[vlc-devel] [PATCH 1/4] vlc_list: helpers for doubly linked lists

[Romain Vimont]

On Tue, Jun 12, 2018 at 09:27:04PM +0300, Rémi Denis-Courmont wrote:
> ---
>  include/vlc_list.h | 261 +++++++++++++++++++++++++++++++++++++++++++++
>  src/Makefile.am    |   1 +
>  2 files changed, 262 insertions(+)
>  create mode 100644 include/vlc_list.h
> 
> diff --git a/include/vlc_list.h b/include/vlc_list.h
> new file mode 100644
> index 0000000000..b334c075c2
> --- /dev/null
> +++ b/include/vlc_list.h
> @@ -0,0 +1,261 @@
> +/******************************************************************************
> + * vlc_list.h
> + ******************************************************************************
> + * Copyright © 2018 Rémi Denis-Courmont
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU Lesser General Public License as published by
> + * the Free Software Foundation; either version 2.1 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public License
> + * along with this program; if not, write to the Free Software Foundation,
> + * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
> + *****************************************************************************/
> +
> +#ifndef VLC_LIST_H
> +# define VLC_LIST_H 1
> +
> +# include <stdbool.h>
> +# include <stddef.h>
> +
> +/**
> + * \defgroup list Linked lists
> + * \ingroup cext
> + * @{
> + * \file
> + * This provides convenience helpers for linked lists.
> + */
> +
> +/**
> + * Doubly-linked list node.
> + *
> + * This data structure provides a doubly-linked list node.
> + * It must be embedded in each member of a list as a node proper.
> + * It also serves as a list head in the object containing the list.
> + */
> +struct vlc_list
> +{
> +    struct vlc_list *prev;
> +    struct vlc_list *next;
> +};
> +
> +/**
> + * Initializes an empty list head.
> + */
> +static inline void vlc_list_init(struct vlc_list *restrict head)
> +{
> +    head->prev = head;
> +    head->next = head;
> +}
> +
> +/**
> + * Adds an element in a list.
> + *
> + * \note This is a common internal function. Do not call this directly.
> + */
> +static inline void vlc_list_add_internal(struct vlc_list *restrict node,
> +                                         struct vlc_list *prev,
> +                                         struct vlc_list *next)
> +{
> +    node->prev = prev;
> +    node->next = next;
> +    prev->next = node;
> +    next->prev = node;
> +}
> +
> +/**
> + * Prepends an element into a list.
> + *
> + * \param node Node of the element to prepend to the list [OUT].
> + * \param head Head of the list to be prepended.
> + */
> +static inline void vlc_list_prepend(struct vlc_list *restrict node,
> +                                    struct vlc_list *head)
> +{
> +    vlc_list_add_internal(node, head, head->next);
> +}
> +
> +/**
> + * Appends an element into a list.
> + *
> + * \param node Node of the element to append to the list [OUT].
> + * \param head Head of the list to be append.
> + */
> +static inline void vlc_list_append(struct vlc_list *restrict node,
> +                                   struct vlc_list *head)
> +{
> +    vlc_list_add_internal(node, head->prev, head);
> +}
> +
> +/**
> + * Removes an element from a list.
> + *
> + * \param node Node of the element to remove from a list.
> + * \warning The element must be inside a list.
> + * Otherwise the behaviour is undefined.
> + */
> +static inline void vlc_list_remove(struct vlc_list *restrict node)
> +{
> +    struct vlc_list *prev = node->prev;
> +    struct vlc_list *next = node->next;
> +
> +    prev->next = next;
> +    next->prev = prev;
> +}
> +
> +/**
> + * Checks if a list is empty.
> + *
> + * \param head Head of the list to be checked [IN].
> + *
> + * \retval false The list is not empty.
> + * \retval true The list is empty.
> + *
> + * \note Obviously the list must have been initialized.
> + * Otherwise, the behaviour is undefined.
> + */
> +static inline bool vlc_list_is_empty(const struct vlc_list *head)
> +{
> +    return head->next == head;
> +}
> +
> +/**
> + * Checks if an element is first in a list.
> + *
> + * \param node List node of the element [IN].
> + * \param head Head of the list to be checked [IN].
> + *
> + * \retval false The element is not first (or is in another list).
> + * \retval true The element is first.
> + */
> +static inline bool vlc_list_is_first(const struct vlc_list *node,
> +                                     const struct vlc_list *head)
> +{
> +    return node->prev == head;
> +}
> +
> +/**
> + * Checks if an element is last in a list.
> + *
> + * \param node List node of the element [IN].
> + * \param head Head of the list to be checked [IN].
> + *
> + * \retval false The element is not last (or is in another list).
> + * \retval true The element is last.
> + */
> +static inline bool vlc_list_is_last(const struct vlc_list *node,
> +                                    const struct vlc_list *head)
> +{
> +    return node->next == head;
> +}
> +
> +/**
> + * List iterator.
> + */
> +struct vlc_list_it
> +{
> +    const struct vlc_list *head;
> +    struct vlc_list *current;
> +    struct vlc_list *next;
> +};
> +
> +static inline
> +struct vlc_list_it vlc_list_it_start(const struct vlc_list *head)
> +{
> +    struct vlc_list *first = head->next;
> +
> +    return (struct vlc_list_it){ head, first, first->next };
> +}
> +
> +static inline bool vlc_list_it_continue(const struct vlc_list_it *restrict it)
> +{
> +    return it->current != it->head;
> +}
> +
> +static inline void vlc_list_it_next(struct vlc_list_it *restrict it)
> +{
> +    struct vlc_list *next = it->next;
> +
> +    it->current = next;
> +    it->next = next->next;
> +}
> +
> +/**
> + * List iteration macro.
> + *
> + * This macro iterates over all elements (excluding the head) of a list,
> + * in order from the first to the last.
> + *
> + * For each iteration, it sets the cursor variable to the current element.
> + *
> + * \param pos Cursor variable.
> + * \param it Storage space fo list iterator internal data.
> + * \param head Head of the list to iterate [IN].
> + * \param type Data type of list elements.
> + * \param member Identifier of the member of the data type
> + *               serving as list node.
> + * \note It it safe to delete the current item while iterating.
> + * It is however <b>not</b> safe to delete another item.
> + */
> +#define vlc_list_foreach(p, it, head, type, member) \
> +    for (struct vlc_list_it it = vlc_list_it_start(head); \

