Pipes, shell scripts and ulimit

Question

I have a command that I'm calling from code:

execvp('generate', ...)

which is an executable program that my code communicates with via stdin, stdout and stderr. This works fine, not a single problem.

I want to change this so I can set resource limits on generate. So I've tried calling:

ulimit -t 1 && generate

But I get a broken pipe when I try to communicate with it.

So I put the line above in a shell script generate_wrapper:

#!/bin/bash
ulimit -t 1 && generate

And I get a broken pipe when I try to communicate with it.

But

$ echo "foo" | generate_wrapper
$ echo "foo" | generate

both give me the correct, identical output. I figured it might be the &&, so I tried just the bare command:

#!/bin/bash
generate

But it still works from the CL, and I still get a broken pipe when I try to communicate with it from code.

I tried to explicitly route the fds, and got:

#!/bin/bash
generate >&1 2>&2 <&0

But no, I still get a broken pipe when I try to communicate with it from code.

So obviously I haven't a clue what I'm doing. Can you help? How do I write a wrapper so I can ulimit a spawned subprocess (rlimit isn't available for pids in my host language) and still communicate with it?

Answer 1

Any reason you don't want to call ulimit (2) in the generating code before execvp?

From the man page:

SYNOPSIS
#include <ulimit.h>
long ulimit (int cmd, ...);

DESCRIPTION
The ulimit() function will get and set process limits.

Answer 2

execvp does not handle system commands but only direct binaries. Also script files are only masked system commands in this way.

I think you need to use system() if you wish to run commands instead of binaries.

dmckee's idea about calling ulimit() before execvp() is also a sound one. This will however affect everything the process does from here on.