In Qt one QNetworkAccessManager is able to support 6 parallel downloads (at least, for Windows). So, in your app you can use several QNAMs with independent downloads. I've met some ads about commercial web crawlers. Their descriptions usually contain phrases about hundreds of threads for multiple downloads. Is this amount reasonable for an ordinary CPU with 2 cores?
It it worth for speedup of web crawling to create more than 6 explicit threads with their own QNAMs and QEventLoops for synchronized (within worker threads) page downloading?