worker: POSIX only supports workers from main thread (issue6460)...
worker: POSIX only supports workers from main thread (issue6460)
The POSIX backend sets signal handlers for SIGINT (maybe avoidable) and
SIGCHLD (necessary for waitpid). Python up to 3.9 only allow this from
the main thread, so disable the worker feature otherwise.
Differential Revision:
https://phab.mercurial-scm.org/D9660
