[gnome-shell/wip/carlosg/async-persistent-data: 8/8] shell-global: Make saving of persistent state asynchronous

[Carlos Garnacho <carlosg src gnome org>]

commit 29eca2fc5530e16ee00c53bcbc73896ce75bae1a
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 | 83 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 73 insertions(+), 10 deletions(-)
---
diff --git a/src/shell-global.c b/src/shell-global.c
index dbd3bbe95..11f99347b 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 +1735,75 @@ 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;
+  GError *error = NULL;
+
+  if (g_file_delete_finish (G_FILE (object), result, &error))
+    {
+      if (!g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+        {
+          g_warning ("Could not delete runtime/persistent state file: %s\n",
+                     error->message);
+        }
+
+      g_hash_table_remove (global->save_ops, object);
+      g_error_free (error);
+    }
+}
+
+static void
+replace_variant_cb (GObject      *object,
+                    GAsyncResult *result,
+                    gpointer      user_data)
+{
+  ShellGlobal *global = user_data;
+  GError *error = NULL;
+
+  if (g_file_replace_contents_finish (G_FILE (object), result, NULL, &error))
+    {
+      if (!g_error_matches (error, G_IO_ERROR, G_IO_ERROR_CANCELLED))
+        {
+          g_warning ("Could not replace runtime/persistent state file: %s\n",
+                     error->message);
+        }
+
+      g_hash_table_remove (global->save_ops, object);
+      g_error_free (error);
+    }
+}
+
+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);
+  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 +1857,7 @@ 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 +1892,7 @@ 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);
 }
 
 /**