Semaphore(信号量),用于做限流处理,比如说同时只允许5五个人访问,超过五个人访问就需要等待,类似这样的需求,下面的案例可以看出执行是五个五个的执行,等上一个五个执行完了,才会执行下一个
import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Semaphore; public class UseSemaphore { public static void main(String[] args) { // 线程池 ExecutorService exec = Executors.newCachedThreadPool(); // 只能5个线程同时访问 final Semaphore semp = new Semaphore(5); // 模拟20个客户端访问 for (int index = 0; index < 20; index++) { final int NO = index; Runnable run = new Runnable() { public void run() { try { // 获取许可 semp.acquire(); System.out.println("Accessing: " + NO); //模拟实际业务逻辑 Thread.sleep((long) (Math.random() * 10000)); // 访问完后,释放 semp.release(); } catch (InterruptedException e) { } } }; exec.execute(run); } try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace(); } //System.out.println(semp.getQueueLength()); // 退出线程池 exec.shutdown(); } }