Issue ReactiveX#71: Added a Prometheus metrics adapter

resilience4j-circuitbreaker/src/jmh/java/io/github/resilience4j/circuitbreaker/CircuitBreakerBenchmark.java

@@ -64,7 +64,6 @@ public void setUp() {
         protectedSupplier = CircuitBreaker.decorateSupplier(circuitBreaker, stringSupplier);
 
         CircuitBreaker circuitBreakerWithSubscriber = CircuitBreaker.ofDefaults("testCircuitBreakerWithSb");
-        circuitBreakerWithSubscriber.getEventStream().subscribe();
         protectedSupplierWithSb = CircuitBreaker.decorateSupplier(circuitBreakerWithSubscriber, stringSupplier);
     }
 

resilience4j-documentation/src/docs/asciidoc/addon_guides/prometheus.adoc

@@ -1,9 +1,10 @@
-=== Prometheus Metrics exporter
+=== Prometheus Metrics Integration
 
 ==== Introduction
 
-Integration of circuit breaker and rate limiter metrics with
-https://github.com/prometheus/client_java[Prometheus simple client]
+Integration with https://github.com/prometheus/client_java[Prometheus simple client]
+
+Module provides exporters for `CircuitBreaker` and `RateLimiter` metrics.
 
 For the circuit breaker library exports 2 metrics:
 
@@ -28,6 +29,15 @@ For the rate limiter following metric with default name `rate_limiter` and label
 
 The names of the rate limiters and circuit breakers are exposed using label `name`.
 
+This module also provides `CallMeter` -- a composite metric to measure single call/request metrics such as:
+    - execution time distribution,
+    - number of attempts and
+    - number of failures.
+
+It is implemented in Prometheus simple client's style, supports labels and produces histogram and counter metrics.
+
+Usage examples provided bellow in this section.
+
 ==== Dashboard Example
 
 image::images/prometheus-dashboard.png[Circuit Breaker Dashboard Example]
@@ -64,4 +74,41 @@ final RateLimiter boo = rateLimiterRegistry.rateLimiter("boo");
 collectorRegistry.register(RateLimiterExports.ofRateLimiterRegistry(rateLimiterRegistry));
 --
 
-For both it is possible to use just a collection of breakers and limiters instead of registry.
+For both it is possible to use just a collection of breakers and limiters instead of registry.
+
+===== Call Meter
+
+Simple example without labels
+
+[source,java]
+--
+final CollectorRegistry registry = new CollectorRegistry();
+
+final CallMeter meter = CallMeter.of("foo_call", "Foo call help", registry);
+
+CallMeter.decorateCompletionStageSupplier(meter, () -> supplyAsync(() -> { /* ... */ }));
+--
+
+Advanced example with labels
+
+[source,java]
+--
+final CollectorRegistry registry = new CollectorRegistry();
+
+final CallMeter meter = CallMeter
+        .builder()
+        .name("foo_call")
+        .help("Foo call help")
+        .labelNames("label_1")
+        .build()
+        .register(registry);
+
+meter.labels("boo").executeRunnable(() -> { /* ... */ });
+
+CallMeter.decorateCompletionStageSupplier(
+    meter.labels("baz"),
+    () -> supplyAsync(() -> { /* ... */ })
+);
+
+--
+

resilience4j-metrics/src/main/java/io/github/resilience4j/metrics/Timer.java

@@ -47,7 +47,7 @@ public interface Timer {
      *
      * @param name the name of the timer
      * @param metricRegistry the MetricRegistry
-     * @return a Bulkhead instance
+     * @return a Timer instance
      */
     static Timer ofMetricRegistry(String name, MetricRegistry metricRegistry) {
         return new TimerImpl(name, metricRegistry);
@@ -57,7 +57,7 @@ static Timer ofMetricRegistry(String name, MetricRegistry metricRegistry) {
      * Creates a timer of a default MetricRegistry
      *
      * @param name the name of the timer
-     * @return a Bulkhead instance
+     * @return a Timer instance
      */
     static Timer of(String name) {
         return new TimerImpl(name, new MetricRegistry());

resilience4j-prometheus/src/main/java/io/github/resilience4j/prometheus/CallCollectors.java

@@ -0,0 +1,16 @@
+package io.github.resilience4j.prometheus;
+
+import io.prometheus.client.Counter;
+import io.prometheus.client.Histogram;
+
+final class CallCollectors {
+    public final Histogram histogram;
+    public final Counter totalCounter;
+    public final Counter errorCounter;
+
+    CallCollectors(Histogram histogram, Counter totalCounter, Counter errorCounter) {
+        this.histogram = histogram;
+        this.totalCounter = totalCounter;
+        this.errorCounter = errorCounter;
+    }
+}