如何强制调用`exec（）`的时间限制？

Question

I'm trying to make an online judge written PHP. My code currently looks like:

exec("gcc /var/www/qwerty.c -o /var/www/binary",$output,$returnval);
print_r($output);
exec("cat /var/www/qwe.txt | /var/www/binary",$output,$returnval);
print_r($output);

However, I want each process spawned by exec to have at most 1 second to run. I'm not sure how to do this. set_time_limit() isn't working

Answer 1

I would use the proc_ functions as suggested by @Adam Wright, but a quick alternative to Linux-like environments is to use the GNU timeout command before your command:

// If it took more than 1 second, $returnval will got the exit code 124
exec('timeout 1 gcc /var/www/qwerty.c -o /var/www/binary', $output, $returnval);

Answer 2

You can probably use ulimit for that:

exec(" ( ulimit -t 1 ; gcc ... | /var/www/binary) ");

That of course only works if the process uses active CPU time, not if it waits for I/O endlessly.

Answer 3

This can be achieved using the proc_ family of functions. Launch your processes using proc_open . Repeatedly poll using proc_status (with some small sleep in-between polls) until either the process has returned or 1 second has passed. If 1 second passes without proc_status indicating the process has finished, use proc_terminate (or proc_close ) to kill it off, and take appropriate action.

I'm not saying that spawning external processes in a PHP script is a good idea, though.