PRB: LPPICTUREDISP Cannot Be Passed Across Process Boundaries

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1, 5.0, 6.0
  • Microsoft OLE Control Developer's Kit (CDK) versions 1.0, 1.1, 1.2

SYMPTOMS

An automation server that implements a Picture object wrapped by the CPictureHolder class in MFC fails when it attempts to pass a pointer to the picture object's IPictureDisp implementation across process boundaries.

CAUSE

IPictureDisp gains access to methods of the Picture object that cannot be marshaled across process boundaries. For example, IPictureDisp supports DISPID_PICT_RENDER to gain access to the Render method of the Picture object. The Render method takes a handle to a device context as the first parameter. Device context handles cannot be marshaled.

Dispatch interfaces can normally be marshalled by using the IDispatch marshaling code, but the Picture object implements IMarshal specifically to cause its marshaling to fail.

STATUS

This behavior is by design.

MORE INFORMATION

The ClassWizard in Visual C++ allows you to select a return type of LPPICTUREDISP for a method. This method might return the IPictureDisp interface obtained by calling CPictureHolder::GetPictureDispatch. However, if this method is called by a controller running in another process, the method fails and returns an error code of E_FAIL.

Because the Picture object causes the marshaling of IPictureDisp to fail, problems can also occur when trying to obtain an IPictureDisp interface across thread boundaries in a multiple-thread apartment model object.

REFERENCES

For more information on marshaling, please see "Inside OLE," second edition, by Kraig Brockschmidt, Chapter 6, "Local/Remote Transparency," published by Microsoft Press.

Additional query words:

Keywords : kbole kbAutomation kbCtrl kbMFC kbVC500 kbVC600
Version : Winnet:1.5,1.51,1.52,2.0,2.1,2.2,5.0.6.0
Platform : WINDOWS
Issue type : kbprb