You should be able to the reaping in a SIGCHLD handler, which upon exit, returns you to the sleep loop. Or include the reaping within the timing loop, eg

while (1) {
    while (remaining) {
        sleep(remaining);
        while (($pid = wait) != -1) {
            ... do reaping stuff
        }
    }
    ... check for new jobs and spawn them ...
}
[download]

Dave.