[Python-Dev] asyncore fixes in Python 2.6 broke Zope's version of medusa

glyph at divmod.com glyph at divmod.com
Fri Mar 6 00:11:49 CET 2009

On 07:30 pm, nas at arctrix.com wrote:
>Chris McDonough <chrism at plope.com> wrote:
>>As far as I can tell, asyncore/asynchat is all "undocumented
>>internals".  Any use of asyncore in anger will use internals;
>>there never was any well-understood API to these modules.

>The implementation requires some intricate and platform specific
>code which is why it would be nice to be a standard library feature.
>I'm sure that Twisted has the necessary parts but the problem, IMHO,
>is that it does so much more else.

... which is exactly why I have volunteered to explain to someone how to 
separate the core event-loop bits (suitable for inclusion in the 
standard library) from the huge pile of protocol implementations which 
are not necessarily useful.

Despite the FUD to the contrary, Twisted's internal factoring is quite 
good; it's not a single, undifferentiated pile of code.  Plus, at this 
point, we're not even talking about actually putting any Twisted code 
into the standard library, just standardizing the "protocol" API, which 
basically boils down to:

  connectionMade() -> your connection has begun
  dataReceived(data) -> you got some bytes, handle them
  connectionLost(reason) -> your connection has gone away (with an object 
explaining why)

and the inverse, "transport", which is:

  write(data) -> deliver some data to the dataReceived on the other end 
of this connection (non-blocking, with buffering)
  loseConnection() -> goodbye

There are a few other minor details related to how you set these up to 
talk to each other and tell when the out-buffer is empty, but it's all 
pretty straightforward.  The main point is that you don't ever call 
recv() or send() and deal with buffering or handling weird errno values. 
For example, if your connection goes away, the notification you get is 
"your connection went away", not "oops you tried to read some bytes, but 
your connection was gone by the time you tried, even though I just told 
you it was ready for reading" or other similarly obtuse failure modes.

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