spring三级缓存以及@Async产生循环引用
spring三级缓存以及@Async产生循环引用
- spring三级缓存介绍
-
- 三级缓存解除循环引用原理
- 源码对应
-
- 1、获取A，从三级缓存中获取，没有获取到
- 2、构造A，将A置入三级缓存
-
- 构造A(创建A实例)
- 置入缓存
- 3、注入属性，构造B
-
- 扫描缓存实例的相关信息
- 注入属性
- 4、获取B，从三级缓存中没有获取到
- 5、构造B，将B置入三级缓存
- 6、注入属性，构造A
- 7、获取A，三个缓存中三级缓存命中
- 8、创建B实例后续步骤
- 9、B构造完成，实例放入一级缓存，二级三级缓存移除
- 10、创建A实例后续步骤
- 11、A构造完成，实例放入一级缓存，二级三级缓存移除
- @Async导致三级缓存没有解除循环引用
-
- 复现
-
- 测试类
- 描述
- 备注
- 启动测试
- 原因分析
- 解决方法
- 参考
spring三级缓存介绍
三级缓存解除循环引用原理
A => B => A
一级缓存 singletonObjects
二级缓存 earlySingletonObjects
三级缓存 singletonFactories
1、获取A，从三级缓存中获取，没有获取到
2、构造A，将A置入三级缓存
3、注入属性，构造B
4、获取B，从三级缓存中没有获取到
5、构造B，将B置入三级缓存
6、注入属性，构造A
7、获取A，从三级缓存中获取，一级没有、二级没有、三级存在。此时通过从三级的BeanFactory构造实例对象，放入二级缓存，移除三级缓存
8、创建B实例后续步骤
9、B构造完成，实例放入一级缓存，二级三级缓存移除
10、创建A实例后续步骤
11、A构造完成，实例放入一级缓存，二级三级缓存移除
源码对应
springboot 2.5.6
1、获取A，从三级缓存中获取，没有获取到
// AbstractBeanFactory#doGetBean 256行
protected <T> T doGetBean(
String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
throws BeansException {
String beanName = transformedBeanName(name);
Object beanInstance;
// 从三个缓存中依次获取，注意方法点进去allowEarlyReference是true
Object sharedInstance = getSingleton(beanName);
...
2、构造A，将A置入三级缓存
构造A(创建A实例)
// AbstractAutowireCapableBeanFactory#doCreateBean 582行
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {
instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 这里会通过构造函数创建Bean实例
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
//省略代码...
置入缓存
// AbstractAutowireCapableBeanFactory#doCreateBean 613行
//省略代码...
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
if (earlySingletonExposure) {
if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean '" + beanName +
"' to allow for resolving potential circular references");
}
// 这里会把生成beanName的BeanFactory置入三级缓存
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
//省略代码...
3、注入属性，构造B
扫描缓存实例的相关信息
InitDestroyAnnotationBeanPostProcessor会解析缓存类中@PostStruct和@PreDestroy等相关信息
CommonAnnotationBeanPostProcessor会解析缓存类中@Recource、@WebServiceRef、@PostStruct和@PreDestroy等相关信息
AutowiredAnnotationBeanPostProcessor会解析缓存类中@Autowired、@Value、@Inject等相关信息
// AbstractAutowireCapableBeanFactory#doCreateBean 594行
//省略代码...
synchronized (mbd.postProcessingLock) {
if (!mbd.postProcessed) {
try {
// 解析缓存注解相关信息
applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
//省略代码...
注入属性
// AbstractAutowireCapableBeanFactory#doCreateBean 619行
//省略代码...
try {
// 这里会将注入对应的属性
populateBean(beanName, mbd, instanceWrapper);
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
//省略代码...
// AbstractAutowireCapableBeanFactory#populateBean 1431行
//省略代码...
// 这里会依次遍历 如果是@Resource会在CommonAnnotationBeanPostProcessor中触发注入
// 如果是@Autowired则会在AutowiredAnnotationBeanPostProcessor中触发注入
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
PropertyValues pvsToUse = bp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
if (filteredPds == null) {
filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = bp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {
return;
}
}
pvs = pvsToUse;
}
//省略代码...
4、获取B，从三级缓存中没有获取到
5、构造B，将B置入三级缓存
6、注入属性，构造A
上面三个其实类似，同前面三步骤差不多
7、获取A，三个缓存中三级缓存命中
// AbstractBeanFactory#doGetBean 256行 入口
// DefaultSingletonBeanRegistry#getSingleton 150
// 此时，一级缓存和二级缓存里面都没有，三级缓存在第二步里面放进去了，此时能拿到对应的ObjectFactory，
//通过它可以获取对应的实例。然后将实例放入二级缓存，将三级缓存中对应的BeanName移除
protected Object getSingleton(String beanName, boolean allowEarlyReference) {
Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {
synchronized (this.singletonObjects) {
// Consistent creation of early reference within full singleton lock
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null) {
ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {
singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
}
}
return singletonObject;
}
8、创建B实例后续步骤
@Async循环引用触发点
这里属性注入完后，剩下bean增强、循环依赖校验、注册
DisposableBean
9、B构造完成，实例放入一级缓存，二级三级缓存移除
// DefaultSingletonBeanRegistry#getSingleton 259行
//省略代码...
