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fixes v8 GC access violation for zombie objects #638

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fixes v8 GC access violation for zombie objects #638

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7c59fab
fix v8 GC access violation after napi ObjectWrap instance is left in …
blagoev Dec 20, 2019
beb4920
handle exceptions disabled case
blagoev Dec 24, 2019
80d6607
specify return value type
blagoev Dec 24, 2019
41c7a89
add a test for constructor exceptions
blagoev Dec 30, 2019
253a9e1
refactored constructor exceptions fix.
blagoev Dec 31, 2019
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31 changes: 28 additions & 3 deletions napi-inl.h
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Original file line number Diff line number Diff line change
Expand Up @@ -3120,7 +3120,7 @@ inline ObjectWrap<T>::ObjectWrap(const Napi::CallbackInfo& callbackInfo) {
napi_status status;
napi_ref ref;
T* instance = static_cast<T*>(this);
status = napi_wrap(env, wrapper, instance, FinalizeCallback, nullptr, &ref);
status = napi_wrap(env, wrapper, instance, FinalizeCallback, (void*)callbackInfo.zombie, &ref);
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Suggested change
status = napi_wrap(env, wrapper, instance, FinalizeCallback, (void*)callbackInfo.zombie, &ref);
ObjectWrapPingPong* ping_pong = static_cast<ObjectWrapPingPong*>(callbackInfo.Data());
callbackInfo.SetData(ping_pong->data);
status = napi_wrap(env, wrapper, instance, FinalizeCallback, nullptr, &ref);

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We can declare

struct ObjectWrapPingPong {
  void* data = nullptr;
  bool object_wrapping_failed = false;
};

in the private section of ObjectWrap<T>.

NAPI_THROW_IF_FAILED_VOID(env, status);
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Reference<Object>* instanceRef = instance;
Expand Down Expand Up @@ -3697,10 +3697,26 @@ inline napi_value ObjectWrap<T>::ConstructorCallbackWrapper(
}

T* instance;
napi_value wrapper = details::WrapCallback([&] {
napi_value wrapper = details::WrapCallback([&] () -> napi_value {
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Suggested change
napi_value wrapper = details::WrapCallback([&] () -> napi_value {
napi_value wrapper = details::WrapCallback([&] {

We don't need this change, because it's OK to return callbackInfo.This(). After all, when control returns to the engine it will throw anyway, so the actual instance will not be relevant, and there won't be a leak on the native side either.

CallbackInfo callbackInfo(env, info);
callbackInfo.zombie = new Zombie();
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Suggested change
callbackInfo.zombie = new Zombie();
ObjectWrapPingPong ping_pong({callbackInfo.Data(), false});
callbackInfo.SetData(&ping_pong);

#ifdef NAPI_CPP_EXCEPTIONS
try {
instance = new T(callbackInfo);
return callbackInfo.This();
}
catch (...) {
callbackInfo.zombie->isZombie = true;
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Suggested change
callbackInfo.zombie->isZombie = true;
if (ping_pong.object_wrapping_failed == false) {
napi_status status = napi_remove_wrap(callbackInfo.Env(), callbackInfo.This(), nullptr);
NAPI_FATAL_IF_FAILED(status,
"ObjectWrap<T>::ConstructorCallbackWrapper",
"Failed to remove wrap from failed ObjectWrap instance construction");
}

throw;
}
#else
instance = new T(callbackInfo);
if (callbackInfo.Env().IsExceptionPending()) {
callbackInfo.zombie->isZombie = true;
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Suggested change
callbackInfo.zombie->isZombie = true;
if (ping_pong.object_wrapping_failed == false) {
napi_status status = napi_remove_wrap(callbackInfo.Env(), callbackInfo.This(), nullptr);
NAPI_FATAL_IF_FAILED(status,
"ObjectWrap<T>::ConstructorCallbackWrapper",
"Failed to remove wrap from failed ObjectWrap instance construction");
}

I guess this part should probably be factored out and a call made to it from above and from here.

return nullptr;
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Suggested change
return nullptr;

It's OK to fall through to the return below.

