Tornado in Depth
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Tornado is a non-blocking light-weight web server and framework. There's been many introductory talks about it, and it's time to look deeper into it: not just what Tornado does, but how it does it and what can we learn from it when designing our own concurrent systems. In this talk I go over the following topics. I cover them in two parts: first I present how to use a certain feature or approach in our applications; then, I dig into Tornado's source code to see how it really works. - Getting Started: quickly get a simple Tornado application up and running. We'll keep digging into, changing and poking this Application for most of the talk. - An Application Listens: what an Application is, how does Tornado start it and how does it process its requests. - Application and IOLoop: we'll look at how the IOLoop receives the connections from the users and passes them on to the Applications. - Scheduled Tasks: we'll see how to schedule tasks and how the IOLoop will run them. - Generators: we'll learn to use generators to handle the responses of our asynchronous calls, and how they work with the IOLoop. Advanced: - Websockets: how to use them and how they work. - IOStream: how do Tornado's non-blocking sockets work. - Database: how to use non-blocking sockets to connect to databases. - Process: how Tornado works with multiple processes. I presented this talk at Europython 2012 and PyGrunn 2012. Code examples: https://bitbucket.org/grimborg/tornado-in-depth/src/tip/examples/
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Tornado in Depth
- 2. thor
- 3. thunder
- 4. tro
- 5. tronar
- 6. tronada
- 7. tornar
- 8. tornada
- 9. tornada
- 11. TORNADO
- 12. what is it? Non-blocking web server Based on epoll / kqueue Handles 1000s of connections Powers FriendFeed
- 14. why do you even care? Know what you use I can't trust what I don't know Learning and sharing: fun!
- 15. what do you use it for? We built a Scalable Distributed Fault tolerant High load ...thing
- 18. TORNADO
- 19. what is it made of? IOLoop Callbacks, Tasks, Timeouts TCPServer Application RequestHandler Generators
- 20. can I extend it? Sure! It's easy How would we make a simple TCPServer?
- 21. 0b_tcpserver.py show me the source!
- 22. GETTING STARTED
- 23. how do I make the simplest app? Define a RequestHandler Implement get Define an Application Tell the application to listen Start the IOLoop
- 24. 01_getting_started.py show me the source!
- 25. what is an Application? Collection of RequestHandlers Implements listen: Starts an HTTPServer Sets the Application as request callback Implements __call__: Handles the user requests
- 26. t1_application_listen.py show me the source!
- 27. what does Application.__call__ do? Parses the URL Decides which handler to use and creates an instance of it (each connection gets one) _executes it (passing any defined transforms to it –e.g, Gzip compression)
- 28. t2_application_call.py show me the source!
- 29. what does RequestHandler._execute do? Calls the handler method Checks XSRF cookie Maybe closes the connection
- 30. t3_request_handler_ _execute.py show me the source!
- 32. Core of Tornado Usable standalone or with WSGI Used for server and client Single instance per process Small! what is the IOLoop?
- 33. Loops forever Executes: Callbacks (asap) Timeouts (when due) Events (when occoured) what does the IOLoop do?
- 34. what is an Event? Something that happened on a socket (fd) (e.g. a user opened a conneciton) Applications define handlers for Events
- 35. how do I wait for an Event? add_handler(fd, handler, events) update_handler(fd, handler, events) remove_handler(fd, handler) “Notify me when I can READ or WRITE, or when there is an ERROR”
- 36. IOLOOP THE LOOP in four steps
- 37. Process Callbacks They were scheduled by previous: Callbacks Event handlers first process the Callbacks
- 38. For each Timeout: Is it due now? Run its callback Calculate the time till next Timeout second process the Timeouts
- 39. Poll timeout: Callbacks? Then 0 Timeouts? Then time until the next Timeout Neither? 1 hour Here the IOLoop blocks third poll for Events
- 40. For each (file descriptor, Event): Call its handler ...and repeat the loop and fourth process the Events
- 42. 01_getting_started.py show me the source!
- 43. Application.listen starts HTTPServer calls IOLoop.add_accept_handler (Application.__call__ will handle the ACCEPT event) and when a client connects... what does the example do?
- 44. what does the example do? IOLoop polls connection TCPServer calls HTTPServer which is HTTPConnection creates read and callsheaders body reads using callbacks request_callback and calls Application.__call__ which is RequestHandler ._execute calls (after parsing URL) RequestHandler calls get or post or ... calls HTTPConnection writes to (in chunks) _auto_finish? finishes yes
- 45. t4_simple_ioloop.py show me the source!
