So, your pauseless GC pauses or requires some form of resource contention (probably mutex-based) to share the state. It's not possible to have a pauseless GC in thread per core, which immediately rules it out for HPC. These are the types of things that the "GC for everything" crowd admits that they don't understand when making such statements.
I misunderstood you. State is shared by mutator threads using atomic::store(memory_order_release). SGCL never stops threads and does not use locks to share state.
