queue(3bsd) | 3bsd | queue(3bsd) |
NAME
SLIST_CLASS_ENTRY
,
SLIST_CLASS_HEAD
,
SLIST_CONCAT
, SLIST_EMPTY
,
SLIST_ENTRY
, SLIST_FIRST
,
SLIST_FOREACH
,
SLIST_FOREACH_FROM
,
SLIST_FOREACH_FROM_SAFE
,
SLIST_FOREACH_SAFE
,
SLIST_HEAD
,
SLIST_HEAD_INITIALIZER
,
SLIST_INIT
,
SLIST_INSERT_AFTER
,
SLIST_INSERT_HEAD
,
SLIST_NEXT
, SLIST_REMOVE
,
SLIST_REMOVE_AFTER
,
SLIST_REMOVE_HEAD
,
SLIST_SWAP
,
STAILQ_CLASS_ENTRY
,
STAILQ_CLASS_HEAD
,
STAILQ_CONCAT
, STAILQ_EMPTY
,
STAILQ_ENTRY
, STAILQ_FIRST
,
STAILQ_FOREACH
,
STAILQ_FOREACH_FROM
,
STAILQ_FOREACH_FROM_SAFE
,
STAILQ_FOREACH_SAFE
,
STAILQ_HEAD
,
STAILQ_HEAD_INITIALIZER
,
STAILQ_INIT
,
STAILQ_INSERT_AFTER
,
STAILQ_INSERT_HEAD
,
STAILQ_INSERT_TAIL
,
STAILQ_LAST
, STAILQ_NEXT
,
STAILQ_REMOVE
,
STAILQ_REMOVE_AFTER
,
STAILQ_REMOVE_HEAD
,
STAILQ_SWAP
,
LIST_CLASS_ENTRY
,
LIST_CLASS_HEAD
,
LIST_CONCAT
, LIST_EMPTY
,
LIST_ENTRY
, LIST_FIRST
,
LIST_FOREACH
,
LIST_FOREACH_FROM
,
LIST_FOREACH_FROM_SAFE
,
LIST_FOREACH_SAFE
,
LIST_HEAD
,
LIST_HEAD_INITIALIZER
,
LIST_INIT
,
LIST_INSERT_AFTER
,
LIST_INSERT_BEFORE
,
LIST_INSERT_HEAD
, LIST_NEXT
,
LIST_PREV
, LIST_REMOVE
,
LIST_SWAP
,
TAILQ_CLASS_ENTRY
,
TAILQ_CLASS_HEAD
,
TAILQ_CONCAT
, TAILQ_EMPTY
,
TAILQ_ENTRY
, TAILQ_FIRST
,
TAILQ_FOREACH
,
TAILQ_FOREACH_FROM
,
TAILQ_FOREACH_FROM_SAFE
,
TAILQ_FOREACH_REVERSE
,
TAILQ_FOREACH_REVERSE_FROM
,
TAILQ_FOREACH_REVERSE_FROM_SAFE
,
TAILQ_FOREACH_REVERSE_SAFE
,
TAILQ_FOREACH_SAFE
,
TAILQ_HEAD
,
TAILQ_HEAD_INITIALIZER
,
TAILQ_INIT
,
TAILQ_INSERT_AFTER
,
TAILQ_INSERT_BEFORE
,
TAILQ_INSERT_HEAD
,
TAILQ_INSERT_TAIL
,
TAILQ_LAST
, TAILQ_NEXT
,
TAILQ_PREV
, TAILQ_REMOVE
,
TAILQ_SWAP
— implementations
of singly-linked lists, singly-linked tail queues, lists and tail
queues
LIBRARY
library “libbsd”
SYNOPSIS
#include
<sys/queue.h>
(See
libbsd(7) for include usage.)
