throng

#!/usr/bin/env python
import os
import time
import argparse
import signal
from subprocess import Popen


class Pool(object):
    def __init__(self, process_count, args):
        self.process_count = process_count
        self.args = args
        self.pool = {}
        self.alive = True

    def handler(self, signal, frame):
        self.alive = False

    def fill(self):
        for _ in range(self.process_count - len(self.pool)):
            p = Popen(self.args)
            self.pool[p.pid] = p

    def wait(self):
        while self.alive:
            result = os.waitpid(-1, os.WNOHANG)
            if result == (0, 0):
                time.sleep(1)
            else:
                self.pool.pop(result[0])
                self.fill()

    def shutdown(self):
        for p in self.pool.values():
            try:
                p.terminate()
            except OSError:
                pass

        for p in self.pool.values():
            p.wait()

    def run(self):
        signal.signal(signal.SIGINT, self.handler)
        signal.signal(signal.SIGTERM, self.handler)
        self.fill()
        self.wait()
        self.shutdown()


if __name__ == '__main__':
    parser = argparse.ArgumentParser()
    parser.add_argument('-j', type=int, default=1, metavar='process_count')

    args, rest = parser.parse_known_args()
    pool = Pool(args.j, rest)
    pool.run()