Why is multi-threaded download slow?

Question

Programming

Created an application for downloading files in a Very multi-threaded mode (with support for more than 10 threads), on a slow Internet (up to 2Mbps) a 2-3 times speed increase compared to analogues (download master, etc.), but on a good Internet (over 50Mbps) the speed is almost 2 times slower than analogues. I can’t understand why, the CPU usage is minimal in any case, so I can’t sin on the algorithm yet. Does anyone have any idea why the speed can be so different?
ps It is also impossible to sin on the speed of the disk subsystem, because the file is loaded completely into RAM and "flushed" to disk after the download is complete, which takes a couple of seconds in total.

Answer 1

Without knowing the architecture of your application, it's generally difficult to judge ... A couple of ideas:
1. Locks, interprocess communication.
2. Random reading on the sender.

Answer 2

DM fills 99% of the channel. Better by 2-3 times this is from Babushkin's laboratory, obviously.