CLASP for MPS; multithreading & GC questions

Thanks to Chris, I managed to compile CLASP for MPS.

I have a question about MPS scanning. MPS folks (Gareth, in CC) told me that the scanning routine (see https://www.ravenbrook.com/project/mps/master/manual/html/topic/scanning.htm... for more) is called asynchronously, even from some SIGSEGV signal handler.

How do you manage that in CLASP?

A concrete use case might be some std::set of Common Lisp symbols. How would you scan it? You cannot expect the scanning routine to get that std::set in a coherent state .... so using C++ iterators could break things.

Any concrete code pointer to CLASP source (or generated C++) code for scanning is welcome!

Regards.