[FFmpeg-devel] [PATCH v3 1/3] lavc/utils.c: use C11 atomics for entangled thread handling

[James Almer]

On 11/25/2017 2:01 PM, Rostislav Pehlivanov wrote:
> Signed-off-by: Rostislav Pehlivanov <atomnuker at gmail.com>
> ---
>  libavcodec/utils.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/utils.c b/libavcodec/utils.c
> index e50de6e89b..3a0f3c11f5 100644
> --- a/libavcodec/utils.c
> +++ b/libavcodec/utils.c
> @@ -56,6 +56,7 @@
>  #include "version.h"
>  #include <stdlib.h>
>  #include <stdarg.h>
> +#include <stdatomic.h>
>  #include <limits.h>
>  #include <float.h>
>  #if CONFIG_ICONV
> @@ -114,7 +115,7 @@ static int (*lockmgr_cb)(void **mutex, enum AVLockOp op) = NULL;
>  
>  
>  volatile int ff_avcodec_locked;
> -static int volatile entangled_thread_counter = 0;
> +static atomic_int entangled_thread_counter = ATOMIC_VAR_INIT(0);
>  static void *codec_mutex;
>  static void *avformat_mutex;
>  
> @@ -1944,11 +1945,11 @@ int ff_lock_avcodec(AVCodecContext *log_ctx, const AVCodec *codec)
>              return -1;
>      }
>  
> -    if (avpriv_atomic_int_add_and_fetch(&entangled_thread_counter, 1) != 1) {
> +    if (atomic_fetch_add(&entangled_thread_counter, 1)) {
>          av_log(log_ctx, AV_LOG_ERROR,
>                 "Insufficient thread locking. At least %d threads are "
>                 "calling avcodec_open2() at the same time right now.\n",
> -               entangled_thread_counter);
> +               atomic_load(&entangled_thread_counter));
>          if (!lockmgr_cb)
>              av_log(log_ctx, AV_LOG_ERROR, "No lock manager is set, please see av_lockmgr_register()\n");
>          ff_avcodec_locked = 1;
> @@ -1967,7 +1968,7 @@ int ff_unlock_avcodec(const AVCodec *codec)
>  
>      av_assert0(ff_avcodec_locked);
>      ff_avcodec_locked = 0;
> -    avpriv_atomic_int_add_and_fetch(&entangled_thread_counter, -1);
> +    atomic_fetch_add(&entangled_thread_counter, -1);

Nit: You could use atomic_fetch_sub() instead of adding -1.

>      if (lockmgr_cb) {
>          if ((*lockmgr_cb)(&codec_mutex, AV_LOCK_RELEASE))
>              return -1;
>