Add MetricsBackend with prometheus counter support

src/util/metricsbackend.h

@@ -0,0 +1,140 @@
+/*
+Minetest
+Copyright (C) 2013-2020 Minetest core developers team
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#pragma once
+#include <memory>
+#include "config.h"
+#include "util/thread.h"
+
+class MetricCounter
+{
+public:
+	MetricCounter() = default;
+
+	virtual ~MetricCounter() {}
+
+	virtual void increment(double number = 1.0) = 0;
+	virtual double get() const = 0;
+};
+
+typedef std::shared_ptr<MetricCounter> MetricCounterPtr;
+
+class SimpleMetricCounter : public MetricCounter
+{
+public:
+	SimpleMetricCounter() = delete;
+
+	virtual ~SimpleMetricCounter() {}
+
+	SimpleMetricCounter(const std::string &name, const std::string &help_str) :
+			MetricCounter(), m_name(name), m_help_str(help_str),
+			m_counter(0.0)
+	{
+	}
+
+	virtual void increment(double number)
+	{
+		MutexAutoLock lock(m_mutex);
+		m_counter += number;
+	}
+	virtual double get() const
+	{
+		MutexAutoLock lock(m_mutex);
+		return m_counter;
+	}
+
+private:
+	std::string m_name;
+	std::string m_help_str;
+
+	mutable std::mutex m_mutex;
+	double m_counter;
+};
+
+class MetricGauge
+{
+public:
+	MetricGauge() = default;
+	virtual ~MetricGauge() {}
+
+	virtual void increment(double number = 1.0) = 0;
+	virtual void decrement(double number = 1.0) = 0;
+	virtual void set(double number) = 0;
+	virtual double get() const = 0;
+};
+
+typedef std::shared_ptr<MetricGauge> MetricGaugePtr;
+
+class SimpleMetricGauge : public MetricGauge
+{
+public:
+	SimpleMetricGauge() = delete;
+
+	SimpleMetricGauge(const std::string &name, const std::string &help_str) :
+			MetricGauge(), m_name(name), m_help_str(help_str), m_gauge(0.0)
+	{
+	}
+
+	virtual ~SimpleMetricGauge() {}
+
+	virtual void increment(double number)
+	{
+		MutexAutoLock lock(m_mutex);
+		m_gauge += number;
+	}
+	virtual void decrement(double number)
+	{
+		MutexAutoLock lock(m_mutex);
+		m_gauge -= number;
+	}
+	virtual void set(double number)
+	{
+		MutexAutoLock lock(m_mutex);
+		m_gauge = number;
+	}
+	virtual double get() const
+	{
+		MutexAutoLock lock(m_mutex);
+		return m_gauge;
+	}
+
+private:
+	std::string m_name;
+	std::string m_help_str;
+
+	mutable std::mutex m_mutex;
+	double m_gauge;
+};
+
+class MetricsBackend
+{
+public:
+	MetricsBackend() = default;
+
+	virtual ~MetricsBackend() {}
+
+	virtual MetricCounterPtr addCounter(
+			const std::string &name, const std::string &help_str);
+	virtual MetricGaugePtr addGauge(
+			const std::string &name, const std::string &help_str);
+};
+
+#if USE_PROMETHEUS
+MetricsBackend *createPrometheusMetricsBackend();
+#endif