classification
Title: An attempt to make asyncio.transport.writelines (selector) use Scatter I/O
Type: enhancement Stage:
Components: asyncio Versions: Python 3.9
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: asvetlov, tzickel, yselivanov
Priority: normal Keywords:

Created on 2020-03-18 21:00 by tzickel, last changed 2020-03-19 06:47 by tzickel.

Pull Requests
URL Status Linked Edit
PR 19062 open tzickel, 2020-03-18 21:00
Messages (2)
msg364565 - (view) Author: (tzickel) * Date: 2020-03-18 21:00
I have a code that tries to be smart and prepare data to be chunked efficiently before sending, so I was happy to read about:

https://docs.python.org/3/library/asyncio-protocol.html#asyncio.WriteTransport.writelines

Only to see that it simply does:

self.write(b''.join(lines))

So I've attempted to write an version that uses sendmsg (scatter I/O) instead (will be attached in PR).

What I've learnt is:
1. It's hard to benchmark (If someone has an good example on checking if it's worth it, feel free to add such).
2. sendmsg has an OS limit on how many items can be done in one call. If the user does not call writer.drain() it might have too many items in the buffer, in that case I concat them (might be an expensive operation ? but that should not be th enormal case).
3. socket.socket.sendmsg can accept any bytes like iterable, but os.writev can only accept sequences, is that a bug ?
4. This is for the selector stream socket for now.
msg364595 - (view) Author: (tzickel) * Date: 2020-03-19 06:47
BTW, if wanted a much more simpler PR can be made, where writelines simply calls sendmsg on the input if no buffer exists, and if not only then concats and acts like the current code base.
History
Date User Action Args
2020-03-19 06:47:39tzickelsetmessages: + msg364595
2020-03-18 21:00:01tzickelcreate