Step 1 - Tight loop delays timers

import 'dart:async';

void burnCpu() {
  final sw = Stopwatch()..start();
  while (sw.elapsedMilliseconds < 500) {}
}

void main() {
  print('start');
  Timer(const Duration(milliseconds: 50), () => print('timer fired'));
  burnCpu();
  print('burn done');
}

• The timer callback waits until burnCpu returns because nothing else runs on this isolate meanwhile.

Step 2 - await does not help inside sync CPU

Future<void> heavyWrong() async {
  final sw = Stopwatch()..start();
  while (sw.elapsedMilliseconds < 800) {}
}

Future<void> main() async {
  await heavyWrong();
}

• The loop never yields; it is still one uninterrupted run on the isolate.

Step 3 - Mitigations (overview)

• Chunk work with await Future<void>.delayed(Duration.zero) occasionally (crude).
• Move real parallel CPU to isolates (later level) or native code.

Practice tasks

• Replace part of a long loop with periodic await Future.delayed(Duration.zero) and verify timers fire sooner (still not ideal for huge work).
• Measure Stopwatch around a JSON encode of a large structure vs a naive string build in a loop.