Keep five process running at almost all time for one minute.

five_alive.py

import multiprocessing
import time

from os import getpid


def worker():
    pid = getpid()
    print 'START %d' % pid
    time.sleep(3)
    print 'STOP  %d' % pid


if __name__ == '__main__':
    from datetime import datetime, timedelta

    concurrent_jobs_count = 5
    minutes_to_run = 1

    end_time = datetime.now() + timedelta(minutes=minutes_to_run)
    jobs = []
    # We only run for the time specified
    while datetime.now() < end_time:
        # Check all processes to see which are still running
        jobs = [x for x in jobs if x.is_alive()]
        # Create new processes to replace finished processes
        while len(jobs) < concurrent_jobs_count:
            jobs.append(multiprocessing.Process(target=worker))
            jobs[-1].start()
        # Wait, just so this isn't looping all the time
        time.sleep(3)