jerrypeng opened a new pull request #5371: fix potential deadlock that can 
occur in addConsumer
    # Motivation
   We have observed a deadlock that happens when consumers are added because 
isConsumersExceededOnTopic and isConsumersExceededOnSubscription are blocking 
calls even though addConsumer is called in async fashion
   ### Modifications
   Make the calls isConsumersExceededOnTopic and 
isConsumersExceededOnSubscription nonblocking by only getting the data from 
cache and not going to ZK.   There can be instances when the data is stale but 
it should be rare since the data is like already in cache.  The more permanent 
solution would be to make those calls async and addConsumer async but that 
requires a big change.  We are currently in the process of refactoring the 
MetadataStore interfaces so lets hold off on those big changes until that 
process is done.

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