SLIST_CLASS_ENTRY
(CLASSTYPE);
SLIST_CLASS_HEAD
(HEADNAME,
CLASSTYPE);
SLIST_CONCAT
(SLIST_HEAD
*head1, SLIST_HEAD
*head2, TYPE,
SLIST_ENTRY NAME);
SLIST_EMPTY
(SLIST_HEAD
*head);
SLIST_ENTRY
(TYPE);
SLIST_FIRST
(SLIST_HEAD
*head);
SLIST_FOREACH
(TYPE
*var, SLIST_HEAD
*head, SLIST_ENTRY
NAME);
SLIST_FOREACH_FROM
(TYPE
*var, SLIST_HEAD
*head, SLIST_ENTRY
NAME);
SLIST_FOREACH_FROM_SAFE
(TYPE
*var, SLIST_HEAD
*head, SLIST_ENTRY
NAME, TYPE
*temp_var);
SLIST_FOREACH_SAFE
(TYPE
*var, SLIST_HEAD
*head, SLIST_ENTRY
NAME, TYPE
*temp_var);
SLIST_HEAD
(HEADNAME,
TYPE);
SLIST_HEAD_INITIALIZER
(SLIST_HEAD
head);
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_NEXT
(TYPE
*elm, SLIST_ENTRY
NAME);
SLIST_REMOVE
(SLIST_HEAD
*head, TYPE *elm,
TYPE,
SLIST_ENTRY NAME);
SLIST_REMOVE_AFTER
(TYPE
*elm, SLIST_ENTRY
NAME);
SLIST_REMOVE_HEAD
(SLIST_HEAD
*head, SLIST_ENTRY
NAME);
SLIST_SWAP
(SLIST_HEAD
*head1, SLIST_HEAD
*head2, TYPE);
STAILQ_CLASS_ENTRY
(CLASSTYPE);
STAILQ_CLASS_HEAD
(HEADNAME,
CLASSTYPE);
STAILQ_CONCAT
(STAILQ_HEAD
*head1, STAILQ_HEAD
*head2);
STAILQ_EMPTY
(STAILQ_HEAD
*head);
STAILQ_ENTRY
(TYPE);
STAILQ_FIRST
(STAILQ_HEAD
*head);
STAILQ_FOREACH
(TYPE
*var, STAILQ_HEAD
*head, STAILQ_ENTRY
NAME);
STAILQ_FOREACH_FROM
(TYPE
*var, STAILQ_HEAD
*head, STAILQ_ENTRY
NAME);
STAILQ_FOREACH_FROM_SAFE
(TYPE
*var, STAILQ_HEAD
*head, STAILQ_ENTRY
NAME, TYPE
*temp_var);
STAILQ_FOREACH_SAFE
(TYPE
*var, STAILQ_HEAD
*head, STAILQ_ENTRY
NAME, TYPE
*temp_var);
STAILQ_HEAD
(HEADNAME,
TYPE);
STAILQ_HEAD_INITIALIZER
(STAILQ_HEAD
head);
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_LAST
(STAILQ_HEAD
*head, TYPE *elm,
STAILQ_ENTRY NAME);
STAILQ_NEXT
(TYPE
*elm, STAILQ_ENTRY
NAME);
STAILQ_REMOVE
(STAILQ_HEAD
*head, TYPE *elm,
TYPE,
STAILQ_ENTRY NAME);
STAILQ_REMOVE_AFTER
(STAILQ_HEAD
*head, TYPE *elm,
STAILQ_ENTRY NAME);
STAILQ_REMOVE_HEAD
(STAILQ_HEAD
*head, STAILQ_ENTRY
NAME);
STAILQ_SWAP
(STAILQ_HEAD
*head1, STAILQ_HEAD
*head2, TYPE);
LIST_CLASS_ENTRY
(CLASSTYPE);
LIST_CLASS_HEAD
(HEADNAME,
CLASSTYPE);
LIST_CONCAT
(LIST_HEAD
*head1, LIST_HEAD
*head2, TYPE,
LIST_ENTRY NAME);
LIST_EMPTY
(LIST_HEAD
*head);
LIST_ENTRY
(TYPE);
LIST_FIRST
(LIST_HEAD
*head);
LIST_FOREACH
(TYPE
*var, LIST_HEAD
*head, LIST_ENTRY
NAME);
LIST_FOREACH_FROM
(TYPE
*var, LIST_HEAD
*head, LIST_ENTRY
NAME);
LIST_FOREACH_FROM_SAFE
(TYPE
*var, LIST_HEAD
*head, LIST_ENTRY
NAME, TYPE
*temp_var);
LIST_FOREACH_SAFE
(TYPE
*var, LIST_HEAD
*head, LIST_ENTRY
NAME, TYPE
*temp_var);
LIST_HEAD
(HEADNAME,
TYPE);
LIST_HEAD_INITIALIZER
(LIST_HEAD
head);
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_NEXT
(TYPE
*elm, LIST_ENTRY
NAME);
LIST_PREV
(TYPE
*elm, LIST_HEAD
*head, TYPE,
LIST_ENTRY NAME);
LIST_REMOVE
(TYPE
*elm, LIST_ENTRY
NAME);
LIST_SWAP
(LIST_HEAD
*head1, LIST_HEAD
*head2, TYPE,
LIST_ENTRY NAME);
TAILQ_CLASS_ENTRY
(CLASSTYPE);
TAILQ_CLASS_HEAD
(HEADNAME,
CLASSTYPE);
