public async Task Start()
{
_current = await _detector.Detect(_token);
_tracker.Publish(new ShardState(ShardState.HighWaterMark, _current.CurrentMark)
{
Action = ShardAction.Started
});
_loop = Task.Factory.StartNew(DetectChanges, TaskCreationOptions.LongRunning | TaskCreationOptions.AttachedToParent);
_timer.Start();
_logger.LogInformation("Started HighWaterAgent");
}
private async Task DetectChanges()
{
// TODO -- need to put some retry & exception handling here.
try
{
_current = await _detector.Detect(_token);
if (_current.CurrentMark > 0)
{
_tracker.MarkHighWater(_current.CurrentMark);
}
}
catch (Exception e)
{
_logger.LogError(e, "Failed while making the initial determination of the high water mark");
}
await Task.Delay(_settings.FastPollingTime, _token);
while (!_token.IsCancellationRequested)
{
HighWaterStatistics statistics = null;
try
{
statistics = await _detector.Detect(_token);
}
catch (Exception e)
{
_logger.LogError(e, "Failed while trying to detect high water statistics");
await Task.Delay(_settings.SlowPollingTime, _token);
continue;
}
var status = statistics.InterpretStatus(_current);
switch (status)
{
case HighWaterStatus.Changed:
await markProgress(statistics, _settings.FastPollingTime);
break;
case HighWaterStatus.CaughtUp:
await markProgress(statistics, _settings.SlowPollingTime);
break;
case HighWaterStatus.Stale:
var safeHarborTime = _current.Timestamp.Add(_settings.StaleSequenceThreshold);
var delayTime = safeHarborTime.Subtract(statistics.Timestamp);
if (delayTime.TotalSeconds > 0)
{
await Task.Delay(delayTime, _token);
}
statistics = await _detector.DetectInSafeZone(safeHarborTime, _token);
await markProgress(statistics, _settings.FastPollingTime);
break;
}
}
_logger.LogInformation("HighWaterAgent has detected a cancellation and has stopped polling");
}