Illustrates the absence of thread safety between various methods of SychronizedSet and its iteraror method.

synchronized_collection_issue.jsh

Collection<Integer> ss = Collections.synchronizedSet(new HashSet<Integer>());
new Thread() {
  public void run() {
    for (int x = 0; x < 1000; x++) {
      ss.addAll(IntStream.range(x*1000, (x + 1)*1000)
          .boxed()
          .collect(Collectors.toList()));
    }
  }
}.start()
for (int x = 0; x < 10; x++) {
  Collection<Integer> t = new HashSet<Integer>(ss);
  // Fix
  //Collections.addAll(new HashSet<Integer>(), ss.toArray(new Integer[0]));
}