Beans created by FactoryBean are not considered as autowiring candidates if another thread holds a singletonLock

[justinas-dabravolskas]

Beans created by FactoryBean are not considered as autowiring candidates if another thread holds a singletonLock. Depending on the use case it will either result in an exception or even worse into a silently ignored bean. This was introduced by 8771b9e so applies to 6.2.2-6.2.6.

Reproducible https://github.com/justinas-dabravolskas/spring-6.2.6-ignored-factorybean

INFO: Creating singleton bean 'component1' in thread "Thread-0" while other thread holds singleton lock for other beans [slowInit]
Exception in thread "Thread-0" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'component1': Unsatisfied dependency expressed through field 'c': No qualifying bean of type 'org.example.beans.Component2' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:788)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:768)
        at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:146)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:509)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1445)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:600)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:523)
        at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:336)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:307)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:334)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:224)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1489)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1450)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveBean(DefaultListableBeanFactory.java:516)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:371)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:364)
        at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1290)
        at org.example.beans.PostConstruct.lambda$postConstruct$0(PostConstruct.java:22)
        at java.base/java.lang.Thread.run(Thread.java:1583)
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.example.beans.Component2' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:2144)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1594)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1519)
        at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.resolveFieldValue(AutowiredAnnotationBeanPostProcessor.java:785)
        ... 18 more

[jhoeller]

Well spotted, thanks for the report! I've taken the opportunity to revise our FactoryBean locking behavior: After the bootstrap phase (and with spring.locking.strict=true), getSingletonFactoryBeanForTypeCheck always locks. In a background bootstrap thread, it never locks. Otherwise, it tries locking and explicitly resolves the bean class for subsequent type-based resolution (even for a component-scanned class) when it fails to acquire the lock. The latter part is what was missing for your scenario in particular since our generics resolution did not kick in (due to the bean class not being resolved for your scanned class).