How to unload assemblies from the GAC?

Question

I am trying to run automated tests on a particular product. The test consists of installing the product into different locations on the hard drive and then performing some operations on it and then closing the application.

The code that launches the process looks like this:

using (Process process = new Process())
            {
                process.StartInfo.FileName = "C:\mylocation\myapp.exe";
                process.Start();
            }

While executing the tests continuously, when the install location of the application changes, I get an exception from the above code that says:

API restriction: The assembly 'file:///C:\alternate_location\myapp.exe' has already loaded from a different location. It cannot be loaded from a new location within the same appdomain.

The tests cannot be run continuously because of this.

What can be done to overcome this? Is there anyway I can unload assemblies form the GAC?

Can I do something in my test application to overcome this OR does something have to be changed in the application that I am testing?

Answer 1

You can't unload assemblies from an application domain once loaded. But you could create a new application domain (AppDomain class), load the assemblies within it, use them, then unload the domain. See here: http://stackoverflow.com/questions/97433/good-example-of-use-of-appdomain

Answer 2

Adding something to the GAC is not an intrinsic part of the component's definition - it's generally done by an installer etc.

The gacutil tool can be used to remove your tool from the GAC. In 1.1, it was in the Framework dir. In newer versions, its in the SDK, e.g., C:\Program Files (x86)\Microsoft Visual Studio 8\SDK\v2.0\Bin

Answer 3

Could you provide more information for us? I haven't been able to reproduce this error.

Process.Start should create a new process with its own AppDomain.

On my machine I created a project Harness which has a project reference to DoNothing which is a strongly signed assembly and a project reference to LaodDoNothing which has a reference to c:\DoNothing.exe. I've pasted the code below from Harness.Main with debug outputs as inline comments. The exes suffixed with unsigned are not signed.

//debug outputs when Main is jitted:'Harness.vshost.exe' (Managed): Loaded 'c:\project\DoNothing\Harness\bin\Debug\DoNothing.exe', Symbols loaded.
//debug outputs when Main is jitted:'Harness.vshost.exe' (Managed): Loaded 'c:\project\DoNothing\Harness\bin\Debug\LoadDoNothing.exe', Symbols loaded.

ZaZaZa.Main();
LoadDoNothing.Program.Main();
using (Process process = new Process())
{
    process.StartInfo.FileName = @"C:\donothingunsigned.exe";
    process.Start(); //debug outputs The thread 0x17f0 has exited with code 0 (0x0).  No assemblies loads are logged to debug because this is a separate process.


}

using (Process process = new Process())
{
    process.StartInfo.FileName = @"C:\3\donothingunsigned2.exe";
    process.Start(); //Debug outputs The thread 0x1014 has exited with code 0 (0x0). No assemblies loads are logged to debug because this is a separate process.
}
AppDomain.CurrentDomain.ExecuteAssembly(@"C:\donothingunsigned.exe"); //debug outputs 'Harness.vshost.exe' (Managed): Loaded 'C:\donothingunsigned.exe'
AppDomain.CurrentDomain.ExecuteAssembly(@"C:\3\donothingunsigned2.exe"); //no debug output because the loader realizes this assembly has already been loaded and uses that.