public boolean keepAddingTasks() {
        return totalQueuedCount.get() < halfRequiredQueueSize;
    }
Determine if we should keep trying to create tasks for subsequent filters as we will give up if the queue is at
least half full.

@return True if the queue is less than half the size we would like it to be.
stroom-processor/stroom-processor-impl/src/main/java/stroom/processor/impl/QueueProcessTasksState.java