std.functional.memoize : thread local or __gshared memoization?

[Timothee Cour via Digitalmars-d]

I could look at source to figure it out but others might wonder and I
couldn't find it in the docs in
https://dlang.org/library/std/functional/memoize.html whether memoize
works per thread (thread local) or globally (__gshared)