TAILQ_CONCAT
(TAILQ_HEAD
*head1, TAILQ_HEAD
*head2, TAILQ_ENTRY
NAME);
TAILQ_EMPTY
(TAILQ_HEAD
*head);
TAILQ_ENTRY
(TYPE);
TAILQ_FIRST
(TAILQ_HEAD
*head);
TAILQ_FOREACH
(TYPE
*var, TAILQ_HEAD
*head, TAILQ_ENTRY
NAME);
TAILQ_FOREACH_FROM
(TYPE
*var, TAILQ_HEAD
*head, TAILQ_ENTRY
NAME);
TAILQ_FOREACH_FROM_SAFE
(TYPE
*var, TAILQ_HEAD
*head, TAILQ_ENTRY
NAME, TYPE
*temp_var);
TAILQ_FOREACH_REVERSE
(TYPE
*var, TAILQ_HEAD
*head, HEADNAME,
TAILQ_ENTRY NAME);
TAILQ_FOREACH_REVERSE_FROM
(TYPE
*var, TAILQ_HEAD
*head, HEADNAME,
TAILQ_ENTRY NAME);
TAILQ_FOREACH_REVERSE_FROM_SAFE
(TYPE
*var, TAILQ_HEAD
*head, HEADNAME,
TAILQ_ENTRY NAME,
TYPE *temp_var);
TAILQ_FOREACH_REVERSE_SAFE
(TYPE
*var, TAILQ_HEAD
*head, HEADNAME,
TAILQ_ENTRY NAME,
TYPE *temp_var);
TAILQ_FOREACH_SAFE
(TYPE
*var, TAILQ_HEAD
*head, TAILQ_ENTRY
NAME, TYPE
*temp_var);
TAILQ_HEAD
(HEADNAME,
TYPE);
TAILQ_HEAD_INITIALIZER
(TAILQ_HEAD
head);
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_LAST
(TAILQ_HEAD
*head,
HEADNAME);
TAILQ_NEXT
(TYPE
*elm, TAILQ_ENTRY
NAME);
TAILQ_PREV
(TYPE
*elm, HEADNAME,
TAILQ_ENTRY NAME);
TAILQ_REMOVE
(TAILQ_HEAD
*head, TYPE *elm,
TAILQ_ENTRY NAME);
TAILQ_SWAP
(TAILQ_HEAD
*head1, TAILQ_HEAD
*head2, TYPE,
TAILQ_ENTRY NAME);
DESCRIPTION
These macros define and operate on four types of data structures which can be used in both C and C++ source code:
- Lists
- Singly-linked lists
- Singly-linked tail queues
- Tail queues
- 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.
- Forward traversal through the list.
- Swapping the contents of two lists.
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. Singly-linked lists add the following functionality:
- O(n) removal of any entry in the list.
- O(n) concatenation of two lists.
Singly-linked tail queues add the following functionality:
- Entries can be added at the end of a list.
- O(n) removal of any entry in the list.
- They may be concatenated.
- 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 tail 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:
- Insertion of a new entry before any element in the list.
- O(1) removal of any entry in the list.
- Each element 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. They add the following functionality over the above:
- O(n) concatenation of two lists.
- They may be traversed backwards.
- To traverse backwards, an entry to begin the traversal and the list in which it is contained must be specified.
Tail queues add the following functionality:
- Entries can be added at the end of a list.
- They may be traversed backwards, from tail to head.
- They may be concatenated.
- 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.
In the macro definitions, TYPE is the name
of a user defined structure. The structure must contain a field called
NAME which is of type
SLIST_ENTRY
, STAILQ_ENTRY
,
LIST_ENTRY
, or TAILQ_ENTRY
.
