Unable to load DLL 'FastTreeNative' when targeting `net472`

[lipchev]

System Information:

• OS & Version: [Windows 10 (x64)]
• ML.NET Version: [Microsoft.ML.FastTree v5.0.0]
• .NET Version: [net472]

Describe the bug
The FastTreeNative.dll isn't being deployed to the output directory, causing a runtime exception when attempting to train a model.

Unable to load DLL 'FastTreeNative'

To Reproduce
Steps to reproduce the behavior:

1. Create a project targeting the NET Framework (e.g. net472)
2. Include the ML.NET & FastTree packages (same behavior with either v4 or v5)
3. Create a simple training pipeline
4. Run the project and observe a runtime exception

Expected behavior
The appropriate FastTreeNative.dll is included in the output directory and no exception is thrown.

Additional context
The same code, targeting net10.0 deploys the FastTreeNative.dll in the runtimes\win-x86\native and runtimes\win-x64\native folders. If I manually copy the file from the net10.0 build to the bin\Debug directory of the framework build, it works as expected.

Possibly related to #5308.

[ericstj]

No Repro for me, do you have a custom build system?

The package copies to the output by packaging the library as runtimes\RID\native\FastTreeNative.dll. This will automatically be handled for packages using PackageReference. Note that ML.NET requires a .NETFramework project to target a supported architecture and not AnyCPU and will emit an error if this is not the case.

If a project is using packages.config then ML.NET ships props files in the package that are meant to approximate this functionality:

machinelearning/eng/pkg/CommonPackage.props

Lines 7 to 30 in 8f9674f

	<ItemGroup Condition="Exists('packages.config') OR
	Exists('$(MSBuildProjectName).packages.config') OR
	Exists('packages.$(MSBuildProjectName).config')">
	<Content Include="$(MSBuildThisFileDirectory)\..\..\runtimes\win-x64\native\*.dll"
	Condition="'$(PlatformTarget)' == 'x64'">
	<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	<Visible>false</Visible>
	<Link>%(Filename)%(Extension)</Link>
	</Content>
	<Content Include="$(MSBuildThisFileDirectory)\..\..\runtimes\win-x86\native\*.dll"
	Condition="'$(PlatformTarget)' == 'x86'">
	<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	<Visible>false</Visible>
	<Link>%(Filename)%(Extension)</Link>
	</Content>
	<Content Include="$(MSBuildThisFileDirectory)\..\..\runtimes\win-arm64\native\*.dll"
	Condition="'$(PlatformTarget)' == 'arm64'">
	<CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
	<Visible>false</Visible>
	<Link>%(Filename)%(Extension)</Link>
	</Content>
	</ItemGroup>

Here's a repro that demonstrates this working.
mlNetFx.zip

You can build this and see that FastTreeNative.dll is in the output.

Please provide a similar repro if you can demonstrate the issue.

[lipchev]

@ericstj Thanks for the quick reply, that was very helpful:

Note that ML.NET requires a .NETFramework project to target a supported architecture and not AnyCPU and will emit an error if this is not the case.

My legacy app, which was indeed using AnyCPU (with the Prefer x86 option unchecked), is referencing a project library project which itself is multi-targeting net472;net10.0.

Forcing the legacy project to build for x64 fixes the issue.

PS I actually saw a suggestion on stackoverflow, about forcing the project to target x64, but didn't bother to try it, as the thread was kinda old...

[ericstj]

I see, I'm surprised that you didn't hit this error --

machinelearning/src/Microsoft.ML/build/netstandard2.0/Microsoft.ML.targets

Lines 16 to 19 in 8f9674f

	<Error Condition="('$(PlatformTarget)' != 'x64' AND '$(PlatformTarget)' != 'x86') AND
	('$(OutputType)' == 'Exe' OR '$(OutputType)'=='WinExe') AND
	!('$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND '$(PlatformTarget)' == '')"
	Text="Microsoft.ML currently supports 'x64' and 'x86' processor architectures. Please ensure your application is targeting 'x64' or 'x86'." />

Could you please send a snippet of your project file before the fix and I can see if we can improve the error condition?

[lipchev]

ML-NET-multi-target-any-cpu.zip

I wasn't able to exactly reproduce the scenario in the sample project..

The legacy app which doesn't directly reference ML.NET builds fine with AnyCPU

  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>{37727C6E-1C23-4F7B-A84B-A3216C5CD2C5}</ProjectGuid>
    <OutputType>Exe</OutputType>
    <RootNamespace>LegacyApp</RootNamespace>
    <AssemblyName>LegacyApp</AssemblyName>
    <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion>
    <FileAlignment>512</FileAlignment>
    <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
    <Deterministic>true</Deterministic>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
    <PlatformTarget>AnyCPU</PlatformTarget>
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\Debug\</OutputPath>
    <DefineConstants>DEBUG;TRACE</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
    <Prefer32Bit>false</Prefer32Bit>
  </PropertyGroup>

And here is the SharedModel.csproj:

<Project Sdk="Microsoft.NET.Sdk">

	<PropertyGroup>
		<TargetFrameworks>net472;net10.0</TargetFrameworks>
		<ImplicitUsings>enable</ImplicitUsings>
		<LangVersion>latest</LangVersion>
		<Nullable>enable</Nullable>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.ML.FastTree" Version="5.0.0" />
	</ItemGroup>
</Project>

There is Microsoft.ML.FastTree.dll but no FastTreeNative.dll in the output directory.

And that's where the similarities with my other solution end:

1. Even though FastTreeNative.dll is missing, the LegacyApp still runs fine (no DllNotFoundException)
2. Changing the <PlatformTarget> to x64 has no effect (the dll is still not present in the output directory)

I was able to confirm that adding a direct reference to ML.NET from the LegacyApp triggers the build error when directly referencing ML.NET package.

I double checked my other solution- toggling the <PlatformTarget> still has the same effect, but I couldn't find anything that could be linked to the cause - but there are quite a few projects in the build..