Shared memory with pointer in C#

Question

MemoryMappedFile seems to be the only way to share memory between processes in .NET(?), however I didn't find a way to map a region to the process' virtual memory space, so it can't be really treated as a memory block since there's no way to get the pointer. I'm using pointer to process bitmap for best performance and reusability.

In c++ this can be easily achieved using boost.

Is there a way share a region of memory between processes and use pointer to read/write data?

Answer 1

For lower level access you can use MemoryMappedViewAccessor.SafeMemoryMappedViewHandle which returns a SafeMemoryMappedViewHandle which has a load of lower level access methods.

Here's an example:

static void Main()
{
    // Open an MMF of 16MB (not backed by a system file; in memory only).
    using var mmf = MemoryMappedFile.CreateOrOpen("mmfMapName", capacity: 16 * 1024 * 1024);

    // Create an MMF view of 8MB starting at offset 4MB.
    const int VIEW_BYTES = 8 * 1024 * 1024;
    using var accessor = mmf.CreateViewAccessor(offset: 4 * 1024 * 1024, VIEW_BYTES);

    // Get a pointer into the unmanaged memory of the view. 
    using var handle = accessor.SafeMemoryMappedViewHandle;

    unsafe
    {
        byte* p = null;

        try
        {
            // Actually get the pointer.
            handle.AcquirePointer(ref p);

            // As an example, fill the memory pointed to via a uint*
            for (uint* q = (uint*)p; q < p + VIEW_BYTES; ++q)
            {
                *q = 0xffffffff;
            }
        }

        finally
        {
            if (p != null)
                handle.ReleasePointer();
        }
    }
}