利用同步器实现互斥锁

package test;

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

/**
 * 互斥锁
 * 
 */
public class Mutex implements Lock {

    /**
     * 自定义同步器，通过继承AbstractQueuedSynchronizer来管理同步状态
     * 同步器是实现锁的关键，在锁的实现中聚合同步器，利用同步器实现锁的语义 锁是面向使用者的，定义了使用者与锁交互的接口，隐藏了实现细节
     * 同步器是面向锁的实现者，它简化了锁的实现方式，屏蔽了同步状态管理、线程的排队、等待与唤醒等底层操作 锁和同步器很好地隔离了使用者与实现者所需要关注的领域
     * 
     */

    private static class Sync extends AbstractQueuedSynchronizer {

        private static final long serialVersionUID = 1L;

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

        // 当状态为零的时候获取锁
        @Override
        public boolean tryAcquire(int acquire) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

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

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

    // 仅需要将操作代理到sync上即可
    private final Sync sync = new Sync();

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

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

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

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

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

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

}