io_uring_wait_cqe_nr(3) liburing Manual io_uring_wait_cqe_nr(3)

io_uring_wait_cqe_nr - wait for one or more io_uring completion events

#include <liburing.h>
int io_uring_wait_cqe_nr(struct io_uring *ring,
                         struct io_uring_cqe **cqe_ptr,
                         unsigned wait_nr);

The io_uring_wait_cqe_nr(3) function returns wait_nr IO completion events from the queue belonging to the ring param, waiting for it if necessary. If the requested number of events are already available in the ring when invoked, no waiting will occur. The cqe_ptr param is filled in on success.

After the caller has submitted a request with io_uring_submit(3), the application can retrieve the completion with io_uring_wait_cqe(3).

Ideally used with a ring setup with IORING_SETUP_SINGLE_ISSUER|IORING_SETUP_DEFER_TASKRUN as that will greatly reduce the number of context switches that an application will see waiting on multiple requests.

On success io_uring_wait_cqe_nr(3) returns 0 and the cqe_ptr param is filled in. On failure it returns -errno. The return value indicates the result of waiting for a CQE, and it has no relation to the CQE result itself.

io_uring_queue_init_params(3), io_uring_submit(3), io_uring_wait_cqes(3)

November 15, 2021 liburing-2.1