MSVC: Use C11 atomics if supported via /experimental:c11atomics

libvmaf/meson.build

@@ -29,21 +29,38 @@ elif host_machine.system() == 'darwin'
 endif
 
 # Header checks
-stdatomic_dependency = []
-if not cc.check_header('stdatomic.h')
-    if cc.get_id() == 'msvc'
-        # we have a custom replacement for MSVC
-        stdatomic_dependency = declare_dependency(
-            include_directories : include_directories('src/compat/msvc'),
-        )
-    elif cc.compiles('''int main() { int v = 0; return __atomic_fetch_add(&v, 1, __ATOMIC_SEQ_CST); }''',
-                     name : 'GCC-style atomics', args : test_args)
-        stdatomic_dependency = declare_dependency(
-            include_directories : include_directories('src/compat/gcc'),
-        )
+if cc.has_header('stdatomic.h', args: test_args)
+    if cc.check_header('stdatomic.h', args: test_args)
+        stdatomic_dependency = declare_dependency(compile_args: '-DHAVE_STDATOMIC_H')
+    elif cc.get_id() == 'msvc'
+        # If stdatomic.h exists but isn't usable under MSVC it may be because recent (VS2022) MSVC
+        # has added support for lock-free atomics where (sizeof(T) <= sizeof(intptr_t))
+        # Note that __STDC_NO_ATOMICS__ remains defined due to lack of locking atomics
+        test_args += '/experimental:c11atomics'
+
+        if not cc.check_header('stdatomic.h', args: test_args)
+            error('stdatomic.h exists but could not be made usable under MSVC with /experimental:c11atomics')
+        endif
+
+        add_project_arguments('/experimental:c11atomics', language: 'c')
+        stdatomic_dependency = declare_dependency(compile_args: '-DHAVE_STDATOMIC_H')
     else
-        error('Atomics not supported')
+        error('stdatomic.h was found but is not usable for some reason; check whether the compiler needs extension flags')
     endif
+elif cc.get_id() == 'msvc'
+    # we have a custom replacement for MSVC before /experimental:c11atomics was added
+    stdatomic_dependency = declare_dependency(
+        compile_args : '-DHAVE_STDATOMIC_H',
+        include_directories : include_directories('src/compat/msvc'),
+    )
+elif cc.compiles('''int main() { int v = 0; return __atomic_fetch_add(&v, 1, __ATOMIC_SEQ_CST); }''',
+                 name : 'GCC-style atomics', args : test_args)
+    stdatomic_dependency = declare_dependency(
+        compile_args : '-DHAVE_STDATOMIC_H',
+        include_directories : include_directories('src/compat/gcc'),
+    )
+else
+    error('Atomics not supported')
 endif
 
 subdir('include')

libvmaf/src/compat/msvc/stdatomic.h

@@ -27,20 +27,29 @@
 #ifndef MSCVER_STDATOMIC_H_
 #define MSCVER_STDATOMIC_H_
 
-#if !defined(__cplusplus) && defined(_MSC_VER)
+#ifdef __cplusplus
+#error "This compatibility header should not be used with C++ files (C++ has its own <stdatomic.h>)"
+#endif
+
+#ifndef _MSC_VER
+#error "This compatibility header should only be used with MSVC (clang-cl might work)"
+#endif
+
+#ifndef __STDC_NO_ATOMICS__
+#error "This compatibility header should only be used with MSVC versions that don't implement <stdatomic.h>"
+#endif
 
 #pragma warning(push)
 #pragma warning(disable:4067)    /* newline for __has_include_next */
 
 #if defined(__clang__) && __has_include_next(<stdatomic.h>)
+   /* ??? This should not happen unless system <stdatomic.h> exists but for some reason the Meson test for it failed. */
    /* use the clang stdatomic.h with clang-cl*/
 #  include_next <stdatomic.h>
-#else /* ! stdatomic.h */
+#else /* ! clang && stdatomic.h */
 
 #include <windows.h>
 
-#include "common/attributes.h"
-
 typedef volatile LONG  __declspec(align(32)) atomic_int;
 typedef volatile ULONG __declspec(align(32)) atomic_uint;
 
@@ -65,6 +74,4 @@ typedef enum {
 
 #pragma warning(pop)
 
-#endif /* !defined(__cplusplus) && defined(_MSC_VER) */
-
 #endif /* MSCVER_STDATOMIC_H_ */

libvmaf/src/feature/feature_extractor.h

@@ -19,7 +19,11 @@
 #ifndef __VMAF_FEATURE_EXTRACTOR_H__
 #define __VMAF_FEATURE_EXTRACTOR_H__
 