// 这在执行链路的上面几层。这里判断是否是新的单例，如果是则置入缓存(一级缓存)中
if (newSingleton) {
addSingleton(beanName, singletonObject);
}
//省略代码...
protected void addSingleton(String beanName, Object singletonObject) {
// 放入一级缓存，从二级缓存和三级缓存中移除
synchronized (this.singletonObjects) {
this.singletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
this.earlySingletonObjects.remove(beanName);
this.registeredSingletons.add(beanName);
}
}
10、创建A实例后续步骤
11、A构造完成，实例放入一级缓存，二级三级缓存移除
逻辑基本同上
@Async导致三级缓存没有解除循环引用
复现
测试类
@Service
@Slf4j
public class AService {
static {
log.info("AService init===>");
}
@Resource
private BService bService;
public String a2bService(){
return bService.get();
}
@Async("async-2")
public void exec(){
log.info("aService exec");
}
}
@Service
@Slf4j
public class BService {
static {
log.info("BService init===>");
}
@Autowired
private AService aService;
public String get(){
return "BService 666";
}
public void exec(){
log.info("BService exec");
}
}
描述
这里
AService和BService在同一个目录下，也没有被在别的类中注入(如果有一个类把两者都注入了，且Bservice先注入，此时如果三个类中该类最先注入，就会导致Bservice先初始化)。在这种情况下，默认就会Aservice先初始化，然后在Bservice初始化，如此，才能复现问题。
如果想要调整类加载顺序，可以通过@DependsOn(value = "AService")或者@Lazy
备注
别开启懒加载，不然启动不会报错。
spring.main.lazy-initialization=true
启动测试
org.springframework.beans.factory.BeanCurrentlyInCreationException: Error creating bean with name 'AService': Bean with name 'AService' has been injected into other beans [BService] in its raw version as part of a circular reference, but has eventually been wrapped. This means that said other beans do not use the final version of the bean. This is often the result of over-eager type matching - consider using 'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:649)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542)
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:944)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:434)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:338)
at com.yichen.casetest.CaseTestApplication.main(CaseTestApplication.java:47)
原因分析
在bean实例后续步骤中，会对bean增强
// AbstractAutowireCapableBeanFactory#doCreateBean 620行
try {
populateBean(beanName, mbd, instanceWrapper);
// 初始化bean，对Bean增强
// 1、invokeAwareMethods
// 2、applyBeanPostProcessorsBeforeInitialization
// 3、invokeInitMethods
// 4、applyBeanPostProcessorsAfterInitialization
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
在
applyBeanPostProcessorsAfterInitialization中，由于使用了异步线程池(用了@EnableAsync)，使得AsyncAnnotationBeanPostProcessor注入了spring容器，它会为原有的bean实例创建CGLIB代理，使得最初的bean和实例化后暴露出去的bean不是同一个，没有通过循环引用校验，抛出了异常。
// AsyncAnnotationBeanPostProcessor的子类
//AbstractAdvisingBeanPostProcessor#postProcessAfterInitialization 86行
// 如果类中有@Async会创建代理
if (isEligible(bean, beanName)) {
ProxyFactory proxyFactory = prepareProxyFactory(bean, beanName);
if (!proxyFactory.isProxyTargetClass()) {
evaluateProxyInterfaces(bean.getClass(), proxyFactory);
}
proxyFactory.addAdvisor(this.advisor);
customizeProxyFactory(proxyFactory);
// Use original ClassLoader if bean class not locally loaded in overriding class loader
ClassLoader classLoader = getProxyClassLoader();
if (classLoader instanceof SmartClassLoader && classLoader != bean.getClass().getClassLoader()) {
classLoader = ((SmartClassLoader) classLoader).getOriginalClassLoader();
}
return proxyFactory.getProxy(classLoader);
}
// AbstractAutowireCapableBeanFactory#doCreateBean 632行
// 循环引用检测
if (earlySingletonExposure) {
Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {
if (exposedObject == bean) {
exposedObject = earlySingletonReference;
}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {
if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name '" + beanName + "' has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been " +
"wrapped. This means that said other beans do not use the final version of the " +
"bean. This is often the result of over-eager type matching - consider using " +
"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
解决方法
1、不用异步线程池，自己实现线程池
2、通过@lazy、@DependsOn，调整类加载顺序，如果让Bservice先加载就不会出错
3、梳理业务逻辑，调整技术实现，让AService和Bservice不循环引用
参考
Using @Async in a circular dependency will throw a BeanCurrentlyInCreationException