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I have a MarshalByRefObject which I needed to serialize and store (in a database), so I could deserialize and reference it later. I have chosen to approach this differently: right now I am running a Windows Service which simply keeps the MarshalByRefObjects "alive" (please note that the RemoteObject is actually a 3rd party object, which I do not create myself):

// This is the object which extends the MarshalByRefObject class
RemoteObject myRemoteObject = new RemoteObject;

TcpServerChannel channel = new TcpServerChannel(6789);
ChannelServices.RegisterChannel(channel, true);

ObjRef objRef = RemotingServices.Marshal((System.MarshalByRefObject)myRemoteObject, id);

In another AppDomain I simply connect and retrieve the object; all works fine:

RemoteObject myLocalObject = (FCEngine.IFCVerificationSession)Activator.GetObject(
                           typeof(FCEngine.IFCVerificationSession),"tcp://localhost:6789/" + id);

Now the problem is that the RemoteObject contains a property which is simply an HBITMAP handle casted to the long type. I can retrieve the handle easily. Normally (locally) I would do:

IntPtr hbitmap = (IntPtr)myLocalObject.ContextImage;
System.Drawing.Bitmap bmp = System.Drawing.Image.FromHbitmap(hbitmap);

This doesn't work in the current case. I get a System.Runtime.InteropServices.ExternalException I guess the problem is that hbitmap is a handle to some memory which doesn't exist in the local AppDomain, but in the Windows Service AppDomain. My question is what my options are:

  • The RemoteObject is pretty complex, it's like a tree in which you traverse the nodes by calling its functions. The 3rd party imposes that I can only traverse the object once. So traversing it Service-side, storing bitmaps in a database, and traversing it remotely again won't work.
  • Ideal would be to be able to call a function in the Windows Service, and pass the hbitmap handle as an argument, returning the actual bitmap. This is not possible in Windows Services.
  • I could store the handle in a database and make the Windows Service poll the database for it. It could then retrieve the bitmap and store it in that same DB for me. I could then again retrieve that bitmap remotely. This is very ugly, since I need the bitmap immediately.

Basically I'd like to know if you have suggestions to not have to perform ugly hacks like the 3rd option...What are my options?

SOLVED Right now I solved the problem by creating a custom object which extends MarshalByRefObject on the service side. This object has a method to retrieve and save a bitmap by passing the handle. I simply approach the object remotely, in the same way I approach my 3rd party object. Too simple of a solution, although a colleague had to point it out.

+1  A: 

HBitmap is a handle, it has no sense to serialize unmanaged handles. You need to serialize the bitmap content, recreate it (bitmap) on a remote side, and then re-assign newly created hbitmap.

P.S. Physically handle is a pointer to pointer, its value is applicable only an the address space is was created.

IMHO.

Dmitry Karpezo
You are correct. Please see the SOLVED section in my post.
Waldo Spek