public int getNumThreadsPerSearch() {
        if (numThreadsPerSearch >= 0) return numThreadsPerSearch;
        return uniquelyInherited(RankProfile::getNumThreadsPerSearch, n -> n >= 0, "num-threads-per-search")
                .orElse(-1);
    }
Returns a read only map view of the rank properties to use in this profile. This is never null.
config-model/src/main/java/com/yahoo/schema/RankProfile.java