Deadlock using CountDownLatch

Deadlock using CountDownLatch

Here CountDownLatch initialized as 10; and there are 4 threads which are used to reduce the count of CountDownLatch, and await () method will wait infinite to get 0 as CountDownLatch value.

Line below the await() method will wait infinitely to decrease the countdown value.

package com.threads;

import java.util.concurrent.CountDownLatch;

public class TestCountDownLatch extends Thread {

       public static void main(String[] args) throws InterruptedException {

              performParallelTask();

       }

      

       public static void performParallelTask() throws InterruptedException {

              CountDownLatch cdl = new CountDownLatch(10);

              for (int i = 0; i < 4; i++) {

                     Thread t = new StopLatchedThread(cdl,i);

                     t.start();

              }

              cdl.await();

             

              // this statement will not execute because cdl.await() method will wait

              // till 0 value of CountDownLatch cdl.

              System.out.println("after await method");

       }

}

package com.threads;

import java.util.concurrent.CountDownLatch;

public class StopLatchedThread extends Thread {

       private final CountDownLatch stopLatch;

       private int threadNo;

       public StopLatchedThread(CountDownLatch stopLatch, int i) {

              this.stopLatch = stopLatch;

              this.threadNo = i;

       }

      

       public void run() {

              try {

                     System.out.println("inside the run method of "+threadNo+ " thread");

              } finally {

                     System.out.println("count down by "+threadNo+ " thread");

                     stopLatch.countDown();

              }

       }

}

Output :

inside the run method of 0 thread

count down by 0 thread

inside the run method of 3 thread

count down by 3 thread

inside the run method of 2 thread

count down by 2 thread

inside the run method of 1 thread

count down by 1 thread