ReentrantLock && AQS

1. ReentrantLock 源代码

使用AQS框架，CAS的操作代替了Synchronized里面的重量级锁， AQS里边维护一个队列，存储需要拿到资源的Thread

a. ReentrantLock 内部类

abstract static class Sync extends AbstractQueuedSynchronizer 

nonfairTryAcquire

tryRelease

static final class NonfairSync extends Sync 

static final class FairSync extends Sync

b. 构造方法

public ReentrantLock() {
    sync = new NonfairSync();
}

public ReentrantLock(boolean fair) {
     sync = fair ? new FairSync() : new NonfairSync();
}

c. 重点方法

public void lock() {
　　sync.lock();
}

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

public void lockInterruptibly() throws InterruptedException {
　　sync.acquireInterruptibly(1);
}

public boolean tryLock() {
　　return sync.nonfairTryAcquire(1);
}

public boolean tryLock(long timeout, TimeUnit unit)
throws InterruptedException {
　　return sync.tryAcquireNanos(1, unit.toNanos(timeout));
}

2. class AbstractQueuedSynchronizer

a. 内部类 

static final class Node

public class ConditionObject 

b. 变量

 private transient volatile Node head;

 private transient volatile Node tail;

private volatile int state;

c. 主要方法

使用For去不断的循环查看前面的Node是Head，如果是，则试着获取锁，直到获取完锁才停止