configmgr: faster / simpler compare for keys.

A surprising amount of time is/was spent comparing keys in the
std::map red/black tree traversing nodes. Since we don't need
the data truly sorted, instead sort in length buckets. Kills
90k rtl_ustring_compare_withLength calls on startup, around
0.9% of headless start.

Change-Id: Ib23aff151ad50d56bbf2ba3e28882cc81898d9ec

1 files changed, 35 insertions, 0 deletions

diff --git a/configmgr/source/config_map.hxx b/configmgr/source/config_map.hxx
new file mode 100644
index 000000000000..0e9f614bb5cd
--- /dev/null
+++ b/configmgr/source/config_map.hxx
@@ -0,0 +1,35 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+#ifndef CONFIG_MAP_HXX
+#define CONFIG_MAP_HXX
+
+#include <map>
+#include <rtl/ustring.hxx>
+
+// The realisation here is that while a map is a reasonably compact
+// representation, there is often no need to have it completely
+// sorted, so we can use a fast in-line length comparison as the
+// initial compare, rather than sorting of sub string contents.
+
+struct LengthContentsCompare
+{
+    inline bool operator()( const OUString &a, const OUString &b ) const
+    {
+        if (a.getLength() == b.getLength())
+            return a < b;
+        else
+            return a.getLength() < b.getLength();
+    }
+};
+
+template< class T > struct config_map : public std::map< OUString, T, LengthContentsCompare > { };
+
+#endif // CONFIG_MAP_HXX
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */