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QUEUE(3)                   Library Functions Manual                   QUEUE(3)

NAME
     SLIST_HEAD, SLIST_HEAD_INITIALIZER, SLIST_ENTRY, SLIST_FIRST,
     SLIST_EMPTY, SLIST_NEXT, SLIST_FOREACH, SLIST_FOREACH_SAFE, SLIST_INIT,
     SLIST_INSERT_AFTER, SLIST_INSERT_HEAD, SLIST_REMOVE_AFTER,
     SLIST_REMOVE_HEAD, SLIST_REMOVE, LIST_HEAD, LIST_HEAD_INITIALIZER,
     LIST_ENTRY, LIST_FIRST, LIST_EMPTY, LIST_NEXT, LIST_FOREACH,
     LIST_FOREACH_SAFE, LIST_INIT, LIST_INSERT_AFTER, LIST_INSERT_BEFORE,
     LIST_INSERT_HEAD, LIST_REMOVE, LIST_REPLACE, LIST_MOVE, SIMPLEQ_HEAD,
     SIMPLEQ_HEAD_INITIALIZER, SIMPLEQ_ENTRY, SIMPLEQ_FIRST, SIMPLEQ_EMPTY,
     SIMPLEQ_NEXT, SIMPLEQ_LAST, SIMPLEQ_FOREACH, SIMPLEQ_FOREACH_SAFE,
     SIMPLEQ_INIT, SIMPLEQ_INSERT_AFTER, SIMPLEQ_INSERT_HEAD,
     SIMPLEQ_INSERT_TAIL, SIMPLEQ_REMOVE_AFTER, SIMPLEQ_REMOVE_HEAD,
     SIMPLEQ_REMOVE, SIMPLEQ_CONCAT, TAILQ_HEAD, TAILQ_HEAD_INITIALIZER,
     TAILQ_ENTRY, TAILQ_FIRST, TAILQ_NEXT, TAILQ_LAST, TAILQ_PREV,
     TAILQ_EMPTY, TAILQ_FOREACH, TAILQ_FOREACH_SAFE, TAILQ_FOREACH_REVERSE,
     TAILQ_FOREACH_REVERSE_SAFE, TAILQ_INIT, TAILQ_INSERT_AFTER,
     TAILQ_INSERT_BEFORE, TAILQ_INSERT_HEAD, TAILQ_INSERT_TAIL, TAILQ_REMOVE,
     TAILQ_REPLACE, TAILQ_CONCAT, STAILQ_HEAD, STAILQ_HEAD_INITIALIZER,
     STAILQ_ENTRY, STAILQ_FIRST, STAILQ_EMPTY, STAILQ_NEXT, STAILQ_LAST,
     STAILQ_FOREACH, STAILQ_FOREACH_SAFE, STAILQ_INIT, STAILQ_INSERT_AFTER,
     STAILQ_INSERT_HEAD, STAILQ_INSERT_TAIL, STAILQ_REMOVE_HEAD,
     STAILQ_REMOVE, STAILQ_CONCAT - implementations of singly-linked lists,
     lists, simple queues, tail queues, and singly-linked tail queues

SYNOPSIS
     #include <sys/queue.h>

     SLIST_HEAD(HEADNAME, TYPE);

     SLIST_HEAD_INITIALIZER(head);

     SLIST_ENTRY(TYPE);

     TYPE *
     SLIST_FIRST(SLIST_HEAD *head);

     int
     SLIST_EMPTY(SLIST_HEAD *head);

     TYPE *
     SLIST_NEXT(TYPE *elm, SLIST_ENTRY NAME);

     SLIST_FOREACH(TYPE *var, SLIST_HEAD *head, SLIST_ENTRY NAME);

     SLIST_FOREACH_SAFE(TYPE *var, SLIST_HEAD *head, SLIST_ENTRY NAME,
         TYPE *tmp);

     SLIST_INIT(SLIST_HEAD *head);

     SLIST_INSERT_HEAD(SLIST_HEAD *head, TYPE *elm, SLIST_ENTRY NAME);

     SLIST_INSERT_AFTER(TYPE *listelm, TYPE *elm, SLIST_ENTRY NAME);

     SLIST_REMOVE(SLIST_HEAD *head, TYPE *elm, TYPE, SLIST_ENTRY NAME);

     SLIST_REMOVE_HEAD(SLIST_HEAD *head, SLIST_ENTRY NAME);

     LIST_HEAD(HEADNAME, TYPE);

     LIST_HEAD_INITIALIZER(head);

     LIST_ENTRY(TYPE);

     TYPE *
     LIST_FIRST(LIST_HEAD *head);

     TYPE *
     LIST_NEXT(TYPE *elm, LIST_ENTRY NAME);

     int
     LIST_EMPTY(LIST_HEAD *head);

