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

[Yury Selivanov]

On 2016-10-07 1:31 PM, Giampaolo Rodola' wrote:
> On Fri, Oct 7, 2016 at 6:52 PM, Yury Selivanov <yselivanov.ml at gmail.com>
> wrote:
>
>> On 2016-10-07 11:16 AM, Guido van Rossum wrote:
>>
>> Maybe a simpler approach would be to write a linter that checks for a
>>> known list of common blocking functions, and anything that calls those
>>> automatically gets the same property?
>>>
>> What if somebody uses logging module and logs to a file?  I think this is
>> something that linters can't infer (how logging is configured).
>>
>> One way to solve this would be to monkeypatch the io and os modules
>> (gevent does that, so it's possible) to issue a warning when it's used in
>> an asyncio context.  This can be done as a module on PyPI.
>>
>> Another way would be to add some kind of IO tracing hooks to CPython.
>
> How about something like this?
> http://www.tornadoweb.org/en/stable/ioloop.html#tornado.ioloop.IOLoop.set_blocking_signal_threshold
>

Yes, we already have a similar mechanism in asyncio -- 
loop.slow_callback_duration property that is used in debug mode. The 
thing it isn't really precise, as you can have a lot of relatively fast 
blocking calls that harm performance, but complete faster than 
slow_callback_duration.

Yury