1491 lines
59 KiB
Java
1491 lines
59 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent.locks;
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import java.util.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 java.util.concurrent.RejectedExecutionException;
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import jdk.internal.misc.Unsafe;
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/**
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* A version of {@link AbstractQueuedSynchronizer} in
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* which synchronization state is maintained as a {@code long}.
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* This class has exactly the same structure, properties, and methods
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* as {@code AbstractQueuedSynchronizer} with the exception
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* that all state-related parameters and results are defined
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* as {@code long} rather than {@code int}. This class
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* may be useful when creating synchronizers such as
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* multilevel locks and barriers that require
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* 64 bits of state.
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*
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* <p>See {@link AbstractQueuedSynchronizer} for usage
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* notes and examples.
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*
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* @since 1.6
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* @author Doug Lea
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*/
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public abstract class AbstractQueuedLongSynchronizer
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extends AbstractOwnableSynchronizer
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implements java.io.Serializable {
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private static final long serialVersionUID = 7373984972572414692L;
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/**
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* Constructor for subclasses to call.
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*/
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// Android-changed: Keep the constructor protected.
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// public AbstractQueuedLongSynchronizer() {}
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protected AbstractQueuedLongSynchronizer() {}
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/*
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* To keep sources in sync, the remainder of this source file is
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* exactly cloned from AbstractQueuedSynchronizer, replacing class
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* name and changing ints related with sync state to longs. Please
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* keep it that way.
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*/
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// Node status bits, also used as argument and return values
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static final int WAITING = 1; // must be 1
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static final int CANCELLED = 0x80000000; // must be negative
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static final int COND = 2; // in a condition wait
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/** CLH Nodes */
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abstract static class Node {
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volatile Node prev; // initially attached via casTail
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volatile Node next; // visibly nonnull when signallable
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Thread waiter; // visibly nonnull when enqueued
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volatile int status; // written by owner, atomic bit ops by others
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// methods for atomic operations
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final boolean casPrev(Node c, Node v) { // for cleanQueue
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return U.weakCompareAndSetReference(this, PREV, c, v);
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}
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final boolean casNext(Node c, Node v) { // for cleanQueue
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return U.weakCompareAndSetReference(this, NEXT, c, v);
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}
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final int getAndUnsetStatus(int v) { // for signalling
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return U.getAndBitwiseAndInt(this, STATUS, ~v);
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}
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final void setPrevRelaxed(Node p) { // for off-queue assignment
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U.putReference(this, PREV, p);
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}
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final void setStatusRelaxed(int s) { // for off-queue assignment
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U.putInt(this, STATUS, s);
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}
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final void clearStatus() { // for reducing unneeded signals
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U.putIntOpaque(this, STATUS, 0);
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}
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private static final long STATUS
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= U.objectFieldOffset(Node.class, "status");
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private static final long NEXT
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= U.objectFieldOffset(Node.class, "next");
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private static final long PREV
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= U.objectFieldOffset(Node.class, "prev");
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}
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// Concrete classes tagged by type
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static final class ExclusiveNode extends Node { }
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static final class SharedNode extends Node { }
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static final class ConditionNode extends Node
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implements ForkJoinPool.ManagedBlocker {
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ConditionNode nextWaiter; // link to next waiting node
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/**
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* Allows Conditions to be used in ForkJoinPools without
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* risking fixed pool exhaustion. This is usable only for
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* untimed Condition waits, not timed versions.
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*/
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public final boolean isReleasable() {
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return status <= 1 || Thread.currentThread().isInterrupted();
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}
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public final boolean block() {
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while (!isReleasable()) LockSupport.park();
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return true;
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}
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}
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/**
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* Head of the wait queue, lazily initialized.
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*/
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private transient volatile Node head;
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/**
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* Tail of the wait queue. After initialization, modified only via casTail.
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*/
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private transient volatile Node tail;
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/**
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* The synchronization state.
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*/
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private volatile long state;
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/**
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* Returns the current value of synchronization state.
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* This operation has memory semantics of a {@code volatile} read.
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* @return current state value
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*/
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protected final long getState() {
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return state;
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}
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/**
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* Sets the value of synchronization state.
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* This operation has memory semantics of a {@code volatile} write.
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* @param newState the new state value
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*/
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protected final void setState(long newState) {
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state = newState;
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}
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/**
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* Atomically sets synchronization state to the given updated
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* value if the current state value equals the expected value.
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* This operation has memory semantics of a {@code volatile} read
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* and write.
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*
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* @param expect the expected value
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* @param update the new value
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* @return {@code true} if successful. False return indicates that the actual
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* value was not equal to the expected value.
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*/
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protected final boolean compareAndSetState(long expect, long update) {
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return U.compareAndSetLong(this, STATE, expect, update);
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}
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// Queuing utilities
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private boolean casTail(Node c, Node v) {
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return U.compareAndSetReference(this, TAIL, c, v);
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}
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/** tries once to CAS a new dummy node for head */
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private void tryInitializeHead() {
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Node h = new ExclusiveNode();
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if (U.compareAndSetReference(this, HEAD, null, h))
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tail = h;
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}
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/**
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* Enqueues the node unless null. (Currently used only for
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* ConditionNodes; other cases are interleaved with acquires.)
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*/
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final void enqueue(Node node) {
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if (node != null) {
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for (;;) {
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Node t = tail;
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node.setPrevRelaxed(t); // avoid unnecessary fence
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if (t == null) // initialize
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tryInitializeHead();
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else if (casTail(t, node)) {
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t.next = node;
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if (t.status < 0) // wake up to clean link
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LockSupport.unpark(node.waiter);
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break;
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}
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}
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}
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}
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/** Returns true if node is found in traversal from tail */
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final boolean isEnqueued(Node node) {
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for (Node t = tail; t != null; t = t.prev)
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if (t == node)
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return true;
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return false;
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}
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/**
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* Wakes up the successor of given node, if one exists, and unsets its
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* WAITING status to avoid park race. This may fail to wake up an
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* eligible thread when one or more have been cancelled, but
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* cancelAcquire ensures liveness.
