How to wrap c++ obj during initialization and unwrap during binded function callback ??

[Sudheer Kumar]

Hello everyone,

   I am struggling wrapping and unwrapping the c++ object (MYCLASS) . below is the sample code i have written for my exact requirement:

  void Update_Rotation(const v8::FunctionCallbackInfo<v8::Value>& info);

class MYCLASS {

 public:

  Point(D_TYPE1 *par1) : rotate(par1) { }

  D_TYPE1 *rotate;

  void run_script()

  {

    v8::V8::InitializeICUDefaultLocation(argv);

    v8::V8::InitializeExternalStartupData(argv);

    std::unique_ptr<v8::Platform> platform = v8::platform::NewDefaultPlatform();

    v8::V8::InitializePlatform(platform.get());

    v8::V8::Initialize();

    v8::Isolate::CreateParams create_params;

    create_params.array_buffer_allocator = v8::ArrayBuffer::Allocator::NewDefaultAllocator();

    v8::Isolate* isolate = v8::Isolate::New(create_params);

    v8::Isolate::Scope isolate_scope(isolate);

v8::Isolate::Scope isolate_scope(isolate);

// Create a stack-allocated handle scope.

v8::HandleScope handle_scope(isolate);

// Create a template for the global object.

v8::Handle<v8::ObjectTemplate> global = v8::ObjectTemplate::New(isolate);

/* Here the internal field count is set to 1 which means the object has one internal field, with an index of 0, that points to a C++ object.*/

global->SetInternalFieldCount(1);

// Bind the 'update_rotation' function

global->Set(v8::String::NewFromUtf8(isolate, "update_rotation", v8::NewStringType::kNormal).ToLocalChecked(),

v8::FunctionTemplate::New(isolate, Update_Rotation));

// Create a new context.

v8::Local<v8::Context> context = v8::Context::New(isolate, NULL, global);

//Persistent<Context> context = v8::Context::New(isolate, NULL, global, nullptr);

// Enter the context for compiling and running the script.

v8::Context::Scope context_scope(context);

Local<Object> obj = global->NewInstance(context).ToLocalChecked();

obj->SetInternalField(0, External::New(isolate, this));

/* My JS script */

v8::Local<v8::String> source = v8::String::NewFromUtf8(isolate, "var rotate_status = update_rotation();",v8::NewStringType::kNormal).ToLocalChecked();

//exception handler

v8::TryCatch try_catch(isolate);

printf("Script : compilation started\n");

// Compile the source code.

v8::Local<v8::Script> script = v8::Script::Compile(context, source).ToLocalChecked();

printf("Script : compilation compilation done\n");

printf("Script : Running started\n");

// Run the script to get the result.

v8::Local<v8::Value> result = script->Run(context).ToLocalChecked();

  }

};

void Update_Rotation(const v8::FunctionCallbackInfo<v8::Value>& info) {

Local<Object> self = info.Holder();

Local<External> wrap = Local<External>::Cast(self->GetInternalField(0));

void* ptr = wrap->Value();

MYCLASS* temp_sp = static_cast<MYCLASS*>(ptr);                           //--> Here i am always getting null pointer

D_TYPE1 *rotate_ptr = static_cast<Point*>(ptr)->rotate;

    rotate_ptr->Update();

}

int main()

{

    D_TYPE1 *sample_rotate_obj = new D_TYPE1();

    MYCLASS test_obj(sample_rotate_obj);

    test_obj.run_script();

}

Can anyone plz suggest how to fix it to get valid pointer to my object?

Thanks in advance ...

Regards

Sudheer

[Sudheer Kumar]

Some info about build environment:

1) v8 version :  7.5.288.23

2) IDE VS2017

[Ben Noordhuis]

To summarize what your code does:

1. It creates an ObjectTemplate for the global template.
2. It passes that ObjectTemplate to Context::New()
3. It then creates a new instance of the same ObjectTemplate and sets
its internal field #0.

In other words, two instances are created: once by you, once
(implicitly) by Context::New().

The one you created manually isn't used. When JS code calls your
update_rotation() method, it does so using the instance that
Context::New() created.

I didn't test but calling context->Global()->SetInternalField() might
fix your issue.

[Sudheer Kumar]

Thanks for your reply Ben,

   

   I have tried as you suggested :

  context->Global()->SetInternalField(0, obj);

   but didn't worked ...

 am I doing anything wrong during the initialization ?