wl_list(3)

NAME
wl_list - Doubly-linked list.

SYNOPSIS

#include <wayland-util.h>

  Public Member Functions
void wl_list_init (struct wl_list *list)
void wl_list_insert (struct wl_list *list, struct wl_list *elm)
void wl_list_remove (struct wl_list *elm)
int wl_list_length (const struct wl_list *list)
int wl_list_empty (const struct wl_list *list)
void wl_list_insert_list (struct wl_list *list, struct wl_list *other)

  Data Fields
struct wl_list * prev
struct wl_list * next

  Related Symbols
(Note that these are not member symbols.)
#define wl_list_for_each(pos, head, member)
#define wl_list_for_each_safe(pos, tmp, head, member)
#define wl_list_for_each_reverse(pos, head, member)
#define wl_list_for_each_reverse_safe(pos, tmp, head, member)

Detailed Description

Doubly-linked list. On its own, an instance of struct wl_list represents the sentinel head of a doubly-linked list, and must be initialized using wl_list_init(). When empty, the list head's next and prev members point to the list head itself, otherwise next references the first element in the list, and prev refers to the last element in the list.

Use the struct wl_list type to represent both the list head and the links between elements within the list. Use wl_list_empty() to determine if the list is empty in O(1).

All elements in the list must be of the same type. The element type must have a struct wl_list member, often named link by convention. Prior to insertion, there is no need to initialize an element's link - invoking wl_list_init() on an individual list element's struct wl_list member is unnecessary if the very next operation is wl_list_insert(). However, a common idiom is to initialize an element's link prior to removal - ensure safety by invoking wl_list_init() before wl_list_remove().

Consider a list reference struct wl_list foo_list, an element type as struct element, and an element's link member as struct wl_list link.

The following code initializes a list and adds three elements to it.

struct wl_list foo_list;
struct element {
        int foo;
        struct wl_list link;
};
struct element e1, e2, e3;
wl_list_init(&foo_list);
wl_list_insert(&foo_list, &e1.link);   // e1 is the first element
wl_list_insert(&foo_list, &e2.link);   // e2 is now the first element
wl_list_insert(&e2.link, &e3.link); // insert e3 after e2

The list now looks like [e2, e3, e1].

The wl_list API provides some iterator macros. For example, to iterate a list in ascending order:

struct element *e;
wl_list_for_each(e, foo_list, link) {
        do_something_with_element(e);
}

See the documentation of each iterator for details.

See also
    http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/linux/list.h

Member Function Documentation

  int wl_list_empty (const struct wl_list * list)
Determines if the list is empty.

Parameters
    list List whose emptiness is to be determined

Returns
    1 if empty, or 0 if not empty

  void wl_list_init (struct wl_list * list)
Initializes the list.

Parameters
    list List to initialize

  void wl_list_insert (struct wl_list * list, struct wl_list * elm)
Inserts an element into the list, after the element represented by list. When list is a reference to the list itself (the head), set the containing struct of elm as the first element in the list.

Note
    If elm is already part of a list, inserting it again will lead to list corruption.

Parameters
    list List element after which the new element is inserted
    elm Link of the containing struct to insert into the list

  void wl_list_insert_list (struct wl_list * list, struct wl_list * other)
Inserts all of the elements of one list into another, after the element represented by list.

Note
    This leaves other in an invalid state.

Parameters
    list List element after which the other list elements will be inserted
    other List of elements to insert

  int wl_list_length (const struct wl_list * list)
Determines the length of the list.

Note
    This is an O(n) operation.

Parameters
    list List whose length is to be determined

Returns
    Number of elements in the list

  void wl_list_remove (struct wl_list * elm)
Removes an element from the list.

Note
    This operation leaves elm in an invalid state.

Parameters
    elm Link of the containing struct to remove from the list

Friends And Related Symbol Documentation

  #define wl_list_for_each( pos, head, member) [related]
Value:
for (pos = wl_container_of((head)->next, pos, member);  \
     &pos->member != (head);                                    \
     pos = wl_container_of(pos->member.next, pos, member))

Iterates over a list.

This macro expresses a for-each iterator for wl_list. Given a list and wl_list link member name (often named link by convention), this macro assigns each element in the list to pos, which can then be referenced in a trailing code block. For example, given a wl_list of struct message elements:

struct message {
        char *contents;
        wl_list link;
};
struct wl_list *message_list;
// Assume message_list now "contains" many messages
struct message *m;
wl_list_for_each(m, message_list, link) {
        do_something_with_message(m);
}

Parameters
    pos Cursor that each list element will be assigned to
    head Head of the list to iterate over
    member Name of the link member within the element struct

  #define wl_list_for_each_reverse( pos, head, member) [related]
Value:
for (pos = wl_container_of((head)->prev, pos, member);  \
     &pos->member != (head);                                    \
     pos = wl_container_of(pos->member.prev, pos, member))

Iterates backwards over a list.

See also
    wl_list_for_each()

Parameters
    pos Cursor that each list element will be assigned to
    head Head of the list to iterate over
    member Name of the link member within the element struct

  #define wl_list_for_each_reverse_safe( pos, tmp, head, member) [related]
Value:
for (pos = wl_container_of((head)->prev, pos, member),  \
     tmp = wl_container_of((pos)->member.prev, tmp, member);    \
     &pos->member != (head);                                    \
     pos = tmp,                                                 \
     tmp = wl_container_of(pos->member.prev, tmp, member))

Iterates backwards over a list, safe against removal of the list element.

Note
    Only removal of the current element, pos, is safe. Removing any other element during traversal may lead to a loop malfunction.

See also
    wl_list_for_each()

Parameters
    pos Cursor that each list element will be assigned to
    tmp Temporary pointer of the same type as pos
    head Head of the list to iterate over
    member Name of the link member within the element struct

  #define wl_list_for_each_safe( pos, tmp, head, member) [related]
Value:
for (pos = wl_container_of((head)->next, pos, member),          \
     tmp = wl_container_of((pos)->member.next, tmp, member);    \
     &pos->member != (head);                                    \
     pos = tmp,                                                 \
     tmp = wl_container_of(pos->member.next, tmp, member))

Iterates over a list, safe against removal of the list element.

Note
    Only removal of the current element, pos, is safe. Removing any other element during traversal may lead to a loop malfunction.

See also
    wl_list_for_each()

Parameters
    pos Cursor that each list element will be assigned to
    tmp Temporary pointer of the same type as pos
    head Head of the list to iterate over
    member Name of the link member within the element struct

Field Documentation

  struct wl_list* wl_list::next
Next list element

  struct wl_list* wl_list::prev
Previous list element

Author

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