from multiprocessing import Pool, cpu_count
from random import randint
from time import sleep


class RandSleep(object):
    """multiprocessing.Pool.imap* needs to pickle the function it send to the
    processes. It can't pickle functions or instance methods. But oddly it
    can pickle instances of custom classes. So write the function as a
    callable class."""

    def __call__(self, max_time):
        sleep_time = randint(0, max_time)
        sleep(sleep_time)
        return sleep_time, max_time


class Sleepy(object):
    def increasing_sleeps(self):
        """Pointless function to show using your own generator"""

        for i in xrange(10):
            yield i

    def sleep_lots(self):
        """Takes the output of increasing_sleeps() and send it to rand_sleep(),
        yielding the result"""

        # Use half of available cores, which is all physical cores if using
        # Hyper-Threading, or use one core on uniprocessor systems.
        cores = max(cpu_count() // 2, 1)
        pool = Pool(cores)
        rand_sleep = RandSleep()
        # imap_unordered returns the results when they are ready,
        # regular imap returns them in the order sent
        for sleep_time, max_time in pool.imap_unordered(rand_sleep, self.increasing_sleeps()):
            yield sleep_time, max_time


sleepy = Sleepy()

for sleep_time, max_time in sleepy.sleep_lots():
    print 'Slept', sleep_time, 'seconds of max', max_time