CountDownLatch 闭锁源码分析

(getState() == 0) ? 1 : -1

否

prev

AQS Node 节点状态// 值为1，表示当前节点被取消；static final int CANCELLED = 1;// 值为-1，表示当前节点的的后继节点将要或者已经被阻塞，在当前节点释放的时候需要unpark后继节点；static final int SIGNAL = -1;// 值为-2，表示当前节点在等待condition，即在condition队列中；static final int CONDITION = -2;// 值为-3，表示releaseShared需要被传播给后续节点（仅在共享模式下使用）；static final int PROPAGATE = -3;// 0：无状态，表示当前节点在队列中等待获取锁。

doAcquireSharedInterruptibly(int arg)

thread

return false;

nextWaiter

创建 SHARED 类型 Node

ws > 0 

for

非空唤醒

只有 ws == SIGNAL 当前节点线程才能被 unpark

结束

LockSupport.unpark(s.thread);

next

continue;

初始化

CountDownLatch downLatch = new CountDownLatch(1);

Node h = head;

 return Thread.interrupted();

创建节点(入队)

shouldParkAfterFailedAcquire 方法

false

unparkSuccessor(h);

激活节点 (出队)

修改为前驱节点为阻塞

是

是否是头节点

final Node node = addWaiter(Node.SHARED);

获取 AQS 头节点

h != null && h != tail

ws < 0

返回

r >= 0

ws == Node.SIGNAL

判断是否拿到锁

sync.releaseShared(1);

等待

new Sync(count);

tryAcquireShared(arg) < 0

注意这里是 await 不是 Object#wait

downLatch.await();

doAcquireSharedInterruptibly 方法

获取等待节点

return nextc == 0;

else

s != null

true

int ws = node.waitStatus;

查找有效的节点

开始

调用 CountDownLatch 中的的实现方法

tryAcquireShared(arg) 

throw new InterruptedException();

LockSupport.park(this);

parkAndCheckInterrupt()

doReleaseShared 方法

int r = tryAcquireShared(arg);

唤醒节点

do {     node.prev = pred = pred.prev; } while (pred.waitStatus > 0);pred.next = node;

break

当前线程进入阻塞

downLatch.countDown();

for (AbstractQueuedSynchronizer.Node t = tail; t != null && t != node; t = t.prev) if (t.waitStatus <= 0) s = t;

测试中断

h == head

p == head

唤醒线程

Thread.interrupted()

解锁

tryReleaseShared(arg)

doReleaseShared();

sync.acquireSharedInterruptibly(1);

int ws = h.waitStatus;

 throw new InterruptedException();

unparkSuccessor(h); 方法

头节点是否为空

s == null || s.waitStatus > 0

final Node p = node.predecessor();