Deca does deal with SMP and concurrency in one way: module-level variables are tagged thread-local in the bitcode by default, at least if they're mutable.

Once the "newsig" branch (it's a rewrite from scratch after the original code had troubles with multi-module compilation) with the new signature system (region, effect, type, mutability) can compile some example code again, I'm merging it back into the main branch.