doc: add v8 fast api contribution guidelines by anonrig · Pull Request #46199 · nodejs/node · GitHub

I'm introducing a guideline to define and share the limitations/caveats and experiences I've gained from researching on this topic. This would help new contributors to add fast APIs to existing functions.

Referencing: nodejs/performance#23

Review requested:

@nodejs/tsc

Instead of calculateX could you maybe have div(a, b) as an example and have divide by 0 as example for when to switch to slow path?

cc @devsnek who has done most of the fast API work in node IIRC

internal C functions is rather ambiguous. Also, V8 internals usually refers to the non-public V8 API, which we try not to use in any case. Lastly, if I remember correctly, V8 API calls are allowed to some degree. Not performing any allocations on the V8 heap is what's critical. (Unless this changed since I last worked on fast API calls.)

I see. Thanks! Can you give an example of V8 API call, without any allocation on the V8 heap?

I might be wrong, but I think @MayaLekova implemented a fast API that relies on GetAlignedPointerFromInternalField in 6cfba9f, for example. @devsnek might know more about the exact conditions for which APIs are allowed.

You are right. You can access pre-existing/pre-allocated data from the fast apis. I thought it was inferred from the documentation (at least I assumed). Is there any specific wording you'd like me to change?

I've updated the documentation.

[...] Not performing any allocations on the V8 heap is what's critical.

Indeed that's still the case, and until we have the current GC architecture, it will stay like this. Possible future relaxation of this rule might come with conservative stack scanning. Please note that this also leads to the limitation for not calling back into JS code (I think this was discussed in this thread too).

Some brief background on the support for various types in V8 could be found in this external doc.

Instead of calculateX could you maybe have div(a, b) as an example and have divide by 0 as example for when to switch to slow path?

I updated the example. Thanks for the hint! 🥇 💯

I think you should mention this file in the src/README.md too.

Awesome @anonrig 🙌🏼

Learned a lot just by reading the PR ^^

CI: https://ci.nodejs.org/job/node-test-pull-request/49099/

Suggested change

      
            * Throwing errors is not available on fast API, but can be done
          
              through the fallback to slow API.
          
            * Throwing errors is not available from within a fast API call, but can be done
          
              through the fallback to the slow API.

Perhaps it's also better to suggest that since in principal, the fast API and the slow API should behave the same to avoid bugs, it's better not to throw errors in the slow API either and just update some flags and return to the JS land to throw?

I agree in principal with @joyeecheung, but that is not a limitation of a V8 Fast API declaration, but an implementation recommendation. I think it should not be included in this documentation, but in a more style specific documentation like README.md?

Why is this a bullet point?

It aligns with other sections in the same file for mentioning the context of the example it's referring to. Do you have a recommendation for an alternative?

lgtm

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----------------------------------- PR info ------------------------------------
Title      doc: add v8 fast api contribution guidelines (#46199)
Author     Yagiz Nizipli  (@anonrig)
Branch     anonrig:docs-fast-api -> nodejs:main
Labels     doc, author ready, commit-queue-squash
Commits    7
 - doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
 - fixup! doc: add v8 fast api contribution guidelines
Committers 1
 - Yagiz Nizipli 
PR-URL: https://github.com/nodejs/node/pull/46199
Reviewed-By: Matteo Collina 
Reviewed-By: Robert Nagy 
Reviewed-By: Darshan Sen 
Reviewed-By: Rafael Gonzaga 
Reviewed-By: James M Snell 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/46199
Reviewed-By: Matteo Collina 
Reviewed-By: Robert Nagy 
Reviewed-By: Darshan Sen 
Reviewed-By: Rafael Gonzaga 
Reviewed-By: James M Snell 
--------------------------------------------------------------------------------
   ℹ  This PR was created on Fri, 13 Jan 2023 14:07:12 GMT
   ✔  Approvals: 5
   ✔  - Matteo Collina (@mcollina) (TSC): https://github.com/nodejs/node/pull/46199#pullrequestreview-1266448194
   ✔  - Robert Nagy (@ronag) (TSC): https://github.com/nodejs/node/pull/46199#pullrequestreview-1248744183
   ✔  - Darshan Sen (@RaisinTen) (TSC): https://github.com/nodejs/node/pull/46199#pullrequestreview-1249572133
   ✔  - Rafael Gonzaga (@RafaelGSS) (TSC): https://github.com/nodejs/node/pull/46199#pullrequestreview-1253500941
   ✔  - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/46199#pullrequestreview-1262907890
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PR-URL: #46199 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Darshan Sen <raisinten@gmail.com> Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>

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ruyadorno mentioned this pull request Feb 1, 2023

v19.6.0 proposal #46455

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juanarbol mentioned this pull request Mar 3, 2023

V18.15.0 proposal #46920

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		* Throwing errors is not available on fast API, but can be done
		through the fallback to slow API.

+              In V8, the options fallback is defined as `FastApiCallbackOptions` inside
+              [`v8-fast-api-calls.h`](../../deps/v8/include/v8-fast-api-calls.h).
+              * C++ land

doc: add v8 fast api contribution guidelines by anonrig · Pull Request #46199 · nodejs/node · GitHub

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doc: add v8 fast api contribution guidelines - #46199

doc: add v8 fast api contribution guidelines#46199nodejs-github-bot merged 7 commits intonodejs:mainnodejs/node:mainfrom anonrig:docs-fast-apianonrig/node:docs-fast-apiCopy head branch name to clipboard

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doc: add v8 fast api contribution guidelines#46199
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