931 lines
24 KiB
Groff
931 lines
24 KiB
Groff
.\" $OpenBSD: queue.3,v 1.60 2014/09/13 01:09:31 guenther Exp $
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.\" $NetBSD: queue.3,v 1.4 1995/07/03 00:25:36 mycroft Exp $
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.\"
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.\" Copyright (c) 1993 The Regents of the University of California.
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.\" All rights reserved.
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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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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)queue.3 8.1 (Berkeley) 12/13/93
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.\"
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.Dd $Mdocdate: September 13 2014 $
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.Dt QUEUE 3
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.Os
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.Sh NAME
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.Nm SLIST_ENTRY ,
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.Nm SLIST_HEAD ,
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.Nm SLIST_HEAD_INITIALIZER ,
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.Nm SLIST_FIRST ,
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.Nm SLIST_NEXT ,
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.Nm SLIST_EMPTY ,
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.Nm SLIST_FOREACH ,
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.Nm SLIST_FOREACH_SAFE ,
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.Nm SLIST_INIT ,
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.Nm SLIST_INSERT_AFTER ,
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.Nm SLIST_INSERT_HEAD ,
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.Nm SLIST_REMOVE_AFTER ,
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.Nm SLIST_REMOVE_HEAD ,
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.Nm SLIST_REMOVE ,
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.Nm LIST_ENTRY ,
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.Nm LIST_HEAD ,
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.Nm LIST_HEAD_INITIALIZER ,
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.Nm LIST_FIRST ,
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.Nm LIST_NEXT ,
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.Nm LIST_EMPTY ,
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.Nm LIST_FOREACH ,
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.Nm LIST_FOREACH_SAFE ,
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.Nm LIST_INIT ,
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.Nm LIST_INSERT_AFTER ,
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.Nm LIST_INSERT_BEFORE ,
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.Nm LIST_INSERT_HEAD ,
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.Nm LIST_REMOVE ,
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.Nm LIST_REPLACE ,
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.Nm SIMPLEQ_ENTRY ,
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.Nm SIMPLEQ_HEAD ,
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.Nm SIMPLEQ_HEAD_INITIALIZER ,
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.Nm SIMPLEQ_FIRST ,
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.Nm SIMPLEQ_NEXT ,
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.Nm SIMPLEQ_EMPTY ,
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.Nm SIMPLEQ_FOREACH ,
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.Nm SIMPLEQ_FOREACH_SAFE ,
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.Nm SIMPLEQ_INIT ,
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.Nm SIMPLEQ_INSERT_AFTER ,
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.Nm SIMPLEQ_INSERT_HEAD ,
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.Nm SIMPLEQ_INSERT_TAIL ,
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.Nm SIMPLEQ_REMOVE_AFTER ,
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.Nm SIMPLEQ_REMOVE_HEAD ,
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.Nm TAILQ_ENTRY ,
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.Nm TAILQ_HEAD ,
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.Nm TAILQ_HEAD_INITIALIZER ,
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.Nm TAILQ_FIRST ,
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.Nm TAILQ_NEXT ,
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.Nm TAILQ_LAST ,
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.Nm TAILQ_PREV ,
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.Nm TAILQ_EMPTY ,
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.Nm TAILQ_FOREACH ,
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.Nm TAILQ_FOREACH_SAFE ,
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.Nm TAILQ_FOREACH_REVERSE ,
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.Nm TAILQ_FOREACH_REVERSE_SAFE ,
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.Nm TAILQ_INIT ,
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.Nm TAILQ_INSERT_AFTER ,
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.Nm TAILQ_INSERT_BEFORE ,
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.Nm TAILQ_INSERT_HEAD ,
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.Nm TAILQ_INSERT_TAIL ,
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.Nm TAILQ_REMOVE ,
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.Nm TAILQ_REPLACE
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.Nd implementations of singly-linked lists, doubly-linked lists, simple queues, and tail queues
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.Sh SYNOPSIS
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.In sys/queue.h
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.Pp
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.Fn SLIST_ENTRY "TYPE"
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.Fn SLIST_HEAD "HEADNAME" "TYPE"
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.Fn SLIST_HEAD_INITIALIZER "SLIST_HEAD head"
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.Ft "struct TYPE *"
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.Fn SLIST_FIRST "SLIST_HEAD *head"
