I think you can use a heuristic approach. E.g. pick a comma in the middle of the CSV, assume it is a delimiter (not inside data) and parse from there in a separate thread. If you find it doesn't parse correctly (perhaps because it is inside data) you might have to throw the results of that thread away. Kind of ugly but would probably allow faster parsing in 99% of cases.

CSVs are a bit of a mess. Non-trivial to parse properly, due to escaping, and the standard (such as it is) is poorly followed. E.g. sometimes people use semi-colon or pipe instead of comma.

See also: 'Why isn’t there a decent file format for tabular data?' https://news.ycombinator.com/item?id=31220841