QUEUE(3)                       Library Routines                       QUEUE(3)




NAME

       SLIST_ENTRY,      SLIST_HEAD,      SLIST_INIT,      SLIST_INSERT_AFTER,
       SLIST_INSERT_HEAD,   SLIST_REMOVE_HEAD,   SLIST_REMOVE,   STAILQ_ENTRY,
       STAILQ_HEAD,   STAILQ_INIT,   STAILQ_INSERT_AFTER,  STAILQ_INSERT_HEAD,
       STAILQ_INSERT_TAIL,  STAILQ_REMOVE_HEAD,   STAILQ_REMOVE,   LIST_ENTRY,
       LIST_HEAD,     LIST_INIT,     LIST_INSERT_AFTER,    LIST_INSERT_BEFORE,
       LIST_INSERT_HEAD,  LIST_REMOVE,  TAILQ_ENTRY,  TAILQ_HEAD,  TAILQ_INIT,
       TAILQ_INSERT_AFTER,       TAILQ_INSERT_BEFORE,       TAILQ_INSERT_HEAD,
       TAILQ_INSERT_TAIL,  TAILQ_REMOVE,  CIRCLEQ_ENTRY,  CIRCLEQ_HEAD,   CIR-
       CLEQ_INIT,     CIRCLEQ_INSERT_AFTER,     CIRCLEQ_INSERT_BEFORE,    CIR-
       CLEQ_INSERT_HEAD, CIRCLEQ_INSERT_TAIL, CIRCLEQ_REMOVE - implementations
       of  singly-linked lists, singly-linked tail queues, lists, tail queues,
       and circular queues


SYNOPSIS

       #include <sys/queue.h>

       SLIST_ENTRY (TYPE);
       SLIST_HEAD (HEADNAME, TYPE);
       SLIST_INIT (SLIST_HEAD *head);
       SLIST_INSERT_AFTER (TYPE *listelm, TYPE *elm, SLIST_ENTRY NAME);
       SLIST_INSERT_HEAD (SLIST_HEAD *head, TYPE *elm, SLIST_ENTRY NAME);
       SLIST_REMOVE_HEAD (SLIST_HEAD *head, SLIST_ENTRY NAME);
       SLIST_REMOVE (SLIST_HEAD *head, TYPE *elm, TYPE, SLIST_ENTRY NAME);

       STAILQ_ENTRY (TYPE);
       STAILQ_HEAD (HEADNAME, TYPE);
       STAILQ_INIT (STAILQ_HEAD *head);
       STAILQ_INSERT_AFTER  (STAILQ_HEAD  *head,  TYPE  *listelm,  TYPE  *elm,
       STAILQ_ENTRY NAME);
       STAILQ_INSERT_HEAD (STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);
       STAILQ_INSERT_TAIL (STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);
       STAILQ_REMOVE_HEAD (STAILQ_HEAD *head, TYPE *elm, STAILQ_ENTRY NAME);
       STAILQ_REMOVE (STAILQ_HEAD *head, TYPE *elm, TYPE, STAILQ_ENTRY NAME);

       LIST_ENTRY (TYPE);
       LIST_HEAD (HEADNAME, TYPE);
       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);

       TAILQ_ENTRY (TYPE);
       TAILQ_HEAD (HEADNAME, TYPE);
       TAILQ_INIT (TAILQ_HEAD *head);
       TAILQ_INSERT_AFTER   (TAILQ_HEAD   *head,  TYPE  *listelm,  TYPE  *elm,
       TAILQ_ENTRY NAME);
       TAILQ_INSERT_BEFORE (TYPE *listelm, TYPE *elm, TAILQ_ENTRY NAME);
       TAILQ_INSERT_HEAD (TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);
       TAILQ_INSERT_TAIL (TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);
       TAILQ_REMOVE (TAILQ_HEAD *head, TYPE *elm, TAILQ_ENTRY NAME);

