> Don’t use Objective-C/Swift on the audio thread.

His argumentation is that Objective-C uses locks internally.

But isn't it possible that those locks (as opposed to application-level locks) cause just negligible pauses, because there's no contention on them?

I guess those internal locks exist to make ObjC's runtime dynamism feasible. One would expect the typical application to not leverage that dynamism (how many apps continously redefine methods under normal operation?).