(Egg on face)
Actually, re-reading the guide, it does go into pretty good detail. I
think I just didn't have the context to understand it at that point on
first reading. Now that I've had time to write a bunch of code and
internalize the concepts, it's crystal clear.
-- ryan
On Tuesday, May 17, 2016 at 11:06:48 AM UTC-7, Ryan Ingram wrote:
>
> Actually it turns out it was my error, misusing HandleScope. It turns out
> the function that constructed the callback data had a HandleScope and the
> returned handle didn't survive the scope closure.
>
> I think the Embedder's Guide should go into more detail about the design
> of HandleScope as it seems critical to understanding how to use the library
> properly. In particular, you need to be very careful that any handle you
> construct doesn't outlive the HandleScope it is constructed in, and how
> EscapableHandleScope solves the problem of wanting to return a handle from
> a function that has a HandleScope.
>
> -- ryan
>
>
> On Monday, May 16, 2016 at 3:22:34 PM UTC-7, Ryan Ingram wrote:
>>
>> What am I doing wrong here? Does FunctionTemplate only support
>> primitives for callback data? (Its type should suggest that, if so...)
>>
>> I'm trying to register native functions to be called back in my embedder,
>> but my function callback data is getting corrupted. I tried saving off the
>> data passed to FunctionTemplate::New and I'm not getting the same data in
>> my callback!
>>
>> Here's a code snippet:
>>
>> v8::Persistent<v8::Value> gDebugData;
>>
>> void RegisterTestFunction( v8::Handle<v8::String> name, v8::Isolate*
>> isolate, v8::Context* context )
>> {
>> v8::Local<v8::Object> data = v8::Object::New(isolate); // In the
>> actual code this is SomeFunctionTemplate->InstanceTemplate()->NewInstance()
>> gDebugData.Reset(isolate, data); // save off pointer for debugging
>>
>> v8::Local<v8::FunctionTemplate> template =
>> FunctionTemplate::New(isolate, &TestFunctionCallback, data);
>> context->Enter();
>> context->Global()->Set( name, template->GetFunction() );
>> context->Exit();
>> }
>>
>> void TestFunctionCallback(const v8::FunctionCallbackInfo<v8::Value>
>> &arguments)
>> {
>> v8::Isolate* isolate = arguments.GetIsolate();
>>
>> // Let's get our context
>> v8::Local<v8::Value> dataValue = arguments.Data();
>> assert( dataValue->IsObject() ); // Fails??
>>
>> // Hmm, let's look at our original context variable...
>> v8::Local<v8::Value> expectedDataValue = v8::Local<v8::Value>::New(
>> isolate, gDebugData );
>> assert( dataValue == expectedDataValue ); // Also fails...
>>
>> assert( expectedDataValue->IsObject() ); // The original pointer is
>> still valid...
>>
>> // Lets find out what we are getting passed
>> v8::TryCatch tryCatch;
>>
>> // This function crashes...
>> v8::Local<v8::String> whatIsIt = dataValue->ToString();
>>
>> if(tryCatch.HasCaught() { tryCatch.ReThrow(); return; }
>> }
>>
>> Crash callstack:
>> 3eb50f46()
>> 3eb483e1()
>> 3eb2fa55()
>> 3eb2b8ea()
>> v8.dll!v8::internal::Invoke(bool is_construct,
>> v8::internal::Handle<v8::internal::JSFunction> function,
>> v8::internal::Handle<v8::internal::Object> receiver, int argc,
>> v8::internal::Handle<v8::internal::Object> * args) Line 108 C++
>> v8.dll!v8::internal::Execution::Call(v8::internal::Isolate * isolate,
>> v8::internal::Handle<v8::internal::Object> callable,
>> v8::internal::Handle<v8::internal::Object> receiver, int argc,
>> v8::internal::Handle<v8::internal::Object> * argv, bool convert_receiver)
>> Line 157 + 0x13 bytes C++
>> v8.dll!v8::internal::Execution::ToString(v8::internal::Isolate *
>> isolate, v8::internal::Handle<v8::internal::Object> obj) Line 517 + 0x95
>> bytes C++
>> v8.dll!v8::Value::ToString() Line 2594 + 0x9 bytes C++
>>
>> If I use "expectedDataValue" in my callback, everything works as desired.
>> But that's not getting passed through to the FunctionCallbackInfo.
>>
>> I am on a relatively old version of v8 (3.30). Is there a way to tell
>> what is inside of dataValue's handle more safely? In the debugger it has a
>> pointer value, although it doesn't look particularly valid...
>>
>> dataValue
>> v8::Handle<v8::Value> {val_=0x0023d608 }
>> expectedDataValue
>> v8::Handle<v8::Value> {val_=0x128daab0 }
>> gDebugData
>> v8::PersistentBase<v8::Value> {val_=0x128d6a90 }
>>
>
--
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