Remove multi-threaded downloads

[AndreyNikiforov]

Multi-threaded downloading is causing issues with duplicate content #155

Need to evaluate if a promise of improved download speed is consistently kept and if it warrants complexity and misbehavior with dups. If not consistent, then remove multi-threaded downloading.

[AndreyNikiforov]

@menkej I am skeptical about multithreaded downloading from a single source [...] I would be curious to see some test results (single threaded vs multi threaded downloading)

I run some test downloads. I am on a 100 MBit connection. No clear lab conditions - Netflix and Skype session running. Downloading 1000 recent files.

default setting (multithreaded)
87,59s user 30,36s system 11% cpu 16:33,71 total
77,79s user 27,50s system 12% cpu 13:58,24 total
77,67s user 27,30s system 13% cpu 12:34,12 total

--threads-num 1
79,00s user 27,64s system 14% cpu 12:34,61 total
79,17s user 27,51s system 11% cpu 15:04,41 total
78,30s user 27,80s system 14% cpu 12:36,18 total

Just three runs. Just 1000 pics. Seeing not much of a difference really.

Multithreading might make sense for parallel image/video conversions and stuff. For download... not so sure...

Maybe it makes a difference on a clear line with a big pipe...

Originally posted by @menkej in #171 (comment)