Correction to comment in prev commit (and removing it here):
spec.loader.exec_module does not spawn new threads, it simply
executes the module in the current thread.
I got confused but turns out "load_plugin" itself is sometimes
not called from the main thread. Specifically (e.g.), since the recent
wizard rewrite, in the qt gui, the wizard loads the hww plugins
from a new thread.
This now better explains the macos hww crashes: they had started
appearing because we upgraded hidapi (which made it more sensitive
to having to import from main thread) AND scanning(->importing) from
the wizard no longer happened on the main thread after the rewrite.
Plugins should be thread-safe in terms of where they are imported from.
Let's log the importer thread's name (added here), to help recognise
related threading issues.
b5d8d31723