mirror of
https://github.com/kuhyx/todo-app.git
synced 2026-11-11 13:27:46 +01:00
Krzysztof kuhy Rudnicki
c740cac2f0
Keeps the diagnostic used to produce docs/desktop-performance-findings.md, so the web proof-of-concept can be measured against the same numbers rather than a freshly-written and differently-behaving probe. Armed only by TODO_FRAME_STATS=1, so it is inert in normal use. It reports: - individual slow frames, not per-second percentiles -- a user-visible hitch is one long frame, which averaging over a 61-frame window hides completely; - event-loop blocking via a periodic timer, which is unambiguous where frame gaps are not (a static UI produces no frames, so an idle user and a stalled isolate look identical); - every frame when TODO_FRAME_STATS_ALL=1, for raster-cost-vs-window-size sweeps. The capture screen gets a spinner under the same flag because cadence can only be sampled while something animates continuously. Its branch is unreachable under the test runner, hence coverage:ignore -- the suite stays at 100%. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
85 lines
3.0 KiB
Dart
85 lines
3.0 KiB
Dart
// coverage:ignore-file
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// TEMPORARY diagnostic instrument (desktop interaction-lag investigation).
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// Guarded by TODO_FRAME_STATS=1 so it is inert in normal use.
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//
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// v3 adds an event-loop blocking monitor, which is the decisive instrument.
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// Frame gaps are ambiguous in a mostly-static UI: no frame is produced when
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// nothing needs drawing, so an idle user looks identical to a stalled isolate.
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// A periodic timer, by contrast, is scheduled regardless of drawing -- if it
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// fires late, the UI isolate was genuinely blocked, and by exactly how long.
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import 'dart:async';
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import 'dart:io';
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import 'package:flutter/scheduler.dart';
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/// Whether the frame-stats instrument is armed for this process.
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bool get frameStatsEnabled => Platform.environment['TODO_FRAME_STATS'] == '1';
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/// A frame whose own work exceeded this is a hitch worth naming. Set to zero
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/// by TODO_FRAME_STATS_ALL=1 so every frame is logged, which is what the
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/// raster-cost-vs-window-size sweep needs.
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int get _slowFrameUs =>
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Platform.environment['TODO_FRAME_STATS_ALL'] == '1' ? -1 : 8000;
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/// How often the event-loop probe is scheduled.
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const _probePeriod = Duration(milliseconds: 16);
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/// Lateness beyond this means the isolate was blocked long enough to be felt.
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const _blockedMs = 24;
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final Stopwatch _clock = Stopwatch();
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Timer? _probe;
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String get _at => (_clock.elapsedMilliseconds / 1000).toStringAsFixed(2);
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/// Installs the frame-timing and event-loop instruments.
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void installFrameStats() {
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if (!frameStatsEnabled) return;
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_clock.start();
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stdout.writeln(
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'[frame-stats v3] armed; logging slow frames and UI-isolate blocking',
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);
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_installFrameTimings();
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_installEventLoopProbe();
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}
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void _installFrameTimings() {
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SchedulerBinding.instance.addTimingsCallback((timings) {
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for (final t in timings) {
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final build = t.buildDuration.inMicroseconds;
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final raster = t.rasterDuration.inMicroseconds;
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if (build + raster > _slowFrameUs) {
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stdout.writeln(
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'[FRAME $_at s] total=${((build + raster) / 1000)
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.toStringAsFixed(1)}ms '
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'(build=${(build / 1000).toStringAsFixed(1)} '
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'raster=${(raster / 1000).toStringAsFixed(1)})',
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);
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}
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}
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});
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}
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/// Schedules a timer every [_probePeriod] and reports how late it actually
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/// fired. Lateness is time the UI isolate spent unable to run anything -- e.g.
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/// a synchronous JSON serialize of the whole note log.
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void _installEventLoopProbe() {
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var expected = _clock.elapsedMicroseconds + _probePeriod.inMicroseconds;
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void tick(Timer _) {
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final now = _clock.elapsedMicroseconds;
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final lateMs = (now - expected) / 1000;
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if (lateMs > _blockedMs) {
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stdout.writeln(
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'[UI-BLOCKED $_at s] event loop stalled '
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'${lateMs.toStringAsFixed(1)}ms',
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);
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}
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expected = now + _probePeriod.inMicroseconds;
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}
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_probe = Timer.periodic(_probePeriod, tick);
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}
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/// Stops the probe. Only needed if the instrument outlives the app.
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void disposeFrameStats() => _probe?.cancel();
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