add header-only prometheus lib to ext

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

@@ -0,0 +1,57 @@
+
+#include <prometheus/simpleapi.h>
+
+// use prometheus namespace
+using namespace prometheus::simpleapi;
+
+class MyClass {
+
+  counter_family_t metric_family { "simple_family", "simple family example" };
+  counter_metric_t metric1 { metric_family.Add({{"name", "counter1"}}) };
+  counter_metric_t metric2 { metric_family.Add({{"name", "counter2"}}) };
+
+  counter_metric_t metric3 { "simple_counter_1", "simple counter 1 without labels example" };
+  counter_metric_t metric4 { "simple_counter_2", "simple counter 2 without labels example" };
+
+  benchmark_family_t benchmark_family { "simple_benchmark_family", "simple benchmark family example" };
+  benchmark_metric_t benchmark1 { benchmark_family.Add({{"benchmark", "1"}}) };
+  benchmark_metric_t benchmark2 { benchmark_family.Add({{"benchmark", "2"}}) };
+
+public:
+
+  MyClass() = default;
+
+  void member_to_do_something() {
+
+    benchmark1.start();
+    const int random_value = std::rand();
+    benchmark1.stop();
+
+    benchmark2.start();
+    if (random_value & 1)  metric1++;
+    if (random_value & 2)  metric2++;
+    if (random_value & 4)  metric3++;
+    if (random_value & 8)  metric4++;
+    benchmark2.stop();
+
+  }
+
+};
+
+int main() {
+
+  MyClass myClass;
+  benchmark_metric_t benchmark { "simple_benchmark", "simple benchmark example" };
+
+  for (;; ) {
+
+    benchmark.start();
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    benchmark.stop();
+
+    myClass.member_to_do_something();
+
+  }
+
+}
+