Semaphore 并发信号

package com.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

/**
 * 并发控制
 **/
public class SemaphoreTest {
    public static void main(String[] args) {
        test1();
    }

    private static void test1() {
        ExecutorService executorService = Executors.newFixedThreadPool(20);
        Semaphore semaphore = new Semaphore(3);//资源最多可被3个线程并发访问
        for (int i = 0; i < 20; i++) {
            executorService.execute(() -> {
                try {
                    boolean b = semaphore.tryAcquire(1, 300, TimeUnit.MILLISECONDS);//获取许可,300超时,返回false
                    System.out.println("SemaphoreTest.run " + Thread.currentThread().getName() + " b = " + b);
                    Thread.sleep(280);
                    semaphore.release(1);//释放许可
                } catch (Exception e) {
                    e.printStackTrace();
                }
            });
        }
        executorService.shutdown();//如果不shutdown工程不会结束
    }

}

可以控制并发的数量