[FFmpeg-devel] [PATCH] all: Don't use ATOMIC_VAR_INIT

[FFmpeg-devel] [PATCH] all: Don't use ATOMIC_VAR_INIT

[Andreas Rheinhardt]

C11 required to use ATOMIC_VAR_INIT to statically initialize
atomic objects with static storage duration. Yet this macro
was unsuitable for initializing structures [1] and was actually
unneeded for all known implementations (this includes our
compatibility fallback implementations which simply wrap the value
in parentheses: #define ATOMIC_VAR_INIT(value) (value)).
Therefore C17 deprecated the macro and C23 actually removed it [2].

Since commit 5ff0eb34d2b1089d3dd9f27fdb51520001709138 we default
to C17 if the compiler supports it; Clang warns about ATOMIC_VAR_INIT
in this mode. Given that no implementation ever needed this macro,
this commit stops using it to avoid this warning.

[1]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2396.htm#dr_485
[2]: https://en.cppreference.com/w/c/atomic/ATOMIC_VAR_INIT

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 configure                | 4 ++--
 fftools/ffmpeg.c         | 2 +-
 libavformat/allformats.c | 4 ++--
 libavutil/cpu.c          | 6 +++---
 libavutil/mem.c          | 2 +-
 5 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/configure b/configure
index b9fa8652c4..e577dcc677 100755
--- a/configure
+++ b/configure
@@ -6610,8 +6610,8 @@ check_headers asm/types.h
 # some configurations also require linking to libatomic, so try
 # both with -latomic and without
 for LATOMIC in "-latomic" ""; do
-    check_builtin stdatomic stdatomic.h                                                 \
-        "atomic_int foo, bar = ATOMIC_VAR_INIT(-1); atomic_store(&foo, 0); foo += bar"  \
+    check_builtin stdatomic stdatomic.h                                \
+        "atomic_int foo, bar = -1; atomic_store(&foo, 0); foo += bar"  \
         $LATOMIC && eval stdatomic_extralibs="\$LATOMIC" && break
 done
 
diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
index d4e5f978f1..5e00d5b645 100644
--- a/fftools/ffmpeg.c
+++ b/fftools/ffmpeg.c
@@ -157,7 +157,7 @@ void term_exit(void)
 
 static volatile int received_sigterm = 0;
 static volatile int received_nb_signals = 0;
-static atomic_int transcode_init_done = ATOMIC_VAR_INIT(0);
+static atomic_int transcode_init_done = 0;
 static volatile int ffmpeg_exited = 0;
 static int64_t copy_ts_first_pts = AV_NOPTS_VALUE;
 
diff --git a/libavformat/allformats.c b/libavformat/allformats.c
index e15d0fa6d7..9df42bb87a 100644
--- a/libavformat/allformats.c
+++ b/libavformat/allformats.c
@@ -576,8 +576,8 @@ extern const FFInputFormat  ff_vapoursynth_demuxer;
 #include "libavformat/muxer_list.c"
 #include "libavformat/demuxer_list.c"
 
-static atomic_uintptr_t indev_list_intptr  = ATOMIC_VAR_INIT(0);
-static atomic_uintptr_t outdev_list_intptr = ATOMIC_VAR_INIT(0);
+static atomic_uintptr_t indev_list_intptr  = 0;
+static atomic_uintptr_t outdev_list_intptr = 0;
 
 const AVOutputFormat *av_muxer_iterate(void **opaque)
 {
diff --git a/libavutil/cpu.c b/libavutil/cpu.c
index 48d195168c..d4f947360a 100644
--- a/libavutil/cpu.c
+++ b/libavutil/cpu.c
@@ -49,8 +49,8 @@
 #include <unistd.h>
 #endif
 
-static atomic_int cpu_flags = ATOMIC_VAR_INIT(-1);
-static atomic_int cpu_count = ATOMIC_VAR_INIT(-1);
+static atomic_int cpu_flags = -1;
+static atomic_int cpu_count = -1;
 
 static int get_cpu_flags(void)
 {
@@ -208,7 +208,7 @@ int av_parse_cpu_caps(unsigned *flags, const char *s)
 
 int av_cpu_count(void)
 {
-    static atomic_int printed = ATOMIC_VAR_INIT(0);
+    static atomic_int printed = 0;
 
     int nb_cpus = 1;
     int count   = 0;
diff --git a/libavutil/mem.c b/libavutil/mem.c
index 62163b4cb3..02d4cb791f 100644
--- a/libavutil/mem.c
+++ b/libavutil/mem.c
@@ -69,7 +69,7 @@ void  free(void *ptr);
  * dynamic libraries and remove -Wl,-Bsymbolic from the linker flags.
  * Note that this will cost performance. */
 
-static atomic_size_t max_alloc_size = ATOMIC_VAR_INIT(INT_MAX);
+static atomic_size_t max_alloc_size = INT_MAX;
 
 void av_max_alloc(size_t max){
     atomic_store_explicit(&max_alloc_size, max, memory_order_relaxed);
-- 
2.40.1

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Re: [FFmpeg-devel] [PATCH] all: Don't use ATOMIC_VAR_INIT

