[eMSF]

Related to this, GNU's libstdc++ shared_ptr implementation actually opts not to use atomic arithmetic when it infers that the program is not using threads.

[menaerus]

I never heard of this and went to check in the source and it really does exist: https://codebrowser.dev/llvm/include/c++/11/ext/concurrence....

[aw1621107]

The code you linked is a compile-time configuration option, which doesn't quite match "infer" IMO. I think GP is thinking of the way that libstdc++ basically relies on the linker to tell it whether libpthread is linked in and skips atomic operations if it isn't [0].

[0]: https://snf.github.io/2019/02/13/shared-ptr-optimization/