[folks] collection comparators: optimize the case of empty collections

[Simon McVittie <smcv src gnome org>]

commit f2a0df2d2262c69d23bccf212f3564ac5aa1f81c
Author: Simon McVittie <simon mcvittie collabora co uk>
Date:   Tue Mar 12 15:27:32 2013 +0000

    collection comparators: optimize the case of empty collections
    
    Comparing integers is a lot faster than constructing one or more
    GObjects to iterate over the hash table. This saves about 3% of the
    user CPU time needed to deal with 2049 simple e-d-s Google contacts,
    each with one email address and no phone numbers etc.
    
    Bug: https://bugzilla.gnome.org/show_bug.cgi?id=695648
    Signed-off-by: Simon McVittie <simon mcvittie collabora co uk>
    Reviewed-by: Philip Withnall <philip tecnocode co uk>

 folks/utils.vala |   30 +++++++++++++++++++++++++++---
 1 files changed, 27 insertions(+), 3 deletions(-)
---
diff --git a/folks/utils.vala b/folks/utils.vala
index a513f83..4225a05 100644
--- a/folks/utils.vala
+++ b/folks/utils.vala
@@ -74,7 +74,15 @@ public class Folks.Utils : Object
       if (a == b)
         return true;
 
-      if (a.size == b.size)
+      var a_size = a.size;
+      var b_size = b.size;
+
+      if (a_size == 0 && b_size == 0)
+        {
+          /* fast path: avoid the actual iteration, which creates GObjects */
+          return true;
+        }
+      else if (a_size == b_size)
         {
           foreach (var key in a.get_keys ())
             {
@@ -125,7 +133,15 @@ public class Folks.Utils : Object
       if (a == b)
         return true;
 
-      if (a.size == b.size)
+      var a_size = a.size;
+      var b_size = b.size;
+
+      if (a_size == 0 && b_size == 0)
+        {
+          /* fast path: avoid the actual iteration, which creates GObjects */
+          return true;
+        }
+      else if (a_size == b_size)
         {
           foreach (var key in a.get_keys ())
             {
@@ -176,7 +192,15 @@ public class Folks.Utils : Object
       if (a == b)
         return true;
 
-      if (a.size == b.size)
+      var a_size = a.size;
+      var b_size = b.size;
+
+      if (a_size == 0 && b_size == 0)
+        {
+          /* fast path: avoid creating the iterator, which is a GObject */
+          return true;
+        }
+      else if (a_size == b_size)
         {
           foreach (var val in a)
             {