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Editorial Team
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Asked: 2026-05-26T05:52:53+00:00

I am writing a C# COM+ drop in for another COM+ dll. It has

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I am writing a C# COM+ drop in for another COM+ dll. It has a very simple interface and I have successfully tested the drop in.

I am using ‘component services’ partly because the old system did and partly because it feel right.

Problem I have is when I register the legacy dll the path to the dll in the properties is the ACTUAL dll, also it just works.

When I register my drop in the path to the dll is mscoree.dll not my dll, and it seems hit and miss as to whether I have to add my dll to the GAC? I have tried code to add it to a cache automatically but it doesn’t work?

Also, as I am using a WCF call with my COM+ call I am running into an issue as to where the configuration dll is currently it appears to be looking for settings in C:\Windows\system32\dllhost.exe.config

What I’d like is for it to look along side the actual dll? Am I missing something?

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1 Answer

  1. Editorial Team

    COM/COM+ is an unmanaged technology. It knows nothing about .NET managed code, so registering your .NET assembly directly in the COM registry could not possibly work. mscoree.dll is the .NET hosting library which loads the managed runtime and presents the unmanaged interfaces to COM which the COM registry requires. When an instance of the COM coclass that your assembly implements is activated, COM+ loads mscoree first, then mscoree has to load your assembly to hook up your implementation to the COM-callable wrapper which mscoree presents to COM+.

    Where mscoree looks for your assembly in order to load it depends on how you registered it. It follows the normal path probing rules of the .NET Fusion loader, which means it will usually be looking in the GAC unless you have specified a codebase during registration (e.g. using the regasm command line argument /codebase).

    Configuration settings for managed code are scoped by AppDomain, and by default the configuration file name for an AppDomain is obtained by adding the suffix .config to the path of the executable of the process hosting the AppDomain. Your component is hosted in COM+, so will execute in process which is an instance of DllHost.exe. So by default the configuration file for your component’s AppDomain is going to be DllHost.exe.config. However, if you specify an Application Root directory for the COM+ application this will change the location where the AppDomain looks for its configuration, to [COM+ Application Root Directory]\[COM+ Application Name].config.

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