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 generally need to poll your child
process in a loop, and wait again if it hasn't exited yet. Most applications will
want to use a higher-level API 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.
Example
let mut waiter = new?;
// Any SIGCHLD after this point will be buffered by the Waiter.
let mut child = new.arg.spawn?;
// Block until *any* child exits. See also `wait_timeout` and `wait_deadline`.
waiter.wait?;
// There's only one child process in this example, so we know that it exited. But in general
// we might not know which child woke us up, and then we'd need to wait and check in a loop.
// See the Waiter examples.
assert!;