840 lines
21 KiB
Groff
840 lines
21 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. 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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. 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 8.2 (Berkeley) 1/24/94
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.\"
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.Dd "January 24, 1994"
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.Dt QUEUE 3
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.Os BSD 4
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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_INIT ,
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.Nm SLIST_INSERT_AFTER ,
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.Nm SLIST_INSERT_HEAD ,
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.Nm SLIST_REMOVE_HEAD ,
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.Nm SLIST_REMOVE ,
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.Nm STAILQ_ENTRY ,
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.Nm STAILQ_HEAD ,
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.Nm STAILQ_INIT ,
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.Nm STAILQ_INSERT_AFTER ,
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.Nm STAILQ_INSERT_HEAD ,
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.Nm STAILQ_INSERT_TAIL ,
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.Nm STAILQ_REMOVE_HEAD ,
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.Nm STAILQ_REMOVE ,
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.Nm LIST_ENTRY ,
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.Nm LIST_HEAD ,
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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 TAILQ_ENTRY ,
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.Nm TAILQ_HEAD ,
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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 CIRCLEQ_ENTRY ,
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.Nm CIRCLEQ_HEAD ,
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.Nm CIRCLEQ_INIT ,
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.Nm CIRCLEQ_INSERT_AFTER ,
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.Nm CIRCLEQ_INSERT_BEFORE ,
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.Nm CIRCLEQ_INSERT_HEAD ,
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.Nm CIRCLEQ_INSERT_TAIL ,
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.Nm CIRCLEQ_REMOVE
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.Nd implementations of singly-linked lists, singly-linked tail queues,
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lists, tail queues, and circular queues
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.Sh SYNOPSIS
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.Fd #include <sys/queue.h>
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.sp
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.Fn SLIST_ENTRY "TYPE"
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.Fn SLIST_HEAD "HEADNAME" "TYPE"
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.Fn SLIST_INIT "SLIST_HEAD *head"
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.Fn SLIST_INSERT_AFTER "TYPE *listelm" "TYPE *elm" "SLIST_ENTRY NAME"
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.Fn SLIST_INSERT_HEAD "SLIST_HEAD *head" "TYPE *elm" "SLIST_ENTRY NAME"
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.Fn SLIST_REMOVE_HEAD "SLIST_HEAD *head" "SLIST_ENTRY NAME"
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.Fn SLIST_REMOVE "SLIST_HEAD *head" "TYPE *elm" "TYPE" "SLIST_ENTRY NAME"
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.sp
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.Fn STAILQ_ENTRY "TYPE"
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.Fn STAILQ_HEAD "HEADNAME" "TYPE"
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.Fn STAILQ_INIT "STAILQ_HEAD *head"
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.Fn STAILQ_INSERT_AFTER "STAILQ_HEAD *head" "TYPE *listelm" "TYPE *elm" "STAILQ_ENTRY NAME"
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.Fn STAILQ_INSERT_HEAD "STAILQ_HEAD *head" "TYPE *elm" "STAILQ_ENTRY NAME"
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.Fn STAILQ_INSERT_TAIL "STAILQ_HEAD *head" "TYPE *elm" "STAILQ_ENTRY NAME"
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.Fn STAILQ_REMOVE_HEAD "STAILQ_HEAD *head" "TYPE *elm" "STAILQ_ENTRY NAME"
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.Fn STAILQ_REMOVE "STAILQ_HEAD *head" "TYPE *elm" "TYPE" "STAILQ_ENTRY NAME"
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.sp
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.Fn LIST_ENTRY "TYPE"
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.Fn LIST_HEAD "HEADNAME" "TYPE"
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.Fn LIST_INIT "LIST_HEAD *head"
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.Fn LIST_INSERT_AFTER "TYPE *listelm" "TYPE *elm" "LIST_ENTRY NAME"
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.Fn LIST_INSERT_BEFORE "TYPE *listelm" "TYPE *elm" "LIST_ENTRY NAME"
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.Fn LIST_INSERT_HEAD "LIST_HEAD *head" "TYPE *elm" "LIST_ENTRY NAME"
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.Fn LIST_REMOVE "TYPE *elm" "LIST_ENTRY NAME"
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.sp
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.Fn TAILQ_ENTRY "TYPE"
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.Fn TAILQ_HEAD "HEADNAME" "TYPE"
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.Fn TAILQ_INIT "TAILQ_HEAD *head"
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.Fn TAILQ_INSERT_AFTER "TAILQ_HEAD *head" "TYPE *listelm" "TYPE *elm" "TAILQ_ENTRY NAME"
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.Fn TAILQ_INSERT_BEFORE "TYPE *listelm" "TYPE *elm" "TAILQ_ENTRY NAME"
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.Fn TAILQ_INSERT_HEAD "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME"
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.Fn TAILQ_INSERT_TAIL "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME"
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.Fn TAILQ_REMOVE "TAILQ_HEAD *head" "TYPE *elm" "TAILQ_ENTRY NAME"
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.sp
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.Fn CIRCLEQ_ENTRY "TYPE"
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.Fn CIRCLEQ_HEAD "HEADNAME" "TYPE"
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.Fn CIRCLEQ_INIT "CIRCLEQ_HEAD *head"
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.Fn CIRCLEQ_INSERT_AFTER "CIRCLEQ_HEAD *head" "TYPE *listelm" "TYPE *elm" "CIRCLEQ_ENTRY NAME"
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.Fn CIRCLEQ_INSERT_BEFORE "CIRCLEQ_HEAD *head" "TYPE *listelm" "TYPE *elm" "CIRCLEQ_ENTRY NAME"
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.Fn CIRCLEQ_INSERT_HEAD "CIRCLEQ_HEAD *head" "TYPE *elm" "CIRCLEQ_ENTRY NAME"
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.Fn CIRCLEQ_INSERT_TAIL "CIRCLEQ_HEAD *head" "TYPE *elm" "CIRCLEQ_ENTRY NAME"
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.Fn CIRCLEQ_REMOVE "CIRCLEQ_HEAD *head" "TYPE *elm" "CIRCLEQ_ENTRY NAME"
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.Sh DESCRIPTION
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These macros define and operate on five types of data structures:
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singly-linked lists, singly-linked tail queues, lists, tail queues,
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and circular queues.
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All five structures support the following functionality:
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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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O(1) removal of an entry from the head of the list.
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.It
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O(n) removal of any entry in 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 five 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,
