private static void UpdateTimeWeightedAvg(PerformanceTimeEntry entry, DateTime now)
{
lock (entry)
{
if (entry.LastMeasureTime != default(DateTime))
{
double milliSoFar = 0;
var deltaTime = (now - entry.LastMeasureTime).TotalMilliseconds;
milliSoFar += entry.TotalTime.TotalMilliseconds;
entry.TotalTime = entry.TotalTime.Add(TimeSpan.FromMilliseconds(deltaTime));
entry.TimeWeightedAverage = (milliSoFar * entry.TimeWeightedAverage + entry.Last * deltaTime) /
entry.TotalTime.TotalMilliseconds;
}
}
}
private void RecordEntryValue(PerformanceTimeEntry entry, Func <double, double> valueFunc)
{
lock (entry)
{
var value = valueFunc(entry.Last);
double total = entry.Instances * entry.Average;
entry.Instances++;
entry.Average = (total + value) / entry.Instances;
entry.Maximum = entry.LastMeasureTime == default(DateTime) ? value : Math.Max(entry.Minimum, value);
entry.Minimum = entry.LastMeasureTime == default(DateTime) ? value : Math.Min(entry.Minimum, value);
var now = DateTime.UtcNow;
UpdateTimeWeightedAvg(entry, now);
entry.LastMeasureTime = now;
entry.Last = value;
}
}
private void LogPerformanceCounter(string name, Func <double, double> valueFunc)
{
if (Interlocked.CompareExchange(ref _perfLoggingTaskEnabled, 1, 0) == 0)
{
//kick off perf logging.
Task.Run(PerformanceLogAsync);
}
lock (_perfCounterDictionary)
{
if (!_perfCounterDictionary.TryGetValue(name, out PerformanceTimeEntry entry))
{
entry = new PerformanceTimeEntry();
_perfCounterDictionary[name] = entry;
}
RecordEntryValue(entry, valueFunc);
}
}
private void UpdateTimeWeightedAvg(PerformanceTimeEntry entry, DateTime now)
{
lock (entry)
{
// For periodically sampled values, we take an average by weighting it with the time since the last
// measurement, effectively assuming that the value has been "the new value" for all of the preceding
// time. For example, consider a "number of active sessions" statistic:
// t=0 value=0
// t=1 value=10 (tavg=10)
// t=2 value=15 (tavg=12.5 - we think of it as having been 10 for 1 second and 15 for 1 second)
// t=6 value=20 (tavg=17.5 - we think of it as having been 12.5 for 2 seconds and 20 for 4 seconds)
if (entry.LastMeasureTime != default(DateTime))
{
var deltaTime = now - entry.LastMeasureTime;
var milliSoFar = entry.TotalTime.TotalMilliseconds;
entry.TotalTime += deltaTime;
entry.TimeWeightedAverage = (milliSoFar * entry.TimeWeightedAverage + entry.Last * deltaTime.TotalMilliseconds) /
entry.TotalTime.TotalMilliseconds;
}
}
}
