Node creates monitorEventLoopDelay's histogram with a lowest discernible
value of 1000 ns, so an empty histogram's percentile() returns 511, the
highest value its first bucket holds. The runtime returned 0.
6397-event-loop-metrics.ts now skips a sampling window that has no
recorded delta. A delta needs two samples after reset(), and a loop that
wakes late runs only one sample in a window, so on a loaded machine the
program printed an empty window under Node and compiled alike. The
program also prints percentile(50) after each reset.
- monitorEventLoopDelay is lowered from the builtin call dispatch, by module and member, so aliased named imports, namespace members and destructured requires all reach it. Shorthand and possibly undefined resolutions take Node's default.
- The runtime validates the resolution as Node does (an integer of at least 1) and throws a catchable RangeError with ERR_OUT_OF_RANGE.
- `'stack' in err` and Object.prototype's keys are true for every Error. The declared-member fold applies only to keys some program class declares and that built-in errors don't carry in runtime slots; other keys stay fenced.
- Library mode's async_free gate refuses the event-loop metrics, which library links leave out. They join the perf_hooks fence family.
Once generic wrappers compile (#1413), the code behind them is reachable.
This closes the general gaps found there:
- performance.eventLoopUtilization() and monitorEventLoopDelay()'s
IntervalHistogram (enable, disable, reset, percentile and the min, max,
mean, stddev, count and exceeds readings), under the fallback
declarations and @types/node. A new runtime unit, scr_perf_loop.c, links
only for programs that read them (the perfLoop feature): an unref'd
sampling interval records into HdrHistogram-shaped buckets, and
utilization measures active time as the main thread's CPU time since
the loop started.
- Catch bindings narrowed by a user type predicate or an assertion read
their members through the checked-dynamic value.
- `??` with a function default of a different signature takes the
optional callback's own function type and adapts the default.
- Optional calls on interface-typed receivers dispatch like the plain
protocol call.
- `any` parameters of function declarations and spelled function types
are checked-dynamic slots, and a generic instantiated at `any` takes
`unknown` there.
- `'key' in err` on Error receivers answers from the declaring subclasses.
- Object.entries over a generic record resolves
`keyof T extends never ? unknown : T[keyof T]` through the binding.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Chris Tate