Thursday 12 May 2016

Why stop() method is deprecated and how to terminate thread?

Stopping a thread with Thread.stop causes it to release all of the monitors that it has locked. If any of the objects previously protected by these monitors were in an inconsistent state, the damaged objects become visible to other threads, which might lead to unpredictable behavior.

How to stop the thread, as stop() method is deprecated in java

1. Infinitely running thread can be stopped using boolean variable.

class MyRunnable implements Runnable {
      volatile boolean stopFlag=true;

      public void run() {
            int i = 0;
            String name = Thread.currentThread().getName();
            while (true) {
               if (stopFlag) {
                  try {
                        System.out.println(i++);
                        Thread.sleep(1000);
                        System.out.println("Please press enter key to stop "+name);
                  } catch (InterruptedException e) {
                        e.printStackTrace();
                  }
               } else{
                  System.out.println(name+" ended.");
                  break;
               }
            }
      }
}

public class StopThread {
      public static void main(String args[]) throws Exception {
            MyRunnable obj = new MyRunnable();
            Thread t = new Thread(obj,"Thread-1");
            t.start();
           
            String name  = Thread.currentThread().getName();
            System.out.println(name +" thread waiting to press enter");

            // Wait till read input
            System.in.read();

            // set stopFlag false
            obj.stopFlag = false;

            System.out.println(name+" thread ended");
      }
}

Output:
0
main thread waiting to press enter
Please press enter key to stop Thread-1
1
Please press enter key to stop Thread-1
2

main thread ended
Please press enter key to stop Thread-1
Thread-1 ended.

2. Infinitely running thread can be stopped using interrupt() method.

When thread is interrupted, if it in waiting state caused by invocation of wait(), sleep or join()  method then its interrupt status will be cleared and it will receive an InterruptedException.

class MyRunnable1 implements Runnable {
   public void run() {
       int i = 0;
       String name = Thread.currentThread().getName();
       try {
            while (!Thread.currentThread().isInterrupted()) {
                Thread.sleep(1000);
                System.out.println(i++ + " press enter key to stop "+ name);
            }
       } catch (InterruptedException e) {
            System.out.println(name + " ended.");
       }
   }
}

public class StopThreadUsingInterrupt {
      public static void main(String args[]) throws Exception {
            MyRunnable1 obj = new MyRunnable1();
           
           
            Thread t = new Thread(obj, "Thread#1");
            t.start();
           
            String name = Thread.currentThread().getName();
            System.out.println(name + " thread waiting to press enter");
           
            System.in.read();
            t.interrupt();
            System.out.println(name + " thread ended.");
      }
}

Output:
      main thread waiting to press enter
      0 press enter key to stop Thread#1
      1 press enter key to stop Thread#1
      2 press enter key to stop Thread#1
      3 press enter key to stop Thread#1
      4 press enter key to stop Thread#1

      main thread ended.
      Thread#1 ended.



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