CODEWITHSUNDEEP
c++windowswinapishared-memory
Chris D
Chris D

Reputation: 75

Memory Mapped Files - Map a structure not a file?

I'm very new to Memory Mapped Files, and I'm a little lost on something.

I know that if I had a file, I could load it and access it from various processes at once using MMaps.

But in my situation, I'm creating a DLL attached to Process A, and that DLL has been given a pointer to a cSurface which Process A has prepared. I need to share that cSurface's data with Process B. I really don't want to have to call up a blank MMap and copy my Process A's surface into it, only to copy it out again in process B.

Is it possible to map my surface as if it were a file so the MMap already points to the surface data when it's created (as it would were I loading SomeTextFile.txt)?

My plan, in theory, would be to receive a pointer to the surface in Proc A, tell windows to share that surface's memory with a given name, and use Mutexes to coordinate access - the idea being that both processes read the same physical copy of the surface with no cumbersome copying.

Is that possible?

Upvotes: 3

Views: 1105

Answers (2)

Chris D
Chris D

Reputation: 75

Thanks for all your comments.

I did some further research and found the answer.

You can use Memory Mapped Files to share either a file, or a blank memory space. If you want to share data already initialised in memory prior to setting up the map, you have to create a blank map and subsequently copy your data into it.

Upvotes: 1

user707582
user707582

Reputation:

Yes, it's all there in the documentation of CreateFileMapping.

You can give your memory mapped file a name. If another process open a mmap with the same name it will point to the same memory. It the handle in CreateFileMapping is put to INVALID_HANDLE_VALUE it keeps it purely in memory. Check the documentation of CreateFileMapping

Upvotes: 2

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