Add a more type safe way of registering gauges (#2642)

Add the `registerGauge` method to `MetricRegistry` that accepts `Gauge<T>` instead of `Metric` which makes it possible to register a gauge as a lambda expression without declaring its type explicitly.

metrics-core/src/main/java/com/codahale/metrics/InstrumentedExecutorService.java

@@ -58,31 +58,31 @@ public InstrumentedExecutorService(ExecutorService delegate, MetricRegistry regi
 
         if (delegate instanceof ThreadPoolExecutor) {
             ThreadPoolExecutor executor = (ThreadPoolExecutor) delegate;
-            registry.register(MetricRegistry.name(name, "pool.size"),
-                    (Gauge<Integer>) executor::getPoolSize);
-            registry.register(MetricRegistry.name(name, "pool.core"),
-                    (Gauge<Integer>) executor::getCorePoolSize);
-            registry.register(MetricRegistry.name(name, "pool.max"),
-                    (Gauge<Integer>) executor::getMaximumPoolSize);
+            registry.registerGauge(MetricRegistry.name(name, "pool.size"),
+                    executor::getPoolSize);
+            registry.registerGauge(MetricRegistry.name(name, "pool.core"),
+                    executor::getCorePoolSize);
+            registry.registerGauge(MetricRegistry.name(name, "pool.max"),
+                    executor::getMaximumPoolSize);
             final BlockingQueue<Runnable> queue = executor.getQueue();
-            registry.register(MetricRegistry.name(name, "tasks.active"),
-                    (Gauge<Integer>) executor::getActiveCount);
-            registry.register(MetricRegistry.name(name, "tasks.completed"),
-                    (Gauge<Long>) executor::getCompletedTaskCount);
-            registry.register(MetricRegistry.name(name, "tasks.queued"),
-                    (Gauge<Integer>) queue::size);
-            registry.register(MetricRegistry.name(name, "tasks.capacity"),
-                    (Gauge<Integer>) queue::remainingCapacity);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.active"),
+                    executor::getActiveCount);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.completed"),
+                    executor::getCompletedTaskCount);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.queued"),
+                    queue::size);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.capacity"),
+                    queue::remainingCapacity);
         } else if (delegate instanceof ForkJoinPool) {
             ForkJoinPool forkJoinPool = (ForkJoinPool) delegate;
-            registry.register(MetricRegistry.name(name, "tasks.stolen"),
-                    (Gauge<Long>) forkJoinPool::getStealCount);
-            registry.register(MetricRegistry.name(name, "tasks.queued"),
-                    (Gauge<Long>) forkJoinPool::getQueuedTaskCount);
-            registry.register(MetricRegistry.name(name, "threads.active"),
-                    (Gauge<Integer>) forkJoinPool::getActiveThreadCount);
-            registry.register(MetricRegistry.name(name, "threads.running"),
-                    (Gauge<Integer>) forkJoinPool::getRunningThreadCount);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.stolen"),
+                    forkJoinPool::getStealCount);
+            registry.registerGauge(MetricRegistry.name(name, "tasks.queued"),
+                    forkJoinPool::getQueuedTaskCount);
+            registry.registerGauge(MetricRegistry.name(name, "threads.active"),
+                    forkJoinPool::getActiveThreadCount);
+            registry.registerGauge(MetricRegistry.name(name, "threads.running"),
+                    forkJoinPool::getRunningThreadCount);
         }
     }
 

metrics-core/src/main/java/com/codahale/metrics/MetricRegistry.java

@@ -76,6 +76,18 @@ protected ConcurrentMap<String, Metric> buildMap() {
         return new ConcurrentHashMap<>();
     }
 
