This is the fourth part of our advanced Java multi-threading tutorial. In this tutorial I show you how you can use multiple locks to speed up complex multi-threaded code, sometimes dramatically.

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Code For This Tutorial

App.java:

public class App {

	public static void main(String[] args) {
		Worker worker = new Worker();
		worker.main();

	}

}

Worker.java:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;


public class Worker {
	
	private Random random = new Random();
	
	private Object lock1 = new Object();
	private Object lock2 = new Object();
	
	private List<Integer> list1 = new ArrayList<Integer>();
	private List<Integer> list2 = new ArrayList<Integer>();
	
	public void stageOne() {
		
		synchronized (lock1) {
			try {
				Thread.sleep(1);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			list1.add(random.nextInt(100));
		}
	
	}
	
	public void stageTwo() {
		
		synchronized (lock2) {
			try {
				Thread.sleep(1);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			list2.add(random.nextInt(100));
		}
		
	}
	
	public void process() {
		for(int i=0; i<1000; i++) {
			stageOne();
			stageTwo();
		}
	}

	public void main() {
		System.out.println("Starting ...");
		
		long start = System.currentTimeMillis();
		
		Thread t1 = new Thread(new Runnable() {
			public void run() {
				process();
			}
		});
		
		Thread t2 = new Thread(new Runnable() {
			public void run() {
				process();
			}
		});
		
		t1.start();
		t2.start();
		
		try {
			t1.join();
			t2.join();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		long end = System.currentTimeMillis();
		
		System.out.println("Time taken: " + (end - start));
		System.out.println("List1: " + list1.size() + "; List2: " + list2.size());
	}
}

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