I've started adding support for using this library for memory primitives and some basic lock-free data structures. http://concurrencykit.org/ Of course when threads are not used, we need some replacement. All the memory barriers and assignments become trivial and locks disappear so the no-threading variant is trivial to implement. My question now is whether to call ck_* functions directly from PETSc source or to always wrap them in Petsc* namespaced macros and inline functions. I would normally always use a Petsc namespace for this kind of thing, but this library has convenient man pages and is, I think, the best thing out there for implementing these primitives. Wrapping everything in a Petsc* namespace would thus make it less direct to get down to the actual semantics (or a man page). Thus I have half a mind to treat it like MPI and just provide non-threaded implementations in petscck.h when !defined(PETSC_HAVE_CONCURRENCYKIT). Is this a bad idea?