void shutDownOperationControllers() {
    if (isOpen.compareAndSet(true, false)) {
      logger.info("Closing the router");
      for (OperationController oc : ocList) {
        oc.shutdown();
      }
    }
  }
Initiate the shutdown of all the OperationControllers. This method can get executed in the context of
both the calling thread of the {@link #close()} method, and the RequestResponseHandler thread of any of the
Operation Controllers.
ambry-router/src/main/java/com/github/ambry/router/NonBlockingRouter.java