/** * TestHarness * 
 * Using CountDownLatch for starting and stopping threads in timing tests * * @author Brian Goetz and Tim Peierls */public class TestHarness {    public long timeTasks(int nThreads, final Runnable task)            throws InterruptedException {        final CountDownLatch startGate = new CountDownLatch(1);        final CountDownLatch endGate = new CountDownLatch(nThreads);        for (int i = 0; i < nThreads; i++) {            Thread t = new Thread() {                public void run() {                    try {                        startGate.await();                        try {                            task.run();                        } finally {                            endGate.countDown();                        }                    } catch (InterruptedException ignored) {                    }                }            };            t.start();        }        long start = System.nanoTime();        startGate.countDown();        endGate.await();        long end = System.nanoTime();        return end - start;    }}

startGate.countDown() ，准备工作完成后，使所有工作线程开始工作；

endGate.await() 使所有工作线程都执行完后，执行下面的代码。