Difference in dll loading between debug and release modes

[Moe Sisko]

Using Visual Studio 2005.

Here's an interesting one.

To reproduce, create new solution with windows application and class
library.

In class library, define class like this :
==
public class SomeClassInDLL
{
public string DoSomething()
{
return DateTime.Now.ToString();
}
}
==

Get the windows app to reference the class library. Add a button, and add
this code :

==
private void button1_Click(object sender, EventArgs e)
{
try
{
MessageBox.Show("about to call DoSomething");
string ret = DoCall();
MessageBox.Show(ret);
}
catch (Exception ex)
{
MessageBox.Show("error : " + ex.GetType().ToString() + " " +
ex.Message);

}
}

private string DoCall()
{
SomeClassInDLL c1 = new SomeClassInDLL();
return c1.DoSomething();
}
==

1) Compile the app in both Debug and Release modes. (into the bin\Debug and
bin\Release directories)
2) Close down visual studio, and run windows app from Windows explorer
3) Click button 1.
4) When the "about to call DoSomething" dialog comes up, in windows
explorer, try to delete the referenced dll file.

5a) if you ran the debug mode version in step 2 : you can delete the dll
file successfully.This is what I expect, since the dll is being called
inside the DoCall function, and not directly in button1_Click.
5b) if you ran the release mode version in step 2 : you cannot delete the
dll file, because it seems to be locked by the application.

==
5a) is the behaviour I have come to expect, since dotnet 1.1 days. Any ideas
why 5b) seems to lock the dll earlier than necessary ? Something to do with
optimization perhaps ?
Is this sort of dll loading behaviour explained somewhere ?

TIA.

 

[Moe Sisko]

On Sun, 22 Feb 2009 21:42:58 -0800, Moe Sisko <null> wrote:

In any case, you shouldn't be deleting DLLs referenced by running
applications. And you shouldn't rely on implementation details of DLL
referencing/loading behavior.

Thanks Pete.
So I'm guessing a better idea would be to use reflection (e.g.
Assembly.LoadFrom) to load the dll explicitly ?
(The real code I'm using is trying to upgrade the dll in question with a new
version, before calling some methods in it.)