private int incrForLoop() {
        int p = pointer.incrementAndGet();
        int size = proxies.size();
        if (p < size) {
            return p;
        }
        while (!pointer.compareAndSet(p, p % size)) {
            p = pointer.get();
        }
        return p % size;
    }
A simple ProxyProvider. Provide proxy as round-robin without heartbeat and error check. It can be used when all proxies are stable.
@author code4crafter@gmail.com
        Date: 17/4/16
        Time: 10:18
@since 0.7.0
webmagic-core/src/main/java/us/codecraft/webmagic/proxy/SimpleProxyProvider.java