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merged 2 commits into from
Jul 16, 2025
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[Mono.Android] trimmer feature switches for DotNetRuntimeType #10296

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[Mono.Android] trimmer feature switches for `DotNetRuntimeType`
jonathanpeppers Jul 14, 2025
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Update BuildReleaseArm64SimpleDotNet.apkdesc
jonathanpeppers Jul 16, 2025
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2 changes: 1 addition & 1 deletion src/Mono.Android.Runtime/Mono.Android.Runtime.csproj
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Expand Up @@ -52,11 +52,11 @@
<ItemGroup>
<Compile Include="$(IntermediateOutputPath)AssemblyInfo.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\AndroidRuntimeInternal.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\DotNetRuntimeType.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\LogCategories.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\LogLevel.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\RuntimeConstants.cs" />
<Compile Include="..\Mono.Android\Android.Runtime\RuntimeNativeMethods.cs" />
<Compile Include="..\Mono.Android\Microsoft.Android.Runtime\RuntimeFeature.cs" />
<Compile Include="Android.Runtime\AndroidEnvironmentInternal.cs" />
</ItemGroup>

Expand Down
40 changes: 8 additions & 32 deletions src/Mono.Android/Android.Runtime/AndroidRuntimeInternal.cs
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@@ -1,36 +1,10 @@
#if INSIDE_MONO_ANDROID_RUNTIME
using System;
using System.Reflection;
using Microsoft.Android.Runtime;

namespace Android.Runtime
{
// The existence of InternalRuntimeTypeHolder and DotNetRuntimeTypeConverter classes looks weird, but
// we must handle a weird situation. AndroidRuntimeInternal needs to know in its static constructor
// what is the current runtime type, but it cannot query JNIEnvInit.RuntimeType, since that type lives
// in the Mono.Android assembly, while AndroidRuntimeInternal lives in Mono.Android.Runtime and it cannot
// access JNIEnvInit and Mono.Android.Runtime doesn't reference Mono.Android but Mono.Android **does** reference
// Mono.Android.Runtime and has access to its internals.
//
// Mono.Android.Runtime, also, includes several source files from Mono.Android - **both** assemblies
// include the same source files. In case of the DotNetRuntimeType enum, this declares two distinct types - one
// in Mono.Android and another in Mono.Android.Runtime, and so if JNIEnvInit.Initialize were to try to set the
// `DotNetRuntimeType RuntimeType;` field/property in either of the classes below, we'd get a compilation error
// to the effect of it being unable to cast `Android.Runtime.DotNetRuntimeType` to `Android.Runtime.DotNetRuntimeType`,
// which is usually as clear as mud :)
//
// To solve this and not duplicate code, the InternalRuntimeTypeHolder class is introduced which acts as a proxy since
// the AndroidRuntimeInternal static constructor must know the runtime type and JNIEnvInit.Initialize takes care of it by
// calling `SetRuntimeType` below long before AndroidRuntimeInternal cctor is invoked.
public static class InternalRuntimeTypeHolder
{
internal static DotNetRuntimeType RuntimeType = DotNetRuntimeType.Unknown;

internal static void SetRuntimeType (uint runtimeType)
{
RuntimeType = DotNetRuntimeTypeConverter.Convert (runtimeType);
}
}

public static class AndroidRuntimeInternal
{
internal static readonly Action<Exception> mono_unhandled_exception;
Expand All @@ -41,11 +15,13 @@ public static class AndroidRuntimeInternal

static AndroidRuntimeInternal ()
{
mono_unhandled_exception = InternalRuntimeTypeHolder.RuntimeType switch {
DotNetRuntimeType.MonoVM => MonoUnhandledException,
DotNetRuntimeType.CoreCLR => CoreClrUnhandledException,
_ => throw new NotSupportedException ($"Internal error: runtime type {InternalRuntimeTypeHolder.RuntimeType} not supported")
};
if (RuntimeFeature.IsMonoRuntime) {
mono_unhandled_exception = MonoUnhandledException;
} else if (RuntimeFeature.IsCoreClrRuntime) {
mono_unhandled_exception = CoreClrUnhandledException;
} else {
throw new NotSupportedException ("Internal error: unknown runtime not supported");
}
}

static void CoreClrUnhandledException (Exception ex)
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32 changes: 0 additions & 32 deletions src/Mono.Android/Android.Runtime/DotNetRuntimeType.cs
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This file was deleted.