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*/
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private static void signalNext(Node h) {
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Node s;
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if (h != null && (s = h.next) != null && s.status != 0) {
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s.getAndUnsetStatus(WAITING);
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LockSupport.unpark(s.waiter);
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}
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}
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/** Wakes up the given node if in shared mode */
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private static void signalNextIfShared(Node h) {
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Node s;
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if (h != null && (s = h.next) != null &&
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(s instanceof SharedNode) && s.status != 0) {
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s.getAndUnsetStatus(WAITING);
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LockSupport.unpark(s.waiter);
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}
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}
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/**
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* Main acquire method, invoked by all exported acquire methods.
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*
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* @param node null unless a reacquiring Condition
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* @param arg the acquire argument
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* @param shared true if shared mode else exclusive
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* @param interruptible if abort and return negative on interrupt
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* @param timed if true use timed waits
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* @param time if timed, the System.nanoTime value to timeout
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* @return positive if acquired, 0 if timed out, negative if interrupted
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*/
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final int acquire(Node node, long arg, boolean shared,
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boolean interruptible, boolean timed, long time) {
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Thread current = Thread.currentThread();
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byte spins = 0, postSpins = 0; // retries upon unpark of first thread
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boolean interrupted = false, first = false;
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Node pred = null; // predecessor of node when enqueued
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/*
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* Repeatedly:
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* Check if node now first
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* if so, ensure head stable, else ensure valid predecessor
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* if node is first or not yet enqueued, try acquiring
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* else if node not yet created, create it
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* else if not yet enqueued, try once to enqueue
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* else if woken from park, retry (up to postSpins times)
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* else if WAITING status not set, set and retry
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* else park and clear WAITING status, and check cancellation
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*/
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for (;;) {
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if (!first && (pred = (node == null) ? null : node.prev) != null &&
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!(first = (head == pred))) {
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if (pred.status < 0) {
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cleanQueue(); // predecessor cancelled
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continue;
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} else if (pred.prev == null) {
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Thread.onSpinWait(); // ensure serialization
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continue;
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}
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}
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if (first || pred == null) {
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boolean acquired;
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try {
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if (shared)
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acquired = (tryAcquireShared(arg) >= 0);
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else
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acquired = tryAcquire(arg);
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} catch (Throwable ex) {
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cancelAcquire(node, interrupted, false);
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throw ex;
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}
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if (acquired) {
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if (first) {
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node.prev = null;
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head = node;
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pred.next = null;
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node.waiter = null;
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if (shared)
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signalNextIfShared(node);
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if (interrupted)
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current.interrupt();
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}
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return 1;
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}
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}
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if (node == null) { // allocate; retry before enqueue
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if (shared)
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node = new SharedNode();
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else
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node = new ExclusiveNode();
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} else if (pred == null) { // try to enqueue
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node.waiter = current;
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Node t = tail;
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node.setPrevRelaxed(t); // avoid unnecessary fence
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if (t == null)
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tryInitializeHead();
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else if (!casTail(t, node))
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node.setPrevRelaxed(null); // back out
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else
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t.next = node;
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} else if (first && spins != 0) {
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--spins; // reduce unfairness on rewaits
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Thread.onSpinWait();
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} else if (node.status == 0) {
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node.status = WAITING; // enable signal and recheck
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} else {
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long nanos;
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spins = postSpins = (byte)((postSpins << 1) | 1);
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if (!timed)
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LockSupport.park(this);
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else if ((nanos = time - System.nanoTime()) > 0L)
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LockSupport.parkNanos(this, nanos);
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else
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break;
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node.clearStatus();
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if ((interrupted |= Thread.interrupted()) && interruptible)
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break;
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}
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}
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return cancelAcquire(node, interrupted, interruptible);
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}
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/**
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* Possibly repeatedly traverses from tail, unsplicing cancelled
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* nodes until none are found.
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*/
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private void cleanQueue() {
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for (;;) { // restart point
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for (Node q = tail, s = null, p, n;;) { // (p, q, s) triples
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if (q == null || (p = q.prev) == null)
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return; // end of list
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if (s == null ? tail != q : (s.prev != q || s.status < 0))
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break; // inconsistent
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if (q.status < 0) { // cancelled
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if ((s == null ? casTail(q, p) : s.casPrev(q, p)) &&
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q.prev == p) {
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p.casNext(q, s); // OK if fails
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if (p.prev == null)
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signalNext(p);
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}
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break;
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}
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if ((n = p.next) != q) { // help finish
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if (n != null && q.prev == p) {
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p.casNext(n, q);
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if (p.prev == null)
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signalNext(p);
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}
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break;
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}
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s = q;
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q = q.prev;
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}
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}
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}
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/**
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* Cancels an ongoing attempt to acquire.
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*
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* @param node the node (may be null if cancelled before enqueuing)
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* @param interrupted true if thread interrupted
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* @param interruptible if should report interruption vs reset
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*/
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private int cancelAcquire(Node node, boolean interrupted,
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boolean interruptible) {
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if (node != null) {
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node.waiter = null;
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node.status = CANCELLED;
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if (node.prev != null)
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cleanQueue();
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}
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if (interrupted) {
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if (interruptible)
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return CANCELLED;
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else
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Thread.currentThread().interrupt();
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}
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return 0;
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}
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// Main exported methods
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/**
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* Attempts to acquire in exclusive mode. This method should query
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* if the state of the object permits it to be acquired in the
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* exclusive mode, and if so to acquire it.
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*
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* <p>This method is always invoked by the thread performing
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* acquire. If this method reports failure, the acquire method
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* may queue the thread, if it is not already queued, until it is
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* signalled by a release from some other thread. This can be used
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* to implement method {@link Lock#tryLock()}.
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*
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* <p>The default
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* implementation throws {@link UnsupportedOperationException}.
