[Python-ideas] PEP 3156 / Tulip question: write/send callback/future (original) (raw)

Eli Bendersky eliben at gmail.com
Fri Jan 18 22:40:44 CET 2013

On Fri, Jan 18, 2013 at 1:02 PM, Guido van Rossum <guido at python.org> wrote:

On Fri, Jan 18, 2013 at 6:56 AM, Eli Bendersky <eliben at gmail.com> wrote: > I'm looking through PEP 3156 and the Tulip code, and either something is > missing or I'm not looking in the right places. > > I can't find any sort of callback / future return for asynchronous writes, > e.g. in transport.

I guess you should read some Twisted tutorial. :-)

Yes, I noticed that Twisted also doesn't have it, so I suspected that influence.

> Should there be no "datasent" parallel to "datareceived" somewhere? Or, > alternatively, "write" returning some sort of future that can be checked > later for status? For connections that aren't infinitely fast it's useful to > know when the data was actually sent/written, or alternatively if an error > has occurred. This is also important for when writing would actually block > because of full buffers. boost::asio has such a handler for asyncwrite. The model is a little different. Glyph has convinced me that it works well in practice. We just buffer what is written (when it can't all be sent immediately). This is enough for most apps that don't serve 100MB files. If the buffer becomes too large, the transport will call .pause() on the protocol until it is drained, then it calls .resume(). (The names of these are TBD, maybe they will end up .pausewriting() and .resumewriting().) There are some default behaviors that we can add here too, e.g. suspending the task. I agree it can be made to work, but how would even simple "done sending" notification work? Or "send error" for that matter? AFAIR, low-level socket async API do provide this information. Are we confident enough it will never be needed to simply hide it away?

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