Calling a COM interface from a worker thread

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I'm automating Word and when I call a function that doesn't return for a long time (for example a call to
app.Run(_T("FilePrint"));) it tends to freeze the UI of my app until it returns from the call, so I tried to run this code from a worker thread, but then COM complains and throws an exception RPC_E_WRONG_THREAD - "0x8001010E: The application called an interface that was marshalled for a different thread."

How can I solve this problem?

btw, there's an explanation about RPC_E_WRONG_THREAD in MSDN - INFO: Explanation of RPC_E_WRONG_THREAD Error[^], but I couldn't figure out anything from it.

Posted 13-Aug-09 6:43am

sashoalm

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Stuart Dootson · Answer 1 · 2009-08-13T06:51:00

Solution 1

Could you do all of the automation, including creation of the Word object, on the worker thread?

Basically you're running foul of COM single-threaded apartments and things, I think. This article[^] explains them well.

Posted 13-Aug-09 6:51am

Stuart Dootson

Jörgen Sigvardsson · Answer 2 · 2010-08-03T09:02:00

Solution 2

You need to marshal calls across threads/apartments. See this[^] article for different ways to perform cross thread marshalling.

CoMarshalInterThreadInterfaceInStream() would probably be the easiest approach. Look it up in the MSDN documentation. It's quite easy to use.

Posted 3-Aug-10 9:02am

Jörgen Sigvardsson

Updated 3-Aug-10 20:22pm

v2