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*
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* @param arg the acquire argument. This value is always the one
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* passed to an acquire method, or is the value saved on entry
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* to a condition wait. The value is otherwise uninterpreted
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* and can represent anything you like.
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* @return {@code true} if successful. Upon success, this object has
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* been acquired.
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* @throws IllegalMonitorStateException if acquiring would place this
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* synchronizer in an illegal state. This exception must be
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* thrown in a consistent fashion for synchronization to work
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* correctly.
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* @throws UnsupportedOperationException if exclusive mode is not supported
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*/
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protected boolean tryAcquire(long arg) {
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throw new UnsupportedOperationException();
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}
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/**
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* Attempts to set the state to reflect a release in exclusive
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* mode.
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*
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* <p>This method is always invoked by the thread performing release.
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*
|
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* <p>The default implementation throws
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* {@link UnsupportedOperationException}.
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|
*
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* @param arg the release argument. This value is always the one
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* passed to a release method, or the current state value upon
|
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* entry to a condition wait. The value is otherwise
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* uninterpreted and can represent anything you like.
|
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* @return {@code true} if this object is now in a fully released
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* state, so that any waiting threads may attempt to acquire;
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* and {@code false} otherwise.
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* @throws IllegalMonitorStateException if releasing would place this
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* synchronizer in an illegal state. This exception must be
|
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* thrown in a consistent fashion for synchronization to work
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* correctly.
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* @throws UnsupportedOperationException if exclusive mode is not supported
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*/
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protected boolean tryRelease(long arg) {
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throw new UnsupportedOperationException();
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}
|
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|
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/**
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* Attempts to acquire in shared mode. This method should query if
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* the state of the object permits it to be acquired in the shared
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* mode, and if so to acquire it.
|
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*
|
|
* <p>This method is always invoked by the thread performing
|
|
* acquire. If this method reports failure, the acquire method
|
|
* may queue the thread, if it is not already queued, until it is
|
|
* signalled by a release from some other thread.
|
|
*
|
|
* <p>The default implementation throws {@link
|
|
* UnsupportedOperationException}.
|
|
*
|
|
* @param arg the acquire argument. This value is always the one
|
|
* passed to an acquire method, or is the value saved on entry
|
|
* to a condition wait. The value is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @return a negative value on failure; zero if acquisition in shared
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* mode succeeded but no subsequent shared-mode acquire can
|
|
* succeed; and a positive value if acquisition in shared
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* mode succeeded and subsequent shared-mode acquires might
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|
* also succeed, in which case a subsequent waiting thread
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|
* must check availability. (Support for three different
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* return values enables this method to be used in contexts
|
|
* where acquires only sometimes act exclusively.) Upon
|
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* success, this object has been acquired.
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|
* @throws IllegalMonitorStateException if acquiring would place this
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|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
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|
* @throws UnsupportedOperationException if shared mode is not supported
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|
*/
|
|
protected long tryAcquireShared(long arg) {
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throw new UnsupportedOperationException();
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|
}
|
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|
|
/**
|
|
* Attempts to set the state to reflect a release in shared mode.
|
|
*
|
|
* <p>This method is always invoked by the thread performing release.
|
|
*
|
|
* <p>The default implementation throws
|
|
* {@link UnsupportedOperationException}.
|
|
*
|
|
* @param arg the release argument. This value is always the one
|
|
* passed to a release method, or the current state value upon
|
|
* entry to a condition wait. The value is otherwise
|
|
* uninterpreted and can represent anything you like.
|
|
* @return {@code true} if this release of shared mode may permit a
|
|
* waiting acquire (shared or exclusive) to succeed; and
|
|
* {@code false} otherwise
|
|
* @throws IllegalMonitorStateException if releasing would place this
|
|
* synchronizer in an illegal state. This exception must be
|
|
* thrown in a consistent fashion for synchronization to work
|
|
* correctly.
|
|
* @throws UnsupportedOperationException if shared mode is not supported
|
|
*/
|
|
protected boolean tryReleaseShared(long arg) {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if synchronization is held exclusively with
|
|
* respect to the current (calling) thread. This method is invoked
|
|
* upon each call to a {@link ConditionObject} method.
|
|
*
|
|
* <p>The default implementation throws {@link
|
|
* UnsupportedOperationException}. This method is invoked
|
|
* internally only within {@link ConditionObject} methods, so need
|
|
* not be defined if conditions are not used.
|
|
*
|
|
* @return {@code true} if synchronization is held exclusively;
|
|
* {@code false} otherwise
|
|
* @throws UnsupportedOperationException if conditions are not supported
|
|
*/
|
|
protected boolean isHeldExclusively() {
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive mode, ignoring interrupts. Implemented
|
|
* by invoking at least once {@link #tryAcquire},
|
|
* returning on success. Otherwise the thread is queued, possibly
|
|
* repeatedly blocking and unblocking, invoking {@link
|
|
* #tryAcquire} until success. This method can be used
|
|
* to implement method {@link Lock#lock}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
*/
|
|
public final void acquire(long arg) {
|
|
if (!tryAcquire(arg))
|
|
acquire(null, arg, false, false, false, 0L);
|
|
}
|
|
|
|
/**
|
|
* Acquires in exclusive mode, aborting if interrupted.
