Set the post process cache when finished instead of one by one.

This should prevent a race condition if running collectstatic is
canceled or its cache is accessed from other processes, leaving the
cache in a corrupt state.

django/contrib/staticfiles/storage.py

@@ -189,8 +189,8 @@ def post_process(self, paths, dry_run=False, **options):
         if dry_run:
             return
 
-        # delete cache of all handled paths
-        self.cache.delete_many([self.cache_key(path) for path in paths])
+        # where to store the new paths
+        hashed_paths = {}
 
         # build a list of adjustable files
         matches = lambda path: matches_patterns(path, self._patterns.keys())
@@ -239,9 +239,12 @@ def post_process(self, paths, dry_run=False, **options):
                         hashed_name = force_unicode(saved_name.replace('\\', '/'))
 
                 # and then set the cache accordingly
-                self.cache.set(self.cache_key(name), hashed_name)
+                hashed_paths[self.cache_key(name)] = hashed_name
                 yield name, hashed_name, processed
 
+        # Finally set the cache
+        self.cache.set_many(hashed_paths)
+
 
 class CachedStaticFilesStorage(CachedFilesMixin, StaticFilesStorage):
     """