Alternative fix for flaky jfr telemetry test (#8203)

Reverts
#8183
Perhaps the problem is that the gc happens before reading jfr events is
started.

Author: laurit

instrumentation/runtime-telemetry-jfr/library/build.gradle.kts

@@ -32,7 +32,6 @@ tasks {
     }
     include("**/*PsGcMemoryMetricTest.*")
     jvmArgs("-XX:+UseParallelGC")
-    jvmArgs("-Xmx128m")
   }
 
   val testSerial by registering(Test::class) {

instrumentation/runtime-telemetry-jfr/library/src/main/java/io/opentelemetry/instrumentation/runtimetelemetryjfr/JfrTelemetry.java

@@ -9,6 +9,7 @@
 import io.opentelemetry.instrumentation.runtimetelemetryjfr.internal.RecordedEventHandler;
 import java.io.Closeable;
 import java.util.List;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.function.Predicate;
 import java.util.logging.Level;
@@ -25,6 +26,7 @@ public final class JfrTelemetry implements Closeable {
   private final OpenTelemetry openTelemetry;
   private final List<RecordedEventHandler> recordedEventHandlers;
   private final RecordingStream recordingStream;
+  private final CountDownLatch startUpLatch = new CountDownLatch(1);
 
   @SuppressWarnings("CatchingUnchecked")
   JfrTelemetry(OpenTelemetry openTelemetry, Predicate<JfrFeature> featurePredicate) {
@@ -39,6 +41,7 @@ public final class JfrTelemetry implements Closeable {
             handler.getThreshold().ifPresent(eventSettings::withThreshold);
             recordingStream.onEvent(handler.getEventName(), handler);
           });
+      recordingStream.onMetadata(event -> startUpLatch.countDown());
       Thread daemonRunner = new Thread(() -> recordingStream.start());
       daemonRunner.setDaemon(true);
       daemonRunner.start();
@@ -84,6 +87,11 @@ RecordingStream getRecordingStream() {
     return recordingStream;
   }
 
+  // Visible for testing
+  CountDownLatch getStartUpLatch() {
+    return startUpLatch;
+  }
+
   /** Stop recording JFR events. */
   @Override
   public void close() {

instrumentation/runtime-telemetry-jfr/library/src/test/java/io/opentelemetry/instrumentation/runtimetelemetryjfr/JfrExtension.java

@@ -14,6 +14,7 @@
 import io.opentelemetry.sdk.testing.assertj.MetricAssert;
 import io.opentelemetry.sdk.testing.exporter.InMemoryMetricReader;
 import java.util.Collection;
+import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 import org.junit.jupiter.api.Assumptions;
 import org.junit.jupiter.api.extension.AfterEachCallback;
@@ -33,7 +34,7 @@ public JfrExtension(Consumer<JfrTelemetryBuilder> builderConsumer) {
   }
 
   @Override
-  public void beforeEach(ExtensionContext context) {
+  public void beforeEach(ExtensionContext context) throws InterruptedException {
     try {
       Class.forName("jdk.jfr.consumer.RecordingStream");
     } catch (ClassNotFoundException exception) {
@@ -46,6 +47,7 @@ public void beforeEach(ExtensionContext context) {
     JfrTelemetryBuilder builder = JfrTelemetry.builder(sdk);
     builderConsumer.accept(builder);
     jfrTelemetry = builder.build();
+    jfrTelemetry.getStartUpLatch().await(30, TimeUnit.SECONDS);
   }
 
   @Override

instrumentation/runtime-telemetry-jfr/library/src/test/java/io/opentelemetry/instrumentation/runtimetelemetryjfr/PsGcMemoryMetricTest.java

@@ -76,23 +76,11 @@ private static void hasGcAttributes(MetricData data) {
         .anyMatch(p -> p.getAttributes().equals(ATTR_PS_OLD_GEN));
   }
 
-  private static void causeGc() {
-    String s = "1234567890";
-    try {
-      while (true) {
-        s = s + s;
-      }
-    } catch (OutOfMemoryError outOfMemoryError) {
-      // ignore
-    }
-  }
-
   @Test
   void shouldHaveGcDurationMetrics() {
     // TODO: Need a reliable way to test old and young gen GC in isolation.
     // Generate some JFR events
-    // using System.gc() here doesn't reliably get us the GC events we need
-    causeGc();
+    System.gc();
 
     Attributes minorGcAttributes =
         Attributes.of(ATTR_GC, "PS Scavenge", ATTR_ACTION, END_OF_MINOR_GC);

instrumentation/runtime-telemetry-jfr/library/src/test/java/io/opentelemetry/instrumentation/runtimetelemetryjfr/SerialGcMemoryMetricTest.java

@@ -30,10 +30,9 @@ void shouldHaveMemoryMetrics() {
   }
 
   @Test
-  void shouldHaveGcDurationMetrics() throws InterruptedException {
+  void shouldHaveGcDurationMetrics() {
     // TODO: Need a reliable way to test old and young gen GC in isolation.
     // Generate some JFR events
-    Thread.sleep(100);
     System.gc();
     Attributes minorGcAttributes = Attributes.of(ATTR_GC, "Copy", ATTR_ACTION, END_OF_MINOR_GC);
     Attributes majorGcAttributes =