Real-time apps with gevent-socketio

pyconsg 2013

Transcript

1. GEVENT-SOCKETIO real-time apps with python Saturday, June 15, 13
2. OVERVIEW • Concepts ✓concurrency ✓parallelism ✓threads ✓processes ✓gevent greenlets • Concepts ✓sockets ✓python sockets ✓WebSockets ✓Socket.IO • Code: A simple Socket.IO example • Code: Socket.IO’s on and emit Saturday, June 15, 13
3. CONCEPTS • Concurrency? • Parallelism? • Threads? • Processes? • Gevent’s greenlets? • Gevent monkey patch Saturday, June 15, 13
4. CONCURRENCY managing access to shared state from different threads Saturday, June 15, 13
5. PARALLELISM utilizing multiple cores to improve computation performance Saturday, June 15, 13
6. THREADS • basic unit of CPU utilization • lightweight process • unlike process, threads do not have their own PCB • runs within a process • shares code, data, heap • can be concurrent and parallel (warning: GIL limitation in python) Saturday, June 15, 13
7. PROCESSES • an instance of a program that is being executed • runs within the kernel • shares code, data, heap, stack • holds information about active processes in data structures called PCB • can be concurrent and parallel Saturday, June 15, 13
8. PYTHON CONTEXT • python (CPython) GIL prevents parallel threads • generally, use python’s multiprocessing • exception... Saturday, June 15, 13
9. PYTHON CONTEXT • exception: cython! • allows for parallel threads by releasing the GIL Saturday, June 15, 13
10. GEVENT • lightweight coroutines, with concurrency capabilities • asynchronous IO (libev/libevent) • lightweight threads called greenlets (cooperative multi- threading) • libev/libevent handles events (“emit” call to send message via socketio in the context of gevent-socketio implementation) • gevent spawns concurrent tasks (lightweight thread of execution - greenlets) Saturday, June 15, 13
11. GREENLETS • spin-off from stackless python • main building-blocks of gevent • “lightweight threads”- different from POSIX threads (pthreads) - no implicit scheduling • we specify when the code runs or when it gets switched away Saturday, June 15, 13
12. EXAMPLE def handle_view(request): jobs = [] jobs.append(gevent.spawn(orm_call, 'Andy')) jobs.append(gevent.spawn(call_facebook_graph_api, 14213)) jobs.append(gevent.spawn(email, 'me@mysite.com')) gevent.joinall() Saturday, June 15, 13
13. MONKEY PATCH • extend/modify run-time code of dynamic languages without altering source code • The order matters! Apply patch first. import gevent.monkey; gevent.monkey.patch_thread() import threading Saturday, June 15, 13
14. CONCEPTS • sockets? • Python sockets • WebSockets? • Socket.IO? ✓namespace & js logic (client-side “controllers”) ✓server ✓router (“urls”) ✓namespace & methods (server-side “controllers”) Saturday, June 15, 13
15. SOCKETS • Berkeley sockets (BSD sockets, equiv to POSIX sockets) • written in C • When a socket is created, a communication endpoint becomes available • A file descriptor is returned • “Everything is a file” Saturday, June 15, 13
16. PYTHON SOCKETS • Berkeley sockets (BSD sockets, equiv to POSIX sockets) • written in C • When a socket is created, a communication endpoint becomes available • A file descriptor is returned • “Everything is a file” • Various languages provide similar interfaces and are essentially wrappers Saturday, June 15, 13
17. PYTHON SOCKETS #  server.py import  socket serversocket  =  socket.socket(socket.AF_INET,  socket.SOCK_STREAM) serversocket.bind(('localhost',  8089)) serversocket.listen(5) while  True:        connection,  address  =  serversocket.accept()        buf  =  connection.recv(64)        if  len(buf)>0:                print  buf Saturday, June 15, 13
18. PYTHON SOCKETS #  client.py import  socket clientsocket  =  socket.socket(socket.AF_INET,  socket.SOCK_STREAM) clientsocket.connect(('localhost',  8089)) clientsocket.send('hello') Saturday, June 15, 13
19. PYTHON SOCKETS python  server.py python  client.py Saturday, June 15, 13
20. WEBSOCKETS • Full-duplex message transfer • Independent TCP-type protocol, not HTTP • “Upgrade” request in HTTP 1.1 • Server can also force an upgrade by sending “426 upgrade required” • stream of messages, not bytes, splitted across data frames, end marked by FIN • connection persists Saturday, June 15, 13