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or for implementing a LIFO queue.
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.Pp
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Singly-linked tail queues add the following functionality:
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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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However:
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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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Singly-linked tailqs are ideal for applications with large datasets and
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few or no removals,
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or for implementing a FIFO queue.
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.Pp
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All doubly linked types of data structures (lists, tail queues, and circle
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queues) additionally allow:
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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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O(1) removal of any entry in the list.
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.El
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However:
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.Bl -enum -compact -offset indent
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.It
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Each elements 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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Linked 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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.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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However:
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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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Circular queues add the following functionality:
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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, from tail to head.
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.El
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However:
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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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The termination condition for traversal is more complex.
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.It
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Code size is about 40% greater and operations run about 45% slower
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than lists.
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.El
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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 of a user defined structure,
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that must contain a field of type
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.Li SLIST_ENTRY ,
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.Li STAILQ_ENTRY ,
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.Li LIST_ENTRY ,
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.Li TAILQ_ENTRY ,
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or
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.Li CIRCLEQ_ENTRY ,
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named
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.Fa NAME .
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The argument
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.Fa HEADNAME
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is the name of a user defined structure that must be declared
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using the macros
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.Li SLIST_HEAD ,
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.Li STAILQ_HEAD ,
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.Li LIST_HEAD ,
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.Li TAILQ_HEAD ,
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or
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.Li CIRCLEQ_HEAD .
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See the examples below for further explanation of how these
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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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.Nm SLIST_HEAD
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macro.
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This structure contains a single pointer to the first element
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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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An
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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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.sp
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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
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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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.sp
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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 macro
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.Nm SLIST_ENTRY
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declares a structure that connects the elements in
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the list.
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.Pp
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The macro
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.Nm SLIST_INIT
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initializes the list referenced by
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.Fa head .
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.Pp
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The macro
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.Nm SLIST_INSERT_HEAD
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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 macro
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.Nm SLIST_INSERT_AFTER
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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 macro
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.Nm SLIST_REMOVE_HEAD
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removes the element
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.Fa elm
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from the head of the list.
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For optimum efficiency,
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elements being removed from the head of the list should explicitly use
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this macro instead of the generic
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.Fa SLIST_REMOVE
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macro.
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.Pp
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The macro
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.Nm SLIST_REMOVE
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removes the element
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.Fa elm
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from the list.
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.Sh SINGLY-LINKED LIST EXAMPLE
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.Bd -literal
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SLIST_HEAD(slisthead, entry) head;
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struct slisthead *headp; /* Singly-linked List head. */
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struct entry {
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...
