@Override
  public void window(MessageCollector collector, TaskCoordinator coordinator) throws Exception {
    if (wrappedTask instanceof WindowableTask) {
      ((WindowableTask) wrappedTask).window(collector, coordinator);
    }
  }
AsyncStreamTaskAdapter allows a StreamTask to be executed in parallel.The class
uses the build-in thread pool to invoke StreamTask.process and triggers
the callbacks once it's done. If the thread pool is null, it follows the legacy
synchronous model to execute the tasks on the run loop thread.
samza-core/src/main/java/org/apache/samza/task/AsyncStreamTaskAdapter.java