gmain: Simplify source id tracking

Simplify our tracking of issued source id integers and fix some bugs.

Previously the source's id was remove from the 'used' table from
source_remove_from_context() which was also called if the source
priority was changed (in which case it would never be added back to the
table).  The source id could be reissued in that case.

In the new approach, we just always keep a hash table of sources, by
source id.  This simplifies the logic and will also allow us to improve
performance of g_main_context_find_source_by_id() which is called in some
fairly common cases, such as g_source_remove().  These improvements will be in
the following commits.

https://bugzilla.gnome.org/show_bug.cgi?id=724839

diff --git a/glib/gmain.c b/glib/gmain.c
index af39be1..404833d 100644 (file)
--- a/glib/gmain.c
+++ b/glib/gmain.c
@@ -240,11 +240,12 @@ struct _GMainContext
 
   gint ref_count;
 
+  GHashTable *sources;              /* guint -> GSource */
+
   GPtrArray *pending_dispatches;
   gint timeout;                        /* Timeout for current iteration */
 
   guint next_id;
-  GHashTable *overflow_used_source_ids; /* set<guint> */
   GList *source_lists;
   gint in_check_or_prepare;
 
@@ -546,8 +547,7 @@ g_main_context_unref (GMainContext *context)
     }
   g_list_free (context->source_lists);
 
-  if (context->overflow_used_source_ids)
-    g_hash_table_destroy (context->overflow_used_source_ids);
+  g_hash_table_destroy (context->sources);
 
   g_mutex_clear (&context->mutex);
 
@@ -602,6 +602,7 @@ g_main_context_new (void)
   g_mutex_init (&context->mutex);
   g_cond_init (&context->cond);
 
+  context->sources = g_hash_table_new (NULL, NULL);
   context->owner = NULL;
   context->waiters = NULL;
 
@@ -1059,61 +1060,6 @@ source_remove_from_context (GSource      *source,
       context->source_lists = g_list_remove (context->source_lists, source_list);
       g_slice_free (GSourceList, source_list);
     }
-
-  if (context->overflow_used_source_ids)
-    g_hash_table_remove (context->overflow_used_source_ids,
-                         GUINT_TO_POINTER (source->source_id));
-  
-}
-
-static void
-assign_source_id_unlocked (GMainContext   *context,
-                           GSource        *source)
-{
-  guint id;
-
-  /* Are we about to overflow back to 0? 
-   * See https://bugzilla.gnome.org/show_bug.cgi?id=687098
-   */
-  if (G_UNLIKELY (context->next_id == G_MAXUINT &&
-                  context->overflow_used_source_ids == NULL))
-    {
-      GSourceIter iter;
-      GSource *source;
-
-      context->overflow_used_source_ids = g_hash_table_new (NULL, NULL);
-  
-      g_source_iter_init (&iter, context, FALSE);
-      while (g_source_iter_next (&iter, &source))
-        {
-          g_hash_table_add (context->overflow_used_source_ids,
-                            GUINT_TO_POINTER (source->source_id));
-        }
-      id = G_MAXUINT;
-      g_hash_table_add (context->overflow_used_source_ids, GUINT_TO_POINTER (id));
-    }
-  else if (context->overflow_used_source_ids == NULL)
-    {
-      id = context->next_id++;
-    }
-  else
-    {
-      /*
-       * If we overran G_MAXUINT, we fall back to randomly probing the
-       * source ids for the current context.  This will be slower the more
-       * sources there are, but we're mainly concerned right now about
-       * correctness and code size.  There's time for a more clever solution
-       * later.
-       */
-      do
-        id = g_random_int ();
-      while (id == 0 ||
-             g_hash_table_contains (context->overflow_used_source_ids,
-                                    GUINT_TO_POINTER (id)));
-      g_hash_table_add (context->overflow_used_source_ids, GUINT_TO_POINTER (id));
-    }
-
-  source->source_id = id;
 }
 
 static guint
@@ -1122,10 +1068,21 @@ g_source_attach_unlocked (GSource      *source,
                           gboolean      do_wakeup)
 {
   GSList *tmp_list;
+  guint id;
+
+  /* The counter may have wrapped, so we must ensure that we do not
+   * reuse the source id of an existing source.
+   */
+  do
+    id = context->next_id++;
+  while (id == 0 || g_hash_table_contains (context->sources, GUINT_TO_POINTER (id)));
 
   source->context = context;
-  assign_source_id_unlocked (context, source);
+  source->source_id = id;
   source->ref_count++;
+
+  g_hash_table_insert (context->sources, GUINT_TO_POINTER (id), source);
+
   source_add_to_context (source, context);
 
   if (!SOURCE_BLOCKED (source))
@@ -2021,6 +1978,8 @@ g_source_unref_internal (GSource      *source,
          if (!SOURCE_DESTROYED (source))
            g_warning (G_STRLOC ": ref_count == 0, but source was still attached to a context!");
          source_remove_from_context (source, context);
+
+          g_hash_table_remove (context->sources, GUINT_TO_POINTER (source->source_id));
        }
 
       if (source->source_funcs->finalize)