An interpreter can start running during `_interpreters.destroy`

Crash report

What happened?

Now that gh-126914 is out of the way, we can try and deal with some of the other issues related to multithreading and subinterpreters that couldn't get dealt with before. Namely, the is_running_main inside _interpreters.destroy doesn't account for the fact that the interpreter could start running again by another thread after that check has already passed.

Quick reproducer:

from threading import Thread
import _interpreters

interp = _interpreters.create()


def run():
    _interpreters.run_string(interp, "1")
    _interpreters.destroy(interp)


threads = [Thread(target=run) for _ in range(1000)]
for thread in threads:
    thread.start()

for thread in threads:
    thread.join()

I think the simplest fix would be to just disallow a subinterpreter from ever set "running main" again after that check has finished. I implemented this already in the (closed) gh-126696, but I'd like to try and refactor that a bit before just copying things over to a new PR.

cc @ericsnowcurrently, let me know if you have a better approach.

CPython versions tested on:

3.13, 3.14, CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

No response

Linked PRs

• gh-127044

从 _interpreters.destroy 路径及其 is_running_main 检查开始，然后使用 _interpreters.run_string 和 _interpreters.destroy 运行 1,000 线程复现程序。查看链接的 PR gh-127044 以及所引用的已关闭 gh-126696；完成的标准是复现程序不再允许解释器在销毁期间开始运行。