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NAME

SYNOPSIS

DESCRIPTION

These macros define and operate on three types of data structures: lists, tail queues, and circular queues. All three structures support the following functionality: Insertion of a new entry at the head of the list. Insertion of a new entry before or after any element in the list. Removal of any entry in the list. Forward traversal through the list. Lists are the simplest of the three data structures and support only the above functionality. Tail queues add the following functionality: Entries can be added at the end of a list. However: All list insertions and removals, except insertion before another element, 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 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, is the name of a user defined structure, that must contain a field of type or named The argument is the name of a user defined structure that must be declared using the macros or See the examples below for further explanation of how these macros are used.

LISTS

A list is headed by a structure defined by the 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 structure is declared as follows: LIST_HEAD(HEADNAME, TYPE) head;

where is the name of the structure to be defined, and 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 and are user selectable.) The macro declares a structure that connects the elements in the list. The macro initializes the list referenced by The macro inserts the new element at the head of the list. The macro inserts the new element after the element The macro inserts the new element before the element The macro removes the element from the list.

LIST EXAMPLE

LIST_HEAD(listhead, entry) head; struct listhead *headp;        /* List head. */ struct entry {    ...
   LIST_ENTRY(entry) entries;    /* List. */
   ...
} *n1, *n2, *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);

n2 = malloc(sizeof(struct entry));    /* Insert before. */ LIST_INSERT_BEFORE(n1, n2, entries);                    /* Forward traversal. */
for (np = head.lh_first; np != NULL; np = np->entries.le_next)    np-> ...

while (head.lh_first != NULL)        /* Delete. */    LIST_REMOVE(head.lh_first, entries);

TAIL QUEUES

A tail queue is headed by a structure defined by the macro. This structure contains a pair of pointers, one to the first element in the tail queue and the other to the last element in the tail queue. The elements are doubly linked so that an arbitrary element can be removed without traversing the tail queue. New elements can be added to the queue after an existing element, before an existing element, at the head of the queue, or at the end the queue. A structure is declared as follows: TAILQ_HEAD(HEADNAME, TYPE) head;

where is the name of the structure to be defined, and 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 and are user selectable.) The macro declares a structure that connects the elements in the tail queue. The macro initializes the tail queue referenced by The macro inserts the new element at the head of the tail queue. The macro inserts the new element at the end of the tail queue. The macro inserts the new element after the element The macro inserts the new element before the element The macro removes the element 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, *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);

n2 = malloc(sizeof(struct entry));    /* Insert before. */ TAILQ_INSERT_BEFORE(n1, n2, entries);                    /* Forward traversal. */
for (np = head.tqh_first; np != NULL; np = np->entries.tqe_next)    np-> ...
                   /* Delete. */
while (head.tqh_first != NULL)    TAILQ_REMOVE(&head, head.tqh_first, entries);

CIRCULAR QUEUES

A circular queue is headed by a structure defined by the 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 structure is declared as follows: CIRCLEQ_HEAD(HEADNAME, TYPE) head;

where is the name of the structure to be defined, and 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 and are user selectable.) The macro declares a structure that connects the elements in the circular queue. The macro initializes the circular queue referenced by The macro inserts the new element at the head of the circular queue. The macro inserts the new element at the end of the circular queue. The macro inserts the new element after the element The macro inserts the new element before the element The macro removes the element 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);                    /* 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-> ...
                   /* Delete. */
while (head.cqh_first != (void *)&head)    CIRCLEQ_REMOVE(&head, head.cqh_first, entries);

HISTORY

The functions first appeared in 4.4BSD.

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