add header-only prometheus lib to ext

ext/prometheus-cpp-lite-1.0/examples/use_benchmark_in_class_example.cpp

@@ -0,0 +1,59 @@
+#include <prometheus/registry.h>
+#include <prometheus/benchmark.h>
+#include <prometheus/text_serializer.h>
+
+#include <array>
+#include <chrono>
+#include <cstdlib>
+#include <memory>
+#include <string>
+#include <thread>
+#include <iostream>
+
+// use prometheus namespace
+using namespace prometheus;
+
+// create global registry for use it from our classes
+static Registry globalRegistry;
+
+class MyClass {
+
+  Benchmark::Family& benchmarkFamily { Benchmark::Family::Build(globalRegistry,
+                                         "benchmark_family", "family for check benchmark functionality") };
+
+  Benchmark& benchmark1 { benchmarkFamily.Add({{"number", "1"}}) };
+  Benchmark& benchmark2 { benchmarkFamily.Add({{"number", "2"}}) };
+
+public:
+
+  MyClass() = default;
+
+  void member_to_do_something() {
+
+    benchmark1.start();
+    benchmark2.start();
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
+    benchmark1.stop();
+    std::this_thread::sleep_for(std::chrono::milliseconds(500));
+    benchmark2.stop();
+
+  }
+
+};
+
+int main() {
+
+  MyClass myClass;
+
+  for (;; ) {
+
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+
+    myClass.member_to_do_something();
+
+    TextSerializer text_serializer;
+    text_serializer.Serialize(std::cout, globalRegistry.Collect());
+
+  }
+}
+