Several appdomains calling the same unmanged dll

Question

Our .NET 3.5 C# application creates multiple appdomains. Each appdomain loads the same unmanaged 3rd party dll. This dll reads a configuration file upon initialization. If the configuration changes during runtime, the dll must be unloaded and loaded again. This dll is not in our scope to rewrite correctly.

Does each appdomain have access to a separtate copy of this unmanaged dll, or does Windows keep one copy of the dll and maintain a usage count? If the latter is is the case, how do we get each instance of the unmanaged dll to reflect its unique configuration?

Answer 1

Takea look at this blog post

Explanation of Processes and AppDomains

Answer 2

I think unmanaged dlls are loaded only once per process by the OS, so every app-domain will have the same loaded instance. To unload a dll, use the FreeLibrary function. However, since multiple app-domains are likely to have loaded the dll, there is no guarantee that FreeLibrary from one app-domain will actually free/unload the dll.

As BillW says, this seems like a design nightmare to me too!