mirror of https://github.com/mkerrisk/man-pages
358 lines
9.7 KiB
Groff
358 lines
9.7 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" and Copyright (c) 2020 by Alejandro Colomar <colomar.6.4.3@gmail.com>
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.\"
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.\" %%%LICENSE_START(BSD_3_CLAUSE_UCB)
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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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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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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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.\" %%%LICENSE_END
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.\"
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.\"
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.TH CIRCLEQ 3 2020-10-21 "GNU" "Linux Programmer's Manual"
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.SH NAME
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CIRCLEQ_EMPTY,
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CIRCLEQ_ENTRY,
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CIRCLEQ_FIRST,
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CIRCLEQ_FOREACH,
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CIRCLEQ_FOREACH_REVERSE,
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CIRCLEQ_HEAD,
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CIRCLEQ_HEAD_INITIALIZER,
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CIRCLEQ_INIT,
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CIRCLEQ_INSERT_AFTER,
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CIRCLEQ_INSERT_BEFORE,
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CIRCLEQ_INSERT_HEAD,
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CIRCLEQ_INSERT_TAIL,
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CIRCLEQ_LAST,
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CIRCLEQ_LOOP_NEXT,
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CIRCLEQ_LOOP_PREV,
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CIRCLEQ_NEXT,
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CIRCLEQ_PREV,
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CIRCLEQ_REMOVE
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\- implementation of a doubly linked circular queue
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.SH SYNOPSIS
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.nf
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.B #include <sys/queue.h>
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.PP
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.BI "int CIRCLEQ_EMPTY(CIRCLEQ_HEAD *" head ");"
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.PP
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.B CIRCLEQ_ENTRY(TYPE);
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.PP
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.BI "struct TYPE *CIRCLEQ_FIRST(CIRCLEQ_HEAD *" head ");"
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.PP
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.BI "CIRCLEQ_FOREACH(struct TYPE *" var ", CIRCLEQ_HEAD *" head ,
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "CIRCLEQ_FOREACH_REVERSE(struct TYPE *" var ", CIRCLEQ_HEAD *" head ","
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.B CIRCLEQ_HEAD(HEADNAME, TYPE);
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.PP
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.BI "CIRCLEQ_HEAD CIRCLEQ_HEAD_INITIALIZER(CIRCLEQ_HEAD " head ");"
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.PP
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.BI "void CIRCLEQ_INIT(CIRCLEQ_HEAD *" head ");"
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.PP
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.BI "void CIRCLEQ_INSERT_AFTER(CIRCLEQ_HEAD *" head ", struct TYPE *" listelm ,
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.BI " struct TYPE *" elm ", CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "void CIRCLEQ_INSERT_BEFORE(CIRCLEQ_HEAD *" head ", struct TYPE *" listelm ,
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.BI " struct TYPE *" elm ", CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "void CIRCLEQ_INSERT_HEAD(CIRCLEQ_HEAD *" head ", struct TYPE *" elm ","
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "void CIRCLEQ_INSERT_TAIL(CIRCLEQ_HEAD *" head ", struct TYPE *" elm ","
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "struct TYPE *CIRCLEQ_LAST(CIRCLEQ_HEAD *" head ");"
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.PP
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.BI "void CIRCLEQ_LOOP_NEXT(CIRCLEQ_HEAD *" head ", struct TYPE *" elm ","
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "void CIRCLEQ_LOOP_PREV(CIRCLEQ_HEAD *" head ", struct TYPE *" elm ","
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "struct TYPE *CIRCLEQ_NEXT(struct TYPE *" elm ", CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "struct TYPE *CIRCLEQ_PREV(struct TYPE *" elm ", CIRCLEQ_ENTRY " NAME ");"
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.PP
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.BI "void CIRCLEQ_REMOVE(CIRCLEQ_HEAD *" head ", struct TYPE *" elm ,
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.BI " CIRCLEQ_ENTRY " NAME ");"
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.fi
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.SH DESCRIPTION
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These macros define and operate on doubly linked circular queues.
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.PP
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In the macro definitions,
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.I 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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.IR CIRCLEQ_ENTRY ,
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named
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.IR NAME .
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The argument
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.I HEADNAME
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is the name of a user-defined structure that must be declared
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using the macro
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.BR CIRCLEQ_HEAD ().
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.PP
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A circular queue is headed by a structure defined by the
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.BR CIRCLEQ_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 circular queue and the other to
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the last element in the circular queue.
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The elements are doubly linked so that an arbitrary element can be
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removed without traversing the circular queue.
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New elements can be added to the circular queue after an existing element,
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before an existing element, at the head of the circular queue,
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or at the end of the circular queue.
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A
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.I CIRCLEQ_HEAD
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structure is declared as follows:
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.PP
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.in +4
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.EX
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CIRCLEQ_HEAD(HEADNAME, TYPE) head;
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.EE
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.in
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.PP
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where
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.I struct HEADNAME
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is the structure to be defined, and
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.I struct TYPE
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is the type of the elements to be linked into the circular queue.
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A pointer to the head of the circular queue can later be declared as:
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.PP
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.in +4
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.EX
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struct HEADNAME *headp;
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.EE
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.in
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.PP
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(The names
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.I head
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and
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.I headp
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are user selectable.)
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.PP
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The macro
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.BR CIRCLEQ_HEAD_INITIALIZER ()
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evaluates to an initializer for the circular queue
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.IR head .
