spring的异步执行使用与源码详解

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2023-05-27
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标签   Spring
目录
  • 异步执行的使用
  • 配置类
  • service层的使用
  • 测试类
  • 源码分析
  • @EnableAsync
  • AsyncConfigurationSelector
  • ProxyAsyncConfiguration
  • AbstractAsyncConfiguration
  • AsyncAnnotationBeanPostProcessor
  • AsyncAnnotationAdvisor
  • AnnotationAsyncExecutionInterceptor

在实际的开发过程中，有些业务逻辑使用异步的方式处理更为合理。比如在某个业务逻辑中，需要把一些数据存入到redis缓存中，这个操作只是一个辅助的功能，成功或者失败对主业务并不会产生根本影响，这个过程可以通过异步的方法去进行。

Spring中通过在方法上设置@Async注解，可使得方法被异步调用。也就是说该方法会在调用时立即返回，而这个方法的实际执行交给Spring的TaskExecutor去完成。

异步执行的使用

配置类

使用@EnableAsync注解开启异步功能。

package com.morris.spring.config;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import java.util.concurrent.Executor;
@Configuration
@EnableAsync // 开启Async
public class AsyncConfig implements AsyncConfigurer {
	@Override
	public Executor getAsyncExecutor() {
		// 自定义线程池
		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
		executor.setCorePoolSize(2);
		executor.setMaxPoolSize(4);
		executor.setQueueCapacity(10);
		executor.setThreadNamePrefix("MyExecutor-");
		executor.initialize();
		return executor;
	}
}

service层的使用

在需要异步执行的方法上面加上@Async注解。

package com.morris.spring.service;
import lombok.extern.slf4j.Slf4j;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.AsyncResult;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
@Slf4j
public class AsyncService {
	@Async
	public void noResult() {
		log.info("execute noResult");
	}
	@Async
	public Future<String> hasResult() throws InterruptedException {
		log.info("execute hasResult");
		TimeUnit.SECONDS.sleep(5);
		return new AsyncResult<>("hasResult success");
	}
	@Async
	public CompletableFuture<String> completableFuture() throws InterruptedException {
		log.info(" execute completableFuture");
		TimeUnit.SECONDS.sleep(5);
		return CompletableFuture.completedFuture("completableFuture success");
	}
}

测试类

package com.morris.spring.demo.async;
import com.morris.spring.config.AsyncConfig;
import com.morris.spring.service.AsyncService;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
/**
 * 异步调用的演示
 */
@Slf4j
public class AsyncDemo {
	@Test
	public void test() throws ExecutionException, InterruptedException {
		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
		applicationContext.register(AsyncService.class);
		applicationContext.register(AsyncConfig.class);
		applicationContext.refresh();
		AsyncService asyncService = applicationContext.getBean(AsyncService.class);
		asyncService.noResult(); // 无结果
		Future<String> future = asyncService.hasResult();
		log.info("hasResult: {}", future.get()); // 有结果
		CompletableFuture<String> completableFuture = asyncService.completableFuture();
		completableFuture.thenAcceptAsync(System.out::println);// 异步回调
		log.info("completableFuture call down");
	}
}

运行结果如下：

INFO  MyExecutor-1 AsyncService:16 - execute noResult
INFO  MyExecutor-2 AsyncService:21 - execute hasResult
INFO  main AsyncDemo:29 - hasResult: hasResult success
INFO  MyExecutor-1 AsyncService:28 -  execute completableFuture
INFO  main AsyncDemo:33 - completableFuture call down

通过日志可以发现AsyncService的方法都是通过线程名为MyExecutor-1的线程执行的，这个名称的前缀是在AsyncConfig中指定的，而不是通过main线程执行的。

两个疑问：

  • 是否可以不配置Executor线程池，Spring会默认创建默认的Executor，还是会报错？
  • Executor线程池中执行任务时如果抛出了异常，可否自定义异常的处理类对异常进行捕获处理？

源码分析

@EnableAsync

@EnableAsync主要是向Spring容器中导入了AsyncConfigurationSelector类。

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {

AsyncConfigurationSelector

AsyncConfigurationSelector的主要方法当然是selectImports()，注意这里会先调用父类的selectImports() org.springframework.context.annotation.AdviceModeImportSelector#selectImports(org.springframework.core.type.AnnotationMetadata)

