"""
This is a simple example of the Producer/Consumer problem in Python.

It makes use of py.magic.greenlet:
<http://codespeak.net/py/dist/greenlet.html>
"""
from py.magic import greenlet
from Queue import Queue
import time

class Producer(object):
    def __init__(self, buffer, name, limit=10):
        self.buffer = buffer
        self.name = name
        self.limit = limit
    
    def run(self):
        """The resumable callback."""
        for i in range(self.limit):
            self.buffer.put(i) # it blocks until there's room for the value
            time.sleep(1)
            print "%s has put %d in the buffer." % (self.name, i)
            cons.switch() # this is needed to pass control to the consumer

class Consumer(object):
    def __init__(self, buffer, name):
        self.buffer = buffer
        self.name = name
    
    def run(self):
        while self.buffer.qsize():
            data = self.buffer.get() # it blocks until some value is available
            time.sleep(1)
            print "%s has got %d from the buffer." % (self.name, data)
            prod.switch() # pass control to the producer
            time.sleep(0.5)
            print "%s is doing something with %s" % (self.name, data)
            prod.switch() # pass it again after value 'processing'
            
if __name__ == '__main__':
    buffer = Queue()
    prod = greenlet(Producer(buffer, "Producer").run)
    cons = greenlet(Consumer(buffer, "Consumer").run)

    prod.switch()