src: avoid env lookups and a global handle in InternalCallbackScope

[nigrosimone]

InternalCallbackScope looks up the Environment from the isolate two times per call, inside async_context_frame::exchange, and it keeps the prior async context frame in a v8::Global also when there is no frame, that is the common case. Every call from native code into JS pays this: MakeCallback, CallbackScope, AsyncWrap, Node-API.

Now the scope passes the Environment it already has, the option is read with an inline accessor instead of copying the shared_ptr, and the global handle is created only when the prior frame is not undefined.

Benchmark: benchmark/napi/make_callback (added here) with benchmark/compare.js, Node 26.3.0 built from source with and without this change, Linux x64, 30 runs per binary. From 202-208 ns to 155-159 ns per call:

                                confidence improvement accuracy (*)   (**)  (***)
napi/make_callback n=1000000           ***     27.55 %      ±5.39% ±7.21%  ±9.45%
napi/make_callback n=10000000          ***     33.68 %      ±2.70% ±3.60%  ±4.70%

Side note: async_context_frame::Scope, used by AsyncResource::MakeCallback, still looks up the Environment twice and always creates a global handle. I would leave it for a separate PR.

Refs: nodejs/performance#24

Disclosure: I used Fable 5.1 (Max) as coding assistant. I built Node with and without the change, ran the benchmark and the tests myself.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.36%. Comparing base (66f26d3) to head (1221198).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66316      +/-   ##
==========================================
- Coverage   90.38%   90.36%   -0.02%     
==========================================
  Files         790      790              
  Lines      274497   274522      +25     
  Branches    52557    52567      +10     
==========================================
- Hits       248100   248076      -24     
- Misses      16879    16927      +48     
- Partials     9518     9519       +1     

Files with missing lines	Coverage Δ
src/api/callback.cc	82.93% <100.00%> (-0.32%)	⬇️
src/async_context_frame.cc	100.00% <100.00%> (ø)
src/env-inl.h	93.99% <100.00%> (+0.02%)	⬆️
src/env.h	97.33% <ø> (ø)

... and 28 files with indirect coverage changes

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[uNetworkingAB]

If the benchmark would (also) compare against a vanilla v8::Function::Call it would show the Node.js mandated (relative) overhead compared to core V8 that is added to all V8 addons that touch Node.js for event delivery. In my own tests, Node.js tend to add 100-200% overhead.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/77972/