Documentation for os.environ should say that os.environ caching behavior is undefined if other threads are setting environment values

Documentation

It says here:

This mapping is captured the first time the os module is imported, typically during Python startup as part of processing site.py. Changes to the environment made after this time are not reflected in os.environ, except for changes made by modifying os.environ directly.

It should mention the caveat that such cashing would cause undefined behavior or/and crashes when other threads would be setting environment values. This would be true at least on Linux and FreeBSD.

The same should be mentioned in the documentation of the function that initializes the Python interpreter and caches environment.

These functions are not thread-safe.

Linked PRs

• gh-152979

Review the os.environ documentation linked in the issue and the documentation for the interpreter-initialization function that caches the environment. Compare the requested thread-safety caveat with linked PR gh-152979. Done means both relevant documentation areas accurately describe the behavior when other threads modify environment values.