On 4/23/20 8:42 AM, William Dauchy wrote: > Hello Jens, > > Thank you for your answer on this newbie question :) > > On Wed, Apr 22, 2020 at 10:57 PM Jens Axboe <axboe@xxxxxxxxx> wrote: >> I don't think the change is correct. That's not saying that the original >> code is necessarily correct, though! Basically there are two cases there: >> >> 1) We haven't gotten a completion yet, we'll wait for it. >> 2) We already found at least one completion. We don't want >> to _wait_ for more, but we can peek and see if there are more. >> >> Hence we don't want to turn case 2 into a loop, we should just >> continue. > > ok so in fact I think I understand that my usage is incorrect: > 1- if I'm in the case of being able to do other things while waiting > for data available using `io_uring_peek_cqe`, I should use it and come > back later when getting a -EAGAIN. > 2- it is useless to do a loop on `io_uring_peek_cqe` because in that > case, I should simply do a `io_uring_wait_cqe` > > is that correct? Right, you rarely want to busy loop on io_uring_peek_cqe(), the normal use case would be to use io_uring_wait_cqe() if you need to wait for a completion to become available. >> How is it currently failing for you? > > While trying to open/read/close multiple files, I first thought that, > because I had one successful `io_uring_wait_cqe`, I could then loop on > `io_uring_peek_cqe` and get all my data. I now realise my assumption > was completely wrong and this example was just written that way to > show two different possibilities of getting results. Ah ok, yes that sounds like a misunderstanding. Events are posted as they become available, availability of one does not mean that everything has completed. -- Jens Axboe