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SLIST_ENTRY(entry) entries; /* Singly-linked List. */
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...
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} *n1, *n2, *n3, *np;
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SLIST_INIT(&head); /* Initialize the 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_REMOVE(&head, n2, entry, entries);/* Deletion. */
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free(n2);
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n3 = head.slh_first;
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SLIST_REMOVE_HEAD(&head, entries); /* Deletion. */
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free(n3);
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/* Forward traversal. */
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for (np = head.slh_first; np != NULL; np = np->entries.sle_next)
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np-> ...
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while (head.slh_first != NULL) { /* List Deletion. */
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n1 = head.slh_first;
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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 SINGLY-LINKED TAIL QUEUES
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A singly-linked tail queue is headed by a structure defined by the
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.Nm STAILQ_HEAD
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macro.
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This structure contains a pair of pointers,
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one to the first element in the tail queue and the other to
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the last element in the tail queue.
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The elements are singly linked for minimum space and pointer
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manipulation overhead at the expense of O(n) removal for arbitrary
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elements.
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New elements can be added to the tail queue after an existing element,
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at the head of the tail queue, or at the end of the tail queue.
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A
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.Fa STAILQ_HEAD
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structure is declared as follows:
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.Bd -literal -offset indent
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STAILQ_HEAD(HEADNAME, TYPE) head;
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.Ed
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.sp
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where
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.Li HEADNAME
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is the name of the structure to be defined, and
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.Li TYPE
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is the type of the elements to be linked into the tail queue.
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A pointer to the head of the tail queue 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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.sp
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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 macro
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.Nm STAILQ_ENTRY
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declares a structure that connects the elements in
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the tail queue.
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.Pp
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The macro
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.Nm STAILQ_INIT
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initializes the tail queue referenced by
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.Fa head .
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.Pp
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The macro
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.Nm STAILQ_INSERT_HEAD
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inserts the new element
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.Fa elm
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at the head of the tail queue.
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.Pp
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The macro
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.Nm STAILQ_INSERT_TAIL
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inserts the new element
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.Fa elm
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at the end of the tail queue.
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.Pp
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The macro
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.Nm STAILQ_INSERT_AFTER
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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 macro
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.Nm STAILQ_REMOVE_HEAD
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removes the element
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.Fa elm
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from the head of the tail queue.
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For optimum efficiency,
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elements being removed from the head of the tail queue should
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use this macro explicitly rather than the generic
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.Fa STAILQ_REMOVE
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macro.
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.Pp
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The macro
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.Nm STAILQ_REMOVE
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removes the element
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.Fa elm
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from the tail queue.
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.Sh SINGLY-LINKED TAIL QUEUE EXAMPLE
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.Bd -literal
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STAILQ_HEAD(stailhead, entry) head;
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struct stailhead *headp; /* Singly-linked tail queue head. */
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struct entry {
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...
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STAILQ_ENTRY(entry) entries; /* Tail queue. */
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...
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} *n1, *n2, *n3, *np;
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STAILQ_INIT(&head); /* Initialize the queue. */
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n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
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STAILQ_INSERT_HEAD(&head, n1, entries);
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n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */
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STAILQ_INSERT_TAIL(&head, n1, entries);
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n2 = malloc(sizeof(struct entry)); /* Insert after. */
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STAILQ_INSERT_AFTER(&head, n1, n2, entries);
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/* Deletion. */
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STAILQ_REMOVE(&head, n2, entry, entries);
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free(n2);
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/* Deletion from the head */
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n3 = head.stqh_first;
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STAILQ_REMOVE_HEAD(&head, entries);
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free(n3);
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/* Forward traversal. */
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for (np = head.stqh_first; np != NULL; np = np->entries.stqe_next)
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np-> ...
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/* TailQ Deletion. */
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while (head.stqh_first != NULL) {
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n1 = head.stqh_first;
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TAILQ_REMOVE_HEAD(&head, entries);
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free(n1);
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}
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/* Faster TailQ Deletion. */
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n1 = head.stqh_first;
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while (n1 != NULL) {
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n2 = n1->entries.stqe_next;
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free(n1);
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n1 = n2;
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}
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STAILQ_INIT(&head);
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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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.Nm LIST_HEAD
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macro.
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This structure contains a single pointer to the first element
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on the list.
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The elements are doubly linked so that an arbitrary element can be
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removed without traversing the list.
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New elements can be added to the list after an existing element,
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before an existing element, or at the head of the list.
