AQS是JUC中很多同步组件的构建基础，简单来讲，它内部实现主要是状态变量state和一个FIFO队列来完成，同步队列的头结点是当前获取到同步状态的结点，获取同步状态state失败的线程，会被构造成一个结点（或共享式或独占式）加入到同步队列尾部（采用自旋CAS来保证此操作的线程安全），随后线程会阻塞；释放时唤醒头结点的后继结点，使其加入对同步状态的争夺中。

　　AQS为我们定义好了顶层的处理实现逻辑，我们在使用AQS构建符合我们需求的同步组件时，只需重写tryAcquire，tryAcquireShared，tryRelease，tryReleaseShared几个方法，来决定同步状态的释放和获取即可，至于背后复杂的线程排队，线程阻塞/唤醒，如何保证线程安全，都由AQS为我们完成了，这也是非常典型的模板方法的应用。AQS定义好顶级逻辑的骨架，并提取出公用的线程入队列/出队列，阻塞/唤醒等一系列复杂逻辑的实现，将部分简单的可由使用者决定的操作逻辑延迟到子类中去实现。

package com.abstractqueuesynchronizer;

import java.util.concurrent.locks.AbstractQueuedSynchronizer;

public class SelfAbstractQueueSynchronizer {


    //继承AbstractQueuedSynchronizer类
    private static class Syn extends AbstractQueuedSynchronizer {
        
        private static final long serialVersionUID = 1L;

        //是否拥有锁
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }
        
        //获取锁
        public boolean tryAcquire(int acquires) {
            if(compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }
        
        //释放所
        protected boolean tryRelease(int releases) {
            if(getState() == 0) 
                throw new IllegalMonitorStateException();
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }
    }
    
    private final Syn syn = new Syn();
    
    public void lock() {
        syn.acquire(1);
    }
    
    public boolean tryLock() {
        return syn.tryAcquire(1);
    }
    
    public void unlock() {
        syn.release(1);
    }
    
    public boolean isLocked() {
        return syn.isHeldExclusively();
    }
}

测试

package com.abstractqueuesynchronizer;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class Main {

    private static CyclicBarrier barrier = new CyclicBarrier(31);
    private static int a = 0;
    private static SelfAbstractQueueSynchronizer test = new SelfAbstractQueueSynchronizer();
    
    public static void main(String[] args) throws InterruptedException, BrokenBarrierException {
        
        for(int i = 0; i < 30; i++) {
            Thread t = new Thread(new Runnable(){

                @Override
                public void run() {
                    for(int i = 0; i < 1000; i++) {
                        unlockIncrement();
                    }
                    try {
                        barrier.await();
                    } catch (Exception e) {
                        e.printStackTrace();;
                    }
                }

            });
            t.start();
        }
        
        barrier.await();
        System.out.println("unlock model a= " + a);
        
        System.out.println("##########################");
        
        barrier.reset();
        a = 0;
        for(int i = 0; i < 30; i++) {
            Thread t = new Thread(new Runnable(){
                @Override
                public void run() {
                    for(int i = 0; i < 1000; i++ ) {
                        lockIncrement();
                    }
                    
                    try {
                        barrier.await();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } catch (BrokenBarrierException e) {
                        e.printStackTrace();
                    }
                }
                
            });
            t.start();
        }
        
        barrier.await();
        System.out.println("lock model a= " + a);
        
    }
    
    public static void unlockIncrement() {
        a++;
    }
    
    public static void lockIncrement() {
        test.lock();
        a++;
        test.unlock();
    }
    
}