code: void removeActorImmediate(Actor act) {
          if ( Thread.currentThread() != this )
              throw new RuntimeException("wrong thread");
          Actor newAct[] = new Actor[actors.length-1];
          int idx = 0;
          for (int i = 0; i < actors.length; i++) {
              Actor actor = actors[i];
              if ( actor != act)
                  newAct[idx++] = actor;
          }
          if ( idx != newAct.length )
              throw new RuntimeException("could not remove actor");
          actors = newAct;
      }
docs: removes immediate must be called from this thread