When youtube-dl runs multiple instances, cookies are overwritten

[bidaian]

Checklist

• I've verified that I'm running youtube-dl version 2019.09.28
• I've checked that all provided URLs are alive and playable in a browser
• I've checked that all URLs and arguments with special characters are properly quoted or escaped
• I've searched the bugtracker for similar bug reports including closed ones
• I've read bugs section in FAQ

Verbose log

[debug] System config: []
[debug] User config: []
[debug] Custom config: []
[debug] Command-line args: [u'-v']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2019.09.28
[debug] Python version 2.7.13 (CPython) - Linux-4.9.0-8-amd64-x86_64-with-debian-9
[debug] exe versions: ffmpeg 3.2.14-1, ffprobe 3.2.14-1, rtmpdump 2.4
[debug] Proxy map: {}
Usage: youtube-dl [OPTIONS] URL [URL...]

Description

If I run more than one simultaneous youtube-dl instance on different sites, with a cookie jar (--cookie), the jars are overwritten each time. The result is that you keep just the cookies from the last write.

That is expected according to the Python documentation on cookiejar but it does not allow for multiple simultaneous downloads from different sites, if cookies are involved.

[dstftw]

Single cookie file is not supposed to be shared across simultaneous youtube-dl instances in the first place.