… waitpid().
My use case was when testing gimp_brush_select_new(). When doing tests,
if I let the brush dialog opened while letting the plug-in exit cleanly
otherwise, it somehow locked the process (I have stared so long at the
code and still don't understand why).
gimp_plug_in_close() would wait for it forever and the only way out was
to kill GIMP completely. I guess we could try to run waitpid() with
WNOHANG (and finally force-kill the child if it really won't exit) but
it made the whole logics extra complicated.
The logics with g_child_watch_add_full() is that we don't stop waiting
for the child and just set a callback to finalize what needs to be. Now
the worst case scenario would be to leave zombie processes dangling
around, but it's better than freezing GIMP.
Finally as a weird side effect, doing this change even unblocked the
process with an unfinished brush selector so we don't even have a zombie
anymore (at least for this specific case). All good in the end!
Last side effect: it can speed up a tiny bit the plug-in close as we
don't wait for processes anymore, which could be more visible at first
startups (when we reload all the plug-ins). Though there is nothing
scientific to my numbers, after multiple "first startups", it seems it
went down from about 3.5 to 3.2 seconds on my specific machine. Nothing
extra fancy, but we take what we can (and speeding up the startup was
never the goal of this change anyway). It doesn't affect Windows which
has its own logics to handle process termination and I preferred not to
touch it.
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