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a simple mutex will never be wait free and as such is never appropriate where a wait free data structure is required (it is not about performance).

Maybe not but I can count on one hand the number of times I've truly needed that property. Compare to a try-lock or a timed lock for example.

In soft/firm/hard real-time, we can't use mutexes at all. Lock/wait-free is our bread and butter.

Did you mean to include "soft" there? And I've never heard of "firm" real time.