Description
The wait and wait_with_output methods of process::Child expect to do the waiting for the child to exit themselves. If you are running many processes at once, and you don't know which one will finish first, this is inconvenient, because the system calls wait and waitpid consume each exit notification as they report it. (waitid can be told not to do that, but it is not fully supported in the libc crate yet.) That places the Child object in an inconsistent state, in which it is not safe to call wait or wait_with_output.
If Child had a set_exit_status method, an application in this situation could use it to keep the objects consistent: something like
fn wait_all(children: &[&mut Child]) -> nix::Result<()> {
use nix::sys::wait::{wait, WaitStatus}
let mut pending : HashMap<u32, &mut Child> =
children.iter().map(|c| (c.id(), c)).collect();
while pending.len() {
let status = try!(wait());
match status {
Exited(pid, ..) | Signaled(pid, ..) => {
let mut child = try!(pending.remove(pid).ok_or(UnexpectedChild(pid)));
child.set_exit_status(status);
},
_ => unreachable!();
}
}
Ok(())
}(In this hypothetical, ExitStatus impls From<nix::WaitStatus>, which I believe nix can make happen without assistance from std.)