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.Ft "struct TYPE *"
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.Fn SLIST_NEXT "struct TYPE *listelm" "FIELDNAME"
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.Ft int
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.Fn SLIST_EMPTY "SLIST_HEAD *head"
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.Fn SLIST_FOREACH "VARNAME" "SLIST_HEAD *head" "FIELDNAME"
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.Fn SLIST_FOREACH_SAFE "VARNAME" "SLIST_HEAD *head" "FIELDNAME" "TEMP_VARNAME"
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.Ft void
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.Fn SLIST_INIT "SLIST_HEAD *head"
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.Ft void
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.Fn SLIST_INSERT_AFTER "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SLIST_INSERT_HEAD "SLIST_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SLIST_REMOVE_AFTER "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SLIST_REMOVE_HEAD "SLIST_HEAD *head" "FIELDNAME"
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.Ft void
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.Fn SLIST_REMOVE "SLIST_HEAD *head" "struct TYPE *elm" "TYPE" "FIELDNAME"
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.Pp
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.Fn LIST_ENTRY "TYPE"
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.Fn LIST_HEAD "HEADNAME" "TYPE"
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.Fn LIST_HEAD_INITIALIZER "LIST_HEAD head"
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.Ft "struct TYPE *"
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.Fn LIST_FIRST "LIST_HEAD *head"
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.Ft "struct TYPE *"
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.Fn LIST_NEXT "struct TYPE *listelm" "FIELDNAME"
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.Ft int
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.Fn LIST_EMPTY "LIST_HEAD *head"
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.Fn LIST_FOREACH "VARNAME" "LIST_HEAD *head" "FIELDNAME"
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.Fn LIST_FOREACH_SAFE "VARNAME" "LIST_HEAD *head" "FIELDNAME" "TEMP_VARNAME"
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.Ft void
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.Fn LIST_INIT "LIST_HEAD *head"
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.Ft void
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.Fn LIST_INSERT_AFTER "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn LIST_INSERT_BEFORE "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn LIST_INSERT_HEAD "LIST_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn LIST_REMOVE "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn LIST_REPLACE "struct TYPE *elm" "struct TYPE *elm2" "FIELDNAME"
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.Pp
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.Fn SIMPLEQ_ENTRY "TYPE"
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.Fn SIMPLEQ_HEAD "HEADNAME" "TYPE"
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.Fn SIMPLEQ_HEAD_INITIALIZER "SIMPLEQ_HEAD head"
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.Ft "struct TYPE *"
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.Fn SIMPLEQ_FIRST "SIMPLEQ_HEAD *head"
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.Ft "struct TYPE *"
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.Fn SIMPLEQ_NEXT "struct TYPE *listelm" "FIELDNAME"
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.Ft int
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.Fn SIMPLEQ_EMPTY "SIMPLEQ_HEAD *head"
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.Fn SIMPLEQ_FOREACH "VARNAME" "SIMPLEQ_HEAD *head" "FIELDNAME"
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.Fn SIMPLEQ_FOREACH_SAFE "VARNAME" "SIMPLEQ_HEAD *head" "FIELDNAME" "TEMP_VARNAME"
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.Ft void
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.Fn SIMPLEQ_INIT "SIMPLEQ_HEAD *head"
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.Ft void
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.Fn SIMPLEQ_INSERT_AFTER "SIMPLEQ_HEAD *head" "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SIMPLEQ_INSERT_HEAD "SIMPLEQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SIMPLEQ_INSERT_TAIL "SIMPLEQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SIMPLEQ_REMOVE_AFTER "SIMPLEQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn SIMPLEQ_REMOVE_HEAD "SIMPLEQ_HEAD *head" "FIELDNAME"
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.Pp
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.Fn TAILQ_ENTRY "TYPE"
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.Fn TAILQ_HEAD "HEADNAME" "TYPE"
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.Fn TAILQ_HEAD_INITIALIZER "TAILQ_HEAD head"
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.Ft "struct TYPE *"
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.Fn TAILQ_FIRST "TAILQ_HEAD *head"
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.Ft "struct TYPE *"
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.Fn TAILQ_NEXT "struct TYPE *listelm" "FIELDNAME"
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.Ft "struct TYPE *"
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.Fn TAILQ_LAST "TAILQ_HEAD *head" "HEADNAME"
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.Ft "struct TYPE *"
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.Fn TAILQ_PREV "struct TYPE *listelm" "HEADNAME" "FIELDNAME"
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.Ft int
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.Fn TAILQ_EMPTY "TAILQ_HEAD *head"
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.Fn TAILQ_FOREACH "VARNAME" "TAILQ_HEAD *head" "FIELDNAME"
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.Fn TAILQ_FOREACH_SAFE "VARNAME" "TAILQ_HEAD *head" "FIELDNAME" "TEMP_VARNAME"
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.Fn TAILQ_FOREACH_REVERSE "VARNAME" "TAILQ_HEAD *head" "HEADNAME" "FIELDNAME"
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.Fn TAILQ_FOREACH_REVERSE_SAFE "VARNAME" "TAILQ_HEAD *head" "HEADNAME" "FIELDNAME" "TEMP_VARNAME"
