.\" Copyright (C) 2022 Jens Axboe <axboe@kernel.dk>
.\"
.\" SPDX-License-Identifier: LGPL-2.0-or-later
.\"
.TH io_uring_prep_futex_waitv 3 "Sep 29, 2023" "liburing-2.5" "liburing Manual"
.SH NAME
io_uring_prep_futex_waitv \- prepare a futex waitv request
.SH SYNOPSIS
.nf
.B #include <linux/futex.h>
.B #include <unistd.h>
.B #include <liburing.h>
.PP
.BI "void io_uring_prep_futex_waitv(struct io_uring_sqe *" sqe ","
.BI "                               struct futex_waitv *" futexv ","
.BI "                               uint32_t " nr_futex ","
.BI "                               unsigned int " flags ");"
.fi
.SH DESCRIPTION
.PP
The
.BR io_uring_prep_futex_waitv (3)
function prepares a futex wait request for multiple futexes at the same time.
The submission queue entry
.I sqe
is setup for waiting on all futexes given by
.I futexv
and
.I nr_futex
is the number of futexes in that array.
.I flags
must be set to the io_uring specific futex flags.

Unlike
.BR io_uring_prep_futex_wait (3),
the desired bitset mask and values are passed in
.IR futexv .

.I flags
are currently unused and hence
.B 0
must be passed.

This function prepares an async
.BR futex (2)
waitv request. See that man page for details.

.SH RETURN VALUE
None
.SH ERRORS
The CQE
.I res
field will contain the result of the operation. See the related man page for
details on possible values. Note that where synchronous system calls will return
.B -1
on failure and set
.I errno
to the actual error value, io_uring never uses
.IR errno .
Instead it returns the negated
.I errno
directly in the CQE
.I res
field.
.SH NOTES
Unlike the sync futex syscalls that wait on a futex, io_uring does not support
passing in a timeout for the request. Instead, applications are encouraged
to use a linked timeout to abort the futex request at a given time, if desired.
.SH SEE ALSO
.BR io_uring_get_sqe (3),
.BR io_uring_submit (3),
.BR io_uring_prep_futex_wait (3),
.BR io_uring_prep_futex_wake (3),
.BR io_uring_prep_link_timeout (3),
.BR futex (2)
.BR futex2 (2)