[GR-60176] JFR Old Object Sampler fixes.

PullRequest: graal/19488

Author: christianhaeubl

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jfr/oldobject/JfrOldObjectSampler.java

@@ -120,9 +120,12 @@ private void remove(JfrOldObject sample) {
             next.increaseSpan(sample.getSpan());
             queue.add(next);
         } else {
-            /* No remaining elements, we can't redistribute the weight. */
+            /*
+             * No younger element, we can't redistribute the weight. The next sample should absorb
+             * the extra span.
+             */
             totalInQueue = totalInQueue.subtract(sample.getSpan());
-            assert totalInQueue.equal(0);
+            assert totalInQueue.aboveOrEqual(0);
         }
         queue.remove(sample);
         release(sample);

substratevm/src/com.oracle.svm.test/src/com/oracle/svm/test/jfr/oldobject/TestOldObjectProfiler.java

@@ -33,8 +33,10 @@
 import java.util.Collections;
 import java.util.List;
 
+import jdk.jfr.Recording;
 import org.graalvm.word.WordFactory;
 import org.junit.Assert;
+import org.junit.BeforeClass;
 import org.junit.Test;
 
 import com.oracle.svm.core.jfr.HasJfrSupport;
@@ -45,6 +47,16 @@
 import jdk.graal.compiler.api.directives.GraalDirectives;
 
 public class TestOldObjectProfiler extends AbstractJfrTest {
+
+    /*
+     * Old object samples will not have allocation ticks set correctly if JfrTicks is not first
+     * initialized. We need to create the first JFR recording to lazily initialize JfrTicks.
+     */
+    @BeforeClass
+    public static void initializeJfrTicks() {
+        GraalDirectives.blackhole(new Recording());
+    }
+
     @Test
     public void testScavenge() {
         int count = 10;