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ReentrantLock Lock

2021-02-27 15:53:22   1  举报

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ReentrantLock lock方法流程

Lock

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(prev=tail)!=null判断是否队列是否存在数据

 pred.next = node;

tryAcquire(1)尝试获取锁

Thread.currentThread().interrupt();

compareAndSetHead(new Node())

pred.waitStatus > 0

 pred.next = node;将原来的尾节点的next指向此节点

      setHead(node);      p.next = null; // help GC      failed = false;

int ws = pred.waitStatus;

return true

return interrupted

return false

state=state+acquires信号量加1，重入锁

非公平锁没有这一步

finallyfailed

tryAcquire（int arg）

ws == Node.SIGNAL

node.prev = tail当前节点prev指向尾节点

setExclusiveOwnerThread(current)将获取锁的线程设置为此线程

end

interrupted = true;

node.prev = pred = pred.prev;

 cancelAcquire(node)

return node;

Node p = node.predecessor();node的前一个节点，若前一个节点为空抛空指针异常

enq(node);入队CLH

 boolean interrupted = false;

node.prev = t;

parkAndCheckInterrupt())休眠此进程返回此线程是否处于中断，并重置中断状态

p==head

t.next = node;

enq(node);入队

t == null

state==0判断此时是否有线程占有锁

tryAcquire(arg)

current == getExclusiveOwnerThread()判断当前获取锁的线程是否是此线程

ws > 0

return t

addWaiter(Node.EXCLUSIVE)将当前线程加入CLH队列

hasQueuedPredecessors()队列中是否存在线程排队，公平锁空队列返回false第二个节点为null或者第二个节点为当前线程返回true

tail = head;

Node t = tail;

ReentrantLock.lock() sync.lock();

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