Honor DoNotRegister for Java.Lang.Throwable handles

[simonrozsival]

---

Pull Request

Java.Lang.Throwable.SetHandle ignored JniHandleOwnership.DoNotRegister and always registered its wrapper. This caused premature registry insertion during typemap activation, before the peer was marked Replaceable, and could displace an existing peer; a reentrant lookup could similarly lose its alias as winner. SetHandle now passes JNIEnv.ToJniObjectReferenceOptions(transfer) for non-null references while retaining None for null. This preserves the wrapper's copy semantics and leaves raw transferred-input cleanup unchanged. The regression tests cover normal registration, borrowed/local/global inputs with combined raw ownership and DoNotRegister flags, existing replaceable-peer preservation, and reentrant alias identity.

Validation

• Original-code API29/CoreCLR reproduction: 56 total, 49 passed, 7 failed. Failures were ThrowableConstructionHonorsDoNotRegister for three DoNotRegister ownership cases, ThrowableActivationPreservesExistingReplaceablePeer, and ThrowableDoNotRegisterPreservesReentrantAlias for three ownership cases.
• With the fix, CoreCLR TransferredReferences + TrimmableTypeMapRuntimeCoverage: 78 passed, 0 failed.
• With the fix, NativeAOT for the same categories: 78 passed, 0 failed. NativeAOT selection was verified by the APK's libMono.Android.NET-Tests.so; it requires PublishAot=true and Optimize=true in Debug. The build emitted the expected experimental-runtime and ILC analysis warnings, with 0 errors.
• The source SDK build succeeded using the local workaround for the unavailable Microsoft.NETCore.App.Ref 10.0.13 feed package. make prepare without that workaround had failed with NU1102.

ANDROID_HOME="$ANDROID_SDK_ROOT" RuntimeFrameworkVersion=10.0.0 DOTNET_ROLL_FORWARD=Major JavaSdkDirectory="$JAVA_HOME" make all MSBUILD_FLAGS="-p:RuntimeFrameworkVersion=10.0.0 -p:GenerateDocumentationFile=True -p:JavaSdkDirectory=$JAVA_HOME -p:AndroidSdkDirectory=$ANDROID_SDK_ROOT"

CoreCLR (Debug, RuntimeIdentifier=android-arm64, PublishAot=false, Optimize=false; install/build):

ANDROID_HOME="$ANDROID_SDK_ROOT" ANDROID_ADB_SERVER_PORT=5063 DOTNET_ROLL_FORWARD=Major JavaSdkDirectory="$JAVA_HOME" ./dotnet-local.sh build -t:Clean,Install -c Debug tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj -p:RuntimeIdentifier=android-arm64 -p:PublishAot=false -p:Optimize=false '-p:IncludeCategories=TransferredReferences%2CTrimmableTypeMapRuntimeCoverage' '-p:AdbTarget=-s emulator-5580' -p:JavaSdkDirectory="$JAVA_HOME" -p:AndroidSdkDirectory="$ANDROID_SDK_ROOT"
cd tests/Mono.Android-Tests/Mono.Android-Tests && ANDROID_ADB_SERVER_PORT=5063 ../../../dotnet-local.sh test Mono.Android.NET-Tests.csproj --no-build -c Debug -p:RuntimeIdentifier=android-arm64 -p:PublishAot=false -p:Optimize=false '-p:IncludeCategories=TransferredReferences%2CTrimmableTypeMapRuntimeCoverage' --device emulator-5580 --report-trx --results-directory ../../../bin/TestDebug/TestResults --timeout 10m

NativeAOT (Debug, RuntimeIdentifier=android-arm64, PublishAot=true, Optimize=true; install/build and test):

ANDROID_HOME="$ANDROID_SDK_ROOT" ANDROID_ADB_SERVER_PORT=5063 DOTNET_ROLL_FORWARD=Major JavaSdkDirectory="$JAVA_HOME" ./dotnet-local.sh build -t:Clean,Install -c Debug tests/Mono.Android-Tests/Mono.Android-Tests/Mono.Android.NET-Tests.csproj -p:RuntimeIdentifier=android-arm64 -p:PublishAot=true -p:Optimize=true '-p:IncludeCategories=TransferredReferences%2CTrimmableTypeMapRuntimeCoverage' '-p:AdbTarget=-s emulator-5580' -p:JavaSdkDirectory="$JAVA_HOME" -p:AndroidSdkDirectory="$ANDROID_SDK_ROOT"
cd tests/Mono.Android-Tests/Mono.Android-Tests && ANDROID_ADB_SERVER_PORT=5063 ../../../dotnet-local.sh test Mono.Android.NET-Tests.csproj --no-build -c Debug -p:RuntimeIdentifier=android-arm64 -p:PublishAot=true -p:Optimize=true '-p:IncludeCategories=TransferredReferences%2CTrimmableTypeMapRuntimeCoverage' --device emulator-5580 --report-trx --results-directory ../../../bin/TestDebug/TestResults --timeout 10m

This demonstrates premature registration and peer-winner displacement, not a permanent GREF leak; no GREF-count test was run. Refs #13010.

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[Copilot]

🟢 Approval recommended

The fix matches the existing ownership conversion contract and has comprehensive regression coverage; the inline suggestion is non-blocking.

1 open finding

• Clear static test hook before invoking it · New

What changed in this PR

Updates Throwable JNI peer construction to honor DoNotRegister, preventing premature registry replacement during typemap activation.

Changes:

• Preserves DoNotRegister while retaining copy semantics.
• Adds ownership, replaceable-peer, and reentrant-alias regression tests.

File	Description
src/​Mono.Android/​Java.Lang/​Throwable.cs	Converts ownership flags into appropriate JNI reference options.
tests/​Mono.Android-Tests/​Mono.Android-Tests/​Java.Interop/​TransferredReferenceTests.cs	Adds regression coverage and flag-aware reference tracking.

🧠 Review effort: Balanced

[simonrozsival]

@dalexsoto review

[dalexsoto]

Throwable construction now preserves DoNotRegister without changing reference-copy or transferred-input cleanup semantics. Typemap activation and reentrant lookup retain the existing peer winner; the complete correctness and integration review leaves no blocking issue.