Article ID: 206076 - View products that this article applies to.
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Note Microsoft Visual C++ 2008, Microsoft Visual C++ 2005, Microsoft Visual C++ .NET 2003, and Microsoft Visual C++ .NET 2002 support both the managed code model that is provided by the Microsoft .NET Framework and the unmanaged native Microsoft Windows code model. The information in this article applies only to unmanaged Visual C++ code.
Marshal.exe is a sample that shows the different ways of marshaling an interface across apartments.
The following file is available for download from the Microsoft Download Center:
Download the Marshal.exe package now.
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For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.
(http://support.microsoft.com/kb/119591/ )How to obtain Microsoft support files from online services
A Single-Threaded Apartment (STA) is a thread that was initialized with CoInitialize() or CoInitializeEx (NULL, COINIT_APARTMENTTHREADED). Also, any other threads in the same process that use COM must also call CoInitialize() or CoInitializeEx() to initialize COM for its thread.
If you create a COM object in one STA thread, you cannot pass an interface pointer to another STA thread and call out on that pointer. Since calls to STA objects are supposed to be serialized, COM enforces this by only allowing one thread to call into the STA object (the thread where it was created). If the interface pointer you pass to the second STA thread is a pointer to a proxy, you will get an error HRESULT of 0x8001010E or RPC_E_WRONG_THREAD (the application called an interface that was marshaled for a different thread). If the interface pointer is a direct pointer to the object, COM will not enforce serialization, you will not get the above error, and the interface method call will be made. However, this is still illegal behavior on the part of the client.
You can still call methods on the STA object from a different STA thread as long as you do it through a proxy. A proxy is a copy of the interface that you get via marshaling/unmarshaling. When you make a call through the proxy, COM makes a thread switch and the call ends up executing in the context of the thread where the STA object was created.
There are three ways to marshal/unmarshal an interface to another STA thread:
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/172314/ )Explanation of RPC_E_WRONG_THREAD error
Article ID: 206076 - Last Review: May 22, 2008 - Revision: 7.0