Allow auto-configured applicationTaskExecutor to use virtual threads

With this commit, when virtual threads are enabled, the auto-configured
applicationTaskExecutor changes from a ThreadPoolTaskExecutor to a
SimpleAsyncTaskExecutor with virtual threads enabled.

As before, any TaskDecorator bean is applied to the auto-configured
executor and the spring.task.execution.thread-name-prefix property is
applied. Other spring.task.execution.* properties are ignored as they
are specific to a pool-based executor.

Closes gh-35710

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/task/TaskExecutionAutoConfiguration.java

@@ -28,6 +28,7 @@ import org.springframework.boot.context.properties.EnableConfigurationProperties
 import org.springframework.boot.task.TaskExecutorBuilder;
 import org.springframework.boot.task.TaskExecutorCustomizer;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.Lazy;
 import org.springframework.core.task.TaskDecorator;
 import org.springframework.core.task.TaskExecutor;
@@ -44,6 +45,8 @@ import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
 @ConditionalOnClass(ThreadPoolTaskExecutor.class)
 @AutoConfiguration
 @EnableConfigurationProperties(TaskExecutionProperties.class)
+@Import({ TaskExecutorConfigurations.VirtualThreadTaskExecutorConfiguration.class,
+		TaskExecutorConfigurations.ThreadPoolTaskExecutorConfiguration.class })
 public class TaskExecutionAutoConfiguration {
 
 	/**

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/task/TaskExecutorConfigurations.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2012-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.autoconfigure.task;
+
+import java.util.concurrent.Executor;
+
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnVirtualThreads;
+import org.springframework.boot.task.TaskExecutorBuilder;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Lazy;
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
+import org.springframework.core.task.TaskDecorator;
+import org.springframework.core.task.TaskExecutor;
+import org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+
+/**
+ * {@link TaskExecutor} configurations to be imported by
+ * {@link TaskExecutionAutoConfiguration} in a specific order.
+ *
+ * @author Andy Wilkinson
+ */
+class TaskExecutorConfigurations {
+
+	@ConditionalOnVirtualThreads
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnMissingBean(Executor.class)
+	static class VirtualThreadTaskExecutorConfiguration {
+
+		@Bean(name = { TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME,
+				AsyncAnnotationBeanPostProcessor.DEFAULT_TASK_EXECUTOR_BEAN_NAME })
+		SimpleAsyncTaskExecutor applicationTaskExecutor(TaskExecutionProperties properties,
+				ObjectProvider<TaskDecorator> taskDecorator) {
+			SimpleAsyncTaskExecutor executor = new SimpleAsyncTaskExecutor(properties.getThreadNamePrefix());
+			executor.setVirtualThreads(true);
+			executor.setTaskDecorator(taskDecorator.getIfUnique());
+			return executor;
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	@ConditionalOnMissingBean(Executor.class)
+	static class ThreadPoolTaskExecutorConfiguration {
+
+		@Lazy
+		@Bean(name = { TaskExecutionAutoConfiguration.APPLICATION_TASK_EXECUTOR_BEAN_NAME,
+				AsyncAnnotationBeanPostProcessor.DEFAULT_TASK_EXECUTOR_BEAN_NAME })
+		ThreadPoolTaskExecutor applicationTaskExecutor(TaskExecutorBuilder builder) {
+			return builder.build();
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/task/TaskExecutionAutoConfigurationTests.java

@@ -17,11 +17,16 @@
 package org.springframework.boot.autoconfigure.task;
 
 import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
 import org.junit.jupiter.api.extension.ExtendWith;
 
 import org.springframework.beans.factory.config.BeanDefinition;
@@ -34,6 +39,7 @@ import org.springframework.boot.test.context.runner.ContextConsumer;
 import org.springframework.boot.test.system.OutputCaptureExtension;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
 import org.springframework.core.task.SyncTaskExecutor;
 import org.springframework.core.task.TaskDecorator;
 import org.springframework.core.task.TaskExecutor;
@@ -98,7 +104,7 @@ class TaskExecutionAutoConfigurationTests {
 	}
 
