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Editorial Team
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Asked: 2026-05-14T03:24:50+00:00

We have a plugin system on a WCF service that checks libraries placed in

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We have a plugin system on a WCF service that checks libraries placed in the bin folder for certain assembly level attributes and loads them. This allows customization of certain service calls based on which client is making the call. This works great most of the time. However, sometimes it seems to lose the dll, which causes the service to revert back to the default implementation for every client. The solution so far has been to just move the dll file out of the bin folder, and back in. This causes asp.net to pick up the file and customizations start working again.

I’m at a loss for why the assembly is getting missed like that after a certain amount of time. Any ideas as to what might be causing this?

Edit: Problem stated more clearly

Our services use a service factory to hand out custom implementations based on what client is calling the code. If there is not a custom implementation, we hand out a default implementation. We use GetAssemblies to check for assemblies that are decorated with an attribute designating them as a custom implementation and associating them with a client. The problem is that GetAssemblies stops returning a client’s custom assembly even though the library remains in the bin folder. Moving the dll out of bin, and back into it will fix the issue for about a week until it happens again

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1 Answer

  1. Editorial Team

    The problem that you are having must be related to the automatic recycling of the appdomain. Apparently appdomain recycle behaves differently from a real restart. On recycle, it will only load dll that is explicitly reference and loaded as needed. See this link
    http://www.chrisvandesteeg.nl/2006/06/15/appdomain-recycle-different-from-real-restart/

    The fact that GetAssemblies will only return you the assembly that is currently loaded into the appdomain, this can explain the anomaly that you are getting with your program. To be safe, if you are dealing with plugin type library, you should always scan the plugin files (dlls) and load them explicitly using Assembly.LoadFrom. Another alternative is to host your WCF services externally in your custom host such as window service so that the life time of the host is not subject to the IIS recycling policy.

    Read this for more information on appdomain recycling
    http://blogs.msdn.com/tess/archive/2006/08/02/asp-net-case-study-lost-session-variables-and-appdomain-recycles.aspx

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