Can't reliably build on .NET 8 on large multi proc machines

[shanselman]

Describe the bug

Can't reliably build on .NET 8 on large multi proc machines. dotnet build always fails with "The process cannot access the file" on some random objs (likely a .targets file issue)

To Reproduce

Steps to reproduce the behavior:

1. clone fresh on a 8-16-32 proc machine
2. dotnet build
3. observe fail
4. now try dotnet build -m:1 and it'll work. 2 or 3 works. Anything >= 4 always fails

Expected behavior

A clear and concise description of what you expected to happen.

Screenshots

If applicable, add screenshots to help explain your problem.

[DamianEdwards]

I reproduced this with .NET 7 too (SDK 7.0.404)

[jtkech]

Which version because from recently we only target net8.0 (OC preview version).

Otherwise in our github actions we needed to build all TFMs one after each other (by specifying the TFM).

As I remember it was failing (but not always) when files are outputed concurrently.

Didn't know about the -m: switch.

Can you try with only -f net8.0 or -f net7.0 depending on your OC version.

I will try asap.

Edited: Just tried, it works but yes I only have 4 cores.

[sebastienros]

@jtkech I believe we updated SourceLink to 8.0.0 in YesSql, it was 1.1.1 before. (The failing step mentions a conflict ot yessql.sourcelink file)

[sebastienros]

I have the same issue with different files. 16 cores. @jtkech your machine might not be fast enough to reproduce the problem. Not specific to sourcelink though.

[sebastienros]

Going back to a commit that targets 6/7/8 I can repro with dotnet build but not with individual -f 6/7/8.

Example:

CSC : error CS2012: Cannot open 'C:\code\orchardcore\src\OrchardCore.Modules\OrchardCore.Seo\obj\Debug\net8.0\OrchardCo
re.Seo.dll' for writing -- 'The process cannot access the file 'C:\code\orchardcore\src\OrchardCore.Modules\OrchardCore
.Seo\obj\Debug\net8.0\OrchardCore.Seo.dll' because it is being used by another process.' [C:\code\orchardcore\src\Orcha
rdCore.Modules\OrchardCore.Seo\OrchardCore.Seo.csproj::TargetFramework=net8.0]

[sebastienros]

On main, which only targets net8.0, I did three rounds of

git clean -xdff
dotnet build
git clean -xdff
dotnet build -f net8.0

Each time the dotnet build failed and the -f net8.0 succeeded.

[sebastienros]

Please try the branch sebros/minmultit to confirm that fixes the problem.

[DamianEdwards]

Please try the branch sebros/minmultit to confirm that fixes the problem.

Seems to work for me now

[Piedone]

FWIW we had the similar "warning MSB3026: Could not copy DLLs" happening with CI builds running dotnet build (but not builds in Visual Studio) forever, like since .NET Core.

[Skrypt]

You can also repro this issue by debugging in VS and VS Code at the same time. Happens to me all the time, forgetting I'm running VS Code, then I need to stop one of the debuggers.

[sebastienros]

I am investigating the problem with some engineers from the SDK. I have a reliable repro and binlog files that shows some information about the issue.