Per-isolate FunctionTemplate cache

[tbl...@icloud.com]

Jochen Eisinger said that "v8 has an per-isolate cache of function templates". I have a few questions about this cache:

If I create multiple FunctionTemplates with different callback data but the same callback function and everything else, does it only create one function template and use the cache for the rest?

If not, why does the cache exist?

~Theodore

[Ben Noordhuis]

It creates multiple function templates. The cache is to speed up
template instantiation, not template creation.

[Toon Verwaest]

I don't know which cache you are talking about. Afaik there's only a "function-template-instantations-cache". That caches JSFunctions per native context resulting from instantiating a function template.

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[tbl...@icloud.com]

Here's what Jochen originally said:

v8 has an per-isolate cache of function templates. As the string is referenced by the function template, it will never go out of scope.
I'd recommend to create a weak handle to the function you create via GetFunction() instead

https://groups.google.com/d/msg/v8-users/Rshbi2HKYCM/LgwY-iJeAQAJ

He later clarified "the function template won't ever get gc'd after you've instantiated it once."

What I really want to know is why this is the case, and what purpose it serves.

~Theodore

[Toon Verwaest]

If you do FunctionTemplate::New you get a caching template. With caching I mean: every time you instantiate the template in the same native context, you'll get the same function out. This is just how it's supposed to work for Blink. This cache keeps the function strongly since even if objects holding functions may disappear temporarily, the identity of the functions needs to be preserved.

For your case it seems like you could just do Function::New, which internally generates a non-caching template. That way there won't be a strong reference from the cache.

I hope this helps,

Toon

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