For an example of what this means, you can look at
v8/test/cctest/test-api.cc and look for GetCallingContext.
-- Mads
On Thu, Jul 9, 2009 at 1:34 PM, Mads Sig Ager<a...@chromium.org> wrote:
> Drew,
>
> quick answer: When you use V8 you have to enter a context before
> giving V8 some code to execute. GetEntered() returns the last context
> that you entered using the API. When you call JavaScript functions,
> the JavaScript engine enters the context in which that function was
> defined. When calling functions across frames, this context will be
> different from the context that you entered through the API.
> GetCurrent will always give you the context of the currently executing
> function (the context in which the currently executing function was
> declared). GetCalling will get you the context of the function that
> called the function you are currently executing.
>
> Cheers, -- Mads
>
> On Thu, Jul 9, 2009 at 1:04 PM, Drew Wilson<atwil...@chromium.org> wrote:
>> Hi all,
>> I've been poking around quite a bit recently in the WebKit JS
>> bindings/constructor code, trying to make some sense of their widespread use
>> of the lexicalGlobalObject() - basically, it seems like looking at the
>> lexicalGlobalObject() is seldom what they actually want, because it means
>> that if you call between frames you unexpectedly start pulling things from a
>> different context.
>> As a very simple example (bear with me, I'll get to the chrome-specific
>> question in a second) - imagine that you have a page containing a child
>> frame. In the parent page, you define this:
>> function getImage() {
>> return new Image();
>> }
>> ...now down in your child frame, you have code that does this:
>> var image1 = new Image();
>> var image2 = parent.window.getImage();
>> assert(image1.__proto__ == image2.__proto__); // Fails in WebKit currently,
>> because the Image constructor lookup uses the lexicalGlobalObject.
>>
>> JSC defines dynamicGlobalObject() and lexicalGlobalObject() - I suspect that
>> they generally want to be using dynamicGlobalObject instead of
>> lexicalGlobalObject when trying to access something from global scope. Or am
>> I missing some subtlety here?
>> That brings me to my Chromium/V8 question - there are 3 context-grabbing
>> functions in V8: GetEntered(), GetCalling(), GetCurrent(). When is it
>> appropriate to use one over the others (what are the effective differences)?
>> The descriptions are kind of terse, and I'm afraid I'm missing some of the
>> subtleties between "the context of the calling JavaScript code" vs "The
>> context on the top of the stack" vs "The last entered context" (for example,
>> I would have naively thought that the calling JavaScript code's context
>> would *inherently* be the last entered one, and hence would be on the top of
>> the stack, but clearly that's not true :)
>> -atw
>> >>
>>
>
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