DotNetCoreBuild: DLL being used by another process, build fails

[fbd]

Using dotnet 5.0.102 and cake.tool 0.38.5. Building via cake results in:

CSC : error CS2012: Cannot open 'C:\src\myapplication\obj\Release\net5.0\Application.dll' for writing -- 'The process cannot access the file 'C:\src\myapplication\obj\Release\net5.0\Application.dll' because it is being used by another process.' [C:\src\myapplication\application.csproj]

about every other time I run dotnet cake. However if I do something like dotnet build; dotnet build; dotnet build; dotnet build; dotnet build; dotnet build; (i.e. build directly multiple times in a row) I get no error. That is, it seems like cake is doing something else I am not aware of or doing something slightly different, however the build script begins like this:

Task("Clean")
    .Does<BuildParameters>((parameters) =>
{
    CleanDirectory(workerbin);
    CleanDirectory(apibin);
    CleanDirectory(nugetDir);
});

Task("Build")
    .IsDependentOn("Clean")
    .Does<BuildParameters>((parameters) =>
{
     var settings = new DotNetCoreBuildSettings
    {
        Framework = "net5.0",
        Configuration = configuration,
        NoRestore = false,
        NoIncremental = true,
    };

    DotNetCoreBuild(solution, settings);
});

The directories being cleaned are in the root of the working directory, while the code being built and the solution file are at "./src/" so the CleanDirectory should not be touching anything in the src folder. I have also tried changing the NoRestore, NoIncremental settings and removing them. This happens both locally and on my build machine, and also when I run the command from as administrator. I also tried to explicitly set the WorkingDirectory, same issue.

Has anyone else been experiencing something like this?

[patriksvensson]

@fbd Cake does not do anything special. This is related to the dotnet process not shutting down properly.
Microsoft added the dotnet build-server command just for this.

Try adding this to your script:

Teardown(ctx => {
    Information("Shutting down .NET core SDK tooling...");
    DotNetCoreBuildServerShutdown(
        new DotNetCoreBuildServerSettings {
            MSBuild = true
        });
});

[fbd]

Thanks for the help!

Although your suggested fixed increased the odds of success (not scientifically measured) I do encounter this error occasionally, but a direct call to dotnet build never seems to be an issue (even though I call it couple times in a row). It also looks like the failure happens when the last of the projects in the solution are being built. So for example project A is built first and then B (which references A), then B fails because the dotnet process that was building A has not completed (I am guessing). I guess there is one difference, dotnet build is invoked directly from the terminal and the other indirectly (i.e. Cake invokes dotnet build). I suppose this is not necessarily related to Cake, but I have tried to emulate this by creating a Powershell script that calls Invoke-Expression to run dotnet build multiple times, but that works just fine.

[augustoproiete]

Is it possible you have any post-build event doing work on any project (or any MSBuild targets hooking up to the end of the build)?

Cake is just calling dotnet build, thus there should be no difference:

Resolved tool to path C:/Program Files/dotnet/dotnet.exe
Executing: "C:/Program Files/dotnet/dotnet.exe" build "NameOfYourSolution.sln" --framework net5.0 --configuration Release --no-incremental

You might want to try to run the exact command-line that Cake runs on your PowerShell tests. You can see what Cake runs by setting the verbosity to diagnostic e.g. dotnet cake build.cake --verbosity=diagnostic

[fbd]

Thanks for your help!

This is definitely not related to Cake like you say, I get those errors if I explicitly use the --framework flag. It is strictly speaking not needed since the TargetFramework is defined in all my .csproj files. Removing the Framework = "net5.0" from the build script seems to be enough and works for me. Hopefully this discussion will be of use to somebody else with the same problem.

Thanks again.

[pascalberger]

Glad you got it working and thanks for letting is know