> Well, after fork, all threads have exited, so you'll be running on the
> behalf of the child process' main - and only - thread, so by
> definition you can't access other threads' thread-specific data, no?

A rather good point :)
How about deleting the mapping (pthread_key_delete) and recreating it
from scratch, then?

> As an alternate solution, I was thinking of calling
> PyThread_delete_key_value(autoTLSkey) in the path of thread bootstrap,
> i.e. starting in Modules/_threadmodule.c t_bootstrap.

That would somewhat alleviate the problem, but only for Python-created
threads. Threads created through other means (for example mod_wsgi, or
database wrappers having their own thread pools) would still face the
original issue.