WIP: Optimize CLI startup time

[bartekpacia]

a stab at fixing #1966

Problem description

The version check is performed synchronously.

This makes shell completions needlessly slow (in case of slow/unreliable network) and kinda defeats the purpose of using them. My bad.

patrol/packages/patrol_cli/lib/src/runner/patrol_command_runner.dart

Lines 375 to 377 in e465db0

	if (_wantsUpdateCheck(commandName)) {
	await _checkForUpdate(commandName);
	}

Resources

• https://stackoverflow.com/a/78657717/7009800 AI-generated garbage answer, such API doesn't exist, see Design an API to support aborting requests dart-lang/http#424

The pub_updater package doesn't provide any way to cancel an update check that is in progress. So it seems to me that the only way to do cancel the version check is to run it in a separate isolate. This seems a bit complex as isolates cannot share memory, but pub_updater.PubUpdater and patrol_cli.Logger must be present in the isolate.

Example 1 (using async, not working as intended)

import 'dart:async';

Future<void> main(List<String> args) async {
  unawaited(_backgroundTask());

  // Simulate main work
  print('start: main task');
  await Future<void>.delayed(const Duration(seconds: 1));
  print('end: main task');
}

/// A low-priority background task.
///  * May take longer than the main task
///  * If it lasts longer than main task, it should be preempted (to not block)
///  * It's low priority so it's fine if it's preempted
Future<void> _backgroundTask() async {
  print('start: background task');
  // Simulate some work
  await Future<void>.delayed(const Duration(seconds: 3));
  print('end: background task');
}

Example 2 (using isolates, working as intended)

import 'dart:async';
import 'dart:isolate' as isolate;

Future<void> main(List<String> args) async {
  unawaited(
    isolate.Isolate.spawn<void>((_) => _backgroundTask(), null),
  );

  // Simulate main work
  print('start: main task');
  await Future<void>.delayed(const Duration(seconds: 1));
  print('end: main task');
}

/// A low-priority background task.
///  * May take longer than the main task
///  * If it lasts longer than main task, it should be preempted (to not block)
///  * It's low priority so it's fine if it's preempted
Future<void> _backgroundTask() async {
  print('start: background task');
  // Simulate some work
  await Future<void>.delayed(const Duration(seconds: 3));
  print('end: background task');
}

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