Fix T74662: Prefetching causes random crashes

Caused by 18b693bdbd6b, due to lack of thread safety.
Beteween calling BKE_sequencer_cache_get_num_items and BKE_sequencer_cache_iterate
New items could be inserted in the cache.

BKE_sequencer_cache_iterate() now use 2 callbcack functions for initial setup
during which buffers with correct length can be initialized and finally iterating.

Additionally drawing of unselected items was fixed again introduced in 18b693bdbd6b.

T74662 is reporting quite different symptoms, than I get on my machine, so I am not
entirely sure this is complete fix.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D7220

1 files changed, 5 insertions, 17 deletions

diff --git a/source/blender/blenkernel/intern/seqcache.c b/source/blender/blenkernel/intern/seqcache.c
index d48930e5665..a2c0434a474 100644
--- a/source/blender/blenkernel/intern/seqcache.c
+++ b/source/blender/blenkernel/intern/seqcache.c
@@ -1401,24 +1401,11 @@ void BKE_sequencer_cache_put(const SeqRenderData *context,
   }
 }
 
-size_t BKE_sequencer_cache_get_num_items(struct Scene *scene)
-{
-  SeqCache *cache = seq_cache_get_from_scene(scene);
-  if (!cache) {
-    return 0;
-  }
-
-  seq_cache_lock(scene);
-  size_t num_items = BLI_ghash_len(cache->hash);
-  seq_cache_unlock(scene);
-
-  return num_items;
-}
-
 void BKE_sequencer_cache_iterate(
     struct Scene *scene,
     void *userdata,
-    bool callback(void *userdata, struct Sequence *seq, int nfra, int cache_type, float cost))
+    bool callback_init(void *userdata, size_t item_count),
+    bool callback_iter(void *userdata, struct Sequence *seq, int nfra, int cache_type, float cost))
 {
   SeqCache *cache = seq_cache_get_from_scene(scene);
   if (!cache) {
@@ -1426,15 +1413,16 @@ void BKE_sequencer_cache_iterate(
   }
 
   seq_cache_lock(scene);
+  bool interrupt = callback_init(userdata, BLI_ghash_len(cache->hash));
+
   GHashIterator gh_iter;
   BLI_ghashIterator_init(&gh_iter, cache->hash);
-  bool interrupt = false;
 
   while (!BLI_ghashIterator_done(&gh_iter) && !interrupt) {
     SeqCacheKey *key = BLI_ghashIterator_getKey(&gh_iter);
     BLI_ghashIterator_step(&gh_iter);
 
-    interrupt = callback(userdata, key->seq, key->nfra, key->type, key->cost);
+    interrupt = callback_iter(userdata, key->seq, key->nfra, key->type, key->cost);
   }
 
   cache->last_key = NULL;