[gnome-shell/wip/chergert/localtime-fix: 2331/2331] environment: reduce calls to g_time_zone_new_local()

[Christian Hergert <chergert src gnome org>]

commit 06b690ff21204ea9ea26d2671eb26b1a1f24caa9
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 | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)
---
diff --git a/js/ui/environment.js b/js/ui/environment.js
index ba378e7d11..8ab9e7d444 100644
--- a/js/ui/environment.js
+++ b/js/ui/environment.js
@@ -12,6 +12,9 @@ imports.gi.versions.TelepathyLogger = '0.2';
 
 const { Clutter, GLib, GObject, Meta, 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
@@ -304,9 +307,25 @@ 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) {
-        let dt = GLib.DateTime.new_from_unix_local(this.getTime() / 1000);
+        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) : '';
     };