基于AQS实现的简单的Semaphore

最新推荐文章于 2025-01-12 02:15:00 发布

张申傲

最新推荐文章于 2025-01-12 02:15:00 发布

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分类专栏： Java并发编程

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本文深入探讨了自定义Semaphore的实现细节，通过继承AQS(AbstractQueuedSynchronizer)并采用共享模式来控制资源访问。文章详细解释了Semaphore的构造、资源获取与释放的过程，以及如何确保线程安全。

/**
 * @Auther: ZhangShenao
 * @Date: 2019/3/3 11:15
 * @Description:自定义Semaphore,内部通过Sync同步器继承了AQS,采用共享的方式获取资源
 */
public class SimpleSemaphore {
    private Sync sync;

    public SimpleSemaphore(int permits){
        sync = new Sync(permits);
    }


    public void acquire(){
        sync.acquireShared(1);
    }

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

    static class Sync extends AbstractQueuedSynchronizer {
        public Sync(int permits) {
            if (permits <= 0) {
                throw new IllegalArgumentException("Permits must be positive!!");
            }
            setState(permits);
        }

        @Override
        protected int tryAcquireShared(int reduce) {
            for (; ; ) {
                int current = getState();
                int remains = current - reduce;
                if (remains < 0 || compareAndSetState(current, remains)) {
                    return remains;
                }
            }
        }

        @Override
        protected boolean tryReleaseShared(int released) {
            for (; ; ) {
                int current = getState();
                int updated = current + released;
                if (updated < current){
                    throw new RuntimeException("Maximum permit count exceeded!!");
                }
                if (compareAndSetState(current, updated)) {
                    return true;
                }
            }
        }


    }
}