JDK5.0新特性系列---11.5.1线程 同步装置之Semaphore
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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(); }}