread interrupted |
|
767 |
* @param interruptible if should report interruption vs reset |
|
2 | 768 |
*/ |
58134 | 769 |
private int cancelAcquire(Node node, boolean interrupted, |
770 |
boolean interruptible) { |
|
771 |
if (node != null) { |
|
772 |
node.waiter = null; |
|
773 |
node.status = CANCELLED; |
|
774 |
if (node.prev != null) |
|
775 |
cleanQueue(); |
|
2 | 776 |
} |
58134 | 777 |
if (interrupted) { |
778 |
if (interruptible) |
|
779 |
return CANCELLED; |
|
780 |
else |
|
781 |
Thread.currentThread().interrupt(); |
|
2 | 782 |
} |
58134 | 783 |
return 0; |
2 | 784 |
} |
785 |
||
786 |
// Main exported methods |
|
787 |
||
788 |
/** |
|
789 |
* Attempts to acquire in exclusive mode. This method should query |
|
790 |
* if the state of the object permits it to be acquired in the |
|
791 |
* exclusive mode, and if so to acquire it. |
|
792 |
* |
|
793 |
* <p>This method is always invoked by the thread performing |
|
794 |
* acquire. If this method reports failure, the acquire method |
|
795 |
* may queue the thread, if it is not already queued, until it is |
|
796 |
* signalled by a release from some other thread. This can be used |
|
797 |
* to implement method {@link Lock#tryLock()}. |
|
798 |
* |
|
799 |
* <p>The default |
|
800 |
* implementation throws {@link UnsupportedOperationException}. |
|
801 |
* |
|
802 |
* @param arg the acquire argument. This value is always the one |
|
803 |
* passed to an acquire method, or is the value saved on entry |
|
804 |
* to a condition wait. The value is otherwise uninterpreted |
|
805 |
* and can represent anything you like. |
|
806 |
* @return {@code true} if successful. Upon success, this object has |
|
807 |
* been acquired. |
|
808 |
* @throws IllegalMonitorStateException if acquiring would place this |
|
809 |
* synchronizer in an illegal state. This exception must be |
|
810 |
* thrown in a consistent fashion for synchronization to work |
|
811 |
* correctly. |
|
812 |
* @throws UnsupportedOperationException if exclusive mode is not supported |
|
813 |
*/ |
|
814 |
protected boolean tryAcquire(int arg) { |
|
815 |
throw new UnsupportedOperationException(); |
|
816 |
} |
|
817 |
||
818 |
/** |
|
819 |
* Attempts to set the state to reflect a release in exclusive |
|
820 |
* mode. |
|
821 |
* |
|
822 |
* <p>This method is always invoked by the thread performing release. |
|
823 |
* |
|
824 |
* <p>The default implementation throws |
|
825 |
* {@link UnsupportedOperationException}. |
|
826 |
* |
|
827 |
* @param arg the release argument. This value is always the one |
|
828 |
* passed to a release method, or the current state value upon |
|
829 |
* entry to a condition wait. The value is otherwise |
|
830 |
* uninterpreted and can represent anything you like. |
|
831 |
* @return {@code true} if this object is now in a fully released |
|
832 |
* state, so that any waiting threads may attempt to acquire; |
|
833 |
* and {@code false} otherwise. |
|
834 |
* @throws IllegalMonitorStateException if releasing would place this |
|
835 |
* synchronizer in an illegal state. This exception must be |
|
836 |
* thrown in a consistent fashion for synchronization to work |
|
837 |
* correctly. |
|
838 |
* @throws UnsupportedOperationException if exclusive mode is not supported |
|
839 |
*/ |
|
840 |
protected boolean tryRelease(int arg) { |
|
841 |
throw new UnsupportedOperationException(); |
|
842 |
} |
|
843 |
||
844 |
/** |
|
845 |
* Attempts to acquire in shared mode. This method should query if |
|
846 |
* the state of the object permits it to be acquired in the shared |
|
847 |
* mode, and if so to acquire it. |
|
848 |
* |
|
849 |
* <p>This method is always invoked by the thread performing |
|
850 |
* acquire. If this method reports failure, the acquire method |
|
851 |
* may queue the thread, if it is not already queued, until it is |
|
852 |
* signalled by a release from some other thread. |
|
853 |
* |
|
854 |
* <p>The default implementation throws {@link |
|
855 |
* UnsupportedOperationException}. |
|
856 |
* |
|
857 |
* @param arg the acquire argument. This value is always the one |
|
858 |
* passed to an acquire method, or is the value saved on entry |
|
859 |
* to a condition wait. The value is otherwise uninterpreted |
|
860 |
* and can represent anything you like. |
|
861 |
* @return a negative value on failure; zero if acquisition in shared |
|
862 |
* mode succeeded but no subsequent shared-mode acquire can |
|
863 |
* succeed; and a positive value if acquisition in shared |
|
864 |
* mode succeeded and subsequent shared-mode acquires might |
|
865 |
* also succeed, in which case a subsequent waiting thread |
|
866 |
* must check availability. (Support for three different |
|
867 |
* return values enables this method to be used in contexts |
|
868 |
* where acquires only sometimes act exclusively.) Upon |
|
869 |
* success, this object has been acquired. |
|
870 |
* @throws IllegalMonitorStateException if acquiring would place this |
|
871 |
* synchronizer in an illegal state. This exception must be |
|
872 |
* thrown in a consistent fashion for synchronization to work |
|
873 |
* correctly. |
|
874 |
* @throws UnsupportedOperationException if shared mode is not supported |
|
875 |
*/ |
|
876 |
protected int tryAcquireShared(int arg) { |
|
877 |
throw new UnsupportedOperationException(); |
|
878 |
} |
|
879 |
||
880 |
/** |
|
881 |
* Attempts to set the state to reflect a release in shared mode. |
|
882 |
* |
|
883 |
* <p>This method is always invoked by the thread performing release. |
|
884 |
* |
|
885 |
* <p>The default implementation throws |
|
886 |
* {@link UnsupportedOperationException}. |
|
887 |
* |
|
888 |
* @param arg the release argument. This value is always the one |
|
889 |
* passed to a release method, or the current state value upon |
|
890 |
* entry to a condition wait. The value is otherwise |
|
891 |
* uninterpreted and can represent anything you like. |
|
892 |
* @return {@code true} if this release of shared mode may permit a |
|
893 |
* waiting acquire (shared or exclusive) to succeed; and |
|
894 |
* {@code false} otherwise |
|
895 |
* @throws IllegalMonitorStateException if releasing would place this |
|
896 |
* synchronizer in an illegal state. This exception must be |
|
897 |
* thrown in a consistent fashion for synchronization to work |
|
898 |
