public void done(T result, Exception error) {
    this.error = error;
    this.result = result;
    this.latch.countDown();
  }
Mark this request as complete and unblock any threads waiting on its completion.
@param result The result for this request
@param error The error that occurred if there was one, or null.
ambry-api/src/main/java/com/github/ambry/router/FutureResult.java