Is AppDomain equivalent to a Process for .NET code?

Question

I have to call some badly written 3rd party COM components that have memory leaks and uses Single Threaded Apartment [STA] within a long running process.

I know separate process will be nice way to implement it and I can restart it occasionally from the long running process.

Can AppDomain be used instead? Is AppDomain thread a STA thread if marked appropiately? Does it have its own memory for COM objects? Is unloading the AppDomain is equivalent of killing the process?

Answer 1

An AppDomain does not provide the same degree of isolation as a process does. In fact if you're worried that the 3rd party component is not in good shape there's a risk, that it will take down your .NET application.

An AppDomain cannot be unloaded if unmanaged code is executing at the time of unload, so you may have a hard time controlling your 3rd party code in an AppDomain. See http://msdn.microsoft.com/en-us/library/system.appdomain.unload.aspx

Even for managed code only, an AppDomain does not provide a robust sandbox solution. E.g. if the loaded code spawns any threads these will take down the entire process in case of unhandled exceptions. This question has a bit more info: .NET - What's the best way to implement a "catch all exceptions handler".

As far as I am aware the best option for hosting code like that in a .NET application is to implement your own CLR host process like IIS and SQL Server does.