public class TestJPPFUuid {
  @Test(timeout=5000)
  public void testUuidCollisions() throws Exception {
    int nbThreads = Runtime.getRuntime().availableProcessors();
    if (nbThreads < 2) nbThreads = 2;
    int nbTasks = 1000;
    ThreadPoolExecutor executor = null;
    try {
      executor = new ThreadPoolExecutor(nbThreads, nbThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>());
      executor.prestartAllCoreThreads();
      for (int i=0; i<10; i++) performExecution(nbTasks, executor);
    } finally {
      if (executor != null) executor.shutdownNow();
    }
  }
 
  public void performExecution(final int nbTasks, final ExecutorService executor) throws Exception {
    List<Future<String>> futures = new ArrayList<Future<String>>(nbTasks);
    Map<String, Boolean> map = new ConcurrentHashMap<String, Boolean>(nbTasks);
    for (int i=0; i<nbTasks; i++) futures.add(executor.submit(new UuidTask()));
    int count = 0;
    for (Future<String> future: futures) {
      String uuid = future.get();
      Boolean prevValue = map.put(uuid, Boolean.TRUE);
      if (prevValue != null) {
        System.out.println("uuid collision for " + uuid);
        count++;
      }
    }
    assertEquals("found " + count  + " collisions", 0, count);
  }
 
  private static class UuidTask implements Callable<String> {
    @Override
    public String call() throws Exception {
      return JPPFUuid.normalUUID();
    }
  }
}