Swift standard library on platforms without threading support?

[Max_Desiatov]

@Joe_Groff

For that specific issue, though, it is incorrect to avoid using <atomic> in a single-threaded system; I'm not sure why that #if is there. <atomic> is still meaningful for a single-threaded system for atomicity relative to signals and other preemption mechanisms.

Well, that's what libcxx has there at the moment ¯\_(ツ)_/¯

I'm not quite sure though if signals make any sense on WebAssembly or AVR, especially if programs for the latter are supposed to run on bare metal?

What would be the best approach for this then? My initial plan was to do something like

#ifndef __wasm__ 
#include <atomic> 
#endif

in Swift runtime headers and to reimplement all users of <atomic> with a nonatomic #ifdefed version? Or maybe it's worth implementing something like SingleThreadedAtomic.{h,cpp} that would stub all required atomic primitives with single-threaded "no-op" implementation?