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A
|
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.Fa LIST_HEAD
|
|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
LIST_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.sp
|
|
where
|
|
.Fa HEADNAME
|
|
is the name of the structure to be defined, and
|
|
.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
|
|
.sp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_ENTRY
|
|
declares a structure that connects the elements in
|
|
the list.
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_INIT
|
|
initializes the list referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_INSERT_HEAD
|
|
inserts the new element
|
|
.Fa elm
|
|
at the head of the list.
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_INSERT_AFTER
|
|
inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_INSERT_BEFORE
|
|
inserts the new element
|
|
.Fa elm
|
|
before the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm LIST_REMOVE
|
|
removes the element
|
|
.Fa elm
|
|
from the list.
|
|
.Sh LIST EXAMPLE
|
|
.Bd -literal
|
|
LIST_HEAD(listhead, entry) head;
|
|
struct listhead *headp; /* List head. */
|
|
struct entry {
|
|
...
|
|
LIST_ENTRY(entry) entries; /* List. */
|
|
...
|
|
} *n1, *n2, *n3, *np;
|
|
|
|
LIST_INIT(&head); /* Initialize the 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);
|
|
|
|
n3 = malloc(sizeof(struct entry)); /* Insert before. */
|
|
LIST_INSERT_BEFORE(n2, n3, entries);
|
|
|
|
LIST_REMOVE(n2, entries); /* Deletion. */
|
|
free(n2);
|
|
|
|
/* Forward traversal. */
|
|
for (np = head.lh_first; np != NULL; np = np->entries.le_next)
|
|
np-> ...
|
|
|
|
while (head.lh_first != NULL) { /* List Deletion. */
|
|
n1 = head.lh_first;
|
|
LIST_REMOVE(n1, entries);
|
|
free(n1);
|
|
}
|
|
|
|
n1 = head.lh_first; /* Faster List Delete. */
|
|
while (n1 != NULL) {
|
|
n2 = n1->entires.le_next;
|
|
free(n1);
|
|
n1 = n2;
|
|
}
|
|
LIST_INIT(&head);
|
|
|
|
.Ed
|
|
.Sh TAIL QUEUES
|
|
A tail queue is headed by a structure defined by the
|
|
.Nm 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 tail queue after an existing element,
|
|
before an existing element, at the head of the tail queue,
|
|
or at the end of the tail queue.
|
|
A
|
|
.Fa TAILQ_HEAD
|
|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
TAILQ_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.sp
|
|
where
|
|
.Li HEADNAME
|
|
is the name of the structure to be defined, and
|
|
.Li 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
|
|
.sp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_ENTRY
|
|
declares a structure that connects the elements in
|
|
the tail queue.
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_INIT
|
|
initializes the tail queue referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_INSERT_HEAD
|
|
inserts the new element
|
|
.Fa elm
|
|
at the head of the tail queue.
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_INSERT_TAIL
|
|
inserts the new element
|
|
.Fa elm
|
|
at the end of the tail queue.
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_INSERT_AFTER
|
|
inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_INSERT_BEFORE
|
|
inserts the new element
|
|
.Fa elm
|
|
before the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm TAILQ_REMOVE
|
|
removes the element
|
|
.Fa elm
|
|
from the tail queue.
|
|
.Sh TAIL QUEUE EXAMPLE
|
|
.Bd -literal
|
|
TAILQ_HEAD(tailhead, entry) head;
|
|
struct tailhead *headp; /* Tail queue head. */
|
|
struct entry {
|
|
...
|
|
TAILQ_ENTRY(entry) entries; /* Tail queue. */
|
|
...
|
|
} *n1, *n2, *n3, *np;
|
|
|
|
TAILQ_INIT(&head); /* Initialize the 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);
|
|
|
|
n3 = malloc(sizeof(struct entry)); /* Insert before. */
|
|
TAILQ_INSERT_BEFORE(n2, n3, entries);
|
|
|
|
TAILQ_REMOVE(&head, n2, entries); /* Deletion. */
|
|
free(n2);
|
|
/* Forward traversal. */
|
|
for (np = head.tqh_first; np != NULL; np = np->entries.tqe_next)
|
|
np-> ...
