[Python-ideas] PEP 3156 / Tulip question: write/send callback/future

[Guido van Rossum]

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. :-)

> Should there be no "data_sent" parallel to "data_received" 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 async_write.

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 .pause_writing()
and .resume_writing().) There are some default behaviors that we can
add here too, e.g. suspending the task.

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