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常用并发辅助类 CountDownLatch Semaphore CyclicBarrier, 都基于ReentrantLock实现。
1 Semaphores are often used to restrict the number of threads than can
* access some (physical or logical) resource. For example, here is
* a class that uses a semaphore to control access to a pool of items:
Semaphores 信号量， 相对常规同步块只能有一个线程对资源进行操作，Semaphores能允许多个线程同时操作资源。
public Semaphore(int permits) { //参数permits表示许可数目，即同时可以允许多少线程进行访问 sync = new NonfairSync(permits);}public Semaphore(int permits, boolean fair) { //这个多了一个参数fair表示是否是公平的，即等待时间越久的越先获取许可 sync = (fair)? new FairSync(permits) : new NonfairSync(permits);}public void acquire() throws InterruptedException { } //获取一个许可public void acquire(int permits) throws InterruptedException { } //获取permits个许可public void release() { } //释放一个许可public void release(int permits) { } //释放permits个许可public boolean tryAcquire() { }; //尝试获取一个许可，若获取成功，则立即返回true，若获取失败，则立即返回falsepublic boolean tryAcquire(long timeout, TimeUnit unit) throws InterruptedException { }; //尝试获取一个许可，若在指定的时间内获取成功，则立即返回true，否则则立即返回falsepublic boolean tryAcquire(int permits) { }; //尝试获取permits个许可，若获取成功，则立即返回true，若获取失败，则立即返回falsepublic boolean tryAcquire(int permits, long timeout, TimeUnit unit) throws InterruptedException { }; //尝试获取permits个许可，若在指定的时间内获取成功，则立即返回true，否则则立即返回falsepublic CountDownLatch(int count) { }; //参数count为计数值public void await() throws InterruptedException { }; //调用await()方法的线程会被挂起，它会等待直到count值为0才继续执行public boolean await(long timeout, TimeUnit unit) throws InterruptedException { }; //和await()类似，只不过等待一定的时间后count值还没变为0的话就会继续执行public void countDown() { }; //将count值减1public class Test { public static void main(String[] args) { final CountDownLatch latch = new CountDownLatch(2); new Thread(){ public void run() { try { System.out.println("子线程"+Thread.currentThread().getName()+"正在执行"); Thread.sleep(3000); System.out.println("子线程"+Thread.currentThread().getName()+"执行完毕"); latch.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } }; }.start(); new Thread(){ public void run() { try { System.out.println("子线程"+Thread.currentThread().getName()+"正在执行"); Thread.sleep(3000); System.out.println("子线程"+Thread.currentThread().getName()+"执行完毕"); latch.countDown(); } catch (InterruptedException e) { e.printStackTrace(); } }; }.start(); try { System.out.println("等待2个子线程执行完毕..."); latch.await(); System.out.println("2个子线程已经执行完毕"); System.out.println("继续执行主线程"); } catch (InterruptedException e) { e.printStackTrace(); } } }public CyclicBarrier(int parties, Runnable barrierAction) {//参数parties指让多少个线程或者任务等待至barrier状态；参数barrierAction为当这些线程都达到barrier状态时会执行的内容。}public CyclicBarrier(int parties) {}public int await() throws InterruptedException, BrokenBarrierException { };//用来挂起当前线程，直至所有线程都到达barrier状态再同时执行后续任务；public int await(long timeout, TimeUnit unit)throws InterruptedException,BrokenBarrierException,TimeoutException { };标签：
原文地址：http://www.cnblogs.com/xiongjianjunjava/p/4326071.html