In the macro definitions, CLASSTYPE is the name of a
user defined class. The class must contain a field called
NAME which is of type
SLIST_CLASS_ENTRY
,
STAILQ_CLASS_ENTRY
,
LIST_CLASS_ENTRY
, or
TAILQ_CLASS_ENTRY
. The argument
HEADNAME is the name of a user defined structure that
must be declared using the macros SLIST_HEAD
,
SLIST_CLASS_HEAD
,
STAILQ_HEAD
,
STAILQ_CLASS_HEAD
,
LIST_HEAD
, LIST_CLASS_HEAD
,
TAILQ_HEAD
, or
TAILQ_CLASS_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 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_CONCAT
concatenates the
list headed by head2 onto the end of the one headed by
head1 removing all entries from the former. Use of
this macro should be avoided as it traverses the entirety of the
head1 list. A singly-linked tail queue should be used
if this macro is needed in high-usage code paths or to operate on long
lists.
The macro SLIST_EMPTY
evaluates to true if
there are no elements in the list.
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_FOREACH
traverses the list
referenced by head in the forward direction, assigning
each element in turn to var.
The macro SLIST_FOREACH_FROM
behaves
identically to SLIST_FOREACH
when
var is NULL, else it treats var
as a previously found SLIST element and begins the loop at
var instead of the first element in the SLIST
referenced by head.
The macro
SLIST_FOREACH_SAFE
traverses the list referenced by
head in the forward direction, assigning each element
in turn to var. However, unlike
SLIST_FOREACH
()
here it is permitted to both remove var as well as
free it from within the loop safely without interfering with the
traversal.
The macro SLIST_FOREACH_FROM_SAFE
behaves
identically to SLIST_FOREACH_SAFE
when
var is NULL, else it treats var
as a previously found SLIST element and begins the loop at
var instead of the first element in the SLIST
referenced by head.
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_NEXT
returns the next
element in the list.
The macro SLIST_REMOVE_AFTER
removes the
element after elm from the list. Unlike
SLIST_REMOVE, this macro does not traverse the entire
list.
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. Use of this macro should be avoided
as it traverses the entire list. A doubly-linked list should be used if this
macro is needed in high-usage code paths or to operate on long lists.
The macro SLIST_SWAP
swaps the contents of
head1 and head2.
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); /* Forward traversal. */ SLIST_FOREACH(np, &head, entries) np-> ... /* Safe forward traversal. */ SLIST_FOREACH_SAFE(np, &head, entries, np_temp) { np->do_stuff(); ... SLIST_REMOVE(&head, np, entry, entries); free(np); } while (!SLIST_EMPTY(&head)) { /* List Deletion. */ n1 = SLIST_FIRST(&head); 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_HEAD_INITIALIZER
evaluates to an initializer for the tail queue
head.
The macro STAILQ_CONCAT
concatenates the
tail queue headed by head2 onto the end of the one
headed by head1 removing all entries from the
former.
The macro STAILQ_EMPTY
evaluates to true
if there are no items on the tail queue.
The macro STAILQ_ENTRY
declares a
structure that connects the elements in the tail queue.
The macro STAILQ_FIRST
returns the first
item on the tail queue or NULL if the tail queue is empty.
The macro STAILQ_FOREACH
traverses the
tail queue referenced by head in the forward
direction, assigning each element in turn to var.
The macro STAILQ_FOREACH_FROM
behaves
identically to STAILQ_FOREACH
when
var is NULL, else it treats var
as a previously found STAILQ element and begins the loop at
var instead of the first element in the STAILQ
referenced by head.
The macro
STAILQ_FOREACH_SAFE
traverses the tail queue
referenced by head in the forward direction, assigning
each element in turn to var. However, unlike
STAILQ_FOREACH
()
here it is permitted to both remove var as well as
free it from within the loop safely without interfering with the
traversal.
The macro STAILQ_FOREACH_FROM_SAFE
behaves
identically to STAILQ_FOREACH_SAFE
when
var is NULL, else it treats var
as a previously found STAILQ element and begins the loop at
var instead of the first element in the STAILQ
referenced by head.
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_LAST
returns the last
item on the tail queue. If the tail queue is empty the return value is
NULL
.
The macro STAILQ_NEXT
returns the next
item on the tail queue, or NULL this item is the last.