       CIRCLEQ_ENTRY (TYPE);
       CIRCLEQ_HEAD (HEADNAME, TYPE);
       CIRCLEQ_INIT (CIRCLEQ_HEAD *head);
       CIRCLEQ_INSERT_AFTER (CIRCLEQ_HEAD *head,  TYPE  *listelm,  TYPE  *elm,
       CIRCLEQ_ENTRY NAME);
       CIRCLEQ_INSERT_BEFORE  (CIRCLEQ_HEAD  *head,  TYPE *listelm, TYPE *elm,
       CIRCLEQ_ENTRY NAME);
       CIRCLEQ_INSERT_HEAD  (CIRCLEQ_HEAD  *head,  TYPE  *elm,   CIRCLEQ_ENTRY
       NAME);
       CIRCLEQ_INSERT_TAIL   (CIRCLEQ_HEAD  *head,  TYPE  *elm,  CIRCLEQ_ENTRY
       NAME);
       CIRCLEQ_REMOVE (CIRCLEQ_HEAD *head, TYPE *elm, CIRCLEQ_ENTRY NAME);


DESCRIPTION

       These macros define and operate  on  five  types  of  data  structures:
       singly-linked lists, singly-linked tail queues, lists, tail queues, and
       circular queues.  All five structures support the following functional-
       ity:

              Insertion of a new entry at the head of the list.
              Insertion of a new entry after any element in the list.
              O(1) removal of an entry from the head of the list.
              O(n) removal of any entry in the list.
              Forward traversal through the list.

       Singly-linked  lists  are  the simplest of the five 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.

       Singly-linked tail queues add the following functionality:

              Entries can be added at the end of a list.

       However:
              All list insertions must specify the head of the list.
              Each head entry requires two pointers rather than one.
              Code size is about 15% greater  and  operations  run  about  20%
              slower than singly-linked lists.

       Singly-linked tailqs 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,  tail  queues,  and
       circle queues) additionally allow:

              Insertion of a new entry before any element in the list.
              O(1) removal of any entry in the list.
       However:
              Each elements requires two pointers rather than one.
              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:

              Entries can be added at the end of a list.
       However:
              All  list  insertions  and removals must specify the head of the
              list.
              Each head entry requires two pointers rather than one.
              Code size is about 15% greater  and  operations  run  about  20%
              slower than singly-linked lists.

       Circular queues add the following functionality:

              Entries can be added at the end of a list.
              They may be traversed backwards, from tail to head.
       However:
              All  list  insertions  and removals must specify the head of the
              list.
              Each head entry requires two pointers rather than one.
              The termination condition for traversal is more complex.
              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,   STAILQ_ENTRY,
       LIST_ENTRY,  TAILQ_ENTRY,  or  CIRCLEQ_ENTRY,  named  NAME The argument
       HEADNAME is the name of a user defined structure that must be  declared
       using  the  macros  SLIST_HEAD,  STAILQ_HEAD, LIST_HEAD, TAILQ_HEAD, or
       CIRCLEQ_HEAD.  See the examples below for further  explanation  of  how
       these macros are used.


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  arbi-
       trary  elements.  New elements can be added to the list after an exist-
       ing 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_ENTRY declares a structure that connects the elements
       in 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 ele-
       ment listelm.

       The macro SLIST_REMOVE_HEAD removes the element elm 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 removes the element elm from the list.


SINGLY-LINKED LIST EXAMPLE

       SLIST_HEAD(slisthead, entry) 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 = head.slh_first;
       SLIST_REMOVE_HEAD(&head, entries); /* Deletion. */
       free(n3);

                                /* Forward traversal. */
       for (np = head.slh_first; np != NULL; np = np->entries.sle_next)
            np-> ...

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


SINGLY-LINKED TAIL QUEUES

       A  singly-linked  tail  queue  is  headed by a structure defined by the
       STAILQ_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 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 tail queue  after
       an  existing  element,  at the head of the tail queue, or at the end of
       the tail queue.  A STAILQ_HEAD structure is declared as follows:

              STAILQ_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 tail queue.  A pointer
       to the head of the tail queue can later be declared as:

              struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       The macro STAILQ_ENTRY declares a structure that connects the  elements
       in the tail queue.

       The macro STAILQ_INIT initializes the tail queue referenced by head.

       The macro STAILQ_INSERT_HEAD inserts the new element elm at the head of
       the tail queue.

       The macro STAILQ_INSERT_TAIL inserts the new element elm at the end  of
       the tail queue.

