1 files changed, 94 insertions, 0 deletions
diff --git a/container-disc/src/main/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetrics.java b/container-disc/src/main/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetrics.java
new file mode 100644
index 00000000000..04fd8572ad4
--- /dev/null
+++ b/container-disc/src/main/java/com/yahoo/container/jdisc/metric/GarbageCollectionMetrics.java
@@ -0,0 +1,94 @@
+package com.yahoo.container.jdisc.metric;
+
+import com.yahoo.jdisc.Metric;
+
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
+import java.time.Clock;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.Map;
+
+/**
+ * @author ollivir
+ */
+public class GarbageCollectionMetrics {
+    private static final String GC_COUNT = "jdisc.gc.count";
+    private static final String GC_TIME = "jdisc.gc.ms";
+    private static final String DIMENSION_KEY = "gcName";
+
+    public static final Duration REPORTING_INTERVAL = Duration.ofSeconds(62);
+
+    static class GcStats {
+        private final Instant when;
+        private final long count;
+        private final Duration totalRuntime;
+
+        private GcStats(Instant when, long count, Duration totalRuntime) {
+            this.when = when;
+            this.count = count;
+            this.totalRuntime = totalRuntime;
+        }
+    }
+
+    private Map<String, LinkedList<GcStats>> gcStatistics;
+
+    private final Clock clock;
+
+    public GarbageCollectionMetrics(Clock clock) {
+        this.clock = clock;
+        this.gcStatistics = new HashMap<>();
+        collectGcStatistics(clock.instant());
+    }
+
+    private void collectGcStatistics(Instant now) {
+        for (GarbageCollectorMXBean gcBean : ManagementFactory.getGarbageCollectorMXBeans()) {
+            String gcName = gcBean.getName().replace(" ", "");
+            GcStats stats = new GcStats(now, gcBean.getCollectionCount(), Duration.ofMillis(gcBean.getCollectionTime()));
+
+            LinkedList<GcStats> window = gcStatistics.computeIfAbsent(gcName, anyName -> new LinkedList<>());
+            window.addLast(stats);
+        }
+    }
+
+    private void cleanStatistics(Instant now) {
+        Instant oldestToKeep = now.minus(REPORTING_INTERVAL);
+
+        for(Iterator<Map.Entry<String, LinkedList<GcStats>>> it = gcStatistics.entrySet().iterator(); it.hasNext(); ) {
+            Map.Entry<String, LinkedList<GcStats>> entry = it.next();
+            LinkedList<GcStats> history = entry.getValue();
+            while(history.isEmpty() == false && oldestToKeep.isAfter(history.getFirst().when)) {
+                history.removeFirst();
+            }
+            if(history.isEmpty()) {
+                it.remove();
+            }
+        }
+    }
+
+    public void emitMetrics(Metric metric) {
+        Instant now = clock.instant();
+
+        collectGcStatistics(now);
+        cleanStatistics(now);
+
+        for (Map.Entry<String, LinkedList<GcStats>> item : gcStatistics.entrySet()) {
+            GcStats reference = item.getValue().getFirst();
+            GcStats latest = item.getValue().getLast();
+            Map<String, String> contextData = new HashMap<>();
+            contextData.put(DIMENSION_KEY, item.getKey());
+            Metric.Context gcContext = metric.createContext(contextData);
+
+            metric.set(GC_COUNT, latest.count - reference.count, gcContext);
+            metric.set(GC_TIME, latest.totalRuntime.minus(reference.totalRuntime).toMillis(), gcContext);
+        }
+    }
+
+    // partial exposure for testing
+    Map<String, LinkedList<GcStats>> getGcStatistics() {
+        return gcStatistics;
+    }
+}