The macro STAILQ_REMOVE_AFTER
removes the
element after elm from the tail queue. Unlike
STAILQ_REMOVE, this macro does not traverse the entire
tail queue.
The macro STAILQ_REMOVE_HEAD
removes the
element at 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. Use of this macro
should be avoided as it traverses the entire list. A doubly-linked tail
queue should be used if this macro is needed in high-usage code paths or to
operate on long tail queues.
The macro STAILQ_SWAP
swaps the contents
of head1 and head2.
SINGLY-LINKED TAIL QUEUE EXAMPLE
STAILQ_HEAD(stailhead, entry) head = STAILQ_HEAD_INITIALIZER(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 = STAILQ_FIRST(&head); STAILQ_REMOVE_HEAD(&head, entries); free(n3); /* Forward traversal. */ STAILQ_FOREACH(np, &head, entries) np-> ... /* Safe forward traversal. */ STAILQ_FOREACH_SAFE(np, &head, entries, np_temp) { np->do_stuff(); ... STAILQ_REMOVE(&head, np, entry, entries); free(np); } /* TailQ Deletion. */ while (!STAILQ_EMPTY(&head)) { n1 = STAILQ_FIRST(&head); STAILQ_REMOVE_HEAD(&head, entries); free(n1); } /* Faster TailQ Deletion. */ n1 = STAILQ_FIRST(&head); while (n1 != NULL) { n2 = STAILQ_NEXT(n1, entries); 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_HEAD_INITIALIZER
evaluates
to an initializer for the list head.
The macro LIST_CONCAT
concatenates the
list headed by head2 onto the end of the one headed by
head1 removing all entries from the former. Use of
this macro should be avoided as it traverses the entirety of the
head1 list. A tail queue should be used if this macro
is needed in high-usage code paths or to operate on long lists.
The macro LIST_EMPTY
evaluates to true if
there are no elements in the list.
The macro LIST_ENTRY
declares a structure
that connects the elements in the list.
The macro LIST_FIRST
returns the first
element in the list or NULL if the list is empty.
The macro LIST_FOREACH
traverses the list
referenced by head in the forward direction, assigning
each element in turn to var.
The macro LIST_FOREACH_FROM
behaves
identically to LIST_FOREACH
when
var is NULL, else it treats var
as a previously found LIST element and begins the loop at
var instead of the first element in the LIST
referenced by head.
The macro
LIST_FOREACH_SAFE
traverses the list referenced by
head in the forward direction, assigning each element
in turn to var. However, unlike
LIST_FOREACH
()
here it is permitted to both remove var as well as
free it from within the loop safely without interfering with the
traversal.
The macro LIST_FOREACH_FROM_SAFE
behaves
identically to LIST_FOREACH_SAFE
when
var is NULL, else it treats var
as a previously found LIST element and begins the loop at
var instead of the first element in the LIST
referenced by head.
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 element
listelm.
The macro LIST_INSERT_BEFORE
inserts the
new element elm before the element
listelm.
The macro LIST_NEXT
returns the next
element in the list, or NULL if this is the last.
The macro LIST_PREV
returns the previous
element in the list, or NULL if this is the first. List
head must contain element
elm.
The macro LIST_REMOVE
removes the element
elm from the list.
The macro LIST_SWAP
swaps the contents of
head1 and head2.
LIST EXAMPLE
LIST_HEAD(listhead, entry) head = LIST_HEAD_INITIALIZER(head); struct listhead *headp; /* List head. */ struct entry { ... LIST_ENTRY(entry) entries; /* List. */ ... } *n1, *n2, *n3, *np, *np_temp; 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. */ LIST_FOREACH(np, &head, entries) np-> ... /* Safe forward traversal. */ LIST_FOREACH_SAFE(np, &head, entries, np_temp) { np->do_stuff(); ... LIST_REMOVE(np, entries); free(np); } while (!LIST_EMPTY(&head)) { /* List Deletion. */ n1 = LIST_FIRST(&head); LIST_REMOVE(n1, entries); free(n1); } n1 = LIST_FIRST(&head); /* Faster List Deletion. */ while (n1 != NULL) { n2 = LIST_NEXT(n1, entries); 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 element, 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_HEAD_INITIALIZER
evaluates
to an initializer for the tail queue head.
The macro TAILQ_CONCAT
concatenates the
tail queue headed by head2 onto the end of the one
headed by head1 removing all entries from the
former.
