File Browser: Improve usage of threads in the creation of thumbnails

Due to asynchronous process, the preview for a given image may be
generated several times.

This regenerates many thumbs unnecessarily.

The solution is to add the `FILE_ENTRY_PREVIEW_LOADING` flag for file
entries that are still in the thread queue.

So this flag is checked not to redraw the thumb when it is still being
created on a different thread.

Differential Revision: https://developer.blender.org/D11150

1 files changed, 15 insertions, 11 deletions

diff --git a/source/blender/editors/space_file/filelist.c b/source/blender/editors/space_file/filelist.c
index 5d1a202e5ca..d32e947d688 100644
--- a/source/blender/editors/space_file/filelist.c
+++ b/source/blender/editors/space_file/filelist.c
@@ -1731,7 +1731,7 @@ static void filelist_cache_previews_push(FileList *filelist, FileDirEntry *entry
     return;
   }
 
-  if (entry->flags & FILE_ENTRY_INVALID_PREVIEW) {
+  if (entry->flags & (FILE_ENTRY_INVALID_PREVIEW | FILE_ENTRY_PREVIEW_LOADING)) {
     return;
   }
 
@@ -1762,6 +1762,7 @@ static void filelist_cache_previews_push(FileList *filelist, FileDirEntry *entry
   FileListEntryPreviewTaskData *preview_taskdata = MEM_mallocN(sizeof(*preview_taskdata),
                                                                __func__);
   preview_taskdata->preview = preview;
+  entry->flags |= FILE_ENTRY_PREVIEW_LOADING;
   BLI_task_pool_push(cache->previews_pool,
                      filelist_cache_preview_runf,
                      preview_taskdata,
@@ -2680,24 +2681,27 @@ bool filelist_cache_previews_update(FileList *filelist)
 
     //      printf("%s: %d - %s - %p\n", __func__, preview->index, preview->path, preview->img);
 
-    if (preview->icon_id) {
-      /* Due to asynchronous process, a preview for a given image may be generated several times,
-       * i.e. entry->image may already be set at this point. */
-      if (entry && !entry->preview_icon_id) {
+    if (entry) {
+      entry->flags &= ~FILE_ENTRY_PREVIEW_LOADING;
+      if (preview->icon_id) {
+        /* The FILE_ENTRY_PREVIEW_LOADING flag should have prevented any other asynchronous
+         * process from trying to generate the same preview icon. */
+        BLI_assert_msg(!entry->preview_icon_id, "Preview icon should not have been generated yet");
+
         /* Move ownership over icon. */
         entry->preview_icon_id = preview->icon_id;
         preview->icon_id = 0;
         changed = true;
       }
       else {
-        BKE_icon_delete(preview->icon_id);
+        /* We want to avoid re-processing this entry continuously!
+         * Note that, since entries only live in cache,
+         * preview will be retried quite often anyway. */
+        entry->flags |= FILE_ENTRY_INVALID_PREVIEW;
       }
     }
-    else if (entry) {
-      /* We want to avoid re-processing this entry continuously!
-       * Note that, since entries only live in cache,
-       * preview will be retried quite often anyway. */
-      entry->flags |= FILE_ENTRY_INVALID_PREVIEW;
+    else {
+      BKE_icon_delete(preview->icon_id);
     }
 
     MEM_freeN(preview);