public CountDownLatch(int count)

// 使當(dāng)前線程在鎖存器倒計數(shù)至零之前一直等待，除非線程被中斷。
void await()
// 使當(dāng)前線程在鎖存器倒計數(shù)至零之前一直等待，除非線程被中斷或超出了指定的等待時間。
boolean await(long timeout, TimeUnit unit)
// 遞減鎖存器的計數(shù)，如果計數(shù)到達(dá)零，則釋放所有等待的線程。
void countDown()
// 返回當(dāng)前計數(shù)。
long getCount()

public class TestCountDownLatch {
  private static final int RUNNER_NUMBER = 5; // 運動員個數(shù)
  private static final Random RANDOM = new Random();
  public static void main(String[] args) {
    // 用于判斷發(fā)令之前運動員是否已經(jīng)完全進(jìn)入準(zhǔn)備狀態(tài)，需要等待5個運動員，所以參數(shù)為5
    CountDownLatch readyLatch = new CountDownLatch(RUNNER_NUMBER);
    // 用于判斷裁判是否已經(jīng)發(fā)令，只需要等待一個裁判，所以參數(shù)為1
    CountDownLatch startLatch = new CountDownLatch(1);
    for (int i = 0; i < RUNNER_NUMBER; i++) {
      Thread t = new Thread(new Runner((i + 1) + "號運動員", readyLatch, startLatch));
      t.start();
    }
    try {
      readyLatch.await();
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    startLatch.countDown();
    System.out.println("裁判：所有運動員準(zhǔn)備完畢，開始...");
  }
  static class Runner implements Runnable {
    private CountDownLatch readyLatch;
    private CountDownLatch startLatch;
    private String name;
    public Runner(String name, CountDownLatch readyLatch, CountDownLatch startLatch) {
      this.name = name;
      this.readyLatch = readyLatch;
      this.startLatch = startLatch;
    }
    public void run() {
      int readyTime = RANDOM.nextInt(1000);
      System.out.println(name + "：我需要" + readyTime + "秒時間準(zhǔn)備.");
      try {
        Thread.sleep(readyTime);
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println(name + "：我已經(jīng)準(zhǔn)備完畢.");
      readyLatch.countDown();
      try {
        startLatch.await(); // 等待裁判發(fā)開始命令
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println(name + "：開跑...");
    }
  }
}