[build2] GCC modulemap informations

[Arthur Laurent]

Thx for these informations, it will help me a lot :)

Le 01/12/2023 à 11:07, Boris Kolpackov a écrit :
> Arthur Laurent via users <users at build2.org> writes:
>
>> i see you have implemented this, but i don't understand how it work exactly
>> inside your build process can i have some precision on how it is implemented
>> if possible ? do you use sockets or pipes ?
> We use pipes, more precisely compiler's stdin/stdout (this allows the user
> to replay the interaction for debugging, etc).
>
>
>> the module mapper server is a thread of build2 ? an external process ?
> build2 is a multi-threaded build system with each rule performing its
> job in a thread. So the rule handles the module mapper communications
> directly in this thread. To put it another way (and simplifying a bit),
> a C/C++ compile rule without the module mapper spawns the compiler
> process and simply blocks waiting for it to finish. With the module
> mapper it instead reads the mapper requests and sends responses. You
> can find the code in build2/libbuild2/cc/compiler-rule.cxx; search
> for gcc_module_mapper and you will find all the relevant places.
>
>
>> and is it really better than file based API ?
> The static module mapper is basically a tidier equivalent of passing
> the module to BMI mapping information on the command line. The main
> difference compared to the dynamic mapper is that you have to have this
> information and the BMIs ready ahead of starting the compiler, which is
> not possible[*], at least not for header units. The dynamic mapper allows
> you to discover this information and produce the BMIs during compilation.
>
> Whether it's better I guess depends on what you are trying to achieve.
> In build2 we use both for different purposes. Specifically, we use
> the dynamic mapper to handle header units and static mapper to handle
> named modules.
>
> [*] To be precise, it is possible but one would need to implement textual
> inclusion with the header unit importation semantics. So far, only Clang
> has something like this with MSVC reportedly unlikely to be able to
> support this directly in the compiler. For background, see:
>
> https://developercommunity.visualstudio.com/t/scanDependencies-does-not-take-into-acc/10029154