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.\" Copyright (c) 2009 Bitgravity Inc
.\" Written by: Kip Macy <kmacy@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd January 30, 2012
.Dt BUF_RING 9
.Os
.Sh NAME
.Nm buf_ring ,
.Nm buf_ring_alloc ,
.Nm buf_ring_free ,
.Nm buf_ring_enqueue ,
.Nm buf_ring_enqueue_bytes ,
.Nm buf_ring_dequeue_mc ,
.Nm buf_ring_dequeue_sc ,
.Nm buf_ring_count ,
.Nm buf_ring_empty ,
.Nm buf_ring_full ,
.Nm buf_ring_peek ,
.Nd multi-producer, {single, multi}-consumer lock-less ring buffer
.Sh SYNOPSIS
.In sys/param.h
.In sys/buf_ring.h
.Ft struct buf_ring *
.Fn buf_ring_alloc "int count" "struct malloc_type *type" "int flags" "struct mtx *sc_lock"
.Ft void
.Fn buf_ring_free "struct buf_ring *br" "struct malloc_type *type"
.Ft int
.Fn buf_ring_enqueue "struct buf_ring *br" "void *buf"
.Ft int
.Fn buf_ring_enqueue_bytes "struct buf_ring *br" "void *buf" "int bytes"
.Ft void *
.Fn buf_ring_dequeue_mc "struct buf_ring *br"
.Ft void *
.Fn buf_ring_dequeue_sc "struct buf_ring *br"
.Ft int
.Fn buf_ring_count "struct buf_ring *br"
.Ft int
.Fn buf_ring_empty "struct buf_ring *br"
.Ft int
.Fn buf_ring_full "struct buf_ring *br"
.Ft void *
.Fn buf_ring_peek "struct buf_ring *br"
.Sh DESCRIPTION
The
.Nm
functions provide a lock-less multi-producer and lock-less multi-consumer as
well as single-consumer ring buffer.
.Pp
The
.Fn buf_ring_alloc
function is used to allocate a buf_ring ring buffer with
.Fa count
slots using malloc_type
.Fa type
and memory flags
.Fa flags .
The single consumer interface is protected by
.Fa sc_lock .
.Pp
The
.Fn buf_ring_free
function is used to free a buf_ring.
The user is responsible for freeing any enqueued items.
.Pp
The
.Fn buf_ring_enqueue
function is used to enqueue a buffer to a buf_ring.
.Pp
The
.Fn buf_ring_enqueue_bytes
function is used to enqueue a buffer to a buf_ring and increment the
number of bytes enqueued by
.Fa bytes .
.Pp
The
.Fn buf_ring_dequeue_mc
function is a multi-consumer safe way of dequeueing elements from a buf_ring.
.Pp
The
.Fn buf_ring_dequeue_sc
function is a single-consumer interface to dequeue elements - requiring
the user to serialize accesses with a lock.
.Pp
The
.Fn buf_ring_count
function returns the number of elements in a buf_ring.
.Pp
The
.Fn buf_ring_empty
function returns
.Dv TRUE
if the buf_ring is empty,
.Dv FALSE
otherwise.
.Pp
The
.Fn buf_ring_full
function returns
.Dv TRUE
if no more items can be enqueued,
.Dv FALSE
otherwise.
.Pp
The
.Fn buf_ring_peek
function returns a pointer to the last element in the buf_ring if the
buf_ring is not empty,
.Dv NULL
otherwise.
.Sh RETURN VALUES
The
.Fn buf_ring_enqueue
and
.Fn buf_ring_enqueue_bytes
functions return
.Er ENOBUFS
if there are no available slots in the buf_ring.
.Sh HISTORY
These functions were introduced in
.Fx 8.0 .
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