Prior to this change, an instance of ConfigurationClassPostProcessor
would throw IllegalStateException if its
postProcessBeanDefinitionRegistry method were called more than once.
This check is important to ensure that @Configuration classes are
not proxied by CGLIB multiple times, and works for most normal use
cases.
However, if the same CCPP instance is used to process multiple
registries/factories/contexts, this check creates a false negative
because it does not distinguish between invocations of
postProcessBeanDefinitionRegistry across different registries.
A use case for this, though admittedly uncommon, would be creating
a CCPP instance and registering it via
ConfigurableApplicationContext#addBeanDefinitionPostProcessor against
several ApplicationContexts. In such a case, the same CCPP instance
will post-process multiple different registry instances, and throw the
above mentioned exception.
With this change, CCPP now performs lightweight tracking of the
registries/beanFactories that it has already processed by recording
the identity hashcodes of these objects. This is only slightly more
complex than the previous boolean-based 'already processed' flags, and
prevents this issue (however rare it may be) from occurring.
Issue: SPR-8527
fd42a65c6c