Java Node.CONDITION屬性代碼示例

/**
 * 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);
}
 

/**
 * 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;
}
 

/**
 * 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;
    }
}
 

/**
 * 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;
}