--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/concurrent/locks/AbstractQueuedLongSynchronizer.java Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,1849 @@
+/*
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * This file is available under and governed by the GNU General Public
+ * License version 2 only, as published by the Free Software Foundation.
+ * However, the following notice accompanied the original version of this
+ * file:
+ *
+ * Written by Doug Lea with assistance from members of JCP JSR-166
+ * Expert Group and released to the public domain, as explained at
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+package java.util.concurrent.locks;
+
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.VarHandle;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Date;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.AbstractQueuedSynchronizer.Node;
+
+/**
+ * A version of {@link AbstractQueuedSynchronizer} in
+ * which synchronization state is maintained as a {@code long}.
+ * This class has exactly the same structure, properties, and methods
+ * as {@code AbstractQueuedSynchronizer} with the exception
+ * that all state-related parameters and results are defined
+ * as {@code long} rather than {@code int}. This class
+ * may be useful when creating synchronizers such as
+ * multilevel locks and barriers that require
+ * 64 bits of state.
+ *
+ * <p>See {@link AbstractQueuedSynchronizer} for usage
+ * notes and examples.
+ *
+ * @since 1.6
+ * @author Doug Lea
+ */
+public abstract class AbstractQueuedLongSynchronizer
+ extends AbstractOwnableSynchronizer
+ implements java.io.Serializable {
+
+ private static final long serialVersionUID = 7373984972572414692L;
+
+ /*
+ To keep sources in sync, the remainder of this source file is
+ exactly cloned from AbstractQueuedSynchronizer, replacing class
+ name and changing ints related with sync state to longs. Please
+ keep it that way.
+ */
+
+ /**
+ * Creates a new {@code AbstractQueuedLongSynchronizer} instance
+ * with initial synchronization state of zero.
+ */
+ protected AbstractQueuedLongSynchronizer() { }
+
+ /**
+ * Head of the wait queue, lazily initialized. Except for
+ * initialization, it is modified only via method setHead. Note:
+ * If head exists, its waitStatus is guaranteed not to be
+ * CANCELLED.
+ */
+ private transient volatile Node head;
+
+ /**
+ * Tail of the wait queue, lazily initialized. Modified only via
+ * method enq to add new wait node.
+ */
+ private transient volatile Node tail;
+
+ /**
+ * The synchronization state.
+ */
+ private volatile long state;
+
+ /**
+ * Returns the current value of synchronization state.
+ * This operation has memory semantics of a {@code volatile} read.
+ * @return current state value
+ */
+ protected final long getState() {
+ return state;
+ }
+
+ /**
+ * Sets the value of synchronization state.
+ * This operation has memory semantics of a {@code volatile} write.
+ * @param newState the new state value
+ */
+ protected final void setState(long newState) {
+ // See JDK-8180620: Clarify VarHandle mixed-access subtleties
+ STATE.setVolatile(this, newState);
+ }
+
+ /**
+ * Atomically sets synchronization state to the given updated
+ * value if the current state value equals the expected value.
+ * This operation has memory semantics of a {@code volatile} read
+ * and write.
+ *
+ * @param expect the expected value
+ * @param update the new value
+ * @return {@code true} if successful. False return indicates that the actual
+ * value was not equal to the expected value.
+ */
+ protected final boolean compareAndSetState(long expect, long update) {
+ return STATE.compareAndSet(this, expect, update);
+ }
+
+ // Queuing utilities
+
+ /**
+ * The number of nanoseconds for which it is faster to spin
+ * rather than to use timed park. A rough estimate suffices
+ * to improve responsiveness with very short timeouts.
+ */
+ static final long SPIN_FOR_TIMEOUT_THRESHOLD = 1000L;
+
+ /**
+ * Inserts node into queue, initializing if necessary. See picture above.
+ * @param node the node to insert
+ * @return node's predecessor
+ */
+ private Node enq(Node node) {
+ for (;;) {
+ Node oldTail = tail;
+ if (oldTail != null) {
+ node.setPrevRelaxed(oldTail);
+ if (compareAndSetTail(oldTail, node)) {
+ oldTail.next = node;
+ return oldTail;
+ }
+ } else {
+ initializeSyncQueue();
+ }
+ }
+ }
+
+ /**
+ * Creates and enqueues node for current thread and given mode.
+ *
+ * @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared
+ * @return the new node
+ */
+ private Node addWaiter(Node mode) {
+ Node node = new Node(mode);
+
+ for (;;) {
+ Node oldTail = tail;
+ if (oldTail != null) {
+ node.setPrevRelaxed(oldTail);
+ if (compareAndSetTail(oldTail, node)) {
+ oldTail.next = node;
+ return node;
+ }
+ } else {
+ initializeSyncQueue();
+ }
+ }
+ }
+
+ /**
+ * Sets head of queue to be node, thus dequeuing. Called only by
+ * acquire methods. Also nulls out unused fields for sake of GC
+ * and to suppress unnecessary signals and traversals.
+ *
+ * @param node the node
+ */
+ private void setHead(Node node) {
+ head = node;
+ node.thread = null;
+ node.prev = null;
+ }
+
+ /**
+ * Wakes up node's successor, if one exists.
+ *
+ * @param node the node
+ */
+ private void unparkSuccessor(Node node) {
+ /*
+ * If status is negative (i.e., possibly needing signal) try
+ * to clear in anticipation of signalling. It is OK if this
+ * fails or if status is changed by waiting thread.
+ */
+ int ws = node.waitStatus;
+ if (ws < 0)
+ node.compareAndSetWaitStatus(ws, 0);
+
+ /*
+ * Thread to unpark is held in successor, which is normally
+ * just the next node. But if cancelled or apparently null,
+ * traverse backwards from tail to find the actual
+ * non-cancelled successor.
+ */
+ Node s = node.next;
+ if (s == null || s.waitStatus > 0) {
+ s = null;
+ for (Node p = tail; p != node && p != null; p = p.prev)
+ if (p.waitStatus <= 0)
+ s = p;
+ }
+ if (s != null)
+ LockSupport.unpark(s.thread);
+ }
+
+ /**
+ * Release action for shared mode -- signals successor and ensures
+ * propagation. (Note: For exclusive mode, release just amounts
+ * to calling unparkSuccessor of head if it needs signal.)
+ */
+ private void doReleaseShared() {
+ /*
+ * Ensure that a release propagates, even if there are other
+ * in-progress acquires/releases. This proceeds in the usual
+ * way of trying to unparkSuccessor of head if it needs
+ * signal. But if it does not, status is set to PROPAGATE to
+ * ensure that upon release, propagation continues.
