#define CALLING_CONVENTION [calling convention]
No return value.
It is possible for the calling convention for a thread function to differ from the default the compiler is using to compile the code. This is the case under Windows. Accordingly, it is necessary to have a define which indicates the calling convention for the thread prototype.
On Windows, with the Microsoft C compiler, the calling convention for a thread function is WINAPI (this is a define which turns into __stdcall).
As such, the implementation of CALLING_CONVENTION on Windows with the Microsoft C compiler looks like this;
#define CALLING_CONVENTION WINAPI
Under GCC, the default calling convention is used and as such, the define is not set, e.g.;