Cannot attach to process in .net 4.0

Question

** post was edited, more info below

I've just watched two great videos about Advanced Dotnet Debugging (by Brian Rasmussen) and I am trying to repeat some steps, but just don't know how to proceed with tis error:

An attempt to set a processes DebugPort or ExceptionPort was made,
but a port already exists in the process.

I've found some answers on google and i generally understand what the error says but I just don't understand one weird fact: when i compile my simple app < .NET 4.0, I can attach as the movie shows, trying to do the same after i compile targetting .NET 4.0 disables me from attaching.

One of google's answers says "try to attach from windbg using noninvasive mode" but.. Brian do not use any of such checkboxes. It just works on his videos.

What's the difference? Where's the catch? Is it Windows 7 vs Vista? Maybe some different compile settings matters?

I am using MS VS 2k10 with MS SDK with Windbg x86 downloaded from msdn and symbols correctly configured to http server. The system is MS Vista x86.

Resources (exact time >= 8:15): http://channel9.msdn.com/posts/MDCC-TechTalk-Advanced-NET-Debugging-part-2

Edit: Error shows when attaching to process that was run from VS. Trying to attach to process that was run /outside VS, windbg doesn't show any content.

Edit2: Windbg had some refreshing problems in my system. Using few times "Windows \ [Undock | Dock all]" menu option i was able to see the content of attached process, that was missing.

So the only question now is: what's the difference when attaching to process started from VS, when it's compiled in once using target < 4.0 and again = 4.0? Why when targetting 4.0 windbg cannot attach to the process in not "noninvasive" mode. What has changed in VS 2k10?

Answer 1

I take it you're debugging from Visual Studio (F5) and then trying to attach. You can only have one active debugger at a time, so that is why you get this error. If you want to launch the process from VS, run it without debugging (Ctrl-F5). If you do that, you should be able to attach from WinDbg.

EDIT : I am sorry, I missed the point about various versions of .NET behaving differently in this respect, so let me try to address your questions again. The reason it "just works" in the video, is because I use run without debugging every time I launch from VS. So if you simply want to follow the examples in the videos, all you need to do is run without debugging.

I started using WinDbg/SOS on CLR2 and x86. Launching a x86 .NET process from VS back then would trigger the error, so I made a habit of just launching without debugging.

However, as you have discovered there are scenarios where you can actually attach to a process that is being debugged by VS. I can reproduce the scenarios you describe, but I can also attach to a x64, .NET 2 process started with debugging from VS2008, but I cannot attach to the same process if the platform is set to x86.

Apparently there are subtle differences that I haven't been aware of, and it doesn't seem to be related exclusively to the .NET version, as I can attach to a x64 .NET2 process even if it is under the control of the VS debugger.

I'll update my answer if I find additional details.