Java ThreadPoolExecutor shutdownNow() Method

The shutdownNow () method of ThreadPoolExecutor class attempts to stop all the tasks which are executing actively, halts the processing of waiting tasks and returns a list of the tasks that were awaiting execution.

Syntax

Parameters

maximumPoolSize - the new maximum

Return

list of tasks that never commenced execution

Throw

SecurityException

Example 1

import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.lang.Thread;
public class ThreadPoolExecutorisShutdownNowExample1   {
              public static void main(final String[] arguments) throws InterruptedException {
                     ThreadPoolExecutor executor = (ThreadPoolExecutor)Executors.newCachedThreadPool();
                     executor.submit(new Task());
                     System.out.println(" Is Executor is shutdown :"+ executor.isShutdown());
                     executor.submit(new Task());
                     executor.shutdownNow();
                     System.out.println("get Task count after:"+ executor.getTaskCount());
                     System.out.println(" Is Executor is shutdown :"+ executor.isShutdown());
                 }  
      static class Task implements Runnable {
      @Override
              public void run() {
                     try {
                            Long duration = (long) (Math.random() * 5);
                            System.out.println("Running Thread Name: " + Thread.currentThread().getName());
                            TimeUnit.SECONDS.sleep(duration);
                            System.out.println("Completed Thread Name: " +Thread.currentThread().getName());
                       } catch (InterruptedException e) {   }
                    }
              }
}

Test it Now

Output:

Is Executor is shutdown :false
get Task count after:2
 Is Executor is shutdown :true
Running Thread Name: pool-1-thread-1
Running Thread Name: pool-1-thread-2

Example 2

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadPoolExecutor;
import java.lang.Thread;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ThreadPoolExecutorisShutdownNowExample2 {
          public static void main(String[] args) {
                 Work0 task1 = new Work0("t1");
                 System.out.println("Starting threads");
                 ThreadPoolExecutor tExecutor = (ThreadPoolExecutor) Executors.newCachedThreadPool();
                 System.out.println("  Maximum pool size: "+ tExecutor.getMaximumPoolSize());
                 System.out.println("get Task count before:"+ tExecutor.getTaskCount());
                 tExecutor.submit(task1); 
                 tExecutor.execute(task1); // start task1
                 tExecutor.shutdownNow(); // shutdown worker threads
                 System.out.println(" Is Executor is shutdown :"+ tExecutor.isShutdown());
                 System.out.println("Threads started, main ends\n");
          }
}
     class Work0 implements Runnable {
                  private final String threadName;
              public Work0(String threadName) {
                          this.threadName = threadName;
                    }
    @Override
  public void run() {
      for(int i=4 ; i<=9;i++)
      {
          if(i==5)
          {
              System.out.println("i=" +i);
              }
          }
      }
}

Test it Now

Output:

Starting threads
  Maximum pool size: 2147483647
get Task count before:0
i=5
 Is Executor is shutdown :true
Threads started, main ends

i=5

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