public final String[] selectImports(AnnotationMetadata importingClassMetadata) {
	Class<?> annType = GenericTypeResolver.resolveTypeArgument(getClass(), AdviceModeImportSelector.class);
	Assert.state(annType != null, "Unresolvable type argument for AdviceModeImportSelector");
	AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(importingClassMetadata, annType);
	if (attributes == null) {
		throw new IllegalArgumentException(String.format(
				"@%s is not present on importing class '%s' as expected",
				annType.getSimpleName(), importingClassMetadata.getClassName()));
	}
	AdviceMode adviceMode = attributes.getEnum(getAdviceModeAttributeName());
	// 模板方法模式，回调子类的selectImports
	String[] imports = selectImports(adviceMode);
	if (imports == null) {
		throw new IllegalArgumentException("Unknown AdviceMode: " + adviceMode);
	}
	return imports;
}

org.springframework.scheduling.annotation.AsyncConfigurationSelector#selectImports

public String[] selectImports(AdviceMode adviceMode) {
	switch (adviceMode) {
		case PROXY:
			// 奇怪？？？@Transaction、@EnableCaching都是注入两个类，一个config，一个registrar导入aop的入口类
			// 而这里只有一个config类ProxyAsyncConfiguration
			return new String[] {ProxyAsyncConfiguration.class.getName()};
		case ASPECTJ:
			return new String[] {ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME};
		default:
			return null;
	}
}

AsyncConfigurationSelector又导入了配置类ProxyAsyncConfiguration。

ProxyAsyncConfiguration

@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyAsyncConfiguration extends AbstractAsyncConfiguration {
	/**
	 * 先看父类AbstractAsyncConfiguration
	 * @return
	 */
	@Bean(name = TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public AsyncAnnotationBeanPostProcessor asyncAdvisor() {
		Assert.notNull(this.enableAsync, "@EnableAsync annotation metadata was not injected");
		// 实例化AsyncAnnotationBeanPostProcessor
		AsyncAnnotationBeanPostProcessor bpp = new AsyncAnnotationBeanPostProcessor();
		bpp.configure(this.executor, this.exceptionHandler);
		Class<? extends Annotation> customAsyncAnnotation = this.enableAsync.getClass("annotation");
		if (customAsyncAnnotation != AnnotationUtils.getDefaultValue(EnableAsync.class, "annotation")) {
			bpp.setAsyncAnnotationType(customAsyncAnnotation);
		}
		bpp.setProxyTargetClass(this.enableAsync.getBoolean("proxyTargetClass"));
		bpp.setOrder(this.enableAsync.<Integer>getNumber("order"));
		return bpp;
	}
}

ProxyAsyncConfiguration向容器中注入了一个AsyncAnnotationBeanPostProcessor。

疑问：这里为啥是BeanPostProcessor，不应该像事务切面或者缓存切面一样，注入一个Advisor和XxxxInterceptor（Advice）吗？

AbstractAsyncConfiguration

AbstractAsyncConfiguration是ProxyAsyncConfiguration的父类。

@Configuration
public abstract class AbstractAsyncConfiguration implements ImportAware {
	@Nullable
	protected AnnotationAttributes enableAsync;
	@Nullable
	protected Supplier<Executor> executor;
	@Nullable
	protected Supplier<AsyncUncaughtExceptionHandler> exceptionHandler;
	/**
	 * 实现了ImportAware.setImportMetadata
	 * 在ProxyAsyncConfiguration初始化后被调用
	 * @param importMetadata
	 */
	@Override
	public void setImportMetadata(AnnotationMetadata importMetadata) {
		// 取得@EnableAsync注解
		this.enableAsync = AnnotationAttributes.fromMap(
				importMetadata.getAnnotationAttributes(EnableAsync.class.getName(), false));
		if (this.enableAsync == null) {
			throw new IllegalArgumentException(
					"@EnableAsync is not present on importing class " + importMetadata.getClassName());
		}
	}
	/**
	 * Collect any {@link AsyncConfigurer} beans through autowiring.
	 */
	@Autowired(required = false)
	void setConfigurers(Collection<AsyncConfigurer> configurers) {
		// configurers默认为空，除非手动注入AsyncConfigurer
		if (CollectionUtils.isEmpty(configurers)) {
			return;
		}
		if (configurers.size() > 1) {
			throw new IllegalStateException("Only one AsyncConfigurer may exist");
		}
		AsyncConfigurer configurer = configurers.iterator().next();
		this.executor = configurer::getAsyncExecutor;
		this.exceptionHandler = configurer::getAsyncUncaughtExceptionHandler;
	}
}

从这里可以看出，可以通过向spring容器中注入AsyncConfigurer来指定执行异步任务的线程池和异常处理器。

AsyncAnnotationBeanPostProcessor

AsyncAnnotationBeanPostProcessor的继承结构图：

20220424174516480.png

AsyncAnnotationBeanPostProcessor主要实现了BeanFactoryAware和BeanPostProcessor接口。

org.springframework.scheduling.annotation.AsyncAnnotationBeanPostProcessor#setBeanFactory

public void setBeanFactory(BeanFactory beanFactory) {
	super.setBeanFactory(beanFactory);
	// 实例化Advisor
	AsyncAnnotationAdvisor advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
	if (this.asyncAnnotationType != null) {
		advisor.setAsyncAnnotationType(this.asyncAnnotationType);
	}
	advisor.setBeanFactory(beanFactory);
	this.advisor = advisor;
}

