#!/usr/bin/env python
# encoding: utf-8
#
# Copyright (c) 2008 Doug Hellmann All rights reserved.
#
"""Using a Condition to control sequencing between workers.
"""
#end_pymotw_header
import multiprocessing
import time

def stage_1(cond):
    """perform first stage of work,
    then notify stage_2 to continue
    """
    name = multiprocessing.current_process().name
    print 'Starting', name
    with cond:
        print '%s done and ready for stage 2' % name
        cond.notify_all()

def stage_2(cond):
    """wait for the condition telling us stage_1 is done"""
    name = multiprocessing.current_process().name
    print 'Starting', name
    with cond:
        cond.wait()
        print '%s running' % name

if __name__ == '__main__':
    condition = multiprocessing.Condition()
    s1 = multiprocessing.Process(name='s1',
                                 target=stage_1,
                                 args=(condition,))
    s2_clients = [
        multiprocessing.Process(name='stage_2[%d]' % i,
                                target=stage_2,
                                args=(condition,))
        for i in range(1, 3)
        ]

    for c in s2_clients:
        c.start()
        time.sleep(1)
    s1.start()

    s1.join()
    for c in s2_clients:
        c.join()