leftover processes running after the .NET VMR build completes

[omajid]

Describe the Bug

When the .NET build completes, some dotnet build server processes may be left running. In some build environments, this can prove troublesome. The build orchestrator doesn't know if it needs to wait for them to complete, or if they should be killed.

Steps to Reproduce

./build.sh --source-only --prep
ps aux | grep dotnet

On .NET 10:

USER         PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         595 95.2  1.3 277138936 860684 pts/0 Sl+ 20:09  53:23 /workdir/dotnet/.dotnet/sdk/10.0.107/Roslyn/bincore/VBCSCompiler -pipename:imA3xujz1+_eM5xw
root        1904 15.7  0.9 136696024 650516 pts/0 Sl+ 20:10   8:44 /workdir/dotnet/.dotnet/dotnet /workdir/dotnet/.dotnet/sdk/10.0.107/MSBuild.dll /noautoresp
root        1905 14.0  0.8 136691216 573260 pts/0 Sl+ 20:10   7:46 /workdir/dotnet/.dotnet/dotnet /workdir/dotnet/.dotnet/sdk/10.0.107/MSBuild.dll /noautoresp
root        1920 13.7  0.7 137343404 511652 pts/0 Sl+ 20:10   7:36 /workdir/dotnet/.dotnet/dotnet /workdir/dotnet/.dotnet/sdk/10.0.107/MSBuild.dll /noautoresp

Other Information

[mthalman]

Moved to https://github.com/dotnet/dotnet since it's a general orchestration behavior, not specific to source-build.

[tmds]

To address a hang in containerized Alpine jobs, the build server shutdown gets skipped when DotNetBuildSourceOnly is set:

https://github.com/dotnet/dotnet/blob/cfadf383e8cc8d3c6792f3ae480f7f35771142d3/repo-projects/Directory.Build.targets#L819-L823

[mthalman]

Good find. I'll move this back to source-build repo.

[mthalman]

[Triage] First step is to determine if the build hang in the Alpine environment still happens. If not, we can just remove the condition for shutting the build server down. Otherwise, we need to find a different solution.