use Proc::Queue to limit the max. number of concurrently forked processes: 
use Proc::Queue size => 2, qw(system_back);

for (1..$total_number_of_runs) {
  system_back "shell_script < $input_file"
}

# and wait for all your children to finish
1 while wait != -1;

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In reply to Re: Is fork() my answer to using dual-cpu? by salva
in thread Is fork() my answer to using dual-cpu? by axl163

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