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Tornado in Depth
The document provides an in-depth overview of Tornado, a non-blocking web server framework that handles thousands of connections using an event-driven model. It discusses the architecture, including components like the IOLoop, RequestHandler, and how to create scalable applications while employing asynchronous programming techniques. It also covers advanced topics such as scheduled tasks, websockets, and database interactions using asyncmongo.
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Tornado in Depth
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- 12. what is it? Non-blockingweb server Based on epoll / kqueue Handles 1000s of connections Powers FriendFeed
- 14. why do youeven care? Know what you use I can't trust what I don't know Learning and sharing: fun!
- 15. what do youuse it for? We built a Scalable Distributed Fault tolerant High load ...thing
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- 19. what is itmade of? IOLoop Callbacks, Tasks, Timeouts TCPServer Application RequestHandler Generators
- 20. can I extendit? Sure! It's easy How would we make a simple TCPServer?
- 21. 0b_tcpserver.py show me thesource!
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- 23. how do Imake the simplest app? Define a RequestHandler Implement get Define an Application Tell the application to listen Start the IOLoop
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- 25. what is anApplication? Collection of RequestHandlers Implements listen: Starts an HTTPServer Sets the Application as request callback Implements __call__: Handles the user requests
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- 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)
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- 29. what does RequestHandler._execute do? Callsthe handler method Checks XSRF cookie Maybe closes the connection
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- 32. Core of Tornado Usablestandalone 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 anEvent? Something that happened on a socket (fd) (e.g. a user opened a conneciton) Applications define handlers for Events
- 35. how do Iwait 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”
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- 37. Process Callbacks They werescheduled by previous: Callbacks Event handlers first process the Callbacks
- 38. For each Timeout: Isit due now? Run its callback Calculate the time till next Timeout second process the Timeouts
- 39. Poll timeout: Callbacks? Then0 Timeouts? Then time until the next Timeout Neither? 1 hour Here the IOLoop blocks third poll for Events
- 40. For each (filedescriptor, Event): Call its handler ...and repeat the loop and fourth process the Events
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- 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 theexample 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
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- 47. how do weschedule a task? Call me back asap Ioloop.add_callback Call me back later Ioloop.add_timeout Call me often PeriodicCallback
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- 49. how does add_callbackwork? Adds the callback to the list of callbacks. (and wraps it in a threadlocal-like stack context)
- 50. what do youmean, threadlocal-like? StackContext Keeps track of the socket connection Handles association between socket and Application classes
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- 52. how does add_timeoutwork? Pushes the timeout to the heap of timeouts. (and wraps it in a threadlocal-like stack context too)
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- 54. how do PeriodicCallbackswork? 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)
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- 58. how does @asynchronouswork? Sets _auto_finish to False (and does some Exception wrapping) The connection remains open after get, post... Close it yourself (whenever you want)
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- 60. I put acallback on your callback Nested callbacks make ugly code.
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- 63. how do Iavoid callbacks? Use Callback (finally!) and yield Or Task
- 64. 04_fetch_gen.py show me thesource!
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- 66. what is aYieldPoint? Something you yield Then stuff happens
- 67. what is aYieldPoint? 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 (withan auto-generated key) Multi List of YeldPoints what is a YieldPoint?
- 69. how do wedo async processing? callback=(yield Callback(“key”)) When a result arrives, send it for the key “key”
- 70. how do wedo async processing? response=yield Wait(“key”) When the result is sent, read it into response.
- 71. 04_fetch_gen.py show me thesource!
- 72. 05_task.py show me thesource!
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- 75. how do weuse websockets? Extend WebSocketHandler (instead of RequestHandler) Implement on_message
- 76. 06_websocket.py show me thesource!
- 77. how do websocketswork? 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 WebSocketwork? _execute Accepts the connection Decides the version of the protocol. Instantiates a WebSocketProtocol class
- 79. how does WebSocketProtocolwork? 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 thesource!
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- 82. what does IOStreamdo? Communicates with the socket Asynchronous Uses IOLoop Callbacks
- 83. how does IOStreamwork? _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 IOStreamwork? _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 IOStreamwork? 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 Iuse IOStream directly? read_until_regex read_until read_bytes read_until_close All take a callback
- 87. how do Iuse streaming callbacks? read_bytes read_until_close Param: streaming_callback Data is sent to callback as it arrives
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- 90. how do Italk to a database? database.connection query(“SQL”) Returns an iterable Very simple
- 91. 07_db.py show me thesource!
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- 94. what is asyncmongo? AsynchronousMongoDB client Uses Tornado's IOLoop
- 95. how do Iuse asyncmongo? asyncmongo.Client db.find takes a callback parameter
- 96. 08_mongo.py show me thesource!
- 97. how does asyncmongowork? 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 writeour 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
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