|
|
* Implemented by first checking interrupt status, then invoking
|
|
* at least once {@link #tryAcquire}, returning on
|
|
* success. Otherwise the thread is queued, possibly repeatedly
|
|
* blocking and unblocking, invoking {@link #tryAcquire}
|
|
* until success or the thread is interrupted. This method can be
|
|
* used to implement method {@link Lock#lockInterruptibly}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final void acquireInterruptibly(long arg)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted() ||
|
|
(!tryAcquire(arg) && acquire(null, arg, false, true, false, 0L) < 0))
|
|
throw new InterruptedException();
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire in exclusive mode, aborting if interrupted,
|
|
* and failing if the given timeout elapses. Implemented by first
|
|
* checking interrupt status, then invoking at least once {@link
|
|
* #tryAcquire}, returning on success. Otherwise, the thread is
|
|
* queued, possibly repeatedly blocking and unblocking, invoking
|
|
* {@link #tryAcquire} until success or the thread is interrupted
|
|
* or the timeout elapses. This method can be used to implement
|
|
* method {@link Lock#tryLock(long, TimeUnit)}.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquire} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final boolean tryAcquireNanos(long arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (!Thread.interrupted()) {
|
|
if (tryAcquire(arg))
|
|
return true;
|
|
if (nanosTimeout <= 0L)
|
|
return false;
|
|
int stat = acquire(null, arg, false, true, true,
|
|
System.nanoTime() + nanosTimeout);
|
|
if (stat > 0)
|
|
return true;
|
|
if (stat == 0)
|
|
return false;
|
|
}
|
|
throw new InterruptedException();
|
|
}
|
|
|
|
/**
|
|
* Releases in exclusive mode. Implemented by unblocking one or
|
|
* more threads if {@link #tryRelease} returns true.
|
|
* This method can be used to implement method {@link Lock#unlock}.
|
|
*
|
|
* @param arg the release argument. This value is conveyed to
|
|
* {@link #tryRelease} but is otherwise uninterpreted and
|
|
* can represent anything you like.
|
|
* @return the value returned from {@link #tryRelease}
|
|
*/
|
|
public final boolean release(long arg) {
|
|
if (tryRelease(arg)) {
|
|
signalNext(head);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared mode, ignoring interrupts. Implemented by
|
|
* first invoking at least once {@link #tryAcquireShared},
|
|
* returning on success. Otherwise the thread is queued, possibly
|
|
* repeatedly blocking and unblocking, invoking {@link
|
|
* #tryAcquireShared} until success.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
*/
|
|
public final void acquireShared(long arg) {
|
|
if (tryAcquireShared(arg) < 0)
|
|
acquire(null, arg, true, false, false, 0L);
|
|
}
|
|
|
|
/**
|
|
* Acquires in shared mode, aborting if interrupted. Implemented
|
|
* by first checking interrupt status, then invoking at least once
|
|
* {@link #tryAcquireShared}, returning on success. Otherwise the
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
|
* is interrupted.
|
|
* @param arg the acquire argument.
|
|
* This value is conveyed to {@link #tryAcquireShared} but is
|
|
* otherwise uninterpreted and can represent anything
|
|
* you like.
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final void acquireSharedInterruptibly(long arg)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted() ||
|
|
(tryAcquireShared(arg) < 0 &&
|
|
acquire(null, arg, true, true, false, 0L) < 0))
|
|
throw new InterruptedException();
|
|
}
|
|
|
|
/**
|
|
* Attempts to acquire in shared mode, aborting if interrupted, and
|
|
* failing if the given timeout elapses. Implemented by first
|
|
* checking interrupt status, then invoking at least once {@link
|
|
* #tryAcquireShared}, returning on success. Otherwise, the
|
|
* thread is queued, possibly repeatedly blocking and unblocking,
|
|
* invoking {@link #tryAcquireShared} until success or the thread
|
|
* is interrupted or the timeout elapses.
|
|
*
|
|
* @param arg the acquire argument. This value is conveyed to
|
|
* {@link #tryAcquireShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @param nanosTimeout the maximum number of nanoseconds to wait
|
|
* @return {@code true} if acquired; {@code false} if timed out
|
|
* @throws InterruptedException if the current thread is interrupted
|
|
*/
|
|
public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (!Thread.interrupted()) {
|
|
if (tryAcquireShared(arg) >= 0)
|
|
return true;
|
|
if (nanosTimeout <= 0L)
|
|
return false;
|
|
int stat = acquire(null, arg, true, true, true,
|
|
System.nanoTime() + nanosTimeout);
|
|
if (stat > 0)
|
|
return true;
|
|
if (stat == 0)
|
|
return false;
|
|
}
|
|
throw new InterruptedException();
|
|
}
|
|
|
|
/**
|
|
* Releases in shared mode. Implemented by unblocking one or more
|
|
* threads if {@link #tryReleaseShared} returns true.
|
|
*
|
|
* @param arg the release argument. This value is conveyed to
|
|
* {@link #tryReleaseShared} but is otherwise uninterpreted
|
|
* and can represent anything you like.
|
|
* @return the value returned from {@link #tryReleaseShared}
|
|
*/
|
|
public final boolean releaseShared(long arg) {
|
|
if (tryReleaseShared(arg)) {
|
|
signalNext(head);
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
// Queue inspection methods
|
|
|
|
/**
|
|
* Queries whether any threads are waiting to acquire. Note that
|
|
* because cancellations due to interrupts and timeouts may occur
|
|
* at any time, a {@code true} return does not guarantee that any
|
|
* other thread will ever acquire.
|
|
*
|
|
* @return {@code true} if there may be other threads waiting to acquire
|
|
*/
|
|
public final boolean hasQueuedThreads() {
|
|
for (Node p = tail, h = head; p != h && p != null; p = p.prev)
|
|
if (p.status >= 0)
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads have ever contended to acquire this
|
|
* synchronizer; that is, if an acquire method has ever blocked.
|
|
*
|
|
* <p>In this implementation, this operation returns in
|
|
* constant time.
|
|
*
|
|
* @return {@code true} if there has ever been contention
|
|
*/
|
|
public final boolean hasContended() {
|
|
return head != null;
|
|
}
|
|
|
|
/**
|
|
* Returns the first (longest-waiting) thread in the queue, or
|
|
* {@code null} if no threads are currently queued.
|
|
*
|
|
* <p>In this implementation, this operation normally returns in
|
|
* constant time, but may iterate upon contention if other threads are
|
|
* concurrently modifying the queue.
