pooling test using a single synchronized instance. based on http://stackoverflow.com/a/13914445/233906

gistfile1.java

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

public class Share {

    private static final int NB_LOOPS = 100000;
    final static int NB_THREADS = 100;
    final byte[] bytes = new byte[100];
    final ExecutorService pool;
    static MessageDigest digest;
    static final AtomicLong grandTotal = new AtomicLong(0);

    Share() throws NoSuchAlgorithmException {
        digest = MessageDigest.getInstance("MD5");
	pool = Executors.newFixedThreadPool(NB_THREADS);
    }

    void go() {

	for (int i = 0; i < NB_THREADS; i++) {
	    pool.execute(new Runnable() {
		public void run() {
		    long start = System.currentTimeMillis();
		    for (int i = 0; i < NB_LOOPS; i++) {
			try {
			    synchronized (digest) {
				digest.update(bytes);
				digest.digest();
			    }
			} catch (Exception ex) {
			    ex.printStackTrace();
			}
			Thread.yield();
		    }// fin for
		    long end = System.currentTimeMillis();
		    System.out.println(end - start);
		    grandTotal.addAndGet(end - start);
		    pool.shutdown();
		}
	    });
	}

    }

    public static void main(String[] args) throws Exception {
	Share share = new Share();
	share.go();
	share.pool.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS);
	System.out.println(grandTotal.get() + " ms");
	System.out.println(TimeUnit.MILLISECONDS.toSeconds(grandTotal.get())
		+ " s");
    }

}