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.Ft void
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.Fn TAILQ_INIT "TAILQ_HEAD *head"
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.Ft void
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.Fn TAILQ_INSERT_AFTER "TAILQ_HEAD *head" "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn TAILQ_INSERT_BEFORE "struct TYPE *listelm" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn TAILQ_INSERT_HEAD "TAILQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn TAILQ_INSERT_TAIL "TAILQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn TAILQ_REMOVE "TAILQ_HEAD *head" "struct TYPE *elm" "FIELDNAME"
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.Ft void
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.Fn TAILQ_REPLACE "TAILQ_HEAD *head" "struct TYPE *elm" "struct TYPE *elm2" "FIELDNAME"
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.Sh DESCRIPTION
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These macros define and operate on four types of data structures:
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singly-linked lists, simple queues, lists, and tail queues.
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All four structures support the following functionality:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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Insertion of a new entry at the head of the list.
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.It
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Insertion of a new entry after any element in the list.
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.It
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Removal of an entry from the head of the list.
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.It
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Forward traversal through the list.
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.El
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.Pp
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Singly-linked lists are the simplest of the four data structures
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and support only the above functionality.
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Singly-linked lists are ideal for applications with large datasets
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and few or no removals, or for implementing a LIFO queue.
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.Pp
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Simple queues add the following functionality:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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Entries can be added at the end of a list.
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.El
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.Pp
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However:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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All list insertions must specify the head of the list.
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.It
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Each head entry requires two pointers rather than one.
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.It
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Code size is about 15% greater and operations run about 20% slower
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than singly-linked lists.
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.El
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.Pp
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Simple queues are ideal for applications with large datasets and
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few or no removals, or for implementing a FIFO queue.
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.Pp
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All doubly linked types of data structures (lists and tail queues)
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additionally allow:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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Insertion of a new entry before any element in the list.
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.It
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Removal of any entry in the list.
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.El
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.Pp
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However:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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Each element requires two pointers rather than one.
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.It
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Code size and execution time of operations (except for removal) is about
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twice that of the singly-linked data-structures.
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.El
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.Pp
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Lists are the simplest of the doubly linked data structures and support
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only the above functionality over singly-linked lists.
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.Pp
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Tail queues add the following functionality:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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Entries can be added at the end of a list.
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.It
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They may be traversed backwards, at a cost.
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.El
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.Pp
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However:
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.Pp
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.Bl -enum -compact -offset indent
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.It
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All list insertions and removals must specify the head of the list.
