Alembic import: fixed memory management for CoW copies of CacheFile blocks

When a CacheFile datablock is copied to an in-main datablock, it means that
the new copy should be independent of the old copy. In this case certain
properties are reset/duplicated. When it is copied to a no-main datablock,
we assume this is a copy-on-write copy that's used for evaluating things,
in which case the handle and object paths are referenced instead of
reset/ duplicated. This prevents us from re-opening the Alembic file every
time a new CoW copy is made.

The same approach is taken when freeing data (only when an in-main datablock
is freed do we actually free the data).

1 files changed, 19 insertions, 6 deletions

diff --git a/source/blender/blenkernel/intern/cachefile.c b/source/blender/blenkernel/intern/cachefile.c
index d0cdfd6aeed..58770b37147 100644
--- a/source/blender/blenkernel/intern/cachefile.c
+++ b/source/blender/blenkernel/intern/cachefile.c
@@ -89,15 +89,22 @@ void BKE_cachefile_free(CacheFile *cache_file)
 {
 	BKE_animdata_free((ID *)cache_file, false);
 
+	if (cache_file->id.tag & LIB_TAG_NO_MAIN) {
+		/* CoW/no-main copies reuse the existing ArchiveReader and mutex */
+		return;
+	}
+
+	if (cache_file->handle) {
 #ifdef WITH_ALEMBIC
-	ABC_free_handle(cache_file->handle);
+		ABC_free_handle(cache_file->handle);
 #endif
-
-	/* CoW copies share the mutex, so it should only be freed if the original
-	 * CacheFile datablock is freed. */
-	if (cache_file->handle_mutex && (cache_file->id.tag & LIB_TAG_COPIED_ON_WRITE) == 0) {
+		cache_file->handle = NULL;
+	}
+	if (cache_file->handle_mutex) {
 		BLI_mutex_free(cache_file->handle_mutex);
+		cache_file->handle_mutex = NULL;
 	}
+
 	BLI_freelistN(&cache_file->object_paths);
 }
 
@@ -112,8 +119,14 @@ void BKE_cachefile_free(CacheFile *cache_file)
 void BKE_cachefile_copy_data(
         Main *UNUSED(bmain), CacheFile *cache_file_dst, const CacheFile *UNUSED(cache_file_src), const int UNUSED(flag))
 {
+	if (cache_file_dst->id.tag & LIB_TAG_NO_MAIN) {
+		/* CoW/no-main copies reuse the existing ArchiveReader and mutex */
+		return;
+	}
+
 	cache_file_dst->handle = NULL;
-	BLI_listbase_clear(&cache_file_dst->object_paths);
+	cache_file_dst->handle_mutex = NULL;
+	BLI_duplicatelist(&cache_file_dst->object_paths, &cache_file_dst->object_paths);
 }
 
 CacheFile *BKE_cachefile_copy(Main *bmain, const CacheFile *cache_file)