DeadLock on simultanously accessing uninitialized RefreshScope-Bean

Hi!

I'm using version 2.0.0.M9. Sometimes my application runs into a deadlock. This happens when two threads are simultanously accessing an uninitialized RefreshScope Bean.

My application uses the annotations NewSpan and Async . Both annotations cause access to a ProbabilityBasedSampler, that's provided as RefreshScope-Bean by ZipkinAutoConfiguration.RefreshScopedProbabilityBasedSamplerConfiguration.defaultTraceSampler(SamplerProperties).

Thread 1 creates a Singleton-Bean, with a @PostConstruct calling a sampled method (@Async-annotation). Thread 2 calls a sampled method (@NewSpan-annotation). ProbabilityBasedSampler and SamplerProperties are not yet initialized.

This is what happens:

1. Thread 1: tries to create the Singleton, accesses DefaultSingletonBeanRegistry.getSingleton(String, ObjectFactory<?>) and locks DefaultSingletonBeanRegistry.singletonObjects

2. Thread 2: calls a @NewSpan-annotated method. This requires the ProbabilityBasedSampler and triggers GenericScope.BeanLifecycleWrapper.getBean() and locks GenericScope.BeanLifecycleWrapper.name

3. Thread 2: to create ProbabilityBasedSampler the SamplerProperties are required. The bean factory tries to get the SamplerProperties-Singleton, but has to wait for the lock on DefaultSingletonBeanRegistry.singletonObjects that is held by Thread 1

4. Thread 1: the @PostConstruct calls a @Async-annotated method, that requires ProbabilityBasedSampler. that triggers GenericScope.BeanLifecycleWrapper.getBean(), but has to wait for the lock GenericScope.BeanLifecycleWrapper.name held by Thread 2

I attach a class that simulates the behaviour of my application setup and the stack trace when this class runs into the deadlock: RefreshScopeDeadLock.zip

Unpack RefreshScopeDeadLock.zip and start with the included reproducer and stack trace. Trace the two-thread interaction through DefaultSingletonBeanRegistry.getSingleton(String, ObjectFactory<?>) and GenericScope.BeanLifecycleWrapper.getBean(), focusing on ProbabilityBasedSampler and SamplerProperties initialization. Done means the reported simultaneous access no longer deadlocks.