| /* |
| * 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, although with |
| // a possibility that a cancelled node may transiently remain |
| // reachable. |
| 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) { |
| boolean interrupted = false; |
| try { |
| for (;;) { |
| final Node p = node.predecessor(); |
| if (p == head && tryAcquire(arg)) { |
| setHead(node); |
| p.next = null; // help GC |
| return interrupted; |
| } |
| if (shouldParkAfterFailedAcquire(p, node)) |
| interrupted |= parkAndCheckInterrupt(); |
| } |
| } catch (Throwable t) { |
| cancelAcquire(node); |
| if (interrupted) |
| selfInterrupt(); |
| 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); |
| boolean interrupted = false; |
| 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)) |
| interrupted |= parkAndCheckInterrupt(); |
| } |
| } catch (Throwable t) { |
| cancelAcquire(node); |
| throw t; |
| } finally { |
| if (interrupted) |
| selfInterrupt(); |
| } |
| } |
| |
| /** |
| * 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 {@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) && |
| 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. |
| * |
| * @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.waitStatus <= 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() { |
| // 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() { |
| Node h, s; |
| if ((h = head) != null) { |
| if ((s = h.next) == null || s.waitStatus > 0) { |
| s = null; // traverse in case of concurrent cancellation |
| for (Node p = tail; p != h && p != null; p = p.prev) { |
| if (p.waitStatus <= 0) |
| s = p; |
| } |
| } |
| if (s != null && s.thread != Thread.currentThread()) |
| return true; |
| } |
| return false; |
| } |
| |
| // 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() { |
| if (!isHeldExclusively()) |
| throw new IllegalMonitorStateException(); |
| 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 ExceptionInInitializerError(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); |
| } |
| } |
