1. AQS

AbstractQueuedSynchronizer:抽象队列同步器，定义了多线程访问共享资源的同步器框架

1.1. 基础概览

包名：java.util.concurrent.locks，可见属于juc多线程并发包，锁下

用到AQS实现的：ReentrantLock/Semaphore/CountDownLatch

1.1.1. 基础属性

属性代码块：

/**
 * Head of the wait queue, lazily initialized.  Except for
 * initialization, it is modified only via method setHead.  Note:
 * If head exists, its waitStatus is guaranteed not to be
 * CANCELLED.
 */
private transient volatile Node head;

/**
 * Tail of the wait queue, lazily initialized.  Modified only via
 * method enq to add new wait node.
 */
private transient volatile Node tail;

/**
 * The synchronization state.
 */
private volatile int state;

它维护了一个volatile int state（代表共享资源）和一个FIFO（先进先出）线程等待队列（多线程争用资源被阻塞时会进入此队列）

引用

• 从ReentrantLock的实现看AQS的原理及应用 </br>
• Java并发之AQS详解 </br>
• Java并发编程AQS详解 </br>