Curiously Recurring Thoughts

Why co_yield ?

co_yield allows us to return a sequence of values to the caller as opposed to co_return where we return only one element. Let’s see an example first, we will be using, as before, Microsoft Visual Studio 2019, with option /await and the preview of the latest standard as language version (see this previous post for more details). MSVC has some handy extensions (i.e.

What is a Coroutine?

A normal function (routine) can only be invoked. Once the function has completed its duty, it returns, its local variables are destroyed (not entirely true, e.g. because of static, but bear with me) and the caller can continue from where it left. The caller can also use the values the function has returned or exploit the side-effects the routine has generated.

What is a mutex?

Before talking about mutexes we need to understand what they are trying to fix. Consider this sum: void add(int& num1, const int& num2) { num1 += num2; } And the corresponding assembly add(int&, int const&): mov eax, DWORD PTR [rsi] add DWORD PTR [rdi], eax ret The increment is at least 2 instructions, first we load num2 from memory to a CPU register (eax) and then we add it to num1, writing the result back to memory.