* correctly. |
|
899 |
* @throws UnsupportedOperationException if shared mode is not supported |
|
900 |
*/ |
|
901 |
protected boolean tryReleaseShared(int arg) { |
|
902 |
throw new UnsupportedOperationException(); |
|
903 |
} |
|
904 |
||
905 |
/** |
|
906 |
* Returns {@code true} if synchronization is held exclusively with |
|
907 |
* respect to the current (calling) thread. This method is invoked |
|
47302
f517fa4f4dc6
8187408: AbstractQueuedSynchronizer wait queue corrupted when thread awaits without holding the lock
dl
parents:
47216
diff
changeset
|
908 |
* upon each call to a {@link ConditionObject} method. |
2 | 909 |
* |
910 |
* <p>The default implementation throws {@link |
|
911 |
* UnsupportedOperationException}. This method is invoked |
|
912 |
* internally only within {@link ConditionObject} methods, so need |
|
913 |
* not be defined if conditions are not used. |
|
914 |
* |
|
915 |
* @return {@code true} if synchronization is held exclusively; |
|
916 |
* {@code false} otherwise |
|
917 |
* @throws UnsupportedOperationException if conditions are not supported |
|
918 |
*/ |
|
919 |
protected boolean isHeldExclusively() { |
|
920 |
throw new UnsupportedOperationException(); |
|
921 |
} |
|
922 |
||
923 |
/** |
|
924 |
* Acquires in exclusive mode, ignoring interrupts. Implemented |
|
925 |
* by invoking at least once {@link #tryAcquire}, |
|
926 |
* returning on success. Otherwise the thread is queued, possibly |
|
927 |
* repeatedly blocking and unblocking, invoking {@link |
|
928 |
* #tryAcquire} until success. This method can be used |
|
929 |
* to implement method {@link Lock#lock}. |
|
930 |
* |
|
931 |
* @param arg the acquire argument. This value is conveyed to |
|
932 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
|
933 |
* can represent anything you like. |
|
934 |
*/ |
|
935 |
public final void acquire(int arg) { |
|
58134 | 936 |
if (!tryAcquire(arg)) |
937 |
acquire(null, arg, false, false, false, 0L); |
|
2 | 938 |
} |
939 |
||
940 |
/** |
|
941 |
* Acquires in exclusive mode, aborting if interrupted. |
|
942 |
* Implemented by first checking interrupt status, then invoking |
|
943 |
* at least once {@link #tryAcquire}, returning on |
|
944 |
* success. Otherwise the thread is queued, possibly repeatedly |
|
945 |
* blocking and unblocking, invoking {@link #tryAcquire} |
|
946 |
* until success or the thread is interrupted. This method can be |
|
947 |
* used to implement method {@link Lock#lockInterruptibly}. |
|
948 |
* |
|
949 |
* @param arg the acquire argument. This value is conveyed to |
|
950 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
|
951 |
* can represent anything you like. |
|
952 |
* @throws InterruptedException if the current thread is interrupted |
|
953 |
*/ |
|
7518 | 954 |
public final void acquireInterruptibly(int arg) |
58134 | 955 |
throws InterruptedException { |
956 |
if (Thread.interrupted() || |
|
957 |
(!tryAcquire(arg) && acquire(null, arg, false, true, false, 0L) < 0)) |
|
2 | 958 |
throw new InterruptedException(); |
959 |
} |
|
960 |
||
961 |
/** |
|
962 |
* Attempts to acquire in exclusive mode, aborting if interrupted, |
|
963 |
* and failing if the given timeout elapses. Implemented by first |
|
964 |
* checking interrupt status, then invoking at least once {@link |
|
965 |
* #tryAcquire}, returning on success. Otherwise, the thread is |
|
966 |
* queued, possibly repeatedly blocking and unblocking, invoking |
|
967 |
* {@link #tryAcquire} until success or the thread is interrupted |
|
968 |
* or the timeout elapses. This method can be used to implement |
|
969 |
* method {@link Lock#tryLock(long, TimeUnit)}. |
|
970 |
* |
|
971 |
* @param arg the acquire argument. This value is conveyed to |
|
972 |
* {@link #tryAcquire} but is otherwise uninterpreted and |
|
973 |
* can represent anything you like. |
|
974 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
|
975 |
* @return {@code true} if acquired; {@code false} if timed out |
|
976 |
* @throws InterruptedException if the current thread is interrupted |
|
977 |
*/ |
|
7518 | 978 |
public final boolean tryAcquireNanos(int arg, long nanosTimeout) |
58134 | 979 |
throws InterruptedException { |
980 |
if (!Thread.interrupted()) { |
|
981 |
if (tryAcquire(arg)) |
|
982 |
return true; |
|
983 |
if (nanosTimeout <= 0L) |
|
984 |
return false; |
|
985 |
int stat = acquire(null, arg, false, true, true, |
|
986 |
System.nanoTime() + nanosTimeout); |
|
987 |
if (stat > 0) |
|
988 |
return true; |
|
989 |
if (stat == 0) |
|
990 |
return false; |
|
991 |
} |
|
992 |
throw new InterruptedException(); |
|
2 | 993 |
} |
994 |
||
995 |
/** |
|
996 |
* Releases in exclusive mode. Implemented by unblocking one or |
|
997 |
* more threads if {@link #tryRelease} returns true. |
|
998 |
* This method can be used to implement method {@link Lock#unlock}. |
|
999 |
* |
|
1000 |
* @param arg the release argument. This value is conveyed to |
|
1001 |
* {@link #tryRelease} but is otherwise uninterpreted and |
|
1002 |
* can represent anything you like. |
|
1003 |
* @return the value returned from {@link #tryRelease} |
|
1004 |
*/ |
|
1005 |
public final boolean release(int arg) { |
|
1006 |
if (tryRelease(arg)) { |
|
58134 | 1007 |
signalNext(head); |
2 | 1008 |
return true; |
1009 |
} |
|
1010 |
return false; |
|
1011 |
} |
|
1012 |
||
1013 |
/** |
|
1014 |
* Acquires in shared mode, ignoring interrupts. Implemented by |
|
1015 |
* first invoking at least once {@link #tryAcquireShared}, |
|
1016 |
* returning on success. Otherwise the thread is queued, possibly |
|
1017 |
* repeatedly blocking and unblocking, invoking {@link |
|
1018 |
* #tryAcquireShared} until success. |
|
1019 |
* |
|
1020 |
* @param arg the acquire argument. This value is conveyed to |
|
1021 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
|
1022 |
* and can represent anything you like. |
|
1023 |
*/ |
|
1024 |
public final void acquireShared(int arg) { |
|
1025 |
if (tryAcquireShared(arg) < 0) |
|
58134 | 1026 |
acquire(null, arg, true, false, false, 0L); |
2 | 1027 |
} |
1028 |
||
1029 |
/** |
|
1030 |
* Acquires in shared mode, aborting if interrupted. Implemented |
|
1031 |
* by first checking interrupt status, then invoking at least once |
|
1032 |
* {@link #tryAcquireShared}, returning on success. Otherwise the |
|
1033 |
