140 lines
3.8 KiB
Groff
140 lines
3.8 KiB
Groff
.\" $NetBSD: pcq.9,v 1.5 2010/12/02 12:54:13 wiz Exp $
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.\"
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Matt Thomas.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd January 8, 2010
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.Dt PCQ 9
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.Os
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.Sh NAME
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.Nm pcq
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.Nd producer/consumer queue
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.Sh SYNOPSIS
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.In sys/pcq.h
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.Ft pcq_t *
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.Fn pcq_create "size_t maxlen" "km_flags_t kmflags"
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.Ft void
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.Fn pcq_destroy "pcq_t *pcq"
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.Ft void *
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.Fn pcq_get "pcq_t *pcq"
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.Ft size_t
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.Fn pcq_maxitems "pcq_t *pcq"
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.Ft void *
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.Fn pcq_peek "pcq_t *pcq"
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.Ft bool
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.Fn pcq_put "pcq_t *pcq" "void *item"
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.Sh DESCRIPTION
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The machine-independent
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.Nm
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interface provides lockless producer/consumer queues.
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A queue
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.Po
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.Vt pcq_t
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.Pc
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allows multiple writers
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.Pq producers ,
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but only a single reader
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.Pq consumer .
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The consumer is expected to be protected by a lock that covers
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the structure that the
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.Vt pcq_t
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is embedded into
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.Po
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e.g., socket lock, ifnet hwlock
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.Pc .
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These queues operate in a first-in, first-out
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.Pq FIFO
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manner.
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The act of inserting or removing an item from a
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.Vt pcq_t
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does not modify the item in any way.
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.Nm
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does not prevent an item from being inserted multiple times into a single
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.Vt pcq_t .
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn pcq_create "maxlen" "kmflags"
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Create a queue that can store at most
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.Fa maxlen
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items at one time.
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.Fa kmflags
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should be either
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.Dv KM_SLEEP ,
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if
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.Fn pcq_create
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is allowed to sleep until resources are available, or
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.Dv KM_NOSLEEP
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if it should return
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.Dv NULL
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immediately, if resources are unavailable.
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.It Fn pcq_destroy "pcq"
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Free the resources held by
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.Fa pcq .
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.It Fn pcq_get "pcq"
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Remove the next item to be consumed from the queue and return
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it.
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If the queue is empty,
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return
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.Dv NULL .
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.It Fn pcq_maxitems "pcq"
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Return the maximum number of items that the queue can store at
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any one time.
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.It Fn pcq_peek "pcq"
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Return the next item to be consumed from the queue but do not remove
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it from the queue.
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If the queue is empty,
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return
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.Dv NULL .
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.It Fn pcq_put "pcq" "item"
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Place an item at the end of the queue.
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If there is no room in the queue for the item, return
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.Dv false ;
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otherwise, return
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.Dv true .
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The item must not have the value of
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.Dv NULL .
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.El
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.Sh CODE REFERENCES
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The
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.Nm
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interface is implemented within the file
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.Pa sys/kern/subr_pcq.c .
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.\" .Sh EXAMPLES
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.Sh SEE ALSO
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.Xr atomic_ops 3 ,
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.Xr queue 9
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.Sh HISTORY
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The
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.Nm
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interface first appeared in
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.Nx 6.0 .
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.Sh AUTHORS
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.An Matt Thomas Aq matt@NetBSD.org
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.\" .Sh CAVEATS
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.\" .Sh BUGS
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.\" .Sh SECURITY CONSIDERATIONS
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