[Python-ideas] re-implementing Twisted for fun and profit
glyph at twistedmatrix.com
Sat Oct 13 06:46:20 CEST 2012
There has been a lot written on this list about asynchronous, microthreaded and event-driven I/O in the last couple of days. There's too much for me to try to respond to all at once, but I would very much like to (possibly re-)introduce one very important point into the discussion.
Would everyone interested in this please please please read <https://github.com/lvh/async-pep/blob/master/pep-3153.rst> several times? Especially this section: <https://github.com/lvh/async-pep/blob/master/pep-3153.rst#why-separate-protocols-and-transports>. If it is not clear, please ask questions about it and I will try to needle someone qualified into improving the explanation.
I am bringing this up because I've seen a significant amount of discussion of level-triggering versus edge-triggering. Once you have properly separated out transport logic from application implementation, triggering style is an irrelevant, private implementation detail of the networking layer. Whether the operating system tells Python "you must call recv() once now" or "you must call recv() until I tell you to stop" should not matter to the application if the application is just getting passed the results of recv() which has already been called. Since not all I/O libraries actually have a recv() to call, you shouldn't have the application have to call it. This is perhaps the central design error of asyncore.
If it needs a name, I suppose I'd call my preferred style "event triggering".
Also, I would like to remind all participants that microthreading, request/response abstraction (i.e. Deferreds, Futures), generator coroutines and a common API for network I/O are all very different tasks and do not need to be accomplished all at once. If you try to build something that does all of this stuff, you get most of Twisted core plus half of Stackless all at once, which is a bit much for the stdlib to bite off in one chunk.
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