From 5e96ed64c9537b27a45b980020e6bfaec66e763a Mon Sep 17 00:00:00 2001
From: Christian Hergert <chergert@redhat.com>
Date: Wed, 4 Oct 2023 13:36:48 -0700
Subject: [PATCH] gmain: avoid a GList traversal when removing source

Currently the GSourceList has it's own allocation plus a secondary
allocation for the GList which contains it (from GMainContext). Not only
are these a pointer chase, but they are on separate cachelines too. Without
changing the code much we can at least keep things on the same cacheline
so that the pointer chase matters less.

Since the GList becomes embedded in the GSourceList you can use a
g_queue_unlink() directly removing the link without traversing the GList
like was done before.

Furthermore, we can simplify some code with g_queue_push_tail_link()
instead of some extra branching.
---
 glib/gmain.c | 40 ++++++++++++++++------------------------
 1 file changed, 16 insertions(+), 24 deletions(-)

diff --git a/glib/gmain.c b/glib/gmain.c
index 8400e9726..25f9c7000 100644
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -275,6 +275,7 @@ typedef struct _GSourceList GSourceList;
 
 struct _GSourceList
 {
+  GList link;
   GSource *head, *tail;
   gint priority;
 };
@@ -319,7 +320,7 @@ struct _GMainContext
   gint timeout;			/* Timeout for current iteration */
 
   guint next_id;
-  GList *source_lists;
+  GQueue source_lists;
   gint in_check_or_prepare;
 
   GPollRec *poll_records;
@@ -669,12 +670,13 @@ g_main_context_unref (GMainContext *context)
       g_source_destroy_internal (source, context, TRUE);
     }
 
-  for (sl_iter = context->source_lists; sl_iter; sl_iter = sl_iter->next)
+  sl_iter = context->source_lists.head;
+  while (sl_iter != NULL)
     {
       list = sl_iter->data;
+      sl_iter = sl_iter->next;
       g_slice_free (GSourceList, list);
     }
-  g_list_free (context->source_lists);
 
   g_hash_table_destroy (context->sources);
 
@@ -771,9 +773,7 @@ g_main_context_new_with_flags (GMainContextFlags flags)
   context->ref_count = 1;
 
   context->next_id = 1;
-  
-  context->source_lists = NULL;
-  
+
   context->poll_func = g_poll;
   
   context->cached_poll_array = NULL;
@@ -1126,7 +1126,7 @@ g_source_iter_next (GSourceIter *iter, GSource **source)
       if (iter->current_list)
 	iter->current_list = iter->current_list->next;
       else
-	iter->current_list = iter->context->source_lists;
+	iter->current_list = iter->context->source_lists.head;
 
       if (iter->current_list)
 	{
@@ -1176,11 +1176,10 @@ find_source_list_for_priority (GMainContext *context,
 			       gint          priority,
 			       gboolean      create)
 {
-  GList *iter, *last;
+  GList *iter;
   GSourceList *source_list;
 
-  last = NULL;
-  for (iter = context->source_lists; iter != NULL; last = iter, iter = iter->next)
+  for (iter = context->source_lists.head; iter; iter = iter->next)
     {
       source_list = iter->data;
 
@@ -1193,10 +1192,11 @@ find_source_list_for_priority (GMainContext *context,
 	    return NULL;
 
 	  source_list = g_slice_new0 (GSourceList);
+          source_list->link.data = source_list;
 	  source_list->priority = priority;
-	  context->source_lists = g_list_insert_before (context->source_lists,
-							iter,
-							source_list);
+          g_queue_insert_before_link (&context->source_lists,
+                                      iter,
+                                      &source_list->link);
 	  return source_list;
 	}
     }
@@ -1205,18 +1205,10 @@ find_source_list_for_priority (GMainContext *context,
     return NULL;
 
   source_list = g_slice_new0 (GSourceList);
+  source_list->link.data = source_list;
   source_list->priority = priority;
+  g_queue_push_tail_link (&context->source_lists, &source_list->link);
 
-  if (!last)
-    context->source_lists = g_list_append (NULL, source_list);
-  else
-    {
-      /* This just appends source_list to the end of
-       * context->source_lists without having to walk the list again.
-       */
-      last = g_list_append (last, source_list);
-      (void) last;
-    }
   return source_list;
 }
 
@@ -1284,7 +1276,7 @@ source_remove_from_context (GSource      *source,
 
   if (source_list->head == NULL)
     {
-      context->source_lists = g_list_remove (context->source_lists, source_list);
+      g_queue_unlink (&context->source_lists, &source_list->link);
       g_slice_free (GSourceList, source_list);
     }
 }