Java 8 - juc - Semaphore

╰半夏微凉° 2023-10-11 22:43 2阅读 0赞

import java.util.concurrent.Semaphore;
    
    /**
     * Semaphore是一个同步工具类，用于控制同时访问某个资源的线程数量。
     * 它通过维护一定数量的许可证（permits）来实现并发控制。
     *
     * 当一个线程要访问资源时，首先需要从Semaphore获取许可证，如果有可用的许可证，则线程可以继续执行，许可证数量减少。
     * 如果没有可用的许可证，线程将被阻塞，直到有许可证可用。
     *
     * 当线程完成对资源的访问后，需要释放许可证，以便其他线程可以获取并访问资源。
     */
    public class SemaphoreExample {
        
        private static final int MAX_CONCURRENT_THREADS = 3;
        private static final Semaphore semaphore = new Semaphore(MAX_CONCURRENT_THREADS);
    
        public static void main(String[] args) {
        
            Thread[] threads = new Thread[5];
    
            for (int i = 0; i < threads.length; i++) {
        
                threads[i] = new Thread(new Worker("Thread " + (i + 1)));
                threads[i].start();
            }
    
            for (Thread thread : threads) {
        
                try {
        
                    thread.join();
                } catch (InterruptedException e) {
        
                    e.printStackTrace();
                }
            }
        }
    
        static class Worker implements Runnable {
        
            private final String name;
    
            public Worker(String name) {
        
                this.name = name;
            }
    
            @Override
            public void run() {
        
                try {
        
                    System.out.println(name + " is trying to acquire a permit.");
                    semaphore.acquire(); // 获取许可证
                    System.out.println(name + " has acquired a permit.");
    
                    // 模拟线程执行一些任务
                    Thread.sleep(2000);
    
                    System.out.println(name + " is releasing the permit.");
                    semaphore.release(); // 释放许可证
                    System.out.println(name + " has released the permit.");
                } catch (InterruptedException e) {
        
                    e.printStackTrace();
                }
            }
        }
    }