util: Document wl_list methods

Add doxygen comment blocks to all wl_list methods.

Signed-off-by: Yong Bakos <ybakos@humanoriented.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
[Pekka: removed "itself" as suggested by Bryce]
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

src/wayland-util.h

@@ -78,73 +78,150 @@ struct wl_interface {
 
 /** \class wl_list
  *
- * \brief doubly-linked list
+ * \brief Doubly-linked list
  *
- * The list head is of "struct wl_list" type, and must be initialized
+ * On its own, an instance of `struct wl_list` represents the sentinel head of
- * using wl_list_init().  All entries in the list must be of the same
+ * a doubly-linked list, and must be initialized using wl_list_init().
- * type.  The item type must have a "struct wl_list" member. This
+ * When empty, the list head's `next` and `prev` members point to the list head
- * member will be initialized by wl_list_insert(). There is no need to
+ * itself, otherwise `next` references the first element in the list, and `prev`
- * call wl_list_init() on the individual item. To query if the list is
+ * refers to the last element in the list.
- * empty in O(1), use wl_list_empty().
  *
- * Let's call the list reference "struct wl_list foo_list", the item type as
+ * Use the `struct wl_list` type to represent both the list head and the links
- * "item_t", and the item member as "struct wl_list link".
+ * 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.
  *
- * The following code will initialize a list:
  * \code
  * struct wl_list foo_list;
  *
- * struct item_t {
+ * struct element {
  *         int foo;
  *         struct wl_list link;
  * };
- * struct item_t item1, item2, item3;
+ * struct element e1, e2, e3;
  *
  * wl_list_init(&foo_list);
- * wl_list_insert(&foo_list, &item1.link);	// Pushes item1 at the head
+ * wl_list_insert(&foo_list, &e1.link);   // e1 is the first element
- * wl_list_insert(&foo_list, &item2.link);	// Pushes item2 at the head
+ * wl_list_insert(&foo_list, &e2.link);   // e2 is now the first element
- * wl_list_insert(&item2.link, &item3.link);	// Pushes item3 after item2
+ * wl_list_insert(&e2.link, &e3.link); // insert e3 after e2
  * \endcode
  *
- * The list now looks like [item2, item3, item1]
+ * The list now looks like <em>[e2, e3, e1]</em>.
+ *
+ * The `wl_list` API provides some iterator macros. For example, to iterate
+ * a list in ascending order:
  *
- * Iterate the list in ascending order:
  * \code
- * item_t *item;
+ * struct element *e;
- * wl_list_for_each(item, foo_list, link) {
+ * wl_list_for_each(e, foo_list, link) {
- * 	Do_something_with_item(item);
+ *         do_something_with_element(e);
  * }
  * \endcode
+ *
+ * See the documentation of each iterator for details.
+ * \sa http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/include/linux/list.h
  */
 struct wl_list {
 	struct wl_list *prev;
 	struct wl_list *next;
 };
 
+/**
+ * Initializes the list.
+ *
+ * \param list List to initialize
+ *
+ * \memberof wl_list
+ */
 void
 wl_list_init(struct wl_list *list);
 
+/**
+ * Inserts an element into the list, after the element represented by \p list.
+ * When \p list is a reference to the list itself (the head), set the containing
+ * struct of \p elm as the first element in the list.
+ *
+ * \note If \p elm is already part of a list, inserting it again will lead to
+ *       list corruption.
+ *
+ * \param list List element after which the new element is inserted
+ * \param elm Link of the containing struct to insert into the list
+ *
+ * \memberof wl_list
+ */
 void
 wl_list_insert(struct wl_list *list, struct wl_list *elm);
 
+/**
+ * Removes an element from the list.
+ *
+ * \note This operation leaves \p elm in an invalid state.
+ *
+ * \param elm Link of the containing struct to remove from the list
+ *
+ * \memberof wl_list
+ */
 void
 wl_list_remove(struct wl_list *elm);
 
+/**
+ * Determines the length of the list.
+ *
+ * \note This is an O(n) operation.
+ *
+ * \param list List whose length is to be determined
+ *
+ * \return Number of elements in the list
+ *
+ * \memberof wl_list
+ */
 int
 wl_list_length(const struct wl_list *list);
 
+/**
+ * Determines if the list is empty.
+ *
+ * \param list List whose emptiness is to be determined
+ *
+ * \return 1 if empty, or 0 if not empty
+ *
+ * \memberof wl_list
+ */
 int
 wl_list_empty(const struct wl_list *list);
 
