public synchronized Map<Throwable, Integer> getExceptions() {
   if (_exceptions == null) {
     return Collections.emptyMap();
   }
   final Map<Throwable, Integer> result = new HashMap<Throwable, Integer>();
   for (final ExceptionWrapper exception : _exceptions.keySet()) {
     result.put(exception.getException(), exception.getCount());
   }
   return result;
 }