How to share a big byte array between C++ and C#

Question

I need to share a huge (many megabytes) byte array between a C++ program residing in a DLL and a C# program.

I need realtime performance, so it is very important I can share it between the two in an efficient way, so making a new copy for it in C# every time after the data is manipulated in C++ is not an option, yet the examples I have found so far seems to depend on this.

Is it possible to share the array in an efficient way? And if so, how?

Answer 1

Does the .NET marshaler pass a copy, not a reference? If so, then call GCHandle.Alloc(array, GCHandleType.Pinned), then you can get the address of this pinned object and pass that to the DLL as a pointer.

Answer 2

Use memory mapped file. System.IO.MemoryMappedFiles in .NET and CreateFileMapping in C++.

Answer 3

In current versions of .NET, any multi-megabyte array will end up on the large object heap and never move. However, to be safe, you should pin the array as fejesjoco said. Then the C++ code can save a pointer into the .NET array and update it in-place.

Answer 4

In vb.net, I've accomplished this by passing a reference to the first byte. There's no type-checking to ensure that what's passed is really an array of the proper size, but as long as the routine is running the array will be pinned.