Concurrency fix and efficiency improvement at low srate from jfrey-xx

[chkothe]

This is a merger of #70 along with the queue fix from #71 (and some tweaks).

[tstenner]

So far, looking good. The locking seems fine to me and the benchmark that exhibited the crash / infinite loop runs through just fine.
Two things: there are a bunch of indentation changes that make it hard to see what changed (or who changed a line last with git blame) and the commit authorship didn't survive the rebasing.

I've split the PR into two commits (@jfrey-xx's changes and yours) and once the CI is happy I'll merge it.

[jfrey-xx]

Thanks a lot for bringing in the changes! It will for sure help a lot here :) Very minor remark, but since I noticed it: in the changelog from tstenner@340d517 I believe that the race condition is actually from #71 ^^

[tstenner]

Thanks a lot for bringing in the changes! It will for sure help a lot here :) Very minor remark, but since I noticed it: in the changelog from tstenner@340d517 I believe that the race condition is actually from #71 ^^

fixed

[chkothe]

Ah sorry, my editor was still set to indent with 4 spaces instead of tabs.