|
|
*
|
|
* @return the first (longest-waiting) thread in the queue, or
|
|
* {@code null} if no threads are currently queued
|
|
*/
|
|
public final Thread getFirstQueuedThread() {
|
|
Thread first = null, w; Node h, s;
|
|
if ((h = head) != null && ((s = h.next) == null ||
|
|
(first = s.waiter) == null ||
|
|
s.prev == null)) {
|
|
// traverse from tail on stale reads
|
|
for (Node p = tail, q; p != null && (q = p.prev) != null; p = q)
|
|
if ((w = p.waiter) != null)
|
|
first = w;
|
|
}
|
|
return first;
|
|
}
|
|
|
|
/**
|
|
* Returns true if the given thread is currently queued.
|
|
*
|
|
* <p>This implementation traverses the queue to determine
|
|
* presence of the given thread.
|
|
*
|
|
* @param thread the thread
|
|
* @return {@code true} if the given thread is on the queue
|
|
* @throws NullPointerException if the thread is null
|
|
*/
|
|
public final boolean isQueued(Thread thread) {
|
|
if (thread == null)
|
|
throw new NullPointerException();
|
|
for (Node p = tail; p != null; p = p.prev)
|
|
if (p.waiter == thread)
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Returns {@code true} if the apparent first queued thread, if one
|
|
* exists, is waiting in exclusive mode. If this method returns
|
|
* {@code true}, and the current thread is attempting to acquire in
|
|
* shared mode (that is, this method is invoked from {@link
|
|
* #tryAcquireShared}) then it is guaranteed that the current thread
|
|
* is not the first queued thread. Used only as a heuristic in
|
|
* ReentrantReadWriteLock.
|
|
*/
|
|
final boolean apparentlyFirstQueuedIsExclusive() {
|
|
Node h, s;
|
|
return (h = head) != null && (s = h.next) != null &&
|
|
!(s instanceof SharedNode) && s.waiter != null;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads have been waiting to acquire longer
|
|
* than the current thread.
|
|
*
|
|
* <p>An invocation of this method is equivalent to (but may be
|
|
* more efficient than):
|
|
* <pre> {@code
|
|
* getFirstQueuedThread() != Thread.currentThread()
|
|
* && hasQueuedThreads()}</pre>
|
|
*
|
|
* <p>Note that because cancellations due to interrupts and
|
|
* timeouts may occur at any time, a {@code true} return does not
|
|
* guarantee that some other thread will acquire before the current
|
|
* thread. Likewise, it is possible for another thread to win a
|
|
* race to enqueue after this method has returned {@code false},
|
|
* due to the queue being empty.
|
|
*
|
|
* <p>This method is designed to be used by a fair synchronizer to
|
|
* avoid <a href="AbstractQueuedSynchronizer.html#barging">barging</a>.
|
|
* Such a synchronizer's {@link #tryAcquire} method should return
|
|
* {@code false}, and its {@link #tryAcquireShared} method should
|
|
* return a negative value, if this method returns {@code true}
|
|
* (unless this is a reentrant acquire). For example, the {@code
|
|
* tryAcquire} method for a fair, reentrant, exclusive mode
|
|
* synchronizer might look like this:
|
|
*
|
|
* <pre> {@code
|
|
* protected boolean tryAcquire(long arg) {
|
|
* if (isHeldExclusively()) {
|
|
* // A reentrant acquire; increment hold count
|
|
* return true;
|
|
* } else if (hasQueuedPredecessors()) {
|
|
* return false;
|
|
* } else {
|
|
* // try to acquire normally
|
|
* }
|
|
* }}</pre>
|
|
*
|
|
* @return {@code true} if there is a queued thread preceding the
|
|
* current thread, and {@code false} if the current thread
|
|
* is at the head of the queue or the queue is empty
|
|
* @since 1.7
|
|
*/
|
|
public final boolean hasQueuedPredecessors() {
|
|
Thread first = null; Node h, s;
|
|
if ((h = head) != null && ((s = h.next) == null ||
|
|
(first = s.waiter) == null ||
|
|
s.prev == null))
|
|
first = getFirstQueuedThread(); // retry via getFirstQueuedThread
|
|
return first != null && first != Thread.currentThread();
|
|
}
|
|
|
|
// Instrumentation and monitoring methods
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting to
|
|
* acquire. The value is only an estimate because the number of
|
|
* threads may change dynamically while this method traverses
|
|
* internal data structures. This method is designed for use in
|
|
* monitoring system state, not for synchronization control.
|
|
*
|
|
* @return the estimated number of threads waiting to acquire
|
|
*/
|
|
public final int getQueueLength() {
|
|
int n = 0;
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (p.waiter != null)
|
|
++n;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire. Because the actual set of threads may change
|
|
* dynamically while constructing this result, the returned
|
|
* collection is only a best-effort estimate. The elements of the
|
|
* returned collection are in no particular order. This method is
|
|
* designed to facilitate construction of subclasses that provide
|
|
* more extensive monitoring facilities.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
Thread t = p.waiter;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire in exclusive mode. This has the same properties
|
|
* as {@link #getQueuedThreads} except that it only returns
|
|
* those threads waiting due to an exclusive acquire.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getExclusiveQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (!(p instanceof SharedNode)) {
|
|
Thread t = p.waiter;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing threads that may be waiting to
|
|
* acquire in shared mode. This has the same properties
|
|
* as {@link #getQueuedThreads} except that it only returns
|
|
* those threads waiting due to a shared acquire.
|
|
*
|
|
* @return the collection of threads
|
|
*/
|
|
public final Collection<Thread> getSharedQueuedThreads() {
|
|
ArrayList<Thread> list = new ArrayList<>();
|
|
for (Node p = tail; p != null; p = p.prev) {
|
|
if (p instanceof SharedNode) {
|
|
Thread t = p.waiter;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
|
|
/**
|
|
* Returns a string identifying this synchronizer, as well as its state.
|
|
* The state, in brackets, includes the String {@code "State ="}
|
|
* followed by the current value of {@link #getState}, and either
|
|
* {@code "nonempty"} or {@code "empty"} depending on whether the
|
|
* queue is empty.
