File in use problems

I am using .NET Core and in a short timespan, I see the following two errors. They are intermittent (build again and the error goes away). I am using VS Code at the same time (if that matters). I have never seen this before. Any clues what might be going on? These are serious issues if at all pervasive.

C:\git\testapps\cpumath>dotnet build
Microsoft (R) Build Engine version 16.1.46-preview+ge12aa7ba78 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 971.7 ms for C:\git\testapps\cpumath\cpumath.csproj.
C:\Program Files\dotnet\sdk\3.0.100-preview4-011022\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(151,5): message NETSDK1057: You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview [C:\git\testapps\cpumath\cpumath.csproj]
C:\Program Files\dotnet\sdk\3.0.100-preview4-011022\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.GenerateAssemblyInfo.targets(133,5): error MSB3713: The file "obj\Debug\netcoreapp3.0\cpumath.AssemblyInfo.cs" could not be created. The process cannot access the file 'C:\git\testapps\cpumath\obj\Debug\netcoreapp3.0\cpumath.AssemblyInfo.cs' because it is being used by another process. [C:\git\testapps\cpumath\cpumath.csproj]
C:\Program Files\dotnet\sdk\3.0.100-preview4-011022\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(151,5): message NETSDK1057: You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview [C:\git\testapps\cpumath\cpumath.csproj]
  cpumath -> C:\git\testapps\cpumath\bin\Debug\net472\cpumath.exe

Build FAILED.

C:\Program Files\dotnet\sdk\3.0.100-preview4-011022\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.GenerateAssemblyInfo.targets(133,5): error MSB3713: The file "obj\Debug\netcoreapp3.0\cpumath.AssemblyInfo.cs" could not be created. The process cannot access the file 'C:\git\testapps\cpumath\obj\Debug\netcoreapp3.0\cpumath.AssemblyInfo.cs' because it is being used by another process. [C:\git\testapps\cpumath\cpumath.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:02.25

And then:

C:\git\testapps\cpumath>dotnet build
Microsoft (R) Build Engine version 15.9.20+g88f5fadfbe for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restoring packages for C:\git\testapps\cpumath\cpumath.csproj...
  Generating MSBuild file C:\git\testapps\cpumath\obj\cpumath.csproj.nuget.g.props.
  Generating MSBuild file C:\git\testapps\cpumath\obj\cpumath.csproj.nuget.g.targets.
  Restore completed in 345.7 ms for C:\git\testapps\cpumath\cpumath.csproj.
C:\Program Files\dotnet\sdk\2.2.105\Microsoft.Common.CurrentVersion.targets(2110,5): warning MSB3101: Could not write state file "obj\Debug\netcoreapp2.2\cpumath.csprojAssemblyReference.cache". The process cannot access the file 'C:\git\testapps\cpumath\obj\Debug\netcoreapp2.2\cpumath.csprojAssemblyReference.cache' because it is being used by another process. [C:\git\testapps\cpumath\cpumath.csproj]
  cpumath -> C:\git\testapps\cpumath\bin\Debug\netcoreapp2.2\cpumath.dll

Build succeeded.

C:\Program Files\dotnet\sdk\2.2.105\Microsoft.Common.CurrentVersion.targets(2110,5): warning MSB3101: Could not write state file "obj\Debug\netcoreapp2.2\cpumath.csprojAssemblyReference.cache". The process cannot access the file 'C:\git\testapps\cpumath\obj\Debug\netcoreapp2.2\cpumath.csprojAssemblyReference.cache' because it is being used by another process. [C:\git\testapps\cpumath\cpumath.csproj]
    1 Warning(s)
    0 Error(s)

Time Elapsed 00:00:04.33

[richlander]

This is still happening to me when VS Code is open (on other projects). I am now seeing it when I “build” from within VS Code. In that scenario, there is no way to avoid VS Code being open.

There is some symmetry to a similar challenge we have with dotnet watch in a container. This PR documents that challenge. I wonder if we need to take a similar approach.

[richlander]

I will continue to monitor this. Yes, VS Code was open the whole time.