+ * Additionally, we must loop in case a new node is added
+ * while we are doing this. Also, unlike other uses of
+ * unparkSuccessor, we need to know if CAS to reset status
+ * fails, if so rechecking.
+ */
+ for (;;) {
+ Node h = head;
+ if (h != null && h != tail) {
+ int ws = h.waitStatus;
+ if (ws == Node.SIGNAL) {
+ if (!h.compareAndSetWaitStatus(Node.SIGNAL, 0))
+ continue; // loop to recheck cases
+ unparkSuccessor(h);
+ }
+ else if (ws == 0 &&
+ !h.compareAndSetWaitStatus(0, Node.PROPAGATE))
+ continue; // loop on failed CAS
+ }
+ if (h == head) // loop if head changed
+ break;
+ }
+ }
+
+ /**
+ * Sets head of queue, and checks if successor may be waiting
+ * in shared mode, if so propagating if either propagate > 0 or
+ * PROPAGATE status was set.
+ *
+ * @param node the node
+ * @param propagate the return value from a tryAcquireShared
+ */
+ private void setHeadAndPropagate(Node node, long propagate) {
+ Node h = head; // Record old head for check below
+ setHead(node);
+ /*
+ * Try to signal next queued node if:
+ * Propagation was indicated by caller,
+ * or was recorded (as h.waitStatus either before
+ * or after setHead) by a previous operation
+ * (note: this uses sign-check of waitStatus because
+ * PROPAGATE status may transition to SIGNAL.)
+ * and
+ * The next node is waiting in shared mode,
+ * or we don't know, because it appears null
+ *
+ * The conservatism in both of these checks may cause
+ * unnecessary wake-ups, but only when there are multiple
+ * racing acquires/releases, so most need signals now or soon
+ * anyway.
+ */
+ if (propagate > 0 || h == null || h.waitStatus < 0 ||
+ (h = head) == null || h.waitStatus < 0) {
+ Node s = node.next;
+ if (s == null || s.isShared())
+ doReleaseShared();
+ }
+ }
+
+ // Utilities for various versions of acquire
+
+ /**
+ * Cancels an ongoing attempt to acquire.
+ *
+ * @param node the node
+ */
+ private void cancelAcquire(Node node) {
+ // Ignore if node doesn't exist
+ if (node == null)
+ return;
+
+ node.thread = null;
+
+ // Skip cancelled predecessors
+ Node pred = node.prev;
+ while (pred.waitStatus > 0)
+ node.prev = pred = pred.prev;
+
+ // predNext is the apparent node to unsplice. CASes below will
+ // fail if not, in which case, we lost race vs another cancel
+ // or signal, so no further action is necessary.
+ Node predNext = pred.next;
+
+ // Can use unconditional write instead of CAS here.
+ // After this atomic step, other Nodes can skip past us.
+ // Before, we are free of interference from other threads.
+ node.waitStatus = Node.CANCELLED;
+
+ // If we are the tail, remove ourselves.
+ if (node == tail && compareAndSetTail(node, pred)) {
+ pred.compareAndSetNext(predNext, null);
+ } else {
+ // If successor needs signal, try to set pred's next-link
+ // so it will get one. Otherwise wake it up to propagate.
+ int ws;
+ if (pred != head &&
+ ((ws = pred.waitStatus) == Node.SIGNAL ||
+ (ws <= 0 && pred.compareAndSetWaitStatus(ws, Node.SIGNAL))) &&
+ pred.thread != null) {
+ Node next = node.next;
+ if (next != null && next.waitStatus <= 0)
+ pred.compareAndSetNext(predNext, next);
+ } else {
+ unparkSuccessor(node);
+ }
+
+ node.next = node; // help GC
+ }
+ }
+
+ /**
+ * Checks and updates status for a node that failed to acquire.
+ * Returns true if thread should block. This is the main signal
+ * control in all acquire loops. Requires that pred == node.prev.
+ *
+ * @param pred node's predecessor holding status
+ * @param node the node
+ * @return {@code true} if thread should block
+ */
+ private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {
+ int ws = pred.waitStatus;
+ if (ws == Node.SIGNAL)
+ /*
+ * This node has already set status asking a release
+ * to signal it, so it can safely park.
+ */
+ return true;
+ if (ws > 0) {
+ /*
+ * Predecessor was cancelled. Skip over predecessors and
+ * indicate retry.
+ */
+ do {
+ node.prev = pred = pred.prev;
+ } while (pred.waitStatus > 0);
+ pred.next = node;
+ } else {
+ /*
+ * waitStatus must be 0 or PROPAGATE. Indicate that we
+ * need a signal, but don't park yet. Caller will need to
+ * retry to make sure it cannot acquire before parking.
+ */
+ pred.compareAndSetWaitStatus(ws, Node.SIGNAL);
+ }
+ return false;
+ }
+
+ /**
+ * Convenience method to interrupt current thread.
+ */
+ static void selfInterrupt() {
+ Thread.currentThread().interrupt();
+ }
+
+ /**
+ * Convenience method to park and then check if interrupted.
+ *
+ * @return {@code true} if interrupted
+ */
+ private final boolean parkAndCheckInterrupt() {
+ LockSupport.park(this);
+ return Thread.interrupted();
+ }
+
+ /*
+ * Various flavors of acquire, varying in exclusive/shared and
+ * control modes. Each is mostly the same, but annoyingly
+ * different. Only a little bit of factoring is possible due to
+ * interactions of exception mechanics (including ensuring that we
+ * cancel if tryAcquire throws exception) and other control, at
+ * least not without hurting performance too much.
+ */
+
+ /**
+ * Acquires in exclusive uninterruptible mode for thread already in
+ * queue. Used by condition wait methods as well as acquire.
+ *
+ * @param node the node
+ * @param arg the acquire argument
+ * @return {@code true} if interrupted while waiting
+ */
+ final boolean acquireQueued(final Node node, long arg) {
+ try {
+ boolean interrupted = false;
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head && tryAcquire(arg)) {
+ setHead(node);
+ p.next = null; // help GC
+ return interrupted;
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ parkAndCheckInterrupt())
+ interrupted = true;
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ /**
+ * Acquires in exclusive interruptible mode.
+ * @param arg the acquire argument
+ */
+ private void doAcquireInterruptibly(long arg)
+ throws InterruptedException {
+ final Node node = addWaiter(Node.EXCLUSIVE);
+ try {
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head && tryAcquire(arg)) {
+ setHead(node);
+ p.next = null; // help GC
+ return;
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ parkAndCheckInterrupt())
+ throw new InterruptedException();
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ /**
+ * Acquires in exclusive timed mode.
