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add asyncweb example

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1 parent 4083044 commit 23f18425feb5cec866de6795b9bbe9bb5140e1ec @minrk committed Dec 6, 2011
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  1. +96 −0 examples/eventloop/asyncweb.py
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96 examples/eventloop/asyncweb.py
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+"""Async web request example with tornado.
+
+Requests to localhost:8888 will be relayed via 0MQ to a slow responder,
+who will take 1-5 seconds to respond. The tornado app will remain responsive
+duriung this time, and when the worker replies, the web request will finish.
+
+A '.' is printed every 100ms to demonstrate that the zmq request is not blocking
+the event loop.
+"""
+
+
+import sys
+import random
+import threading
+import time
+
+import zmq
+from zmq.eventloop import ioloop, zmqstream
+
+"""
+ioloop.install() must be called prior to instantiating *any* tornado objects,
+and ideally before importing anything from tornado, just to be safe.
+
+install() sets the singleton instance of tornado.ioloop.IOLoop with zmq's
+IOLoop. If this is not done properly, multiple IOLoop instances may be
+created, which will have the effect of some subset of handlers never being
+called, because only one loop will be running.
+"""
+
+ioloop.install()
+
+import tornado
+from tornado import web
+
+
+def slow_responder():
+ """thread for slowly responding to replies."""
+ ctx = zmq.Context.instance()
+ socket = ctx.socket(zmq.REP)
+ socket.linger = 0
+ socket.bind('tcp://127.0.0.1:5555')
+ i=0
+ while True:
+ msg = socket.recv()
+ print "\nworker received %r\n" % msg
+ time.sleep(random.randint(1,5))
+ socket.send(msg + " to you too, #%i" % i)
+ i+=1
+
+def dot():
+ """callback for showing that IOLoop is still responsive while we wait"""
+ sys.stdout.write('.')
+ sys.stdout.flush()
+
+def printer(msg):
+ print (msg)
+
+class TestHandler(web.RequestHandler):
+
+ @web.asynchronous
+ def get(self):
+ ctx = zmq.Context.instance()
+ s = ctx.socket(zmq.REQ)
+ s.connect('tcp://127.0.0.1:5555')
+ # send request to worker
+ s.send('hello')
+ loop = ioloop.IOLoop.instance()
+ self.stream = zmqstream.ZMQStream(s)
+ self.stream.on_recv(self.handle_reply)
+
+ def handle_reply(self, msg):
+ # finish web request with worker's reply
+ reply = msg[0]
+ print "\nfinishing with %r\n" % reply,
+ self.stream.close()
+ self.write(reply)
+ self.finish()
+
+def main():
+ worker = threading.Thread(target=slow_responder)
+ worker.daemon=True
+ worker.start()
+
+ application = web.Application([(r"/", TestHandler)])
+ beat = ioloop.PeriodicCallback(dot, 100)
+ beat.start()
+ application.listen(8888)
+ try:
+ ioloop.IOLoop.instance().start()
+ except KeyboardInterrupt:
+ print ' Interrupted'
+
+
+if __name__ == "__main__":
+ main()
+

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