[glib/th/gsignal-cleanup: 31/33] gsignal: use stack allocate temporary buffer in g_signal_new_valist()

[Thomas Haller <thaller src gnome org>]

commit cc4ffe47427c8af135d93107e09dcaae95538183
Author: Thomas Haller <thaller redhat com>
Date:   Tue Jan 26 13:38:18 2021 +0100

    gsignal: use stack allocate temporary buffer in g_signal_new_valist()
    
    g_signal_new_valist() is called by g_signal_new(), which is probably
    the most common way to create a signal.
    
    Also, in almost all cases is the number of signal parameters small.
    
    Let's optimize for that by using a stack allocated buffer if we have
    few parameters.

 gobject/gsignal.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)
---
diff --git a/gobject/gsignal.c b/gobject/gsignal.c
index 4e50a2be2..937e106f8 100644
--- a/gobject/gsignal.c
+++ b/gobject/gsignal.c
@@ -1952,30 +1952,38 @@ g_signal_new_valist (const gchar       *signal_name,
                      GSignalFlags       signal_flags,
                      GClosure          *class_closure,
                      GSignalAccumulator accumulator,
-                    gpointer           accu_data,
+                     gpointer           accu_data,
                      GSignalCMarshaller c_marshaller,
                      GType              return_type,
                      guint              n_params,
                      va_list            args)
 {
+  /* Somewhat arbitrarily reserve 200 bytes. That should cover the majority
+   * of cases where n_params is small and still be small enough for what we
+   * want to put on the stack. */
+  GType param_types_stack[200 / sizeof (GType)];
+  GType *param_types_heap = NULL;
   GType *param_types;
   guint i;
   guint signal_id;
 
+  param_types = param_types_stack;
   if (n_params > 0)
     {
-      param_types = g_new (GType, n_params);
+      if (G_UNLIKELY (n_params > G_N_ELEMENTS (param_types_stack)))
+        {
+          param_types_heap = g_new (GType, n_params);
+          param_types = param_types_heap;
+        }
 
       for (i = 0; i < n_params; i++)
-       param_types[i] = va_arg (args, GType);
+        param_types[i] = va_arg (args, GType);
     }
-  else
-    param_types = NULL;
 
   signal_id = g_signal_newv (signal_name, itype, signal_flags,
-                            class_closure, accumulator, accu_data, c_marshaller,
-                            return_type, n_params, param_types);
-  g_free (param_types);
+                             class_closure, accumulator, accu_data, c_marshaller,
+                             return_type, n_params, param_types);
+  g_free (param_types_heap);
 
   return signal_id;
 }