MSBuild: parallel builds and .Net projects - build

Question

I've written a MSBuild project files which try to build in parallel all the configs of my VS2010 solution:
<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003" ToolsVersion="4.0">
<ItemGroup>
<BuildFile Include="$(SourceRoot)MyProject.sln" />
<Config Include="Debug">
<Configuration>Debug</Configuration>
</Config>
<Config Include="Release">
<Configuration>Release</Configuration>
</Config>
</ItemGroup>
<Target Name="BuildAll" Outputs="%(Config.Configuration)">
<Message Text="Start building for configuration: %(Config.Configuration)" />
<MSBuild Projects="#(BuildFile)"
Properties="Configuration=%(Config.Configuration)"
Targets="Build" />
</Target>
</Project>
And I launch msbuild with:
msbuild /m /p:BuildInParallel=true /t:BuildAll buildall.proj
The problem is that my solution have many .Net projects which all have the same output folder. These projects use also the same external assemblies.
So very often, two output executables are generated at the same time and their dependencies copied at the same time. This leads to errors like:
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(3001,9):
error MSB3021:
Unable to copy file "xxx\NLog.dll" to "D:\src\Blackbird\shared\bin\debug\NLog.xml". The process
cannot access the file 'xxx\NLog.dll because it is being used by another process.
which I think means: "2 different projects use NLog and try to copy its assembly in the output folder at the same time"...
Is there a way to get around that? I really would like to avoid to modify all the projects in the solution.
Looking at the task source code "C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(3001,9)", I've seen that it is possible to make msbuild retry the copy:
<Copy
SourceFiles="#(ReferenceCopyLocalPaths)"
DestinationFiles="#(ReferenceCopyLocalPaths->'$(OutDir)%(DestinationSubDirectory)%(Filename)%(Extension)')"
SkipUnchangedFiles="$(SkipCopyUnchangedFiles)"
OverwriteReadOnlyFiles="$(OverwriteReadOnlyFiles)"
Retries="$(CopyRetryCount)"
RetryDelayMilliseconds="$(CopyRetryDelayMilliseconds)"
UseHardlinksIfPossible="$(CreateHardLinksForCopyLocalIfPossible)"
Condition="'$(UseCommonOutputDirectory)' != 'true'"
>
I've try to set the variables CopyRetryCount, CopyRetryDelayMilliseconds, ... I was hoping that if the copy fails, another copy done a few milliseconds later would succeed. But I've been unable to set these parameters. How can I change them?
Is there another solution?

Answer 1

I've found the solution
<MSBuild Projects="#(BuildFile)"
Properties="Configuration=%(Config.Configuration);Retries=10;RetryDelayMilliseconds=50"
Targets="Build" />
It works as expected but now it generates a warning before retrying the copy
C:\Windows\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(3001,9):
warning MSB3026: Could not copy
"D:\src\xxx\System.Data.SQLite.pdb" to "..\Debug\System.Data.SQLite.pdb".
Beginning retry 1 in 50ms. The process cannot access the file
'..\Debug\System.Data.SQLite.pdb' because it is being used by another process.
During my last test, it generated 36 times this warning! Is there a way for suppressing the warning MSB0326?

Answer 2

In general, anything that runs during build must not acquire an exclusive lock on its inputs - only shared-read lock. It appears that something in your build process (probably NLog, whatever that is) violates this - it takes exclusive lock on the input "xxx\NLog.dll", so when another msbuild node tries to copy the same input it fails.
Retry is a reasonable workaround for the particular symptom you have - though it's not guaranteed to always succeed.

Answer 3

I had the same problem. I needed to add appropriate exception to my AntiVirus to avoid sacanning DLLs produced by MsBuild.