在AsyncAnnotationBeanPostProcessor实例化时实例化了切面AsyncAnnotationAdvisor。

每个bean实例化完后都会调用AsyncAnnotationBeanPostProcessor.postProcessAfterInitialization()判断是否要生成代理对象。

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) {
	... ...
	/**
	 * @see AbstractBeanFactoryAwareAdvisingPostProcessor#isEligible(java.lang.Object, java.lang.String)
	 */
	// isEligible会判断哪些bean要生成代理
	// 就是使用advisor中的pointcut进行匹配
	if (isEligible(bean, beanName)) {
		// 创建代理
		ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
		if (!proxyFactory.isProxyTargetClass()) {
			evaluateProxyInterfaces(bean.getClass(), proxyFactory);
		}
		proxyFactory.addAdvisor(this.advisor);
		customizeProxyFactory(proxyFactory);
		return proxyFactory.getProxy(getProxyClassLoader());
	}
	// No proxy needed.
	return bean;
}

AsyncAnnotationAdvisor

切面AsyncAnnotationAdvisor包括通知AnnotationAsyncExecutionInterceptor和切点ComposablePointcut。

public AsyncAnnotationAdvisor(
		@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
	Set<Class<? extends Annotation>> asyncAnnotationTypes = new LinkedHashSet<>(2);
	asyncAnnotationTypes.add(Async.class);
	try {
		asyncAnnotationTypes.add((Class<? extends Annotation>)
				ClassUtils.forName("javax.ejb.Asynchronous", AsyncAnnotationAdvisor.class.getClassLoader()));
	}
	catch (ClassNotFoundException ex) {
		// If EJB 3.1 API not present, simply ignore.
	}
	this.advice = buildAdvice(executor, exceptionHandler); // 创建AnnotationAsyncExecutionInterceptor
	this.pointcut = buildPointcut(asyncAnnotationTypes); // 创建ComposablePointcut
}
protected Advice buildAdvice(
@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
	AnnotationAsyncExecutionInterceptor interceptor = new AnnotationAsyncExecutionInterceptor(null);
	interceptor.configure(executor, exceptionHandler);
	return interceptor;
}
protected Pointcut buildPointcut(Set<Class<? extends Annotation>> asyncAnnotationTypes) {
	ComposablePointcut result = null;
	for (Class<? extends Annotation> asyncAnnotationType : asyncAnnotationTypes) {
		Pointcut cpc = new AnnotationMatchingPointcut(asyncAnnotationType, true); // 类
		Pointcut mpc = new AnnotationMatchingPointcut(null, asyncAnnotationType, true); // 方法
		if (result == null) {
			result = new ComposablePointcut(cpc);
		}
		else {
			result.union(cpc); // 类和方法的组合切点
		}
		result = result.union(mpc);
	}
	return (result != null ? result : Pointcut.TRUE);
}

AnnotationMatchingPointcut切面其实就是查看类或者方法上面有没有@Async注解。

AnnotationAsyncExecutionInterceptor

AnnotationAsyncExecutionInterceptor类主要负责增强逻辑的实现。

org.springframework.aop.interceptor.AsyncExecutionInterceptor#invoke

public Object invoke(final MethodInvocation invocation) throws Throwable {
	Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
	Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
	final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
	// 获得线程池
	AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
	if (executor == null) {
		throw new IllegalStateException(
				"No executor specified and no default executor set on AsyncExecutionInterceptor either");
	}
	// 将目标方法的执行封装为Callable，方便提交到线程池
	Callable<Object> task = () -> {
		try {
			// 执行目标方法
			Object result = invocation.proceed();
			if (result instanceof Future) {
				return ((Future<?>) result).get();
			}
		}
		catch (ExecutionException ex) {
			handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
		}
		catch (Throwable ex) {
			handleError(ex, userDeclaredMethod, invocation.getArguments());
		}
		return null;
	};
	// 提交任务
	return oSubmit(task, executor, invocation.getMethod().getReturnType());
}

org.springframework.aop.interceptor.AsyncExecutionAspectSupport#determineAsyncExecutor