+ *
+ * @param arg the acquire argument
+ * @param nanosTimeout max wait time
+ * @return {@code true} if acquired
+ */
+ private boolean doAcquireNanos(long arg, long nanosTimeout)
+ throws InterruptedException {
+ if (nanosTimeout <= 0L)
+ return false;
+ final long deadline = System.nanoTime() + nanosTimeout;
+ final Node node = addWaiter(Node.EXCLUSIVE);
+ try {
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head && tryAcquire(arg)) {
+ setHead(node);
+ p.next = null; // help GC
+ return true;
+ }
+ nanosTimeout = deadline - System.nanoTime();
+ if (nanosTimeout <= 0L) {
+ cancelAcquire(node);
+ return false;
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD)
+ LockSupport.parkNanos(this, nanosTimeout);
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ /**
+ * Acquires in shared uninterruptible mode.
+ * @param arg the acquire argument
+ */
+ private void doAcquireShared(long arg) {
+ final Node node = addWaiter(Node.SHARED);
+ try {
+ boolean interrupted = false;
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head) {
+ long r = tryAcquireShared(arg);
+ if (r >= 0) {
+ setHeadAndPropagate(node, r);
+ p.next = null; // help GC
+ if (interrupted)
+ selfInterrupt();
+ return;
+ }
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ parkAndCheckInterrupt())
+ interrupted = true;
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ /**
+ * Acquires in shared interruptible mode.
+ * @param arg the acquire argument
+ */
+ private void doAcquireSharedInterruptibly(long arg)
+ throws InterruptedException {
+ final Node node = addWaiter(Node.SHARED);
+ try {
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head) {
+ long r = tryAcquireShared(arg);
+ if (r >= 0) {
+ setHeadAndPropagate(node, r);
+ p.next = null; // help GC
+ return;
+ }
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ parkAndCheckInterrupt())
+ throw new InterruptedException();
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ /**
+ * Acquires in shared timed mode.
+ *
+ * @param arg the acquire argument
+ * @param nanosTimeout max wait time
+ * @return {@code true} if acquired
+ */
+ private boolean doAcquireSharedNanos(long arg, long nanosTimeout)
+ throws InterruptedException {
+ if (nanosTimeout <= 0L)
+ return false;
+ final long deadline = System.nanoTime() + nanosTimeout;
+ final Node node = addWaiter(Node.SHARED);
+ try {
+ for (;;) {
+ final Node p = node.predecessor();
+ if (p == head) {
+ long r = tryAcquireShared(arg);
+ if (r >= 0) {
+ setHeadAndPropagate(node, r);
+ p.next = null; // help GC
+ return true;
+ }
+ }
+ nanosTimeout = deadline - System.nanoTime();
+ if (nanosTimeout <= 0L) {
+ cancelAcquire(node);
+ return false;
+ }
+ if (shouldParkAfterFailedAcquire(p, node) &&
+ nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD)
+ LockSupport.parkNanos(this, nanosTimeout);
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ }
+ } catch (Throwable t) {
+ cancelAcquire(node);
+ throw t;
+ }
+ }
+
+ // Main exported methods
+
+ /**
+ * Attempts to acquire in exclusive mode. This method should query
+ * if the state of the object permits it to be acquired in the
+ * exclusive mode, and if so to acquire it.
+ *
+ * <p>This method is always invoked by the thread performing
+ * acquire. If this method reports failure, the acquire method
+ * may queue the thread, if it is not already queued, until it is
+ * signalled by a release from some other thread. This can be used
+ * to implement method {@link Lock#tryLock()}.
+ *
+ * <p>The default
+ * implementation throws {@link UnsupportedOperationException}.
+ *
+ * @param arg the acquire argument. This value is always the one
+ * passed to an acquire method, or is the value saved on entry
+ * to a condition wait. The value is otherwise uninterpreted
+ * and can represent anything you like.
+ * @return {@code true} if successful. Upon success, this object has
+ * been acquired.
+ * @throws IllegalMonitorStateException if acquiring would place this
+ * synchronizer in an illegal state. This exception must be
+ * thrown in a consistent fashion for synchronization to work
+ * correctly.
+ * @throws UnsupportedOperationException if exclusive mode is not supported
+ */
+ protected boolean tryAcquire(long arg) {
+ throw new UnsupportedOperationException();
+ }
+
+ /**
+ * Attempts to set the state to reflect a release in exclusive
+ * mode.
+ *
+ * <p>This method is always invoked by the thread performing release.
+ *
+ * <p>The default implementation throws
+ * {@link UnsupportedOperationException}.
+ *
+ * @param arg the release argument. This value is always the one
+ * passed to a release method, or the current state value upon
+ * entry to a condition wait. The value is otherwise
+ * uninterpreted and can represent anything you like.
+ * @return {@code true} if this object is now in a fully released
+ * state, so that any waiting threads may attempt to acquire;
+ * and {@code false} otherwise.
+ * @throws IllegalMonitorStateException if releasing would place this
+ * synchronizer in an illegal state. This exception must be
+ * thrown in a consistent fashion for synchronization to work
+ * correctly.
+ * @throws UnsupportedOperationException if exclusive mode is not supported
+ */
+ protected boolean tryRelease(long arg) {
+ throw new UnsupportedOperationException();
+ }
+
+ /**
+ * Attempts to acquire in shared mode. This method should query if
+ * the state of the object permits it to be acquired in the shared
+ * mode, and if so to acquire it.
+ *
+ * <p>This method is always invoked by the thread performing
+ * acquire. If this method reports failure, the acquire method
+ * may queue the thread, if it is not already queued, until it is
+ * signalled by a release from some other thread.
+ *
+ * <p>The default implementation throws {@link
+ * UnsupportedOperationException}.
+ *
+ * @param arg the acquire argument. This value is always the one
+ * passed to an acquire method, or is the value saved on entry
+ * to a condition wait. The value is otherwise uninterpreted
+ * and can represent anything you like.
+ * @return a negative value on failure; zero if acquisition in shared
+ * mode succeeded but no subsequent shared-mode acquire can
+ * succeed; and a positive value if acquisition in shared
+ * mode succeeded and subsequent shared-mode acquires might
+ * also succeed, in which case a subsequent waiting thread
+ * must check availability. (Support for three different
+ * return values enables this method to be used in contexts
+ * where acquires only sometimes act exclusively.) Upon
+ * success, this object has been acquired.
+ * @throws IllegalMonitorStateException if acquiring would place this
+ * synchronizer in an illegal state. This exception must be
+ * thrown in a consistent fashion for synchronization to work
+ * correctly.
+ * @throws UnsupportedOperationException if shared mode is not supported
+ */
+ protected long tryAcquireShared(long arg) {
+ throw new UnsupportedOperationException();
+ }
+
+ /**
+ * Attempts to set the state to reflect a release in shared mode.
