public bool Equals(ResponseKey other)
 {
     return ID == other.ID
         && Sequence == other.Sequence;
 }
 internal ResponseTracking Get(Guid id, int sequence)
 {
     ResponseKey k = new ResponseKey(id, sequence);
     ResponseTracking t;
     _lock.EnterWriteLock();
     try
     {
         _items.TryGetValue(k, out t);
     }
     finally
     {
         _lock.ExitWriteLock();
     }
     return t;
 }