Control can have several threads concurrently semaphore

import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Semaphore;public class SemaphoreTest { public static void main(String[] args) { ExecutorService service = Executors.newCachedThreadPool(); final Semaphore sp = new Semaphore(5); for(int i=0;i<10;i++){ Runnable runnable = new Runnable(){ public void run(){ try { sp.acquire(); } catch (InterruptedException e1) { e1.printStackTrace(); } System.out.println("线程" + Thread.currentThread().getName() + "进入，当前已有" + (5-sp.availablePermits()) + "个并发"); try { Thread.sleep((long)(Math.random()*10000)); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("线程" + Thread.currentThread().getName() + "即将离开"); sp.release(); //下面代码有时候执行不准确，因为其没有和上面的代码合成原子单元 System.out.println("线程" + Thread.currentThread().getName() + "已离开，当前已有" + (3-sp.availablePermits()) + "个并发"); } }; service.execute(runnable); } }}

Control can have several threads concurrently semaphore