[FFmpeg-devel] default lock mechanism in libavcodec/utils.c

[Michael Niedermayer]

On Wed, Jan 29, 2014 at 11:49:41AM +0530, anshul wrote:
> On 01/29/2014 11:11 AM, anshul wrote:
> >On 01/28/2014 08:31 PM, Michael Niedermayer wrote:
> >>if you had avcodec_unregister_all() you will have to deal with
> >>libgstreamer and libvlc calling it while your app is also
> >>calling it and maybe another lib calling register and yet another
> >>still using avcodec. all happening at the same time
> >>
> >>this can be solved in various ways, a lock and reference counting is
> >>one, another is to use some code that gets called on exit or
> >>lib unloading by the OS.
> >>I think none of these will be really easy to do portably
> >
> >If I am planning to use some code that gets called when library is
> >unloaded.
> >I do need static avcodec lock acess out of library, I have
> >attached one patch
> >so that user might be able to call this function in his destructor
> >of library
> >
> >But your idea about reference count is very good, but I don't
> >where to keep that
> >reference count variable, only thing that strike my mind was to
> >make reference count variable global.
> >If you have any other way then making it global please ...
> >
> >
> >Thanks
> >Anshul
> >
> >
> forgot to add return 0; my new patch with same thing
> 
> Thanks
> Anshul Maheshwari

>  internal.h |    1 +
>  utils.c    |    8 ++++++++
>  2 files changed, 9 insertions(+)
> 47599b4e3f49bde9a68d3e398958472e4b18b61f  0001-added-ff_destroy_lock_avcodec-so-that-it-can-be-call.patch
> From 731dd24ba9b138f626baa9908fdb67f74ef64fe5 Mon Sep 17 00:00:00 2001
> From: Anshul Maheshwari <er.anshul.maheshwari at gmail.com>
> Date: Wed, 29 Jan 2014 11:39:11 +0530
> Subject: [PATCH] added ff_destroy_lock_avcodec so that it can be called by
>  user if they want to free the mutex
> 
> ---
>  libavcodec/internal.h | 1 +
>  libavcodec/utils.c    | 8 ++++++++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/libavcodec/internal.h b/libavcodec/internal.h
> index 8aa0ac1..2c85b7b 100644
> --- a/libavcodec/internal.h
> +++ b/libavcodec/internal.h
> @@ -151,6 +151,7 @@ void avpriv_color_frame(AVFrame *frame, const int color[4]);
>  extern volatile int ff_avcodec_locked;
>  int ff_lock_avcodec(AVCodecContext *log_ctx);
>  int ff_unlock_avcodec(void);
> +int ff_destroy_lock_avcodec(void);
>  
>  int avpriv_lock_avformat(void);
>  int avpriv_unlock_avformat(void);
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index c8fd8c6..20cc00b 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -3318,6 +3318,14 @@ int ff_unlock_avcodec(void)
>      return 0;
>  }
>  
> +int ff_destroy_lock_avcodec(void)
> +{
> +    if(lockmgr_cb) {
> +        if (lockmgr_cb(&codec_mutex, AV_LOCK_DESTROY))
> +            return -1;
> +    }
> +    return 0;
> +}

ff_ prefixed functions are internal  and considering its in internal.h
maybe thats what you intended but nothing calls it so this is just
unused and undocumneted code.
and if it wasnt internal people wouldnt know when or from where to
call this without documentation

also the function name should make it clear that it is unsafe to be
called when anything is still running or might use the lib afterwards
maybe
av_cleanup_on_lib_unload()
would be a better name for that ...


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