invokeAll: Batch Execution

invokeAll provides a way to submit all the callable tasks to the Thread Pool at a time.

<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) throws InterruptedException
Executes the given tasks, returning a list of Futures holding their status and results when all complete. Future.isDone() is true for each element of the returned list.

import java.util.concurrent.*;
import java.util.*;

public class CallableTask<String> implements Callable<String>{
 String name;

 CallableTask(String name){
  this.name = name;
 }

 public String call(){
  try{
   Thread.sleep(1000);
   System.out.println(name +" Finishes Execution");
  }
  catch(Exception e){
   System.out.println("Task Interrupted " + e);
  }
  return (String)(new Date() + " :: " + name);
 }
}

import java.util.concurrent.*;
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>());

  List<CallableTask<String>> l1 = new ArrayList<> ();
  List<Future<String>> f1;

  /* Create 5 Callable Tasks */
  CallableTask<String> task1 = new CallableTask<> ("Task1");
  CallableTask<String> task2 = new CallableTask<> ("Task2");
  CallableTask<String> task3 = new CallableTask<> ("Task3");
  CallableTask<String> task4 = new CallableTask<> ("Task4");
  CallableTask<String> task5 = new CallableTask<> ("Task5");

  /* Adding the tasks to the list of type Callable */
  l1.add(task1);
  l1.add(task2);
  l1.add(task3);
  l1.add(task4);
  l1.add(task5);

  /*Submitting all the tasks in the list l1 to the Thread pool */
  f1 = exec.invokeAll(l1);
  exec.shutdown();
  exec.awaitTermination(3, TimeUnit.SECONDS);

  /* Priniting the resultes returned by the tasks */
  for(Future obj : f1)
   System.out.println(obj.get());
 }
}

Output

Task2 Finishes Execution
Task1 Finishes Execution
Task3 Finishes Execution
Task5 Finishes Execution
Task4 Finishes Execution
Sun Mar 09 13:35:20 IST 2014 :: Task1
Sun Mar 09 13:35:20 IST 2014 :: Task2
Sun Mar 09 13:35:20 IST 2014 :: Task3
Sun Mar 09 13:35:21 IST 2014 :: Task4
Sun Mar 09 13:35:21 IST 2014 :: Task5

   

ExecutorService 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(task1, "Task1 Execution Finished");
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. Once the task is finished the result 'Task1 Execution Finished' is returned to the Future Object.

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