     LIST_FOREACH(TYPE *var, LIST_HEAD *head, LIST_ENTRY NAME);

     LIST_FOREACH_SAFE(TYPE *var, LIST_HEAD *head, LIST_ENTRY NAME,
         TYPE *tmp);

     LIST_INIT(LIST_HEAD *head);

     LIST_INSERT_AFTER(TYPE *listelm, TYPE *elm, LIST_ENTRY NAME);

     LIST_INSERT_BEFORE(TYPE *listelm, TYPE *elm, LIST_ENTRY NAME);

     LIST_INSERT_HEAD(LIST_HEAD *head, TYPE *elm, LIST_ENTRY NAME);

     LIST_REMOVE(TYPE *elm, LIST_ENTRY NAME);

     LIST_REPLACE(TYPE *elm, TYPE *new, LIST_ENTRY NAME);

     LIST_MOVE(LIST_HEAD *head1, LIST_HEAD *head2, LIST_ENTRY NAME);

     SIMPLEQ_HEAD(HEADNAME, TYPE);

     SIMPLEQ_HEAD_INITIALIZER(head);

     SIMPLEQ_ENTRY(TYPE);

     TYPE *
     SIMPLEQ_FIRST(SIMPLEQ_HEAD *head);

     int
     SIMPLEQ_EMPTY(SIMPLEQ_HEAD *head);

     TYPE *
     SIMPLEQ_NEXT(TYPE *elm, SIMPLEQ_ENTRY NAME);

     TYPE *
     SIMPLEQ_LAST(SIMPLEQ_HEAD *head, TYPE *elm, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_FOREACH(TYPE *var, SIMPLEQ_HEAD *head, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_FOREACH_SAFE(TYPE *var, SIMPLEQ_HEAD *head, SIMPLEQ_ENTRY NAME,
         TYPE *tmp);

     SIMPLEQ_INIT(SIMPLEQ_HEAD *head);

     SIMPLEQ_INSERT_HEAD(SIMPLEQ_HEAD *head, TYPE *elm, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_INSERT_TAIL(SIMPLEQ_HEAD *head, TYPE *elm, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_INSERT_AFTER(SIMPLEQ_HEAD *head, TYPE *listelm, TYPE *elm,
         SIMPLEQ_ENTRY NAME);

     SIMPLEQ_REMOVE_HEAD(SIMPLEQ_HEAD *head, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_REMOVE_AFTER(SIMPLEQ_HEAD *head, TYPE *elm, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_REMOVE(SIMPLEQ_HEAD *head, TYPE *elm, TYPE, SIMPLEQ_ENTRY NAME);

     SIMPLEQ_CONCAT(SIMPLEQ_HEAD *head1, SIMPLEQ_HEAD *head2);

     TAILQ_HEAD(HEADNAME, TYPE);

     TAILQ_HEAD_INITIALIZER(head);

     TAILQ_ENTRY(TYPE);

     TYPE *
     TAILQ_FIRST(TAILQ_HEAD *head);

     TYPE *
     TAILQ_NEXT(TYPE *elm, TAILQ_ENTRY NAME);

     TYPE *
     TAILQ_LAST(TAILQ_HEAD *head, HEADNAME);

     TYPE *
     TAILQ_PREV(TYPE *elm, HEADNAME, TAILQ_ENTRY NAME);

     int
     TAILQ_EMPTY(TAILQ_HEAD *head);

     TAILQ_FOREACH(TYPE *var, TAILQ_HEAD *head, TAILQ_ENTRY NAME);

     TAILQ_FOREACH_SAFE(TYPE *var, TAILQ_HEAD *head, TAILQ_ENTRY NAME,
         TYPE *tmp);

     TAILQ_FOREACH_REVERSE(TYPE *var, TAILQ_HEAD *head, HEADNAME,
         TAILQ_ENTRY NAME);

     TAILQ_FOREACH_REVERSE_SAFE(TYPE *var, TAILQ_HEAD *head, HEADNAME,
         TAILQ_ENTRY NAME, TYPE *tmp);

     TAILQ_INIT(TAILQ_HEAD *head);

     TAILQ_INSERT_HEAD(TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);

     TAILQ_INSERT_TAIL(TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);

     TAILQ_INSERT_AFTER(TAILQ_HEAD *head, TYPE *listelm, TYPE *elm,
         TAILQ_ENTRY NAME);

     TAILQ_INSERT_BEFORE(TYPE *listelm, TYPE *elm, TAILQ_ENTRY NAME);

     TAILQ_REMOVE(TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);

     TAILQ_REPLACE(TAILQ_HEAD *head, TYPE *elm, TYPE *new, TAILQ_ENTRY NAME);

     TAILQ_CONCAT(TAILQ_HEAD *head1, TAILQ_HEAD *head2, TAILQ_ENTRY NAME);

