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, 61 insertions, 1 deletions

diff --git a/zencore/include/zencore/stats.h b/zencore/include/zencore/stats.h
index 2e567d614..884bb53f6 100644
--- a/zencore/include/zencore/stats.h
+++ b/zencore/include/zencore/stats.h
@@ -221,10 +221,70 @@ private:
 	Histogram m_Histogram;
 };
 
+/** Metrics for network requests
+
+    Aggregates tracking of duration, payload sizes into a single
+	class
+
+  */
+class RequestStats
+{
+public:
+	RequestStats(int32_t SampleCount = 514);
+	~RequestStats();
+
+	void	 Update(int64_t Duration, int64_t Bytes);
+	uint64_t Count() const;
+
+	// Timing
+
+	int64_t		   MaxDuration() const { return m_BytesHistogram.Max(); }
+	int64_t		   MinDuration() const { return m_BytesHistogram.Min(); }
+	double		   MeanDuration() const { return m_BytesHistogram.Mean(); }
+	SampleSnapshot DurationSnapshot() const { return m_RequestTimeHistogram.Snapshot(); }
+	double		   Rate1() { return m_RequestMeter.Rate1(); }
+	double		   Rate5() { return m_RequestMeter.Rate5(); }
+	double		   Rate15() { return m_RequestMeter.Rate15(); }
+	double		   MeanRate() const { return m_RequestMeter.MeanRate(); }
+
+	// Bytes
+
+	int64_t		   MaxBytes() const { return m_BytesHistogram.Max(); }
+	int64_t		   MinBytes() const { return m_BytesHistogram.Min(); }
+	double		   MeanBytes() const { return m_BytesHistogram.Mean(); }
+	SampleSnapshot BytesSnapshot() const { return m_BytesHistogram.Snapshot(); }
+	double		   ByteRate1() { return m_BytesMeter.Rate1(); }
+	double		   ByteRate5() { return m_BytesMeter.Rate5(); }
+	double		   ByteRate15() { return m_BytesMeter.Rate15(); }
+	double		   ByteMeanRate() const { return m_BytesMeter.MeanRate(); }
+
+	struct Scope
+	{
+		Scope(OperationTiming& Outer);
+		~Scope();
+
+		void Cancel();
+
+	private:
+		OperationTiming& m_Outer;
+		uint64_t		 m_StartTick;
+	};
+
+	void EmitSnapshot(std::string_view Tag, CbObjectWriter& Cbo);
+
+private:
+	Meter	  m_RequestMeter;
+	Meter	  m_BytesMeter;
+	Histogram m_RequestTimeHistogram;
+	Histogram m_BytesHistogram;
+};
+
 void EmitSnapshot(std::string_view Tag, OperationTiming& Stat, CbObjectWriter& Cbo);
-void EmitSnapshot(std::string_view Tag, const Histogram& Stat, CbObjectWriter& Cbo);
+void EmitSnapshot(std::string_view Tag, const Histogram& Stat, CbObjectWriter& Cbo, double ConversionFactor);
 void EmitSnapshot(std::string_view Tag, Meter& Stat, CbObjectWriter& Cbo);
 
+void EmitSnapshot(const Histogram& Stat, CbObjectWriter& Cbo, double ConversionFactor);
+
 }  // namespace zen::metrics
 
 namespace zen {