追踪spring @Async

laywin
958 阅读5分钟
  • 背景

最近看到项目里面有通过spring @Async声明式的方式来进行异步调用，第一时间就让我警惕起来，原因在于通常情况下我们都是通过JDK的ThreadPoolExecutor来做这个事儿，ThreadPoolExecutor也会有相关参数需要优化的地方，例如线程池的配置，阻塞队列的大小（可能会被OOM）等等，而通过注解异步执行的背后一定会有一个threadpool。 尽管声明式的使用方式使得程序变的更加简单，但一定得深挖一下。

  • 基本用法

通过在由@Configuration注解的类上配置@EnableAsync来开启spring异步方法执行的能力

@Configuration
@EnableAsync
public class MyJob {

	@Async
	public CompletableFuture<String> doSomething() {
		return CompletableFuture.supplyAsync(this::doJob);
	}

	private String doJob() {
		System.out.println("start the work...");
		System.out.println("sleep 5 seconds to simulate the work");
	   try {
		   Thread.sleep(5000);
	   } catch (InterruptedException e) {
		   e.printStackTrace();
	   }
	   System.out.println("end the work...");
	   return "done";
	}
}

@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringTest {

	@Resource
	private MyJob myJob;

	private CountDownLatch countDownLatch = new CountDownLatch(1);


	@Test
	public void testSpringAsync() {
		CompletableFuture<String> completableFuture= myJob.doSomething();
		completableFuture.whenComplete((s, throwable) -> {
			System.out.println("this is the result: " + s);
			countDownLatch.countDown();
		});

		System.out.println("wait the work done!");

		try {
			countDownLatch.await();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
}

result:

wait the work done!
start the work...
sleep 5 seconds to simulate the work
end the work...
this is the result: done

可以看到doSomething方法的执行异步了。

  • 追踪
  1. 通过@EnableAsync来开启异步方法执行的能力

重点在导入AsyncConfigurationSelector来对异步配置进行选择

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(AsyncConfigurationSelector.class)
public @interface EnableAsync {
    AdviceMode mode() default AdviceMode.PROXY;
    ...
}
  1. 由AsyncConfigurationSelector来对异步配置进行选择

AdviceMode 在@EnableAsync中默认配置为AdviceMode.PROXY,ProxyAsyncConfiguration则主要配置了AsyncAnnotationBeanPostProcessor

public class AsyncConfigurationSelector extends AdviceModeImportSelector<EnableAsync> {
    ...
	public String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
				return new String[] {ProxyAsyncConfiguration.class.getName()};
			case ASPECTJ:
				return new String[] {ASYNC_EXECUTION_ASPECT_CONFIGURATION_CLASS_NAME};
			default:
				return null;
		}
	}

}

@Configuration
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyAsyncConfiguration extends AbstractAsyncConfiguration {

	@Bean(name = TaskManagementConfigUtils.ASYNC_ANNOTATION_PROCESSOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public AsyncAnnotationBeanPostProcessor asyncAdvisor() {
                ...
		AsyncAnnotationBeanPostProcessor bpp = new AsyncAnnotationBeanPostProcessor();
		...
	}

}
  1. AsyncAnnotationBeanPostProcessor实现了BeanFactoryAware接口，在setBeanFactory的时候会创建AsyncAnnotationAdvisor
public class AsyncAnnotationBeanPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor {

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		super.setBeanFactory(beanFactory);

		AsyncAnnotationAdvisor advisor = new AsyncAnnotationAdvisor(this.executor, this.exceptionHandler);
		if (this.asyncAnnotationType != null) {
			advisor.setAsyncAnnotationType(this.asyncAnnotationType);
		}
		advisor.setBeanFactory(beanFactory);
		this.advisor = advisor;
	}

}
  1. AsyncAnnotationAdvisor主要创建了advice和pointcut,advice环绕方法的执行，pointcut用来匹配目标方法
public class AsyncAnnotationAdvisor extends AbstractPointcutAdvisor implements BeanFactoryAware {
        ...
	@SuppressWarnings("unchecked")
	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);
		this.pointcut = buildPointcut(asyncAnnotationTypes);
	}

	protected Advice buildAdvice(
			@Nullable Supplier<Executor> executor, @Nullable Supplier<AsyncUncaughtExceptionHandler> exceptionHandler) {

