The select call in POSIX-compliant systems is useful when carrying out non-blocking I/O, letting one know when a file descriptor is "ready" for an I/O operation. Is there anything analogous for the waitpid system call? I know that one can use the WNOHANG flag to make an individual waitpid call non-blocking, in the same way that one can use, say, the MSG_DONTWAIT flag to make an individual recvfrom socket call non-blocking. However, sometimes the timeout feature offered by select is more convenient, and allows one to avoid a loop that repeatedly calls recvfrom as quickly as possible; select also allows one to monitor multiple file descriptors simultaneously. Is there anything offered by Unix-like systems (or Linux specifically) that gives similar functionality for monitoring child processes?
I'm going to expand on the possibility suggested by Craig Estey, and throw signalfd into the mix.
Instead of setting up a signal handler to handle SIGCHLD, set up signalfd to do the job instead. That way, you'll have a file descriptor that will become ready when SIGCHLD has been signaled, and then you can use select() to wait for it, with a time out.
I've been using signalfd as a way of catching signals for quite a while now. It's Linux specific (OK by the tags you've attached to the question!), and it's far, far easier to handle a signal in the context of the main thread of execution, instead of being limited with what one can do inside a conventional signal handler. The response time to the signal might not be quite so fast, but if an application already has a reactor such as select, or poll, or zmq_poll, or indeed any fd input to any GUI framework's event loop handler, it's an awful lot easier.