@Override
    public synchronized Request poll(Task task) {
        Request poll = priorityQueuePlus.poll();
        if (poll != null) {
            return poll;
        }
        poll = noPriorityQueue.poll();
        if (poll != null) {
            return poll;
        }
        return priorityQueueMinus.poll();
    }
Priority scheduler. Request with higher priority will poll earlier. <br>

@author code4crafter@gmail.com <br>
@since 0.2.1
webmagic-core/src/main/java/us/codecraft/webmagic/scheduler/PriorityScheduler.java