Add scaffold for new metrics API with counters

src/telemetry/Manager.h

@@ -0,0 +1,168 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#pragma once
+
+#include <cstdint>
+#include <initializer_list>
+#include <string_view>
+#include <vector>
+
+#include "zeek/Span.h"
+#include "zeek/telemetry/Counter.h"
+
+namespace zeek::telemetry {
+
+/**
+ * Manages a collection of metric families.
+ */
+class Manager {
+public:
+	class Impl;
+
+	explicit Manager(Impl* ptr) : pimpl(ptr)
+	{
+	//nop
+	}
+
+	Manager(const Manager&) = delete;
+
+	Manager& operator=(const Manager&) = delete;
+
+	/**
+	 * @returns a counter metric family. Creates the family lazily if necessary.
+	 * @param prefix The prefix (namespace) this family belongs to.
+	 * @param name The human-readable name of the metric, e.g., `requests`.
+	 * @param labels Names for all label dimensions of the metric.
+	 * @param helptext Short explanation of the metric.
+	 * @param unit Unit of measurement.
+	 * @param isSum Indicates whether this metric accumulates something, where
+	 *              only the total value is of interest.
+	 */
+	template <class ValueType = int64_t>
+	CounterFamily<ValueType>
+	counterFamily(std::string_view prefix, std::string_view name,
+	              Span<const std::string_view> labels,
+	              std::string_view helptext,
+	              std::string_view unit = "1", bool isSum = false) {
+		if constexpr (std::is_same<ValueType, int64_t>::value)
+			{
+			return intCounterFam(prefix, name, labels, helptext, unit, isSum);
+			}
+		else
+			{
+			static_assert(std::is_same<ValueType, double>::value,
+			              "metrics only support int64_t and double values");
+			return dblCounterFam(prefix, name, labels, helptext, unit, isSum);
+			}
+	}
+
+	/// @copydoc counterFamily
+	template <class ValueType = int64_t>
+	CounterFamily<ValueType>
+	counterFamily(std::string_view prefix, std::string_view name,
+	              std::initializer_list<std::string_view> labels,
+	              std::string_view helptext, std::string_view unit = "1",
+	              bool isSum = false)
+	{
+		auto lblSpan = Span{labels.begin(), labels.size()};
+		return counterFamily<ValueType>(prefix, name, lblSpan, helptext,
+		                                unit, isSum);
+	}
+
+	/**
+	 * Accesses a counter instance. Creates the hosting metric family as well
+	 * as the counter lazily if necessary.
+	 * @param prefix The prefix (namespace) this family belongs to.
+	 * @param name The human-readable name of the metric, e.g., `requests`.
+	 * @param labels Values for all label dimensions of the metric.
+	 * @param helptext Short explanation of the metric.
+	 * @param unit Unit of measurement.
+	 * @param isSum Indicates whether this metric accumulates something, where
+	 *              only the total value is of interest.
+	 */
+	template <class ValueType = int64_t>
+	Counter<ValueType>
+	counterInstance(std::string_view prefix, std::string_view name,
+	                Span<const LabelView> labels, std::string_view helptext,
+	                std::string_view unit = "1", bool isSum = false)
+		{
+		return withLabelNames(labels, [&, this](auto labelNames)
+			{
+			auto family = counterFamily<ValueType>(prefix, name, labelNames,
+			                                       helptext, unit, isSum);
+			return family.getOrAdd(labels);
+			});
+		}
+
+	/// @copydoc counterInstance
+	template <class ValueType = int64_t>
+	Counter<ValueType>
+	counterInstance(std::string_view prefix, std::string_view name,
+	                std::initializer_list<LabelView> labels,
+	                std::string_view helptext, std::string_view unit = "1",
+	                bool isSum = false)
+		{
+		auto lblSpan = Span{labels.begin(), labels.size()};
+		return counterInstance(prefix, name, lblSpan, helptext, unit, isSum);
+		}
+
+	/**
+	 * Accesses a counter singleton, i.e., a counter that belongs to a family
+	 * without label dimensions (which thus only has a single member). Creates
+	 * the hosting metric family as well as the counter lazily if necessary.
+	 * @param prefix The prefix (namespace) this family belongs to.
+	 * @param name The human-readable name of the metric, e.g., `requests`.
+	 * @param helptext Short explanation of the metric.
+	 * @param unit Unit of measurement.
+	 * @param isSum Indicates whether this metric accumulates something, where
+	 *              only the total value is of interest.
+	 */
+	template <class ValueType = int64_t>
+	Counter<ValueType>
+	counterSingleton(std::string_view prefix, std::string_view name,
+	                 std::string_view helptext, std::string_view unit = "1",
+	                 bool isSum = false)
+		{
+		auto labels = Span<const std::string_view>{};
+		auto fam = counterFamily<ValueType>(prefix, name, labels, helptext,
+		                                    unit, isSum);
+		return fam.getOrAdd({});
+	}
+
+private:
+	IntCounterFamily
+	intCounterFam(std::string_view prefix, std::string_view name,
+	              Span<const std::string_view> labels,
+	              std::string_view helptext, std::string_view unit, bool isSum);
+
+	DblCounterFamily
+	dblCounterFam(std::string_view prefix, std::string_view name,
+	              Span<const std::string_view> labels,
+	              std::string_view helptext, std::string_view unit, bool isSum);
+
+	template <class F>
+	static void withLabelNames(Span<const LabelView> xs, F continuation)
+		{
+		if (xs.size() <= 10) {
+			std::string_view buf[10];
+			for (size_t index = 0; index < xs.size(); ++index)
+				buf[index] = xs[index].first;
+			return continuation(Span{buf, xs.size()});
+		} else {
+			std::vector<std::string_view> buf;
+			for (auto x : xs)
+				buf.emplace_back(x.first, x.second);
+			return continuation(Span{buf});
+		}
+		}
+
+	Impl* pimpl;
+};
+
+} // namespace zeek::telemetry
+
+namespace zeek {
+
+extern telemetry::Manager* telemetry_mgr;
+
+} // namespace zeek