Hmm, there seems to be other services using 'synchronized' as well. The Service javadoc says:

>  A service is a thing which can be started and stopped.  A service may be started or stopped from any thread.  In general, injections will always happen from the same thread that will call {@code start()}, and uninjections will always happen from the same thread that had called {@code stop()}.  However no other guarantees are made with respect to locking or thread safety; a robust service implementation should always take care to protect any mutable state appropriately.

So I guess the methods are synchronized due to this last comment. In our case the mutual state is _beanManager_.