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.It
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Each head entry requires two pointers rather than one.
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.It
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Code size is about 15% greater and operations run about 20% slower
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than singly-linked lists.
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.El
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.Pp
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An additional type of data structure, circular queues, violated the C
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language aliasing rules and were miscompiled as a result.
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All code using them should be converted to another structure;
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tail queues are usually the easiest to convert to.
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.Pp
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In the macro definitions,
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.Fa TYPE
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is the name tag of a user defined structure that must contain a field of type
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.Li SLIST_ENTRY ,
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.Li LIST_ENTRY ,
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.Li SIMPLEQ_ENTRY ,
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or
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.Li TAILQ_ENTRY ,
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named
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.Fa FIELDNAME .
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The argument
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.Fa HEADNAME
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is the name tag of a user defined structure that must be declared
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using the macros
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.Fn SLIST_HEAD ,
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.Fn LIST_HEAD ,
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.Fn SIMPLEQ_HEAD ,
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or
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.Fn TAILQ_HEAD .
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See the examples below for further explanation of how these macros are used.
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.Sh SINGLY-LINKED LISTS
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A singly-linked list is headed by a structure defined by the
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.Fn SLIST_HEAD
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macro.
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This structure contains a single pointer to the first element on the list.
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The elements are singly linked for minimum space and pointer manipulation
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overhead at the expense of O(n) removal for arbitrary elements.
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New elements can be added to the list after an existing element or
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at the head of the list.
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A
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.Fa SLIST_HEAD
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structure is declared as follows:
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.Bd -literal -offset indent
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SLIST_HEAD(HEADNAME, TYPE) head;
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.Ed
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.Pp
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where
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.Fa HEADNAME
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is the name of the structure to be defined, and struct
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.Fa TYPE
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is the type of the elements to be linked into the list.
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A pointer to the head of the list can later be declared as:
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.Bd -literal -offset indent
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struct HEADNAME *headp;
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.Ed
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.Pp
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(The names
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.Li head
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and
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.Li headp
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are user selectable.)
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.Pp
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The
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.Fa HEADNAME
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facility is often not used, leading to the following bizarre code:
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.Bd -literal -offset indent
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SLIST_HEAD(, TYPE) head, *headp;
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.Ed
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.Pp
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The
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.Fn SLIST_ENTRY
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macro declares a structure that connects the elements in the list.
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.Pp
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The
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.Fn SLIST_INIT
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macro initializes the list referenced by
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.Fa head .
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.Pp
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The list can also be initialized statically by using the
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.Fn SLIST_HEAD_INITIALIZER
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macro like this:
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.Bd -literal -offset indent
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SLIST_HEAD(HEADNAME, TYPE) head = SLIST_HEAD_INITIALIZER(head);
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.Ed
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.Pp
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The
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.Fn SLIST_INSERT_HEAD
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macro inserts the new element
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.Fa elm
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at the head of the list.
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.Pp
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The
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.Fn SLIST_INSERT_AFTER
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macro inserts the new element
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.Fa elm
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after the element
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.Fa listelm .
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.Pp
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The
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.Fn SLIST_REMOVE_HEAD
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macro removes the first element of the list pointed by
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.Fa head .
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.Pp
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The
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.Fn SLIST_REMOVE_AFTER
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macro removes the list element immediately following
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.Fa elm .
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.Pp
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The
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.Fn SLIST_REMOVE
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macro removes the element
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.Fa elm
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of the list pointed by
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.Fa head .
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.Pp
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|
The
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.Fn SLIST_FIRST
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and
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.Fn SLIST_NEXT
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macros can be used to traverse the list:
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.Bd -literal -offset indent
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for (np = SLIST_FIRST(&head); np != NULL; np = SLIST_NEXT(np, FIELDNAME))
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.Ed
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.Pp
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|
Or, for simplicity, one can use the
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.Fn SLIST_FOREACH
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macro:
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.Bd -literal -offset indent
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SLIST_FOREACH(np, head, FIELDNAME)
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.Ed
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.Pp
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|
The macro
|
|
.Fn SLIST_FOREACH_SAFE
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traverses the list referenced by head in a
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forward direction, assigning each element in turn to var.