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.PP
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The macro
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.BR CIRCLEQ_EMPTY ()
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evaluates to true if there are no items on the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_ENTRY ()
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declares a structure that connects the elements in
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the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_FIRST ()
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returns the first item on the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_FOREACH ()
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traverses the circular queue referenced by
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.I head
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in the forward direction, assigning each element in turn to
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.IR var .
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.I var
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is set to
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.I &head
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if the loop completes normally, or if there were no elements.
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.PP
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The macro
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.BR CIRCLEQ_FOREACH_REVERSE ()
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traverses the circular queue referenced by
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.I head
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in the reverse direction, assigning each element in turn to
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.IR var .
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.PP
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The macro
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.BR CIRCLEQ_INIT ()
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initializes the circular queue referenced by
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.IR head .
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.PP
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The macro
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.BR CIRCLEQ_INSERT_HEAD ()
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inserts the new element
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.I elm
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at the head of the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_INSERT_TAIL ()
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inserts the new element
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.I elm
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at the end of the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_INSERT_AFTER ()
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inserts the new element
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.I elm
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after the element
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.IR listelm .
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.PP
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The macro
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.BR CIRCLEQ_INSERT_BEFORE ()
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inserts the new element
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.I elm
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before the element
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.IR listelm .
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.PP
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The macro
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.BR CIRCLEQ_LAST ()
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returns the last item on the circular queue.
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.PP
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The macro
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.BR CIRCLEQ_NEXT ()
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returns the next item on the circular queue, or
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.I &head
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if this item is the last one.
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.PP
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The macro
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.BR CIRCLEQ_PREV ()
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returns the previous item on the circular queue, or
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.I &head
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if this item is the first one.
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.PP
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The macro
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.BR CIRCLEQ_LOOP_NEXT ()
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returns the next item on the circular queue.
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If
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.I elm
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is the last element on the circular queue, the first element is returned.
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.PP
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The macro
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.BR CIRCLEQ_LOOP_PREV ()
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returns the previous item on the circular queue.
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If
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.I elm
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is the first element on the circular queue, the last element is returned.
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.PP
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The macro
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.BR CIRCLEQ_REMOVE ()
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removes the element
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.I elm
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from the circular queue.
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.SH RETURN VALUE
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.BR CIRCLEQ_EMPTY ()
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returns nonzero if the queue is empty,
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and zero if the queue contains at least one entry.
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.PP
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.BR CIRCLEQ_FIRST (),
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.BR CIRCLEQ_LAST (),
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.BR CIRCLEQ_NEXT (),
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and
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.BR CIRCLEQ_PREV ()
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return a pointer to the first, last, next or previous
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.I TYPE
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structure, respectively.
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.PP
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.BR CIRCLEQ_HEAD_INITIALIZER ()
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returns an initializer that can be assigned to the queue
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.IR head .
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.SH CONFORMING TO
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Not in POSIX.1, POSIX.1-2001 or POSIX.1-2008.
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Present on the BSDs
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(CIRCLEQ macros first appeared in 4.4BSD).
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.SH BUGS
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The macros
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.BR CIRCLEQ_FOREACH ()
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and
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.BR CIRCLEQ_FOREACH_REVERSE ()
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don't allow
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.I var
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to be removed or freed within the loop,
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as it would interfere with the traversal.
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The macros
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.BR CIRCLEQ_FOREACH_SAFE ()
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and
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.BR CIRCLEQ_FOREACH_REVERSE_SAFE (),
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which are present on the BSDs but are not present in glibc,
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fix this limitation by allowing
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.I var
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to safely be removed from the list and freed from within the loop
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without interfering with the traversal.
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.SH EXAMPLES
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.EX
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#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/queue.h>
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struct entry {
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int data;
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CIRCLEQ_ENTRY(entry) entries; /* Queue. */
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};
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CIRCLEQ_HEAD(circlehead, entry);
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int
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main(void)
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{
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struct entry *n1, *n2, *n3, *np;
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struct circlehead head; /* Queue head. */
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int i;
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CIRCLEQ_INIT(&head); /* Initialize the queue. */
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n1 = malloc(sizeof(struct entry)); /* Insert at the head. */
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CIRCLEQ_INSERT_HEAD(&head, n1, entries);
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n1 = malloc(sizeof(struct entry)); /* Insert at the tail. */
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CIRCLEQ_INSERT_TAIL(&head, n1, entries);
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n2 = malloc(sizeof(struct entry)); /* Insert after. */
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CIRCLEQ_INSERT_AFTER(&head, n1, n2, entries);
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n3 = malloc(sizeof(struct entry)); /* Insert before. */
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CIRCLEQ_INSERT_BEFORE(&head, n2, n3, entries);
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CIRCLEQ_REMOVE(&head, n2, entries); /* Deletion. */
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free(n2);
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/* Forward traversal. */
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i = 0;
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CIRCLEQ_FOREACH(np, &head, entries)
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np->data = i++;
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/* Reverse traversal. */
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CIRCLEQ_FOREACH_REVERSE(np, &head, entries)
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printf("%i\en", np->data);
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/* Queue deletion. */
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n1 = CIRCLEQ_FIRST(&head);
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while (n1 != (void *)&head) {
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n2 = CIRCLEQ_NEXT(n1, entries);
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free(n1);
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n1 = n2;
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}
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CIRCLEQ_INIT(&head);
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
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.BR insque (3),
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.BR queue (7)
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