+    /**
+     * Given a {@link Gauge}, registers it under the given name and returns it
+     *
+     * @param name the name of the gauge
+     * @param <T>  the type of the gauge's value
+     * @return the registered {@link Gauge}
+     * @since 4.2.10
+     */
+    public <T> Gauge<T> registerGauge(String name, Gauge<T> metric) throws IllegalArgumentException {
+        return register(name, metric);
+    }
+
     /**
      * Given a {@link Metric}, registers it under the given name.
      *
@@ -93,7 +105,7 @@ public <T extends Metric> T register(String name, T metric) throws IllegalArgume
         }
 
         if (metric instanceof MetricRegistry) {
-            final MetricRegistry childRegistry = (MetricRegistry)metric;
+            final MetricRegistry childRegistry = (MetricRegistry) metric;
             final String childName = name;
             childRegistry.addListener(new MetricRegistryListener() {
                 @Override

metrics-core/src/test/java/com/codahale/metrics/MetricRegistryTest.java

@@ -615,15 +615,29 @@ public void removingDeepChildMetricsAfterRegister() {
         assertThat(deepChildMetrics.size()).isEqualTo(1);
         assertThat(childMetrics.size()).isEqualTo(3);
     }
-    
+
     @Test
     public void registerNullMetric() {
-        MetricRegistry registry = new MetricRegistry();   
+        MetricRegistry registry = new MetricRegistry();
         try {
             registry.register("any_name", null);
             Assert.fail("NullPointerException must be thrown !!!");
         } catch (NullPointerException e) {
             Assert.assertEquals("metric == null", e.getMessage());
         }
     }
+
+    @Test
+    public void infersGaugeType() {
+        Gauge<Long> gauge = registry.registerGauge("gauge", () -> 10_000_000_000L);
+
+        assertThat(gauge.getValue()).isEqualTo(10_000_000_000L);
+    }
+
+    @Test
+    public void registersGaugeAsLambda() {
+        registry.registerGauge("gauge", () -> 3.14);
+
+        assertThat(registry.gauge("gauge").getValue()).isEqualTo(3.14);
+    }
 }

metrics-ehcache/src/main/java/com/codahale/metrics/ehcache/InstrumentedEhcache.java

@@ -1,6 +1,5 @@
 package com.codahale.metrics.ehcache;
 
-import com.codahale.metrics.Gauge;
 import com.codahale.metrics.MetricRegistry;
 import com.codahale.metrics.Timer;
 import net.sf.ehcache.CacheException;
@@ -118,56 +117,56 @@ public class InstrumentedEhcache extends EhcacheDecoratorAdapter {
     public static Ehcache instrument(MetricRegistry registry, final Ehcache cache) {
 
         final String prefix = name(cache.getClass(), cache.getName());
-        registry.register(name(prefix, "hits"),
-                (Gauge<Long>) () -> cache.getStatistics().cacheHitCount());
+        registry.registerGauge(name(prefix, "hits"),
+                () -> cache.getStatistics().cacheHitCount());
 
-        registry.register(name(prefix, "in-memory-hits"),
-                (Gauge<Long>) () -> cache.getStatistics().localHeapHitCount());
+        registry.registerGauge(name(prefix, "in-memory-hits"),
+                () -> cache.getStatistics().localHeapHitCount());
 
-        registry.register(name(prefix, "off-heap-hits"),
-                (Gauge<Long>) () -> cache.getStatistics().localOffHeapHitCount());
+        registry.registerGauge(name(prefix, "off-heap-hits"),
+                () -> cache.getStatistics().localOffHeapHitCount());
 
-        registry.register(name(prefix, "on-disk-hits"),
-                (Gauge<Long>) () -> cache.getStatistics().localDiskHitCount());
+        registry.registerGauge(name(prefix, "on-disk-hits"),
+                () -> cache.getStatistics().localDiskHitCount());
 
-        registry.register(name(prefix, "misses"),
-                (Gauge<Long>) () -> cache.getStatistics().cacheMissCount());
+        registry.registerGauge(name(prefix, "misses"),
+                () -> cache.getStatistics().cacheMissCount());
 
