Builds of solutions with multiple inter-dependent .NET Core projects frequently fail with CS2012 "Cannot open" file errors

Steps to reproduce

With a solution with multiple .NET Core projects with many sharing project dependencies:

• dotnet restore
• dotnet build

Expected behavior

Solution builds.

Actual behavior

Solution sometimes builds, but also often fails with errors similar to:

CSC : error CS2012: Cannot open 'C:\a\w\1\s\src\Project\obj\Debug\netstandard1.4\Project.dll' for writing -- 'The process cannot access the file 'C:\a\w\1\s\src\Project\obj\Debug\netstandard1.4\Project.dll' because it is being used by another process.'

Sometimes there are warnings:

warning MSB3026: Could not copy "obj\Debug\netstandard1.4\Project.dll" to "bin\Debug\netstandard1.4\Project.dll". Beginning retry 1 in 1000ms. The process cannot access the file 'C:\a\w\1\s\src\Project\bin\Debug\netstandard1.4\Project.dll' because it is being used by another process. [C:\a\w\1\s\src\Project\Project.csproj]

Errors and warnings can occur for different projects.

Switching from dotnet build to msbuild /maxcpucount:1 avoids the problems.

The errors occur more frequently on build servers (Azure VMs, Standard F2S) than on laptop (i7-5600U, 16GB, SSD).

Our build script replaces version numbers in AssemblyInfo.cs files, so many projects are rebuilt on every build.

Executing dotnet build --no-incremental also seems to increase failure rate locally (where otherwise repeated builds may not build all projects).

Environment data

dotnet --info output:

.NET Command Line Tools (1.0.0-preview3-004056)

Product Information:
 Version:            1.0.0-preview3-004056
 Commit SHA-1 hash:  ccc4968bc3

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64

[sherlock1982]

Well it’s really easy to reproduce with NET SDK 2.0.2

dotnet publish -o /home/user/publish_dir 

Will publish everything from a solution into one folder in case argument of -o is an absolute directory. This is super convenient and a way to go in case you make sure projects are compatible. Though publish commands can fight for files of course.

[benyitzhaki]

this still occurs in 2.1.1, linux. fails sometimes when running the dotnet test, happens mostly on our builder machine but not only