[gnome-shell/wip/carlosg/async-persistent-data] shell-global: Make saving of persistent state asynchronous

[Carlos Garnacho <carlosg src gnome org>]

commit 4c596ae704a79f662353e139c74044ed6abbdd67
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Dec 3 13:09:47 2018 +0100

    shell-global: Make saving of persistent state asynchronous
    
    This is an expensive operation that is best avoided in the main loop. Given
    the call doesn't care much about returning error or status, it can just
    be made async within.
    
    Every operation on a given file will be destructive wrt previous
    operations on the same file, so we just cancel any pending operation on
    it before batching the current one.
    
    Closes: https://gitlab.gnome.org/GNOME/gnome-shell/issues/815

 src/shell-global.c | 64 +++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 54 insertions(+), 10 deletions(-)
---
diff --git a/src/shell-global.c b/src/shell-global.c
index dbd3bbe95..087112853 100644
--- a/src/shell-global.c
+++ b/src/shell-global.c
@@ -87,6 +87,8 @@ struct _ShellGlobal {
   GSList *leisure_closures;
   guint leisure_function_id;
 
+  GHashTable *save_ops;
+
   /* For sound notifications */
   ca_context *sound_context;
 
@@ -325,6 +327,10 @@ shell_global_init (ShellGlobal *global)
                                      NULL);
 
   g_strfreev (search_path);
+
+  global->save_ops = g_hash_table_new_full (g_file_hash,
+                                            (GEqualFunc) g_file_equal,
+                                            g_object_unref, g_object_unref);
 }
 
 static void
@@ -344,6 +350,8 @@ shell_global_finalize (GObject *object)
   g_free (global->imagedir);
   g_free (global->userdatadir);
 
+  g_hash_table_unref (global->save_ops);
+
   G_OBJECT_CLASS(shell_global_parent_class)->finalize (object);
 }
 
@@ -1727,20 +1735,56 @@ shell_global_get_session_mode (ShellGlobal *global)
 }
 
 static void
-save_variant (GFile      *dir,
-              const char *property_name,
-              GVariant   *variant)
+delete_variant_cb (GObject      *object,
+                   GAsyncResult *result,
+                   gpointer      user_data)
+{
+  ShellGlobal *global = user_data;
+
+  if (g_file_delete_finish (G_FILE (object), result, NULL))
+    g_hash_table_remove (global->save_ops, object);
+}
+
+static void
+replace_variant_cb (GObject      *object,
+                    GAsyncResult *result,
+                    gpointer      user_data)
+{
+  ShellGlobal *global = user_data;
+
+  if (g_file_replace_contents_finish (G_FILE (object), result, NULL, NULL))
+    g_hash_table_remove (global->save_ops, object);
+}
+
+static void
+save_variant (ShellGlobal *global,
+              GFile       *dir,
+              const char  *property_name,
+              GVariant    *variant)
 {
   GFile *path = g_file_get_child (dir, property_name);
+  GCancellable *cancellable;
+
+  cancellable = g_hash_table_lookup (global->save_ops, path);
+  if (cancellable)
+    g_cancellable_cancel (cancellable);
+
+  cancellable = g_cancellable_new ();
+  g_hash_table_insert (global->save_ops, g_object_ref (path), cancellable);
 
   if (variant == NULL || g_variant_get_data (variant) == NULL)
-    (void) g_file_delete (path, NULL, NULL);
+    {
+      g_file_delete_async (path, G_PRIORITY_DEFAULT, cancellable,
+                           delete_variant_cb, global);
+    }
   else
     {
-      gsize size = g_variant_get_size (variant);
-      g_file_replace_contents (path, g_variant_get_data (variant), size,
-                               NULL, FALSE, G_FILE_CREATE_REPLACE_DESTINATION,
-                               NULL, NULL, NULL);
+      g_file_replace_contents_async (path,
+                                     g_variant_get_data (variant),
+                                     g_variant_get_size (variant),
+                                     NULL, FALSE,
+                                     G_FILE_CREATE_REPLACE_DESTINATION,
+                                     cancellable, replace_variant_cb, global);
     }
 
   g_object_unref (path);
@@ -1794,7 +1838,7 @@ shell_global_set_runtime_state (ShellGlobal  *global,
                                 const char   *property_name,
                                 GVariant     *variant)
 {
-  save_variant (global->runtime_state_path, property_name, variant);
+  save_variant (global, global->runtime_state_path, property_name, variant);
 }
 
 /**
@@ -1829,7 +1873,7 @@ shell_global_set_persistent_state (ShellGlobal *global,
                                    const char  *property_name,
                                    GVariant    *variant)
 {
-  save_variant (global->userdatadir_path, property_name, variant);
+  save_variant (global, global->userdatadir_path, property_name, variant);
 }
 
 /**