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We have a service running that connects with hundreds of devices over TCP. Every time we want to do an update of this service we need to restart it and this causes a connection loss for all devices.

To prevent this we want to divide our application into a connection part and a business logic/datalayer part. This will give us the option to update the business logic/datalayer without restarting the connection part. This could be done with WCF services, but the system should response as fast a possible and introducing another connection to something will cause an extra delay.

Would it be possible to update a dll file without restarting the application and give the application an instruction so it will load the new dll and discharge the old one? Off course as long as the interface between the layers don't break.

Willem de Jong
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    You'll have to make an additional AppDOmain in which you load the assembly's that should be replacable in runtime. When you need to replace, you destroy the appdomain and build a new one which will load the new assembly. This is a greatly oversimplified version what you could do with multiple AppDomains – Marvin Smit Nov 14 '13 at 13:55
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    More on @MarvinSmit's suggestion: http://stackoverflow.com/questions/8972352/communication-between-appdomains – OnoSendai Nov 14 '13 at 14:01

2 Answers2

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According to MSDN:

"There is no way to unload an individual assembly without unloading all of the application domains that contain it. Even if the assembly goes out of scope, the actual assembly file will remain loaded until all application domains that contain it are unloaded."

Reference: http://msdn.microsoft.com/en-us/library/ms173101(v=vs.90).aspx

My approach would probably involve some sort of local communication between communication layer and business logic, each on a different context (AppDomain) - via named pipes or memory mapped files, for example.

OnoSendai
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Here is a good example of loading / unloading assembly dynamically.

http://www.c-sharpcorner.com/uploadfile/girish.nehte/how-to-unload-an-assembly-loaded-dynamically-using-reflection/

Be careful about speed since the MethodInfo.Invoke is slow you might want to look into using DynamicMethod. Also creating / destroying app domains is slow.

http://www.wintellect.com/blogs/krome/getting-to-know-dynamicmethod

Also you can use what is called a "plugin" framework. Codeplex has one called the MEF "Managed Extensibility Framework"

http://mef.codeplex.com/

goroth
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