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|
However, unlike
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|
.Fn SLIST_FOREACH
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|
it is permitted to remove var as well
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|
as free it from within the loop safely without interfering with the traversal.
|
|
.Pp
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|
The
|
|
.Fn SLIST_EMPTY
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macro should be used to check whether a simple list is empty.
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|
.Sh SINGLY-LINKED LIST EXAMPLE
|
|
.Bd -literal
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|
SLIST_HEAD(listhead, entry) head;
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struct entry {
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...
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SLIST_ENTRY(entry) entries; /* Simple list. */
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...
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} *n1, *n2, *np;
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SLIST_INIT(&head); /* Initialize simple list. */
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n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
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SLIST_INSERT_HEAD(&head, n1, entries);
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n2 = malloc(sizeof(struct entry)); /* Insert after. */
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SLIST_INSERT_AFTER(n1, n2, entries);
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SLIST_FOREACH(np, &head, entries) /* Forward traversal. */
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np-> ...
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while (!SLIST_EMPTY(&head)) { /* Delete. */
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n1 = SLIST_FIRST(&head);
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SLIST_REMOVE_HEAD(&head, entries);
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free(n1);
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}
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|
.Ed
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|
.Sh LISTS
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|
A list is headed by a structure defined by the
|
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.Fn LIST_HEAD
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macro.
|
|
This structure contains a single pointer to the first element on the list.
|
|
The elements are doubly linked so that an arbitrary element can be
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|
removed without traversing the list.
|
|
New elements can be added to the list after an existing element,
|
|
before an existing element, or at the head of the list.
|
|
A
|
|
.Fa LIST_HEAD
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|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
LIST_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa HEADNAME
|
|
is the name of the structure to be defined, and struct
|
|
.Fa TYPE
|
|
is the type of the elements to be linked into the list.
|
|
A pointer to the head of the list can later be declared as:
|
|
.Bd -literal -offset indent
|
|
struct HEADNAME *headp;
|
|
.Ed
|
|
.Pp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The
|
|
.Fa HEADNAME
|
|
facility is often not used, leading to the following bizarre code:
|
|
.Bd -literal -offset indent
|
|
LIST_HEAD(, TYPE) head, *headp;
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fn LIST_ENTRY
|
|
macro declares a structure that connects the elements in the list.
|
|
.Pp
|
|
The
|
|
.Fn LIST_INIT
|
|
macro initializes the list referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The list can also be initialized statically by using the
|
|
.Fn LIST_HEAD_INITIALIZER
|
|
macro like this:
|
|
.Bd -literal -offset indent
|
|
LIST_HEAD(HEADNAME, TYPE) head = LIST_HEAD_INITIALIZER(head);
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fn LIST_INSERT_HEAD
|
|
macro inserts the new element
|
|
.Fa elm
|
|
at the head of the list.
|
|
.Pp
|
|
The
|
|
.Fn LIST_INSERT_AFTER
|
|
macro inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The
|
|
.Fn LIST_INSERT_BEFORE
|
|
macro inserts the new element
|
|
.Fa elm
|
|
before the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The
|
|
.Fn LIST_REMOVE
|
|
macro removes the element
|
|
.Fa elm
|
|
from the list.
|
|
.Pp
|
|
The
|
|
.Fn LIST_REPLACE
|
|
macro replaces the list element
|
|
.Fa elm
|
|
with the new element
|
|
.Fa elm2 .
|
|
.Pp
|
|
The
|
|
.Fn LIST_FIRST
|
|
and
|
|
.Fn LIST_NEXT
|
|
macros can be used to traverse the list:
|
|
.Bd -literal -offset indent
|
|
for (np = LIST_FIRST(&head); np != NULL; np = LIST_NEXT(np, FIELDNAME))
|
|
.Ed
|
|
.Pp
|
|
Or, for simplicity, one can use the
|
|
.Fn LIST_FOREACH
|
|
macro:
|
|
.Bd -literal -offset indent
|
|
LIST_FOREACH(np, head, FIELDNAME)
|
|
.Ed
|
|
.Pp
|
|
The macro
|
|
.Fn LIST_FOREACH_SAFE
|
|
traverses the list referenced by head in a
|
|
forward direction, assigning each element in turn to var.
