After SERVER-43987 is backported, predicates are required with OperationContext::waitForConditionOrInterrupt(). Master currently uses a future-based API but 4.2 still uses condVar and waitForConditionOrInterrupt for writeConcern waiting. The backport of SERVER-43987 was done in a way that tried to minimize code changes. But that made the code less readable. We should make better use of the required predicates for better readability.