[CCUnix] add function to call a process with a timeout

[grayswandyr]

The subject says it all.

[c-cube]

That would be useful indeed, but I haven't found a way of doing it without multi-threads. Technical suggestions welcome.

[hcarty]

Could this go into a CCProcess or similar module under containers.threads? It could provide similar functionality to Lwt's https://ocsigen.org/lwt/3.1.0/api/Lwt_process

[c-cube]

@hcarty I think it should be in the unix sub-library anyway, but the problem is I'm not sure how to do it even with threads (Thread.kill doesn't work, and I think it's a bit messy to kill the subprocess while the thread is running).

Maybe we can do sth where we fork manually and setup a ulimit/rlimit, or setup some alarm (Unix.alarm?) before exec'ing the command. Do you know if alarm is preserved by exec?

[c-cube]

I tried this little experiment:

let f () =
  let st = Unix.gettimeofday() in
  let pid = Unix.fork() in
  if pid=0 then (
    Unix.alarm 4;
    Unix.execv "sleep" [| "sleep"; "10" |]
  ) else (
    Unix.waitpid [] pid;
    Printf.printf "done (%.2f)" (Unix.gettimeofday() -. st)
  );;

f();;

and it does print "done" after 4s. So it might work. What do you think?

[hcarty]

That's pretty promising - I didn't realize the signal would persist like that.

It would be nice to have something which doesn't rely on Unix.fork for better Windows compatibility. If I can get some time for it I'll try to work something out with threads and killing the subprocess after its time is up. And capture the subprocess's output if I'm feeling adventurous.