I see the intention to avoid the declaration on the caller-side, but it
feels weird to require a parameter for which the caller should mostly
pass a random string (which does not conflict with any existing variable
name).

But I think there is no perfect solution.

> +         vlc_list_it_continue(&it) \
> +          && ((p) = vlc_list_entry(it.current, type, member), true); \

Nice :)

> +         vlc_list_it_next(&it))
> +
> +/**
> + * Converts a list node pointer to an element pointer.
> + *
> + * \param ptr list node pointer
> + * \param type list data element type name
> + * \param member list node member within the data element compound type
> + */
> +#define vlc_list_entry(ptr, type, member) container_of(ptr, type, member)

Should include <vlc_common.h> for container_of()?

> +
> +static inline void *vlc_list_first_or_null(const struct vlc_list *head,
> +                                           size_t offset)
> +{
> +    if (vlc_list_is_empty(head))
> +        return NULL;
> +    return ((char *)(head->next)) - offset;
> +}
> +
> +static inline void *vlc_list_last_or_null(const struct vlc_list *head,
> +                                          size_t offset)
> +{
> +    if (vlc_list_is_empty(head))
> +        return NULL;
> +    return ((char *)(head->prev)) - offset;
> +}
> +
> +/**
> + * Gets the first element.
> + *
> + * \param head Head of list whose last element to get [IN].
> + *
> + * \return the first entry in a list or NULL if empty.
> + */
> +#define vlc_list_first_entry_or_null(head, type, member) \
> +        ((type *)vlc_list_first_or_null(head, offsetof (type, member)))
> +
> +/**
> + * Gets the last element.
> + *
> + * \param head Head of list whose last element to get [IN].
> + *
> + * \return the last entry in a list or NULL if empty.
> + */
> +#define vlc_list_last_entry_or_null(head, type, member) \
> +        ((type *)vlc_list_last_or_null(head, offsetof (type, member)))
> +
> +/** \todo Merging lists, splitting lists. */
> +
> +/** @} */
> +
> +#endif /* VLC_LIST_H */
> diff --git a/src/Makefile.am b/src/Makefile.am
> index a13a3147d0..56552deab2 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -60,6 +60,7 @@ pluginsinclude_HEADERS = \
>  	../include/vlc_input_item.h \
>  	../include/vlc_interface.h \
>  	../include/vlc_keystore.h \
> +	../include/vlc_list.h \
>  	../include/vlc_md5.h \
>  	../include/vlc_messages.h \
>  	../include/vlc_meta.h \
> -- 
> 2.17.1
> 
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