[PATCH wayland v6] util: Document wl_list methods
Yong Bakos
junk at humanoriented.com
Fri Sep 23 02:59:37 UTC 2016
From: Yong Bakos <ybakos at humanoriented.com>
Add doxygen comment blocks to all wl_list methods.
Signed-off-by: Yong Bakos <ybakos at humanoriented.com>
---
v6: Change description to doubly-linked list (pq)
v5: Change description to linked-list [err]
Clarify uses of `wl_list_init` (pq)
v4: Fix variable name in sample code. (pq)
Remove implemenetation details of pointer state. (pq)
Remove note about __typeof__ entirely.
- it's not helpful as a note or a code comment either
Change sample code indentation to just spaces. (pq)
Use _list suffix for list in sample code. (pq)
Use 'iterate' instead of enumerate, for consistency. (pq)
Note that only removing 'pos' is safe for *_safe methods. (pq, giucam)
v3: Standardize on term 'element', to match param names, tests, and other text.
Use 'relates' for macros (instead of 'memberof').
v2: Refine the writing for clarity.
Add dox for wl_list macros, omitted in v1.
Add notices for unsafe operations and invalid states (giucam, pq)
src/wayland-util.h | 224 +++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 184 insertions(+), 40 deletions(-)
diff --git a/src/wayland-util.h b/src/wayland-util.h
index cacc122..71c26a1 100644
--- a/src/wayland-util.h
+++ b/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
- * using wl_list_init(). All entries in the list must be of the same
- * type. The item type must have a "struct wl_list" member. This
- * member will be initialized by wl_list_insert(). There is no need to
- * call wl_list_init() on the individual item. To query if the list is
- * empty in O(1), use wl_list_empty().
+ * 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.
*
- * Let's call the list reference "struct wl_list foo_list", the item type as
- * "item_t", and the item member as "struct wl_list link".
+ * 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.
*
- * The following code will initialize a list:
* \code
* struct wl_list foo_list;
*
- * struct item_t {
- * int foo;
- * struct wl_list link;
+ * 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, &item2.link); // Pushes item2 at the head
- * wl_list_insert(&item2.link, &item3.link); // Pushes item3 after item2
+ * 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
* \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;
- * wl_list_for_each(item, foo_list, link) {
- * Do_something_with_item(item);
+ * struct element *e;
+ * wl_list_for_each(e, foo_list, link) {
+ * 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 itself 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
@@ -152,41 +229,82 @@ wl_list_insert_list(struct wl_list *list, struct wl_list *other);
*
* \code
* struct example_container {
- * struct wl_listener destroy_listener;
- * // other members...
+ * struct wl_listener destroy_listener;
+ * // other members...
* };
*
* void example_container_destroy(struct wl_listener *listener, void *data)
* {
- * struct example_container *ctr;
+ * struct example_container *ctr;
*
- * ctr = wl_container_of(listener, ctr, destroy_listener);
- * // destroy ctr...
+ * ctr = wl_container_of(listener, ctr, destroy_listener);
+ * // destroy ctr...
* }
* \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
- * stores. Sample does not need be a valid pointer; a null or
- * an uninitialised pointer will suffice.
+ * \param ptr Valid pointer to the contained member
+ * \param sample Pointer to a struct whose type contains \p ptr
+ * \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); \
--
2.7.2
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