Before introducing the service map and using it for folder runners, the
entries in folderCfgs and folderRunners for the same key/folder were
removed under a single lock. Stopping the folder happens separately
before that with just the read lock. Now with the service map stopping
the folder and removing it from the map is a single operation. And that
still happens with just a read-lock. However even with a full lock it’s
still problematic: After the folder stopped, the runner isn’t present
anymore while the folder-config still is and sais the folder isn't
paused.
The index handler in turn looks at the folder config that is not paused,
thus assumes the runner has to be present -> nil deref on the runner.
A better solution might be to push most of these fmut maps into the
folder - they anyway are needed in there. Then there's just a single
map/source of info that's necessarily consistent. That's quite a bit of
work though, and probably/likely there will be corner cases there too.
Instead of separately tracking the token.
Also changes serviceMap to have a channel version of RemoveAndWait, so
that it's possible to do the removal under a lock but wait outside of
the lock. And changed where we do that in connection close, reversing
the change that happened when I added the serviceMap in 40b3b9ad1.
