jvm.gc.live.data.size and max not updating for optavgpause/optthruput collectors (#2874)

With the OpenJ9 non-generational collectors `optavgpause` and `optthruput`, a NPE was happening in the notification listener which caused some code in it to not be executed. Namely, setting the live and max data size was being effectively skipped for these collectors.

Now we check for `null` and only the allocated bytes counter is skipped when no allocation pool name is set.

Author: shakuzen

micrometer-core/src/main/java/io/micrometer/core/instrument/binder/jvm/JvmGcMetrics.java

@@ -195,7 +195,10 @@ private boolean isGenerationalGcConfigured() {
     }
 
     private void countPoolSizeDelta(Map<String, MemoryUsage> before, Map<String, MemoryUsage> after, Counter counter,
-            AtomicLong previousPoolSize, String poolName) {
+            AtomicLong previousPoolSize, @Nullable String poolName) {
+        if (poolName == null) {
+            return;
+        }
         final long beforeBytes = before.get(poolName).getUsed();
         final long afterBytes = after.get(poolName).getUsed();
         final long delta = beforeBytes - previousPoolSize.get();

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/jvm/JvmGcMetricsTest.java

@@ -34,7 +34,6 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.within;
 import static org.awaitility.Awaitility.await;
-import static org.junit.jupiter.api.Assumptions.assumeTrue;
 
 /**
  * Tests for {@link JvmGcMetrics}.
@@ -65,12 +64,18 @@ void noJvmImplementationSpecificApiSignatures() {
     }
 
     @Test
-    void metersAreBound() {
-        assertThat(registry.find("jvm.gc.live.data.size").gauge()).isNotNull();
-        assertThat(registry.find("jvm.gc.memory.allocated").counter()).isNotNull();
-        assertThat(registry.find("jvm.gc.max.data.size").gauge().value()).isGreaterThan(0);
+    void gcMetricsAvailableAfterGc() {
+        System.gc();
+        await().timeout(200, TimeUnit.MILLISECONDS).alias("NotificationListener takes time after GC")
+                .untilAsserted(() ->
+                        assertThat(registry.find("jvm.gc.live.data.size").gauge().value()).isPositive());
+        assertThat(registry.find("jvm.gc.memory.allocated").counter().count()).isPositive();
+        assertThat(registry.find("jvm.gc.max.data.size").gauge().value()).isPositive();
 
-        assumeTrue(binder.isGenerationalGc);
+        if (!binder.isGenerationalGc) {
+            return;
+        }
+        // cannot guarantee an object was promoted, so cannot check for positive count
         assertThat(registry.find("jvm.gc.memory.promoted").counter()).isNotNull();
     }