|
|
However, unlike
|
|
.Fn LIST_FOREACH
|
|
it is permitted to remove var as well
|
|
as free it from within the loop safely without interfering with the traversal.
|
|
.Pp
|
|
The
|
|
.Fn LIST_EMPTY
|
|
macro should be used to check whether a list is empty.
|
|
.Sh LIST EXAMPLE
|
|
.Bd -literal
|
|
LIST_HEAD(listhead, entry) head;
|
|
struct entry {
|
|
...
|
|
LIST_ENTRY(entry) entries; /* List. */
|
|
...
|
|
} *n1, *n2, *np;
|
|
|
|
LIST_INIT(&head); /* Initialize list. */
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
|
|
LIST_INSERT_HEAD(&head, n1, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert after. */
|
|
LIST_INSERT_AFTER(n1, n2, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert before. */
|
|
LIST_INSERT_BEFORE(n1, n2, entries);
|
|
/* Forward traversal. */
|
|
LIST_FOREACH(np, &head, entries)
|
|
np-> ...
|
|
|
|
while (!LIST_EMPTY(&head)) /* Delete. */
|
|
n1 = LIST_FIRST(&head);
|
|
LIST_REMOVE(n1, entries);
|
|
free(n1);
|
|
}
|
|
.Ed
|
|
.Sh SIMPLE QUEUES
|
|
A simple queue is headed by a structure defined by the
|
|
.Fn SIMPLEQ_HEAD
|
|
macro.
|
|
This structure contains a pair of pointers, one to the first element in the
|
|
simple queue and the other to the last element in the simple queue.
|
|
The elements are singly linked.
|
|
New elements can be added to the queue after an existing element,
|
|
at the head of the queue or at the tail of the queue.
|
|
A
|
|
.Fa SIMPLEQ_HEAD
|
|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
SIMPLEQ_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa HEADNAME
|
|
is the name of the structure to be defined, and struct
|
|
.Fa TYPE
|
|
is the type of the elements to be linked into the queue.
|
|
A pointer to the head of the queue can later be declared as:
|
|
.Bd -literal -offset indent
|
|
struct HEADNAME *headp;
|
|
.Ed
|
|
.Pp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_ENTRY
|
|
macro declares a structure that connects the elements in
|
|
the queue.
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_INIT
|
|
macro initializes the queue referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The queue can also be initialized statically by using the
|
|
.Fn SIMPLEQ_HEAD_INITIALIZER
|
|
macro like this:
|
|
.Bd -literal -offset indent
|
|
SIMPLEQ_HEAD(HEADNAME, TYPE) head = SIMPLEQ_HEAD_INITIALIZER(head);
|
|
.Ed
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_INSERT_AFTER
|
|
macro inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_INSERT_HEAD
|
|
macro inserts the new element
|
|
.Fa elm
|
|
at the head of the queue.
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_INSERT_TAIL
|
|
macro inserts the new element
|
|
.Fa elm
|
|
at the end of the queue.
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_REMOVE_AFTER
|
|
macro removes the queue element immediately following
|
|
.Fa elm .
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_REMOVE_HEAD
|
|
macro removes the first element
|
|
from the queue.
