sigchld 
This is a low-level utility for child process management. Unix doesn't provide a portable* API
for waiting for a child process to exit with a timeout. The closest thing is waiting for
the SIGCHLD signal to be delivered, but Unix signal handling is quite complicated and
error-prone. This crate implements SIGCHLD handling (using signal_hook internally for
compatibility with other signal handling libraries) and allows any number of threads to wait
for that signal, with an optional timeout.
Note that SIGCHLD indicates that any child process has exited, but there's no (100%
reliable) way to know which child it was. You need to poll your child process in
a loop, and wait again if it hasn't exited yet. Most applications will want a higher-level
crate that does this loop internally; I'll list such crates here as they're implemented.
* Linux supports signalfd, but there's no equivalent on e.g. macOS.