Function parseTrace

performance-tests/trace-parser.mjs:826–910

(traceJson)

}

export function parseTrace(traceJson) {
  const events = traceJson.traceEvents || [];

  // Find main renderer thread
  const mainThread = findMainRendererThread(events);

  if (!mainThread) {
    throw new Error('Could not find main renderer thread (CrRendererMain)');
  }

  // Compute trace bounds (DevTools MetaHandler logic)
  const traceBounds = computeTraceBounds(events);
  const traceBoundsUs = {
    min: traceBounds.minUs,
    max: traceBounds.maxUs,
    range: traceBounds.maxUs - traceBounds.minUs,
  };

  // Get ALL main thread events (ph=X with positive duration) for window calculation
  // This matches DevTools's topMostMainThreadAppender.getEntries() behavior
  const allMainThreadEntries = events.filter(e =>
    e.ph === 'X' && e.dur > 0 &&
    e.pid === mainThread.pid &&
    e.tid === mainThread.tid
  );

  // Calculate the auto-zoomed window using DevTools's MainThreadActivity.calculateWindow
  const windowUs = calculateWindow(traceBoundsUs, allMainThreadEntries);
  const windowMinMs = windowUs.min / 1000;
  const windowMaxMs = windowUs.max / 1000;
  const windowRangeMs = windowUs.range / 1000;

  // Filter to VISIBLE events only for stats computation
  const mainThreadEvents = events.filter(e =>
    e.ph === 'X' &&
    e.dur && e.dur > 0 &&
    e.pid === mainThread.pid &&
    e.tid === mainThread.tid &&
    isVisibleEvent(e)
  );

  if (mainThreadEvents.length === 0) {
    throw new Error('No visible events found for main thread');
  }

  // Calculate stats using DevTools algorithm with absolute ms timestamps
  const stats = statsForTimeRange(mainThreadEvents, windowMinMs, windowMaxMs);

  // Add ProfileCall scripting contribution from CPU profile synthesis
  // (SamplesIntegrator synthesizes ProfileCall events for non-idle CPU samples
  // that fall in gaps within RunTask intervals not covered by visible scripting events)
  const profileCallMs = computeProfileCallScripting(
    events, mainThread.pid, mainThread.tid,
    windowUs.min, windowUs.max
  );

  if (profileCallMs > 0) {
    stats.scripting = (stats.scripting || 0) + profileCallMs;