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.\" Written by: Kip Macy <kmacy@FreeBSD.org>
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.Dd September 27, 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_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 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_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
function return
.Er ENOBUFS
if there are no available slots in the buf_ring.
.Sh HISTORY
These functions were introduced in
.Fx 8.0 .