sh via Ruby: Running ulimit and a program in the same line

Question

I am trying to run some computational-intense program from Ruby via the following command:

%x(heavy_program)

However, I sometimes want to limit the running time of the program. So I tried doing

%x(ulimit -St #{max_time} & heavy_program)

But it seems to fail; the "&" trick does not work even when I try it in a running sh shell outside Ruby.

I'm sure there's a better way of doing this...

Answer 1

use either && or ;:

%x(ulimit -St #{max_time} && heavy_program)

%x(ulimit -St #{max_time}; heavy_program)

However using ulimit may be not what you really need, consider this code:

require 'timeout'
Timeout(max_time){ %x'heavy_program' }

ulimit limits CPU time, and timeout limits total running time, as we, humans, usually count it.

so, for example, if you run sleep 999999 shell command with ulimit -St 5 - it will run not for 5 seconds, but for all 999999 because sleep uses negligible amount of CPU time