		AnnotationAsyncExecutionInterceptor interceptor = new AnnotationAsyncExecutionInterceptor(null);
		interceptor.configure(executor, exceptionHandler);
		return interceptor;
	}

	/**
	 * Calculate a pointcut for the given async annotation types, if any.
	 * @param asyncAnnotationTypes the async annotation types to introspect
	 * @return the applicable Pointcut object, or {@code null} if none
	 */
	protected Pointcut buildPointcut(Set<Class<? extends Annotation>> asyncAnnotationTypes) {
		ComposablePointcut result = null;
		for (Class<? extends Annotation> asyncAnnotationType : asyncAnnotationTypes) {
			Pointcut cpc = new AnnotationMatchingPointcut(asyncAnnotationType, true);
			Pointcut mpc = new AnnotationMatchingPointcut(null, asyncAnnotationType, true);
			if (result == null) {
				result = new ComposablePointcut(cpc);
			}
			else {
				result.union(cpc);
			}
			result = result.union(mpc);
		}
		return (result != null ? result : Pointcut.TRUE);
	}

}
  1. 主要看第4步中buildAdvice中的AnnotationAsyncExecutionInterceptor,AnnotationAsyncExecutionInterceptor继承了AsyncExecutionInterceptor，AsyncExecutionInterceptor继承了AsyncExecutionAspectSupport
public class AnnotationAsyncExecutionInterceptor extends AsyncExecutionInterceptor {
        ...
}

public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport implements MethodInterceptor, Ordered {

	/**
	 * Create a new instance with a default {@link AsyncUncaughtExceptionHandler}.
	 * @param defaultExecutor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
	 * or {@link java.util.concurrent.ExecutorService}) to delegate to;
	 * as of 4.2.6, a local executor for this interceptor will be built otherwise
	 */
	public AsyncExecutionInterceptor(@Nullable Executor defaultExecutor) {
		super(defaultExecutor);
	}

	/**
	 * Create a new {@code AsyncExecutionInterceptor}.
	 * @param defaultExecutor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
	 * or {@link java.util.concurrent.ExecutorService}) to delegate to;
	 * as of 4.2.6, a local executor for this interceptor will be built otherwise
	 * @param exceptionHandler the {@link AsyncUncaughtExceptionHandler} to use
	 */
	public AsyncExecutionInterceptor(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
		super(defaultExecutor, exceptionHandler);
	}

	/**
	 * Intercept the given method invocation, submit the actual calling of the method to
	 * the correct task executor and return immediately to the caller.
	 * @param invocation the method to intercept and make asynchronous
	 * @return {@link Future} if the original method returns {@code Future}; {@code null}
	 * otherwise.
	 */
	@Override
	@Nullable
	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);

		AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
		if (executor == null) {
			throw new IllegalStateException(
					"No executor specified and no default executor set on AsyncExecutionInterceptor either");
		}

		Callable<Object> task = () -> {
			try {
				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;
		};

		return doSubmit(task, executor, invocation.getMethod().getReturnType());
	}

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

AsyncExecutionAspectSupport主要有2点值得关注，第一是提供了Executor的默认创建方式，即通过spring容器来获取TaskExecutor Bean,第二是对异步执行方法返回值的适配

public abstract class AsyncExecutionAspectSupport implements BeanFactoryAware {
	/**
	 * Create a new {@link AsyncExecutionAspectSupport} with the given exception handler.
	 * @param defaultExecutor the {@code Executor} (typically a Spring {@code AsyncTaskExecutor}
	 * or {@link java.util.concurrent.ExecutorService}) to delegate to, unless a more specific
	 * executor has been requested via a qualifier on the async method, in which case the
	 * executor will be looked up at invocation time against the enclosing bean factory
	 * @param exceptionHandler the {@link AsyncUncaughtExceptionHandler} to use
	 */
	public AsyncExecutionAspectSupport(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
		this.defaultExecutor = new SingletonSupplier<>(defaultExecutor, () -> getDefaultExecutor(this.beanFactory));
		this.exceptionHandler = SingletonSupplier.of(exceptionHandler);
	}