* thread is queued, possibly repeatedly blocking and unblocking, |
|
1034 |
* invoking {@link #tryAcquireShared} until success or the thread |
|
1035 |
* is interrupted. |
|
18576 | 1036 |
* @param arg the acquire argument. |
2 | 1037 |
* This value is conveyed to {@link #tryAcquireShared} but is |
1038 |
* otherwise uninterpreted and can represent anything |
|
1039 |
* you like. |
|
1040 |
* @throws InterruptedException if the current thread is interrupted |
|
1041 |
*/ |
|
7518 | 1042 |
public final void acquireSharedInterruptibly(int arg) |
58134 | 1043 |
throws InterruptedException { |
1044 |
if (Thread.interrupted() || |
|
1045 |
(tryAcquireShared(arg) < 0 && |
|
1046 |
acquire(null, arg, true, true, false, 0L) < 0)) |
|
2 | 1047 |
throw new InterruptedException(); |
1048 |
} |
|
1049 |
||
1050 |
/** |
|
1051 |
* Attempts to acquire in shared mode, aborting if interrupted, and |
|
1052 |
* failing if the given timeout elapses. Implemented by first |
|
1053 |
* checking interrupt status, then invoking at least once {@link |
|
1054 |
* #tryAcquireShared}, returning on success. Otherwise, the |
|
1055 |
* thread is queued, possibly repeatedly blocking and unblocking, |
|
1056 |
* invoking {@link #tryAcquireShared} until success or the thread |
|
1057 |
* is interrupted or the timeout elapses. |
|
1058 |
* |
|
1059 |
* @param arg the acquire argument. This value is conveyed to |
|
1060 |
* {@link #tryAcquireShared} but is otherwise uninterpreted |
|
1061 |
* and can represent anything you like. |
|
1062 |
* @param nanosTimeout the maximum number of nanoseconds to wait |
|
1063 |
* @return {@code true} if acquired; {@code false} if timed out |
|
1064 |
* @throws InterruptedException if the current thread is interrupted |
|
1065 |
*/ |
|
7518 | 1066 |
public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout) |
1067 |
throws InterruptedException { |
|
58134 | 1068 |
if (!Thread.interrupted()) { |
1069 |
if (tryAcquireShared(arg) >= 0) |
|
1070 |
return true; |
|
1071 |
if (nanosTimeout <= 0L) |
|
1072 |
return false; |
|
1073 |
int stat = acquire(null, arg, true, true, true, |
|
1074 |
System.nanoTime() + nanosTimeout); |
|
1075 |
if (stat > 0) |
|
1076 |
return true; |
|
1077 |
if (stat == 0) |
|
1078 |
return false; |
|
1079 |
} |
|
1080 |
throw new InterruptedException(); |
|
2 | 1081 |
} |
1082 |
||
1083 |
/** |
|
1084 |
* Releases in shared mode. Implemented by unblocking one or more |
|
1085 |
* threads if {@link #tryReleaseShared} returns true. |
|
1086 |
* |
|
1087 |
* @param arg the release argument. This value is conveyed to |
|
1088 |
* {@link #tryReleaseShared} but is otherwise uninterpreted |
|
1089 |
* and can represent anything you like. |
|
1090 |
* @return the value returned from {@link #tryReleaseShared} |
|
1091 |
*/ |
|
1092 |
public final boolean releaseShared(int arg) { |
|
1093 |
if (tryReleaseShared(arg)) { |
|
58134 | 1094 |
signalNext(head); |
2 | 1095 |
return true; |
1096 |
} |
|
1097 |
return false; |
|
1098 |
} |
|
1099 |
||
1100 |
// Queue inspection methods |
|
1101 |
||
1102 |
/** |
|
1103 |
* Queries whether any threads are waiting to acquire. Note that |
|
1104 |
* because cancellations due to interrupts and timeouts may occur |
|
1105 |
* at any time, a {@code true} return does not guarantee that any |
|
1106 |
* other thread will ever acquire. |
|
1107 |
* |
|
1108 |
* @return {@code true} if there may be other threads waiting to acquire |
|
1109 |
*/ |
|
1110 |
public final boolean hasQueuedThreads() { |
|
48540
221cf8307606
8191483: AbstractQueuedSynchronizer cancel/cancel race
dl
parents:
48046
diff
changeset
|
1111 |
for (Node p = tail, h = head; p != h && p != null; p = p.prev) |
58134 | 1112 |
if (p.status >= 0) |
48540
221cf8307606
8191483: AbstractQueuedSynchronizer cancel/cancel race
dl
parents:
48046
diff
changeset
|
1113 |
return true; |
221cf8307606
8191483: AbstractQueuedSynchronizer cancel/cancel race
dl
parents:
48046
diff
changeset
|
1114 |
return false; |
2 | 1115 |
} |
1116 |
||
1117 |
/** |
|
1118 |
* Queries whether any threads have ever contended to acquire this |
|
34348
ba5c2f2fc9d7
8143087: Miscellaneous changes imported from jsr166 CVS 2015-11
dl
parents:
33674
diff
changeset
|
1119 |
* synchronizer; that is, if an acquire method has ever blocked. |
2 | 1120 |
* |
1121 |
* <p>In this implementation, this operation returns in |
|
1122 |
* constant time. |
|
1123 |
* |
|
1124 |
* @return {@code true} if there has ever been contention |
|
1125 |
*/ |
|
1126 |
public final boolean hasContended() { |
|
1127 |
return head != null; |
|
1128 |
} |
|
1129 |
||
1130 |
/** |
|
1131 |
* Returns the first (longest-waiting) thread in the queue, or |
|
1132 |
* {@code null} if no threads are currently queued. |
|
1133 |
* |
|
1134 |
* <p>In this implementation, this operation normally returns in |
|
1135 |
* constant time, but may iterate upon contention if other threads are |
|
1136 |
* concurrently modifying the queue. |
|
1137 |
* |
|
1138 |
* @return the first (longest-waiting) thread in the queue, or |
|
1139 |
* {@code null} if no threads are currently queued |
|
1140 |
*/ |
|
1141 |
public final Thread getFirstQueuedThread() { |
|
58134 | 1142 |
Thread first = null, w; Node h, s; |
1143 |
if ((h = head) != null && ((s = h.next) == null || |
|
1144 |
(first = s.waiter) == null || |
|
1145 |
s.prev == null)) { |
|
1146 |
// traverse from tail on stale reads |
|
1147 |
for (Node p = tail, q; p != null && (q = p.prev) != null; p = q) |
|
1148 |
if ((w = p.waiter) != null) |
|
1149 |
first = w; |
|
2 | 1150 |
} |
58134 | 1151 |
return first; |
2 | 1152 |
} |
1153 |
||
1154 |
/** |
|
1155 |
* Returns true if the given thread is currently queued. |
|
1156 |
* |
|
1157 |
* <p>This implementation traverses the queue to determine |
|
1158 |
* presence of the given thread. |
|
1159 |
* |
|
1160 |
* @param thread the thread |
|
1161 |
* @return {@code true} if the given thread is on the queue |
|
1162 |
* @throws NullPointerException if the thread is null |
|
1163 |
*/ |
|
1164 |
public final boolean isQueued(Thread thread) { |
|
1165 |
if (thread == null) |
|
1166 |
throw new NullPointerException(); |
|
1167 |
for (Node p = tail; p != null; p = p.prev) |
|
58134 | 1168 |
if (p.waiter == thread) |
2 | 1169 |
return true; |
1170 |
return false; |
|
1171 |
} |
|
1172 |
||
1173 |
/** |
|
1174 |