The macro TAILQ_EMPTY
evaluates to true if
there are no items on the tail queue.
The macro TAILQ_ENTRY
declares a structure
that connects the elements in the tail queue.
The macro TAILQ_FIRST
returns the first
item on the tail queue or NULL if the tail queue is empty.
The macro TAILQ_FOREACH
traverses the tail
queue referenced by head in the forward direction,
assigning each element in turn to var.
var is set to NULL
if the loop
completes normally, or if there were no elements.
The macro TAILQ_FOREACH_FROM
behaves
identically to TAILQ_FOREACH
when
var is NULL, else it treats var
as a previously found TAILQ element and begins the loop at
var instead of the first element in the TAILQ
referenced by head.
The macro TAILQ_FOREACH_REVERSE
traverses
the tail queue referenced by head in the reverse
direction, assigning each element in turn to var.
The macro TAILQ_FOREACH_REVERSE_FROM
behaves identically to TAILQ_FOREACH_REVERSE
when
var is NULL, else it treats var
as a previously found TAILQ element and begins the reverse loop at
var instead of the last element in the TAILQ
referenced by head.
The macros TAILQ_FOREACH_SAFE
and
TAILQ_FOREACH_REVERSE_SAFE
traverse the list
referenced by head in the forward or reverse direction
respectively, assigning each element in turn to var.
However, unlike their unsafe counterparts,
TAILQ_FOREACH
and
TAILQ_FOREACH_REVERSE
make it possible to both
remove var as well as free it from within the loop
safely without interfering with the traversal.
The macro TAILQ_FOREACH_FROM_SAFE
behaves
identically to TAILQ_FOREACH_SAFE
when
var is NULL, else it treats var
as a previously found TAILQ element and begins the loop at
var instead of the first element in the TAILQ
referenced by head.
The macro TAILQ_FOREACH_REVERSE_FROM_SAFE
behaves identically to TAILQ_FOREACH_REVERSE_SAFE
when var is NULL, else it treats
var as a previously found TAILQ element and begins the
reverse loop at var instead of the last element in the
TAILQ referenced by head.
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 element
listelm.
The macro TAILQ_INSERT_BEFORE
inserts the
new element elm before the element
listelm.
The macro TAILQ_LAST
returns the last item
on the tail queue. If the tail queue is empty the return value is
NULL
.
The macro TAILQ_NEXT
returns the next item
on the tail queue, or NULL if this item is the last.
The macro TAILQ_PREV
returns the previous
item on the tail queue, or NULL if this item is the first.
The macro TAILQ_REMOVE
removes the element
elm from the tail queue.
The macro TAILQ_SWAP
swaps the contents of
head1 and head2.
TAIL QUEUE EXAMPLE
TAILQ_HEAD(tailhead, entry) head = TAILQ_HEAD_INITIALIZER(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. */ TAILQ_FOREACH(np, &head, entries) np-> ... /* Safe forward traversal. */ TAILQ_FOREACH_SAFE(np, &head, entries, np_temp) { np->do_stuff(); ... TAILQ_REMOVE(&head, np, entries); free(np); } /* Reverse traversal. */ TAILQ_FOREACH_REVERSE(np, &head, tailhead, entries) np-> ... /* TailQ Deletion. */ while (!TAILQ_EMPTY(&head)) { n1 = TAILQ_FIRST(&head); TAILQ_REMOVE(&head, n1, entries); free(n1); } /* Faster TailQ Deletion. */ n1 = TAILQ_FIRST(&head); while (n1 != NULL) { n2 = TAILQ_NEXT(n1, entries); free(n1); n1 = n2; } TAILQ_INIT(&head);
DIAGNOSTICS
When debugging queue(3)
, it can be useful
to trace queue changes. To enable tracing, define the macro
QUEUE_MACRO_DEBUG_TRACE at compile time.
It can also be useful to trash pointers that have been unlinked
from a queue, to detect use after removal. To enable pointer trashing,
define the macro QUEUE_MACRO_DEBUG_TRASH at compile
time. The macro QMD_IS_TRASHED
(void
*ptr) returns true if ptr has been trashed by
the QUEUE_MACRO_DEBUG_TRASH option.
SEE ALSO
HISTORY
The queue
functions first appeared in
4.4BSD.
September 8, 2016 | Linux 6.10.2-arch1-1 |