Fix threading conflict when doing Cycles background render

It is possible to have same image used multiple times at different frames,
which means we can not free it's buffers without any guard. From quick tests
this seems to be doing what it is supposed to.

Need more testing and port this to 2.79.

3 files changed, 15 insertions, 2 deletions

diff --git a/source/blender/blenkernel/BKE_image.h b/source/blender/blenkernel/BKE_image.h
index 3f8be511212..3c716f39dd0 100644
--- a/source/blender/blenkernel/BKE_image.h
+++ b/source/blender/blenkernel/BKE_image.h
@@ -58,6 +58,7 @@ void   BKE_images_exit(void);
 void    BKE_image_free_packedfiles(struct Image *image);
 void    BKE_image_free_views(struct Image *image);
 void    BKE_image_free_buffers(struct Image *image);
+void    BKE_image_free_buffers_ex(struct Image *image, bool do_lock);
 /* call from library */
 void    BKE_image_free(struct Image *image);
 
diff --git a/source/blender/blenkernel/intern/image.c b/source/blender/blenkernel/intern/image.c
index bbe6814f6b7..902076c2d14 100644
--- a/source/blender/blenkernel/intern/image.c
+++ b/source/blender/blenkernel/intern/image.c
@@ -303,8 +303,11 @@ static void image_free_anims(Image *ima)
  * Simply free the image data from memory,
  * on display the image can load again (except for render buffers).
  */
-void BKE_image_free_buffers(Image *ima)
+void BKE_image_free_buffers_ex(Image *ima, bool do_lock)
 {
+	if (do_lock) {
+		BLI_spin_lock(&image_spin);
+	}
 	image_free_cached_frames(ima);
 
 	image_free_anims(ima);
@@ -323,6 +326,15 @@ void BKE_image_free_buffers(Image *ima)
 	}
 
 	ima->ok = IMA_OK;
+
+	if (do_lock) {
+		BLI_spin_unlock(&image_spin);
+	}
+}
+
+void BKE_image_free_buffers(Image *ima)
+{
+	BKE_image_free_buffers_ex(ima, false);
 }
 
 /** Free (or release) any data used by this image (does not free the image itself). */
diff --git a/source/blender/makesrna/intern/rna_image_api.c b/source/blender/makesrna/intern/rna_image_api.c
index 344c1781b46..5c706d9d8db 100644
--- a/source/blender/makesrna/intern/rna_image_api.c
+++ b/source/blender/makesrna/intern/rna_image_api.c
@@ -291,7 +291,7 @@ static void rna_Image_filepath_from_user(Image *image, ImageUser *image_user, ch
 
 static void rna_Image_buffers_free(Image *image)
 {
-	BKE_image_free_buffers(image);
+	BKE_image_free_buffers_ex(image, true);
 }
 
 #else