MSBuild /m:4 fails because it builds the same project twice

Question

My team has a large solution (~500 csproj's). We use VS2012, and build using TFS Build, which uses MSBuild 4. Currently we build serially, but we want to build in parallel (using msbuild /maxcpucount:4). However, when I try it on my 4-proc machine, I get a weird failure:

11:2>CSC : fatal error CS0042: Unexpected error creating debug information file 'C:\Common\obj\Debug\Common.PDB' -- 'C:\Common\obj\Debug\Common.pdb: The process cannot access the file because it is being used by another process. [C:\Common\Common.csproj]

Looking at the log, 2 msbuild nodes were trying to build that same csproj, and thus colliding on writing some output:

10>Project "C:\Utils\Utils.csproj" (10) is building "C:\Common\Common.csproj" (11) on node 4 (default targets). 46:2>Project "C:\Objects\Objects.csproj" (46:2) is building "C:\Common\Common.csproj" (11:2) on node 1 (default targets).

Why would MSBuild try to build the same project twice?

score 5 · Accepted Answer · answered Jul 01 '13 at 15:39

Cause: Someone was calling <MSBuild Projects="Common.csproj" Properties="..." />. Then, MSBuild thinks that it should build Common.csproj again with those different properties, and it happened to occur at the same time with the regular compilation of Common.csproj.

Fix: Call <MSBuild ... /> without those unneeded properties.

Test:

Common.targets

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Target Name="Build">
    <Message Importance="high" Text="Build in $(MSBuildThisFile)" />
  </Target>
  <Target Name="After" DependsOnTargets="Build">
    <Message Importance="high" Text="After in $(MSBuildThisFile)" />
  </Target>
</Project>

Other.targets

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Target Name="Build">
    <Message Importance="high" Text="Build in $(MSBuildThisFile)" />
    <MSBuild Projects="common.targets" Targets="Build" />   <!-- regular builds -->
    <MSBuild Projects="common.targets"                      <!-- custom invocation with properties -->
             Targets="After"
             Properties="myprop=myvalue"
             />
  </Target>
</Project>

Run:

> msbuild other.targets /clp:verbosity=minimal
  Build in other.targets
  Build in common.targets
  Build in common.targets    <<<< Common.targets Build is invoked again
  After in common.targets

And indeed, removing Properties="myprop=myvalue" solves the issue.

score 1 · Answer 2 · answered Dec 14 '21 at 18:20

1

I found someone had added two project references (from the same project) and that apparently caused msbuild to build twice also.. something to watch out for

answered Dec 14 '21 at 18:20

James Grayson

11
1

This does not provide an answer to the question. Once you have sufficient [reputation](https://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](https://stackoverflow.com/help/privileges/comment); instead, [provide answers that don't require clarification from the asker](https://meta.stackexchange.com/questions/214173/why-do-i-need-50-reputation-to-comment-what-can-i-do-instead). - [From Review](/review/late-answers/30587303) – MD. RAKIB HASAN Dec 21 '21 at 11:01
Original asker here. This is actually a different and equally-valid answer, and is of value to future people encountering this issue. So upvote from me. – Jonathan Dec 26 '21 at 07:51

MSBuild /m:4 fails because it builds the same project twice

2 Answers2

Linked