MSBuild task restore target sometimes fails if multiple projects share a project reference

[appel1]

As part of our build script for CI we do something like this to prepare our projects, about 1500 csproj projects using the 2017 format. They all share a project reference to a common project.

<ItemGroup>
  <TargetProjects Include="src\**\*.csproj"/>
</ItemGroup>
<MSBuild Projects="@(TargetProjects)" Targets="Restore" BuildInParallel="True"/>

When we do this we sometimes, like every other build or so, one or more of the following errors.

C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\Common7\IDE\CommonExtensions\Microsoft\NuGet\NuGet.targets(121,5): error : The process cannot access the file 'CommonProject\obj\CommonProject.csproj.nuget.dgspec.json' because it is being used by another process. [src\proj1\proj1.csproj]

A workaround is to set BuildInParallel to False but that reduces performance quite a bit.

Is BuildInParallel not supported or is this some other kind of configuration error?

[livarcocc]

This seems like a configuration error to me. If you run restore on your solution or a root project that references the entirety of your projects, Restore will run through all your projects and restore them all without you needing to have that customization.

If you run the way you are doing, each msbuild execution sort of becomes independent and runs into the potential and competing or changing same files, potentially leading to the issue you are seeing.

[appel1]

Ok. So not supported.

I guess I need to generate a .sln file then. Maintaining one with VS is too much hassle, and quite unpleasant because of slow performance with many projects.

Or is there some built in mechanism for this that I've missed?