When we originally wrote MONGO_MAKE_LATCH here, we considered various macros to accept information from wrapping classes. We eventually decided against this tact in favor of simplicity. We now think it might be worthwhile to absorb this information, especially when the class that needs a mutex is templated. This will require a new macro ala MONGO_MAKE_LATCH_FOR_TYPE that passes its captured type as a template to the registry macro in some form. That macro will need to be able to invoke a unique template instantiation to achieve registry, which means an extra type in its template.