GC JVM runtime metrics proposal

instrumentation/runtime-metrics/library/src/main/java/io/opentelemetry/instrumentation/runtimemetrics/Gc.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.runtimemetrics;
+
+import com.sun.management.GarbageCollectionNotificationInfo;
+import io.opentelemetry.api.OpenTelemetry;
+import io.opentelemetry.api.common.AttributeKey;
+import io.opentelemetry.api.common.Attributes;
+import io.opentelemetry.api.metrics.LongHistogram;
+import io.opentelemetry.api.metrics.Meter;
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
+import java.util.List;
+import javax.management.Notification;
+import javax.management.NotificationEmitter;
+import javax.management.NotificationFilter;
+import javax.management.NotificationListener;
+import javax.management.openmbean.CompositeData;
+
+public final class Gc {
+
+  // Visible for testing
+  static final Gc INSTANCE = new Gc();
+
+  private static final AttributeKey<String> GC_KEY = AttributeKey.stringKey("gc");
+  private static final AttributeKey<String> CAUSE_KEY = AttributeKey.stringKey("cause");
+  private static final AttributeKey<String> ACTION_KEY = AttributeKey.stringKey("action");
+
+  private static final NotificationFilter GC_FILTER =
+      notification ->
+          notification
+              .getType()
+              .equals(GarbageCollectionNotificationInfo.GARBAGE_COLLECTION_NOTIFICATION);
+
+  public static void registerObservers(OpenTelemetry openTelemetry) {
+    INSTANCE.registerObservers(openTelemetry, ManagementFactory.getGarbageCollectorMXBeans());
+  }
+
+  // Visible for testing
+  void registerObservers(OpenTelemetry openTelemetry, List<GarbageCollectorMXBean> gcBeans) {
+    Meter meter = openTelemetry.getMeter("io.opentelemetry.runtime-metrics");
+
+    LongHistogram gcTime =
+        meter
+            .histogramBuilder("process.runtime.jvm.gc.time")
+            .setDescription("Time spent performing JVM garbage collection actions")
+            .setUnit("ms")
+            .ofLongs()
+            .build();
+
+    for (GarbageCollectorMXBean gcBean : ManagementFactory.getGarbageCollectorMXBeans()) {
+      if (!(gcBean instanceof NotificationEmitter)) {
+        continue;
+      }
+      NotificationEmitter notificationEmitter = (NotificationEmitter) gcBean;
+      notificationEmitter.addNotificationListener(
+          new GcNotificationListener(gcTime), GC_FILTER, null);
+    }
+  }
+
+  private static final class GcNotificationListener implements NotificationListener {
+
+    private final LongHistogram gcTime;
+
+    private GcNotificationListener(LongHistogram gcTime) {
+      this.gcTime = gcTime;
+    }
+
+    @Override
+    public void handleNotification(Notification notification, Object handback) {
+      GarbageCollectionNotificationInfo notificationInfo =
+          GarbageCollectionNotificationInfo.from((CompositeData) notification.getUserData());
+      gcTime.record(
+          notificationInfo.getGcInfo().getDuration(),
+          Attributes.of(
+              GC_KEY,
+              notificationInfo.getGcName(),
+              CAUSE_KEY,
+              notificationInfo.getGcCause(),
+              ACTION_KEY,
+              notificationInfo.getGcAction()));
+    }
+  }
+
+  private Gc() {}
+}