openharmonyinsight/skills/oh-memory-leak-detection

NAPI Memory Leak Detection

Quick Start

Functions working with napi_value need scope management to prevent leaks.

Detection Checklist:

• [ ] Function returns napi_value?
• [ ] Function has napi_value& parameter?
• [ ] Function calls napi_create_*?
• [ ] Creates temporary napi_value variables?
• [ ] Async callback without HandleScope?
• [ ] Gets napi_value from other functions?

For detailed background on JS/C++ memory management, see references/background.md

Common Patterns

Pattern 1: Function Returns napi_value

Use HandleEscape when returning napi_value to parent scope.

// ❌ LEAK
napi_value Func(napi_env env) {
    napi_value result = nullptr;
    napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &result);
    return result;
}

// ✅ FIXED
napi_value Func(napi_env env) {
    HandleEscape handleEscape(env);
    napi_value result = nullptr;
    napi_create_string_utf8(env, "hello", NAPI_AUTO_LENGTH, &result);
    return handleEscape.Escape(result);
}

Pattern 2: Function with napi_value& Parameter

Use HandleScope when receiving napi_value& as output parameter.

// ❌ LEAK
void Func(napi_env env, napi_value& objValue) {
    napi_value temp = nullptr;
    napi_new_instance(env, cls, 0, nullptr, &temp);
    objValue = temp;
}

// ✅ FIXED
void Func(napi_env env, napi_value& objValue) {
    HandleScope handleScope(env);
    napi_value temp = nullptr;
    napi_new_instance(env, cls, 0, nullptr, &temp);
    objValue = temp;
}

Pattern 3: Property Setting with Temporaries

Temporary napi_value variables created during property setting need management.

// ❌ LEAK
napi_value CreateInfo(napi_env env, const Data& data) {
    napi_value obj = nullptr;
    napi_create_object(env, &obj);
    
    napi_value name = CreateJsValue(env, data.name);    // Leak
    napi_value pid = CreateJsValue(env, data.pid);      // Leak
    napi_set_named_property(env, obj, "name", name);
    napi_set_named_property(env, obj, "pid", pid);
    
    return obj;
}

// ✅ FIXED
napi_value CreateInfo(napi_env env, const Data& data) {
    HandleEscape handleEscape(env);
    napi_value obj = nullptr;
    napi_create_object(env, &obj);
    
    napi_value name = CreateJsValue(env, data.name);
    napi_value pid = CreateJsValue(env, data.pid);
    napi_set_named_property(env, obj, "name", name);
    napi_set_named_property(env, obj, "pid", pid);
    
    return handleEscape.Escape(obj);
}

Pattern 4: Getting napi_value from Other Functions

When calling functions that return napi_value, the returned value needs scope management.

// ❌ LEAK
bool Func(napi_env env) {
    auto executorNapiVal = jsObj_->GetNapiValue();
    // executorNapiVal escapes when function returns
}

// ✅ FIXED
bool Func(napi_env env) {
    HandleScope handleScope(env);
    auto executorNapiVal = jsObj_->GetNapiValue();
    // Use executorNapiVal within this scope
}

Pattern 5: Async Callbacks

Async tasks need their own HandleScope to manage napi_value created in callbacks.

// ❌ LEAK
void AsyncBad(napi_env env, napi_value callback) {
    std::thread([env, callback]() {
        napi_value result = nullptr;
        napi_create_string_utf8(env, "async result", NAPI_AUTO_LENGTH, &result);
    }).detach();
}

// ✅ FIXED
void AsyncGood(napi_env env, napi_value callback, std::shared_ptr<AbilityHandler> handler) {
    std::string data = "async result";
    auto task = [env, callback, data]() {
        HandleScope handleScope(env);
        napi_value result = nullptr;
        napi_create_string_utf8(env, data.c_str(), NAPI_AUTO_LENGTH, &result);
        napi_call_function(env, callback, 1, &result, nullptr);
    };
    handler->PostTask(task, "AsyncTask");
}

Pattern 6: napi_value Used in Conditional Expressions

When napi_value is used in conditional checks, it needs scope management.