* Returns {@code true} if the apparent first queued thread, if one |
|
1175 |
* exists, is waiting in exclusive mode. If this method returns |
|
1176 |
* {@code true}, and the current thread is attempting to acquire in |
|
1177 |
* shared mode (that is, this method is invoked from {@link |
|
1178 |
* #tryAcquireShared}) then it is guaranteed that the current thread |
|
1179 |
* is not the first queued thread. Used only as a heuristic in |
|
1180 |
* ReentrantReadWriteLock. |
|
1181 |
*/ |
|
1182 |
final boolean apparentlyFirstQueuedIsExclusive() { |
|
1183 |
Node h, s; |
|
58134 | 1184 |
return (h = head) != null && (s = h.next) != null && |
1185 |
!(s instanceof SharedNode) && s.waiter != null; |
|
2 | 1186 |
} |
1187 |
||
1188 |
/** |
|
1189 |
* Queries whether any threads have been waiting to acquire longer |
|
1190 |
* than the current thread. |
|
1191 |
* |
|
1192 |
* <p>An invocation of this method is equivalent to (but may be |
|
1193 |
* more efficient than): |
|
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|
1194 |
* <pre> {@code |
34348
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changeset
|
1195 |
* getFirstQueuedThread() != Thread.currentThread() |
ba5c2f2fc9d7
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|
1196 |
* && hasQueuedThreads()}</pre> |
2 | 1197 |
* |
1198 |
* <p>Note that because cancellations due to interrupts and |
|
1199 |
* timeouts may occur at any time, a {@code true} return does not |
|
1200 |
* guarantee that some other thread will acquire before the current |
|
1201 |
* thread. Likewise, it is possible for another thread to win a |
|
1202 |
* race to enqueue after this method has returned {@code false}, |
|
1203 |
* due to the queue being empty. |
|
1204 |
* |
|
1205 |
* <p>This method is designed to be used by a fair synchronizer to |
|
23020
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chegar
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changeset
|
1206 |
* avoid <a href="AbstractQueuedSynchronizer.html#barging">barging</a>. |
2 | 1207 |
* Such a synchronizer's {@link #tryAcquire} method should return |
1208 |
* {@code false}, and its {@link #tryAcquireShared} method should |
|
1209 |
* return a negative value, if this method returns {@code true} |
|
1210 |
* (unless this is a reentrant acquire). For example, the {@code |
|
1211 |
* tryAcquire} method for a fair, reentrant, exclusive mode |
|
1212 |
* synchronizer might look like this: |
|
1213 |
* |
|
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|
1214 |
* <pre> {@code |
2 | 1215 |
* protected boolean tryAcquire(int arg) { |
1216 |
* if (isHeldExclusively()) { |
|
1217 |
* // A reentrant acquire; increment hold count |
|
1218 |
* return true; |
|
1219 |
* } else if (hasQueuedPredecessors()) { |
|
1220 |
* return false; |
|
1221 |
* } else { |
|
1222 |
* // try to acquire normally |
|
1223 |
* } |
|
1224 |
* }}</pre> |
|
1225 |
* |
|
1226 |
* @return {@code true} if there is a queued thread preceding the |
|
1227 |
* current thread, and {@code false} if the current thread |
|
1228 |
* is at the head of the queue or the queue is empty |
|
1229 |
* @since 1.7 |
|
1230 |
*/ |
|
1231 |
public final boolean hasQueuedPredecessors() { |
|
58134 | 1232 |
Thread first = null; Node h, s; |
1233 |
if ((h = head) != null && ((s = h.next) == null || |
|
1234 |
(first = s.waiter) == null || |
|
1235 |
s.prev == null)) |
|
1236 |
first = getFirstQueuedThread(); // retry via getFirstQueuedThread |
|
1237 |
return first != null && first != Thread.currentThread(); |
|
2 | 1238 |
} |
1239 |
||
1240 |
// Instrumentation and monitoring methods |
|
1241 |
||
1242 |
/** |
|
1243 |
* Returns an estimate of the number of threads waiting to |
|
1244 |
* acquire. The value is only an estimate because the number of |
|
1245 |
* threads may change dynamically while this method traverses |
|
1246 |
* internal data structures. This method is designed for use in |
|
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|
1247 |
* monitoring system state, not for synchronization control. |
2 | 1248 |
* |
1249 |
* @return the estimated number of threads waiting to acquire |
|
1250 |
*/ |
|
1251 |
public final int getQueueLength() { |
|
1252 |
int n = 0; |
|
1253 |
for (Node p = tail; p != null; p = p.prev) { |
|
58134 | 1254 |
if (p.waiter != null) |
2 | 1255 |
++n; |
1256 |
} |
|
1257 |
return n; |
|
1258 |
} |
|
1259 |
||
1260 |
/** |
|
1261 |
* Returns a collection containing threads that may be waiting to |
|
1262 |
* acquire. Because the actual set of threads may change |
|
1263 |
* dynamically while constructing this result, the returned |
|
1264 |
* collection is only a best-effort estimate. The elements of the |
|
1265 |
* returned collection are in no particular order. This method is |
|
1266 |
* designed to facilitate construction of subclasses that provide |
|
1267 |
* more extensive monitoring facilities. |
|
1268 |
* |
|
1269 |
* @return the collection of threads |
|
1270 |
*/ |
|
1271 |
public final Collection<Thread> getQueuedThreads() { |
|
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diff
changeset
|
1272 |
ArrayList<Thread> list = new ArrayList<>(); |
2 | 1273 |
for (Node p = tail; p != null; p = p.prev) { |
58134 | 1274 |
Thread t = p.waiter; |
2 | 1275 |
if (t != null) |
1276 |
list.add(t); |
|
1277 |
} |
|
1278 |
return list; |
|
1279 |
} |
|
1280 |
||
1281 |
/** |
|
1282 |
* Returns a collection containing threads that may be waiting to |
|
1283 |
* acquire in exclusive mode. This has the same properties |
|
1284 |
* as {@link #getQueuedThreads} except that it only returns |
|
1285 |
* those threads waiting due to an exclusive acquire. |
|
1286 |
* |
|
1287 |
* @return the collection of threads |
|
1288 |
*/ |
|
1289 |
public final Collection<Thread> getExclusiveQueuedThreads() { |
|
32990
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diff
changeset
|
1290 |
ArrayList<Thread> list = new ArrayList<>(); |
2 | 1291 |
for (Node p = tail; p != null; p = p.prev) { |
58134 | 1292 |
if (!(p instanceof SharedNode)) { |
1293 |
Thread t = p.waiter; |
|
2 | 1294 |
if (t != null) |
1295 |
list.add(t); |
|
1296 |
} |
|
1297 |
} |
|
1298 |
return list; |
|
1299 |
} |
|
1300 |
||
1301 |
/** |
|
1302 |
* Returns a collection containing threads that may be waiting to |
|
1303 |
* acquire in shared mode. This has the same properties |
|
1304 |