|
|
*
|
|
* @return a string identifying this synchronizer, as well as its state
|
|
*/
|
|
public String toString() {
|
|
return super.toString()
|
|
+ "[State = " + getState() + ", "
|
|
+ (hasQueuedThreads() ? "non" : "") + "empty queue]";
|
|
}
|
|
|
|
// Instrumentation methods for conditions
|
|
|
|
/**
|
|
* Queries whether the given ConditionObject
|
|
* uses this synchronizer as its lock.
|
|
*
|
|
* @param condition the condition
|
|
* @return {@code true} if owned
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final boolean owns(ConditionObject condition) {
|
|
return condition.isOwnedBy(this);
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads are waiting on the given condition
|
|
* associated with this synchronizer. Note that because timeouts
|
|
* and interrupts may occur at any time, a {@code true} return
|
|
* does not guarantee that a future {@code signal} will awaken
|
|
* any threads. This method is designed primarily for use in
|
|
* monitoring of the system state.
|
|
*
|
|
* @param condition the condition
|
|
* @return {@code true} if there are any waiting threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final boolean hasWaiters(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.hasWaiters();
|
|
}
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting on the
|
|
* given condition associated with this synchronizer. Note that
|
|
* because timeouts and interrupts may occur at any time, the
|
|
* estimate serves only as an upper bound on the actual number of
|
|
* waiters. This method is designed for use in monitoring system
|
|
* state, not for synchronization control.
|
|
*
|
|
* @param condition the condition
|
|
* @return the estimated number of waiting threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final int getWaitQueueLength(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.getWaitQueueLength();
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing those threads that may be
|
|
* waiting on the given condition associated with this
|
|
* synchronizer. Because the actual set of threads may change
|
|
* dynamically while constructing this result, the returned
|
|
* collection is only a best-effort estimate. The elements of the
|
|
* returned collection are in no particular order.
|
|
*
|
|
* @param condition the condition
|
|
* @return the collection of threads
|
|
* @throws IllegalMonitorStateException if exclusive synchronization
|
|
* is not held
|
|
* @throws IllegalArgumentException if the given condition is
|
|
* not associated with this synchronizer
|
|
* @throws NullPointerException if the condition is null
|
|
*/
|
|
public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
|
|
if (!owns(condition))
|
|
throw new IllegalArgumentException("Not owner");
|
|
return condition.getWaitingThreads();
|
|
}
|
|
|
|
/**
|
|
* Condition implementation for a {@link AbstractQueuedLongSynchronizer}
|
|
* serving as the basis of a {@link Lock} implementation.
|
|
*
|
|
* <p>Method documentation for this class describes mechanics,
|
|
* not behavioral specifications from the point of view of Lock
|
|
* and Condition users. Exported versions of this class will in
|
|
* general need to be accompanied by documentation describing
|
|
* condition semantics that rely on those of the associated
|
|
* {@code AbstractQueuedLongSynchronizer}.
|
|
*
|
|
* <p>This class is Serializable, but all fields are transient,
|
|
* so deserialized conditions have no waiters.
|
|
*/
|
|
public class ConditionObject implements Condition, java.io.Serializable {
|
|
private static final long serialVersionUID = 1173984872572414699L;
|
|
/** First node of condition queue. */
|
|
private transient ConditionNode firstWaiter;
|
|
/** Last node of condition queue. */
|
|
private transient ConditionNode lastWaiter;
|
|
|
|
/**
|
|
* Creates a new {@code ConditionObject} instance.
|
|
*/
|
|
public ConditionObject() { }
|
|
|
|
// Signalling methods
|
|
|
|
/**
|
|
* Removes and transfers one or all waiters to sync queue.
|
|
*/
|
|
private void doSignal(ConditionNode first, boolean all) {
|
|
while (first != null) {
|
|
ConditionNode next = first.nextWaiter;
|
|
if ((firstWaiter = next) == null)
|
|
lastWaiter = null;
|
|
if ((first.getAndUnsetStatus(COND) & COND) != 0) {
|
|
enqueue(first);
|
|
if (!all)
|
|
break;
|
|
}
|
|
first = next;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Moves the longest-waiting thread, if one exists, from the
|
|
* wait queue for this condition to the wait queue for the
|
|
* owning lock.
|
|
*
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
public final void signal() {
|
|
ConditionNode first = firstWaiter;
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
if (first != null)
|
|
doSignal(first, false);
|
|
}
|
|
|
|
/**
|
|
* Moves all threads from the wait queue for this condition to
|
|
* the wait queue for the owning lock.
|
|
*
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
public final void signalAll() {
|
|
ConditionNode first = firstWaiter;
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
if (first != null)
|
|
doSignal(first, true);
|
|
}
|
|
|
|
// Waiting methods
|
|
|
|
/**
|
|
* Adds node to condition list and releases lock.
|
|
*
|
|
* @param node the node
|
|
* @return savedState to reacquire after wait
|
|
*/
|
|
private long enableWait(ConditionNode node) {
|
|
if (isHeldExclusively()) {
|
|
node.waiter = Thread.currentThread();
|
|
node.setStatusRelaxed(COND | WAITING);
|
|
ConditionNode last = lastWaiter;
|
|
if (last == null)
|
|
firstWaiter = node;
|
|
else
|
|
last.nextWaiter = node;
|
|
lastWaiter = node;
|
|
long savedState = getState();
|
|
if (release(savedState))
|
|
return savedState;
|
|
}
|
|
node.status = CANCELLED; // lock not held or inconsistent
|
|
throw new IllegalMonitorStateException();
|
|
}
|
|
|
|
/**
|
|
* Returns true if a node that was initially placed on a condition
|
|
* queue is now ready to reacquire on sync queue.
|
|
* @param node the node
|
|
* @return true if is reacquiring
|
|
*/
|
|
private boolean canReacquire(ConditionNode node) {
|
|
// check links, not status to avoid enqueue race
|
|
return node != null && node.prev != null && isEnqueued(node);
|
|
}
|
|
|
|
/**
|
|
* Unlinks the given node and other non-waiting nodes from
|
|
* condition queue unless already unlinked.
