Attempt to remove non-JNI local reference errors on Android

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#663 4 comentarios 1 reacción 0 asignados Ver en GitHub

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Evaluación

Dificultad
2/5
Tiempo estimado
1-3 horas
Aptitud para principiantes
75/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Tranquilo
Stack tecnológico
android, swift
Área
mobile-dev

Línea de trabajo

Comienza en JavaObjectHolder.init(object:environment:), donde las referencias jobject entrantes se promueven y se activa la advertencia. Reproduce las llamadas de Android JNI en el emulador de Android 15 con la aplicación FlutterSwift y verifica después que los controladores frecuentes de mensajes del canal de plataforma emitan cero advertencias "Attempt to remove non-JNI local reference".

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

android

Using FlutterSwift with the latest swift-java and Android SDK, I see

2026-04-01 15:37:27.149  7457-7457  ktone.InfernoUI         com.lukktone.InfernoUI               W  Attempt to remove non-JNI local reference

in the Android logs.

Proposed fix is to remove DeleteLocalRef on incoming references in JavaObjectHolder.init to fix Android JNI warnings. (This is by @ampcode-com, I haven't had a chance to review, I hate AI-generated PRs as much as the next person but I haven't had the cycles to look into the root cause myself yet.)

Root Cause

JavaObjectHolder.init(object:environment:) promotes the incoming jobject to a global reference via NewGlobalRef, then checks if the original is a local reference and calls DeleteLocalRef on it. This is problematic because:

  1. JNI parameter references are not owned by native code. When Java calls a native method, the jobject parameters are local references managed by the JNI frame. The JNI specification states these are automatically cleaned up when the native method returns. Native code should not call DeleteLocalRef on them.

  2. ART's CheckJNI detects this. Android's runtime (ART) has CheckJNI enabled by default, which distinguishes between locally-created references (via FindClass, NewObject, etc.) and parameter references. Calling DeleteLocalRef on a parameter reference triggers the warning.

  3. GetObjectRefType returns JNILocalRefType for both cases, so the existing check cannot distinguish parameter references from locally-created references.

Fix

Remove the DeleteLocalRef call entirely. After NewGlobalRef creates a new strong reference to the Java object, the original local reference (whether a parameter or locally-created) will be cleaned up automatically when the JNI frame is popped. This is safe and correct per the JNI specification:

"Local references are valid for the duration of a native method call. They are freed automatically after the native method returns." — JNI Specification

The only scenario where explicit DeleteLocalRef is needed is to avoid local reference table overflow when creating many local references in a loop within a single native method call. JavaObjectHolder.init does not fall into this category.

Testing

Tested on Android 15 (API 36) emulator with a FlutterSwift application that makes frequent JNI calls (platform channel message handlers). Before the fix, every message handler invocation produced 1–3 "Attempt to remove non-JNI local reference" warnings. After the fix, zero warnings are emitted

Lenguaje dominante
Swift
Estrellas
1.3k
Forks
127
Merge medio
2 d 14 h
PR fusionados (30 d)
5

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