man/io_uring_wait_cqe_nr.3

.\" Copyright (C) 2021 Stefan Roesch <shr@fb.com>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_wait_cqe_nr 3 "November 15, 2021" "liburing-2.1" "liburing Manual"
.SH NAME
io_uring_wait_cqe_nr \- wait for one or more io_uring completion events
.SH SYNOPSIS
.nf
.B #include <liburing.h>
.PP
.BI "int io_uring_wait_cqe_nr(struct io_uring *" ring ","
.BI "                         struct io_uring_cqe **" cqe_ptr ","
.BI "                         unsigned " wait_nr ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_wait_cqe_nr (3)
function returns
.I wait_nr
IO completion events from the queue belonging to the
.I 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
.I cqe_ptr
param is filled in on success.

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

Ideally used with a ring setup with
.BR 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.

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