|
|
*/
|
|
private void unlinkCancelledWaiters(ConditionNode node) {
|
|
if (node == null || node.nextWaiter != null || node == lastWaiter) {
|
|
ConditionNode w = firstWaiter, trail = null;
|
|
while (w != null) {
|
|
ConditionNode next = w.nextWaiter;
|
|
if ((w.status & COND) == 0) {
|
|
w.nextWaiter = null;
|
|
if (trail == null)
|
|
firstWaiter = next;
|
|
else
|
|
trail.nextWaiter = next;
|
|
if (next == null)
|
|
lastWaiter = trail;
|
|
} else
|
|
trail = w;
|
|
w = next;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Implements uninterruptible condition wait.
|
|
* <ol>
|
|
* <li>Save lock state returned by {@link #getState}.
|
|
* <li>Invoke {@link #release} with saved state as argument,
|
|
* throwing IllegalMonitorStateException if it fails.
|
|
* <li>Block until signalled.
|
|
* <li>Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* </ol>
|
|
*/
|
|
public final void awaitUninterruptibly() {
|
|
ConditionNode node = new ConditionNode();
|
|
long savedState = enableWait(node);
|
|
LockSupport.setCurrentBlocker(this); // for back-compatibility
|
|
boolean interrupted = false, rejected = false;
|
|
while (!canReacquire(node)) {
|
|
if (Thread.interrupted())
|
|
interrupted = true;
|
|
else if ((node.status & COND) != 0) {
|
|
try {
|
|
if (rejected)
|
|
node.block();
|
|
else
|
|
ForkJoinPool.managedBlock(node);
|
|
} catch (RejectedExecutionException ex) {
|
|
rejected = true;
|
|
} catch (InterruptedException ie) {
|
|
interrupted = true;
|
|
}
|
|
} else
|
|
Thread.onSpinWait(); // awoke while enqueuing
|
|
}
|
|
LockSupport.setCurrentBlocker(null);
|
|
node.clearStatus();
|
|
acquire(node, savedState, false, false, false, 0L);
|
|
if (interrupted)
|
|
Thread.currentThread().interrupt();
|
|
}
|
|
|
|
/**
|
|
* Implements interruptible condition wait.
|
|
* <ol>
|
|
* <li>If current thread is interrupted, throw InterruptedException.
|
|
* <li>Save lock state returned by {@link #getState}.
|
|
* <li>Invoke {@link #release} with saved state as argument,
|
|
* throwing IllegalMonitorStateException if it fails.
|
|
* <li>Block until signalled or interrupted.
|
|
* <li>Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li>If interrupted while blocked in step 4, throw InterruptedException.
|
|
* </ol>
|
|
*/
|
|
public final void await() throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
ConditionNode node = new ConditionNode();
|
|
long savedState = enableWait(node);
|
|
LockSupport.setCurrentBlocker(this); // for back-compatibility
|
|
boolean interrupted = false, cancelled = false, rejected = false;
|
|
while (!canReacquire(node)) {
|
|
if (interrupted |= Thread.interrupted()) {
|
|
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
|
|
break; // else interrupted after signal
|
|
} else if ((node.status & COND) != 0) {
|
|
try {
|
|
if (rejected)
|
|
node.block();
|
|
else
|
|
ForkJoinPool.managedBlock(node);
|
|
} catch (RejectedExecutionException ex) {
|
|
rejected = true;
|
|
} catch (InterruptedException ie) {
|
|
interrupted = true;
|
|
}
|
|
} else
|
|
Thread.onSpinWait(); // awoke while enqueuing
|
|
}
|
|
LockSupport.setCurrentBlocker(null);
|
|
node.clearStatus();
|
|
acquire(node, savedState, false, false, false, 0L);
|
|
if (interrupted) {
|
|
if (cancelled) {
|
|
unlinkCancelledWaiters(node);
|
|
throw new InterruptedException();
|
|
}
|
|
Thread.currentThread().interrupt();
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Implements timed condition wait.
|
|
* <ol>
|
|
* <li>If current thread is interrupted, throw InterruptedException.
|
|
* <li>Save lock state returned by {@link #getState}.
|
|
* <li>Invoke {@link #release} with saved state as argument,
|
|
* throwing IllegalMonitorStateException if it fails.
|
|
* <li>Block until signalled, interrupted, or timed out.
|
|
* <li>Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li>If interrupted while blocked in step 4, throw InterruptedException.
|
|
* </ol>
|
|
*/
|
|
public final long awaitNanos(long nanosTimeout)
|
|
throws InterruptedException {
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
ConditionNode node = new ConditionNode();
|
|
long savedState = enableWait(node);
|
|
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout;
|
|
long deadline = System.nanoTime() + nanos;
|
|
boolean cancelled = false, interrupted = false;
|
|
while (!canReacquire(node)) {
|
|
if ((interrupted |= Thread.interrupted()) ||
|
|
(nanos = deadline - System.nanoTime()) <= 0L) {
|
|
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
|
|
break;
|
|
} else
|
|
LockSupport.parkNanos(this, nanos);
|
|
}
|
|
node.clearStatus();
|
|
acquire(node, savedState, false, false, false, 0L);
|
|
if (cancelled) {
|
|
unlinkCancelledWaiters(node);
|
|
if (interrupted)
|
|
throw new InterruptedException();
|
|
} else if (interrupted)
|
|
Thread.currentThread().interrupt();
|
|
long remaining = deadline - System.nanoTime(); // avoid overflow
|
|
return (remaining <= nanosTimeout) ? remaining : Long.MIN_VALUE;
|
|
}
|
|
|
|
/**
|
|
* Implements absolute timed condition wait.
|
|
* <ol>
|
|
* <li>If current thread is interrupted, throw InterruptedException.
|
|
* <li>Save lock state returned by {@link #getState}.
