Over the last two weeks we’ve been working on a new feature designed for V8 embedders, called “V8 extras.” The intent is to allow embedders to write self-hosted (i.e. JavaScript) implementations of various features, with more power and less drawbacks than the existing V8 extensions mechanism. Notably, we are building on top of recent snapshotting work to ensure that the code for V8 extras is included in the snapshot, and so should not have negative impact on context startup time.
You can see a working, albeit in-progress, example of a V8 extra in this CL <https://codereview.chromium.org/1118673002>, which uses them to implement readable streams from the Streams Standard. General features on display include: - The inclusion of the extras via the v8_extra_library_files GYP variable - The use of V8 native functions, such as %CreatePrivateOwnSymbol, in the .js files (but see below) - The use of the extrasExports object to export functions and values to the embedder. This object can be accessed through the V8 C++ API with v8::Context::GetExtrasExportsObject(). There are a number of changes we’re still working on implementing before we could comfortably say that this feature is ready: - We do not want to allow extras direct access to V8 native functions, but instead only to a small number of pre-specified ones. The details on how to do this are still being worked out, but it will probably involve a slight change to the authoring format of the extras files, to become e.g. script whose completion value is a function that gets such a utility object passed in. - We need a story for segregating “experimental” extras from shipping ones, similar to what is being done in V8 already for harmony features. Experimental extras cannot live in the snapshot, since they must be able to be turned off at runtime, while shipping ones will be compiled in. - We eventually want to expose an easy way for the embedder to supply functions or values to the extras code. This is not actually needed for streams, but for example if we were to implement something like TextEncoder or URL as an extra, it would be crucial. Overall though, we are quite excited about the possibilities this opens up, by allowing embedders a performant way to implement features in JavaScript. Best, Domenic Denicola Jochen Eisinger Yang Guo -- -- v8-users mailing list [email protected] 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
