Visual Studio 2008 locks dll in bin folder and doesn't let go of it

Question

Hi,

I am working on a solution consisting of 8 .NET projects. Since I am practicing TDD, I have to re-compile my solution very often. Lately I have been getting the following error about every second time when trying to compile:

Error 2 Unable to copy file "obj\Debug\Zeiterfassung.Tests.dll" to "bin\Debug\Zeiterfassung.Tests.dll". The process cannot access the file 'bin\Debug\Zeiterfassung.Tests.dll' because it is being used by another process.

Zeiterfassung.Tests.dll is the dll generated by one of my projects (it's the unit testing project). It's always this dll that cannot be copied and causes the error. Everything else works fine 100% of the time.

In about 9/10 times I can "solve" the problem by recompiling my solution again. But when the problem is getting really bad, the project just won't compile successfully no matter how often I try and I have to restart the IDE.

I used microsoft's handle.exe to ascertain which process is locking the DLL and it is devenv.exe. I also tried deleting the DLL by hand and it really can't be deleted until I restart the IDE.

Last but not least, I tried adding <GenerateResourceNeverLockTypeAssemblies>true</GenerateResourceNeverLockTypeAssemblies> to my project as suggested in another forum, but this did not help.

Please help! This problem is really starting to drive me nuts.

Edit: I might also add that I made sure my unit tests are finished when this problem occurrs. Still, the dll remains locked. I am running my tests via the Resharper unit test explorer.

Answer 1

I've faced the same problem before. Process Explorer is able to delete the handle.

Answer 2

The most likely problem is a threading issue. You probably had an itinerant thread that is still executing, and it has the reference to the .DLL.

Answer 3

Visual Studio has had one or another problem like this since Day 1. It would be nice to give you a set of simple solutions that always work, but frankly, sometimes, it has just "tripped over its own feet".

In that case, the simple solution is to exit and restart. Even closing the solution and reopening may not help.

Answer 4

By "I tried adding true to my project as suggested in another forum" do you mean that you created a property named GenerateResourceNeverLockTypeAssemblies and set it to true as suggested at http://social.msdn.microsoft.com/Forums/en-US/msbuild/thread/6f76db9a-ea37-42b3-a016-571912c28032? If not try that out.

Answer 5

Looks like the bug disappeared (fingers crossed...) after I moved my test project, checked out an earlier version of the project from the repository and replaced all code files with the newer versions.