COMException thrown when executing DLL method from separate thread in .NET 4.5.2

Asked Mar 08 '17 at 20:57

Active Apr 20 '17 at 20:47

Viewed 189 times

I have a .NET service that references XpdfPrint.dll that is used for printing. The print method of XpdfPrint library is executed in separate thread that looks like this:

Thread xPdfPrintThread = new Thread(() => 
{
    try
    {
        xPDF.printPDF4();
    }
    catch (COMException e)
    {
        // check for the specific errorcode and log an error
    }
 });

This worked good and well until I changed target framework from .NET 3.5 to .NET 4.5.2. Now, the call to printPDF4() is failing with:

Exception: Error HRESULT E_FAIL has returned from a call to a COM component.

If I take the call out of the thread and execute it, it completes fine. Any idea on why upgrading .NET to 4.5.2 would break this?

Update: Instantiating the COM object within the thread instead of outside the thread resolves the issue. I still have no clue why this behaves differently in .NET 4.5.2.

edited Apr 20 '17 at 20:47

asked Mar 08 '17 at 20:57

Srki Rakic

Which thread creates the COM object? – Michael Gunter Mar 08 '17 at 21:02
@MichaelGunter the thread that starts xPdfPrintThread. In other words xPDF object in example above is instantiated outside the thread that executes printPDF4(). – Srki Rakic Mar 08 '17 at 21:05
Try manually setting the apartment state in the main thread and/or the background thread. – Michael Gunter Mar 08 '17 at 21:14
I wonder whether it's necessary to call CoInitialize/CoInitializeEx explicitly when it's a .NET service. Don't think so, but perhaps worth investigating. – Bent Tranberg Mar 08 '17 at 21:21
@MichaelGunter manually setting the apartment state results in System.AccessViolationException. – Srki Rakic Mar 08 '17 at 21:35
Inside which method does that exception occur? – Michael Gunter Mar 08 '17 at 21:37
@MichaelGunter Sorry I didn't mention that. It's failing at the same method call. xPDF.printPDF4();. Also, instantiating the COM object within the thread instead of outside the thread resolves the issue. – Srki Rakic Mar 08 '17 at 21:57
Sounds like a marshaling issue. I have been googling to find anything that may be different between the two versions of .NET and haven't found anything. :( – Michael Gunter Mar 08 '17 at 21:59
@MichaelGunter I couldn't find anything either. – Srki Rakic Mar 09 '17 at 03:38

COMException thrown when executing DLL method from separate thread in .NET 4.5.2

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