对于想学习Agent开发的朋友可以关注我的新项目HelloAgentR工程手记1/100天——项目工作流搭建一、HybridData 是什么HybridData来自 Facebook 的fbjni库com.facebook.jni.HybridData它是一个将 C 对象指针封装在 Java 对象中的桥梁类。本质上是 Java 层持有 C 层对象的句柄实现了 Java 和 C 之间一对一的对象绑定。二、内存管理流程┌─────────────────────────────────────────────────┐ │ Java 层 │ │ ┌──────────────────────────────┐ │ │ │ HermesExecutor │ │ │ │ mHybridData ──────────────────┐ │ │ └──────────────────────────────┘ │ │ │ ▼ │ │ ┌──────────────────────────────┐ │ │ │ HybridData (fbjni) │ │ │ │ 内部持有 C 指针 (long) │ │ │ └──────────────────────────────┘ │ └─────────────────────────────────────────────────┘ │ JNI ▼ ┌─────────────────────────────────────────────────┐ │ C 层 │ │ ┌──────────────────────────────┐ │ │ │ HermesExecutorHolder (C) │ │ │ │ │ │ │ │ │ │ │ └──────────────────────────────┘ │ └─────────────────────────────────────────────────┘二、核心工作原理public class HermesExecutor extends JavaScriptExecutor { private static String mode_ ; static { loadLibrary(); } public static void loadLibrary() throws UnsatisfiedLinkError { if (mode_ null) { // libhermes must be loaded explicitly to invoke its JNI_OnLoad. SoLoader.loadLibrary( hermes ); SoLoader.loadLibrary( hermes_executor ); // libhermes_executor is built differently for Debug Release so we load the proper mode. mode_ ReactBuildConfig.DEBUG ? Debug : Release ; } } HermesExecutor(Nullable RuntimeConfig config, boolean enableDebugger, String debuggerName) { super( config null ? initHybridDefaultConfig(enableDebugger, debuggerName) : initHybrid(enableDebugger, debuggerName, config.getHeapSizeMB())); } Override public String getName() { return HermesExecutor mode_ ; } private static native HybridData initHybridDefaultConfig( boolean enableDebugger, String debuggerName); private static native HybridData initHybrid( boolean enableDebugger, String debuggerName, long heapSizeMB); }HermesExecutor继承JavaScriptExecutorJavaScriptExecutor中定义了一个mHybridData字段private final HybridData mHybridData;HermesExecutor构造函数调用initHybridDefaultConfig或initHybrid返回一个HybridData对象initHybridDefaultConfig和initHybrid都是native方法在OnLoad.cpp中注册了这两个方法并且这两个方法都是HermesExecutorHolder类中static void registerNatives() { registerHybrid( {makeNativeMethod( initHybrid , HermesExecutorHolder::initHybrid), makeNativeMethod( initHybridDefaultConfig , HermesExecutorHolder::initHybridDefaultConfig)}); }initHybrid中会创建HermesExecutorFactory对象然后调用makeCxxInstance它是实现了 Java 和 C 之间一对一的对象绑定的关键static jni::local_refjhybriddata initHybrid( jni::alias_refjclass, bool enableDebugger, std::string debuggerName, jlong heapSizeMB) { JReactMarker::setLogPerfMarkerIfNeeded(); auto runtimeConfig makeRuntimeConfig(heapSizeMB); std::call_once(flag, []() { facebook::hermes::HermesRuntime::setFatalHandler(hermesFatalHandler); }); auto factory std::make_uniqueHermesExecutorFactory( installBindings, JSIExecutor::defaultTimeoutInvoker, runtimeConfig); factory-setEnableDebugger(enableDebugger); if (!debuggerName.empty()) { factory-setDebuggerName(debuggerName); } return makeCxxInstance(std::move(factory)); }makeCxxInstance中会创建T对象在这个案例中T为C层的HermesExecutorHolderOnLoad.cppstatic local_refdetail::HybridData makeCxxInstance(Args... args) { return makeHybridData( std::unique_ptrT(new T(std::forwardArgs(args)...))); }makeHybridData中创建了一个HybridData对象并返回到Java层static local_refdetail::HybridData makeHybridData( std::unique_ptrT cxxPart) { auto hybridData detail::HybridData::create(); setNativePointer(hybridData, std::move(cxxPart)); return hybridData; }setNativePointer中t是HybridData对象new_value是HermesExecutorHolder对象void setNativePointer( basic_strong_refT, Alloc t, std::unique_ptrdetail::BaseHybridClass new_value) { getHolder(*t)-setNativePointer(std::move(new_value)); }看完getHolder就明白了它是取出HybridData对象中的mDestructor字段local_refHybridDestructor::javaobject getHolder(const T* t) { static auto holderField getDestructorField(t-getClass()); return t-getFieldValue(holderField); } inline JFieldHybridDestructor::javaobject getDestructorField( const local_refJClass c) { return c-template getFieldHybridDestructor::javaobject( mDestructor ); }setNativePointer最终会将mDestructor.mNativePointer指向HermesExecutorHolder对象getHolder(*t)-setNativePointer(std::move(new_value)); 变成 HybridDestructor-setNativePointer(std::move(new_value)); //fbjni-0.7.0/prefab/modules/fbjni/include/fbjni/fbjni.cpp:227-237 void HybridDestructor::setNativePointer( std::unique_ptrdetail::BaseHybridClass new_value) { static auto pointerField javaClassStatic()-getFieldjlong(mNativePointer); auto old_value std::unique_ptrdetail::BaseHybridClass( reinterpret_castdetail::BaseHybridClass*(getFieldValue(pointerField))); if (new_value old_value) { FBJNI_LOGF(Attempt to set C native pointer twice); } setFieldValue(pointerField, reinterpret_castjlong(new_value.release())); }这就是“Java 对象 - native 指针 - C 实例”的回路。HermesExecutor (Java对象) -HybridData-mDestructor.mNativePointer(指针)-HermesExecutorHolder(C对象)四、在 RN 中的应用场景HybridData 在 React Native 中无处不在覆盖了几乎所有核心子系统子系统Java 类C 对应作用旧架构 BridgeCatalystInstanceImplCatalystInstanceImpl.cpp → InstanceJS 桥的核心实例新架构 BridgelessReactInstanceJReactInstance.cpp → ReactInstance新架构的运行时实例JS 引擎HermesExecutor / JSCExecutor对应的 C executorJS 执行引擎JS RuntimeHermesInstance / JSCInstanceC runtime factory创建和管理 JS 运行时数据类型WritableNativeMap / WritableNativeArrayC dynamic 对象JS 与 Java 间的数据传递TurboModuleTurboModuleManagerC TurboModule 管理新架构的模块系统Fabric 渲染ComponentFactoryC 组件注册表新架构的渲染系统运行时工具RuntimeExecutor / RuntimeSchedulerC executor/schedulerJS 任务调度