Provide a method to clear a histogram

Signed-off-by: Zak Cutner <[email protected]>

Author: zakcutner

src/encoding/protobuf.rs

@@ -739,6 +739,35 @@ mod tests {
                 );
                 assert_eq!(1, value.count);
                 assert_eq!(11, value.buckets.len());
+                assert_eq!(1u64, value.buckets.iter().map(|bucket| bucket.count).sum());
+            }
+            _ => panic!("wrong value type"),
+        }
+
+        histogram.clear();
+
+        let metric_set = encode(&registry).unwrap();
+
+        let family = metric_set.metric_families.first().unwrap();
+        assert_eq!("my_histogram", family.name);
+        assert_eq!("My histogram.", family.help);
+
+        assert_eq!(
+            openmetrics_data_model::MetricType::Histogram as i32,
+            extract_metric_type(&metric_set)
+        );
+
+        match extract_metric_point_value(&metric_set) {
+            openmetrics_data_model::metric_point::Value::HistogramValue(value) => {
+                assert_eq!(
+                    Some(openmetrics_data_model::histogram_value::Sum::DoubleValue(
+                        0.0
+                    )),
+                    value.sum
+                );
+                assert_eq!(0, value.count);
+                assert_eq!(11, value.buckets.len());
+                assert_eq!(0u64, value.buckets.iter().map(|bucket| bucket.count).sum());
             }
             _ => panic!("wrong value type"),
         }

src/metrics/histogram.rs

@@ -101,6 +101,17 @@ impl Histogram {
         }
     }
 
+    /// Clears all observations.
+    pub fn clear(&self) {
+        let mut inner = self.inner.write();
+        inner.sum = Default::default();
+        inner.count = Default::default();
+
+        for (_, value) in &mut inner.buckets {
+            *value = 0;
+        }
+    }
+
     pub(crate) fn get(&self) -> (f64, u64, MappedRwLockReadGuard<Vec<(f64, u64)>>) {
         let inner = self.inner.read();
         let sum = inner.sum;
@@ -149,6 +160,7 @@ mod tests {
     fn histogram() {
         let histogram = Histogram::new(exponential_buckets(1.0, 2.0, 10));
         histogram.observe(1.0);
+        histogram.clear();
     }
 
     #[test]