abstractqueuedlongsynchronizer.java

JAVA 所有包

     * monitoring of the system state.
     *
     * @param condition the condition
     * @return <tt>true</tt> if there are any waiting threads
     * @throws IllegalMonitorStateException if exclusive synchronization
     *         is not held
     * @throws IllegalArgumentException if the given condition is
     *         not associated with this synchronizer
     * @throws NullPointerException if the condition is null
     */
    public final boolean hasWaiters(ConditionObject condition) {
        if (!owns(condition))
            throw new IllegalArgumentException("Not owner");
        return condition.hasWaiters();
    }

    /**
     * Returns an estimate of the number of threads waiting on the
     * given condition associated with this synchronizer. Note that
     * because timeouts and interrupts may occur at any time, the
     * estimate serves only as an upper bound on the actual number of
     * waiters.  This method is designed for use in monitoring of the
     * system state, not for synchronization control.
     *
     * @param condition the condition
     * @return the estimated number of waiting threads
     * @throws IllegalMonitorStateException if exclusive synchronization
     *         is not held
     * @throws IllegalArgumentException if the given condition is
     *         not associated with this synchronizer
     * @throws NullPointerException if the condition is null
     */
    public final int getWaitQueueLength(ConditionObject condition) {
        if (!owns(condition))
            throw new IllegalArgumentException("Not owner");
        return condition.getWaitQueueLength();
    }

    /**
     * Returns a collection containing those threads that may be
     * waiting on the given condition associated with this
     * synchronizer.  Because the actual set of threads may change
     * dynamically while constructing this result, the returned
     * collection is only a best-effort estimate. The elements of the
     * returned collection are in no particular order.
     *
     * @param condition the condition
     * @return the collection of threads
     * @throws IllegalMonitorStateException if exclusive synchronization
     *         is not held
     * @throws IllegalArgumentException if the given condition is
     *         not associated with this synchronizer
     * @throws NullPointerException if the condition is null
     */
    public final Collection<Thread> getWaitingThreads(ConditionObject condition) {
        if (!owns(condition))
            throw new IllegalArgumentException("Not owner");
        return condition.getWaitingThreads();
    }

    /**
     * Condition implementation for a {@link
     * 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
     * <tt>AbstractQueuedLongSynchronizer</tt>.
     *
     * <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 <tt>ConditionObject</tt> instance.
         */
        public ConditionObject() { }

        // Internal methods

        /**
         * Adds a new waiter to wait queue.
         * @return its new wait node
         */
        private Node addConditionWaiter() {
            Node node = new Node(Thread.currentThread(), Node.CONDITION);
            Node t = lastWaiter;
            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);
        }

        /**
         * Returns true if given node is on this condition queue.
         * Call only when holding lock.
         */
        private boolean isOnConditionQueue(Node node) {
            return node.next != null || node == lastWaiter;
        }

        /**
         * Unlinks a cancelled waiter node from condition queue.  This
         * is called when cancellation occurred during condition wait,
         * not lock wait, and is called only after lock has been
         * re-acquired by a cancelled waiter and the node is not known
         * to already have been dequeued.  It 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.
         */
        private void unlinkCancelledWaiter(Node node) {
            Node t = firstWaiter;
            Node trail = null;
            while (t != null) {
                if (t == node) {
                    Node next = t.nextWaiter;
                    if (trail == null)
                        firstWaiter = next;
                    else
                        trail.nextWaiter = next;
                    if (lastWaiter == node)
                        lastWaiter = trail;
                    break;
                }
                trail = t;
                t = t.nextWaiter;
            }
        }

        // 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 exception
         * </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 (isOnConditionQueue(node))
                unlinkCancelledWaiter(node);
            if (interruptMode != 0)
                reportInterruptAfterWait(interruptMode);
        }

        /**
         * Implements timed condition wait.
         * <ol>
         * <li> If current thread is interrupted, throw InterruptedException
         * <li> Save lock state returned by {@link #getState}
         * <li> Invoke {@link #release} with
         *      saved state as argument, throwing
         *      IllegalMonitorStateException  if it fails.
         * <li> Block until signalled, interrupted, or timed out
         * <li> Reacquire by invoking specialized version of
         *      {@link #acquire} with saved state as argument.
         * <li> If interrupted while blocked in step 4, throw InterruptedException
         * </ol>
         */
        public final long awaitNanos(long nanosTimeout) throws InterruptedException {
            if (Thread.interrupted())
                throw new InterruptedException();
            Node node = addConditionWaiter();
            long savedState = fullyRelease(node);
            long lastTime = System.nanoTime();
            int interruptMode = 0;
            while (!isOnSyncQueue(node)) {
                if (nanosTimeout <= 0L) {
                    transferAfterCancelledWait(node);
                    break;
                }
                LockSupport.parkNanos(this, nanosTimeout);
                if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
                    break;

                long now = System.nanoTime();
                nanosTimeout -= now - lastTime;
                lastTime = now;
            }
            if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
                interruptMode = REINTERRUPT;
            if (isOnConditionQueue(node))
                unlinkCancelledWaiter(node);
            if (interruptMode != 0)
                reportInterruptAfterWait(interruptMode);
            return