- 46. Scheduled tasks
- 47. how do we schedule a task? Call me back asap Ioloop.add_callback Call me back later Ioloop.add_timeout Call me often PeriodicCallback
- 48. 02_scheduled_tasks.py show me the source!
- 49. how does add_callback work? Adds the callback to the list of callbacks. (and wraps it in a threadlocal-like stack context)
- 50. what do you mean, threadlocal-like? StackContext Keeps track of the socket connection Handles association between socket and Application classes
- 51. t6_add_callback.py show me the source!
- 52. how does add_timeout work? Pushes the timeout to the heap of timeouts. (and wraps it in a threadlocal-like stack context too)
- 53. t7_add_timeout.py show me the source!
- 54. how do PeriodicCallbacks work? start Schedules the next timeout to call _run Marks the PeriodicCallback as running stop Removes the next timeout Marks the PeriodicCallback as stopped _run Calls the callback (unless stop was called)
- 55. t8_periodic_callback.py show me the source!
- 58. how does @asynchronous work? Sets _auto_finish to False (and does some Exception wrapping) The connection remains open after get, post... Close it yourself (whenever you want)
- 59. 03_fetch_async.py show me the source!
- 60. I put a callback on your callback Nested callbacks make ugly code.
- 62. generators
- 63. how do I avoid callbacks? Use Callback (finally!) and yield Or Task
- 64. 04_fetch_gen.py show me the source!
- 65. Yield points
- 66. what is a YieldPoint? Something you yield Then stuff happens
- 67. what is a YieldPoint? Callback Sends a result for a key Wait Waits till a result for a key arrives WaitMany Same as Wait, for many keys
- 68. Task Wait + Callback (with an auto-generated key) Multi List of YeldPoints what is a YieldPoint?
- 69. how do we do async processing? callback=(yield Callback(“key”)) When a result arrives, send it for the key “key”
- 70. how do we do async processing? response=yield Wait(“key”) When the result is sent, read it into response.
- 71. 04_fetch_gen.py show me the source!
- 72. 05_task.py show me the source!
- 73. t9_yield_points.py show me the source!
- 74. websockets
- 75. how do we use websockets? Extend WebSocketHandler (instead of RequestHandler) Implement on_message
- 76. 06_websocket.py show me the source!
- 77. how do websockets work? Similar to @asynchronous (the connection is kept open) After writing, read for more (asynchronously—see IOStream) To Application, it looks like a RequestHandler
- 78. how does WebSocket work? _execute Accepts the connection Decides the version of the protocol. Instantiates a WebSocketProtocol class
- 79. how does WebSocketProtocol work? accept_connection Sends the required initial message Reads the next message (asynchronously) _write_response Writes a response on the socket Reads the next message (asynchronously)
- 80. ta_websocket.py show me the source!
- 81. iostream
- 82. what does IOStream do? Communicates with the socket Asynchronous Uses IOLoop Callbacks
- 83. how does IOStream work? _add_io_state “Notify me when I can READ or WRITE, or when ERROR” schedules Callback for an event (READ, WRITE, ...) _handle_events Can I read? Call _handle_read Can I write? Call _handle_write Handles errors
- 84. how does IOStream work? _handle_read Store data in read buffer Call the read callback (_read_from_buffer) _handle_write Write data from the buffer into the socket (handling funny circumstances) Call the write callback (if it exists)
- 85. how does IOStream work? connect socket.connect _add_io_state(WRITE) read Set callback Data in read buffer? Return it Read buffer empty? _add_io_state(READ) write Add data to write buffer _add_io_state(WRITE)
- 86. how do I use IOStream directly? read_until_regex read_until read_bytes read_until_close All take a callback
- 87. how do I use streaming callbacks? read_bytes read_until_close Param: streaming_callback Data is sent to callback as it arrives
- 88. 0a_async_callback.py show me the source!
- 89. database
- 90. how do I talk to a database? database.connection query(“SQL”) Returns an iterable Very simple
- 91. 07_db.py show me the source!
- 92. Not async!
- 93. asyncmongo
- 94. what is asyncmongo? Asynchronous MongoDB client Uses Tornado's IOLoop
- 95. how do I use asyncmongo? asyncmongo.Client db.find takes a callback parameter
- 96. 08_mongo.py show me the source!
- 97. how does asyncmongo work? Implements a Connection Many: ConnectionPool Sends data via Tornado's IOStream Commands send via Cursor Cursor.send_message Uses Connection to communicate asynchronously
- 98. can we write our own asyncmysql? Difficult C driver has blocking calls mysql_query mysql_store_result mysql_use_result Alternative Use Twisted's txMySQL with tornado.platform.twisted Slower
- 99. Q A&