mutex.java

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

class Mutex implements Lock {
    // 静态内部类，自定义同步器
    private static class Sync extends AbstractQueuedSynchronizer {

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

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

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

        // 返回一个condition,每个condition都包含一个condition队列
        Condition newCondition() {
            return new ConditionObject();
        }
    }

    // 仅需将操作代理到Sync上面即可
    private final Sync sync = new Sync();
    public void lock() {
        sync.acquire(1);
    }

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

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

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

    public boolean isLocked() {
        return sync.isHeldExclusively();
    }

    public boolean hasQueuedThreads() {
        return sync.hasQueuedThreads();
    }

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

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