get child process return status without blocking the parent
 

Hello,

I need to get the return status from a child process in C.
The problem with wait/waitpid is that I can't afford to interrupt the parent process which is generally on a select loop.
I can try to install a signal handler for SIGCHLD, but I am concerned with concurrency issues with the data structure where I keep data related to the children processes.

Any suggestion is more than welcome.
Thank you.

You can pass wait() the WNOHANG flag, and it will refuse to block if the child hasn't exited - you can tell this has happened by the return value (see man page for details).

You should simply ensure that only the parent process maintains the data-structure of child process status. Really, no child should assume that this data structure is reliable: only the parent really knows, and then only when it formally executes a rendezvous with that child-pid by means of wait() in the manner that JohnGraham previously described.

Frankly, I would suggest moving the select-loop to a child process, which subsequently sends the incoming requests to its parent by means of a thread-safe queue. The parent's role thus becomes 100% devoted to keeping up with its unruly children. ;) But now it only has to deal with waiting for one type of thing, which is a CPU-initiated not an I/O-initiated event. The child (or children) that are waiting on sockets don't have to wait for anything else. Over a great many years, I have found that this "do-nothing parent" strategy shakes-out a lot of otherwise thorny problems. (Consider, as a prime example, the role of the init process ("process #1") in any Unix/Linux system . . .)

Thank you for your replies.

Digging into man pages I found signalfd which notifies a signal via a fd. This way I can receive the notification through select.

Cheers.