|
|
/* TailQ Deletion. */
|
|
while (head.tqh_first != NULL) {
|
|
n1 = head.tqh_first;
|
|
TAILQ_REMOVE(&head, head.tqh_first, entries);
|
|
free(n1);
|
|
}
|
|
/* Faster TailQ Deletion. */
|
|
n1 = head.tqh_first;
|
|
while (n1 != NULL) {
|
|
n2 = n1->entries.tqe_next;
|
|
free(n1);
|
|
n1 = n2;
|
|
}
|
|
TAILQ_INIT(&head);
|
|
.Ed
|
|
.Sh CIRCULAR QUEUES
|
|
A circular queue is headed by a structure defined by the
|
|
.Nm CIRCLEQ_HEAD
|
|
macro.
|
|
This structure contains a pair of pointers,
|
|
one to the first element in the circular queue and the other to the
|
|
last element in the circular queue.
|
|
The elements are doubly linked so that an arbitrary element can be
|
|
removed without traversing the 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 CIRCLEQ_HEAD
|
|
structure is declared as follows:
|
|
.Bd -literal -offset indent
|
|
CIRCLEQ_HEAD(HEADNAME, TYPE) head;
|
|
.Ed
|
|
.sp
|
|
where
|
|
.Li HEADNAME
|
|
is the name of the structure to be defined, and
|
|
.Li TYPE
|
|
is the type of the elements to be linked into the circular queue.
|
|
A pointer to the head of the circular queue can later be declared as:
|
|
.Bd -literal -offset indent
|
|
struct HEADNAME *headp;
|
|
.Ed
|
|
.sp
|
|
(The names
|
|
.Li head
|
|
and
|
|
.Li headp
|
|
are user selectable.)
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_ENTRY
|
|
declares a structure that connects the elements in
|
|
the circular queue.
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_INIT
|
|
initializes the circular queue referenced by
|
|
.Fa head .
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_INSERT_HEAD
|
|
inserts the new element
|
|
.Fa elm
|
|
at the head of the circular queue.
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_INSERT_TAIL
|
|
inserts the new element
|
|
.Fa elm
|
|
at the end of the circular queue.
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_INSERT_AFTER
|
|
inserts the new element
|
|
.Fa elm
|
|
after the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_INSERT_BEFORE
|
|
inserts the new element
|
|
.Fa elm
|
|
before the element
|
|
.Fa listelm .
|
|
.Pp
|
|
The macro
|
|
.Nm CIRCLEQ_REMOVE
|
|
removes the element
|
|
.Fa elm
|
|
from the circular queue.
|
|
.Sh CIRCULAR QUEUE EXAMPLE
|
|
.Bd -literal
|
|
CIRCLEQ_HEAD(circleq, entry) head;
|
|
struct circleq *headp; /* Circular queue head. */
|
|
struct entry {
|
|
...
|
|
CIRCLEQ_ENTRY entries; /* Circular queue. */
|
|
...
|
|
} *n1, *n2, *np;
|
|
|
|
CIRCLEQ_INIT(&head); /* Initialize the circular queue. */
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
|
|
CIRCLEQ_INSERT_HEAD(&head, n1, entries);
|
|
|
|
n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */
|
|
CIRCLEQ_INSERT_TAIL(&head, n1, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert after. */
|
|
CIRCLEQ_INSERT_AFTER(&head, n1, n2, entries);
|
|
|
|
n2 = malloc(sizeof(struct entry)); /* Insert before. */
|
|
CIRCLEQ_INSERT_BEFORE(&head, n1, n2, entries);
|
|
|
|
CIRCLEQ_REMOVE(&head, n1, entries); /* Deletion. */
|
|
free(n1);
|
|
/* Forward traversal. */
|
|
for (np = head.cqh_first; np != (void *)&head; np = np->entries.cqe_next)
|
|
np-> ...
|
|
/* Reverse traversal. */
|
|
for (np = head.cqh_last; np != (void *)&head; np = np->entries.cqe_prev)
|
|
np-> ...
|
|
/* CircleQ Deletion. */
|
|
while (head.cqh_first != (void *)&head) {
|
|
n1 = head.cqh_first;
|
|
CIRCLEQ_REMOVE(&head, head.cqh_first, entries);
|
|
free(n1);
|
|
}
|
|
/* Faster CircleQ Deletion. */
|
|
n1 = head.cqh_first;
|
|
while (n1 != (void *)&head) {
|
|
n2 = n1->entries.cqh_next;
|
|
free(n1);
|
|
n1 = n2;
|
|
}
|
|
CIRCLEQ_INIT(&head);
|
|
.Ed
|
|
.Sh HISTORY
|
|
The
|
|
.Nm queue
|
|
functions first appeared in 4.4BSD.
|