gh-111956: Add thread-safe one-time initialization.

[colesbury]

The one-time initialization (_PyOnceFlag) is used in two places:

• Python/Python-ast.c
• Python/getargs.c

• Issue: Thread-safe one-time initialization #111956

[colesbury]

@ericsnowcurrently, when you have some time, would you please look at this?

One question: I'm unsure of what int value should be used here to indicate an error or success. I have gone with 0=error and 1=success here because that requires fewer modifications to the use sites, which already use that convention. I am unsure if -1=error, 0=success would be better.

[ericsnowcurrently]

Aside from one small thing, LGTM.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[ericsnowcurrently]

I'm unsure of what int value should be used here to indicate an error or success. I have gone with 0=error and 1=success here because that requires fewer modifications to the use sites, which already use that convention. I am unsure if -1=error, 0=success would be better.

The typical convention in the case of success vs. error is -1 for error and 0 for success. The 0/1 convention is more for true/false situations.

[colesbury]

@ericsnowcurrently that makes sense. I'll change it to -1=error, 0=success.

[colesbury]

@ericsnowcurrently, I changed the code to use -1=error 0=success and updated asdl_c.py/Python-ast.c. It ended up being a large change to that file, but fixed one bug where we ignored errors in init_identifiers due to a mismatch in return code assumptions.

[ericsnowcurrently]

LGTM

FWIW, I haven't combed through the asdl_c.py changes but would expect the test suite to catch any mistakes in there. It's also a good sign that you caught the bug in init_identifiers(). 😄

[ericsnowcurrently]

I'll merge this in the morning if no one beats me to it.