React Native 0.77 Bridgeless JSI HostObject Lifetime and Thread Invariant

--- description: React Native 0.77 Bridgeless JSI HostObject Lifetime and Thread Invariant - Enforces strict thread-safe C++ memory management and reference tracking for JSI HostObjects in React Native 0.77 bridgeless mode. Prevents SIGSEGV crashes caused by Hermes garbage collection cycles deallocating native state while asynchronous background worker threads retain raw pointers or execute TurboModule callbacks. Mandates the use of thread-safe smart pointers, explicit invalidation tokens, and strict JS-thread dispatch for JSI runtime interactions. globs: **/*.{h,hpp,cpp,mm,m}, src/**/Native*Spec.{ts,tsx}, src/**/specs/**/*.{ts,tsx} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/rn-bridgeless-jsi-hostobject-lifetime-invariant" --- # React Native 0.77 Bridgeless JSI HostObject Lifetime and Thread Invariant > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Accessing Dangling JSI HostObjects or Capturing Raw Native Pointers Across Concurrent TurboModule Threads ## System Constraints You are a Principal Mobile Architect specializing in React Native 0.77 Bridgeless Architecture, Hermes VM internals, and JSI C++ core memory management. You must enforce strict HostObject lifetime guardrails, ensuring raw native pointers never escape thread bounds and Hermes GC does not trigger dangling pointer access or double-free panics in concurrent TurboModules. ## Strict Guidelines - Engineers MUST ALWAYS encapsulate C++ native state held inside a jsi::HostObject within a std::shared_ptr and explicitly decouple background worker execution using std::weak_ptr or shared invalidation states. - Engineers MUST NOT access, read, or mutate jsi::Runtime, jsi::Value, or jsi::Object instances on any thread other than the JS thread owning that runtime. - Code MUST marshal all asynchronous native TurboModule results back to the Hermes JavaScript thread via react::CallInvoker or Bridgeless JSCallInvoker before executing JS callbacks or resolving Promises. - Engineers MUST NOT capture raw 'this' pointers or un-owned C++ references inside lambda closures dispatched to background thread pools or dispatch queues. - Services MUST implement explicit teardown hooks (e.g., invalidate() in TurboModule lifecycle) that atomically release native resources and invalidate pending asynchronous tasks before HostObject destructor finalization. - Components NEVER assume jsi::HostObject C++ destructor timing coincides with JavaScript scope exit; native code must remain resilient to non-deterministic Hermes GC sweeps. ## Bad vs Good Implementations ### Unsafe Raw Pointer Capture vs. Weak-Referenced Invalidation via CallInvoker #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Capturing raw 'this' in a detached thread allows Hermes garbage collection to sweep the HostObject and call delete[] rawBuffer_ on the JS thread while the background thread is actively reading or writing, producing a fatal SIGSEGV / use-after-free vulnerability. ```cpp #include <jsi/jsi.h> #include <ReactCommon/CallInvoker.h> #include <thread> class UnsafeBufferHostObject : public facebook::jsi::HostObject { public: uint8_t* rawBuffer_; size_t size_; UnsafeBufferHostObject(size_t size) : size_(size) { rawBuffer_ = new uint8_t[size]; } ~UnsafeBufferHostObject() { delete[] rawBuffer_; // Dangling pointer hazard during concurrent background access } facebook::jsi::Value get(facebook::jsi::Runtime& rt, const facebook::jsi::PropNameID& name) override { if (name.utf8(rt) == "processAsync") { // ANTI-PATTERN: Capturing raw 'this' across threads while Hermes GC can collect the HostObject return facebook::jsi::Function::createFromHostFunction(rt, name, 0, [this](facebook::jsi::Runtime& rt, const facebook::jsi::Value&, const facebook::jsi::Value*, size_t) -> facebook::jsi::Value { std::thread([this]() { // Crash: rawBuffer_ accessed after GC deallocated UnsafeBufferHostObject this->rawBuffer_[0] = 0xFF; }).detach(); return facebook::jsi::Value::undefined(); }); } return facebook::jsi::Value::undefined(); } }; ``` #### Production Standard (Correct) > **Standard**: Encapsulates shared native state inside a std::shared_ptr and passes a std::weak_ptr to the background worker. The worker verifies object validity via .lock() before memory mutation and uses CallInvoker to marshal the callback invocation safely onto the Hermes runtime thread. ```cpp #include <jsi/jsi.h> #include <ReactCommon/CallInvoker.h> #include <memory> #include <vector> #include <thread> class SafeBufferState { public: std::vector<uint8_t> buffer; explicit SafeBufferState(size_t size) : buffer(size) {} }; class SafeBufferHostObject : public facebook::jsi::HostObject, public std::enable_shared_from_this<SafeBufferHostObject> { private: std::shared_ptr<SafeBufferState> state_; std::shared_ptr<facebook::react::CallInvoker> jsInvoker_; public: SafeBufferHostObject(size_t size, std::shared_ptr<facebook::react::CallInvoker> jsInvoker) : state_(std::make_shared<SafeBufferState>(size)), jsInvoker_(std::move(jsInvoker)) {} facebook::jsi::Value get(facebook::jsi::Runtime& rt, const facebook::jsi::PropNameID& name) override { if (name.utf8(rt) == "processAsync") { // Safe: std::weak_ptr prevents resurrection & safely validates lifetime across threads std::weak_ptr<SafeBufferState> weakState = state_; std::shared_ptr<facebook::react::CallInvoker> invoker = jsInvoker_; return facebook::jsi::Function::createFromHostFunction(rt, name, 1, [weakState, invoker](facebook::jsi::Runtime& rt, const facebook::jsi::Value&, const facebook::jsi::Value* args, size_t count) -> facebook::jsi::Value { auto jsCallback = std::make_shared<facebook::jsi::Value>(rt, args[0]); std::thread([weakState, invoker, jsCallback]() { auto sharedState = weakState.lock(); if (!sharedState) { return; // HostObject and native state deallocated; safely bail out } sharedState->buffer[0] = 0xFF; // Marshaling back to Hermes JS thread via CallInvoker invoker->invokeAsync([jsCallback](facebook::jsi::Runtime& runtime) { if (jsCallback->isObject() && jsCallback->asObject(runtime).isFunction(runtime)) { jsCallback->asObject(runtime).asFunction(runtime).call(runtime, true); } }); }).detach(); return facebook::jsi::Value::undefined(); }); } return facebook::jsi::Value::undefined(); } }; ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: React Native 0.77 Bridgeless JSI HostObject Lifetime and Thread Invariant

React Native 0.77 Bridgeless JSI HostObject Lifetime and Thread Invariant defines an industrial-grade behavioral standard for mobile engineering. Enforces strict thread-safe C++ memory management and reference tracking for JSI HostObjects in React Native 0.77 bridgeless mode. Prevents SIGSEGV crashes caused by Hermes garbage collection cycles deallocating native state while asynchronous background worker threads retain raw pointers or execute TurboModule callbacks. Mandates the use of thread-safe smart pointers, explicit invalidation tokens, and strict JS-thread dispatch for JSI runtime interactions. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Accessing Dangling JSI HostObjects or Capturing Raw Native Pointers Across Concurrent TurboModule Threads Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Accessing Dangling JSI HostObjects or Capturing Raw Native Pointers Across Concurrent TurboModule Threads	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS encapsulate C++ native state held inside a jsi

Engineers MUST ALWAYS encapsulate C++ native state held inside a jsi::HostObject within a std::shared_ptr and explicitly decouple background worker execution using std::weak_ptr or shared invalidation states.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.