+ *
+ * <p>This method is always invoked by the thread performing release.
+ *
+ * <p>The default implementation throws
+ * {@link UnsupportedOperationException}.
+ *
+ * @param arg the release argument. This value is always the one
+ * passed to a release method, or the current state value upon
+ * entry to a condition wait. The value is otherwise
+ * uninterpreted and can represent anything you like.
+ * @return {@code true} if this release of shared mode may permit a
+ * waiting acquire (shared or exclusive) to succeed; and
+ * {@code false} otherwise
+ * @throws IllegalMonitorStateException if releasing would place this
+ * synchronizer in an illegal state. This exception must be
+ * thrown in a consistent fashion for synchronization to work
+ * correctly.
+ * @throws UnsupportedOperationException if shared mode is not supported
+ */
+ protected boolean tryReleaseShared(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 non-waiting {@link ConditionObject} method.
+ * (Waiting methods instead invoke {@link #release}.)
+ *
+ * <p>The default implementation throws {@link
+ * UnsupportedOperationException}. This method is invoked
+ * internally only within {@link ConditionObject} methods, so need
+ * not be defined if conditions are not used.
+ *
+ * @return {@code true} if synchronization is held exclusively;
+ * {@code false} otherwise
+ * @throws UnsupportedOperationException if conditions are not supported
+ */
+ protected boolean isHeldExclusively() {
+ throw new UnsupportedOperationException();
+ }
+
+ /**
+ * Acquires in exclusive mode, ignoring interrupts. Implemented
+ * by invoking at least once {@link #tryAcquire},
+ * returning on success. Otherwise the thread is queued, possibly
+ * repeatedly blocking and unblocking, invoking {@link
+ * #tryAcquire} until success. This method can be used
+ * to implement method {@link Lock#lock}.
+ *
+ * @param arg the acquire argument. This value is conveyed to
+ * {@link #tryAcquire} but is otherwise uninterpreted and
+ * can represent anything you like.
+ */
+ public final void acquire(long arg) {
+ if (!tryAcquire(arg) &&
+ acquireQueued(addWaiter(Node.EXCLUSIVE), arg))
+ selfInterrupt();
+ }
+
+ /**
+ * Acquires in exclusive mode, aborting if interrupted.
+ * Implemented by first checking interrupt status, then invoking
+ * at least once {@link #tryAcquire}, returning on
+ * success. Otherwise the thread is queued, possibly repeatedly
+ * blocking and unblocking, invoking {@link #tryAcquire}
+ * until success or the thread is interrupted. This method can be
+ * used to implement method {@link Lock#lockInterruptibly}.
+ *
+ * @param arg the acquire argument. This value is conveyed to
+ * {@link #tryAcquire} but is otherwise uninterpreted and
+ * can represent anything you like.
+ * @throws InterruptedException if the current thread is interrupted
+ */
+ public final void acquireInterruptibly(long arg)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (!tryAcquire(arg))
+ doAcquireInterruptibly(arg);
+ }
+
+ /**
+ * Attempts to acquire in exclusive mode, aborting if interrupted,
+ * and failing if the given timeout elapses. Implemented by first
+ * checking interrupt status, then invoking at least once {@link
+ * #tryAcquire}, returning on success. Otherwise, the thread is
+ * queued, possibly repeatedly blocking and unblocking, invoking
+ * {@link #tryAcquire} until success or the thread is interrupted
+ * or the timeout elapses. This method can be used to implement
+ * method {@link Lock#tryLock(long, TimeUnit)}.
+ *
+ * @param arg the acquire argument. This value is conveyed to
+ * {@link #tryAcquire} but is otherwise uninterpreted and
+ * can represent anything you like.
+ * @param nanosTimeout the maximum number of nanoseconds to wait
+ * @return {@code true} if acquired; {@code false} if timed out
+ * @throws InterruptedException if the current thread is interrupted
+ */
+ public final boolean tryAcquireNanos(long arg, long nanosTimeout)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ return tryAcquire(arg) ||
+ doAcquireNanos(arg, nanosTimeout);
+ }
+
+ /**
+ * Releases in exclusive mode. Implemented by unblocking one or
+ * more threads if {@link #tryRelease} returns true.
+ * This method can be used to implement method {@link Lock#unlock}.
+ *
+ * @param arg the release argument. This value is conveyed to
+ * {@link #tryRelease} but is otherwise uninterpreted and
+ * can represent anything you like.
+ * @return the value returned from {@link #tryRelease}
+ */
+ public final boolean release(long arg) {
+ if (tryRelease(arg)) {
+ Node h = head;
+ if (h != null && h.waitStatus != 0)
+ unparkSuccessor(h);
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Acquires in shared mode, ignoring interrupts. Implemented by
+ * first invoking at least once {@link #tryAcquireShared},
+ * returning on success. Otherwise the thread is queued, possibly
+ * repeatedly blocking and unblocking, invoking {@link
+ * #tryAcquireShared} until success.
+ *
+ * @param arg the acquire argument. This value is conveyed to
+ * {@link #tryAcquireShared} but is otherwise uninterpreted
+ * and can represent anything you like.
+ */
+ public final void acquireShared(long arg) {
+ if (tryAcquireShared(arg) < 0)
+ doAcquireShared(arg);
+ }
+
+ /**
+ * Acquires in shared mode, aborting if interrupted. Implemented
+ * by first checking interrupt status, then invoking at least once
+ * {@link #tryAcquireShared}, returning on success. Otherwise the
+ * thread is queued, possibly repeatedly blocking and unblocking,
+ * invoking {@link #tryAcquireShared} until success or the thread
+ * is interrupted.
+ * @param arg the acquire argument.
+ * This value is conveyed to {@link #tryAcquireShared} but is
+ * otherwise uninterpreted and can represent anything
+ * you like.
+ * @throws InterruptedException if the current thread is interrupted
+ */
+ public final void acquireSharedInterruptibly(long arg)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ if (tryAcquireShared(arg) < 0)
+ doAcquireSharedInterruptibly(arg);
+ }
+
+ /**
+ * Attempts to acquire in shared mode, aborting if interrupted, and
+ * failing if the given timeout elapses. Implemented by first
+ * checking interrupt status, then invoking at least once {@link
+ * #tryAcquireShared}, returning on success. Otherwise, the
+ * thread is queued, possibly repeatedly blocking and unblocking,
+ * invoking {@link #tryAcquireShared} until success or the thread
+ * is interrupted or the timeout elapses.
+ *
+ * @param arg the acquire argument. This value is conveyed to
+ * {@link #tryAcquireShared} but is otherwise uninterpreted
+ * and can represent anything you like.
