wait() should either return Ok or panic

readme.md

ok

$ cargo run ls

bad

$ cargo run cmd-not-exists

Cargo.toml

[package]
name = "rust-demo-spawn"
version = "0.1.0"
authors = ["Hugo Wang <w@mitnk.com>"]

[dependencies]
nix = "0.10.0"
libc = "0.2.0"

main.rs

extern crate nix;
extern crate libc;

use std::env;
use std::process::Command;
use std::os::unix::process::CommandExt;

use nix::sys::signal;


extern "C" fn handle_sigchld(_: i32) {
    match nix::sys::wait::waitpid(None, None) {
        Ok(x) => {
            println!("waitpid ok: {:?}", x);
        }
        Err(e) => {
            println!("waitpid error: {:?}", e);
        }
    }
}

fn main() {
    let sig_action = signal::SigAction::new(
        signal::SigHandler::Handler(handle_sigchld),
        signal::SaFlags::empty(),
        signal::SigSet::empty(),
    );
    unsafe {
        match signal::sigaction(signal::SIGCHLD, &sig_action) {
            Ok(_) => {}
            Err(e) => println!("sigaction error: {:?}", e),
        }
    }

    let args: Vec<String> = env::args().collect();
    println!("{:?}", args);

    let mut p = Command::new(&args[1]);

    p.before_exec(move || {
        unsafe {
            let pid = libc::getpid();
            let code = libc::setpgid(0, pid);
            println!("code: {}", code);
        }
        Ok(())
    });

    match p.spawn() {
        Ok(mut child) => {
            println!("spawn ok: {:?}", child);
            match child.wait() {
                Ok(x) => println!("ok: {:?}", x),
                Err(e) => println!("err: {:?}", e),
            }
        }
        Err(e) => {
            println!("spawn error: {:?}", e);
        }
    }

    println!("the end.");
}