Prometheus, heavy memory calls removed (#27)

util/stats/src/lib.rs

@@ -19,10 +19,47 @@
 use std::{
     iter::FromIterator,
     ops::{Add, Deref, Div, Sub},
+    time::Instant,
 };
 
 #[macro_use]
 extern crate log;
+pub extern crate prometheus;
+
+/// Implements a prometheus metrics collector
+pub trait PrometheusMetrics {
+    fn prometheus_metrics(&self, registry: &mut prometheus::Registry);
+}
+
+/// Adds a new prometheus counter with the specified value
+pub fn prometheus_counter(reg: &mut prometheus::Registry, name: &str, help: &str, value: i64) {
+    let c = prometheus::IntCounter::new(name, help).expect("name and help must be non-empty");
+    c.inc_by(value);
+    reg.register(Box::new(c))
+        .expect("prometheus identifiers must be unique");
+}
+
+/// Adds a new prometheus gauge with the specified gauge
+pub fn prometheus_gauge(reg: &mut prometheus::Registry, name: &str, help: &str, value: i64) {
+    let g = prometheus::IntGauge::new(name, help).expect("name and help must be non-empty");
+    g.set(value);
+    reg.register(Box::new(g))
+        .expect("prometheus identifiers must be are unique");
+}
+
+/// Adds a new prometheus counter with the time spent in running the specified function
+pub fn prometheus_optime<F: Fn() -> T, T>(r: &mut prometheus::Registry, name: &str, f: &F) -> T {
+    let start = Instant::now();
+    let t = f();
+    let elapsed = start.elapsed();
+    prometheus_gauge(
+        r,
+        &format!("optime_{}", name),
+        &format!("Time to perform {}", name),
+        elapsed.as_millis() as i64,
+    );
+    t
+}
 
 /// Sorted corpus of data.
 #[derive(Debug, Clone, PartialEq)]