-        registry.register(name(prefix, "in-memory-misses"),
-                (Gauge<Long>) () -> cache.getStatistics().localHeapMissCount());
+        registry.registerGauge(name(prefix, "in-memory-misses"),
+                () -> cache.getStatistics().localHeapMissCount());
 
-        registry.register(name(prefix, "off-heap-misses"),
-                (Gauge<Long>) () -> cache.getStatistics().localOffHeapMissCount());
+        registry.registerGauge(name(prefix, "off-heap-misses"),
+                () -> cache.getStatistics().localOffHeapMissCount());
 
-        registry.register(name(prefix, "on-disk-misses"),
-                (Gauge<Long>) () -> cache.getStatistics().localDiskMissCount());
+        registry.registerGauge(name(prefix, "on-disk-misses"),
+                () -> cache.getStatistics().localDiskMissCount());
 
-        registry.register(name(prefix, "objects"),
-                (Gauge<Long>) () -> cache.getStatistics().getSize());
+        registry.registerGauge(name(prefix, "objects"),
+                () -> cache.getStatistics().getSize());
 
-        registry.register(name(prefix, "in-memory-objects"),
-                (Gauge<Long>) () -> cache.getStatistics().getLocalHeapSize());
+        registry.registerGauge(name(prefix, "in-memory-objects"),
+                () -> cache.getStatistics().getLocalHeapSize());
 
-        registry.register(name(prefix, "off-heap-objects"),
-                (Gauge<Long>) () -> cache.getStatistics().getLocalOffHeapSize());
+        registry.registerGauge(name(prefix, "off-heap-objects"),
+                () -> cache.getStatistics().getLocalOffHeapSize());
 
-        registry.register(name(prefix, "on-disk-objects"),
-                (Gauge<Long>) () -> cache.getStatistics().getLocalDiskSize());
+        registry.registerGauge(name(prefix, "on-disk-objects"),
+                () -> cache.getStatistics().getLocalDiskSize());
 
-        registry.register(name(prefix, "mean-get-time"),
-                (Gauge<Double>) () -> cache.getStatistics().cacheGetOperation().latency().average().value());
+        registry.registerGauge(name(prefix, "mean-get-time"),
+                () -> cache.getStatistics().cacheGetOperation().latency().average().value());
 
-        registry.register(name(prefix, "mean-search-time"),
-                (Gauge<Double>) () -> cache.getStatistics().cacheSearchOperation().latency().average().value());
+        registry.registerGauge(name(prefix, "mean-search-time"),
+                () -> cache.getStatistics().cacheSearchOperation().latency().average().value());
 
-        registry.register(name(prefix, "eviction-count"),
-                (Gauge<Long>) () -> cache.getStatistics().cacheEvictionOperation().count().value());
+        registry.registerGauge(name(prefix, "eviction-count"),
+                () -> cache.getStatistics().cacheEvictionOperation().count().value());
 
-        registry.register(name(prefix, "searches-per-second"),
-                (Gauge<Double>) () -> cache.getStatistics().cacheSearchOperation().rate().value());
+        registry.registerGauge(name(prefix, "searches-per-second"),
+                () -> cache.getStatistics().cacheSearchOperation().rate().value());
 
-        registry.register(name(prefix, "writer-queue-size"),
-                (Gauge<Long>) () -> cache.getStatistics().getWriterQueueLength());
+        registry.registerGauge(name(prefix, "writer-queue-size"),
+                () -> cache.getStatistics().getWriterQueueLength());
 
         return new InstrumentedEhcache(registry, cache);
     }

metrics-ehcache/src/test/java/com/codahale/metrics/ehcache/InstrumentedEhcacheTest.java

