That's...not precisely true. The C++ standard doesn't specify how std::async works, and for a while GCC just ran the operation sequentially, and later both GCC

That's...not precisely true. The C++ standard doesn't specify how std::async works, and for a while GCC just ran the operation sequentially, and later both GCC and Clang launched new OS threads by default. https://stackoverflow.com/q/10059239/1858225 https://stackoverflow.com/q/10059239/1858225