Add new Timer class to the telemetry API

src/telemetry/Manager.cc

@@ -4,9 +4,12 @@
 
 #include "caf/telemetry/metric_registry.hpp"
 
+#include <thread>
+
 #include "zeek/3rdparty/doctest.h"
 
 #include "zeek/telemetry/Detail.h"
+#include "zeek/telemetry/Timer.h"
 
 namespace zeek::telemetry {
 
@@ -524,6 +527,16 @@ SCENARIO("telemetry managers provide access to histogram families")
 				auto second = family.GetOrAdd({{"protocol", "udp"}});
 				CHECK_NE(first, second);
 				}
+			AND_THEN("Timers add observations to histograms")
+				{
+				auto hg = family.GetOrAdd({{"protocol", "tst"}});
+				CHECK_EQ(hg.Sum(), 0.0);
+				{
+					Timer observer{hg};
+					std::this_thread::sleep_for(1ms);
+				}
+				CHECK_NE(hg.Sum(), 0.0);
+				}
 			}
 		}
 	}

src/telemetry/Timer.h

@@ -0,0 +1,55 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#pragma once
+
+#include <chrono>
+
+namespace zeek::telemetry {
+
+/// Convenience helper for measuring durations such as latency using a histogram
+/// with second resolution. The measurement starts when creating the objects and
+/// finishes when the Timer goes out of scope.
+class Timer {
+public:
+	using Clock = std::chrono::steady_clock;
+
+	[[nodiscard]] explicit Timer(DblHistogram h) : h_(h)
+		{
+		start_ = Clock::now();
+		}
+
+	Timer(const Timer&) = delete;
+
+	Timer&operator=(const Timer&) = delete;
+
+	~Timer()
+		{
+		Observe(h_, start_);
+		}
+
+	/// @return The histogram handle.
+	auto Handle() const noexcept
+		{
+		return h_;
+		}
+
+	/// @return The recorded start time.
+	auto Started() const noexcept
+	{
+	return start_;
+	}
+
+	/// Calls `h.Observe` with the time passed since `start`.
+	static void Observe(DblHistogram h, Clock::time_point start)
+	{
+		using DblSec = std::chrono::duration<double>;
+		if ( auto end = Clock::now(); end > start )
+			h.Observe(std::chrono::duration_cast<DblSec>(end - start).count());
+	}
+
+private:
+	DblHistogram h_;
+	Clock::time_point start_;
+};
+
+} // namespace zeek::telemetry