Semaphore 用法 在调用accquire之后到release之间，别的线程会阻塞，当然前提是信用量已经没有可用的了。

 1 package com.citi.test.mutiplethread.demo08;
 2 
 3 import java.util.concurrent.Executor;
 4 import java.util.concurrent.Semaphore;
 5 
 6 public class BoundedExecutor {
 7     private final Executor exec;
 8     private final Semaphore semaphore;
 9     public BoundedExecutor(Executor exec,int bound) {
10         this.exec=exec;
11         this.semaphore=new Semaphore(bound);
12     } 
13     public void submitTask(final Runnable runnable) throws InterruptedException{
14         //获取一个许可 在acquire之后如果信号量已经没有了，那么下个线程再进来会等待，直到有线程调用release方法
15         semaphore.acquire();
16         try {
17             exec.execute(new Runnable() {
18                 @Override
19                 public void run() {
20                     try {
21                         runnable.run();
22                     }finally{
23                         semaphore.release();
24                     }
25                 }
26             });
27         } catch (Exception e) {
28             semaphore.release();
29         }
30     }
31 }