Prevent name conflicts and rename jvm_classes_loaded (#681)

Signed-off-by: Fabian Stäber <[email protected]>

Author: fstab

simpleclient/src/main/java/io/prometheus/client/CollectorRegistry.java

@@ -48,10 +48,13 @@ public CollectorRegistry(boolean autoDescribe) {
    */
   public void register(Collector m) {
     List<String> names = collectorNames(m);
+    assertNoDuplicateNames(m, names);
     synchronized (namesCollectorsLock) {
       for (String name : names) {
         if (namesToCollectors.containsKey(name)) {
-          throw new IllegalArgumentException("Collector already registered that provides name: " + name);
+          throw new IllegalArgumentException("Failed to register Collector of type " + m.getClass().getSimpleName()
+                  + ": " + name + " is already in use by another Collector of type "
+                  + namesToCollectors.get(name).getClass().getSimpleName());
         }
       }
       for (String name : names) {
@@ -61,6 +64,16 @@ public void register(Collector m) {
     }
   }
 
+  private void assertNoDuplicateNames(Collector m, List<String> names) {
+    Set<String> uniqueNames = new HashSet<String>();
+    for (String name : names) {
+      if (!uniqueNames.add(name)) {
+        throw new IllegalArgumentException("Failed to register Collector of type " + m.getClass().getSimpleName()
+                + ": The Collector exposes the same name multiple times: " + name);
+      }
+    }
+  }
+
   /**
    * Unregister a Collector.
    */

simpleclient_hotspot/src/main/java/io/prometheus/client/hotspot/ClassLoadingExports.java

@@ -20,7 +20,7 @@
  * </pre>
  * Example metrics being exported:
  * <pre>
- *   jvm_classes_loaded{} 1000
+ *   jvm_classes_currently_loaded{} 1000
  *   jvm_classes_loaded_total{} 2000
  *   jvm_classes_unloaded_total{} 500
  * </pre>
@@ -38,7 +38,7 @@ public ClassLoadingExports(ClassLoadingMXBean clBean) {
 
   void addClassLoadingMetrics(List<MetricFamilySamples> sampleFamilies) {
     sampleFamilies.add(new GaugeMetricFamily(
-          "jvm_classes_loaded",
+          "jvm_classes_currently_loaded",
           "The number of classes that are currently loaded in the JVM",
           clBean.getLoadedClassCount()));
     sampleFamilies.add(new CounterMetricFamily(

simpleclient_hotspot/src/test/java/io/prometheus/client/hotspot/ClassLoadingExportsTest.java

@@ -13,7 +13,7 @@
 public class ClassLoadingExportsTest {
 
   private ClassLoadingMXBean mockClassLoadingsBean = Mockito.mock(ClassLoadingMXBean.class);
-  private CollectorRegistry registry = new CollectorRegistry();
+  private CollectorRegistry registry = new CollectorRegistry(true);
   private ClassLoadingExports collectorUnderTest;
 
   private static final String[] EMPTY_LABEL = new String[0];
@@ -31,7 +31,7 @@ public void testClassLoading() {
     assertEquals(
             1000,
             registry.getSampleValue(
-                    "jvm_classes_loaded", EMPTY_LABEL, EMPTY_LABEL),
+                    "jvm_classes_currently_loaded", EMPTY_LABEL, EMPTY_LABEL),
             .0000001);
     assertEquals(
             2000L,