多線程之CountDownLatch
阿新 • • 發佈：2018-03-24
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下面請看一個應用場景：
有1個driver和5個worker，需要滿足以下兩點要求：
當driver完成了全部的工作之後才允許worker們開始工作；
當所有的worker都完成了自己的工作之後，driver主線程才能結束。
public class Driver {
public static void main(String[] args) throws InterruptedException {
CountDownLatch startSignal = new CountDownLatch(1);
CountDownLatch doneSignal = new CountDownLatch(5);
// 依次創建並啟動5個worker線程
for (int i = 0; i < 5; ++i) {
new Thread(new Worker(startSignal, doneSignal)).start();
}
System.out.println("Driver is doing something...");
System.out.println("Driver is Finished, start all workers ...");
startSignal.countDown(); // Driver執行完畢，發出開始信號，使所有的worker線程開始執行
doneSignal.await(); // 等待所有的worker線程執行結束
System.out.println("Finished.");
}
}
class Worker implements Runnable{
private final CountDownLatch startSignal;
private final CountDownLatch doneSignal;
Worker(CountDownLatch startSignal, CountDownLatch doneSignal) {
this.startSignal = startSignal;
this.doneSignal = doneSignal;
}
public void run() {
try {
startSignal.await(); // 等待Driver線程執行完畢，獲得開始信號
System.out.println("Working now ...");
doneSignal.countDown(); // 當前worker執行完畢，釋放一個完成信號
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
運行結果：
Driver is doing something...
Driver is Finished, start all workers ...
Working now ...
Working now ...
Working now ...
Working now ...
Working now ...
Finished.
此處修改CountDownLatch個數為一個代碼如下：public class Driver {
public static void main(String[] args) throws Exception {
CountDownLatch latch = new CountDownLatch(5);
for (int i = 0; i < 5; ++i) {
new Thread(new Worker( latch),"t"+i).start();
}
latch.await();
System.out.println("結束");
}
static class Worker implements Runnable {
private final CountDownLatch latch1;
public Worker(CountDownLatch latch1) {
this.latch1=latch1;
}
public void run() {
System.out.println(Thread.currentThread().getName()+"開始幹活 work"+"id是"+Thread.currentThread().getId()+" ");
latch1.countDown();
}
}
}
結果為：
t4開始幹活 workid是14
t1開始幹活 workid是11
t2開始幹活 workid是12
t3開始幹活 workid是13
t0開始幹活 workid是10
結束
多線程之CountDownLatch