31 changes: 15 additions & 16 deletions src/Mono.Android/Android.Runtime/JNIEnv.cs
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@@ -1,6 +1,7 @@
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Reflection;
Expand All @@ -12,7 +13,7 @@

using Java.Interop;
using Java.Interop.Tools.TypeNameMappings;
using System.Diagnostics.CodeAnalysis;
using Microsoft.Android.Runtime;

namespace Android.Runtime {
public static partial class JNIEnv {
Expand Down Expand Up @@ -100,16 +101,12 @@ internal static void PropagateUncaughtException (IntPtr env, IntPtr javaThreadPt
Logger.Log (LogLevel.Info, "MonoDroid", "UNHANDLED EXCEPTION:");
Logger.Log (LogLevel.Info, "MonoDroid", javaException.ToString ());

switch (JNIEnvInit.RuntimeType) {
case DotNetRuntimeType.MonoVM:
MonoDroidUnhandledException (innerException ?? javaException);
break;
case DotNetRuntimeType.CoreCLR:
// TODO: what to do here?
break;

default:
throw new NotSupportedException ($"Internal error: runtime type {JNIEnvInit.RuntimeType} not supported");
if (RuntimeFeature.IsMonoRuntime) {
MonoDroidUnhandledException (innerException ?? javaException);
} else if (RuntimeFeature.IsCoreClrRuntime) {
// TODO: what to do here?
} else {
throw new NotSupportedException ("Internal error: unknown runtime not supported");
}
} catch (Exception e) {
Logger.Log (LogLevel.Error, "monodroid", "Exception thrown while raising AppDomain.UnhandledException event: " + e.ToString ());
Expand Down Expand Up @@ -453,11 +450,13 @@ static unsafe IntPtr monovm_typemap_managed_to_java (Type type, byte* mvidptr)

IntPtr ret;
fixed (byte* mvidptr = mvid_data) {
ret = JNIEnvInit.RuntimeType switch {
DotNetRuntimeType.MonoVM => monovm_typemap_managed_to_java (type, mvidptr),
DotNetRuntimeType.CoreCLR => RuntimeNativeMethods.clr_typemap_managed_to_java (type.FullName, (IntPtr)mvidptr),
_ => throw new NotSupportedException ($"Internal error: runtime type {JNIEnvInit.RuntimeType} not supported")
};
if (RuntimeFeature.IsMonoRuntime) {
ret = monovm_typemap_managed_to_java (type, mvidptr);
} else if (RuntimeFeature.IsCoreClrRuntime) {
ret = RuntimeNativeMethods.clr_typemap_managed_to_java (type.FullName, (IntPtr)mvidptr);
} else {
throw new NotSupportedException ("Internal error: unknown runtime not supported");
}
}

if (ret == IntPtr.Zero) {
Expand Down
23 changes: 11 additions & 12 deletions src/Mono.Android/Android.Runtime/JNIEnvInit.cs
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Expand Up @@ -34,7 +34,6 @@ internal struct JnienvInitializeArgs {
public bool jniRemappingInUse;
public bool marshalMethodsEnabled;
public IntPtr grefGCUserPeerable;
public uint runtimeType;
public bool managedMarshalMethodsLookupEnabled;
}
#pragma warning restore 0649
Expand All @@ -50,8 +49,6 @@ internal struct JnienvInitializeArgs {

internal static JniRuntime? androidRuntime;

public static DotNetRuntimeType RuntimeType { get; private set; } = DotNetRuntimeType.Unknown;

[UnmanagedCallersOnly]
static unsafe void RegisterJniNatives (IntPtr typeName_ptr, int typeName_len, IntPtr jniClass, IntPtr methods_ptr, int methods_len)
{
Expand Down Expand Up @@ -91,9 +88,10 @@ internal static void InitializeJniRuntime (JniRuntime runtime)
[UnmanagedCallersOnly]
internal static unsafe void Initialize (JnienvInitializeArgs* args)
{
// This looks weird, see comments in RuntimeTypeInternal.cs
RuntimeType = DotNetRuntimeTypeConverter.Convert (args->runtimeType);
InternalRuntimeTypeHolder.SetRuntimeType (args->runtimeType);
// Should not be allowed
if (RuntimeFeature.IsMonoRuntime && RuntimeFeature.IsCoreClrRuntime) {
throw new NotSupportedException ("Internal error: both RuntimeFeature.IsMonoRuntime and RuntimeFeature.IsCoreClrRuntime are enabled");
}

