Need a way to subscribe to DriverWarning as events with a callback

[vnktshr21]

With warnings.warn, if users have to asynchronously process driver warnings, then they need to override the warnings.showwarning function with a custom handler which would process driver warnings differently. This implies a global override, more things for users to maintain and a possibility of not handling certain other warnings in the application correctly. Would be good to have a warning event mechanism built into driver session which the users can subscribe to, by passing a callback function. This event mechanism can co-exist with the current warnings.warn. This way, users can adopt whatever approach makes sense for the application.

ie:

• if they want to raise exceptions for warnings, then they can simply do
  warnings.simplefilter("error", DriverWarning)
• if they want to asynchronously handle warnings without stopping the execution flow, then they can do
  session.warning_event.subscribe(driverwarninghandler(DriverWarning)) and define

def driverwarninghandler(DriverWarning):
    <log to file, set a flag, push to a queue, raise few warnings and ignore others, etc>

[bkeryan]

It sounds like warnings.catch_warnings() may be thread-safe in future versions of Python:
https://discuss.python.org/t/thread-safe-warning-filters/76074/10

[vnktshr21]

Along with thread-safe override option, it would help if warnings.showwarning could be overridden for a specific class of warning, even if its going to be a global override. That would work for the use case I've mentioned and would not need us to have an additional warning event mechanism in nimi-python. Could not find any issue/discussion already for this. Created a discussion topic.

[ni-jfitzger]

@vnktshr21 Is asynchronous handling actually useful?
Do you know of specific warnings where it's okay to handle things that way?

When I think of warnings, I think of things like the PLL coming unlocked and possibly invalidating data. That's not the sort of thing where I'd want to keep going.