21. SOCKET.IO • javascript library with client side and server-side components • 6 transports ✓WebSocket ✓Adobe Flash Socket ✓AJAX long polling ✓AJAX multipart streaming ✓Forever IFrame ✓JSONP polling • Most capable transport selected at runtime no change required to its abstracted API! socket.io-transports analogous to orm-(db adaptors and databases) Saturday, June 15, 13
22. SOCKET.IO • many implementations for different languages, not just the original (nodejs) javascript implementation ✓python ✓perl ✓java ✓golang ✓erlang • why? Because fundamentally, Socket.IO is logic built on top of sockets. And as we already know, various languages have their own interfaces to Berkeley sockets! Saturday, June 15, 13
23. NAMESPACE & JS FUNCTIONS <script  src="/static/js/socket.io.js"></script> <script>   WEB_SOCKET_SWF_LOCATION="/static/flashsocket/WebSocketMain.swf" var  socket  =  io.connect("/chat"); //  ..  other  js  logic </script> • flash transport (WEB_SOCKET_SWF_LOCATION) optional • install socket.io.js client (which comes with WebSocketMain.swf which we can use optionally) via nodeenv, npm and bower • establish a “socket” js object via io.connect() • “/chat” is a Socket.IO namespace which is like a “controller” and NOT a url (“router”) (client-side “Controllers”) Saturday, June 15, 13
24. SOCKET.IO SERVER from gevent import monkey from socketio.server import SocketIOServer monkey.patch_all() PORT = 5000 if __name__ == '__main__': print 'Listening on http://127.0.0.1:%s and on port 10843 (flash policy server)' % PORT SocketIOServer(('', PORT), app, resource="socket.io").serve_forever() Saturday, June 15, 13
25. SOCKET.IO ROUTER (“URL”) @app.route('/socket.io/<path:remaining>') def  socketio(remaining):        try:                socketio_manage(request.environ,  {'/chat':  ChatNamespace},   request)        except:                app.logger.error("Exception  while  handling  socketio   connection",  exc_info=True)        return  Response() Saturday, June 15, 13
26. NAMESPACE & METHODS class  ChatNamespace(BaseNamespace,  RoomsMixin,  BroadcastMixin):        nicknames  =  []        def  initialize(self):                ...        def  log(self,  message):                ...        def  on_join(self,  room):                ...        def  on_nickname(self,  nickname):                ...                return  True,  nickname        def  recv_disconnect(self):                ...                return  True        def  on_user_message(self,  msg):                ...                return  True (server-side “Controllers”) Saturday, June 15, 13
27. NAMESPACE & JS FUNCTIONS $(function()  {        var  WEB_SOCKET_SWF_LOCATION  =  '/static/js/socketio/WebSocketMain.swf',        socket  =  io.connect('/chat');        socket.on('connect',  function  ()  {                $('#chat').addClass('connected');                socket.emit('join',  window.room);        });        socket.on('announcement',  function  (msg)  {                $('#lines').append($('<p>').append($('<em>').text(msg)));        });        socket.on('nicknames',  function  (nicknames)  {                $('#nicknames').empty().append($('<span>Online:  </span>'));                for  (var  i  in  nicknames)  {                    $('#nicknames').append($('<b>').text(nicknames[i]));                }        });        socket.on('msg_to_room',  message);        socket.on('reconnect',  function  ()  {                $('#lines').remove();                message('System',  'Reconnected  to  the  server');        });        socket.on('reconnecting',  function  ()  {                message('System',  'Attempting  to  re-­‐connect  to  the  server');        }); (client-side “Controllers”) Saturday, June 15, 13
28. EXAMPLE DJANGO • https://github.com/calvinchengx/pyconsg2013 Saturday, June 15, 13
29. RESOURCES • http://sdiehl.github.io/gevent-tutorial/ • https://github.com/abourget/gevent-socketio • My notes & source code https://learn-gevent-socketio.readthedocs.org/en/latest/ https://github.com/calvinchengx/pyconsg2013 https://github.com/calvinchengx/learnsocketio Saturday, June 15, 13
30. Q&A • Get in touch @calvinchengx • http://calvinx.com Saturday, June 15, 13