private void pushEndOfPeriodToNow() {
        long currentNanos = nanoTimeSupplier.getAsLong();
        cumulativeLoadNanos += activeIntervals.size() * (currentNanos - endOfPeriodNanos);
        for (ActiveIntervalInfo activeInterval : activeIntervals) {
            cumulativeLoadNanosByThread.merge(activeInterval.threadNameTemplate,
                                              currentNanos - endOfPeriodNanos,
                                              Long::sum);
        }
        endOfPeriodNanos = currentNanos;
    }
Returns the metrics for the current time period up to now, and starts a new period.
zkfacade/src/main/java/com/yahoo/vespa/curator/stats/LatencyStats.java