[nigrosimone]

With no async hook and no executionAsyncResource() user, every InternalCallbackScope pushes and pops the async ids on the stack, only for executionAsyncId() and triggerAsyncId() to read the top. This swaps the two ids in place instead: they are all that those two and process.nextTick() read, so the readers pay nothing.

executionAsyncResource() is the only reader of the stack. The scopes that skip it form a chain in AsyncHooks, counted in a new field kLazyScopes, and JS asks C++ for the innermost one only while that count is not zero. The checks for a corrupted stack stay: test/async-hooks test-improper-order and test-emit-*-on-destroyed fail without them, because the main script runs in a scope that starts before any hook.

compare.js on napi/make_callback, 30 runs, Linux x64, one core, on main (3e5c8af, with #66395):

                                                     confidence improvement accuracy (*)   (**)  (***)
napi/make_callback n=1000000 type='AsyncResource'            **      6.57 %  ±4.56% ±6.07% ±7.91%
napi/make_callback n=1000000 type='Call'                            -2.91 %  ±5.61% ±7.51% ±9.86%
napi/make_callback n=1000000 type='MakeCallback'              *      7.47 %  ±5.64% ±7.50% ±9.77%
napi/make_callback n=10000000 type='AsyncResource'          ***      8.54 %  ±3.42% ±4.55% ±5.93%
napi/make_callback n=10000000 type='Call'                           -1.02 %  ±4.35% ±5.79% ±7.54%
napi/make_callback n=10000000 type='MakeCallback'           ***      7.30 %  ±2.85% ±3.80% ±4.96%

MakeCallback goes from 128.0 to 119.3 ns at n=1e7. test/async-hooks, the async hooks, AsyncLocalStorage, AsyncResource and nextTick tests in test/parallel, and the new addon test pass.

The new field and the chain are the part to look at first, the design was discussed in nodejs/performance#24.

Disclosure: I used Opus 5.5 (Max) as coding assistant

[codecov]

Codecov Report

❌ Patch coverage is 88.15789% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.57%. Comparing base (3e5c8af) to head (21a6ea2).
⚠️ Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/internal/async_hooks.js	70.58%	5 Missing ⚠️
src/api/callback.cc	94.11%	1 Missing and 1 partial ⚠️
src/async_wrap.cc	92.30%	0 Missing and 1 partial ⚠️
src/env.cc	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #66511      +/-   ##
==========================================
- Coverage   92.86%   90.57%   -2.29%     
==========================================
  Files         428      797     +369     
  Lines      195100   278432   +83332     
  Branches    30147    53510   +23363     
==========================================
+ Hits       181175   252200   +71025     
- Misses      13597    16582    +2985     
- Partials      328     9650    +9322     

Files with missing lines	Coverage Δ
src/env.h	97.40% <ø> (ø)
src/node_internals.h	80.70% <100.00%> (ø)
src/async_wrap.cc	83.58% <92.30%> (ø)
src/env.cc	84.26% <90.90%> (ø)
src/api/callback.cc	81.78% <94.11%> (ø)
lib/internal/async_hooks.js	98.60% <70.58%> (+0.35%)	⬆️

... and 498 files with indirect coverage changes

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[nigrosimone]

About the Codecov report: 21a6ea2 adds a test for the two gaps that can be covered, the lazy resource held as a Global (an fs callback) and a context pushed on the stack above a lazy scope.

The lines still reported, popAsyncContext() in lib/internal/async_hooks.js and the check in AsyncHooks::pop_async_context(), are the corrupted stack path. test-improper-order and test-emit-*-on-destroyed go through them, but the child process exits from C++ before it writes its coverage.