Flaky LibTest/isolate/Isolate/ping_A03_t02.dart test.

[mkustermann]

This test looks as follows:

entryPoint(message) {
  Random random = new Random();
  int s = 0;
  while (true) {
    s = -s + random.nextInt(100);
  }
}

Future test(List<Object?> values) async {
  ReceivePort onExit = new ReceivePort();
  Isolate isolate = await Isolate.spawn(entryPoint, null, // message
      onExit: onExit.sendPort,
      errorsAreFatal: true);
  // check
  List<Future> pingResponses = [];
  for (Object? value in values) {
    ReceivePort pingPort = new ReceivePort();
    isolate.ping(pingPort.sendPort,
        response: value, priority: Isolate.beforeNextEvent);
    Future pingResponse =
        pingPort.first.timeout(TWO_SECONDS, onTimeout: () {
      pingPort.close();
      return "timeout";
    });
    pingResponses.add(pingResponse);
  }
  for (var response in await Future.wait(pingResponses)) {
    Expect.equals("timeout", response);
  }
  // clean up
  isolate.kill(priority: Isolate.immediate);
  await onExit.first;
  asyncEnd();
}

Sometimes one of the pings doesn't result in a timeout, the reason for that is that this test is racy: await Isolate.spawn() returns when the isolate was created, not when the isolate's entrypoint function has been invoked. Therefore there is a small time window when the isolate is created, receives a ping, responds to the ping and then invokes the entrypoint, which can make this test fail.

A more robust test would make the entrypoint send a message inside it's main function that it's ready to do the synchronous loop, then the main isolate can expect pings to timeout. Since the isolate is in an infinite synchronous loop.

[aam]

see dart-lang/sdk#45111.
I raised it with assumption that vm isolate message processing is racy, not that there is anything wrong the test.

[aam]

Please fix corresponding co19_2 tests as they continue to be flaky.