// ❌ LEAK
napi_value Func1(napi_env env) {
    napi_value xxx = nullptr;
    napi_create_double(env, 42.0, &xxx);
    return xxx;
}

bool TestFunc(napi_env env) {
    if (Func1(env) == someValue) {
        // Func1 returns napi_value that leaks
    }
    return true;
}

// ✅ FIXED
napi_value Func1(napi_env env) {
    HandleEscape handleEscape(env);
    napi_value xxx = nullptr;
    napi_create_double(env, 42.0, &xxx);
    return handleEscape.Escape(xxx);
}

Quick Fix Templates

Template 1: Function Returning napi_value

napi_value FunctionName(napi_env env, /* parameters */) {
    HandleEscape handleEscape(env);
    // ... function body ...
    return handleEscape.Escape(result);
}

Template 2: Function with napi_value& Parameter

void FunctionName(napi_env env, napi_value& output, /* parameters */) {
    HandleScope handleScope(env);
    // ... function body ...
    output = value;
}

Template 3: Function Creating Multiple Properties

napi_value CreateJsObject(napi_env env, const DataType& data) {
    HandleEscape handleEscape(env);
    napi_value obj = nullptr;
    napi_create_object(env, &obj);
    
    napi_value prop1 = CreateJsValue(env, data.field1);
    napi_value prop2 = CreateJsValue(env, data.field2);
    napi_set_named_property(env, obj, "prop1", prop1);
    napi_set_named_property(env, obj, "prop2", prop2);
    
    return handleEscape.Escape(obj);
}

Functions to Review

Functions that commonly return napi_value and need scope management:

Create Functions:

• Convert2JSValue
• CreateJsAppStateData, CreateJsAbilityStateData, CreateJsProcessData
• CreateJsMissionInfo, CreateJsWant, CreateJsWantParams
• CreateJsError

Wrap Functions:

• WrapVoidToJS, WrapStringToJS, WrapInt32ToJS
• WrapConfiguration, WrapElementName
• WrapWant, WrapWantAgent, WrapWantParams
• WrapAbilityResult

Custom Functions: Any function with Create or Wrap in the name that returns napi_value

Testing

ASAN Detection

export ASAN_OPTIONS=detect_leaks=1
./build.sh --product-name <product> --build-target ability_runtime --ccache

Manual Testing

// Call function repeatedly to detect memory growth
for (int i = 0; i < 10000; i++) {
    auto result = FunctionToTest(env);
}
// Monitor memory usage for continuous growth

XTS Memory Leak Detection

Wiki: https://wiki.huawei.com/domains/1048/wiki/8/WIKI202511108963910

Workflow:

1. Configure device
2. Flash version
3. Sync code and push diff
4. Compile .so files
5. Push .so and replace with symbol version
6. Enable detection switch and restart device
7. Capture logs
8. Extract leak stack traces

Key Principles

1. HandleEscape when returning napi_value to parent scope
2. HandleScope when receiving napi_value& as output parameter
3. All napi_create_* calls create JS objects that need scope management
4. Async callbacks need their own HandleScope
5. Temporary napi_value variables must be managed
6. Functions returning napi_value need HandleEscape
7. napi_value used in expressions needs scope management

Common napi_create_* Functions

These functions create JS objects and return napi_value:

Primitives:

• napi_create_int32, napi_create_uint32, napi_create_int64
• napi_create_double, napi_create_bigint_int64, napi_create_bigint_uint64

Strings:

• napi_create_string_utf8, napi_create_string_utf16, napi_create_string_latin1

Objects:

• napi_create_object, napi_create_array, napi_create_array_with_length

Functions and Classes:

• napi_create_function, napi_new_instance

Additional Resources

• Background knowledge: references/background.md
• Detailed cases: references/detailed-cases.md
• Contact: Chen Rui (00951372), Deng Wenjun (00850728) for uncertain cases