|
|
* <li>Invoke {@link #release} with saved state as argument,
|
|
* throwing IllegalMonitorStateException if it fails.
|
|
* <li>Block until signalled, interrupted, or timed out.
|
|
* <li>Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li>If interrupted while blocked in step 4, throw InterruptedException.
|
|
* <li>If timed out while blocked in step 4, return false, else true.
|
|
* </ol>
|
|
*/
|
|
public final boolean awaitUntil(Date deadline)
|
|
throws InterruptedException {
|
|
long abstime = deadline.getTime();
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
ConditionNode node = new ConditionNode();
|
|
long savedState = enableWait(node);
|
|
boolean cancelled = false, interrupted = false;
|
|
while (!canReacquire(node)) {
|
|
if ((interrupted |= Thread.interrupted()) ||
|
|
System.currentTimeMillis() >= abstime) {
|
|
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
|
|
break;
|
|
} else
|
|
LockSupport.parkUntil(this, abstime);
|
|
}
|
|
node.clearStatus();
|
|
acquire(node, savedState, false, false, false, 0L);
|
|
if (cancelled) {
|
|
unlinkCancelledWaiters(node);
|
|
if (interrupted)
|
|
throw new InterruptedException();
|
|
} else if (interrupted)
|
|
Thread.currentThread().interrupt();
|
|
return !cancelled;
|
|
}
|
|
|
|
/**
|
|
* Implements timed condition wait.
|
|
* <ol>
|
|
* <li>If current thread is interrupted, throw InterruptedException.
|
|
* <li>Save lock state returned by {@link #getState}.
|
|
* <li>Invoke {@link #release} with saved state as argument,
|
|
* throwing IllegalMonitorStateException if it fails.
|
|
* <li>Block until signalled, interrupted, or timed out.
|
|
* <li>Reacquire by invoking specialized version of
|
|
* {@link #acquire} with saved state as argument.
|
|
* <li>If interrupted while blocked in step 4, throw InterruptedException.
|
|
* <li>If timed out while blocked in step 4, return false, else true.
|
|
* </ol>
|
|
*/
|
|
public final boolean await(long time, TimeUnit unit)
|
|
throws InterruptedException {
|
|
long nanosTimeout = unit.toNanos(time);
|
|
if (Thread.interrupted())
|
|
throw new InterruptedException();
|
|
ConditionNode node = new ConditionNode();
|
|
long savedState = enableWait(node);
|
|
long nanos = (nanosTimeout < 0L) ? 0L : nanosTimeout;
|
|
long deadline = System.nanoTime() + nanos;
|
|
boolean cancelled = false, interrupted = false;
|
|
while (!canReacquire(node)) {
|
|
if ((interrupted |= Thread.interrupted()) ||
|
|
(nanos = deadline - System.nanoTime()) <= 0L) {
|
|
if (cancelled = (node.getAndUnsetStatus(COND) & COND) != 0)
|
|
break;
|
|
} else
|
|
LockSupport.parkNanos(this, nanos);
|
|
}
|
|
node.clearStatus();
|
|
acquire(node, savedState, false, false, false, 0L);
|
|
if (cancelled) {
|
|
unlinkCancelledWaiters(node);
|
|
if (interrupted)
|
|
throw new InterruptedException();
|
|
} else if (interrupted)
|
|
Thread.currentThread().interrupt();
|
|
return !cancelled;
|
|
}
|
|
|
|
// support for instrumentation
|
|
|
|
/**
|
|
* Returns true if this condition was created by the given
|
|
* synchronization object.
|
|
*
|
|
* @return {@code true} if owned
|
|
*/
|
|
final boolean isOwnedBy(AbstractQueuedLongSynchronizer sync) {
|
|
return sync == AbstractQueuedLongSynchronizer.this;
|
|
}
|
|
|
|
/**
|
|
* Queries whether any threads are waiting on this condition.
|
|
* Implements {@link AbstractQueuedLongSynchronizer#hasWaiters(ConditionObject)}.
|
|
*
|
|
* @return {@code true} if there are any waiting threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final boolean hasWaiters() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if ((w.status & COND) != 0)
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/**
|
|
* Returns an estimate of the number of threads waiting on
|
|
* this condition.
|
|
* Implements {@link AbstractQueuedLongSynchronizer#getWaitQueueLength(ConditionObject)}.
|
|
*
|
|
* @return the estimated number of waiting threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final int getWaitQueueLength() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
int n = 0;
|
|
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if ((w.status & COND) != 0)
|
|
++n;
|
|
}
|
|
return n;
|
|
}
|
|
|
|
/**
|
|
* Returns a collection containing those threads that may be
|
|
* waiting on this Condition.
|
|
* Implements {@link AbstractQueuedLongSynchronizer#getWaitingThreads(ConditionObject)}.
|
|
*
|
|
* @return the collection of threads
|
|
* @throws IllegalMonitorStateException if {@link #isHeldExclusively}
|
|
* returns {@code false}
|
|
*/
|
|
protected final Collection<Thread> getWaitingThreads() {
|
|
if (!isHeldExclusively())
|
|
throw new IllegalMonitorStateException();
|
|
ArrayList<Thread> list = new ArrayList<>();
|
|
for (ConditionNode w = firstWaiter; w != null; w = w.nextWaiter) {
|
|
if ((w.status & COND) != 0) {
|
|
Thread t = w.waiter;
|
|
if (t != null)
|
|
list.add(t);
|
|
}
|
|
}
|
|
return list;
|
|
}
|
|
}
|
|
|
|
// Unsafe
|
|
private static final Unsafe U = Unsafe.getUnsafe();
|
|
private static final long STATE
|
|
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "state");
|
|
private static final long HEAD
|
|
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "head");
|
|
private static final long TAIL
|
|
= U.objectFieldOffset(AbstractQueuedLongSynchronizer.class, "tail");
|
|
|
|
static {
|
|
Class<?> ensureLoaded = LockSupport.class;
|
|
}
|
|
}
|