详解AQS中的condition源码原理

Lock lock = new ReentrantLock(); Condition condition = lock.newCondition(); public void conditionWait() throws InterruptedException { lock.lock(); try { // if(xxxx)判断不满足条件，等待，释放锁 condition.await(); } finally { lock.unlock(); } } public void conditionSignal() throws InterruptedException { lock.lock(); try { // 做完事情了，通知condition上等待的开始抢占 condition.signal(); } finally { lock.unlock(); } }

public final void await() throws InterruptedException { if (Thread.interrupted()) throw new InterruptedException(); // 添加本线程到等待队列尾部 Node node = addConditionWaiter(); // 释放锁，唤醒同步队列中的后继节点 int savedState = fullyRelease(node); int interruptMode = 0; // 如果已经在同步队列中了，说明被成功sign唤醒 while (!isOnSyncQueue(node)) { // 阻塞挂起 LockSupport.park(this); // 确认是否需要中断时就退出 if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) break; } // 在同步队列中，那就按同步队列的规则在队列中用CAS竞争同步状态 if (acquireQueued(node, savedState) && interruptMode != THROW_IE) interruptMode = REINTERRUPT; // 清理已经不是CONDITION状态的等待队列节点 if (node.nextWaiter != null) unlinkCancelledWaiters(); if (interruptMode != 0) reportInterruptAfterWait(interruptMode); }

if (!isHeldExclusively()) throw new IllegalMonitorStateException();

Node first = firstWaiter; if (first != null) doSignal(first);

if (!node.compareAndSetWaitStatus(Node.CONDITION, 0)) return false;

Node p = enq(node);

int ws = p.waitStatus; if (ws > 0 || !p.compareAndSetWaitStatus(ws, Node.SIGNAL)) LockSupport.unpark(node.thread);

do { Node next = first.nextWaiter; first.nextWaiter = null; transferForSignal(first); first = next; } while (first != null);