Java并发编程之Condition源码分析（推荐）

public final void await() throws InterruptedException {
		//判断是否当前线程是否被中断中断则抛出中断异常
      if (Thread.interrupted())
        throw new InterruptedException();
		//加入等待队列
      Node node = addConditionWaiter();
		//释放当前线程锁
      int savedState = fullyRelease(node);
      int interruptMode = 0;
		//判断是否在同步阻塞队列，如果不在一直循环到被加入
      while (!isOnSyncQueue(node)) {
		//阻塞当前线程
        LockSupport.park(this);
		//判断是否被中断
        if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)
          break;
      }
		//获取锁，如果获取中被中断则设置中断状态
      if (acquireQueued(node, savedState) && interruptMode != THROW_IE)
        interruptMode = REINTERRUPT;
		//清除等待队列中被"激活"的节点
      if (node.nextWaiter != null) // clean up if cancelled
        unlinkCancelledWaiters();
		//如果当前线程被中断，处理中断逻辑
      if (interruptMode != 0)
        reportInterruptAfterWait(interruptMode);
    }

private Node addConditionWaiter() {
 		//获取等待队列尾部节点
      Node t = lastWaiter;
      //如果尾部状态不为CONDITION，如果已经被"激活"，清理之，然后重新获取尾部节点
      if (t != null && t.waitStatus != Node.CONDITION) {
        unlinkCancelledWaiters();
        t = lastWaiter;
      }
		//创建以当前线程为基础的节点，并将节点模式设置成CONDITION
      Node node = new Node(Thread.currentThread(), Node.CONDITION);
		//如果尾节点不存在，说明队列为空，将头节点设置成当前节点
      if (t == null)
        firstWaiter = node;
		//如果尾节点存在，将此节点设置成尾节点的下个节点
      else
        t.nextWaiter = node;
		//将尾节点设置成当前节点
      lastWaiter = node;
      return node;
    }

final int fullyRelease(Node node) {
    boolean failed = true;
    try {
		//获取阻塞队列中当前线程节点的锁状态值
      int savedState = getState();
		//释放当前线程节点锁
      if (release(savedState)) {
        failed = false;
        return savedState;
      } else {
        throw new IllegalMonitorStateException();
      }
    } finally {
		//释放失败讲节点等待状态设置成关闭
      if (failed)
        node.waitStatus = Node.CANCELLED;
    }
  }

final boolean isOnSyncQueue(Node node) {
		//判断当前节点是否是CONDITION或者前置节点是否为空如果为空直接返回false
    if (node.waitStatus == Node.CONDITION || node.prev == null)
      return false;
		//如果下个节点存在，则在同步阻塞队列中返回true
    if (node.next != null) // If has successor, it must be on queue
      return true;
		//遍历查找当前节点是否在同步阻塞队列中
    return findNodeFromTail(node);
  }
  private boolean findNodeFromTail(Node node) {
    Node t = tail;
    for (;;) {
      if (t == node)
        return true;
      if (t == null)
        return false;
      t = t.prev;
    }
  }

private int checkInterruptWhileWaiting(Node node) {
      return Thread.interrupted() ?
        (transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
        0;
    }

final boolean transferAfterCancelledWait(Node node) {
    if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
      enq(node);
      return true;
    }
    while (!isOnSyncQueue(node))
      Thread.yield();
    return false;
  }

private void unlinkCancelledWaiters() {
		//获取等待队列头节点
      Node t = firstWaiter;
      Node trail = null;
      while (t != null) {
		//获取下个节点
        Node next = t.nextWaiter;
		//如果状态不为CONDITION说明已经加入阻塞队列需要清理掉
        if (t.waitStatus != Node.CONDITION) {
          t.nextWaiter = null;
          if (trail == null)
            firstWaiter = next;
          else
			//获取下个节点
            trail.nextWaiter = next;
          if (next == null)
            lastWaiter = trail;
        }
        else
          trail = t;
        t = next;
      }
    }

private void reportInterruptAfterWait(int interruptMode)
      throws InterruptedException {
		//如果是THROW_IE模式直接抛出异常
      if (interruptMode == THROW_IE)
        throw new InterruptedException();
		//如果是REINTERRUPT模式标记线程中断由上层处理中断
      else if (interruptMode == REINTERRUPT)
        selfInterrupt();
    }

public final void signal() {
		//是否当前线程持有锁
      if (!isHeldExclusively())
        throw new IllegalMonitorStateException();
      Node first = firstWaiter;
		//通知"激活"头节点线程
      if (first != null)
        doSignal(first);
    }

 protected final boolean isHeldExclusively() {
      return getExclusiveOwnerThread() == Thread.currentThread();
    }

private void doSignal(Node first) {
      do {
		//头指头后移一位，如果后面的节点为空，则将尾指头也指向空，说明队列为空了
        if ( (firstWaiter = first.nextWaiter) == null)
          lastWaiter = null;
		//清空头节点的下个节点
        first.nextWaiter = null;
		//如果"激活"失败者取下个继续，直到成功或者遍历完
      } while (!transferForSignal(first) &&
           (first = firstWaiter) != null);
    }

final boolean transferForSignal(Node node) {
		//将CONDITION状态设置成0
    if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
      return false;
		//加入到同步阻塞队列
    Node p = enq(node);
    int ws = p.waitStatus;
		//状态异常直接激活
    if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
      LockSupport.unpark(node.thread);
    return true;
  }