[Andreas Rheinhardt]

Andreas Rheinhardt:
> C11 required to use ATOMIC_VAR_INIT to statically initialize
> atomic objects with static storage duration. Yet this macro
> was unsuitable for initializing structures [1] and was actually
> unneeded for all known implementations (this includes our
> compatibility fallback implementations which simply wrap the value
> in parentheses: #define ATOMIC_VAR_INIT(value) (value)).
> Therefore C17 deprecated the macro and C23 actually removed it [2].
> 
> Since commit 5ff0eb34d2b1089d3dd9f27fdb51520001709138 we default
> to C17 if the compiler supports it; Clang warns about ATOMIC_VAR_INIT
> in this mode. Given that no implementation ever needed this macro,
> this commit stops using it to avoid this warning.
> 
> [1]: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2396.htm#dr_485
> [2]: https://en.cppreference.com/w/c/atomic/ATOMIC_VAR_INIT
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  configure                | 4 ++--
>  fftools/ffmpeg.c         | 2 +-
>  libavformat/allformats.c | 4 ++--
>  libavutil/cpu.c          | 6 +++---
>  libavutil/mem.c          | 2 +-
>  5 files changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/configure b/configure
> index b9fa8652c4..e577dcc677 100755
> --- a/configure
> +++ b/configure
> @@ -6610,8 +6610,8 @@ check_headers asm/types.h
>  # some configurations also require linking to libatomic, so try
>  # both with -latomic and without
>  for LATOMIC in "-latomic" ""; do
> -    check_builtin stdatomic stdatomic.h                                                 \
> -        "atomic_int foo, bar = ATOMIC_VAR_INIT(-1); atomic_store(&foo, 0); foo += bar"  \
> +    check_builtin stdatomic stdatomic.h                                \
> +        "atomic_int foo, bar = -1; atomic_store(&foo, 0); foo += bar"  \
>          $LATOMIC && eval stdatomic_extralibs="\$LATOMIC" && break
>  done
>  
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index d4e5f978f1..5e00d5b645 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -157,7 +157,7 @@ void term_exit(void)
>  
>  static volatile int received_sigterm = 0;
>  static volatile int received_nb_signals = 0;
> -static atomic_int transcode_init_done = ATOMIC_VAR_INIT(0);
> +static atomic_int transcode_init_done = 0;
>  static volatile int ffmpeg_exited = 0;
>  static int64_t copy_ts_first_pts = AV_NOPTS_VALUE;
>  
> diff --git a/libavformat/allformats.c b/libavformat/allformats.c
> index e15d0fa6d7..9df42bb87a 100644
> --- a/libavformat/allformats.c
> +++ b/libavformat/allformats.c
> @@ -576,8 +576,8 @@ extern const FFInputFormat  ff_vapoursynth_demuxer;
>  #include "libavformat/muxer_list.c"
>  #include "libavformat/demuxer_list.c"
>  
> -static atomic_uintptr_t indev_list_intptr  = ATOMIC_VAR_INIT(0);
> -static atomic_uintptr_t outdev_list_intptr = ATOMIC_VAR_INIT(0);
> +static atomic_uintptr_t indev_list_intptr  = 0;
> +static atomic_uintptr_t outdev_list_intptr = 0;
>  
>  const AVOutputFormat *av_muxer_iterate(void **opaque)
>  {
> diff --git a/libavutil/cpu.c b/libavutil/cpu.c
> index 48d195168c..d4f947360a 100644
> --- a/libavutil/cpu.c
> +++ b/libavutil/cpu.c
> @@ -49,8 +49,8 @@
>  #include <unistd.h>
>  #endif
>  
> -static atomic_int cpu_flags = ATOMIC_VAR_INIT(-1);
> -static atomic_int cpu_count = ATOMIC_VAR_INIT(-1);
> +static atomic_int cpu_flags = -1;
> +static atomic_int cpu_count = -1;
>  
>  static int get_cpu_flags(void)
>  {
> @@ -208,7 +208,7 @@ int av_parse_cpu_caps(unsigned *flags, const char *s)
>  
>  int av_cpu_count(void)
>  {
> -    static atomic_int printed = ATOMIC_VAR_INIT(0);
> +    static atomic_int printed = 0;
>  
>      int nb_cpus = 1;
>      int count   = 0;
> diff --git a/libavutil/mem.c b/libavutil/mem.c
> index 62163b4cb3..02d4cb791f 100644
> --- a/libavutil/mem.c
> +++ b/libavutil/mem.c
> @@ -69,7 +69,7 @@ void  free(void *ptr);
>   * dynamic libraries and remove -Wl,-Bsymbolic from the linker flags.
>   * Note that this will cost performance. */
>  
> -static atomic_size_t max_alloc_size = ATOMIC_VAR_INIT(INT_MAX);
> +static atomic_size_t max_alloc_size = INT_MAX;
>  
>  void av_max_alloc(size_t max){
>      atomic_store_explicit(&max_alloc_size, max, memory_order_relaxed);

Will apply this patch tomorrow unless there are objections.

- Andreas

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