ready for review

Author: konstntokas

CHANGES.md

@@ -10,6 +10,12 @@
   - `position`: to set the position of the respective icon button 
      in the viewer's sidebar.
 
+### Other changes
+* Added a new abstract class `PreloadDataStore` that defines the return type of the
+  `preload_data` method in `xcube.core.store.DataStore`. The `PreloadDataStore` is a
+  mutable data store containing a `preload_handle` field, which holds the handle
+  associated with a preload job.
+
 
 ## Changes in 1.8.3
 

xcube/core/store/store.py

@@ -509,8 +509,8 @@ def preload_data(
               on the possible options.
 
         Returns:
-            A handle for the preload process. The default implementation
-            returns an empty preload handle.
+            A mutable data store containing the preload handle.
+            The default implementation contains an empty preload handle.
         """
         cache_store = new_data_store("file")
         cache_store.preload_handle = NullPreloadHandle()