@@ -12,6 +12,7 @@
 
 import static com.codahale.metrics.MetricRegistry.name;
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
 
 public class InstrumentedEhcacheTest {
     private static final CacheManager MANAGER = CacheManager.create();
@@ -24,6 +25,27 @@ public void setUp() {
         final Cache c = new Cache(new CacheConfiguration("test", 100));
         MANAGER.addCache(c);
         this.cache = InstrumentedEhcache.instrument(registry, c);
+        assertThat(registry.getGauges().entrySet().stream()
+                .map(e -> entry(e.getKey(), e.getValue().getValue())))
+                .containsOnly(
+                        entry("net.sf.ehcache.Cache.test.eviction-count", 0L),
+                        entry("net.sf.ehcache.Cache.test.hits", 0L),
+                        entry("net.sf.ehcache.Cache.test.in-memory-hits", 0L),
+                        entry("net.sf.ehcache.Cache.test.in-memory-misses", 0L),
+                        entry("net.sf.ehcache.Cache.test.in-memory-objects", 0L),
+                        entry("net.sf.ehcache.Cache.test.mean-get-time", Double.NaN),
+                        entry("net.sf.ehcache.Cache.test.mean-search-time", Double.NaN),
+                        entry("net.sf.ehcache.Cache.test.misses", 0L),
+                        entry("net.sf.ehcache.Cache.test.objects", 0L),
+                        entry("net.sf.ehcache.Cache.test.off-heap-hits", 0L),
+                        entry("net.sf.ehcache.Cache.test.off-heap-misses", 0L),
+                        entry("net.sf.ehcache.Cache.test.off-heap-objects", 0L),
+                        entry("net.sf.ehcache.Cache.test.on-disk-hits", 0L),
+                        entry("net.sf.ehcache.Cache.test.on-disk-misses", 0L),
+                        entry("net.sf.ehcache.Cache.test.on-disk-objects", 0L),
+                        entry("net.sf.ehcache.Cache.test.searches-per-second", 0.0),
+                        entry("net.sf.ehcache.Cache.test.writer-queue-size", 0L)
+                );
     }
 
     @Test

metrics-httpasyncclient/src/main/java/com/codahale/metrics/httpasyncclient/InstrumentedNClientConnManager.java

@@ -1,6 +1,5 @@
 package com.codahale.metrics.httpasyncclient;
 
-import com.codahale.metrics.Gauge;
 import com.codahale.metrics.MetricRegistry;
 import org.apache.http.config.Registry;
 import org.apache.http.conn.DnsResolver;
@@ -20,26 +19,18 @@ public class InstrumentedNClientConnManager extends PoolingNHttpClientConnection
 
     public InstrumentedNClientConnManager(final ConnectingIOReactor ioreactor, final NHttpConnectionFactory<ManagedNHttpClientConnection> connFactory, final SchemePortResolver schemePortResolver, final MetricRegistry metricRegistry, final Registry<SchemeIOSessionStrategy> iosessionFactoryRegistry, final long timeToLive, final TimeUnit tunit, final DnsResolver dnsResolver, final String name) {
         super(ioreactor, connFactory, iosessionFactoryRegistry, schemePortResolver, dnsResolver, timeToLive, tunit);
-        metricRegistry.register(name(NHttpClientConnectionManager.class, name, "available-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getAvailable();
-            });
-        metricRegistry.register(name(NHttpClientConnectionManager.class, name, "leased-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getLeased();
-            });
-        metricRegistry.register(name(NHttpClientConnectionManager.class, name, "max-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getMax();
-            });
-        metricRegistry.register(name(NHttpClientConnectionManager.class, name, "pending-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getPending();
-            });
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricRegistry.registerGauge(name(NHttpClientConnectionManager.class, name, "available-connections"),
+                () -> getTotalStats().getAvailable());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricRegistry.registerGauge(name(NHttpClientConnectionManager.class, name, "leased-connections"),
+                () -> getTotalStats().getLeased());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricRegistry.registerGauge(name(NHttpClientConnectionManager.class, name, "max-connections"),
+                () -> getTotalStats().getMax());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricRegistry.registerGauge(name(NHttpClientConnectionManager.class, name, "pending-connections"),
+                () -> getTotalStats().getPending());
     }
 
