AtomicVsSynchonise.java

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;

public class AtomicVsSynchronize {
	static final Object LOCK1 = new Object();
	static final Object LOCK2 = new Object();
	static int i1 = 0;
	static int i2 = 0;
	static final AtomicInteger ai1 = new AtomicInteger();
	static final AtomicInteger ai2 = new AtomicInteger();

	public static void main(String... args) throws ExecutionException, InterruptedException {
		for (int i = 0; i < 5; i++) {
			testSyncInt();
			testAtomicInt();
		}
	}

	private static void testSyncInt() throws ExecutionException, InterruptedException {

		final int runs = 999999;
		ExecutorService es = Executors.newFixedThreadPool(4);
		long start = System.nanoTime();
		List<Future<Void>> futures = new ArrayList<>();
		for (int t = 0; t < 8; t++) {
			futures.add(es.submit(new Callable<Void>() {
				public Void call() throws Exception {
					for (int i = 0; i < runs; i += 2) {
						synchronized (LOCK1) {
							i1++;
						}
						synchronized (LOCK2) {
							i2++;
						}
					}
					return null;
				}
			}));
		}
		for (Future<Void> future : futures) {
			future.get();
		}
		es.shutdown();
		long time = System.nanoTime() - start;
		System.out.printf("sync + incr: Each increment took an average of %.1f ns%n", (double) time / runs / 2);
	}

	private static void testAtomicInt() throws ExecutionException, InterruptedException {
		final int runs = 999999;
		ExecutorService es = Executors.newFixedThreadPool(4);
		long start = System.nanoTime();
		List<Future<Void>> futures = new ArrayList<>();
		for (int t = 0; t < 8; t++) {
			futures.add(es.submit(new Callable<Void>() {
				public Void call() throws Exception {
					for (int i = 0; i < runs; i += 2) {
						ai1.incrementAndGet();
						ai2.incrementAndGet();
					}
					return null;
				}
			}));
		}
		for (Future<Void> future : futures) {
			future.get();
		}
		es.shutdown();
		long time = System.nanoTime() - start;
		System.out.printf("incrementAndGet: Each increment took an average of %.1f ns%n", (double) time / runs / 2);
	}
}