Fix SimpleAsyncTaskExecutor virtual thread path

This commit makes sure that the SimpleAsyncTaskExecutor only creates a
virtual thread when the virtualThreadDelegate is set, and not an
additional kernel thread as well.

See gh-30241

Author: poutsma

spring-core/src/main/java/org/springframework/core/task/SimpleAsyncTaskExecutor.java

@@ -260,9 +260,10 @@ protected void doExecute(Runnable task) {
 		if (this.virtualThreadDelegate != null) {
 			this.virtualThreadDelegate.startVirtualThread(nextThreadName(), task);
 		}
-
-		Thread thread = (this.threadFactory != null ? this.threadFactory.newThread(task) : createThread(task));
-		thread.start();
+		else {
+			Thread thread = (this.threadFactory != null ? this.threadFactory.newThread(task) : createThread(task));
+			thread.start();
+		}
 	}
 
 

spring-core/src/test/java21/org/springframework/core/task/VirtualThreadTaskExecutorTests.java

@@ -16,6 +16,8 @@
 
 package org.springframework.core.task;
 
+import java.util.concurrent.atomic.AtomicInteger;
+
 import org.junit.jupiter.api.Test;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -34,6 +36,7 @@ void virtualThreadsWithoutName() {
 		executeAndWait(executor, task, monitor);
 		assertThat(task.getThreadName()).isEmpty();
 		assertThat(task.isVirtual()).isTrue();
+		assertThat(task.runtCount()).isOne();
 	}
 
 	@Test
@@ -44,6 +47,7 @@ void virtualThreadsWithNamePrefix() {
 		executeAndWait(executor, task, monitor);
 		assertThat(task.getThreadName()).isEqualTo("test-0");
 		assertThat(task.isVirtual()).isTrue();
+		assertThat(task.runtCount()).isOne();
 	}
 
 	@Test
@@ -54,6 +58,7 @@ void simpleWithVirtualThreadFactory() {
 		executeAndWait(executor, task, monitor);
 		assertThat(task.getThreadName()).isEqualTo("test");
 		assertThat(task.isVirtual()).isTrue();
+		assertThat(task.runtCount()).isOne();
 	}
 
 	@Test
@@ -66,6 +71,7 @@ void simpleWithVirtualThreadFlag() {
 		executeAndWait(executor, task, monitor);
 		assertThat(task.getThreadName()).startsWith(customPrefix);
 		assertThat(task.isVirtual()).isTrue();
+		assertThat(task.runtCount()).isOne();
 	}
 
 	private void executeAndWait(TaskExecutor executor, Runnable task, Object monitor) {
@@ -115,6 +121,8 @@ public final void run() {
 
 	private static final class ThreadNameHarvester extends AbstractNotifyingRunnable {
 
+		private final AtomicInteger runCount = new AtomicInteger();
+
 		private String threadName;
 
 		private boolean virtual;
@@ -131,11 +139,16 @@ public boolean isVirtual() {
 			return this.virtual;
 		}
 
+		public int runtCount() {
+			return this.runCount.get();
+		}
+
 		@Override
 		protected void doRun() {
 			Thread thread = Thread.currentThread();
 			this.threadName = thread.getName();
 			this.virtual = thread.isVirtual();
+			runCount.incrementAndGet();
 		}
 	}