使用Lock来实现信号量Semaphore

最新推荐文章于 2025-07-20 08:53:16 发布

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最新推荐文章于 2025-07-20 08:53:16 发布

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分类专栏：并发编程 Java 编程 Java并发实战-学习笔记

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本文介绍了一种基于ReentrantLock实现的自定义信号量SemaphoreOnLock。该信号量使用条件变量来控制对有限资源的访问，确保了多线程环境下资源使用的互斥性和公平性。

@ThreadSafe
public class SemaphoreOnLock {
    private final Lock lock = new ReentrantLock();
    // CONDITION PREDICATE: permitsAvailable (permits > 0)
    private final Condition permitsAvailable = lock.newCondition();
    @GuardedBy("lock") private int permits;

    SemaphoreOnLock(int initialPermits) {
        lock.lock();
        try {
            permits = initialPermits;
        } finally {
            lock.unlock();
        }
    }

    // BLOCKS-UNTIL: permitsAvailable
    public void acquire() throws InterruptedException {
        lock.lock();
        try {
            while (permits <= 0)
                permitsAvailable.await();
            --permits;
        } finally {
            lock.unlock();
        }
    }

    public void release() {
        lock.lock();
        try {
            ++permits;
            permitsAvailable.signal();
        } finally {
            lock.unlock();
        }
    }
}