Is it necessary to check if v8::Local is empty before using it?

[Gautham B A]

Hi all,

Please consider the following code -

void ParseJSON(v8::Isolate *isolate, const v8::Local<v8::String> &v8_str) {

  v8::HandleScope handle_scope(isolate);

  auto v8val_json = v8::JSON::Parse(isolate, v8_str);

  v8::Local<v8::Object> v8obj_json;

  if (!v8val_json.ToLocal(&v8obj_json)) {

    // Empty

    return;

  }

  // v8obj_json is a v8::Local. Is this check necessary?

  if (!v8obj_json.IsEmpty()) {

    return;

  }

  auto field_zero = v8obj_json->Get(0);

}

When I obtain a v8::Local object from a v8::MaybeLocal, is it necessary to check if the v8::Local object is empty before accessing it?

Thanks,

--Gautham

[Ben Noordhuis]

No, the .ToLocal() call took care of that.

[Gautham B A]

Thanks. So, once I have a non-empty v8::Local object (v8obj_json in this case), am I guaranteed that its value won't turn empty? - I'm asking this in the context of calling v8::V8::TerminateExecution(isolate). Please consider the following code -

v8::Local<v8::Object> v8obj_json;

if (!v8val_json.ToLocal(&v8obj_json)) { // v8val_json is a v8::MaybeLocal 

  return;

}

// Let's say we terminate the execution after getting a v8::Local object

v8::V8::TerminateExecution(isolate);

// Will v8obj_json become empty?

[Ben Noordhuis]

On Tue, May 15, 2018 at 12:26 PM, Gautham B A
<gautham....@gmail.com> wrote:
> Thanks. So, once I have a non-empty v8::Local object (v8obj_json in this
> case), am I guaranteed that its value won't turn empty? - I'm asking this in
> the context of calling v8::V8::TerminateExecution(isolate). Please consider
> the following code -
>
> v8::Local<v8::Object> v8obj_json;
> if (!v8val_json.ToLocal(&v8obj_json)) { // v8val_json is a v8::MaybeLocal
> return;
> }
>
> // Let's say we terminate the execution after getting a v8::Local object
> v8::V8::TerminateExecution(isolate);
>
> // Will v8obj_json become empty?
> auto field_zero = v8obj_json->Get(0);

That's a different question, with a different answer. The handle
won't go empty when a termination exception is in effect but you
should nevertheless stop calling into V8 because that won't work
(reliably) when it's shutting down.