import java.util.ArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
*Java 5.0里新增加了4个协调线程间进程的同步装置,它们分别是:Semaphore,CountDownLatch,CyclicBarrier和Exchanger
*Semaphore可以控制运行线程的个数
*Semaphore是一个用来管理资源池的工具,可以看成是个通行证,线程要想从资源池拿到资源必须先拿到通行证,如果线程暂时拿不到通告证,线程就会被阻断,进入等待状态.
*/
/**
*使用Semaphore的关键技术点如下:
*1.在构造Semaphore对象时,必须提供通行证的数目,如"newSemaphore(3)"将创建一个具有3个通行证的Semaphore对象,一旦该对象被创建,其通行证数量是不能改变的.
*2.Semaphore的acquire方法取得一个通行证,如果通行证已经发完了,当前线程将进入等待状态,直到有其他线程释放了通行证.
*3.Semaphore的release方法释放了资源池.
*/
public class SemaphoreTest {
/**
* 模拟资源池的类
* 只为池发放2个通行证,即同时只允许2个线程获得池中的资源
*/
public static class Pool{
ArrayList<String> pool = null; //保存资源池中的资源
Semaphore pass = null; //通行证
Lock lock = new ReentrantLock();
public Pool(int size){
//初始化资源池
pool = new ArrayList<String>();
for(int i = 0; i < size; i++){
pool.add("Resource " + i);
}
//发送2个通行证
pass = new Semaphore(2);
}
public String get()throws InterruptedException{
//获取通行证,只有得到通行证后才能得到资源
System.out.println("Try to get a pass...");
pass.acquire();
System.out.println("Got a pass");
return getResource();
}
private String getResource(){
lock.lock();
String result = pool.remove(0);
System.out.println("资源 " + result + "被取走");
lock.unlock();
return result;
}
public void put(String resource){
//归还通行证,并那还资源
System.out.println("Released a pass");
pass.release();
releaseResource(resource);
}
private void releaseResource(String resource){
lock.lock();
System.out.println("资源 " + resource + " 被归还");
pool.add(resource);
lock.unlock();
}
}
public static void testPool(){
//准备10个资源的资源池
final Pool aPool = new Pool(10);
Runnable worker = new Runnable(){
@Override
public void run() {
String resource = null;
try{
resource = aPool.get();//取得resource
//用resource做工作
System.out.println("I finished on " + resource);
Thread.sleep(500);
System.out.println("I finished on " + resource);
}catch(InterruptedException ex){
}
aPool.put(resource);
}
};
//启动5个任务
ExecutorService service = Executors.newCachedThreadPool();
for(int i = 0; i<5; i++){
service.submit(worker);
}
service.shutdown();
}
public static void main(String... args){
SemaphoreTest.testPool();
}
}
本文转自远哥博客园博客，原文链接：http://www.cnblogs.com/taven/archive/2011/12/17/2291474.html，如需转载请自行联系原作者