	/**
	 * Retrieve or build a default executor for this advice instance.
	 * An executor returned from here will be cached for further use.
	 * <p>The default implementation searches for a unique {@link TaskExecutor} bean
	 * in the context, or for an {@link Executor} bean named "taskExecutor" otherwise.
	 * If neither of the two is resolvable, this implementation will return {@code null}.
	 * @param beanFactory the BeanFactory to use for a default executor lookup
	 * @return the default executor, or {@code null} if none available
	 * @since 4.2.6
	 * @see #findQualifiedExecutor(BeanFactory, String)
	 * @see #DEFAULT_TASK_EXECUTOR_BEAN_NAME
	 */
	@Nullable
	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 {
					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;
	}


	/**
	 * Delegate for actually executing the given task with the chosen executor.
	 * @param task the task to execute
	 * @param executor the chosen executor
	 * @param returnType the declared return type (potentially a {@link Future} variant)
	 * @return the execution result (potentially a corresponding {@link Future} handle)
	 */
	@Nullable
	protected Object doSubmit(Callable<Object> task, AsyncTaskExecutor executor, Class<?> returnType) {
		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;
		}
	}
}
  1. 追踪TaskExecutor的默认创建方式

在spring-boot-autoconfigure中可以查到如下配置类,默认情况下会创建一个coresize为8，maxsize为Integer.MAX_VALUE，队列大小为Integer.MAX_VALUE的线程池。

@ConditionalOnClass(ThreadPoolTaskExecutor.class)
@Configuration
@EnableConfigurationProperties(TaskExecutionProperties.class)
public class TaskExecutionAutoConfiguration {

	/**
	 * Bean name of the application {@link TaskExecutor}.
	 */
	public static final String APPLICATION_TASK_EXECUTOR_BEAN_NAME = "applicationTaskExecutor";

	private final TaskExecutionProperties properties;

	private final ObjectProvider<TaskExecutorCustomizer> taskExecutorCustomizers;

	private final ObjectProvider<TaskDecorator> taskDecorator;

	public TaskExecutionAutoConfiguration(TaskExecutionProperties properties,
			ObjectProvider<TaskExecutorCustomizer> taskExecutorCustomizers,
			ObjectProvider<TaskDecorator> taskDecorator) {
		this.properties = properties;
		this.taskExecutorCustomizers = taskExecutorCustomizers;
		this.taskDecorator = taskDecorator;
	}

	@Bean
	@ConditionalOnMissingBean
	public TaskExecutorBuilder taskExecutorBuilder() {
		TaskExecutionProperties.Pool pool = this.properties.getPool();
		TaskExecutorBuilder builder = new TaskExecutorBuilder();
		builder = builder.queueCapacity(pool.getQueueCapacity());
		builder = builder.corePoolSize(pool.getCoreSize());
		builder = builder.maxPoolSize(pool.getMaxSize());
		builder = builder.allowCoreThreadTimeOut(pool.isAllowCoreThreadTimeout());
		builder = builder.keepAlive(pool.getKeepAlive());
		builder = builder.threadNamePrefix(this.properties.getThreadNamePrefix());
		builder = builder.customizers(this.taskExecutorCustomizers);
		builder = builder.taskDecorator(this.taskDecorator.getIfUnique());
		return builder;
	}

	@Lazy
	@Bean(name = { APPLICATION_TASK_EXECUTOR_BEAN_NAME,
			AsyncAnnotationBeanPostProcessor.DEFAULT_TASK_EXECUTOR_BEAN_NAME })
	@ConditionalOnMissingBean(Executor.class)
	public ThreadPoolTaskExecutor applicationTaskExecutor(TaskExecutorBuilder builder) {
		return builder.build();
	}

}
  • 结论

至此，对通过注解异步方法执行的最踪基本完成，spring 声明式的方式使得应用程序的构建变得更加简便，特别是在基础能力的封装上，例如过去对事务，缓存，定时任务等相关的应用，但重点在于我们得清楚声明式背后的逻辑。

avatar
文章
阅读
粉丝