[Security-sig] PEP 522: Allow BlockingIOError in security sensitive APIs on Linux

[Donald Stufft]

> On Jun 23, 2016, at 8:33 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> 
> The argument chain runs:
> 
> - if such software doesn't exist, it doesn't matter which behaviour we choose
> - if we're wrong and it does exist, we can choose how it fails:
>  - blocking (with associated potential for init system deadlock)
>  - throwing an exception
> 
> Given the choice between debugging an apparent system hang and an
> unexpected exception when testing against a new version of a platform,
> I'll choose the exception every time.


I think the biggest argument to blocking is that there really exist two sort of situations that blocking can happen in:

* It blocks for a tiny amount (maybe <1s) and nobody ever notices and people feel like things “just work”.
* It blocks for a long amount of time (possibly forever depending on where in the boot sequence Python is being used) and it hangs for a long time (or forever).

In the second case I think it’s pretty obvious that an exception is better than hanging forever, but in the first case an exception might actually cause people to go out of their way to do something bad to “stop the pain”. My personal preference is waffling back and forth between them based on which of the two above I feel are more likely to occur in practice.

—
Donald Stufft