* as {@link #getQueuedThreads} except that it only returns |
|
1305 |
* those threads waiting due to a shared acquire. |
|
1306 |
* |
|
1307 |
* @return the collection of threads |
|
1308 |
*/ |
|
1309 |
public final Collection<Thread> getSharedQueuedThreads() { |
|
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diff
changeset
|
1310 |
ArrayList<Thread> list = new ArrayList<>(); |
2 | 1311 |
for (Node p = tail; p != null; p = p.prev) { |
58134 | 1312 |
if (p instanceof SharedNode) { |
1313 |
Thread t = p.waiter; |
|
2 | 1314 |
if (t != null) |
1315 |
list.add(t); |
|
1316 |
} |
|
1317 |
} |
|
1318 |
return list; |
|
1319 |
} |
|
1320 |
||
1321 |
/** |
|
1322 |
* Returns a string identifying this synchronizer, as well as its state. |
|
1323 |
* The state, in brackets, includes the String {@code "State ="} |
|
1324 |
* followed by the current value of {@link #getState}, and either |
|
1325 |
* {@code "nonempty"} or {@code "empty"} depending on whether the |
|
1326 |
* queue is empty. |
|
1327 |
* |
|
1328 |
* @return a string identifying this synchronizer, as well as its state |
|
1329 |
*/ |
|
1330 |
public String toString() { |
|
32990
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25859
diff
changeset
|
1331 |
return super.toString() |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
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parents:
25859
diff
changeset
|
1332 |
+ "[State = " + getState() + ", " |
299a81977f48
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dl
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diff
changeset
|
1333 |
+ (hasQueuedThreads() ? "non" : "") + "empty queue]"; |
2 | 1334 |
} |
1335 |
||
1336 |
// Instrumentation methods for conditions |
|
1337 |
||
1338 |
/** |
|
1339 |
* Queries whether the given ConditionObject |
|
1340 |
* uses this synchronizer as its lock. |
|
1341 |
* |
|
1342 |
* @param condition the condition |
|
18576 | 1343 |
* @return {@code true} if owned |
2 | 1344 |
* @throws NullPointerException if the condition is null |
1345 |
*/ |
|
1346 |
public final boolean owns(ConditionObject condition) { |
|
1347 |
return condition.isOwnedBy(this); |
|
1348 |
} |
|
1349 |
||
1350 |
/** |
|
1351 |
* Queries whether any threads are waiting on the given condition |
|
1352 |
* associated with this synchronizer. Note that because timeouts |
|
18576 | 1353 |
* and interrupts may occur at any time, a {@code true} return |
1354 |
* does not guarantee that a future {@code signal} will awaken |
|
2 | 1355 |
* any threads. This method is designed primarily for use in |
1356 |
* monitoring of the system state. |
|
1357 |
* |
|
1358 |
* @param condition the condition |
|
18576 | 1359 |
* @return {@code true} if there are any waiting threads |
2 | 1360 |
* @throws IllegalMonitorStateException if exclusive synchronization |
1361 |
* is not held |
|
1362 |
* @throws IllegalArgumentException if the given condition is |
|
1363 |
* not associated with this synchronizer |
|
1364 |
* @throws NullPointerException if the condition is null |
|
1365 |
*/ |
|
1366 |
public final boolean hasWaiters(ConditionObject condition) { |
|
1367 |
if (!owns(condition)) |
|
1368 |
throw new IllegalArgumentException("Not owner"); |
|
1369 |
return condition.hasWaiters(); |
|
1370 |
} |
|
1371 |
||
1372 |
/** |
|
1373 |
* Returns an estimate of the number of threads waiting on the |
|
1374 |
* given condition associated with this synchronizer. Note that |
|
1375 |
* because timeouts and interrupts may occur at any time, the |
|
1376 |
* estimate serves only as an upper bound on the actual number of |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1377 |
* waiters. This method is designed for use in monitoring system |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1378 |
* state, not for synchronization control. |
2 | 1379 |
* |
1380 |
* @param condition the condition |
|
1381 |
* @return the estimated number of waiting threads |
|
1382 |
* @throws IllegalMonitorStateException if exclusive synchronization |
|
1383 |
* is not held |
|
1384 |
* @throws IllegalArgumentException if the given condition is |
|
1385 |
* not associated with this synchronizer |
|
1386 |
* @throws NullPointerException if the condition is null |
|
1387 |
*/ |
|
1388 |
public final int getWaitQueueLength(ConditionObject condition) { |
|
1389 |
if (!owns(condition)) |
|
1390 |
throw new IllegalArgumentException("Not owner"); |
|
1391 |
return condition.getWaitQueueLength(); |
|
1392 |
} |
|
1393 |
||
1394 |
/** |
|
1395 |
* Returns a collection containing those threads that may be |
|
1396 |
* waiting on the given condition associated with this |
|
1397 |
* synchronizer. Because the actual set of threads may change |
|
1398 |
* dynamically while constructing this result, the returned |
|
1399 |
* collection is only a best-effort estimate. The elements of the |
|
1400 |
* returned collection are in no particular order. |
|
1401 |
* |
|
1402 |
* @param condition the condition |
|
1403 |
* @return the collection of threads |
|
1404 |
* @throws IllegalMonitorStateException if exclusive synchronization |
|
1405 |
* is not held |
|
1406 |
* @throws IllegalArgumentException if the given condition is |
|
1407 |
* not associated with this synchronizer |
|
1408 |
* @throws NullPointerException if the condition is null |
|
1409 |
*/ |
|
1410 |
public final Collection<Thread> getWaitingThreads(ConditionObject condition) { |
|
1411 |
if (!owns(condition)) |
|
1412 |
throw new IllegalArgumentException("Not owner"); |
|
1413 |
return condition.getWaitingThreads(); |
|
1414 |
} |
|
1415 |
||
1416 |
/** |
|
47302
f517fa4f4dc6
8187408: AbstractQueuedSynchronizer wait queue corrupted when thread awaits without holding the lock
dl
parents:
47216
diff
changeset
|
1417 |
* Condition implementation for a {@link AbstractQueuedSynchronizer} |
f517fa4f4dc6
8187408: AbstractQueuedSynchronizer wait queue corrupted when thread awaits without holding the lock
dl
parents:
47216
diff
changeset
|
1418 |
* serving as the basis of a {@link Lock} implementation. |
2 | 1419 |
* |
1420 |
* <p>Method documentation for this class describes mechanics, |
|
1421 |
* not behavioral specifications from the point of view of Lock |
|
1422 |
* and Condition users. Exported versions of this class will in |
|
1423 |
* general need to be accompanied by documentation describing |
|
