Use a single APC and completion routine

[LeonarddeR]

Link to issue number:

Related to #14899, #14312, #14627
Fixes #14895

Summary of the issue:

Despite several attempts to fix this, NVDA's IoThread can crash without a clear cause.

Description of user facing changes

Less crashes, most likely, as tests indicate that this is the case.

Description of development approach

As proposed by @jcsteh , rather than creating a new function pointer for every APC or completion routine call, use a single internal APC and completion routine and use an internal cache to store the python functions, not the actual APC functions.

Testing strategy:

Steps to reproduce from #14895.

Known issues with pull request:

None known

Change log entries:

Deprecations:

• IoThread.autoDeleteApcReference is deprecated. It was introduced in NVDA 2023.1 and was never meant to be part of the public API. Until deprecation, it behaves as a no-op, i.e. a context manager yielding nothing.

Code Review Checklist:

• Pull Request description:
  • description is up to date
  • change log entries
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• API is compatible with existing add-ons.
• Documentation:
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• Security precautions taken.

[LeonarddeR]

@MarcoZehe Could you please give this try build a spin?

[MarcoZehe]

@LeonarddeR Obtained it and am currently running it off the installer, without installing it first. Should that be enough, or does it need elevated privileges somewhere to test this properly?

[LeonarddeR]

I don't think elevated privileges are necessary for your test case.

[LeonarddeR]

I used this build without crashes today. Let's mark it ready for review.

[MarcoZehe]

FWIW, I can definitely also confirm that this PR fixes the problem. With a regular alpha build, and working in Firefox or Thunderbird, especially in text fields, I get these crashes several times per day, sometimes even several per hour. With the try build, none of those. This definitely takes care of the issue I was having.

[ruifontes]

Also agree!
Using Windows 11 22h2, a HT Basic Braille Plus.

[seanbudd]

Thanks @LeonarddeR , the approach generally looks good to me, I have some concerns in regards to API backwards compatibility.