Asynchronous COMET query with Tornado and Prototype

Posted by grundic on Stack Overflow See other posts from Stack Overflow or by grundic
Published on 2010-02-23T11:00:53Z Indexed on 2010/03/12 5:07 UTC
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Hello everyone. I'm trying to write simple web application using Tornado and JS Prototype library. So, the client can execute long running job on server. I wish, that this job runs Asynchronously - so that others clients could view page and do some stuff there.

Here what i've got:

#!/usr/bin/env/ pytthon

import tornado.httpserver
import tornado.ioloop
import tornado.options
import tornado.web
from tornado.options import define, options

import os
import string
from time import sleep
from datetime import datetime

define("port", default=8888, help="run on the given port", type=int)

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.render("templates/index.html", title="::Log watcher::", c_time=datetime.now())

class LongHandler(tornado.web.RequestHandler):
    @tornado.web.asynchronous
    def get(self):
        self.wait_for_smth(callback=self.async_callback(self.on_finish))
        print("Exiting from async.")
        return

    def wait_for_smth(self, callback):
        t=0
        while (t < 10):
            print "Sleeping 2 second, t={0}".format(t)
            sleep(2)
            t += 1
        callback()

    def on_finish(self):
        print ("inside finish")
        self.write("Long running job complete")
        self.finish()



def main():
    tornado.options.parse_command_line()

    settings = {
        "static_path": os.path.join(os.path.dirname(__file__), "static"),
        }

    application = tornado.web.Application([
        (r"/", MainHandler),
        (r"/longPolling", LongHandler)
        ], **settings
    )
    http_server = tornado.httpserver.HTTPServer(application)
    http_server.listen(options.port)
    tornado.ioloop.IOLoop.instance().start()


if __name__ == "__main__":
    main()

This is server part. It has main view (shows little greeting, current server time and url for ajax query, that executes long running job. If you press a button, a long running job executes. And server hangs :( I can't view no pages, while this job is running. Here is template page:

<html>
<head>
    <title>{{ title }}</title>

    <script type="text/javascript" language="JavaScript" src="{{ static_url("js/prototype.js")}}"></script>


    <script type='text/javascript' language='JavaScript'>
        offset=0
        last_read=0

        function test(){
            new Ajax.Request("http://172.22.22.22:8888/longPolling",
            {
                method:"get",
                asynchronous:true,
                onSuccess: function (transport){
                    alert(transport.responseText);
                }
            })
        }


    </script>
</head>
<body>
    Current time is {{c_time}}
    <br>
    <input type="button" value="Test" onclick="test();"/>
</body>
</html>

what am I doing wrong? How can implement long pooling, using Tornado and Prototype (or jQuery)

PS: I have looked at Chat example, but it too complicated. Can't understand how it works :(

PSS Download full example

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