+ * @param nanosTimeout the maximum number of nanoseconds to wait
+ * @return {@code true} if acquired; {@code false} if timed out
+ * @throws InterruptedException if the current thread is interrupted
+ */
+ public final boolean tryAcquireSharedNanos(long arg, long nanosTimeout)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ return tryAcquireShared(arg) >= 0 ||
+ doAcquireSharedNanos(arg, nanosTimeout);
+ }
+
+ /**
+ * Releases in shared mode. Implemented by unblocking one or more
+ * threads if {@link #tryReleaseShared} returns true.
+ *
+ * @param arg the release argument. This value is conveyed to
+ * {@link #tryReleaseShared} but is otherwise uninterpreted
+ * and can represent anything you like.
+ * @return the value returned from {@link #tryReleaseShared}
+ */
+ public final boolean releaseShared(long arg) {
+ if (tryReleaseShared(arg)) {
+ doReleaseShared();
+ return true;
+ }
+ return false;
+ }
+
+ // Queue inspection methods
+
+ /**
+ * Queries whether any threads are waiting to acquire. Note that
+ * because cancellations due to interrupts and timeouts may occur
+ * at any time, a {@code true} return does not guarantee that any
+ * other thread will ever acquire.
+ *
+ * <p>In this implementation, this operation returns in
+ * constant time.
+ *
+ * @return {@code true} if there may be other threads waiting to acquire
+ */
+ public final boolean hasQueuedThreads() {
+ return head != tail;
+ }
+
+ /**
+ * Queries whether any threads have ever contended to acquire this
+ * synchronizer; that is, if an acquire method has ever blocked.
+ *
+ * <p>In this implementation, this operation returns in
+ * constant time.
+ *
+ * @return {@code true} if there has ever been contention
+ */
+ public final boolean hasContended() {
+ return head != null;
+ }
+
+ /**
+ * Returns the first (longest-waiting) thread in the queue, or
+ * {@code null} if no threads are currently queued.
+ *
+ * <p>In this implementation, this operation normally returns in
+ * constant time, but may iterate upon contention if other threads are
+ * concurrently modifying the queue.
+ *
+ * @return the first (longest-waiting) thread in the queue, or
+ * {@code null} if no threads are currently queued
+ */
+ public final Thread getFirstQueuedThread() {
+ // handle only fast path, else relay
+ return (head == tail) ? null : fullGetFirstQueuedThread();
+ }
+
+ /**
+ * Version of getFirstQueuedThread called when fastpath fails.
+ */
+ private Thread fullGetFirstQueuedThread() {
+ /*
+ * The first node is normally head.next. Try to get its
+ * thread field, ensuring consistent reads: If thread
+ * field is nulled out or s.prev is no longer head, then
+ * some other thread(s) concurrently performed setHead in
+ * between some of our reads. We try this twice before
+ * resorting to traversal.
+ */
+ Node h, s;
+ Thread st;
+ if (((h = head) != null && (s = h.next) != null &&
+ s.prev == head && (st = s.thread) != null) ||
+ ((h = head) != null && (s = h.next) != null &&
+ s.prev == head && (st = s.thread) != null))
+ return st;
+
+ /*
+ * Head's next field might not have been set yet, or may have
+ * been unset after setHead. So we must check to see if tail
+ * is actually first node. If not, we continue on, safely
+ * traversing from tail back to head to find first,
+ * guaranteeing termination.
+ */
+
+ Thread firstThread = null;
+ for (Node p = tail; p != null && p != head; p = p.prev) {
+ Thread t = p.thread;
+ if (t != null)
+ firstThread = t;
+ }
+ return firstThread;
+ }
+
+ /**
+ * Returns true if the given thread is currently queued.
+ *
+ * <p>This implementation traverses the queue to determine
+ * presence of the given thread.
+ *
+ * @param thread the thread
+ * @return {@code true} if the given thread is on the queue
+ * @throws NullPointerException if the thread is null
+ */
+ public final boolean isQueued(Thread thread) {
+ if (thread == null)
+ throw new NullPointerException();
+ for (Node p = tail; p != null; p = p.prev)
+ if (p.thread == thread)
+ return true;
+ return false;
+ }
+
+ /**
+ * Returns {@code true} if the apparent first queued thread, if one
+ * exists, is waiting in exclusive mode. If this method returns
+ * {@code true}, and the current thread is attempting to acquire in
+ * shared mode (that is, this method is invoked from {@link
+ * #tryAcquireShared}) then it is guaranteed that the current thread
+ * is not the first queued thread. Used only as a heuristic in
+ * ReentrantReadWriteLock.
+ */
+ final boolean apparentlyFirstQueuedIsExclusive() {
+ Node h, s;
+ return (h = head) != null &&
+ (s = h.next) != null &&
+ !s.isShared() &&
+ s.thread != null;
+ }
+
+ /**
+ * Queries whether any threads have been waiting to acquire longer
+ * than the current thread.
+ *
+ * <p>An invocation of this method is equivalent to (but may be
+ * more efficient than):
+ * <pre> {@code
+ * getFirstQueuedThread() != Thread.currentThread()
+ * && hasQueuedThreads()}</pre>
+ *
+ * <p>Note that because cancellations due to interrupts and
+ * timeouts may occur at any time, a {@code true} return does not
+ * guarantee that some other thread will acquire before the current
+ * thread. Likewise, it is possible for another thread to win a
+ * race to enqueue after this method has returned {@code false},
+ * due to the queue being empty.
+ *
+ * <p>This method is designed to be used by a fair synchronizer to
+ * avoid <a href="AbstractQueuedSynchronizer.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(int arg) {
+ * if (isHeldExclusively()) {
+ * // A reentrant acquire; increment hold count
+ * return true;
+ * } else if (hasQueuedPredecessors()) {
+ * return false;
+ * } else {
+ * // try to acquire normally
+ * }
+ * }}</pre>
+ *
+ * @return {@code true} if there is a queued thread preceding the
+ * current thread, and {@code false} if the current thread
+ * is at the head of the queue or the queue is empty
+ * @since 1.7
+ */
+ public final boolean hasQueuedPredecessors() {
+ // The correctness of this depends on head being initialized
+ // before tail and on head.next being accurate if the current
+ // thread is first in queue.
+ Node t = tail; // Read fields in reverse initialization order
+ Node h = head;
+ Node s;
+ return h != t &&
+ ((s = h.next) == null || s.thread != Thread.currentThread());
+ }
+
+
+ // Instrumentation and monitoring methods
+
+ /**
+ * Returns an estimate of the number of threads waiting to
+ * acquire. The value is only an estimate because the number of
+ * threads may change dynamically while this method traverses
+ * internal data structures. This method is designed for use in
+ * monitoring system state, not for synchronization control.
