private Upstream[] pickTwoUpstreams(final List<Upstream> upstreamList) {
        Upstream[] upstreams = new Upstream[2];
        for (int i = 0; i < PICK_TIMES; i++) {
            int a = random.nextInt(upstreamList.size());
            int b = random.nextInt(upstreamList.size() - 1);
            // prevent random nodes from being the same.
            if (b >= a) {
                b += 1;
            }
            upstreams[0] = upstreamList.get(a);
            upstreams[1] = upstreamList.get(b);
            if (upstreams[0].isHealthy() && upstreams[1].isHealthy()) {
                break;
            }
        }
        return upstreams;
    }
select two nodes randomly.

@param upstreamList the upstream list
@return two upstream
shenyu-loadbalancer/src/main/java/org/apache/shenyu/loadbalancer/spi/P2cLoadBalancer.java