[FFmpeg-devel] [PATCH 1/2] lavu/dict: Add new flag to allow multiple equal keys.

[wm4]

On Sun, 13 Mar 2016 21:00:23 +0100
Thilo Borgmann <thilo.borgmann at mail.de> wrote:

> Am 13.03.16 um 15:08 schrieb wm4:
> > On Sat, 12 Mar 2016 15:13:21 +0100
> > Thilo Borgmann <thilo.borgmann at mail.de> wrote:
> >   
> >> From a1d9ce388c69eabb256e6b351c2acd36d7f4076e Mon Sep 17 00:00:00 2001
> >> From: Thilo Borgmann <thilo.borgmann at mail.de>
> >> Date: Sat, 12 Mar 2016 14:52:17 +0100
> >> Subject: [PATCH 1/2] lavu/dict: Add new flag to allow multiple equal keys.
> >>
> >> ---
> >>  libavutil/dict.c | 5 ++++-
> >>  libavutil/dict.h | 5 +++--
> >>  2 files changed, 7 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/libavutil/dict.c b/libavutil/dict.c
> >> index 8bb65a1..70c0184 100644
> >> --- a/libavutil/dict.c
> >> +++ b/libavutil/dict.c
> >> @@ -70,9 +70,12 @@ int av_dict_set(AVDictionary **pm, const char *key, const char *value,
> >>                  int flags)
> >>  {
> >>      AVDictionary *m = *pm;
> >> -    AVDictionaryEntry *tag = av_dict_get(m, key, NULL, flags);
> >> +    AVDictionaryEntry *tag = NULL;
> >>      char *oldval = NULL, *copy_key = NULL, *copy_value = NULL;
> >>  
> >> +    if (!(flags & AV_DICT_MULTIKEY)) {
> >> +        tag = av_dict_get(m, key, NULL, flags);
> >> +    }
> >>      if (flags & AV_DICT_DONT_STRDUP_KEY)
> >>          copy_key = (void *)key;
> >>      else
> >> diff --git a/libavutil/dict.h b/libavutil/dict.h
> >> index b0aa784..c589bcd 100644
> >> --- a/libavutil/dict.h
> >> +++ b/libavutil/dict.h
> >> @@ -76,6 +76,7 @@
> >>  #define AV_DICT_DONT_OVERWRITE 16   ///< Don't overwrite existing entries.
> >>  #define AV_DICT_APPEND         32   /**< If the entry already exists, append to it.  Note that no
> >>                                        delimiter is added, the strings are simply concatenated. */
> >> +#define AV_DICT_MULTIKEY       64   /**< Allow to store several equal keys in the dictionary */
> >>  
> >>  typedef struct AVDictionaryEntry {
> >>      char *key;
> >> @@ -118,8 +119,8 @@ int av_dict_count(const AVDictionary *m);
> >>   *
> >>   * @param pm pointer to a pointer to a dictionary struct. If *pm is NULL
> >>   * a dictionary struct is allocated and put in *pm.
> >> - * @param key entry key to add to *pm (will be av_strduped depending on flags)
> >> - * @param value entry value to add to *pm (will be av_strduped depending on flags).
> >> + * @param key entry key to add to *pm (will either be av_strduped or added as a new key depending on flags)
> >> + * @param value entry value to add to *pm (will be av_strduped or added as a new key depending on flags).
> >>   *        Passing a NULL value will cause an existing entry to be deleted.
> >>   * @return >= 0 on success otherwise an error code <0
> >>   */  
> > 
> > Changing the semantics of AVDictionary just like this seems rather
> > questionable...  
> 
> It changes nothing for existing code, just adds a new feature. I don't
> think it hurts anyone or anything...

It only breaks basic assumptions about a basic data type...

> > Are you sure you don't want a list instead?  
> 
> AVDictionary serves the purpose perfectly and already handles all the
> key value seperation, parsing and error resilience... do we have a list
> container ready to do that?
> I'm not happy to use a deprecated thing either but AVTree seems not to
> be ready yet (parsing from string, keeping insertion order of keys even
> when rebalancing and most importantly enumeration (sequentially search
> for keys) seems not to be ready for multiple keys - although the tree
> itself can handle mutliple equal keys). This is why I decided to go with
> adding a new flag to the AVDictionary rather than doing it with AVTree
> nearly from scratch...