I think the parent comment was talking about what you would need if you weren't using io_ring. First, in the main async thread, you attempt a non blocking read.

I think the parent comment was talking about what you would need if you weren't using io_ring. First, in the main async thread, you attempt a non blocking read. If that succeeds, great. If not, you hand over to another thread to do a blocking read, which is what libuv currently does for all reads. Due to the race that you described, there's a chance that by the time it gets there it will be a non blocking read, but that's ok. Overall, the main thread often gets data straight away when it's available, and is never blocked when it's not. If you're using io_uring, the data is read into the user buffer by the kernel during the async call, so there's no race. There's no point having a separate fast path in that case, because the io_uring call can just return the data immediately if it's available.