[Python-Dev] PEP 3156 - Asynchronous IO Support Rebooted (original) (raw)

Guido van Rossum guido at python.org
Sat Jan 5 05:51:58 CET 2013

On Fri, Jan 4, 2013 at 8:19 PM, Glyph <glyph at twistedmatrix.com> wrote:

On Jan 4, 2013, at 3:56 PM, Guido van Rossum <guido at python.org> wrote:

On Mon, Dec 24, 2012 at 2:58 PM, Glyph <glyph at twistedmatrix.com> wrote: In my humble (but entirely, verifiably correct) opinion, thinking of this as a "default" is propagating a design error in the BSD sockets API. Datagram and stream sockets have radically different semantics. In Twisted, "dataReceived" and "datagramReceived" are different methods for a good reason. Again, it's very very easy to fall into the trap of thinking that a TCP segment is a datagram and writing all your application code as if it were. After all, it probably works over localhost most of the time! This difference in semantics mirrored by a difference in method naming has helped quite a few people grok the distinction between streaming and datagrams over the years; I think it would be a good idea if Tulip followed suit.

Suppose PEP 3156 / Tulip uses datareceived() for streams and datagramreceived() for datagram protocols (which seems reasonable enough), what API should a datagram transport have for sending datagrams? writedatagram() and writedatagramlist()? Twisted just have a different method called write() which has a different signature (data, address). Probably writedatagram is better. Why writedatagramlist though? Twisted's writeSequence is there to provide the (eventual) opportunity to optimize by writev; since datagrams are always sent one at a time anyway, writedatagramlist would seem to be a very minor optimization.

That makes sense (you can see I haven't tried to use UDP in a long time :-).

Should write_datagram() perhaps return a future? Or is there still a use case for buffering datagrams?

-- --Guido van Rossum (python.org/~guido)

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