Stephen Hutchinson:
> The atexit() handler in the avisynth demuxer was added because
> there was a conflict in AvxSynth that arose due to their use
> of C++ global objects, particularly in relation to having
> added a logging function relying on log4cpp.
>
> This conflict was responsible for causing a segfault on exit.
> It did not affect Windows with the (at the time) upstream
> AviSynth 2.5 and 2.6, nor does it affect AviSynth+.
>
> Unfortunately, none of this was actually shielded by ifdefs
> indicating the fact it was only needed for AvxSynth, so four
> years ago when AviSynth+ replaced AvxSynth as the handler
> for AviSynth scripts on Unix-like OSes, the fact that the
> atexit handler was no longer necessary was overlooked.
>
> Signed-off-by: Stephen Hutchinson <qyo...@gmail.com>
> ---
> libavformat/avisynth.c | 45 ------------------------------------------
> 1 file changed, 45 deletions(-)
>
> diff --git a/libavformat/avisynth.c b/libavformat/avisynth.c
> index 625bdf7e3a..5d1ecc0bf6 100644
> --- a/libavformat/avisynth.c
> +++ b/libavformat/avisynth.c
> @@ -115,9 +115,6 @@ typedef struct AviSynthContext {
> int error;
>
> uint32_t flags;
> -
> - /* Linked list pointers. */
> - struct AviSynthContext *next;
> } AviSynthContext;
>
> static const int avs_planes_packed[1] = { 0 };
> @@ -133,15 +130,7 @@ static const int avs_planes_rgba[4] = { AVS_PLANAR_G,
> AVS_PLANAR_B,
>
> static AVMutex avisynth_mutex = AV_MUTEX_INITIALIZER;
>
> -/* A conflict between C++ global objects, atexit, and dynamic loading
> requires
> - * us to register our own atexit handler to prevent double freeing. */
> static AviSynthLibrary avs_library;
> -static int avs_atexit_called = 0;
> -
> -/* Linked list of AviSynthContexts. An atexit handler destroys this list. */
> -static AviSynthContext *avs_ctx_list = NULL;
> -
> -static av_cold void avisynth_atexit_handler(void);
>
> static av_cold int avisynth_load_library(void)
> {
> @@ -185,7 +174,6 @@ static av_cold int avisynth_load_library(void)
> LOAD_AVS_FUNC(avs_get_env_property, 1);
> #undef LOAD_AVS_FUNC
>
> - atexit(avisynth_atexit_handler);
> return 0;
>
> fail:
> @@ -214,30 +202,11 @@ static av_cold int
> avisynth_context_create(AVFormatContext *s)
> }
> }
>
> - if (!avs_ctx_list) {
> - avs_ctx_list = avs;
> - } else {
> - avs->next = avs_ctx_list;
> - avs_ctx_list = avs;
> - }
> -
> return 0;
> }
>
> static av_cold void avisynth_context_destroy(AviSynthContext *avs)
> {
> - if (avs_atexit_called)
> - return;
> -
> - if (avs == avs_ctx_list) {
> - avs_ctx_list = avs->next;
> - } else {
> - AviSynthContext *prev = avs_ctx_list;
> - while (prev->next != avs)
> - prev = prev->next;
> - prev->next = avs->next;
> - }
> -
> if (avs->clip) {
> avs_library.avs_release_clip(avs->clip);
> avs->clip = NULL;
> @@ -248,20 +217,6 @@ static av_cold void
> avisynth_context_destroy(AviSynthContext *avs)
> }
> }
>
> -static av_cold void avisynth_atexit_handler(void)
> -{
> - AviSynthContext *avs = avs_ctx_list;
> -
> - while (avs) {
> - AviSynthContext *next = avs->next;
> - avisynth_context_destroy(avs);
> - avs = next;
> - }
> - dlclose(avs_library.library);
> -
> - avs_atexit_called = 1;
> -}
> -
> /* Create AVStream from audio and video data. */
> static int avisynth_create_stream_video(AVFormatContext *s, AVStream *st)
> {
avisynth_context_destroy() is currently always called while holding the
lock (i.e. avisynth_mutex). Is this even necessary? It is clear that
avisynth_load_library() (and the check for whether it should be called)
need the lock, but does anything else (like
avs_create_script_environment) really need it?
- Andreas
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