}
return callbackInfo.This();
#endif
});

return wrapper;
Expand Down Expand Up @@ -3823,7 +3839,16 @@ inline napi_value ObjectWrap<T>::InstanceSetterCallbackWrapper(
}

template <typename T>
inline void ObjectWrap<T>::FinalizeCallback(napi_env env, void* data, void* /*hint*/) {
inline void ObjectWrap<T>::FinalizeCallback(napi_env env, void* data, void* hint) {
if (hint != nullptr) {
Zombie* zombie = (Zombie*)hint;
bool isZombie = zombie->isZombie;
delete zombie;
if (isZombie) {
return;
}
}

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This becomes unnecessary.

T* instance = reinterpret_cast<T*>(data);
instance->Finalize(Napi::Env(env));
delete instance;
Expand Down
6 changes: 6 additions & 0 deletions napi.h
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Expand Up @@ -1396,6 +1396,10 @@ namespace Napi {
RangeError(napi_env env, napi_value value);
};

struct Zombie {
bool isZombie = false;
};

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This becomes unnecessary.

class CallbackInfo {
public:
CallbackInfo(napi_env env, napi_callback_info info);
Expand All @@ -1414,6 +1418,8 @@ namespace Napi {
void* Data() const;
void SetData(void* data);

Zombie* zombie;
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Suggested change
Zombie* zombie;

Let's not expose more public fields. We can do a ping-pong with SetData() and Data().


private:
const size_t _staticArgCount = 6;
napi_env _env;
Expand Down
19 changes: 19 additions & 0 deletions test/objectwrap.cc
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Expand Up @@ -172,11 +172,30 @@ class Test : public Napi::ObjectWrap<Test> {

std::string Test::s_staticMethodText;

#ifdef NAPI_CPP_EXCEPTIONS
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We should perform this test in both cases – if C++ exceptions are enabled, as well as if they are not enabled.

class TestConstructorExceptions : public Napi::ObjectWrap<TestConstructorExceptions> {
public:
TestConstructorExceptions(const Napi::CallbackInfo& info) :
Napi::ObjectWrap<TestConstructorExceptions>(info) {
throw Napi::Error::New(info.Env(), "Constructor exceptions should not cause v8 GC to fail");
}

static void Initialize(Napi::Env env, Napi::Object exports) {
exports.Set("TestConstructorExceptions", DefineClass(env, "TestConstructorExceptions", {}));
}
};
#endif


Napi::Object InitObjectWrap(Napi::Env env) {
testStaticContextRef = Napi::Persistent(Napi::Object::New(env));
testStaticContextRef.SuppressDestruct();

Napi::Object exports = Napi::Object::New(env);
Test::Initialize(env, exports);

#ifdef NAPI_CPP_EXCEPTIONS
TestConstructorExceptions::Initialize(env, exports);
#endif
Comment on lines +202 to +204
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This initialization should be unconditional.

return exports;
}
12 changes: 12 additions & 0 deletions test/objectwrap.js
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Expand Up @@ -256,9 +256,21 @@ const test = (binding) => {
testFinalize(clazz);
};

const testConstructorExceptions = () => {
const TestConstructorExceptions = binding.objectwrap.TestConstructorExceptions;
if (TestConstructorExceptions) {
console.log("Runnig test testConstructorExceptions");
assert.throws(() => { new TestConstructorExceptions(); });
global.gc();
console.log("Test testConstructorExceptions complete");
}
}

// `Test` is needed for accessing exposed symbols
testObj(new Test(), Test);
testClass(Test);

testConstructorExceptions();
}

test(require(`./build/${buildType}/binding.node`));
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Suggested change
test(require(`./build/${buildType}/binding.node`));
test(require(`./build/${buildType}/binding.node`));
test(require(`./build/${buildType}/binding_noexcept.node`));

Please test both scenarios!

Expand Down