Their planned semantics don't allow for that - there's no backpressure in that system, so it might race ahead and process up to e.g. item 100 while still working on item 1.

If everything fits in memory, that's completely fine. And then yeah, this is wildly overcomplicated, just use a waitgroup and a slice and write each result into its slice index and wait for everything to finish - that matches your Java example.

But when it doesn't fit in memory, that means you have unbounded buffer growth that might OOM.