code: @Override
      public boolean cancel(boolean ignored) {
          boolean cancelled = false;
          if (latch.getCount() == 1) {
              latch.countDown();
              output = null;
              cancelled = true;
          }
          return cancelled;
      }
docs: Cancel the command and notify any waiting consumers. This does
  not cause the redis server to stop executing the command.
  
  @param ignored Ignored parameter.
  
  @return true if the command was cancelled.