Subj : Re: String property & DOM synchro
To   : netscape.public.mozilla.jseng
From : Lorenzo Pastrana
Date : Tue Jun 29 2004 01:32 pm


"Brendan Eich" <brendan@meer.net> wrote in message
news:cbpnm2$reu1@ripley.netscape.com...
> Lorenzo Pastrana wrote:
>
> >>You really have to show your code for me to help effectively.
>
> Again, please show more code -- mail me if you want to keep it
confidential.

.... ok that's not a confidentiality problem, I'm on a 'generic' model, the
line I posted is the actual code that handles the strings.. more code would
mean spending your precious time on unrelated problems...
Any way I'll post a little more, but you'll agree that's pure good will since
you won't learn mutch more than I told you in plain english ;-p

JSBool jslangage::generic_getter(
    JSContext *_cx, JSObject *_obj, jsval _id, jsval *_vp)
{
  jslangage* jsl = (jslangage*)JS_GetContextPrivate(_cx);
  jsobj* pobj = (jsobj*) JS_GetPrivate(_cx,_obj);

  const sphAttributeDecl* decl = jsl->LookupAttribute(pobj, _id);
  if(decl == NULL)
  {
    return JS_TRUE;
  }

  sphMsgData ret(decl->atype);
  _Kernel.Send_Message(pobj->handle, decl->getMsg, NULL, ret);

  // applies conversion see below
  *_vp = jsl->to_jsval(ret,_obj,decl->name,_id);

  return JS_TRUE;
}

jsval jslangage::to_jsval(
    sphMsgData& _data, JSObject * _father, const sphChar* _prop, jsval _id)
{
    switch ((u32) _data.get_type())
    {
    case HOBJ: // Generic object
        {
            // Builds the corresponding object if not done yet
            // (using JS_DefineObject on _father with _prop)
            // This object has all messages mapping infos as private data,
            // see the generic_getter for details on mechanism
            // This function will be called again for pobj props access
            JSObject* pobj = GetObject(_data,_father,_prop);
            return OBJECT_TO_JSVAL(pobj);
        }
    case VCT: // Special case for 'leaf' types
        // This object has all id/messages mapping infos
        // as private data and updates the DOM on access
        return OBJECT_TO_JSVAL(
                jsvct::JSNew(jscontext,(vct&)_data,_father,_attr,_id)
            );
    [...SNIP...]
    case STR:
        // This works for simple Get/Set but on
        // obj.strprop.concat(otherstr); it fails to update the DOM
        return STRING_TO_JSVAL(
            jsNewString(jscontext,
             (char*)((str&)_data).Export(),
             ((str&)_data).GetLength()));
    case BINT:
      return BOOLEAN_TO_JSVAL((bint) _data);
    case U32:
      return INT_TO_JSVAL((u32) _data);
    }
}

> You may be misusing the JS_NewString API.

It might be, but anyway this is not a memory management problem really :

    - I want to rely on SM's JSString 'sandard' implementation in JS space
    - I dont own JSString code and I'm not inclined to branch
    - My DOM engine is accessed by messages, so the buffer I provide to
        JS_NewString is allready a copy.
    - The string implementation I'm using in the background does not want
        to 'share' it's buffer (usual encapsulation/ownership problem)..
    - Since the new JSString works on a copy of the data, it needs to be
        re-synched into the DOM after modifications

    - At this point I'm missing some notification mechanism called by
        JSString or whatever other solution :-/

Actually, since the DOM concept has been introduced, I believe this kind of
cases will occur more often, the singularity of JSString is that it has
data AND methods /w side effects, I'd be curious how other DOMs handle this
but it sounds to me that I'm not in an implementation issue completely,
    you tell me.

> Note that calling that API hands off ownership of the char []
> passed by reference. If you want the JS engine to make its own
> copy of that memory, use JS_NewStringCopy[NZ].
>
> /be

.