[Python-Dev] Issue #8863 adds a new PYTHONNOFAULTHANDLER environment variable

["Martin v. Löwis"]

>> The GIL is likely held by a different thread, then.
>> _PyThreadState_Current will point to the state of this other thread.
> 
> I tested when the GIL released: the fault handler is unable to retrieve "the" 
> thread state and so the backtrace is not printed. Which thread state should be 
> retrieve? I don't know yet: maybe the last active thread state?
> 
> It doesn't look trivial to fix this issue because if there is no thread (only 
> the main thread), release the GIL clears the thread state pointer (to it to 
> NULL) without storing it somewhere else (whereas with multiple threads, the 
> last active thread is stored in "gil_last_holder". I should ask Antoine (or 
> someone one) how the new GIL works.

I don't think this is possible to fix. Just put a sleep() call before
the crash, and have a parallel thread perform a while-loop to see what
I mean: it should give you a stack trace of the wrong thread, possibly
touching transient objects which go away while you inspect them.

> Another variable might be created to store the (pointer to the) last active 
> thread state.

Please understand: the last active thread may not be the one that got
the signal. Instead, it may be another thread that keeps running while
your thread crashes.

Regards,
Martin