     STAILQ_HEAD(HEADNAME, TYPE);

     STAILQ_HEAD_INITIALIZER(head);

     STAILQ_ENTRY(TYPE);

     TYPE *
     STAILQ_FIRST(STAILQ_HEAD *head);

     int
     STAILQ_EMPTY(STAILQ_HEAD *head);

     TYPE *
     STAILQ_NEXT(TYPE *elm, STAILQ_ENTRY NAME);

     TYPE *
     STAILQ_LAST(STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);

     STAILQ_FOREACH(TYPE *var, STAILQ_HEAD *head, STAILQ_ENTRY NAME);

     STAILQ_FOREACH_SAFE(TYPE *var, STAILQ_HEAD *head, STAILQ_ENTRY NAME,
         TYPE *tmp);

     STAILQ_INIT(STAILQ_HEAD *head);

     STAILQ_INSERT_HEAD(STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);

     STAILQ_INSERT_TAIL(STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);

     STAILQ_INSERT_AFTER(STAILQ_HEAD *head, TYPE *listelm, TYPE *elm,
         STAILQ_ENTRY NAME);

     STAILQ_REMOVE_HEAD(STAILQ_HEAD *head, STAILQ_ENTRY NAME);

     STAILQ_REMOVE(STAILQ_HEAD *head, TYPE *elm, TYPE, STAILQ_ENTRY NAME);

     STAILQ_CONCAT(STAILQ_HEAD *head1, STAILQ_HEAD *head2);

DESCRIPTION
     These macros define and operate on five types of data structures: singly-
     linked lists, simple queues, lists, tail queues, and singly-linked tail
     queues.  All five structures support the following functionality:
           1.   Insertion of a new entry at the head of the list.
           2.   Insertion of a new entry after any element in the list.
           3.   Removal of any entry in the list.
           4.   Forward traversal through the list.

     Singly-linked lists are the simplest of the four data structures and
     support only the above functionality.  Singly-linked lists are ideal for
     applications with large datasets and few or no removals, or for
     implementing a LIFO queue.

     Simple queues add the following functionality:
           1.   Entries can be added at the end of a list.
           2.   They may be concatenated.
     However:
           1.   Entries may not be added before any element in the list.
           2.   All list insertions and removals must specify the head of the
                list.
           3.   Each head entry requires two pointers rather than one.

     Simple queues are ideal for applications with large datasets and few or
     no removals, or for implementing a FIFO queue.

     All doubly linked types of data structures (lists and tail queues)
     additionally allow:
           1.   Insertion of a new entry before any element in the list.
           2.   O(1) removal of any entry in the list.
     However:
           1.   Each element requires two pointers rather than one.
           2.   Code size and execution time of operations (except for
                removal) is about twice that of the singly-linked data-
                structures.

     Linked lists are the simplest of the doubly linked data structures and
     support only the above functionality over singly-linked lists.

     Tail queues add the following functionality:
           1.   Entries can be added at the end of a list.
           2.   They may be concatenated.
     However:
           1.   All list insertions and removals, except insertion before
                another element, must specify the head of the list.
           2.   Each head entry requires two pointers rather than one.
           3.   Code size is about 15% greater and operations run about 20%
                slower than lists.

     Circular queues add the following functionality:
           1.   Entries can be added at the end of a list.
           2.   They may be traversed backwards, from tail to head.
     However:
           1.   All list insertions and removals must specify the head of the
                list.
           2.   Each head entry requires two pointers rather than one.
           3.   The termination condition for traversal is more complex.
           4.   Code size is about 40% greater and operations run about 45%
                slower than lists.

     In the macro definitions, TYPE is the name of a user defined structure,
     that must contain a field of type SLIST_ENTRY, LIST_ENTRY, SIMPLEQ_ENTRY,
     TAILQ_ENTRY, or STAILQ_ENTRY, named NAME.  The argument HEADNAME is the
     name of a user defined structure that must be declared using the macros
     LIST_HEAD, SIMPLEQ_HEAD, SLIST_HEAD, or TAILQ_HEAD.  See the examples
     below for further explanation of how these macros are used.

   Summary of Operations
     The following table summarizes the supported macros for each type of data
     structure.

