Listens to the result of a ChannelFuture. The result of the asynchronous Channel I/O operation is notified once this listener is added by calling ChannelFuture#addListener(GenericFutureListener).

Return the control to the caller quickly

operationComplete(Future) is directly called by an I/O thread. Therefore, performing a time consuming task or a blocking operation in the handler method can cause an unexpected pause during I/O. If you need to perform a blocking operation on I/O completion, try to execute the operation in a different thread using a thread pool.