 	@Test
-	void taskExecutorAutoConfiguredIsLazy() {
+	void whenThreadPoolTaskExecutorIsAutoConfiguredThenItIsLazy() {
 		this.contextRunner.run((context) -> {
 			assertThat(context).hasSingleBean(Executor.class).hasBean("applicationTaskExecutor");
 			BeanDefinition beanDefinition = context.getSourceApplicationContext()
@@ -109,6 +115,51 @@ class TaskExecutionAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	@DisabledForJreRange(max = JRE.JAVA_20)
+	void whenVirtualThreadsAreEnabledThenSimpleAsyncTaskExecutorWithVirtualThreadsIsAutoConfigured() {
+		this.contextRunner.withPropertyValues("spring.threads.virtual.enabled=true").run((context) -> {
+			assertThat(context).hasSingleBean(Executor.class).hasBean("applicationTaskExecutor");
+			assertThat(context).getBean("applicationTaskExecutor").isInstanceOf(SimpleAsyncTaskExecutor.class);
+			SimpleAsyncTaskExecutor taskExecutor = context.getBean("applicationTaskExecutor",
+					SimpleAsyncTaskExecutor.class);
+			assertThat(virtualThreadName(taskExecutor)).startsWith("task-");
+		});
+	}
+
+	@Test
+	@DisabledForJreRange(max = JRE.JAVA_20)
+	void whenTaskNamePrefixIsConfiguredThenSimpleAsyncTaskExecutorWithVirtualThreadsUsesIt() {
+		this.contextRunner
+			.withPropertyValues("spring.threads.virtual.enabled=true",
+					"spring.task.execution.thread-name-prefix=custom-")
+			.run((context) -> {
+				SimpleAsyncTaskExecutor taskExecutor = context.getBean("applicationTaskExecutor",
+						SimpleAsyncTaskExecutor.class);
+				assertThat(virtualThreadName(taskExecutor)).startsWith("custom-");
+			});
+	}
+
+	@Test
+	@DisabledForJreRange(max = JRE.JAVA_20)
+	void whenVirtualThreadsAreAvailableButNotEnabledThenThreadPoolTaskExecutorIsAutoConfigured() {
+		this.contextRunner.run((context) -> {
+			assertThat(context).hasSingleBean(Executor.class).hasBean("applicationTaskExecutor");
+			assertThat(context).getBean("applicationTaskExecutor").isInstanceOf(ThreadPoolTaskExecutor.class);
+		});
+	}
+
+	@Test
+	@DisabledForJreRange(max = JRE.JAVA_20)
+	void whenTaskDecoratorIsDefinedThenSimpleAsyncTaskExecutorWithVirtualThreadsUsesIt() {
+		this.contextRunner.withPropertyValues("spring.threads.virtual.enabled=true")
+			.withUserConfiguration(TaskDecoratorConfig.class)
+			.run((context) -> {
+				SimpleAsyncTaskExecutor executor = context.getBean(SimpleAsyncTaskExecutor.class);
+				assertThat(executor).extracting("taskDecorator").isSameAs(context.getBean(TaskDecorator.class));
+			});
+	}
+
 	@Test
 	void taskExecutorWhenHasCustomTaskExecutorShouldBackOff() {
 		this.contextRunner.withUserConfiguration(CustomTaskExecutorConfig.class).run((context) -> {
@@ -117,6 +168,17 @@ class TaskExecutionAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	@DisabledForJreRange(max = JRE.JAVA_20)
+	void whenVirtualThreadsAreEnabledAndCustomTaskExecutorIsDefinedThenSimpleAsyncTaskExecutorThatUsesVirtualThreadsBacksOff() {
+		this.contextRunner.withUserConfiguration(CustomTaskExecutorConfig.class)
+			.withPropertyValues("spring.threads.virtual.enabled=true")
+			.run((context) -> {
+				assertThat(context).hasSingleBean(Executor.class);
+				assertThat(context.getBean(Executor.class)).isSameAs(context.getBean("customTaskExecutor"));
+			});
+	}
+
 	@Test
 	void taskExecutorBuilderShouldApplyCustomizer() {
 		this.contextRunner.withUserConfiguration(TaskExecutorCustomizerConfig.class).run((context) -> {
@@ -159,6 +221,20 @@ class TaskExecutionAutoConfigurationTests {
 		};
 	}
 
+	private String virtualThreadName(SimpleAsyncTaskExecutor taskExecutor) throws InterruptedException {
+		AtomicReference<Thread> threadReference = new AtomicReference<>();
+		CountDownLatch latch = new CountDownLatch(1);
+		taskExecutor.execute(() -> {
+			Thread currentThread = Thread.currentThread();
+			threadReference.set(currentThread);
+			latch.countDown();
+		});
+		latch.await(30, TimeUnit.SECONDS);
+		Thread thread = threadReference.get();
+		assertThat(thread).extracting("virtual").as("%s is virtual", thread).isEqualTo(true);
+		return thread.getName();
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class CustomTaskExecutorBuilderConfig {
 

spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/task-execution-and-scheduling.adoc

@@ -1,6 +1,9 @@
 [[features.task-execution-and-scheduling]]
 == Task Execution and Scheduling
-In the absence of an `Executor` bean in the context, Spring Boot auto-configures a `ThreadPoolTaskExecutor` with sensible defaults that can be automatically associated to asynchronous task execution (`@EnableAsync`) and Spring MVC asynchronous request processing.
+In the absence of an `Executor` bean in the context, Spring Boot auto-configures an `AsyncTaskExecutor`.
+When virtual threads are enabled (using Java 21+ and configprop:spring.threads.virtual.enabled[] set to `true`) this will be a `SimpleAsyncTaskExecutor` that uses virtual threads.
+Otherwise, it will be a `ThreadPoolTaskExecutor` with sensible defaults.
+In either case, the auto-configured executor will be automatically used for asynchronous task execution (`@EnableAsync`) and Spring MVC asynchronous request processing.
 
 [TIP]
 ====
@@ -10,7 +13,7 @@ Depending on your target arrangement, you could change your `Executor` into a `T
 The auto-configured `TaskExecutorBuilder` allows you to easily create instances that reproduce what the auto-configuration does by default.
 ====
 
-The thread pool uses 8 core threads that can grow and shrink according to the load.
+When a `ThreadPoolTaskExecutor` is auto-configured, the thread pool uses 8 core threads that can grow and shrink according to the load.
 Those default settings can be fine-tuned using the `spring.task.execution` namespace, as shown in the following example:
 
 [source,yaml,indent=0,subs="verbatim",configprops,configblocks]