Item batching can be very slow, especially on Linux

[dsplaisted]

Changing an item include to include some additional metadata resulted in extreme slowdowns for me, especially on Linux:

OS	Without metadata	With metadata
Windows	10 ms	8234 ms
Linux	68 ms	143022 ms

The change that caused this was changing from:

<_RuntimeTargetPublishItems Include="@(FileDefinitions)" Exclude="@(__RuntimeTargetPublishItems)" />

To:

<_RuntimeTargetPublishItems Include="@(FileDefinitions)" Exclude="@(__RuntimeTargetPublishItems)" 
                            DestinationSubPath="%(FileDefinitions.Path)" />

Repro steps

• git clone https://github.com/dsplaisted/msbuild-slow-batching
• cd msbuild-slow-batching
• cd TestApp
• dotnet build /clp:PerformanceSummary
• Observe the difference in execution time between the FastBatching and SlowBatching targets in the performance summary

EXPECTED: Execution times are comparable
ACTUAL: SlowBatching execution time is several orders of magnitude slower than FastBatching

Repro details

The repro project is an app targeting netcoreapp1.1 referencing a library which targets netstandard1.5. The app project has the following targets added to it:

  <Target Name="SetupItemsForBatching" AfterTargets="Build" DependsOnTargets="_ComputeLockFileCopyLocal">
    <ItemGroup>
      <TestItems1 Include="@(_ActiveTFMFileDependencies->WithMetadataValue('FileGroup', 'RuntimeTarget'))" />
      <TestItems2 Include="@(FileDefinitions)" Exclude="@(TestItems1)" />
    </ItemGroup>
  </Target>

  <Target Name="SlowBatching" AfterTargets="Build" DependsOnTargets="SetupItemsForBatching">
    <ItemGroup>
      <SlowBatchItems Include="@(FileDefinitions)" Exclude="@(TestItems2)"
                      DestinationSubPath="%(FileDefinitions.Path)"/>
    </ItemGroup>
  </Target>

  <Target Name="FastBatching" AfterTargets="Build" DependsOnTargets="SetupItemsForBatching">
    <ItemGroup>
      <FastBatchItems Include="@(FileDefinitions)" Exclude="@(TestItems2)" />      
    </ItemGroup>
  </Target>

[ladipro]

Tried to repro with current bits but the target _ComputeLockFileCopyLocal as referenced in the repro project does not exist anymore. @dsplaisted, would it be possible to update the repro to build with current .NET SDK?