Yes, and that's exactly what a lot of things do.

The problem with this is that you can do worse than single-threaded (although not asymptotically speaking) in the worst case.

Consider what happens if you've got something along the lines of the following:

    ",",",",",",",",","

If every parser thread (but the first, the one parsing from the start, of course) picks the wrong parity (i.e. if they should start quoted or not) repeatedly, you end up throwing away all the work of every thread but the first. And meanwhile, your first thread has to do the additional work of figuring out when to invalidate the other threads.

This is unlikely to happen, but definitely possible.

It's vaguely similar to recursive descent parsing, with vaguely similar drawbacks too.

One other similar approach is to parse eagerly as you say, but with a higher-priority thread that goes through the thread from the start only keeping track of as much state as is necessary, checking / invalidating the other threads as necessary. For CSV I think the required info is only the parity of quotes, though I could be wrong.