Control the startup sequence of two threads.

Control the startup sequence of two threads.

In the interview, I encountered the following question: How can I control thread B to start after thread A starts for 3 seconds or after thread A finishes running?

The question shows that thread B's start time must meet two conditions:

1. 3 seconds after thread A starts

2. After thread A finishes running

That is to say, as long as one of the above two conditions is met, thread B will start.

Use CountDownLatch to control the call sequence. The Code is as follows:

 1 public class RunA implements Runnable { 2     private CountDownLatch cdl; 3     public RunA(CountDownLatch cdl){ 4         this.cdl = cdl; 5     } 6     @Override 7     public void run() { 8         // TODO Auto-generated method stub 9         try {10             Thread.sleep(1000);11             cdl.countDown();12             System.out.println("A run over");13         } catch (InterruptedException e) {14             // TODO Auto-generated catch block15             e.printStackTrace();16         }17     }18 }

 

 1 public class RunB implements Runnable { 2     private CountDownLatch cdl; 3     public RunB(CountDownLatch cdl){ 4         this.cdl = cdl; 5     } 6     @Override 7     public void run() { 8         // TODO Auto-generated method stub 9         try {10             cdl.await(3000, TimeUnit.MILLISECONDS);11             System.out.println("B run over");12         } catch (InterruptedException e) {13             // TODO Auto-generated catch block14             e.printStackTrace();15         }16     }17 }

 

1 public class Test {2     public static void main(String[] args) {3         CountDownLatch cdl = new CountDownLatch(1);4         Thread ta = new Thread(new RunA(cdl));5         Thread tb = new Thread(new RunB(cdl));6         ta.start();7         tb.start();8     }9 }