/// <summary>
/// This MetricStatsEngineQueue uses a readwrite lock (allows multiple readers, but only one writer, at a time) to mediate
/// between metrics that need to merge into one of the engines (readers), and the harvest job (writer), which replaces the
/// queue and merges the engines in the old queue to create the harvest payload.
///
/// In this method, get the read lock and call a method that will pick an engine and merge metric.
/// </summary>
/// <param name="metric"></param>
/// <returns></returns>
public bool MergeMetric(IAllMetricStatsCollection metric)
{
if (_lock.TryEnterReadLock(50))
{
try
{
Queue <MetricStatsCollection> statsEngineQueue = this._statsEngineQueue;
if (statsEngineQueue == null)
{
// We've already been harvested. Caller should try again, at which point a whole new MetricStatsEngineQueue
// will have been created for the next harvest cycle.
return(false);
}
MergeMetricUnderLock(statsEngineQueue, metric);
return(true);
}
finally
{
_lock.ExitReadLock();
}
}
return(false);
}
/// <summary>
/// Take a stats engine (metrics aggregate Dictionary) off the queue and merge metric into it, then put it back
/// on the queue. Create one if all the existing ones are "checked out" -- others can use it later.
///
/// We are one of (possibly) several readers of the stats engine queue under the readwrite lock, so harvest will
/// wait for us to finish before fetching/replacing the entire queue
/// </summary>
/// <param name="statsEngineQueue"></param>
/// <param name="metric"></param>
private void MergeMetricUnderLock(Queue <MetricStatsCollection> statsEngineQueue, IAllMetricStatsCollection metrics)
{
MetricStatsCollection statsEngineToMergeWith = null;
try
{
lock (_queueReadersLock)
{
if (statsEngineQueue.Count > 0)
{
statsEngineToMergeWith = statsEngineQueue.Dequeue();
}
}
// make a new stats engine if there aren't enough to go around right now
if (statsEngineToMergeWith == null)
{
statsEngineToMergeWith = CreateMetricStatsEngine();
Interlocked.Increment(ref _statsEngineCount);
}
metrics.AddMetricsToEngine(statsEngineToMergeWith);
}
catch (Exception e)
{
Log.Warn($"Exception dequeueing/creating stats engine: {e}");
}
finally
{
if (statsEngineToMergeWith != null)
{
try
{
lock (_queueReadersLock)
{
statsEngineQueue.Enqueue(statsEngineToMergeWith);
}
}
catch (Exception e)
{
// should never happen
Log.Warn($"Exception returning stats engine to queue: {e}");
}
}
}
}
