執行緒 CountDownLatch 用法

說明

CountDownLatch 用法簡述：

• CountDownLatch，一個同步輔助類，在完成一組正在其他執行緒中執行的操作之前，它允許一個或多個執行緒一直等待
• **countDown方法，當前執行緒結束執行後呼叫，計數減一 **
• **awaint方法，呼叫此方法會一直阻塞當前執行緒，直到計時器的值為0 **

程式碼，例如：

public class CountDownLatchDemo {

	final static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"
 
);

	final static String startTime = sdf.format(new Date());

	public static void main(String[] args) throws InterruptedException {
		//併發： CountDownLatch 它允許一個或多個執行緒一直等待，直到其他執行緒的操作執行完後再執行
		CountDownLatch latch = new CountDownLatch(2);// 兩個賽跑者
		Runer runer1 = new Runer("劉翔", 2000, latch);
		Runer runer2 =
 
 new Runer("羅伯斯", 5000, latch);
		runer1.start();// 劉翔 開始跑步
		runer2.start();// 羅伯斯 開始跑步
		latch.await();// 等待所有人賽跑結束
		System.out.println("all runer done at " + sdf.format(new Date()));
	}

	static class Runer extends Thread {
		String runerName;
		int runTime;
		CountDownLatch latch;

		public Runer(String runerName,
 
 int runTime, CountDownLatch latch) {
			this.runerName = runerName;
			this.runTime = runTime;
			this.latch = latch;
		}

		public void run() {
			System.out.println("Runer " + runerName + " do run begin at " + startTime);
			doRun();// 跑步
			System.out.println("Runer " + runerName + " do run complete at " + sdf.format(new Date()));
			latch.countDown();// 終點結束，計數器減一

		}
		private void doRun() {
			try {
				Thread.sleep(runTime);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}