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"""Graceful shutdown, an example use case for :class:`~toro.Lock`.
``poll`` continuously fetches http://tornadoweb.org, and after 5 seconds,
``shutdown`` stops the IOLoop. We want any request that ``poll`` has begun to
complete before the loop stops, so ``poll`` acquires the lock before starting
each HTTP request and releases it when the request completes. ``shutdown`` also
acquires the lock before stopping the IOLoop.
(Inspired by a post_ to the Tornado mailing list.)
.. _post: https://groups.google.com/d/topic/python-tornado/CXg5WwufOvU/discussion
"""
# start-file
import datetime
from tornado import ioloop, gen, httpclient
import toro
lock = toro.Lock()
loop = ioloop.IOLoop.current()
@gen.coroutine
def poll():
client = httpclient.AsyncHTTPClient()
while True:
with (yield lock.acquire()):
print 'Starting request'
response = yield client.fetch('http://www.tornadoweb.org/')
print response.code
# Wait a tenth of a second before next request
yield gen.Task(loop.add_timeout, datetime.timedelta(seconds=0.1))
@gen.coroutine
def shutdown():
# Get the lock: this ensures poll() isn't in a request when we stop the
# loop
print 'shutdown() is acquiring the lock'
yield lock.acquire()
loop.stop()
print 'Loop stopped.'
if __name__ == '__main__':
# Start polling
poll()
# Arrange to shutdown cleanly 5 seconds from now
loop.add_timeout(datetime.timedelta(seconds=5), shutdown)
loop.start()
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