Extend synchronization primitives to allow cross-chunk sync #11
Description
Imagine we want to do type inference on columns of CSV. We'd start with some initial guess for each column and then process the file in chunks, as we always do. Now one of the workers discovers that a column that was until now considered an Int has to be a Float64. How should we spread this information to the other chunks? Should this be a responsibility of the consume context? Should we define specific callback that would work as a barrier -- we'd stop parsing, wait for all results to enter the barrier, sync their schemas, and release them? Doing this in sync_tasks is problematic, because that only synchronizes chunks belonging to one of the two buffers.
More design work is needed on this issue.