Untested simplistic pseudocode that ignores a potential error point (0 == fork() is for the child side of the fork and it's not tested here). Forked processes are regular processes on *nix, just children of the original program.

$SIG{CHLD} = "IGNORE";
while ( program_should_be_running() )
{
    # Might want a sleep or a usleep (from Time::HiRes) here.
    if ( my $pid = fork )
    {
        # Do nothing...? This is the "permanent" parent process.
        # $pid is the child $$
    }
    else
    {
        run_your_sub(); # Processes could stack up fast.
    }
}
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