1424 |
* condition semantics that rely on those of the associated |
|
18576 | 1425 |
* {@code AbstractQueuedSynchronizer}. |
2 | 1426 |
* |
1427 |
* <p>This class is Serializable, but all fields are transient, |
|
1428 |
* so deserialized conditions have no waiters. |
|
1429 |
*/ |
|
1430 |
public class ConditionObject implements Condition, java.io.Serializable { |
|
1431 |
private static final long serialVersionUID = 1173984872572414699L; |
|
1432 |
/** First node of condition queue. */ |
|
58134 | 1433 |
private transient ConditionNode firstWaiter; |
2 | 1434 |
/** Last node of condition queue. */ |
58134 | 1435 |
private transient ConditionNode lastWaiter; |
2 | 1436 |
|
1437 |
/** |
|
18576 | 1438 |
* Creates a new {@code ConditionObject} instance. |
2 | 1439 |
*/ |
1440 |
public ConditionObject() { } |
|
1441 |
||
58134 | 1442 |
// Signalling methods |
2 | 1443 |
|
1444 |
/** |
|
58134 | 1445 |
* Removes and transfers one or all waiters to sync queue. |
2 | 1446 |
*/ |
58134 | 1447 |
private void doSignal(ConditionNode first, boolean all) { |
1448 |
while (first != null) { |
|
1449 |
ConditionNode next = first.nextWaiter; |
|
1450 |
if ((firstWaiter = next) == null) |
|
1451 |
lastWaiter = null; |
|
1452 |
if ((first.getAndUnsetStatus(COND) & COND) != 0) { |
|
1453 |
enqueue(first); |
|
1454 |
if (!all) |
|
1455 |
break; |
|
1456 |
} |
|
2 | 1457 |
first = next; |
1458 |
} |
|
1459 |
} |
|
1460 |
||
1461 |
/** |
|
1462 |
* Moves the longest-waiting thread, if one exists, from the |
|
1463 |
* wait queue for this condition to the wait queue for the |
|
1464 |
* owning lock. |
|
1465 |
* |
|
1466 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
|
1467 |
* returns {@code false} |
|
1468 |
*/ |
|
1469 |
public final void signal() { |
|
58134 | 1470 |
ConditionNode first = firstWaiter; |
2 | 1471 |
if (!isHeldExclusively()) |
1472 |
throw new IllegalMonitorStateException(); |
|
1473 |
if (first != null) |
|
58134 | 1474 |
doSignal(first, false); |
2 | 1475 |
} |
1476 |
||
1477 |
/** |
|
1478 |
* Moves all threads from the wait queue for this condition to |
|
1479 |
* the wait queue for the owning lock. |
|
1480 |
* |
|
1481 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
|
1482 |
* returns {@code false} |
|
1483 |
*/ |
|
1484 |
public final void signalAll() { |
|
58134 | 1485 |
ConditionNode first = firstWaiter; |
2 | 1486 |
if (!isHeldExclusively()) |
1487 |
throw new IllegalMonitorStateException(); |
|
1488 |
if (first != null) |
|
58134 | 1489 |
doSignal(first, true); |
1490 |
} |
|
1491 |
||
1492 |
// Waiting methods |
|
1493 |
||
1494 |
/** |
|
1495 |
* Adds node to condition list and releases lock. |
|
1496 |
* |
|
1497 |
* @param node the node |
|
1498 |
* @return savedState to reacquire after wait |
|
1499 |
*/ |
|
1500 |
private int enableWait(ConditionNode node) { |
|
1501 |
if (isHeldExclusively()) { |
|
1502 |
node.waiter = Thread.currentThread(); |
|
1503 |
node.setStatusRelaxed(COND | WAITING); |
|
1504 |
ConditionNode last = lastWaiter; |
|
1505 |
if (last == null) |
|
1506 |
firstWaiter = node; |
|
1507 |
else |
|
1508 |
last.nextWaiter = node; |
|
1509 |
lastWaiter = node; |
|
1510 |
int savedState = getState(); |
|
1511 |
if (release(savedState)) |
|
1512 |
return savedState; |
|
1513 |
} |
|
1514 |
node.status = CANCELLED; // lock not held or inconsistent |
|
1515 |
throw new IllegalMonitorStateException(); |
|
1516 |
} |
|
1517 |
||
1518 |
/** |
|
1519 |
* Returns true if a node that was initially placed on a condition |
|
1520 |
* queue is now ready to reacquire on sync queue. |
|
1521 |
* @param node the node |
|
1522 |
* @return true if is reacquiring |
|
1523 |
*/ |
|
1524 |
private boolean canReacquire(ConditionNode node) { |
|
1525 |
// check links, not status to avoid enqueue race |
|
1526 |
return node != null && node.prev != null && isEnqueued(node); |
|
1527 |
} |
|
1528 |
||
1529 |
/** |
|
1530 |
* Unlinks the given node and other non-waiting nodes from |
|
1531 |
* condition queue unless already unlinked. |
|
1532 |
*/ |
|
1533 |
private void unlinkCancelledWaiters(ConditionNode node) { |
|
1534 |
if (node == null || node.nextWaiter != null || node == lastWaiter) { |
|
1535 |
ConditionNode w = firstWaiter, trail = null; |
|
1536 |
while (w != null) { |
|
1537 |
ConditionNode next = w.nextWaiter; |
|
1538 |
if ((w.status & COND) == 0) { |
|
1539 |
w.nextWaiter = null; |
|
1540 |
if (trail == null) |
|
1541 |
firstWaiter = next; |
|
1542 |
else |
|
1543 |
trail.nextWaiter = next; |
|
1544 |
if (next == null) |
|
1545 |
lastWaiter = trail; |
|
1546 |
} else |
|
1547 |
trail = w; |
|
1548 |
w = next; |
|
1549 |
} |
|
1550 |
} |
|
2 | 1551 |
} |
1552 |
||
1553 |
/** |
|
1554 |
* Implements uninterruptible condition wait. |
|
1555 |
* <ol> |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1556 |
* <li>Save lock state returned by {@link #getState}. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1557 |
* <li>Invoke {@link #release} with saved state as argument, |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1558 |
* throwing IllegalMonitorStateException if it fails. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1559 |
* <li>Block until signalled. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1560 |
* <li>Reacquire by invoking specialized version of |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1561 |
* {@link #acquire} with saved state as argument. |
2 | 1562 |
* </ol> |
1563 |
*/ |
|
1564 |
public final void awaitUninterruptibly() { |
|
58134 | 1565 |
ConditionNode node = new ConditionNode(); |
1566 |
int savedState = enableWait(node); |
|
1567 |
LockSupport.setCurrentBlocker(this); // for back-compatibility |
|
2 | 1568 |
boolean interrupted = false; |
58134 | 1569 |
while (!canReacquire(node)) { |
2 | 1570 |
if (Thread.interrupted()) |
1571 |
interrupted = true; |
|
58134 | 1572 |
else if ((node.status & COND) != 0) { |
1573 |
try { |
|
1574 |
ForkJoinPool.managedBlock(node); |
|
1575 |
} catch (InterruptedException ie) { |
|
1576 |
interrupted = true; |
|
1577 |
} |
|
1578 |
} else |
|
1579 |
Thread.onSpinWait(); // awoke while enqueuing |
|
2 | 1580 |
} |
58134 | 1581 |
LockSupport.setCurrentBlocker(null); |
1582 |
node.clearStatus(); |
|
1583 |
acquire(node, savedState, false, false, false, 0L); |
|
1584 |
if (interrupted) |
|
1585 |
Thread.currentThread().interrupt(); |
