On Tue, 7 Mar 2017 02:47:36 +0700
Muhammad Faiz <mfc...@gmail.com> wrote:
> Signed-off-by: Muhammad Faiz <mfc...@gmail.com>
> ---
> libavcodec/allcodecs.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
> index eee322b..1d05fc1 100644
> --- a/libavcodec/allcodecs.c
> +++ b/libavcodec/allcodecs.c
> @@ -24,6 +24,8 @@
> * Provide registration of all codecs, parsers and bitstream filters for
> libavcodec.
> */
>
> +#include <stdatomic.h>
> +
> #include "config.h"
> #include "avcodec.h"
> #include "version.h"
> @@ -60,11 +62,14 @@
>
> void avcodec_register_all(void)
> {
> - static int initialized;
> + static atomic_int initialized;
> + static atomic_int ready;
>
> - if (initialized)
> + if (atomic_exchange_explicit(&initialized, 1, memory_order_relaxed)) {
> + while (!atomic_load_explicit(&ready, memory_order_relaxed))
> + ;
> return;
> - initialized = 1;
> + }
>
> /* hardware accelerators */
> REGISTER_HWACCEL(H263_VAAPI, h263_vaapi);
> @@ -716,4 +721,6 @@ void avcodec_register_all(void)
> REGISTER_PARSER(VP8, vp8);
> REGISTER_PARSER(VP9, vp9);
> REGISTER_PARSER(XMA, xma);
> +
> + atomic_store_explicit(&ready, 1, memory_order_relaxed);
> }
avcodec_register() is already "safe" by attempting to do lock-free and
wait-free list insertion (not very convincing IMHO, but it's there).
Should that code be removed? Does anyone know why avcodec_register() is
even still public API? The same affects some other things.
Also, if you want to do it right, please use ff_thread_once() to do it
without busy waiting. It works like pthread_once(), which was invented
to avoid such constructions.
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