Multi-processor Compilation and #import directive

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Multi-processor Compilation and #import directive

Peter Boulton 21

I've just built a new dev box, which has a 12 core processor. I understand that it's possible to tell the compiler to use multi-processors on the C++/General page.

However, #import is not supported with this option and generates C2813 errors. I've read somewhere that it's possible to have these files compiled with a single processor whilst the remaining files, which don't contain #import, benefit from the multiprocessor compilation.

In the Visual Studio 2019 Property Pages for a C++ project, how do you specify that certain source files (the ones that contain #import...) are compiled with /MP1 while everything else is compiled with /MP?

Or can this only be achieved outside of the GUI (and please excuse my ignorance)... how?

TIA

Pete

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Answer 1

David Lowndes 4,726

Try selecting the individual file(s) that have #import in Solution Explorer and changing the /MP option for just those files.

Peter Boulton 21 Reputation points

2021-05-28T09:17:41.573+00:00
Ah thank you! I have a feeling I rather missed the obvious there. :-( Appreciate the response.

Now, unfortunately, I find that nearly all the source files in my rather large project #include or depend on files that ultimately contain #import, and therefore need to be exceptions! Back to single core compiles! In my solution, the issue traces back to:

#import "C:\program files\common files\system\ado\msadox.dll" #ifdef _WIN64 #import "C:\program files\common files\system\ado\msado15.dll" rename("EOF","EndOfFile") #else #include "msado15.tlh" #endif // #import "C:\Program Files\Common Files\System\ado\msjro.dll" no_namespace #pragma warning (default: 4146)

I'm not sure whether there is a solution that would work round this issue for me.

Many thanks again!
David Lowndes 4,726 Reputation points

2021-05-28T09:33:22.763+00:00

I can't think of any magic bullet Peter. Presumably you'd have to re-arrange your code to minimize that dependency as much as possible. Whether you'd see any significant gain over the time taken to do so, is questionable.
Peter Boulton 21 Reputation points

2021-05-28T10:02:20.687+00:00

Hi David,

Many thanks for responding (again) so quickly and helpfully.

When I was compiling with /MP and was getting all the C2813 errors I would certainly say the Output window was flowing through much faster than without the /MP option, although that may have been because compilation stops when it hits C2813, and there were a lot of them!

It's a shame - I have built a lovely new machine with a Ryzen 5900X with 12 cores/25 virtual and all I can use is one of the cores! Maybe in the future.... :-)

Thanks again!

Pete

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Multi-processor Compilation and #import directive

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