[vlc-devel] [PATCH 1/4] vlc_list: helpers for doubly linked lists
Rémi Denis-Courmont
remi at remlab.net
Wed Jun 13 11:55:17 CEST 2018
pos is an l-value, not necessarily a variable. If you look at existing array macros usages, quite often the l-values for array and size are not variables, so I don't think we should make that assumption.
Le 13 juin 2018 12:45:19 GMT+03:00, Steve Lhomme <robux4 at ycbcr.xyz> a écrit :
>On 2018-06-13 11:24 AM, Romain Vimont wrote:
>> 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).
>
>Since pos is already a variable that avoids shadowing, can't we use
>pos##some_suffix internally ? (which a proper STRINGIFY macro)
>
>>
>> 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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