How to check if AppDomain is unloaded?

Question

I'm using a bunch of objects in another AppDomain through proxy. They are in a separate domain because I need to hot-swap assemblies that contain those objects, so I Unload an AppDomain after I'm done using the assemblies it's hosting.

I want to check sometimes if I've unloaded an AppDomain in the past (or it somehow got unloaded on its own or something) for testing purposes. Is there a way to do this?

The obvious way is to do something that would throw an AppDomainUnloadedException, but I'm hoping there is some other way.

Some programmers try entirely too hard to avoid using a *bool* variable. There is no "or something". — Hans Passant, Dec 17 '15 at 11:47
@HansPassant Since it's for testing purposes there is usually an *or something*, even if you're adamantly certain there shouldn't be. — GregRos, Dec 17 '15 at 11:50

score 3 · Accepted Answer · answered Dec 17 '15 at 11:25

I believe that you can use a combination of storing references of AppDomain in some given Dictionary<AppDomain, bool> where the bool is if its loaded or unloaded, and handle AppDomain.DomainUnload event.

Dictionary<AppDomain, bool> appDomainState = new Dictionary<AppDomain, bool>();

AppDomain appDomain = ...; // AppDomain creation
appDomain.DomainUnload += (sender, e) => appDomainState[appDomain] = false;
appDomainState.Add(appDomain, true);

This way you'll be able to check if an AppDomain is unloaded:

// "false" is "unloaded"
if(!appDomainState[appDomainReference]) 
{
}

Alternatively, you can use AppDomain.Id as key:

Dictionary<int, bool> appDomainState = new Dictionary<int, bool>();

AppDomain appDomain = ...; // AppDomain creation
appDomain.DomainUnload += (sender, e) => appDomainState[appDomain.Id] = false;
appDomainState.Add(appDomain.Id, true);

...and the if statement would look as follows:

// "false" is "unloaded"
if(!appDomainState[someAppDomainId]) 
{
}

Thank you for the suggestion. I will do this if there is no direct way to check if the domain has been unloaded (since it's for testing purposes, the fewer failure points, the better). — GregRos, Dec 17 '15 at 11:29
@GregRos No problem. If I'm not mistaken, this will be your best bet. Obviously, you might change how you store the `AppDomain` state: it can be a dictionary as I suggested you, a list of classes using a custom type `AppDomainState` which might have a property `Unloaded`... — Matías Fidemraizer, Dec 17 '15 at 11:30

score 1 · Answer 2 · edited May 23 '17 at 12:15

1

You can list all appdomains in your program with the code from this stackoverflow link. Then you can compare them by ID or FriendlyName or something similar.

edited May 23 '17 at 12:15

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answered Dec 17 '15 at 15:39

Dieter Meemken

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How to check if AppDomain is unloaded?

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