 }

metrics-httpclient/src/main/java/com/codahale/metrics/httpclient/InstrumentedHttpClientConnectionManager.java

@@ -1,6 +1,5 @@
 package com.codahale.metrics.httpclient;
 
-import com.codahale.metrics.Gauge;
 import com.codahale.metrics.MetricRegistry;
 import org.apache.http.config.Registry;
 import org.apache.http.config.RegistryBuilder;
@@ -104,26 +103,18 @@ public InstrumentedHttpClientConnectionManager(MetricRegistry metricsRegistry,
         this.metricsRegistry = metricsRegistry;
         this.name = name;
 
-        metricsRegistry.register(name(HttpClientConnectionManager.class, name, "available-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getAvailable();
-            });
-        metricsRegistry.register(name(HttpClientConnectionManager.class, name, "leased-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getLeased();
-            });
-        metricsRegistry.register(name(HttpClientConnectionManager.class, name, "max-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getMax();
-            });
-        metricsRegistry.register(name(HttpClientConnectionManager.class, name, "pending-connections"),
-            (Gauge<Integer>) () -> {
-                // this acquires a lock on the connection pool; remove if contention sucks
-                return getTotalStats().getPending();
-            });
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricsRegistry.registerGauge(name(HttpClientConnectionManager.class, name, "available-connections"),
+                () -> getTotalStats().getAvailable());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricsRegistry.registerGauge(name(HttpClientConnectionManager.class, name, "leased-connections"),
+                () -> getTotalStats().getLeased());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricsRegistry.registerGauge(name(HttpClientConnectionManager.class, name, "max-connections"),
+                () -> getTotalStats().getMax());
+        // this acquires a lock on the connection pool; remove if contention sucks
+        metricsRegistry.registerGauge(name(HttpClientConnectionManager.class, name, "pending-connections"),
+                () -> getTotalStats().getPending());
     }
 
     @Override

metrics-httpclient/src/test/java/com/codahale/metrics/httpclient/InstrumentedHttpClientConnectionManagerTest.java

@@ -7,6 +7,8 @@
 import org.mockito.Mockito;
 
 import static junit.framework.TestCase.assertTrue;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
 import static org.mockito.ArgumentMatchers.any;
 
 
@@ -16,7 +18,12 @@ public class InstrumentedHttpClientConnectionManagerTest {
     @Test
     public void shouldRemoveGauges() {
         final InstrumentedHttpClientConnectionManager instrumentedHttpClientConnectionManager = InstrumentedHttpClientConnectionManager.builder(metricRegistry).build();
-        Assert.assertEquals(4, metricRegistry.getGauges().size());
+        assertThat(metricRegistry.getGauges().entrySet().stream()
+                .map(e -> entry(e.getKey(), e.getValue().getValue())))
+                .containsOnly(entry("org.apache.http.conn.HttpClientConnectionManager.available-connections", 0),
+                        entry("org.apache.http.conn.HttpClientConnectionManager.leased-connections", 0),
+                        entry("org.apache.http.conn.HttpClientConnectionManager.max-connections", 20),
+                        entry("org.apache.http.conn.HttpClientConnectionManager.pending-connections", 0));
 
         instrumentedHttpClientConnectionManager.close();
         Assert.assertEquals(0, metricRegistry.getGauges().size());
@@ -36,7 +43,7 @@ public void configurableViaBuilder() {
                 .close();
 
         ArgumentCaptor<String> argumentCaptor = ArgumentCaptor.forClass(String.class);
-        Mockito.verify(registry, Mockito.atLeast(1)).register(argumentCaptor.capture(), any());
+        Mockito.verify(registry, Mockito.atLeast(1)).registerGauge(argumentCaptor.capture(), any());
         assertTrue(argumentCaptor.getValue().contains("some-other-name"));
     }
 }