[GitHub] [incubator-druid] nishantmonu51 opened a new pull request #3956: Thread safe reads for aggregators in IncrementalIndex

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nishantmonu51 opened a new pull request #3956: Thread safe reads for aggregators in IncrementalIndex
URL: https://github.com/apache/incubator-druid/pull/3956
 
 
   Aggregators are *NOT* thread safe and if two threads concurrently try
   to read/write to the aggregator the reader may read absurd values since
   the aggregate method is not *atomic*.
   
   In case of IncrementalIndex the writes are protected by a sync block
   but the reads are unprotected, so its possible for the queries to read
   absurd values in aggregator.get().
   
   This PR adds a test that can reproduce that behavior by wrapping
   Aggregators inside a ThreadSafetyAssertionAggregator.
   
   TODO: test any performance impacts.

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