private void OnTimer()
{
if (_eventSource.IsEnabled())
{
DateTime now;
TimeSpan elapsed;
int pollingIntervalInMilliseconds;
DiagnosticCounter[] counters;
lock (s_counterGroupLock)
{
now = DateTime.UtcNow;
elapsed = now - _timeStampSinceCollectionStarted;
pollingIntervalInMilliseconds = _pollingIntervalInMilliseconds;
counters = new DiagnosticCounter[_counters.Count];
_counters.CopyTo(counters);
}
// MUST keep out of the scope of s_counterGroupLock because this will cause WritePayload
// callback can be re-entrant to CounterGroup (i.e. it's possible it calls back into EnableTimer()
// above, since WritePayload callback can contain user code that can invoke EventSource constructor
// and lead to a deadlock. (See https://github.com/dotnet/runtime/issues/40190 for details)
foreach (DiagnosticCounter counter in counters)
{
// NOTE: It is still possible for a race condition to occur here. An example is if the session
// that subscribed to these batch of counters was disabled and it was immediately enabled in
// a different session, some of the counter data that was supposed to be written to the old
// session can now "overflow" into the new session.
// This problem pre-existed to this change (when we used to hold lock in the call to WritePayload):
// the only difference being the old behavior caused the entire batch of counters to be either
// written to the old session or the new session. The behavior change is not being treated as a
// significant problem to address for now, but we can come back and address it if it turns out to
// be an actual issue.
counter.WritePayload((float)elapsed.TotalSeconds, pollingIntervalInMilliseconds);
}
lock (s_counterGroupLock)
{
_timeStampSinceCollectionStarted = now;
TimeSpan delta = now - _nextPollingTimeStamp;
delta = _pollingIntervalInMilliseconds > delta.TotalMilliseconds ? TimeSpan.FromMilliseconds(_pollingIntervalInMilliseconds) : delta;
if (_pollingIntervalInMilliseconds > 0)
{
_nextPollingTimeStamp += TimeSpan.FromMilliseconds(_pollingIntervalInMilliseconds * Math.Ceiling(delta.TotalMilliseconds / _pollingIntervalInMilliseconds));
}
}
}
}
internal void Remove(DiagnosticCounter eventCounter)
{
lock (s_counterGroupLock) // Lock the CounterGroup
_counters.Remove(eventCounter);
}
internal void Add(DiagnosticCounter eventCounter)
{
lock (s_counterGroupLock) // Lock the CounterGroup
_counters.Add(eventCounter);
}