CP-1935: Added some reset methods for counters, guages, and histograms

core/include/prometheus/counter.h

@@ -34,6 +34,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Counter: public MetricBase {
   /// \brief Create a counter that starts at 0.
   Counter(const bool alert_if_no_family = true);
 
+  /// \brief Resets the counter.
+  void Reset();
+
   /// \brief Increment the counter by a given amount.
   ///
   /// The counter will not change if the given amount is negative.

core/include/prometheus/gauge.h

@@ -30,6 +30,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Gauge: public MetricBase {
   /// \brief Create a gauge that starts at the given amount.
   Gauge(const double value = 0, const bool alert_if_no_family = true);
 
+  /// \brief Reset the gauge.
+  void Reset(const double value = 0);
+
   /// \brief Increment the gauge by the given amount.
   void Increment(const double value = 1);
 

core/include/prometheus/histogram.h

@@ -47,6 +47,9 @@ class PROMETHEUS_CPP_CORE_EXPORT Histogram: public MetricBase {
   /// The bucket boundaries cannot be changed once the histogram is created.
   Histogram(const BucketBoundaries& buckets, const bool alert_if_no_family = true);
 
+  /// \brief Reset the histogram.
+  void Reset();
+
   /// \brief Observe the given amount.
   ///
   /// The given amount selects the 'observed' bucket. The observed bucket is

core/include/prometheus/metric_base.h

@@ -14,7 +14,7 @@ namespace prometheus {
 class PROMETHEUS_CPP_CORE_EXPORT MetricBase {
  public:
   MetricBase(const bool alert_if_no_family = true);
-  
+
   /// \brief    Prints a message to stderr if the metric doesn't have a family
   bool HasFamily();
 

core/src/counter.cc

@@ -5,6 +5,11 @@ namespace prometheus {
 
 Counter::Counter(const bool alert_if_no_family) : MetricBase(alert_if_no_family) {};
 
+void Counter::Reset() {
+  value_ = 0;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
 
 void Counter::Increment(const double value) {
   if (value < 0.0) return;

core/src/gauge.cc

@@ -7,6 +7,12 @@ namespace prometheus {
 
 Gauge::Gauge(const double value, const bool alert_if_no_family) : MetricBase(alert_if_no_family), value_(value) {}
 
+void Gauge::Reset(const double value) {
+  value_ = value;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
+
 void Gauge::Increment(const double value) {
   if (value < 0.0) return;
   value_ = value_ + value;

core/src/histogram.cc

@@ -13,6 +13,15 @@ Histogram::Histogram(const BucketBoundaries& buckets, const bool alert_if_no_fam
                         std::end(bucket_boundaries_)));
 }
 
+void Histogram::Reset() {
+  for (unsigned int bucket_index = 0; bucket_index < bucket_counts_.size(); ++bucket_index) {
+    bucket_counts_[bucket_index] = 0;
+  }  
+  sum_ = 0;
+  last_update_ = std::time(nullptr);
+  AlertIfNoFamily();
+}
+
 void Histogram::Observe(const double value) {
   // TODO: determine bucket list size at which binary search would be faster
   const auto bucket_index = static_cast<std::size_t>(std::distance(