异步下载与同步下载多个文件

Question

I have an iOS app in which I need to download multiple audio files before a player can start. (All the files need to be downloaded first because they all play simultaneously as a multi-track song.)

I know about the advantages of downloading asynchronously from the main thread (not blocking the UI, etc.) but I'm wondering if there's any advantage to downloading each of the files asynchronously from each other, vs. all on the same background thread. Which approach would download all the files fastest, if there's a difference?

Answer 1

It's really a matter of network bandwidth. Most likely if you tried to download 10 files at the same time, it will take as long (and possibly longer) than downloading the same 10 files one at a time.

A user's Internet connection only allows so much data per second. Assuming that is maxed out for each download, downloading more than one file at a time means that the max throughput has to be split between the files.

Your best option is to setup a concurrent operation queue. Queue each download as a separate operation. Then experiment by setting up the operation queue to support anywhere from 1 to n concurrent operations. Do the tests multiple times at different times and track how long it takes to complete all of the downloads. See which results in the best overall average. Keep in mind the results could be different for a user on a slow 2G cellular connection vs. someone on a super fast home Wi-Fi connection.