Data race condition

The value of the shared data will be determined by the interleaving of thread execution. Thread shared data is accessed without holding an appropriate lock, possibly causing a race condition
/src/mongo/db/repl/topology_version_observer.cpp:203: MISSING_LOCK 151215 Accessing "this->this->_cache" without holding lock "mongo::repl::TopologyVersionObserver._mutex". Elsewhere, "mongo::repl::TopologyVersionObserver._cache" is written to with "TopologyVersionObserver._mutex" held 3 out of 3 times.