Re: share a structure array containing multidimensional char array

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

Oh, but 256*256 is only 64.000 bytes!

You can declare your structure like this:

[Serializable]
[StructLayout(LayoutKind.Sequential)]
public struct msg_file_s
{
public byte[,] mb_buffer;
public byte[] other;
}

The "writer" has to serialize the structure data and provide the size of the total number of bytes in the shared memory segment to the "reader", for instance as an int value at the start of the MM segment. Without this length info there is no way to know the size and number of the individual structures stored in the MM segment.

Then, the reader needs to deserialize the memory buffer as follows:

// pBuf is the pointer that points to the shared memory buffer returned by the MapViewOfFile Win32 API.

static void GetObjectData2(IntPtr pBuf)
{
// get size of data bytes in MM segment
int len = Marshal.ReadInt32(pBuf, 0);
// copy the MM data to a managed array
byte[] data = new byte[len];
Marshal.Copy(new IntPtr((int)pBuf + sizeof(int)), data, 0, len);
// deserialize the managed byte[] to the struct representation
BinaryFormatter bf = new BinaryFormatter();
MemoryStream ms = new MemoryStream(data);
msg_file_s[] sa = (msg_file_s[]) bf.Deserialize(ms);
// use the array of structs...
foreach(msg_file_s s in sa)
{
// use structure data
int x = s.mb_buffer.GetUpperBound(0);
int y = s.mb_buffer.GetUpperBound(1);
...
}

}
}


Willy.


"Aykut Ergin" <AykutErgin@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message news:6EEA35B1-D8CF-499B-AA9D-40873B3C732E@xxxxxxxxxxxxxxxx
Hi,

My original structure is like shown below
struct msg_file_s
{
unsigned char mb_buffer[256][256];
unsigned char other[64];
};

struct msg_file_s msg_file[16];

This structure will execute on communication dll ( written with C++ ).
Applications will use this dll.
We have not the chance to edit it because we use for several projects for 15
years.
We use this MMF with VC++ 5 / VC++ 6 / BCB 6 on NT4 / 2000 / 2003 / XP.
We do not have any problem.

Best Regards
--
Aykut ERGİN
Nortel Netaş
Software Design Engineer



"Willy Denoyette [MVP]" wrote:

"Aykut Ergin" <AykutErgin@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:139D98E6-5572-4BB8-8FAD-E312F04F871A@xxxxxxxxxxxxxxxx
>I want to share a structure array containing multi dimensional char >array
> between C# and C++, by using memory mapped file.
>
> I already have C++ code for handling memory mapped file.
> I am passing pointer to the structure array as shown below for C++;
> I am able to work with pointer ( for C++ ).
> C++ code works fine.
>
> I am working on converting code for memory mapped file in C#.
> My problems:
> 1. How should I define structure array in C# ( for the below structure
> array
> ).
> 2. How should I define pointer to structure array in C# ( for the below
> structure array ).
>
> Any help related to this would be highly appreciated.
>
> C++ implementation:
>
> struct msg_file_s
> {
> unsigned char mb_buffer[1000][1000];
> .....
> .....
> };
>
> struct msg_file_s msg_file[16];
> struct msg_file_s *msg_file_ptr;
>
>
> HANDLE api_map_memory(struct msg_file_s **msg_file_ptr)
> {
> HANDLE hKernel = CreateFileMapping ( (HANDLE) 0xFFFFFFFF,
> > NULL,
>
> PAGE_READWRITE,
> 0,
>
> sizeof( struct msg_file_s ),
>
> _T("TEST"));
>
> *msg_file_ptr = (struct msg_file_s *) MapViewOfFile( hKernel,
>
> FILE_MAP_READ | FILE_MAP_WRITE,
> 0,
> 0,
> 0 > );
> return(hKernel);
> }
>
>
> map_memory_file(int index)
> {
> msg_file_ptr = &msg_file[index];
> hKernel = api_map_memory(&msg_file_ptr);
> }
>
> /****************************************************************************/
>
> C# implementation:
>
> [StructLayout(LayoutKind.Sequential)]
> unsafe struct msg_file_s
> {
> [MarshalAs(UnmanagedType.LPArray, ArraySubType= UnmanagedType.U1,
> SizeConst = 100, SizeParamIndex=2)]
> byte[,] mb_buffer;
> }
>
>
> -- > Aykut ERGİN
> Nortel Netaş
> Software Design Engineer
>



Are you sure you want to pass such a huge amount of data through Shared
memory (MM file)?
I see in your declaration that one element is already 1000000 bytes, how
large are the other elements? and how large is the array of structures you
want to share?

Note that passing data through Shared Memory requires a lot more memory
because you'll have to marshal the data from unmanaged memory to managed
memory before you will be able to access the managed presentation of the
unmanaged data. Note that the extra marshaling will reduce the performance
advantage of the shared memory "transfer" significantly, if not completely.

Willy.






.

Relevant Pages

  • Re: Fast string operations
    ... Looping: I thought looping over arrays in managed code was "slow" ... array handling and such. ... The problem with TrimHelper is that it always returns a new string instance. ... The customer perceives this as a memory leak. ...
    (microsoft.public.dotnet.languages.csharp)
  • Re: How to point to a global memory block from multiple apps?
    ... > How is MyArrlinked tothe memory mapped file? ... > memory mappoed file to my array memory, ... the mapping address may actually be different in each ...
    (microsoft.public.vb.winapi)
  • Re: High Memory Consumption of Classes and Arrays
    ... Only the array itself has overhead. ... memory as a reference type. ... > least consume 40 bytes of memory. ...
    (microsoft.public.dotnet.framework.performance)
  • Re: Fast linked list
    ... > amounts of memory rather than huge chunks of it. ... random insertions into a vector/dynamic array are not as slow ... to cause a cache miss. ... some hard numbers on speed differences between lists and arrays. ...
    (microsoft.public.vc.language)
  • Re: OOP and C++ and C (was Re: Dennis Ritchie -- An Appreciation)
    ... different layout in memory. ... memory is one large array like structure. ... That's the fundamental abstraction that our hardware attempts to ...
    (comp.lang.c)