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_FIRST
|
|
and
|
|
.Fn SIMPLEQ_NEXT
|
|
macros can be used to traverse the queue.
|
|
The
|
|
.Fn SIMPLEQ_FOREACH
|
|
is used for queue traversal:
|
|
.Bd -literal -offset indent
|
|
SIMPLEQ_FOREACH(np, head, FIELDNAME)
|
|
.Ed
|
|
.Pp
|
|
The macro
|
|
.Fn SIMPLEQ_FOREACH_SAFE
|
|
traverses the queue referenced by head in a
|
|
forward direction, assigning each element in turn to var.
|
|
However, unlike
|
|
.Fn SIMPLEQ_FOREACH
|
|
it is permitted to remove var as well
|
|
as free it from within the loop safely without interfering with the traversal.
|
|
.Pp
|
|
The
|
|
.Fn SIMPLEQ_EMPTY
|
|
macro should be used to check whether a list is empty.
|
|
.Sh SIMPLE QUEUE EXAMPLE
|
|
.Bd -literal
|
|
SIMPLEQ_HEAD(listhead, entry) head = SIMPLEQ_HEAD_INITIALIZER(head);
|
|
struct entry {
|
|
...
|
|
SIMPLEQ_ENTRY(entry) entries; /* Simple queue. */
|
|
...
|
|
} *n1, *n2, *np;
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
|
|
SIMPLEQ_INSERT_HEAD(&head, n1, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert after. */
|
|
SIMPLEQ_INSERT_AFTER(&head, n1, n2, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert at the tail. */
|
|
SIMPLEQ_INSERT_TAIL(&head, n2, entries);
|
|
/* Forward traversal. */
|
|
SIMPLEQ_FOREACH(np, &head, entries)
|
|
np-> ...
|
|
/* Delete. */
|
|
while (!SIMPLEQ_EMPTY(&head)) {
|
|
n1 = SIMPLEQ_FIRST(&head);
|
|
SIMPLEQ_REMOVE_HEAD(&head, entries);
|
|
free(n1);
|
|
}
|
|
.Ed
|
|
.Sh TAIL QUEUES
|
|
A tail queue is headed by a structure defined by the
|
|
.Fn TAILQ_HEAD
|
|
macro.
|
|
This structure contains a pair of pointers,
|
|
one to the first element in the tail queue and the other to
|
|
the last element in the tail queue.
|
|
The elements are doubly linked so that an arbitrary element can be
|
|
removed without traversing the tail queue.
|
|
New elements can be added to the queue after an existing element,
|
|
before an existing element, at the head of the queue, or at the end
|
|
of the queue.
|
|
A
|
|
.Fa TAILQ_HEAD
|
|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
TAILQ_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.Pp
|
|
where
|
|
.Fa HEADNAME
|
|
is the name of the structure to be defined, and struct
|
|
.Fa TYPE
|
|
is the type of the elements to be linked into the tail queue.
|
|
A pointer to the head of the tail queue can later be declared as:
|
|
.Bd -literal -offset indent
|
|
struct HEADNAME *headp;
|
|
.Ed
|
|
.Pp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_ENTRY
|
|
macro declares a structure that connects the elements in
|
|
the tail queue.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_INIT
|
|
macro initializes the tail queue referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The tail queue can also be initialized statically by using the
|
|
.Fn TAILQ_HEAD_INITIALIZER
|
|
macro.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_INSERT_HEAD
|
|
macro inserts the new element
|
|
.Fa elm
|
|
at the head of the tail queue.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_INSERT_TAIL
|
|
macro inserts the new element
|
|
.Fa elm
|
|
at the end of the tail queue.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_INSERT_AFTER
|
|
macro inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_INSERT_BEFORE
|
|
macro inserts the new element
|
|
.Fa elm
|
|
before the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_REMOVE
|
|
macro removes the element
|
|
.Fa elm
|
|
from the tail queue.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_REPLACE
|
|
macro replaces the list element
|
|
.Fa elm
|
|
with the new element
|
|
.Fa elm2 .
|
|
.Pp
|
|
.Fn TAILQ_FOREACH
|
|
and
|
|
.Fn TAILQ_FOREACH_REVERSE
|
|
are used for traversing a tail queue.
|
|
.Fn TAILQ_FOREACH
|
|
starts at the first element and proceeds towards the last.
|
|
.Fn TAILQ_FOREACH_REVERSE
|
|
starts at the last element and proceeds towards the first.
