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Description
Bug report
Bug description:
Currently, "pre-finalization" (callbacks executed while the interpreter is still fully intact) looks like this:
Lines 2023 to 2038 in642e5df
| wait_for_thread_shutdown(tstate); | |
| // Make any remaining pending calls. | |
| _Py_FinishPendingCalls(tstate); | |
| /* The interpreter is still entirely intact at this point, and the | |
| * exit funcs may be relying on that. In particular, if some thread | |
| * or exit func is still waiting to do an import, the import machinery | |
| * expects Py_IsInitialized() to return true. So don't say the | |
| * runtime is uninitialized until after the exit funcs have run. | |
| * Note that Threading.py uses an exit func to do a join on all the | |
| * threads created thru it, so this also protects pending imports in | |
| * the threads created via Threading. | |
| */ | |
| _PyAtExit_Call(tstate->interp); |
Threads are joined first, then pending calls are executed, and finally atexit callbacks are executed. The problem is that any of these three can create one another, such as a pending call creating a thread, or an atexit handler scheduling a pending call. The best way to demonstrate this is by creating a new thread inside of an atexit callback:
importatexitimportthreadingimporttimedefrun():print(24)time.sleep(1)print(42)@atexit.registerdefstart_thread():threading.Thread(target=run).start()
On 3.13+ (and probably earlier), you'll get one of these three outputs:
24is printed.- Nothing is printed.
- A fatal error occurs due to the stdout lock being unavailable.
This is because the thread created is incorrectly non-daemon, because the call tothreading._shutdown (which should join it) has already happened.
@ericsnowcurrently, I discussed this with you at the PyCon sprints. I think we came to the agreement that the best way to fix this is by looping until all three of them execute no callbacks.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux