ReentrantLock源码解读及流程图

unlock()

compareAndSetWaitStatus(SIGNAL);

Yes

FairSync

tryRelease(int releases)

acquire(1)

公平锁是直接发起acquire

tryAcquire()

Sync

tryAcquire(arg)

pred.waitStatus > 0

do..while

tryAcquire(int acquires)

lock()

No

实现

发起请求

pred.waitStatus == Node.SIGNAL

cancelAcquire(Node node)

为什么可重入

setExclusiveOwnerThread(Thread.currentThread())

acquireQueued()

release()

继承

    protected final void setExclusiveOwnerThread(Thread thread) {        exclusiveOwnerThread = thread;    }    // private transient Thread exclusiveOwnerThread; 在AQS父类中有一个属性exclusiveOwnerThread; 用来标识当前持有锁的线程对象。

NonFairSync   lock()源码解读

node.prev = pred = pred.prev;

parkAndCheckInterrupt()

hasQueuedPredecessors()

公平锁

addWaiter(Node mode)

Lock

addWaiter(Node.EXCULSIVE)

        protected final boolean tryRelease(int releases) {            //获取当前状态值减去参数值            int c = getState() - releases;            if (Thread.currentThread() != getExclusiveOwnerThread())                throw new IllegalMonitorStateException();            boolean free = false;            // c == 0 代表state 已经释放了所有的锁次数            if (c == 0) {                free = true;                //将当前代表独占锁属性置空                setExclusiveOwnerThread(null);            }            //初始化state值为0            setState(c);            return free;        }

锁流程图

什么是ReentrantLock

current == exclusiveOwnerThread

举例一个场景：       银行排队。只能有一个人进去办理业务，其他人排队。span style=\"font-size: inherit;\

enq(final Node node)

ReentrantLock

setExclusiveOwnerThread(Thread thread)

什么是中断操作?

非公平锁独有方法

null == tail

场景需求

NonFairSync

selfInterrupt()

        final void lock() {            acquire(1);        }

enq(node)

shouldParkAfterFailedAcquire()

非公平锁

ReentrantLock结构组成

    public void unlock() {        sync.release(1);    }

    public final boolean release(int arg) {        //尝试释放锁        if (tryRelease(arg)) {            Node h = head;            if (h != null && h.waitStatus != 0)                //唤醒后继节点或从尾节点扫描状态值正常的且距离h节点最近的节点                unparkSuccessor(h);            return true;        }        return false;    }

NonFairSync   unlock()源码分析

什么是中断操作

AbstractQueuedSynchronizer

unparkSuccessor(Node node)

enq()

提供了关于锁的操作规范

addWaiter()

acquire(int arg)

head ==node.predecessor()

setState(getState()+1)

compareAndSetHead(new Node())