multi-thread（八）Semaphore

Semaphore.acquire()：Acquires a permit from this semaphore, blocking until one is available

与Executors.newFixedThreadPool( 2 )作用相似

CyclicBarrier.await(): Waits until all parties have invoked await on this barrier. 

CountDownLatch.await(): Causes the current thread to wait until the latch has counted down to zero

/**
 * @author timeriver.wang
 * @date 2014-03-10 2:02:52 PM
 */
public class SemaphoreTest {
    public static void main( String[] args ) {
        ExecutorService service = Executors.newCachedThreadPool();
        final Semaphore sp = new Semaphore( 3 );
        for ( int i = 0; i < 9; i++ ) {
            Runnable runnable = new Runnable() {
                public void run() {
                    try {
                        sp.acquire();
                    }
                    catch ( InterruptedException e1 ) {
                        e1.printStackTrace();
                    }
                    System.out.println( Thread.currentThread() + "进入，当前已有" + ( 3 - sp.availablePermits() ) + "个并发" );
                    try {
                        Thread.sleep( (long) ( Math.random() * 10000 ) );
                    }
                    catch ( InterruptedException e ) {
                        e.printStackTrace();
                    }
                    System.out.println( Thread.currentThread() + "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( Thread.currentThread() + "已离开，当前已有" + ( 3 - sp.availablePermits() ) + "个并发" );
                }
            };
            service.execute( runnable );
        }
    }

}