IntPtr total_timing_sequence = IntPtr.Zero;
IntPtr partial_timing_sequence = IntPtr.Zero;
Expand All @@ -114,12 +112,13 @@ internal static unsafe void Initialize (JnienvInitializeArgs* args)
} else {
typeManager = new AndroidTypeManager (args->jniAddNativeMethodRegistrationAttributePresent != 0);
}
valueManager = RuntimeType switch
{
DotNetRuntimeType.MonoVM => new AndroidValueManager(),
DotNetRuntimeType.CoreCLR => ManagedValueManager.GetOrCreateInstance(),
_ => throw new NotSupportedException ($"No value manager for runtime type: {RuntimeType}"),
};
if (RuntimeFeature.IsMonoRuntime) {
valueManager = new AndroidValueManager ();
} else if (RuntimeFeature.IsCoreClrRuntime) {
valueManager = ManagedValueManager.GetOrCreateInstance ();
} else {
throw new NotSupportedException ("Internal error: unknown runtime not supported");
}
androidRuntime = new AndroidRuntime (
args->env,
args->javaVm,
Expand Down
13 changes: 8 additions & 5 deletions src/Mono.Android/Java.Interop/TypeManager.cs
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Expand Up @@ -8,6 +8,7 @@
using Java.Interop.Tools.TypeNameMappings;

using Android.Runtime;
using Microsoft.Android.Runtime;

namespace Java.Interop {

Expand Down Expand Up @@ -267,11 +268,13 @@ static Type monovm_typemap_java_to_managed (string java_type_name)
return type;
}

type = JNIEnvInit.RuntimeType switch {
DotNetRuntimeType.MonoVM => monovm_typemap_java_to_managed (class_name),
DotNetRuntimeType.CoreCLR => clr_typemap_java_to_managed (class_name),
_ => throw new NotSupportedException ($"Internal error: runtime type {JNIEnvInit.RuntimeType} not supported")
};
if (RuntimeFeature.IsMonoRuntime) {
type = monovm_typemap_java_to_managed (class_name);
} else if (RuntimeFeature.IsCoreClrRuntime) {
type = clr_typemap_java_to_managed (class_name);
} else {
throw new NotSupportedException ("Internal error: unknown runtime not supported");
}

if (type != null) {
TypeManagerMapDictionaries.JniToManaged.Add (class_name, type);
Expand Down
14 changes: 13 additions & 1 deletion src/Mono.Android/Microsoft.Android.Runtime/RuntimeFeature.cs
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Expand Up @@ -5,9 +5,21 @@ namespace Microsoft.Android.Runtime;

static class RuntimeFeature
{
const bool ManagedTypeMapEnabledByDefault = false;
const bool IsMonoRuntimeEnabledByDefault = true;
const bool IsCoreClrRuntimeEnabledByDefault = false;

const string FeatureSwitchPrefix = "Microsoft.Android.Runtime.RuntimeFeature.";

[FeatureSwitchDefinition ($"{FeatureSwitchPrefix}{nameof (ManagedTypeMap)}")]
internal static bool ManagedTypeMap { get; } =
AppContext.TryGetSwitch ($"{FeatureSwitchPrefix}{nameof (ManagedTypeMap)}", out bool isEnabled) ? isEnabled : false;
AppContext.TryGetSwitch ($"{FeatureSwitchPrefix}{nameof (ManagedTypeMap)}", out bool isEnabled) ? isEnabled : ManagedTypeMapEnabledByDefault;

[FeatureSwitchDefinition ($"{FeatureSwitchPrefix}{nameof (IsMonoRuntime)}")]
internal static bool IsMonoRuntime { get; } =
AppContext.TryGetSwitch ($"{FeatureSwitchPrefix}{nameof (IsMonoRuntime)}", out bool isEnabled) ? isEnabled : IsMonoRuntimeEnabledByDefault;
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I wonder if we should enforce that the feature switch is always set explicitly and throw if it isn't. I'm worried that we could introduce a regression and for example we would drop the Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime on CoreCLR in the SDK and now both IsMonoRuntime and IsCoreClrRuntime would be true.