+ *
+ * @return the estimated number of threads waiting to acquire
+ */
+ public final int getQueueLength() {
+ int n = 0;
+ for (Node p = tail; p != null; p = p.prev) {
+ if (p.thread != null)
+ ++n;
+ }
+ return n;
+ }
+
+ /**
+ * Returns a collection containing threads that may be waiting to
+ * acquire. Because the actual set of threads may change
+ * dynamically while constructing this result, the returned
+ * collection is only a best-effort estimate. The elements of the
+ * returned collection are in no particular order. This method is
+ * designed to facilitate construction of subclasses that provide
+ * more extensive monitoring facilities.
+ *
+ * @return the collection of threads
+ */
+ public final Collection<Thread> getQueuedThreads() {
+ ArrayList<Thread> list = new ArrayList<>();
+ for (Node p = tail; p != null; p = p.prev) {
+ Thread t = p.thread;
+ if (t != null)
+ list.add(t);
+ }
+ return list;
+ }
+
+ /**
+ * Returns a collection containing threads that may be waiting to
+ * acquire in exclusive mode. This has the same properties
+ * as {@link #getQueuedThreads} except that it only returns
+ * those threads waiting due to an exclusive acquire.
+ *
+ * @return the collection of threads
+ */
+ public final Collection<Thread> getExclusiveQueuedThreads() {
+ ArrayList<Thread> list = new ArrayList<>();
+ for (Node p = tail; p != null; p = p.prev) {
+ if (!p.isShared()) {
+ Thread t = p.thread;
+ if (t != null)
+ list.add(t);
+ }
+ }
+ return list;
+ }
+
+ /**
+ * Returns a collection containing threads that may be waiting to
+ * acquire in shared mode. This has the same properties
+ * as {@link #getQueuedThreads} except that it only returns
+ * those threads waiting due to a shared acquire.
+ *
+ * @return the collection of threads
+ */
+ public final Collection<Thread> getSharedQueuedThreads() {
+ ArrayList<Thread> list = new ArrayList<>();
+ for (Node p = tail; p != null; p = p.prev) {
+ if (p.isShared()) {
+ Thread t = p.thread;
+ if (t != null)
+ list.add(t);
+ }
+ }
+ return list;
+ }
+
+ /**
+ * Returns a string identifying this synchronizer, as well as its state.
+ * The state, in brackets, includes the String {@code "State ="}
+ * followed by the current value of {@link #getState}, and either
+ * {@code "nonempty"} or {@code "empty"} depending on whether the
+ * queue is empty.
+ *
+ * @return a string identifying this synchronizer, as well as its state
+ */
+ public String toString() {
+ return super.toString()
+ + "[State = " + getState() + ", "
+ + (hasQueuedThreads() ? "non" : "") + "empty queue]";
+ }
+
+
+ // Internal support methods for Conditions
+
+ /**
+ * Returns true if a node, always one that was initially placed on
+ * a condition queue, is now waiting to reacquire on sync queue.
+ * @param node the node
+ * @return true if is reacquiring
+ */
+ final boolean isOnSyncQueue(Node node) {
+ if (node.waitStatus == Node.CONDITION || node.prev == null)
+ return false;
+ if (node.next != null) // If has successor, it must be on queue
+ return true;
+ /*
+ * node.prev can be non-null, but not yet on queue because
+ * the CAS to place it on queue can fail. So we have to
+ * traverse from tail to make sure it actually made it. It
+ * will always be near the tail in calls to this method, and
+ * unless the CAS failed (which is unlikely), it will be
+ * there, so we hardly ever traverse much.
+ */
+ return findNodeFromTail(node);
+ }
+
+ /**
+ * Returns true if node is on sync queue by searching backwards from tail.
+ * Called only when needed by isOnSyncQueue.
+ * @return true if present
+ */
+ private boolean findNodeFromTail(Node node) {
+ // We check for node first, since it's likely to be at or near tail.
+ // tail is known to be non-null, so we could re-order to "save"
+ // one null check, but we leave it this way to help the VM.
+ for (Node p = tail;;) {
+ if (p == node)
+ return true;
+ if (p == null)
+ return false;
+ p = p.prev;
+ }
+ }
+
+ /**
+ * Transfers a node from a condition queue onto sync queue.
+ * Returns true if successful.
+ * @param node the node
+ * @return true if successfully transferred (else the node was
+ * cancelled before signal)
+ */
+ final boolean transferForSignal(Node node) {
+ /*
+ * If cannot change waitStatus, the node has been cancelled.
+ */
+ if (!node.compareAndSetWaitStatus(Node.CONDITION, 0))
+ return false;
+
+ /*
+ * Splice onto queue and try to set waitStatus of predecessor to
+ * indicate that thread is (probably) waiting. If cancelled or
+ * attempt to set waitStatus fails, wake up to resync (in which
+ * case the waitStatus can be transiently and harmlessly wrong).
+ */
+ Node p = enq(node);
+ int ws = p.waitStatus;
+ if (ws > 0 || !p.compareAndSetWaitStatus(ws, Node.SIGNAL))
+ LockSupport.unpark(node.thread);
+ return true;
+ }
+
+ /**
+ * Transfers node, if necessary, to sync queue after a cancelled wait.
+ * Returns true if thread was cancelled before being signalled.
+ *
+ * @param node the node
+ * @return true if cancelled before the node was signalled
+ */
+ final boolean transferAfterCancelledWait(Node node) {
+ if (node.compareAndSetWaitStatus(Node.CONDITION, 0)) {
+ enq(node);
+ return true;
+ }
+ /*
+ * If we lost out to a signal(), then we can't proceed
+ * until it finishes its enq(). Cancelling during an
+ * incomplete transfer is both rare and transient, so just
+ * spin.
+ */
+ while (!isOnSyncQueue(node))
+ Thread.yield();
+ return false;
+ }
+
+ /**
+ * Invokes release with current state value; returns saved state.
+ * Cancels node and throws exception on failure.
+ * @param node the condition node for this wait
+ * @return previous sync state
+ */
+ final long fullyRelease(Node node) {
+ try {
+ long savedState = getState();
+ if (release(savedState))
+ return savedState;
+ throw new IllegalMonitorStateException();
+ } catch (Throwable t) {
+ node.waitStatus = Node.CANCELLED;
+ throw t;
+ }
+ }
+
+ // 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.
