To Pool or not to Pool java crypto service providers

Question

Solution

• MessageDigest => create new instances as often as needed
• KeyFactory => use a single shared instance
• SecureRandom => use a StackObject

Answer 1

If you give 100 threads access to a shared MessageDigest and get them to calculate 1,000,000 hashes each then on my machine the first thread finishes in 70,160ms and the last finishes in 98,748ms.

If the threads create a new instance of MessageDigest each time, then the first thread finishes in 43,392ms and the last 58,691ms.

Edit:
In fact with this example, with only two threads the example creating new instances runs quicker.

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Share {

  final byte[] bytes = new byte[100];
  final MessageDigest sharedDigest;
  final ExecutorService pool;
  int threads = 100;

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

  void go() {

    for (int i=0; i