Java ExecutorService

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Today we are going to describe briefly Java ExecutorService mechanism. Some time ago we have shown you how you can easily speed up your programs execution using threads in Java – How to speed up applications using threads in java. Back then we have discussed the barrier concept – a place in your code where main thread waits for other threads that are running. Back then we had to use our custom Lock object to synchronize program execution.
Java 6 introduced the ExecutorService mechanism using which synchronizing your program execution is much more easier. Take a look at the example code.

package com.itcuties.java.threads;

import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * ExecutorService example. 
 * Waiting for threads to finish their work.
 * 
 * @author itcuties
 *
 */
public class ExecutorServiceExample {

	// Run threads
	public static void main(String[] args)  {
		System.out.println("["+System.currentTimeMillis()+"]["+Thread.currentThread().getName()+"]:: starting");
		
		// Executor service that can execute up to 5 threads
		ExecutorService executor = Executors.newFixedThreadPool(5);
		
		for (int i=0; i < 10; i++) {
			Runnable thread = new Runnable() {
				// Sample thread - prints out random numbers
				public void run() {
					Random random = new Random();
					for (int i=0; i < 10; i++) {
						System.out.println("["+System.currentTimeMillis()+"]["+Thread.currentThread().getName()+"]:: lucky numer is " + random.nextInt(10000));
					}
				}};
				
			
			executor.execute(thread);
			
		}
		
		// Accept no more new threads
		executor.shutdown();
		
		// Waiting for all the threads to finish
		while(!executor.isTerminated()) {
			try {
				Thread.sleep(100);
				
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		
		System.out.println("["+System.currentTimeMillis()+"]["+Thread.currentThread().getName()+"]:: done");
		
	}
	
}

Then you run this code you will get the following output:

[1356644101826][main]:: starting
[1356644101856][pool-1-thread-3]:: lucky numer is 1382
[1356644101856][pool-1-thread-2]:: lucky numer is 2354
[1356644101856][pool-1-thread-1]:: lucky numer is 3254
[1356644101856][pool-1-thread-4]:: lucky numer is 8874
[1356644101856][pool-1-thread-1]:: lucky numer is 5498
...
[1356644101856][pool-1-thread-5]:: lucky numer is 423
[1356644101856][pool-1-thread-5]:: lucky numer is 5269
[1356644101856][pool-1-thread-5]:: lucky numer is 6121
[1356644101856][pool-1-thread-5]:: lucky numer is 3681
[1356644101856][pool-1-thread-5]:: lucky numer is 7692
[1356644101856][pool-1-thread-5]:: lucky numer is 8842
[1356644101956][main]:: done

As you can see it takes only like 4 lines of code implement barrier concept in your code.

// 1. Executor service that can execute up to 5 threads
ExecutorService executor = Executors.newFixedThreadPool(5);
...
// 2. Execute a thread in the Executor
executor.execute(thread);
…
// 3. Shutdown the executor - it will take no new threads for execution
executor.shutdown();

// 4. Wait for the Executor to process all the threads
while(!executor.isTerminated()) {...}

Download this sample code here.

This code is available on our GitHub repository as well.