The goal (what we've used them for now) is to have a unique copy of a
string so we can track the source of a string. We attach
Persistent<v8::Object> properties to the string so that a string from one
source can be differentiated from a string from another source.
Specifically, we track strings that are user-input.
I was a little fast and loose with the comment about "add some external
data to x". More precisely, I create a subclass that extends
v8::String::ExternalStringResource and the subclass has a
Persistent<v8::Object> member.
Is there another way to differentiate between two strings of identical
form/content/representation?
On Monday, April 17, 2023 at 8:40:23 AM UTC-7 pth...@google.com wrote:
> The purpose of internalized strings is to have a canonical, unique
> representation of a string. So yes if strings are internalized that
> are duplicates of already internalized values, we "throw away"/discard that
> duplicate and point them to the unique string instead (i.e. the string
> becomes a ThinString).
> If you want to take ownership of the buffer of an internalized string, you
> can by externalizing the internalized string (as opposed to internalizing
> an external string).
>
> Maybe you can tell us what your intent is? Because you mentioned "add some
> external data to x" I am not sure if external strings are really what you
> are looking for. The purpose of external strings is only to allow embedders
> to have ownership of the string buffer, not to attach arbitrary data to
> strings.
>
> On Mon, Apr 17, 2023 at 4:30 PM Bruce MacNaughton <bmacna...@gmail.com>
> wrote:
>
>> "(either one or two byte) because defaulting to throw away the external
>> data" should be "(either one or two byte) BEFORE defaulting to throw away
>> the external data"
>>
>> On Monday, April 17, 2023 at 7:12:19 AM UTC-7 Bruce MacNaughton wrote:
>>
>>> This is my first relatively deep dive into v8 strings; if I
>>> misinterpreted what's going on, please correct me.
>>>
>>> When a string is used as a key:
>>>
>>> const x = 'xyzzy';
>>> // add some external data to x
>>> const obj = { [x]: 1234 };
>>>
>>> the external data is lost because StringTable:::LookupKey() finds an
>>> entry (data->FindEntry()) and returns a Handle<String> to it. That String
>>> is *not* internalized, so
>>> String::MakeThin() is called on the original string (as 'this') with the
>>> Handle<String> returned by FindEntry(). MakeThin() finds
>>> this->IsExternalString() true so calls MigrateExternalString(),
>>> internalized is *not* an External string, so FinalizeExternalString() is
>>> called, discarding the external data.
>>>
>>> whew.
>>>
>>> It seems like, to propagate the external data that, in LookupString(),
>>> if string->IsExternal() and !result->IsExternal() then result should be
>>> reconstructed as an External string.
>>>
>>> It may be that the way it works is intended, but it's not clear because
>>> MigrateExternalString() in string.cc checks to see if 'internalized' is an
>>> external string (either one or two byte) because defaulting to throw away
>>> the external data.
>>>
>>> But maybe there are considerations with the shared heap that I have yet
>>> to understand.
>>>
>>> Basic question: is this is a bug or intentional design?
>>>
>>>
>>> --
>> --
>> v8-users mailing list
>> v8-u...@googlegroups.com
>> http://groups.google.com/group/v8-users
>> ---
>> You received this message because you are subscribed to the Google Groups
>> "v8-users" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to v8-users+u...@googlegroups.com.
>> To view this discussion on the web visit
>> https://groups.google.com/d/msgid/v8-users/e88c1553-4a78-435f-bc75-cc42f0b3f147n%40googlegroups.com
>>
>> <https://groups.google.com/d/msgid/v8-users/e88c1553-4a78-435f-bc75-cc42f0b3f147n%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
--
--
v8-users mailing list
v8-users@googlegroups.com
http://groups.google.com/group/v8-users
---
You received this message because you are subscribed to the Google Groups
"v8-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to v8-users+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/v8-users/ad4e1dae-d9c7-49d0-91f1-a79c19d090afn%40googlegroups.com.