+ *
+ * @since 1.6
+ */
+ public class ConditionObject implements Condition, java.io.Serializable {
+ private static final long serialVersionUID = 1173984872572414699L;
+ /** First node of condition queue. */
+ private transient Node firstWaiter;
+ /** Last node of condition queue. */
+ private transient Node lastWaiter;
+
+ /**
+ * Creates a new {@code ConditionObject} instance.
+ */
+ public ConditionObject() { }
+
+ // Internal methods
+
+ /**
+ * Adds a new waiter to wait queue.
+ * @return its new wait node
+ */
+ private Node addConditionWaiter() {
+ Node t = lastWaiter;
+ // If lastWaiter is cancelled, clean out.
+ if (t != null && t.waitStatus != Node.CONDITION) {
+ unlinkCancelledWaiters();
+ t = lastWaiter;
+ }
+
+ Node node = new Node(Node.CONDITION);
+
+ if (t == null)
+ firstWaiter = node;
+ else
+ t.nextWaiter = node;
+ lastWaiter = node;
+ return node;
+ }
+
+ /**
+ * Removes and transfers nodes until hit non-cancelled one or
+ * null. Split out from signal in part to encourage compilers
+ * to inline the case of no waiters.
+ * @param first (non-null) the first node on condition queue
+ */
+ private void doSignal(Node first) {
+ do {
+ if ( (firstWaiter = first.nextWaiter) == null)
+ lastWaiter = null;
+ first.nextWaiter = null;
+ } while (!transferForSignal(first) &&
+ (first = firstWaiter) != null);
+ }
+
+ /**
+ * Removes and transfers all nodes.
+ * @param first (non-null) the first node on condition queue
+ */
+ private void doSignalAll(Node first) {
+ lastWaiter = firstWaiter = null;
+ do {
+ Node next = first.nextWaiter;
+ first.nextWaiter = null;
+ transferForSignal(first);
+ first = next;
+ } while (first != null);
+ }
+
+ /**
+ * Unlinks cancelled waiter nodes from condition queue.
+ * Called only while holding lock. This is called when
+ * cancellation occurred during condition wait, and upon
+ * insertion of a new waiter when lastWaiter is seen to have
+ * been cancelled. This method is needed to avoid garbage
+ * retention in the absence of signals. So even though it may
+ * require a full traversal, it comes into play only when
+ * timeouts or cancellations occur in the absence of
+ * signals. It traverses all nodes rather than stopping at a
+ * particular target to unlink all pointers to garbage nodes
+ * without requiring many re-traversals during cancellation
+ * storms.
+ */
+ private void unlinkCancelledWaiters() {
+ Node t = firstWaiter;
+ Node trail = null;
+ while (t != null) {
+ Node next = t.nextWaiter;
+ if (t.waitStatus != Node.CONDITION) {
+ t.nextWaiter = null;
+ if (trail == null)
+ firstWaiter = next;
+ else
+ trail.nextWaiter = next;
+ if (next == null)
+ lastWaiter = trail;
+ }
+ else
+ trail = t;
+ t = next;
+ }
+ }
+
+ // public methods
+
+ /**
+ * Moves the longest-waiting thread, if one exists, from the
+ * wait queue for this condition to the wait queue for the
+ * owning lock.
+ *
+ * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+ * returns {@code false}
+ */
+ public final void signal() {
+ if (!isHeldExclusively())
+ throw new IllegalMonitorStateException();
+ Node first = firstWaiter;
+ if (first != null)
+ doSignal(first);
+ }
+
+ /**
+ * Moves all threads from the wait queue for this condition to
+ * the wait queue for the owning lock.
+ *
+ * @throws IllegalMonitorStateException if {@link #isHeldExclusively}
+ * returns {@code false}
+ */
+ public final void signalAll() {
+ if (!isHeldExclusively())
+ throw new IllegalMonitorStateException();
+ Node first = firstWaiter;
+ if (first != null)
+ doSignalAll(first);
+ }
+
+ /**
+ * Implements uninterruptible condition wait.
+ * <ol>
+ * <li>Save lock state returned by {@link #getState}.
+ * <li>Invoke {@link #release} with saved state as argument,
+ * throwing IllegalMonitorStateException if it fails.
+ * <li>Block until signalled.
+ * <li>Reacquire by invoking specialized version of
+ * {@link #acquire} with saved state as argument.
+ * </ol>
+ */
+ public final void awaitUninterruptibly() {
+ Node node = addConditionWaiter();
+ long savedState = fullyRelease(node);
+ boolean interrupted = false;
+ while (!isOnSyncQueue(node)) {
+ LockSupport.park(this);
+ if (Thread.interrupted())
+ interrupted = true;
+ }
+ if (acquireQueued(node, savedState) || interrupted)
+ selfInterrupt();
+ }
+
+ /*
+ * For interruptible waits, we need to track whether to throw
+ * InterruptedException, if interrupted while blocked on
+ * condition, versus reinterrupt current thread, if
+ * interrupted while blocked waiting to re-acquire.
+ */
+
+ /** Mode meaning to reinterrupt on exit from wait */
+ private static final int REINTERRUPT = 1;
+ /** Mode meaning to throw InterruptedException on exit from wait */
+ private static final int THROW_IE = -1;
+
+ /**
+ * Checks for interrupt, returning THROW_IE if interrupted
+ * before signalled, REINTERRUPT if after signalled, or
+ * 0 if not interrupted.
+ */
+ private int checkInterruptWhileWaiting(Node node) {
+ return Thread.interrupted() ?
+ (transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
+ 0;
+ }
+
+ /**
+ * Throws InterruptedException, reinterrupts current thread, or
+ * does nothing, depending on mode.
+ */
+ private void reportInterruptAfterWait(int interruptMode)
+ throws InterruptedException {
+ if (interruptMode == THROW_IE)
+ throw new InterruptedException();
+ else if (interruptMode == REINTERRUPT)
+ selfInterrupt();
+ }
+
+ /**
+ * Implements interruptible condition wait.
+ * <ol>
+ * <li>If current thread is interrupted, throw InterruptedException.
+ * <li>Save lock state returned by {@link #getState}.
+ * <li>Invoke {@link #release} with saved state as argument,
+ * throwing IllegalMonitorStateException if it fails.
+ * <li>Block until signalled or interrupted.
+ * <li>Reacquire by invoking specialized version of
+ * {@link #acquire} with saved state as argument.
+ * <li>If interrupted while blocked in step 4, throw InterruptedException.
+ * </ol>
+ */
+ public final void await() throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ Node node = addConditionWaiter();
+ long savedState = fullyRelease(node);
+ int interruptMode = 0;
+ while (!isOnSyncQueue(node)) {
+ LockSupport.park(this);
+ if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+ break;
+ }
+ if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+ interruptMode = REINTERRUPT;
+ if (node.nextWaiter != null) // clean up if cancelled
+ unlinkCancelledWaiters();
+ if (interruptMode != 0)
+ reportInterruptAfterWait(interruptMode);
+ }
+
+ /**
+ * Implements timed condition wait.