|
|
.Bd -literal -offset indent
|
|
TAILQ_FOREACH(np, &head, FIELDNAME)
|
|
TAILQ_FOREACH_REVERSE(np, &head, HEADNAME, FIELDNAME)
|
|
.Ed
|
|
.Pp
|
|
The macros
|
|
.Fn TAILQ_FOREACH_SAFE
|
|
and
|
|
.Fn TAILQ_FOREACH_REVERSE_SAFE
|
|
traverse the list referenced by head
|
|
in a forward or reverse direction respectively,
|
|
assigning each element in turn to var.
|
|
However, unlike their unsafe counterparts,
|
|
they permit both the removal of var
|
|
as well as freeing it from within the loop safely
|
|
without interfering with the traversal.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_FIRST ,
|
|
.Fn TAILQ_NEXT ,
|
|
.Fn TAILQ_LAST
|
|
and
|
|
.Fn TAILQ_PREV
|
|
macros can be used to manually traverse a tail queue or an arbitrary part of
|
|
one.
|
|
.Pp
|
|
The
|
|
.Fn TAILQ_EMPTY
|
|
macro should be used to check whether a tail queue is empty.
|
|
.Sh TAIL QUEUE EXAMPLE
|
|
.Bd -literal
|
|
TAILQ_HEAD(tailhead, entry) head;
|
|
struct entry {
|
|
...
|
|
TAILQ_ENTRY(entry) entries; /* Tail queue. */
|
|
...
|
|
} *n1, *n2, *np;
|
|
|
|
TAILQ_INIT(&head); /* Initialize queue. */
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
|
|
TAILQ_INSERT_HEAD(&head, n1, entries);
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */
|
|
TAILQ_INSERT_TAIL(&head, n1, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert after. */
|
|
TAILQ_INSERT_AFTER(&head, n1, n2, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert before. */
|
|
TAILQ_INSERT_BEFORE(n1, n2, entries);
|
|
/* Forward traversal. */
|
|
TAILQ_FOREACH(np, &head, entries)
|
|
np-> ...
|
|
/* Manual forward traversal. */
|
|
for (np = n2; np != NULL; np = TAILQ_NEXT(np, entries))
|
|
np-> ...
|
|
/* Delete. */
|
|
while ((np = TAILQ_FIRST(&head))) {
|
|
TAILQ_REMOVE(&head, np, entries);
|
|
free(np);
|
|
}
|
|
|
|
.Ed
|
|
.Sh NOTES
|
|
It is an error to assume the next and previous fields are preserved
|
|
after an element has been removed from a list or queue.
|
|
Using any macro (except the various forms of insertion) on an element
|
|
removed from a list or queue is incorrect.
|
|
An example of erroneous usage is removing the same element twice.
|
|
.Pp
|
|
The
|
|
.Fn SLIST_END ,
|
|
.Fn LIST_END ,
|
|
.Fn SIMPLEQ_END
|
|
and
|
|
.Fn TAILQ_END
|
|
macros are deprecated; they provided symmetry with the historical
|
|
.Fn CIRCLEQ_END
|
|
and just expand to
|
|
.Dv NULL .
|
|
.Pp
|
|
Trying to free a list in the following way is a common error:
|
|
.Bd -literal -offset indent
|
|
LIST_FOREACH(var, head, entry)
|
|
free(var);
|
|
free(head);
|
|
.Ed
|
|
.Pp
|
|
Since
|
|
.Va var
|
|
is free'd, the FOREACH macros refer to a pointer that may have been
|
|
reallocated already.
|
|
A similar situation occurs when the current element is deleted
|
|
from the list.
|
|
In cases like these the data structure's FOREACH_SAFE macros should be used
|
|
instead.
|
|
.Sh HISTORY
|
|
The
|
|
.Nm queue
|
|
functions first appeared in
|
|
.Bx 4.4 .
|
|
The historical circle queue macros were deprecated in
|
|
.Ox 5.5 .
|