protected AsyncTaskExecutor determineAsyncExecutor(Method method) {
	AsyncTaskExecutor executor = this.executors.get(method);
	if (executor == null) {
		Executor targetExecutor;
		/**
		 * @see org.springframework.scheduling.annotation.AnnotationAsyncExecutionInterceptor#getExecutorQualifier(java.lang.reflect.Method)
		 */
		// 获得@Async注解中的value属性中指定的taskExecutor名称
		String qualifier = getExecutorQualifier(method);
		if (StringUtils.hasLength(qualifier)) {
			targetExecutor = findQualifiedExecutor(this.beanFactory, qualifier);
		}
		else {
			// 获取默认的taskExecutor
			targetExecutor = this.defaultExecutor.get();
		}
		if (targetExecutor == null) {
			return null;
		}
		executor = (targetExecutor instanceof AsyncListenableTaskExecutor ?
				(AsyncListenableTaskExecutor) targetExecutor : new TaskExecutorAdapter(targetExecutor));
		this.executors.put(method, executor);
	}
	return executor;
}

determineAsyncExecutor()负责获取异步任务执行的线程池，线程池的查找步骤如下：

  1. 从spring容器中寻找@Async注解中的value属性中指定的taskExecutor
  2. 寻找默认的defaultExecutor

默认的defaultExecutor是怎么来的？

org.springframework.aop.interceptor.AsyncExecutionAspectSupport#configure

public void configure(@Nullable Supplier<Executor> defaultExecutor,
		@Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {
	// defaultExecutor默认为从beanFactory获取TaskExecutor或者bean名字为taskExecutor的Executor，beanFactory.getBean(TaskExecutor.class)
	this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
	// exceptionHandler默认为SimpleAsyncUncaughtExceptionHandler
	this.exceptionHandler = new SingletonSupplier<>(exceptionHandler, SimpleAsyncUncaughtExceptionHandler::new);
}

defaultExecutor首先取参数传入的defaultExecutor，这个参数来自接口AsyncConfigurer.getAsyncExecutor()，如果参数为null，那么就调用getDefaultExecutor()，注意这个方法子类AsyncExecutionInterceptor重写了：

org.springframework.aop.interceptor.AsyncExecutionInterceptor#getDefaultExecutor

protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
	Executor defaultExecutor = super.getDefaultExecutor(beanFactory);
	return (defaultExecutor != null ? defaultExecutor : new SimpleAsyncTaskExecutor());
}

如果找不到defaultExecutor就会创建一个SimpleAsyncTaskExecutor。

再来看看父类的AsyncExecutionAspectSupport#getDefaultExecutor： org.springframework.aop.interceptor.AsyncExecutionAspectSupport#getDefaultExecutor

protected Executor getDefaultExecutor(@Nullable BeanFactory beanFactory) {
	if (beanFactory != null) {
		try {
			// Search for TaskExecutor bean... not plain Executor since that would
			// match with ScheduledExecutorService as well, which is unusable for
			// our purposes here. TaskExecutor is more clearly designed for it.
			return beanFactory.getBean(TaskExecutor.class);
		}
		catch (NoUniqueBeanDefinitionException ex) {
			logger.debug("Could not find unique TaskExecutor bean", ex);
			try {
				// 找名为taskExecutor的Executor
				return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
			}
			catch (NoSuchBeanDefinitionException ex2) {
				if (logger.isInfoEnabled()) {
					logger.info("More than one TaskExecutor bean found within the context, and none is named " +
							"'taskExecutor'. Mark one of them as primary or name it 'taskExecutor' (possibly " +
							"as an alias) in order to use it for async processing: " + ex.getBeanNamesFound());
				}
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
			logger.debug("Could not find default TaskExecutor bean", ex);
			try {
				return beanFactory.getBean(DEFAULT_TASK_EXECUTOR_BEAN_NAME, Executor.class);
			}
			catch (NoSuchBeanDefinitionException ex2) {
				logger.info("No task executor bean found for async processing: " +
						"no bean of type TaskExecutor and no bean named 'taskExecutor' either");
			}
			// Giving up -> either using local default executor or none at all...
		}
	}
	return null;
}

先从beanFactory中获取TaskExecutor类型的对象，然后再找名为taskExecutor的Executor对象。

org.springframework.aop.interceptor.AsyncExecutionAspectSupport#doSubmit

protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
	// 执行任务
	if (CompletableFuture.class.isAssignableFrom(returnType)) {
		return CompletableFuture.supplyAsync(() -> {
			try {
				return task.call();
			}
			catch (Throwable ex) {
				throw new CompletionException(ex);
			}
		}, executor);
	}
	else if (ListenableFuture.class.isAssignableFrom(returnType)) {
		return ((AsyncListenableTaskExecutor) executor).submitListenable(task);
	}
	else if (Future.class.isAssignableFrom(returnType)) {
		return executor.submit(task);
	}
	else {
		executor.submit(task);
		return null;
	}
}

doSubmit()负责将任务提交至线程池中，并对各种方法的返回值进行处理。

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