|
2 | 1586 |
} |
1587 |
||
1588 |
/** |
|
1589 |
* Implements interruptible condition wait. |
|
1590 |
* <ol> |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1591 |
* <li>If current thread is interrupted, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1592 |
* <li>Save lock state returned by {@link #getState}. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1593 |
* <li>Invoke {@link #release} with saved state as argument, |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1594 |
* throwing IllegalMonitorStateException if it fails. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1595 |
* <li>Block until signalled or interrupted. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1596 |
* <li>Reacquire by invoking specialized version of |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1597 |
* {@link #acquire} with saved state as argument. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1598 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
2 | 1599 |
* </ol> |
1600 |
*/ |
|
1601 |
public final void await() throws InterruptedException { |
|
1602 |
if (Thread.interrupted()) |
|
1603 |
throw new InterruptedException(); |
|
58134 | 1604 |
ConditionNode node = new ConditionNode(); |
1605 |
int savedState = enableWait(node); |
|
1606 |
LockSupport.setCurrentBlocker(this); // for back-compatibility |
|
1607 |
boolean interrupted = false, cancelled = false; |
|
1608 |
while (!canReacquire(node)) { |
|
1609 |
if (interrupted |= Thread.interrupted()) { |
|
1610 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
|
1611 |
break; // else interrupted after signal |
|
1612 |
} else if ((node.status & COND) != 0) { |
|
1613 |
try { |
|
1614 |
ForkJoinPool.managedBlock(node); |
|
1615 |
} catch (InterruptedException ie) { |
|
1616 |
interrupted = true; |
|
1617 |
} |
|
1618 |
} else |
|
1619 |
Thread.onSpinWait(); // awoke while enqueuing |
|
2 | 1620 |
} |
58134 | 1621 |
LockSupport.setCurrentBlocker(null); |
1622 |
node.clearStatus(); |
|
1623 |
acquire(node, savedState, false, false, false, 0L); |
|
1624 |
if (interrupted) { |
|
1625 |
if (cancelled) { |
|
1626 |
unlinkCancelledWaiters(node); |
|
1627 |
throw new InterruptedException(); |
|
1628 |
} |
|
1629 |
Thread.currentThread().interrupt(); |
|
1630 |
} |
|
2 | 1631 |
} |
1632 |
||
1633 |
/** |
|
1634 |
* Implements timed condition wait. |
|
1635 |
* <ol> |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1636 |
* <li>If current thread is interrupted, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1637 |
* <li>Save lock state returned by {@link #getState}. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1638 |
* <li>Invoke {@link #release} with saved state as argument, |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1639 |
* throwing IllegalMonitorStateException if it fails. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1640 |
* <li>Block until signalled, interrupted, or timed out. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1641 |
* <li>Reacquire by invoking specialized version of |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1642 |
* {@link #acquire} with saved state as argument. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1643 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
2 | 1644 |
* </ol> |
1645 |
*/ |
|
7518 | 1646 |
public final long awaitNanos(long nanosTimeout) |
1647 |
throws InterruptedException { |
|
2 | 1648 |
if (Thread.interrupted()) |
1649 |
throw new InterruptedException(); |
|
58134 | 1650 |
ConditionNode node = new ConditionNode(); |
1651 |
int savedState = enableWait(node); |
|
1652 |
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout; |
|
1653 |
long deadline = System.nanoTime() + nanos; |
|
1654 |
boolean cancelled = false, interrupted = false; |
|
1655 |
while (!canReacquire(node)) { |
|
1656 |
if ((interrupted |= Thread.interrupted()) || |
|
1657 |
(nanos = deadline - System.nanoTime()) <= 0L) { |
|
1658 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
|
1659 |
break; |
|
1660 |
} else |
|
1661 |
LockSupport.parkNanos(this, nanos); |
|
2 | 1662 |
} |
58134 | 1663 |
node.clearStatus(); |
1664 |
acquire(node, savedState, false, false, false, 0L); |
|
1665 |
if (cancelled) { |
|
1666 |
unlinkCancelledWaiters(node); |
|
1667 |
if (interrupted) |
|
1668 |
throw new InterruptedException(); |
|
1669 |
} else if (interrupted) |
|
1670 |
Thread.currentThread().interrupt(); |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1671 |
long remaining = deadline - System.nanoTime(); // avoid overflow |
58134 | 1672 |
return (remaining <= nanosTimeout) ? remaining : Long.MIN_VALUE; |
2 | 1673 |
} |
1674 |
||
1675 |
/** |
|
1676 |
* Implements absolute timed condition wait. |
|
1677 |
* <ol> |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1678 |
* <li>If current thread is interrupted, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1679 |
* <li>Save lock state returned by {@link #getState}. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1680 |
* <li>Invoke {@link #release} with saved state as argument, |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1681 |
* throwing IllegalMonitorStateException if it fails. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1682 |
* <li>Block until signalled, interrupted, or timed out. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1683 |
* <li>Reacquire by invoking specialized version of |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1684 |
* {@link #acquire} with saved state as argument. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1685 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1686 |
* <li>If timed out while blocked in step 4, return false, else true. |
2 | 1687 |
* </ol> |
1688 |
*/ |
|
7518 | 1689 |
public final boolean awaitUntil(Date deadline) |
1690 |
throws InterruptedException { |
|
2 | 1691 |
long abstime = deadline.getTime(); |
1692 |
if (Thread.interrupted()) |
|
1693 |
throw new InterruptedException(); |
|
58134 | 1694 |
ConditionNode node = new ConditionNode(); |
1695 |
int savedState = enableWait(node); |
|
1696 |
boolean cancelled = false, interrupted = false; |
|
1697 |
while (!canReacquire(node)) { |
|
1698 |
if ((interrupted |= Thread.interrupted()) || |
|
1699 |
System.currentTimeMillis() >= abstime) { |
|
1700 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
