Google App Engin SDK memcache cas test

cas_test.py

"""
- /init to initialize service
- /update?uid=XXX to tell service XXX is active
- /count to get how many clients are active within last TIME_LIMIT sec.
"""

KEY = 'users'
TIME_LIMIT = 10
MAX_RETRIES = 3

import time
from google.appengine.ext import webapp
from google.appengine.ext.webapp import util
from google.appengine.api import memcache
from django.utils import simplejson as json

class InitalizeHandler(webapp.RedirectHandler):
    def get(self):
        memcache.set(KEY, "{}")
        self.response.out.write("OK")

class UpdateHandler(webapp.RequestHandler):
    def get(self):
        uid = self.request.get('uid')
        client = memcache.Client()
        for i in range(MAX_RETRIES):
            users = json.loads(client.gets(KEY))
            users[uid] = time.time()
            if client.cas(KEY, json.dumps(users)):
                self.response.out.write('OK')
                return
        else:
            self.response.out.write('FAILED')

class CountHandler(webapp.RequestHandler):
    def get(self):
        users = json.loads(memcache.get(KEY) or "{}")
        count = len([uid for uid,timestamp in users.items()
                     if time.time() < timestamp + TIME_LIMIT])
        self.response.out.write('count: %d' % count)

def main():
    application = webapp.WSGIApplication([('/init', InitalizeHandler),
                                          ('/update', UpdateHandler),
                                          ('/count', CountHandler)],
                                         debug=True)
    util.run_wsgi_app(application)

if __name__ == '__main__':
    main()