+ * <ol>
+ * <li>If current thread is interrupted, throw InterruptedException.
+ * <li>Save lock state returned by {@link #getState}.
+ * <li>Invoke {@link #release} with saved state as argument,
+ * throwing IllegalMonitorStateException if it fails.
+ * <li>Block until signalled, interrupted, or timed out.
+ * <li>Reacquire by invoking specialized version of
+ * {@link #acquire} with saved state as argument.
+ * <li>If interrupted while blocked in step 4, throw InterruptedException.
+ * </ol>
+ */
+ public final long awaitNanos(long nanosTimeout)
+ throws InterruptedException {
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ // We don't check for nanosTimeout <= 0L here, to allow
+ // awaitNanos(0) as a way to "yield the lock".
+ final long deadline = System.nanoTime() + nanosTimeout;
+ long initialNanos = nanosTimeout;
+ Node node = addConditionWaiter();
+ long savedState = fullyRelease(node);
+ int interruptMode = 0;
+ while (!isOnSyncQueue(node)) {
+ if (nanosTimeout <= 0L) {
+ transferAfterCancelledWait(node);
+ break;
+ }
+ if (nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD)
+ LockSupport.parkNanos(this, nanosTimeout);
+ if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+ break;
+ nanosTimeout = deadline - System.nanoTime();
+ }
+ if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+ interruptMode = REINTERRUPT;
+ if (node.nextWaiter != null)
+ unlinkCancelledWaiters();
+ if (interruptMode != 0)
+ reportInterruptAfterWait(interruptMode);
+ long remaining = deadline - System.nanoTime(); // avoid overflow
+ return (remaining <= initialNanos) ? 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();
+ Node node = addConditionWaiter();
+ long savedState = fullyRelease(node);
+ boolean timedout = false;
+ int interruptMode = 0;
+ while (!isOnSyncQueue(node)) {
+ if (System.currentTimeMillis() >= abstime) {
+ timedout = transferAfterCancelledWait(node);
+ break;
+ }
+ LockSupport.parkUntil(this, abstime);
+ if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+ break;
+ }
+ if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+ interruptMode = REINTERRUPT;
+ if (node.nextWaiter != null)
+ unlinkCancelledWaiters();
+ if (interruptMode != 0)
+ reportInterruptAfterWait(interruptMode);
+ return !timedout;
+ }
+
+ /**
+ * Implements timed condition wait.
+ * <ol>
+ * <li>If current thread is interrupted, throw InterruptedException.
+ * <li>Save lock state returned by {@link #getState}.
+ * <li>Invoke {@link #release} with saved state as argument,
+ * throwing IllegalMonitorStateException if it fails.
+ * <li>Block until signalled, interrupted, or timed out.
+ * <li>Reacquire by invoking specialized version of
+ * {@link #acquire} with saved state as argument.
+ * <li>If interrupted while blocked in step 4, throw InterruptedException.
+ * <li>If timed out while blocked in step 4, return false, else true.
+ * </ol>
+ */
+ public final boolean await(long time, TimeUnit unit)
+ throws InterruptedException {
+ long nanosTimeout = unit.toNanos(time);
+ if (Thread.interrupted())
+ throw new InterruptedException();
+ // We don't check for nanosTimeout <= 0L here, to allow
+ // await(0, unit) as a way to "yield the lock".
+ final long deadline = System.nanoTime() + nanosTimeout;
+ Node node = addConditionWaiter();
+ long savedState = fullyRelease(node);
+ boolean timedout = false;
+ int interruptMode = 0;
+ while (!isOnSyncQueue(node)) {
+ if (nanosTimeout <= 0L) {
+ timedout = transferAfterCancelledWait(node);
+ break;
+ }
+ if (nanosTimeout > SPIN_FOR_TIMEOUT_THRESHOLD)
+ LockSupport.parkNanos(this, nanosTimeout);
+ if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
+ break;
+ nanosTimeout = deadline - System.nanoTime();
+ }
+ if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
+ interruptMode = REINTERRUPT;
+ if (node.nextWaiter != null)
+ unlinkCancelledWaiters();
+ if (interruptMode != 0)
+ reportInterruptAfterWait(interruptMode);
+ return !timedout;
+ }
+
+ // support for instrumentation
+
+ /**
+ * Returns true if this condition was created by the given
+ * synchronization object.
+ *
+ * @return {@code true} if owned
+ */
+ final boolean isOwnedBy(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 (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+ if (w.waitStatus == Node.CONDITION)
+ return true;
+ }
+ return false;
+ }
+
+ /**
+ * Returns an estimate of the number of threads waiting on
+ * this condition.
+ * Implements {@link 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 (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+ if (w.waitStatus == Node.CONDITION)
+ ++n;
+ }
+ return n;
+ }
+
+ /**
+ * Returns a collection containing those threads that may be
+ * waiting on this Condition.
+ * Implements {@link 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 (Node w = firstWaiter; w != null; w = w.nextWaiter) {
+ if (w.waitStatus == Node.CONDITION) {
+ Thread t = w.thread;
+ if (t != null)
+ list.add(t);
+ }
+ }
+ return list;
+ }
+ }
+
+ // VarHandle mechanics
+ private static final VarHandle STATE;
+ private static final VarHandle HEAD;
+ private static final VarHandle TAIL;
+
+ static {
+ try {
+ MethodHandles.Lookup l = MethodHandles.lookup();
+ STATE = l.findVarHandle(AbstractQueuedLongSynchronizer.class, "state", long.class);
+ HEAD = l.findVarHandle(AbstractQueuedLongSynchronizer.class, "head", Node.class);
+ TAIL = l.findVarHandle(AbstractQueuedLongSynchronizer.class, "tail", Node.class);
+ } catch (ReflectiveOperationException e) {
+ throw new Error(e);
+ }
+
+ // Reduce the risk of rare disastrous classloading in first call to
+ // LockSupport.park: https://bugs.openjdk.java.net/browse/JDK-8074773
+ Class<?> ensureLoaded = LockSupport.class;
+ }
+
+ /**
+ * Initializes head and tail fields on first contention.
+ */
+ private final void initializeSyncQueue() {
+ Node h;
+ if (HEAD.compareAndSet(this, null, (h = new Node())))
+ tail = h;
+ }
+
+ /**
+ * CASes tail field.
+ */
+ private final boolean compareAndSetTail(Node expect, Node update) {
+ return TAIL.compareAndSet(this, expect, update);
+ }
+}