+#ifdef HAVE_STDATOMIC_H
 #include <stdatomic.h>
+#else
+#error "Meson target is missing stdatomic_depedency"
+#endif
 #include <stdint.h>
 #include <stdlib.h>
 

libvmaf/src/framesync.h

@@ -20,7 +20,11 @@
 #define __VMAF_FRAME_SYNC_H__
 
 #include <pthread.h>
+#ifdef HAVE_STDATOMIC_H
 #include <stdatomic.h>
+#else
+#error "Meson target is missing stdatomic_depedency"
+#endif
 #include <stdint.h>
 #include <stdlib.h>
 #include "libvmaf/libvmaf.h"

libvmaf/src/ref.h

@@ -19,7 +19,11 @@
 #ifndef __VMAF_SRC_REF_H__
 #define __VMAF_SRC_REF_H__
 
+#ifdef HAVE_STDATOMIC_H
 #include <stdatomic.h>
+#else
+#error "Meson target is missing stdatomic_depedency"
+#endif
 
 typedef struct VmafRef {
     atomic_int cnt;

libvmaf/test/meson.build

@@ -26,7 +26,7 @@ test_feature_collector = executable('test_feature_collector',
     ['test.c', 'test_feature_collector.c', '../src/log.c', '../src/predict.c', '../src/svm.cpp', '../src/metadata_handler.c'],
     include_directories : [libvmaf_inc, test_inc, include_directories('../src/feature/'), include_directories('../src')],
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
-    dependencies: cuda_dependency
+    dependencies: [stdatomic_dependency, cuda_dependency]
 )
 
 test_log = executable('test_log',
@@ -46,7 +46,7 @@ test_model = executable('test_model',
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
     c_args : [vmaf_cflags_common, '-DJSON_MODEL_PATH="'+join_paths(meson.project_source_root(), '../model/')+'"'],
     cpp_args : vmaf_cflags_common,
-    dependencies : [thread_lib, cuda_dependency],
+    dependencies : [stdatomic_dependency, thread_lib, cuda_dependency],
 )
 
 test_predict = executable('test_predict',
@@ -57,7 +57,7 @@ test_predict = executable('test_predict',
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
     c_args : vmaf_cflags_common,
     cpp_args : vmaf_cflags_common,
-    dependencies : [thread_lib, cuda_dependency],
+    dependencies : [stdatomic_dependency, thread_lib, cuda_dependency],
 )
 
 test_feature_extractor = executable('test_feature_extractor',
@@ -88,6 +88,7 @@ test_cpu = executable('test_cpu',
 test_ref = executable('test_ref',
     ['test.c', 'test_ref.c', '../src/ref.c'],
     include_directories : [libvmaf_inc, test_inc, include_directories('../src/')],
+    dependencies: stdatomic_dependency
 )
 
 test_feature = executable('test_feature',
@@ -99,14 +100,14 @@ test_ciede = executable('test_ciede',
     ['test.c', 'test_ciede.c'],
     include_directories : [libvmaf_inc, test_inc, include_directories('../src/')],
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
-    dependencies: cuda_dependency
+    dependencies: [stdatomic_dependency, cuda_dependency]
 )
 
 test_cambi = executable('test_cambi',
     ['test.c', 'test_cambi.c', '../src/picture.c', '../src/mem.c', '../src/ref.c'],
     include_directories : [libvmaf_inc, test_inc, include_directories('../src/')],
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
-    dependencies: cuda_dependency
+    dependencies: [stdatomic_dependency, cuda_dependency]
 )
 
 test_luminance_tools = executable('test_luminance_tools',
@@ -126,6 +127,7 @@ test_psnr = executable('test_psnr',
     ['test.c', 'test_psnr.c', '../src/picture.c'],
     include_directories : [libvmaf_inc, test_inc, include_directories('../src/')],
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
+    dependencies : stdatomic_dependency
 )
 
 test_framesync = executable('test_framesync',
@@ -134,7 +136,7 @@ test_framesync = executable('test_framesync',
     link_with : get_option('default_library') == 'both' ? libvmaf.get_static_lib() : libvmaf,
     c_args : vmaf_cflags_common,
     cpp_args : vmaf_cflags_common,
-    dependencies : thread_lib,
+    dependencies : [stdatomic_dependency, thread_lib],
 )
 
 if get_option('enable_cuda')