Support for asynchronous HTTP response processing (#19)

This change introduces WriteResponseAsync which can be used to move potentially slow request handler code (like upstream lookups) off the I/O service thread to ensure we are always able to serve as many HTTP requests as possible. The current implementation defaults to 16 async worker threads and there is currently no back-pressure.

- Added RequestStats - Metrics for network requests. Aggregates tracking of duration, payload sizes into a single class for ease of use
- Added some metrics on upstream communication

Co-authored-by: Per Larsson <[email protected]>

1 files changed, 63 insertions, 8 deletions

diff --git a/zencore/stats.cpp b/zencore/stats.cpp
index 6afd217e4..0c0647999 100644
--- a/zencore/stats.cpp
+++ b/zencore/stats.cpp
@@ -419,6 +419,58 @@ OperationTiming::Scope::Cancel()
 
 //////////////////////////////////////////////////////////////////////////
 
+RequestStats::RequestStats(int32_t SampleCount) : m_RequestTimeHistogram{SampleCount}, m_BytesHistogram{SampleCount}
+{
+}
+
+RequestStats::~RequestStats()
+{
+}
+
+void
+RequestStats::Update(int64_t Duration, int64_t Bytes)
+{
+	m_RequestMeter.Mark(1);
+	m_RequestTimeHistogram.Update(Duration);
+
+	m_BytesMeter.Mark(Bytes);
+	m_BytesHistogram.Update(Bytes);
+}
+
+uint64_t
+RequestStats::Count() const
+{
+	return m_RequestMeter.Count();
+}
+
+//////////////////////////////////////////////////////////////////////////
+
+void
+EmitSnapshot(Meter& Stat, CbObjectWriter& Cbo)
+{
+	Cbo << "count" << Stat.Count();
+	Cbo << "rate_mean" << Stat.MeanRate();
+	Cbo << "rate_1" << Stat.Rate1() << "rate_5" << Stat.Rate5() << "rate_15" << Stat.Rate15();
+}
+
+void
+RequestStats::EmitSnapshot(std::string_view Tag, CbObjectWriter& Cbo)
+{
+	Cbo.BeginObject(Tag);
+
+	Cbo.BeginObject("requests");
+	metrics::EmitSnapshot(m_RequestMeter, Cbo);
+	metrics::EmitSnapshot(m_RequestTimeHistogram, Cbo, GetHifreqTimerToSeconds());
+	Cbo.EndObject();
+
+	Cbo.BeginObject("bytes");
+	metrics::EmitSnapshot(m_BytesMeter, Cbo);
+	metrics::EmitSnapshot(m_BytesHistogram, Cbo, 1.0);
+	Cbo.EndObject();
+
+	Cbo.EndObject();
+}
+
 void
 EmitSnapshot(std::string_view Tag, OperationTiming& Stat, CbObjectWriter& Cbo)
 {
@@ -427,7 +479,6 @@ EmitSnapshot(std::string_view Tag, OperationTiming& Stat, CbObjectWriter& Cbo)
 	SampleSnapshot Snap = Stat.Snapshot();
 
 	Cbo << "count" << Stat.Count();
-
 	Cbo << "rate_mean" << Stat.MeanRate();
 	Cbo << "rate_1" << Stat.Rate1() << "rate_5" << Stat.Rate5() << "rate_15" << Stat.Rate15();
 
@@ -442,18 +493,22 @@ EmitSnapshot(std::string_view Tag, OperationTiming& Stat, CbObjectWriter& Cbo)
 }
 
 void
-EmitSnapshot(std::string_view Tag, const Histogram& Stat, CbObjectWriter& Cbo)
+EmitSnapshot(std::string_view Tag, const Histogram& Stat, CbObjectWriter& Cbo, double ConversionFactor)
 {
 	Cbo.BeginObject(Tag);
+	EmitSnapshot(Stat, Cbo, ConversionFactor);
+	Cbo.EndObject();
+}
 
+void
+EmitSnapshot(const Histogram& Stat, CbObjectWriter& Cbo, double ConversionFactor)
+{
 	SampleSnapshot Snap = Stat.Snapshot();
 
-	Cbo << "count" << Stat.Count() << "avg" << Stat.Mean();
-	Cbo << "min" << Stat.Min() << "max" << Stat.Max();
-	Cbo << "p75" << Snap.Get75Percentile() << "p95" << Snap.Get95Percentile() << "p99" << Snap.Get99Percentile() << "p999"
-		<< Snap.Get999Percentile();
-
-	Cbo.EndObject();
+	Cbo << "count" << Stat.Count() * ConversionFactor << "avg" << Stat.Mean() * ConversionFactor;
+	Cbo << "min" << Stat.Min() * ConversionFactor << "max" << Stat.Max() * ConversionFactor;
+	Cbo << "p75" << Snap.Get75Percentile() * ConversionFactor << "p95" << Snap.Get95Percentile() * ConversionFactor << "p99"
+		<< Snap.Get99Percentile() * ConversionFactor << "p999" << Snap.Get999Percentile() * ConversionFactor;
 }
 
 void