Opening a Memory Mapped File causes FileNotFoundException when deployed in IIS

Question

Following the code example from this website, I created a windows console application that creates a mapped memory file:

        using (var file = MemoryMappedFile.CreateNew("myFile", 24))
        {
            var bytes = new byte[24];
            for (var i = 0; i < bytes.Length; i++)
                bytes[i] = (byte)(65 + i);

            using (var writer = file.CreateViewAccessor(0, bytes.Length))
            {
                writer.WriteArray<byte>(0, bytes, 0, bytes.Length);
            }
            Console.WriteLine("Run memory mapped file reader before exit");
            Console.WriteLine("Press any key to exit ...");
            Console.ReadLine();
        }

in a new asp.net web application I read the MMF using the code:

 protected void Page_Load(object sender, EventArgs e)
    {
        string sOutput = "";

        using (var file = MemoryMappedFile.OpenExisting("myFile"))
        {
            using (var reader = file.CreateViewAccessor(0, 24))
            {
                var bytes = new byte[24];
                reader.ReadArray<byte>(0, bytes, 0, bytes.Length);

                for (var i = 0; i < bytes.Length; i++)
                    sOutput += (char)bytes[i] + " ";

            }
        }

        Response.Write(sOutput);
    }

In the development IIS Express the file is read as expected and the page displays the data from the mapped memory file.

However, When deployed to IIS I get the exception System.IO.FileNotFoundException at the locationMemoryMappedFile.OpenExisting("myFile")

I tried changing the app pool identity to the same as the one running the MMF console application but this does didn't work.

Answer 1

Add "Global\\" prefix to the mapName. That is the only way it worked for me. When we try to access shared memory created in the first process it runs in a different security context and shared memory objects are not visible unless they are created in the global namespace.

This is the code that worked for me. I used CreateOrOpen in a WinForm application and I used OpenExisting in an IIS process:

mSec = new MemoryMappedFileSecurity();
mSec.AddAccessRule(new AccessRule<MemoryMappedFileRights>(new SecurityIdentifier(WellKnownSidType.WorldSid, null), MemoryMappedFileRights.FullControl, AccessControlType.Allow));

mmf = MemoryMappedFile.CreateOrOpen("Global\\\MmfName", 100, MemoryMappedFileAccess.ReadWrite, MemoryMappedFileOptions.None, mSec, HandleInheritability.Inheritable);

mmf = MemoryMappedFile.OpenExisting("Global\\\MmfName");