使用AQS自己实现一把锁

使用AQS自己实现一把锁

其实是想一把锁需要两点：  1. 锁状态( 0当前有线程在使用 1当前无线程在使用)   2.持有锁的线程（当前线程） 

总结：就是当前如果有线程通过竞争cas成功了，则将 【锁状态】设为1,将持有锁的线程记录起来。  这样就能防止其他线程再获取。

我们知道要是实现一个自定义的 Lock 实现类，首先要实现 Lock 接口，并且定义一个内部类继承 AQS 类，重写他的方法

package com.middle.aqsdemo;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * @author 15510
 * @create 2019-07-31 17:10
 */
public class SimplifyReentrantLock implements Lock {

    private final Sync sync = new Sync();

    /**
     * AQS的子类Sync
     */
    private static class Sync extends AbstractQueuedSynchronizer {

        @Override
        protected boolean isHeldExclusively() {
            //是否处于占用状态
            return getState() == 1;
        }

        @Override
        protected boolean tryAcquire(int arg) {
            //当状态为0是获取锁
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        @Override
        protected boolean tryRelease(int arg) {
            //释放锁，将状态设置为0
            if (getState() == 0) {
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }

        Condition newCondition() {
            return new ConditionObject();
        }

    }

    @Override
    public void lock() { sync.acquire(1); }

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

    @Override
    public Condition newCondition() { return sync.newCondition(); }

    @Override
    public boolean tryLock() { return sync.tryAcquire(1); }

    @Override
    public void lockInterruptibly() throws InterruptedException { }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return false;
    }
}

package com.middle.aqsdemo;

import java.util.concurrent.locks.Condition;

/**
 * @author 15510
 * @create 2019-07-31 17:12
 */
public class SimplifyReentrantLockDemo {

    public static void main(String[] args) {
        SimplifyReentrantLock lock = new SimplifyReentrantLock();
        Condition condition = lock.newCondition();

        new Thread(() -> {
            lock.lock();
            try {
                System.out.println("进入等待!");
                condition.await(); // 释放锁
                System.out.println("接收到通知！继续执行！");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.unlock();
        }, "conditionAwaitThread").start();

        new Thread(() -> {
            try {
                System.out.println("模拟3秒后发送通知过！");
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            lock.lock();
            System.out.println("发送通知！");
            condition.signal();
            lock.unlock();
        }, "conditionSignalThread").start();
    }
}

执行结果

进入等待!
模拟3秒后发送通知过！
发送通知！
接收到通知！继续执行！

Process finished with exit code 0