gevent_queue_example.py

"""
From: http://sdiehl.github.com/gevent-tutorial/#queues

In this example we have the boss running simultaneously to the workers and have a restriction on the Queue that it can contain no more than three elements. This restriction means that the put operation will block until there is space on the queue. Conversely the get operation will block if there are no elements on the queue to fetch, it also takes a timeout argument to allow for the queue to exit with the exception gevent.queue.Empty if no work can found within the time frame of the Timeout.
"""

import gevent
from gevent.queue import Queue, Empty

tasks = Queue(maxsize=3)

def worker(n):
    try:
        while True:
            task = tasks.get(timeout=1) # decrements queue size by 1
            print('Worker %s got task %s' % (n, task))
            gevent.sleep(0)
    except Empty:
        print('Quitting time!')

def boss():
    """
    Boss will wait to hand out work until a individual worker is
    free since the maxsize of the task queue is 3.
    """

    for i in xrange(1,10):
        tasks.put(i)
    print('Assigned all work in iteration 1')

    for i in xrange(10,20):
        tasks.put(i)
    print('Assigned all work in iteration 2')

gevent.joinall([
    gevent.spawn(boss),
    gevent.spawn(worker, 'steve'),
    gevent.spawn(worker, 'john'),
    gevent.spawn(worker, 'bob'),
])