     +----------------------+-------+------+---------+-------+--------+
     |                      | SLIST | LIST | SIMPLEQ | TAILQ | STAILQ |
     +----------------------+-------+------+---------+-------+--------+
     |_FIRST                |   +   |  +   |    +    |   +   |   +    |
     |_EMPTY                |   +   |  +   |    +    |   +   |   +    |
     |_NEXT                 |   +   |  +   |    +    |   +   |   +    |
     |_PREV                 |   -   |  -   |    -    |   +   |   -    |
     |_LAST                 |   -   |  -   |    +    |   +   |   +    |
     |_FOREACH              |   +   |  +   |    +    |   +   |   +    |
     |_FOREACH_SAFE         |   +   |  +   |    +    |   +   |   +    |
     |_FOREACH_REVERSE      |   -   |  -   |    -    |   +   |   -    |
     |_FOREACH_REVERSE_SAFE |   -   |  -   |    -    |   +   |   -    |
     |_INSERT_HEAD          |   +   |  +   |    +    |   +   |   +    |
     |_INSERT_AFTER         |   +   |  +   |    +    |   +   |   +    |
     |_INSERT_BEFORE        |   -   |  +   |    -    |   +   |   -    |
     |_INSERT_TAIL          |   -   |  -   |    +    |   +   |   +    |
     |_REMOVE               |   +   |  +   |    +    |   +   |   +    |
     |_REMOVE_HEAD          |   +   |  -   |    +    |   -   |   +    |
     |_REMOVE_AFTER         |   -   |  -   |    +    |   -   |   +    |
     |_REPLACE              |   -   |  +   |    -    |   +   |   -    |
     |_CONCAT               |   -   |  -   |    +    |   +   |   +    |
     +----------------------+-------+------+---------+-------+--------+
SINGLY-LINKED LISTS
     A singly-linked list is headed by a structure defined by the SLIST_HEAD()
     macro.  This structure contains a single pointer to the first element on
     the list.  The elements are singly linked for minimum space and pointer
     manipulation overhead at the expense of O(n) removal for arbitrary
     elements.  New elements can be added to the list after an existing
     element or at the head of the list.  An SLIST_HEAD structure is declared
     as follows:

           SLIST_HEAD(HEADNAME, TYPE) head;

     where HEADNAME is the name of the structure to be defined, and 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:

           struct HEADNAME *headp;

     (The names head and headp are user selectable.)

     The macro SLIST_HEAD_INITIALIZER() evaluates to an initializer for the
     list head.

     The macro SLIST_ENTRY() declares a structure that connects the elements
     in the list.

     The macro SLIST_FIRST() returns the first element in the list or NULL if
     the list is empty.

     The macro SLIST_EMPTY() evaluates to true if there are no elements in the
     list.

     The macro SLIST_NEXT() returns the next element in the list.

     SLIST_FOREACH() traverses the list referenced by head in the forward
     direction, assigning each element in turn to var.

     The SAFE version uses tmp to hold the next element, so var may be freed
     or removed from the list.

     The macro SLIST_INIT() initializes the list referenced by head.

     The macro SLIST_INSERT_HEAD() inserts the new element elm at the head of
     the list.

     The macro SLIST_INSERT_AFTER() inserts the new element elm after the
     element listelm.

     The macro SLIST_REMOVE() removes the element elm from the list.

     The macro SLIST_REMOVE_HEAD() removes the first element from the head of
     the list.  For optimum efficiency, elements being removed from the head
     of the list should explicitly use this macro instead of the generic
     SLIST_REMOVE() macro.

     The macro SLIST_REMOVE_AFTER() removes the element after the one
     specified.  For optimum efficiency, elements being removed after a
     specified one should explicitly use this macro instead of the generic
     SLIST_REMOVE()

SINGLY-LINKED LIST EXAMPLE
     SLIST_HEAD(slisthead, entry) head =
         SLIST_HEAD_INITIALIZER(head);
     struct slisthead *headp;                /* Singly-linked List head. */
     struct entry {
             ...
             SLIST_ENTRY(entry) entries;     /* Singly-linked List. */
             ...
     } *n1, *n2, *n3, *np;

     SLIST_INIT(&head);                      /* Initialize the list. */

     n1 = malloc(sizeof(struct entry));      /* Insert at the head. */
     SLIST_INSERT_HEAD(&head, n1, entries);

     n2 = malloc(sizeof(struct entry));      /* Insert after. */
     SLIST_INSERT_AFTER(n1, n2, entries);

     SLIST_REMOVE(&head, n2, entry, entries);/* Deletion. */
     free(n2);

     n3 = SLIST_FIRST(&head);
     SLIST_REMOVE_HEAD(&head, entries);      /* Deletion from the head. */
     free(n3);

     SLIST_FOREACH(np, &head, entries)       /* Forward traversal. */
             np-> ...

     while (!SLIST_EMPTY(&head)) {           /* List Deletion. */
             n1 = SLIST_FIRST(&head);
             SLIST_REMOVE_HEAD(&head, entries);
             free(n1);
     }

LISTS
     A list is headed by a structure defined by the LIST_HEAD() 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
     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 LIST_HEAD structure is declared as follows:

           LIST_HEAD(HEADNAME, TYPE) head;

     where HEADNAME is the name of the structure to be defined, and 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:

           struct HEADNAME *headp;

     (The names head and headp are user selectable.)

     The macro LIST_ENTRY() declares a st