public void increment() {
        concurrentCount.accumulateAndGet(0, (currentConcurrentCount, ignored) -> {
            final int newConcurrentCount = currentConcurrentCount + 1;

            // Increase high watermark if we are higher than it
            highWaterMark.accumulateAndGet(newConcurrentCount, (currentMaxCount, ignored2) ->
                    Math.max(newConcurrentCount, currentMaxCount));

            // Increase the count of the number of concurrent things
            return newConcurrentCount;
        });
    }
Increment the number of concurrent things happening, i.e. call it before doing
the concurrent activity.
stroom-util/src/main/java/stroom/util/concurrent/HighWaterMarkTracker.java