       The  macro  STAILQ_INSERT_AFTER  inserts  the new element elm after the
       element listelm.

       The macro STAILQ_REMOVE_HEAD removes the element elm from the  head  of
       the  tail  queue.   For optimum efficiency, elements being removed from
       the head of the tail queue should use this macro explicitly rather than
       the generic STAILQ_REMOVE macro.

       The macro STAILQ_REMOVE removes the element elm from the tail queue.


SINGLY-LINKED TAIL QUEUE EXAMPLE

       STAILQ_HEAD(stailhead, entry) head;
       struct stailhead *headp;      /* Singly-linked tail queue head. */
       struct entry {
            ...
            STAILQ_ENTRY(entry) entries;  /* Tail queue. */
            ...
       } *n1, *n2, *n3, *np;

       STAILQ_INIT(&head);           /* Initialize the queue. */

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

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

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

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

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

                                /* Forward traversal. */
       for (np = head.stqh_first; np != NULL; np = np->entries.stqe_next)
            np-> ...
                                /* TailQ Deletion. */
       while (head.stqh_first != NULL) {
            n1 = head.stqh_first;
            TAILQ_REMOVE_HEAD(&head, entries);
            free(n1);
       }
                                /* Faster TailQ Deletion. */
       n1 = head.stqh_first;
       while (n1 != NULL) {
            n2 = n1->entries.stqe_next;
            free(n1);
            n1 = n2;
       }
       STAILQ_INIT(&head);


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 structure that connects the elements in
       the list.

       The macro LIST_INIT initializes the list referenced by head.

       The  macro  LIST_INSERT_HEAD inserts the new element elm at the head of
       the list.

       The macro LIST_INSERT_AFTER inserts the new element elm after the  ele-
       ment listelm.

       The  macro  LIST_INSERT_BEFORE  inserts  the new element elm before the
       element listelm.

       The macro LIST_REMOVE removes the element elm from the list.


LIST EXAMPLE

       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);


TAIL QUEUES

       A tail queue is headed by a structure defined by the 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 ele-
       ment, at the head of the tail queue, or at the end of the  tail  queue.
       A TAILQ_HEAD structure is declared as follows:

              TAILQ_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 tail queue.   A  pointer
       to the head of the tail queue can later be declared as:

              struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       The  macro  TAILQ_ENTRY declares a structure that connects the elements
       in the tail queue.

       The macro TAILQ_INIT initializes the tail queue referenced by head.

       The macro TAILQ_INSERT_HEAD inserts the new element elm at the head  of
       the tail queue.

       The  macro  TAILQ_INSERT_TAIL inserts the new element elm at the end of
       the tail queue.

       The macro TAILQ_INSERT_AFTER inserts the new element elm after the ele-
       ment listelm.

       The  macro  TAILQ_INSERT_BEFORE  inserts the new element elm before the
       element listelm.

       The macro TAILQ_REMOVE removes the element elm from the tail queue.


TAIL QUEUE EXAMPLE

       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);


CIRCULAR QUEUES

       A circular queue is headed by a structure defined by  the  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  CIR-
       CLEQ_HEAD structure is declared as follows:

              CIRCLEQ_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  circular  queue.   A
       pointer to the head of the circular queue can later be declared as:

              struct HEADNAME *headp;

       (The names head and headp are user selectable.)

       The macro CIRCLEQ_ENTRY declares a structure that connects the elements
       in the circular queue.

       The macro CIRCLEQ_INIT initializes the  circular  queue  referenced  by
       head.

       The  macro  CIRCLEQ_INSERT_HEAD inserts the new element elm at the head
       of the circular queue.

       The macro CIRCLEQ_INSERT_TAIL inserts the new element elm at the end of
       the circular queue.

       The  macro  CIRCLEQ_INSERT_AFTER  inserts the new element elm after the
       element listelm.

       The macro CIRCLEQ_INSERT_BEFORE inserts the new element elm before  the
       element listelm.

       The  macro  CIRCLEQ_REMOVE  removes  the  element elm from the circular
       queue.


CIRCULAR QUEUE EXAMPLE

       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);


HISTORY

       The queue functions first appeared in 4.4BSD.



GNO                               11 May 1997                         QUEUE(3)

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