Report GC metrics.

service/src/main/java/org/whispersystems/textsecuregcm/metrics/AbstractGarbageCollectionGauge.java

@@ -0,0 +1,19 @@
+package org.whispersystems.textsecuregcm.metrics;
+
+import com.codahale.metrics.Gauge;
+
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
+
+abstract class AbstractGarbageCollectionGauge implements Gauge<Long> {
+
+    private final GarbageCollectorMXBean garbageCollectorMXBean;
+
+    public AbstractGarbageCollectionGauge() {
+        this.garbageCollectorMXBean = (GarbageCollectorMXBean)ManagementFactory.getGarbageCollectorMXBeans();
+    }
+
+    protected GarbageCollectorMXBean getGarbageCollectorMXBean() {
+        return garbageCollectorMXBean;
+    }
+}

service/src/main/java/org/whispersystems/textsecuregcm/metrics/GarbageCollectionCountGauge.java

@@ -0,0 +1,12 @@
+package org.whispersystems.textsecuregcm.metrics;
+
+/**
+ * A gauge that reports the total number of collections that have occurred in this JVM's lifetime.
+ */
+public class GarbageCollectionCountGauge extends AbstractGarbageCollectionGauge {
+
+    @Override
+    public Long getValue() {
+        return getGarbageCollectorMXBean().getCollectionCount();
+    }
+}

service/src/main/java/org/whispersystems/textsecuregcm/metrics/GarbageCollectionTimeGauge.java

@@ -0,0 +1,12 @@
+package org.whispersystems.textsecuregcm.metrics;
+
+/**
+ * A gauge that reports the cumulative amount of time (in milliseconds) spent on garbage collection.
+ */
+public class GarbageCollectionTimeGauge extends AbstractGarbageCollectionGauge {
+
+    @Override
+    public Long getValue() {
+        return getGarbageCollectorMXBean().getCollectionTime();
+    }
+}