How to implement shared memory in .NET?

Update: Hey, here’s a page I just found with a compleate implmentation.

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Using C++/CLI, it’s quite easy to setup shared memory as per normal C++ API (C++/CLI being able to interact with the managed and native HEAP/memory references). The UnmanagedMemoryStream can then be used to expose a Stream object to C#.

I did not attach the .h file, but you can infer the layout of the pmapped native typedef fairly easially ;). You may also want to evaluate the possible use of a BufferedStream depending on your reader/writer use case. And the code is from a project which I do not use any more so I can not remember the status of it’s bug regression.

Here’s the C++/CLI class which establishes a file mapping and exposes an UnmanagedMemoryStream;

public ref class MemMapp
{
    public:
        __clrcall MemMapp(String^ file)  
        { 
            map = NULL;

            if(!File::Exists(file)) throw gcnew ApplicationException("Can not find file " + file);

            marshal_context^ x = gcnew marshal_context();
            const char *nname = x->marshal_as<const char*>(file);

            map = (pmapped) malloc(sizeof(mapped));
            ZeroMemory(map, sizeof(mapped));
            map->name = strdup(nname);
            InitMap(map);
        }
        void __clrcall MapBytes(long long loc, long length)
        {
            map->low = loc & 0xffffffff;
            map->high = (loc >> 32) & 0xffffffff;
            map->size = length & 0xffffffff;
            if(!GetMapForFile(map))
                throw gcnew ApplicationException("can not map range " + loc + " :" + length);

            if(map->size = 0)
                map->size = MAXMAX&0xffffffff;

        }
        UnmanagedMemoryStream ^View()
        { 
            return gcnew UnmanagedMemoryStream((unsigned char *) map->blok, map->size, map->size, FileAccess::Read); 
        }
        long long __clrcall FileSize()
        {
            DWORD high, low;
            long long rv;

            low = GetFileSize(map->hFile, &high);
            maxmax = high;
            maxmax << 32;
            maxmax += low;

            rv = high;
            rv << 32;
            rv = rv & low;
            return rv;
        }
        property unsigned int MinBufSiz { unsigned int get() { return map->dwbufz; } }
        property long long BufBase { long long get() { return (map->high << 32) + map->low; } }
        property long long BufLim { long long get() { return ((map->high << 32) + map->low) + map->size; } }
        property long long MAXMAX { long long get() { return maxmax; } }
        static MemMapp() { }
        __clrcall ~MemMapp() { if(map != NULL) { CloseMap(map); free(map->name); free(map); map = NULL; } }
    protected:
        __clrcall !MemMapp() { if(map != NULL) { CloseMap(map); free(map->name); free(map); map = NULL; } }
        pmapped map;
        long long maxmax;
};

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Here’s CLoseMap at least… I just found it… it was not compiled with /CLR

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bool CloseMap(pmapped map)
{
    if(map->blok != NULL) {
        UnmapViewOfFile(map->blok);
        map->blok = NULL;
    }
    if(map->hMap != INVALID_HANDLE_VALUE && map->hMap != NULL) {
        CloseHandle(map->hMap);
        map->hMap = INVALID_HANDLE_VALUE;
    }
    if(map->hFile != INVALID_HANDLE_VALUE && map->hFile != NULL) {
        CloseHandle(map->hFile);
        map->hFile = INVALID_HANDLE_VALUE;
    }
    return false;
}