|
1701 |
break; |
|
1702 |
} else |
|
1703 |
LockSupport.parkUntil(this, abstime); |
|
2 | 1704 |
} |
58134 | 1705 |
node.clearStatus(); |
1706 |
acquire(node, savedState, false, false, false, 0L); |
|
1707 |
if (cancelled) { |
|
1708 |
unlinkCancelledWaiters(node); |
|
1709 |
if (interrupted) |
|
1710 |
throw new InterruptedException(); |
|
1711 |
} else if (interrupted) |
|
1712 |
Thread.currentThread().interrupt(); |
|
1713 |
return !cancelled; |
|
2 | 1714 |
} |
1715 |
||
1716 |
/** |
|
1717 |
* Implements timed condition wait. |
|
1718 |
* <ol> |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1719 |
* <li>If current thread is interrupted, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1720 |
* <li>Save lock state returned by {@link #getState}. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1721 |
* <li>Invoke {@link #release} with saved state as argument, |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1722 |
* throwing IllegalMonitorStateException if it fails. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1723 |
* <li>Block until signalled, interrupted, or timed out. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1724 |
* <li>Reacquire by invoking specialized version of |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1725 |
* {@link #acquire} with saved state as argument. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1726 |
* <li>If interrupted while blocked in step 4, throw InterruptedException. |
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1727 |
* <li>If timed out while blocked in step 4, return false, else true. |
2 | 1728 |
* </ol> |
1729 |
*/ |
|
7518 | 1730 |
public final boolean await(long time, TimeUnit unit) |
1731 |
throws InterruptedException { |
|
2 | 1732 |
long nanosTimeout = unit.toNanos(time); |
1733 |
if (Thread.interrupted()) |
|
1734 |
throw new InterruptedException(); |
|
58134 | 1735 |
ConditionNode node = new ConditionNode(); |
1736 |
int savedState = enableWait(node); |
|
1737 |
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout; |
|
1738 |
long deadline = System.nanoTime() + nanos; |
|
1739 |
boolean cancelled = false, interrupted = false; |
|
1740 |
while (!canReacquire(node)) { |
|
1741 |
if ((interrupted |= Thread.interrupted()) || |
|
1742 |
(nanos = deadline - System.nanoTime()) <= 0L) { |
|
1743 |
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0) |
|
1744 |
break; |
|
1745 |
} else |
|
1746 |
LockSupport.parkNanos(this, nanos); |
|
2 | 1747 |
} |
58134 | 1748 |
node.clearStatus(); |
1749 |
acquire(node, savedState, false, false, false, 0L); |
|
1750 |
if (cancelled) { |
|
1751 |
unlinkCancelledWaiters(node); |
|
1752 |
if (interrupted) |
|
1753 |
throw new InterruptedException(); |
|
1754 |
} else if (interrupted) |
|
1755 |
Thread.currentThread().interrupt(); |
|
1756 |
return !cancelled; |
|
2 | 1757 |
} |
1758 |
||
1759 |
// support for instrumentation |
|
1760 |
||
1761 |
/** |
|
1762 |
* Returns true if this condition was created by the given |
|
1763 |
* synchronization object. |
|
1764 |
* |
|
1765 |
* @return {@code true} if owned |
|
1766 |
*/ |
|
1767 |
final boolean isOwnedBy(AbstractQueuedSynchronizer sync) { |
|
1768 |
return sync == AbstractQueuedSynchronizer.this; |
|
1769 |
} |
|
1770 |
||
1771 |
/** |
|
1772 |
* Queries whether any threads are waiting on this condition. |
|
18576 | 1773 |
* Implements {@link AbstractQueuedSynchronizer#hasWaiters(ConditionObject)}. |
2 | 1774 |
* |
1775 |
* @return {@code true} if there are any waiting threads |
|
1776 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
|
1777 |
* returns {@code false} |
|
1778 |
*/ |
|
1779 |
protected final boolean hasWaiters() { |
|
1780 |
if (!isHeldExclusively()) |
|
1781 |
throw new IllegalMonitorStateException(); |
|
58134 | 1782 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1783 |
if ((w.status & COND) != 0) |
|
2 | 1784 |
return true; |
1785 |
} |
|
1786 |
return false; |
|
1787 |
} |
|
1788 |
||
1789 |
/** |
|
1790 |
* Returns an estimate of the number of threads waiting on |
|
1791 |
* this condition. |
|
18576 | 1792 |
* Implements {@link AbstractQueuedSynchronizer#getWaitQueueLength(ConditionObject)}. |
2 | 1793 |
* |
1794 |
* @return the estimated number of waiting threads |
|
1795 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
|
1796 |
* returns {@code false} |
|
1797 |
*/ |
|
1798 |
protected final int getWaitQueueLength() { |
|
1799 |
if (!isHeldExclusively()) |
|
1800 |
throw new IllegalMonitorStateException(); |
|
1801 |
int n = 0; |
|
58134 | 1802 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1803 |
if ((w.status & COND) != 0) |
|
2 | 1804 |
++n; |
1805 |
} |
|
1806 |
return n; |
|
1807 |
} |
|
1808 |
||
1809 |
/** |
|
1810 |
* Returns a collection containing those threads that may be |
|
1811 |
* waiting on this Condition. |
|
18576 | 1812 |
* Implements {@link AbstractQueuedSynchronizer#getWaitingThreads(ConditionObject)}. |
2 | 1813 |
* |
1814 |
* @return the collection of threads |
|
1815 |
* @throws IllegalMonitorStateException if {@link #isHeldExclusively} |
|
1816 |
* returns {@code false} |
|
1817 |
*/ |
|
1818 |
protected final Collection<Thread> getWaitingThreads() { |
|
1819 |
if (!isHeldExclusively()) |
|
1820 |
throw new IllegalMonitorStateException(); |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1821 |
ArrayList<Thread> list = new ArrayList<>(); |
58134 | 1822 |
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) { |
1823 |
if ((w.status & COND) != 0) { |
|
1824 |
Thread t = w.waiter; |
|
2 | 1825 |
if (t != null) |
1826 |
list.add(t); |
|
1827 |
} |
|
1828 |
} |
|
1829 |
return list; |
|
1830 |
} |
|
1831 |
} |
|
1832 |
||
58134 | 1833 |
// Unsafe |
1834 |
private static final Unsafe U = Unsafe.getUnsafe(); |
|
1835 |
private static final long STATE |
|
1836 |
= U.objectFieldOffset(AbstractQueuedSynchronizer.class, "state"); |
|
1837 |
private static final long HEAD |
|
1838 |
= U.objectFieldOffset(AbstractQueuedSynchronizer.class, "head"); |
|
1839 |
private static final long TAIL |
|
1840 |
= U.objectFieldOffset(AbstractQueuedSynchronizer.class, "tail"); |
|
2 | 1841 |
|
1842 |
static { |
|
32990
299a81977f48
8134855: Bulk integration of java.util.concurrent.locks classes
dl
parents:
25859
diff
changeset
|
1843 |
Class<?> ensureLoaded = LockSupport.class; |
2 | 1844 |
} |
1845 |
} |