From 81be494e9b0dffe762d70c1f3de67dadb468d698 Mon Sep 17 00:00:00 2001
From: Danny Thomas <dannyt@netflix.com>
Date: Tue, 3 Sep 2024 00:21:22 +0000
Subject: [PATCH] Improve GC measures

---
 .../spectator/jvm/JavaFlightRecorder.java     | 20 +++++++++----------
 .../spectator/jvm/JavaFlightRecorderTest.java | 12 +++++++++++
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/spectator-ext-jvm/src/main/java17/com/netflix/spectator/jvm/JavaFlightRecorder.java b/spectator-ext-jvm/src/main/java17/com/netflix/spectator/jvm/JavaFlightRecorder.java
index 57f0d337a..cc92989c3 100644
--- a/spectator-ext-jvm/src/main/java17/com/netflix/spectator/jvm/JavaFlightRecorder.java
+++ b/spectator-ext-jvm/src/main/java17/com/netflix/spectator/jvm/JavaFlightRecorder.java
@@ -35,9 +35,9 @@ public class JavaFlightRecorder {
   private static final String JavaThreadStatistics = PREFIX + "JavaThreadStatistics";
   private static final String VirtualThreadPinned = PREFIX + "VirtualThreadPinned";
   private static final String VirtualThreadSubmitFailed = PREFIX + "VirtualThreadSubmitFailed";
+  private static final String YoungGarbageCollection = PREFIX + "YoungGarbageCollection";
   private static final String ZAllocationStall = PREFIX + "ZAllocationStall";
   private static final String ZYoungGarbageCollection = PREFIX + "ZYoungGarbageCollection";
-  private static final String ZOldGarbageCollection = PREFIX + "ZOldGarbageCollection";
 
   private JavaFlightRecorder() {
   }
@@ -62,7 +62,7 @@ public static AutoCloseable monitorDefaultEvents(Registry registry, Executor exe
     collectCompilerStatistics(registry, rs);
     collectThreadStatistics(registry, rs);
     collectVirtualThreadEvents(registry, rs);
-    collectZgcEvents(registry, rs);
+    collectGcEvents(registry, rs);
     executor.execute(rs::start);
     return rs::close;
   }
@@ -113,17 +113,15 @@ private static void collectVirtualThreadEvents(Registry registry, RecordingStrea
     );
   }
 
-  private static void collectZgcEvents(Registry registry, RecordingStream rs) {
-    consume(ZYoungGarbageCollection, rs, event ->
-      registry.timer("jvm.zgc.youngCollection", "tenuringThreshold", event.getString("tenuringThreshold"))
-        .record(event.getDuration()));
-
-    consume(ZOldGarbageCollection, rs, event ->
-      registry.timer("jvm.zgc.oldCollection")
-        .record(event.getDuration()));
+  private static void collectGcEvents(Registry registry, RecordingStream rs) {
+    Consumer<RecordedEvent> tenuringThreshold = event ->
+      registry.gauge("jvm.gc.tenuringThreshold")
+        .set(event.getLong("tenuringThreshold"));
+    consume(YoungGarbageCollection, rs, tenuringThreshold);
+    consume(ZYoungGarbageCollection, rs, tenuringThreshold);
 
     consume(ZAllocationStall, rs, event ->
-      registry.timer("jvm.zgc.allocationStall", "type", event.getString("type"))
+      registry.timer("jvm.gc.allocationStall", "type", event.getString("type"))
         .record(event.getDuration()));
   }
 
diff --git a/spectator-ext-jvm/src/test/java17/com/netflix/spectator/jvm/JavaFlightRecorderTest.java b/spectator-ext-jvm/src/test/java17/com/netflix/spectator/jvm/JavaFlightRecorderTest.java
index b03d83489..40fbf3974 100644
--- a/spectator-ext-jvm/src/test/java17/com/netflix/spectator/jvm/JavaFlightRecorderTest.java
+++ b/spectator-ext-jvm/src/test/java17/com/netflix/spectator/jvm/JavaFlightRecorderTest.java
@@ -31,6 +31,8 @@
 
 public class JavaFlightRecorderTest {
 
+  public static volatile Object obj;
+
   @Test
   public void isSupported() {
     assertTrue(JavaFlightRecorder.isSupported());
@@ -41,6 +43,12 @@ public void checkDefaultMeasures() throws Exception {
     Registry registry = new DefaultRegistry();
     ExecutorService executor = Executors.newSingleThreadExecutor();
     try (var closable = JavaFlightRecorder.monitorDefaultEvents(registry, executor)) {
+      // allocate rapidly to trigger a GC, black holing using the approach from
+      // https://github.com/openjdk/jdk/blob/master/test/hotspot/jtreg/gc/testlibrary/Allocation.java
+      for (int i = 0; i < 100; i++) {
+        obj = new byte[4 * 1024 * 1024];
+        obj = null;
+      }
       Thread.sleep(6000);
     }
     executor.shutdownNow();
@@ -48,6 +56,10 @@ public void checkDefaultMeasures() throws Exception {
     Map<Id, Measurement> measures = registry.measurements()
       .collect(Collectors.toMap(Measurement::id, m -> m));
 
+    Measurement tenuringThreshold = measures.get(Id.create("jvm.gc.tenuringThreshold"));
+    assertNotEquals(null, tenuringThreshold);
+    assertTrue(tenuringThreshold.value() > 0);
+
     Measurement classesLoaded = measures.get(Id.create("jvm.classloading.classesLoaded"));
     Measurement classesUnloaded = measures.get(Id.create("jvm.classloading.classesUnloaded"));
     assertNotEquals(null, classesLoaded);