So I've patched my local copy of v8 to support "Data" as internal
object fields instead of "Value".
It required changing all the v8::XX::Cast(Value *) methods to
Cast(Data *) and adding an ObjectTemplate::Cast(Data *) like so:
> ObjectTemplate* ObjectTemplate::Cast(v8::Data* that) {
> if (IsDeadCheck("v8::ObjectTemplate::Cast()")) return 0;
> i::Handle<i::Object> obj = Utils::OpenHandle(that);
> ApiCheck(obj->IsObjectTemplateInfo(),
> "v8::ObjectTemplate::Cast()",
> "Could not convert to ObjectTemplate");
> return static_cast<ObjectTemplate*>(that);
> }
With that, building the structure outlined before seems to work fine.
I'd still be interested to know whether this is kosher.
Matthias
On Mon, Jun 8, 2009 at 12:12 PM, Matthias Ernst<[email protected]> wrote:
> Hi,
>
> Synopsis: I'm wondering how I can have a v8::Object point to a v8::Template.
>
> Here's what I'm doing: I'm hacking away at a protocol buffer wrapper.
>
> In my design, every protocol message type (represented by a
> proto2::Descriptor*) is mapped to an ObjectTemplate.
> Each property of the message type becomes an Accessor that calls back into
> C++. The Accessor's "data" contains the proto2::FieldDescriptor and -in the
> case of a sub-message- the object template used to wrap that submessage's
> type.
>
> So for a message Outer { Inner inner; }, the layout I'd like to have is as
> such:
> ObjectTemplate"Outer" {
> Accessor"inner" : {
> Callback"read and wrap submessage",
> Data: Handle->Object{
> External<FieldDescriptor"inner" *>,
> Handle->ObjectTemplate"Inner" -> ... <= *******
> }
> }
> }
>
> I would like the whole structure to be managed by the V8 GC (the proto
> descriptors are static data), i.e. I'd like the inner ObjectTemplates to be
> GC'ed once I drop the outer one.
>
> However, and here's my actual problem, I cannot get the callback data to
> refer to the inner v8::ObjectTemplate (*****), because the latter does not
> extend v8::Value but only v8::Data. The only way I can imagine is using an
> External wrapping a Persistent* but that would defeat the GC.
>
> So, is there a fundamental reason why "Data" cannot be used even as an
> internal field of an Object?
> I see that internally, in objects.h, an AccessorInfo's "Data" is not
> required to be a JSObject but just an Object.
>
> Would horrible things happen if I coerced a Handle<ObjectTemplate> to be a
> Handle<Value> and store it as internal fields of the callback Data? Could we
> change Object::Set/GetInternalField to use Handle<Data>?
>
> Thx
> Matthias
>
>
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