[gnome-shell/wip/rstrode/login-screen-extensions: 116/134] environment: reduce calls to g_time_zone_new_local()

[Ray Strode <halfline src gnome org>]

commit b6a11643194362f927af68128b3cd7094e711fd5
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Feb 27 13:46:44 2020 -0800

    environment: reduce calls to g_time_zone_new_local()
    
    Creating a new GTimeZone for the local timezone can be quite expensive if
    done repeatedly. It requires an open(), mmap(), and parsing of
    /etc/localtime.
    
    This patch was provided by Florian, and I've tested it as far back as
    3.28.4 to ensure that we are really reducing the number of open() calls
    on the compositor thread.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/1051
    
    Signed-off-by: Christian Hergert <chergert redhat com>

 js/ui/environment.js | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)
---
diff --git a/js/ui/environment.js b/js/ui/environment.js
index e22ec74020..f3f2d17c7c 100644
--- a/js/ui/environment.js
+++ b/js/ui/environment.js
@@ -11,6 +11,9 @@ imports.gi.versions.TelepathyLogger = '0.2';
 
 const { Clutter, GLib, Shell, St } = imports.gi;
 const Gettext = imports.gettext;
+const System = imports.system;
+
+let _localTimeZone = null;
 
 // We can't import shell JS modules yet, because they may have
 // variable initializations, etc, that depend on init() already having
@@ -110,9 +113,26 @@ function init() {
         }
     };
 
+    // Override to clear our own timezone cache as well
+    const origClearDateCaches = System.clearDateCaches;
+    System.clearDateCaches = function () {
+        _localTimeZone = null;
+        origClearDateCaches();
+    };
+
     // Work around https://bugzilla.mozilla.org/show_bug.cgi?id=508783
     Date.prototype.toLocaleFormat = function(format) {
-        return Shell.util_format_date(format, this.getTime());
+        if (_localTimeZone === null)
+            _localTimeZone = GLib.TimeZone.new_local();
+
+        let dt = GLib.DateTime.new(_localTimeZone,
+            this.getYear(),
+            this.getMonth() + 1,
+            this.getDate(),
+            this.getHours(),
+            this.getMinutes(),
+            this.getSeconds());
+        return dt ? dt.format(format) : '';
     };
 
     let slowdownEnv = GLib.getenv('GNOME_SHELL_SLOWDOWN_FACTOR');