Fix Jetty 12 HTTP server metrics collection without virtual threads

instrumentation/jetty/jetty-12.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v12_0/Jetty12Helper.java

@@ -9,6 +9,7 @@
 import io.opentelemetry.instrumentation.api.instrumenter.Instrumenter;
 import io.opentelemetry.javaagent.bootstrap.servlet.AppServerBridge;
 import io.opentelemetry.javaagent.bootstrap.servlet.ServletAsyncContext;
+import java.util.concurrent.atomic.AtomicBoolean;
 import javax.annotation.Nullable;
 import org.eclipse.jetty.server.HttpStream;
 import org.eclipse.jetty.server.Request;
@@ -27,21 +28,33 @@ public boolean shouldStart(Context parentContext, Request request) {
 
   public Context start(Context parentContext, Request request, Response response) {
     Context context = instrumenter.start(parentContext, request);
-    request.addFailureListener(throwable -> end(context, request, response, throwable));
+    // Use AtomicBoolean to ensure the span ends exactly once
+    AtomicBoolean spanEnded = new AtomicBoolean(false);
+
+    request.addFailureListener(
+        throwable -> {
+          if (spanEnded.compareAndSet(false, true)) {
+            end(context, request, response, throwable);
+          }
+        });
     // detect request completion
     // https://github.com/jetty/jetty.project/blob/52d94174e2c7a6e794c6377dcf9cd3ed0b9e1806/jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/handler/EventsHandler.java#L75
     request.addHttpStreamWrapper(
         stream ->
             new HttpStream.Wrapper(stream) {
               @Override
               public void succeeded() {
-                end(context, request, response, null);
+                if (spanEnded.compareAndSet(false, true)) {
+                  end(context, request, response, null);
+                }
                 super.succeeded();
               }
 
               @Override
               public void failed(Throwable throwable) {
-                end(context, request, response, throwable);
+                if (spanEnded.compareAndSet(false, true)) {
+                  end(context, request, response, throwable);
+                }
                 super.failed(throwable);
               }
             });

instrumentation/jetty/jetty-12.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/jetty/v12_0/Jetty12ServerInstrumentation.java

@@ -67,6 +67,10 @@ public static AdviceScope start(Object source, Request request, Response respons
 
       public void end(Request request, Response response, @Nullable Throwable throwable) {
         scope.close();
+        // Don't end the span here - it will be ended by the HttpStream callbacks
+        // registered in Jetty12Helper.start(). This ensures metrics are captured
+        // correctly regardless of whether virtual threads are enabled.
+        // Only end immediately if there's an exception, as the callbacks may not fire.
         if (throwable != null) {
           helper().end(context, request, response, throwable);
         }