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I'll add something that throws on startup if both are set to true.


[FeatureSwitchDefinition ($"{FeatureSwitchPrefix}{nameof (IsCoreClrRuntime)}")]
internal static bool IsCoreClrRuntime { get; } =
AppContext.TryGetSwitch ($"{FeatureSwitchPrefix}{nameof (IsCoreClrRuntime)}", out bool isEnabled) ? isEnabled : IsCoreClrRuntimeEnabledByDefault;
}
1 change: 0 additions & 1 deletion src/Mono.Android/Mono.Android.csproj
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Expand Up @@ -220,7 +220,6 @@
<Compile Include="Android.Runtime\BoundExceptionType.cs" />
<Compile Include="Android.Runtime\CharSequence.cs" />
<Compile Include="Android.Runtime\CPUArchitecture.cs" />
<Compile Include="Android.Runtime\DotNetRuntimeType.cs" />
<Compile Include="Android.Runtime\Extensions.cs" />
<Compile Include="Android.Runtime\GeneratedEnumAttribute.cs" />
<Compile Include="Android.Runtime\IJavaObject.cs" />
Expand Down
12 changes: 12 additions & 0 deletions ...n.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.CoreCLR.targets
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Expand Up @@ -20,6 +20,18 @@ This file contains the CoreCLR-specific MSBuild logic for .NET for Android.
<AllowReadyToRunWithoutRuntimeIdentifier Condition=" '$(PublishReadyToRun)' == 'true' and '$(RuntimeIdentifiers)' != '' ">true</AllowReadyToRunWithoutRuntimeIdentifier>
</PropertyGroup>

<!-- Default feature switches -->
<ItemGroup>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime"
Value="false"
Trim="true"
/>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsCoreClrRuntime"
Value="true"
Trim="true"
/>
</ItemGroup>

<Target Name="_CLRUseLocalRuntimePacks" AfterTargets="ResolveFrameworkReferences"
Condition=" '$(_CLRLocalRuntimePath)' != '' And '$(_AndroidRuntime)' == 'CoreCLR' ">
<PropertyGroup>
Expand Down
22 changes: 22 additions & 0 deletions ...in.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.MonoVM.targets
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@@ -0,0 +1,22 @@
<!--
***********************************************************************************************
Microsoft.Android.Sdk.MonoVM.targets

This file contains the MonoVM-specific MSBuild logic for .NET for Android.
***********************************************************************************************
-->
<Project>

<!-- Default feature switches -->
<ItemGroup>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime"
Value="true"
Trim="true"
/>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsCoreClrRuntime"
Value="false"
Trim="true"
/>
</ItemGroup>

</Project>
12 changes: 12 additions & 0 deletions ...Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.NativeAOT.targets
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Expand Up @@ -29,6 +29,18 @@ This file contains the NativeAOT-specific MSBuild logic for .NET for Android.
<CompressSymbols>false</CompressSymbols>
</PropertyGroup>

<!-- Default feature switches -->
<ItemGroup>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsMonoRuntime"
Value="false"
Trim="true"
/>
<RuntimeHostConfigurationOption Include="Microsoft.Android.Runtime.RuntimeFeature.IsCoreClrRuntime"
Value="false"
Trim="true"
/>
</ItemGroup>

<!-- Make IlcCompile depend on the trimmer -->
<PropertyGroup>
<IlcCompileDependsOn>
Expand Down
3 changes: 1 addition & 2 deletions src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.targets
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Expand Up @@ -33,7 +33,6 @@
<Import Project="Microsoft.Android.Sdk.DefaultProperties.targets" />
<Import Project="$(MSBuildThisFileDirectory)..\tools\Xamarin.Android.Common.Debugging.props"
Condition="Exists('$(MSBuildThisFileDirectory)..\tools\Xamarin.Android.Common.Debugging.props') And '$(DesignTimeBuild)' != 'true' "/>
<Import Project="Microsoft.Android.Sdk.CoreCLR.targets" Condition=" '$(_AndroidRuntime)' == 'CoreCLR' " />
<Import Project="Microsoft.Android.Sdk.NativeAOT.targets" Condition=" '$(_AndroidRuntime)' == 'NativeAOT' " />
<Import Project="Microsoft.Android.Sdk.$(_AndroidRuntime).targets" Condition=" '$(_AndroidRuntime)' != '' " />

</Project>
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