shutdownNow : Immediate shutdown

Attempts to stop all actively executing tasks, halts the processing of waiting tasks, and returns a list of the tasks that were awaiting execution.

class WorkerThread implements Runnable{
 String taskName;

 WorkerThread(String taskName){
  this.taskName = taskName;
 }

 public String toString(){
  return taskName;
 }

 public void run(){
  try{
   Thread t1 = Thread.currentThread();
   System.out.println(t1.getName() + " executing the task " + taskName);
   t1.sleep(1000);
   System.out.println(t1.getName() + " completed the task " + taskName);
  }
  catch(Exception e){
   System.out.println(e);
  }
 }
}

import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.*;

class SimpleThreadPool{
 public static void main(String args[])throws Exception{
  ExecutorService exec = new ThreadPoolExecutor(3, 3, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());

  WorkerThread tasks[] = new WorkerThread[10];
  for(int i=0; i<10; i++){
   tasks[i] = new WorkerThread("task" + i);
   exec.execute(tasks[i]);
  }

  List<Runnable> l1 = exec.shutdownNow();
  exec.awaitTermination(10, TimeUnit.SECONDS);
  System.out.println("Waiting Threads are ");
  Iterator i1 = l1.iterator();
  while(i1.hasNext()){
   System.out.println(i1.next());
  }
 }
}

Sample Output

pool-1-thread-2 executing the task task1
pool-1-thread-1 executing the task task0
pool-1-thread-3 executing the task task2
java.lang.InterruptedException: sleep interrupted
java.lang.InterruptedException: sleep interrupted
java.lang.InterruptedException: sleep interrupted
Waiting Threads are
task3
task4
task5
task6
task7
task8
task9

   

awaitTermination() Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.

Executor exec = new ThreadPoolExecutor(3, 3, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());

Above statement create a thread pool of size 3. So it can run 3 tasks at a time, Since 3 threads are reside in the pool.

exec.submit(tasks[i])

Submit the tasks to the thread pool. When the task is submitted, ThreadPool assigns a thread to execute the run method of the Runnable Object.

RejectedExecutionException                                                 Check whether threadpool shutdown or not                                                 Home