I am creating a TCP service that forks a new process each time a client connects. Before the fork I set up a pipe so the child can send statistics gathered during the connection back to the parent. The parent closes the writing end and the child closes the reading end, and the parent maintains an array of reading-end file descriptors, one per child.
I am not sure what to do with these file descriptors when the child finishes with the connection and exits. Does the child need to notify the parent via the pipe that it is about to exit so the parent can close the pipe? Or can the parent detect the broken pipe automatically after the child exits and close it?
The code in the parent program is running a loop with select() detecting activity on the listening socket and on the read ends of the children's pipes. Each child may send multiple messages to the parent as it runs.
In general, what should the parent process do with a pipe file descriptor when a child exits?
In your case, the parent process shall close writing end of the pipe right after fork. Then it can read its statistic data until EOF (end-of-file) and then close the reading end of the pipe.