[Python-ideas] Flagging blocking functions not to be used with asyncio

[Martin Teichmann]

Hi,

> Honestly before writing a lot of code here I'd like to hear more from
> Martin about the spread of mistakes he's observed among his users.

Over the weekend, I tried to classify the mistakes I found. Most of
the times, it's something like "I'm just doing a quick lookup on the
database, that shouldn't be a problem". For people coming from a
threading background, this are indeed fast operations, they don't
consider such calls as blocking. In the end, it all boils down to some
read operation down in some non-asyncio code.

This is why I got my idea to flag such calls. Unfortunately, I
realized that it is nearly impossible to tell whether a read call is
blocking or not. We would need to know whether the file descriptor we
read from was created as non-blocking, or whether it was an actual
file, and how fast the file storage is for this file (SSD: maybe fine,
Network: to slow, magnetic disk: dunno). All of this is unfortunately
not a Python issue, but an issue for the underlying operating system.

So I guess I have to tell my users to program carefully and think
about what they're reading from. No automatic detection of problems
seems to be possible, at least not easily.

Greetings

Martin