Skip removing stale entries when runnin on virtual thread (#18113)

Author: laurit

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/internal/cache/weaklockfree/AbstractWeakConcurrentMap.java

@@ -236,6 +236,13 @@ protected V defaultValue(K key) {
 
   /** Cleans all unused references. */
   public static void expungeStaleEntries() {
+    // Skip expunging stale entries if we are running on a virtual thread.
+    // See https://github.com/open-telemetry/opentelemetry-java-instrumentation/issues/17847
+    // Stale entries are also expunged from the background thread, see the runCleanup method below.
+    if (ThreadUtil.isVirtualThread(Thread.currentThread())) {
+      return;
+    }
+
     Reference<?> reference;
     while ((reference = REFERENCE_QUEUE.poll()) != null) {
       removeWeakKey((WeakKey<?>) reference);

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/internal/cache/weaklockfree/ThreadUtil.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.api.internal.cache.weaklockfree;
+
+import javax.annotation.Nullable;
+
+class ThreadUtil {
+
+  @Nullable private static final Class<?> virtualThreadClass = findVirtualThreadClass();
+
+  @Nullable
+  private static Class<?> findVirtualThreadClass() {
+    try {
+      return Class.forName("java.lang.BaseVirtualThread");
+    } catch (ClassNotFoundException e) {
+      return null;
+    }
+  }
+
+  static boolean isVirtualThread(Thread thread) {
+    return virtualThreadClass != null && virtualThreadClass.isInstance(thread);
+  }
+
+  private ThreadUtil() {}
+}

instrumentation-api/src/test/java/io/opentelemetry/instrumentation/api/internal/cache/weaklockfree/ThreadUtilTest.java

@@ -0,0 +1,28 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.api.internal.cache.weaklockfree;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+class ThreadUtilTest {
+
+  @Test
+  @EnabledForJreRange(min = JRE.JAVA_21)
+  void isVirtualThread() throws Exception {
+    assertThat(ThreadUtil.isVirtualThread(new Thread())).isFalse();
+    Object builder = Thread.class.getMethod("ofVirtual").invoke(null);
+    Thread thread =
+        (Thread)
+            Class.forName("java.lang.Thread$Builder$OfVirtual")
+                .getMethod("unstarted", Runnable.class)
+                .invoke(builder, (Runnable) () -> {});
+    assertThat(ThreadUtil.isVirtualThread(thread)).isTrue();
+  }
+}