+/**
+ * Inserts all of the elements of one list into another, after the element
+ * represented by \p list.
+ *
+ * \note This leaves \p other in an invalid state.
+ *
+ * \param list List element after which the other list elements will be inserted
+ * \param other List of elements to insert
+ *
+ * \memberof wl_list
+ */
 void
 wl_list_insert_list(struct wl_list *list, struct wl_list *other);
 
 /**
- * Retrieves a pointer to the containing struct of a given member item.
+ * Retrieves a pointer to a containing struct, given a member name.
  *
- * This macro allows conversion from a pointer to a item to its containing
+ * This macro allows "conversion" from a pointer to a member to its containing
  * struct. This is useful if you have a contained item like a wl_list,
- * wl_listener, or wl_signal, provided via a callback or other means and would
+ * wl_listener, or wl_signal, provided via a callback or other means, and would
  * like to retrieve the struct that contains it.
  *
  * To demonstrate, the following example retrieves a pointer to
@@ -165,28 +242,69 @@ wl_list_insert_list(struct wl_list *list, struct wl_list *other);
  * }
  * \endcode
  *
- * \param ptr A valid pointer to the contained item.
+ * \note `sample` need not be a valid pointer. A null or uninitialised pointer
+ *       is sufficient.
  *
- * \param sample A pointer to the type of content that the list item
+ * \param ptr Valid pointer to the contained member
- * stores. Sample does not need be a valid pointer; a null or
+ * \param sample Pointer to a struct whose type contains \p ptr
- * an uninitialised pointer will suffice.
+ * \param member Named location of \p ptr within the \p sample type
  *
- * \param member The named location of ptr within the sample type.
+ * \return The container for the specified pointer
- *
- * \return The container for the specified pointer.
  */
 #define wl_container_of(ptr, sample, member)				\
 	(__typeof__(sample))((char *)(ptr) -				\
 			     offsetof(__typeof__(*sample), member))
-/* If the above macro causes problems on your compiler you might be
- * able to find an alternative name for the non-standard __typeof__
- * operator and add a special case here */
 
+/**
+ * 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 \p pos, which can then be referenced in
+ * a trailing code block. For example, given a wl_list of `struct message`
+ * elements:
+ *
+ * \code
+ * 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);
+ * }
+ * \endcode
+ *
+ * \param pos Cursor that each list element will be assigned to
+ * \param head Head of the list to iterate over
+ * \param member Name of the link member within the element struct
+ *
+ * \relates wl_list
+ */
 #define wl_list_for_each(pos, head, member)				\
 	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, safe against removal of the list element.
+ *
+ * \note Only removal of the current element, \p pos, is safe. Removing
+ *       any other element during traversal may lead to a loop malfunction.
+ *
+ * \sa wl_list_for_each()
+ *
+ * \param pos Cursor that each list element will be assigned to
+ * \param tmp Temporary pointer of the same type as \p pos
+ * \param head Head of the list to iterate over
+ * \param member Name of the link member within the element struct
+ *
+ * \relates wl_list
+ */
 #define wl_list_for_each_safe(pos, tmp, head, member)			\
 	for (pos = wl_container_of((head)->next, pos, member),		\
 	     tmp = wl_container_of((pos)->member.next, tmp, member);	\
@@ -194,11 +312,37 @@ wl_list_insert_list(struct wl_list *list, struct wl_list *other);
 	     pos = tmp,							\
 	     tmp = wl_container_of(pos->member.next, tmp, member))
 
+/**
+ * Iterates backwards over a list.
+ *
+ * \sa wl_list_for_each()
+ *
+ * \param pos Cursor that each list element will be assigned to
+ * \param head Head of the list to iterate over
+ * \param member Name of the link member within the element struct
+ *
+ * \relates wl_list
+ */
 #define wl_list_for_each_reverse(pos, head, member)			\
 	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, safe against removal of the list element.
+ *
+ * \note Only removal of the current element, \p pos, is safe. Removing
+ *       any other element during traversal may lead to a loop malfunction.
+ *
+ * \sa wl_list_for_each()
+ *
+ * \param pos Cursor that each list element will be assigned to
+ * \param tmp Temporary pointer of the same type as \p pos
+ * \param head Head of the list to iterate over
+ * \param member Name of the link member within the element struct
+ *
+ * \relates wl_list
+ */
 #define wl_list_for_each_reverse_safe(pos, tmp, head, member)		\
 	for (pos = wl_container_of((head)->prev, pos, member),	\
 	     tmp = wl_container_of((pos)->member.prev, tmp, member);	\