Question

119             while(remainLength > 0){
120                if(remainLength >= MAX_LENGTH){
121                   log("WorkHandler::workLoop, remain %d > max %d \n", remainLength, MAX_LENGTH);
122                   currentSentLength = send(client->getFd(), sBuffer, MAX_LENGTH, MSG_NOSIGNAL);
123                   log("currentSentLength %d \n", currentSentLength);
124                }
125                else{
126                   log("WorkHandler::workLoop, remain %d < max %d \n", remainLength, MAX_LENGTH);
127                   currentSentLength = send(client->getFd(), sBuffer, remainLength, MSG_NOSIGNAL);
128                   log("currentSentLength %d \n", currentSentLength);
129                }
130
131
132                if(currentSentLength == -1){
133                   log("WorkHandler::workLoop, connection has been lost \n");
134                   break;
135                }
136                sBuffer += currentSentLength;
137                log("sBuffer %d\n", sBuffer);
138
139                remainLength -= currentSentLength;
140                log("remainLength %d \n", remainLength);
141
142             }

I have this code and the send function sometimes gets stuck. Some people points out that using non bloking I/O. I am using epoll so I think it is a little bit hard to change the whole design to non blocking mode. Is there any way to prevent blocking the send function?

Thanks in advance..

Answer 1

If you don’t want send to block, you’ll need non-blocking I/O. There’s no way around that.

You don’t have to put the socket in non-blocking mode though, the MSG_DONTWAIT flag can be used on a per-call basis. But you will need to deal with EAGAIN/EWOULDBLOCK error codes.

From the man page linked above:

The flags argument is the bitwise OR of zero or more of the following flags.

so you can combine that with MSG_NOSIGNAL.