swscale: switch to refstruct for hw_priv

This is a bit more forward-facing than a bare allocation, and importantly,
allows the `swscale/utils.c` code to remain agnostic about how to correctly
uninit this struct.

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Niklas Haas <git@haasn.dev>

libswscale/swscale_internal.h

@@ -696,7 +696,7 @@ struct SwsInternal {
     Half2FloatTables *h2f_tables;
 
     // Hardware specific private data
-    void *hw_priv;
+    void *hw_priv; /* refstruct */
 };
 //FIXME check init (where 0)
 

libswscale/utils.c

@@ -50,6 +50,7 @@
 #include "libavutil/mem.h"
 #include "libavutil/opt.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/refstruct.h"
 #include "libavutil/slicethread.h"
 #include "libavutil/thread.h"
 #include "libavutil/aarch64/cpu.h"
@@ -2248,9 +2249,7 @@ void sws_freeContext(SwsContext *sws)
     if (!c)
         return;
 
-#if CONFIG_UNSTABLE && CONFIG_VULKAN
-    ff_sws_vk_uninit(sws);
-#endif
+    av_refstruct_unref(&c->hw_priv);
 
     for (i = 0; i < FF_ARRAY_ELEMS(c->graph); i++)
         ff_sws_graph_free(&c->graph[i]);

libswscale/vulkan/ops.c

@@ -21,14 +21,12 @@
 #include "../ops_internal.h"
 #include "../swscale_internal.h"
 #include "libavutil/mem.h"
+#include "libavutil/refstruct.h"
 #include "ops.h"
 
-void ff_sws_vk_uninit(SwsContext *sws)
+static void ff_sws_vk_uninit(AVRefStructOpaque opaque, void *obj)
 {
-    SwsInternal *c = sws_internal(sws);
-    FFVulkanOpsCtx *s = c->hw_priv;
-    if (!s)
-        return;
+    FFVulkanOpsCtx *s = obj;
 
 #if CONFIG_LIBSHADERC || CONFIG_LIBGLSLANG
     if (s->spvc)
@@ -36,7 +34,6 @@ void ff_sws_vk_uninit(SwsContext *sws)
 #endif
     ff_vk_exec_pool_free(&s->vkctx, &s->e);
     ff_vk_uninit(&s->vkctx);
-    av_freep(&c->hw_priv);
 }
 
 int ff_sws_vk_init(SwsContext *sws, AVBufferRef *dev_ref)
@@ -45,7 +42,8 @@ int ff_sws_vk_init(SwsContext *sws, AVBufferRef *dev_ref)
     SwsInternal *c = sws_internal(sws);
 
     if (!c->hw_priv) {
-        c->hw_priv = av_mallocz(sizeof(FFVulkanOpsCtx));
+        c->hw_priv = av_refstruct_alloc_ext(sizeof(FFVulkanOpsCtx), 0, NULL,
+                                            ff_sws_vk_uninit);
         if (!c->hw_priv)
             return AVERROR(ENOMEM);
     }

libswscale/vulkan/ops.h

@@ -38,6 +38,5 @@ typedef struct FFVulkanOpsCtx {
 } FFVulkanOpsCtx;
 
 int ff_sws_vk_init(SwsContext *sws, AVBufferRef *dev_ref);
-void ff_sws_vk_uninit(SwsContext *sws);
 
 #endif /* SWSCALE_VULKAN_OPS_H */