ConditionObject
Condition在ReentrantLock中，实际上是创建AQS的ConditionObject对象，主要的成员变量有Node类型的firstWaiter和lastWaiter，作为头节点和尾节点，是单向链表。当调用await时，加入队列，signal时，加入到AQS的阻塞队列。
await方法
把节点移到Condition队列后挂起
public final void await() throws InterruptedException {
if (Thread.interrupted())
throw new InterruptedException();
Node node = addConditionWaiter();//添加一个节点成为尾节点
int savedState = fullyRelease(node);//释放所有持有的锁
int interruptMode = 0;
while (!isOnSyncQueue(node)) {//要么中断，要么进入阻塞队列，退出while循环
LockSupport.park(this);//挂起
if ((interruptMode = checkInterruptWhileWaiting(node)) != 0)//中断过，就跳出循环
break;
}
if (acquireQueued(node, savedState) && interruptMode != THROW_IE)//是否被中断。acquireQueued之前讲过
interruptMode = REINTERRUPT;
if (node.nextWaiter != null) // clean up if cancelled如果尾节点不为空
unlinkCancelledWaiters();//将不是CONDITION状态的移除出去
if (interruptMode != 0)
reportInterruptAfterWait(interruptMode);//重新中断
}addConditionWaiter，如果尾节点不在队列里，先移除已取消的节点，添加一个节点成为尾节点
private Node addConditionWaiter() {
Node t = lastWaiter;
// If lastWaiter is cancelled, clean out.如果尾节点不为空，但是状态不是CONDITION，说明已取消，不想在Condition的队列里，就移除
if (t != null && t.waitStatus != Node.CONDITION) {
unlinkCancelledWaiters();//将不是CONDITION状态的移除出去
t = lastWaiter;
}
Node node = new Node(Thread.currentThread(), Node.CONDITION);//创建状态是CONDITION的节点
if (t == null)
firstWaiter = node;
else
t.nextWaiter = node;
lastWaiter = node;//加入到尾节点
return node;
}fullyRelease方法
final int fullyRelease(Node node) {
boolean failed = true;
try {
int savedState = getState();
if (release(savedState)) {
failed = false;
return savedState;
} else {
throw new IllegalMonitorStateException();
}
} finally {
if (failed)//如果释放失败，状态就变成CANCELLED，而不是CONDITION，所以会在addConditionWaiter方法中被移除
node.waitStatus = Node.CANCELLED;
}
}isOnSyncQueue方法
final boolean isOnSyncQueue(Node node) {
if (node.waitStatus == Node.CONDITION || node.prev == null)//如果状态是CONDITION或者前置节点为空，说明还在Condition队列里
return false;
if (node.next != null) // If has successor, it must be on queue如果有后续节点了，肯定是在阻塞队列里
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);//从阻塞队列的尾节点遍历，如果找到当前node，说明在阻塞队列里返回true
}checkInterruptWhileWaiting方法，唤醒前已经中断，返回THROW_IE，唤醒后中断，返回REINTERRUPT，没有中断，返回0
private int checkInterruptWhileWaiting(Node node) {
return Thread.interrupted() ?
(transferAfterCancelledWait(node) ? THROW_IE : REINTERRUPT) :
0;
}
final boolean transferAfterCancelledWait(Node node) {
//如果cas操作成功，且预期值是CONDITION状态，说明在唤醒前就中断了，并加入阻塞队列
if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) {
enq(node);
return true;
}
while (!isOnSyncQueue(node))//一直到阻塞队列里，在唤醒后才中断
Thread.yield();
return false;
}signal方法
唤醒Condition队列的节点
public final void signal() {
if (!isHeldExclusively())//非独占抛异常
throw new IllegalMonitorStateException();
Node first = firstWaiter;//获取头结点
if (first != null)
doSignal(first);//唤醒头节点
}
//如果头结点已经取消，就继续往下个节点寻找
private void doSignal(Node first) {
do {
if ( (firstWaiter = first.nextWaiter) == null)//把下一个节点移到头结点
lastWaiter = null;
first.nextWaiter = null;//help gc
} while (!transferForSignal(first) &&
(first = firstWaiter) != null);
}
final boolean transferForSignal(Node node) {
/*
* 如果cas操作没成功，说明已经取消了，就继续下一个节点
*/
if (!compareAndSetWaitStatus(node, Node.CONDITION, 0))
return false;
/*
* 没有取消，就加入阻塞队列，这个方法在aqs讲过了
*
*/
Node p = enq(node);
int ws = p.waitStatus;//前置节点的状态
//大于0，说明前置节点已取消，就轮到当前节点，可以唤醒
//小于等于哦，把前置节点的状态设置为-1，如果失败了，唤醒
if (ws > 0 || !compareAndSetWaitStatus(p, ws, Node.SIGNAL))
LockSupport.unpark(node.thread);//唤醒
return true;
}