ibusManager: Preload all ibus input sources in user configuration

Normally users switch xkb input sources and ibus input sources.
But currently the first input source only is running. It's also good
to preload all ibus engines in the logging session so that users switch
input sources quickly without the launching time of input sources.

The following is the ibus change:
https://github.com/ibus/ibus/commit/cff35929a9

https://bugzilla.gnome.org/show_bug.cgi?id=695428

js/misc/ibusManager.js

@@ -1,13 +1,14 @@
 // -*- mode: js; js-indent-level: 4; indent-tabs-mode: nil -*-
 
 const Gio = imports.gi.Gio;
+const GLib = imports.gi.GLib;
 const Lang = imports.lang;
+const Mainloop = imports.mainloop;
 const Signals = imports.signals;
 
 try {
     var IBus = imports.gi.IBus;
-    if (!('new_async' in IBus.Bus))
-        throw "IBus version is too old";
+    _checkIBusVersion();
     const IBusCandidatePopup = imports.ui.ibusCandidatePopup;
 } catch (e) {
     var IBus = null;
@@ -16,6 +17,22 @@ try {
 
 let _ibusManager = null;
 
+function _checkIBusVersion() {
+    var requiredMajor = 1;
+    var requiredMinor = 5;
+    var requiredMicro = 2;
+
+    if ((IBus.MAJOR_VERSION > requiredMajor) ||
+        (IBus.MAJOR_VERSION == requiredMajor && IBus.MINOR_VERSION > requiredMinor) ||
+        (IBus.MAJOR_VERSION == requiredMajor && IBus.MINOR_VERSION == requiredMinor &&
+         IBus.MICRO_VERSION >= requiredMicro))
+        return;
+
+    throw "Found IBus version %d.%d.%d but required is %d.%d.%d".
+        format(IBus.MAJOR_VERSION, IBus.MINOR_VERSION, IBus.MINOR_VERSION,
+               requiredMajor, requiredMinor, requiredMicro);
+}
+
 function getIBusManager() {
     if (_ibusManager == null)
         _ibusManager = new IBusManager();
@@ -28,6 +45,7 @@ const IBusManager = new Lang.Class({
     // This is the longest we'll keep the keyboard frozen until an input
     // source is active.
     _MAX_INPUT_SOURCE_ACTIVATION_TIME: 4000, // ms
+    _PRELOAD_ENGINES_DELAY_TIME: 30, // sec
 
     _init: function() {
         if (!IBus)
@@ -42,6 +60,7 @@ const IBusManager = new Lang.Class({
         this._ready = false;
         this._registerPropertiesId = 0;
         this._currentEngineName = null;
+        this._preloadEnginesId = 0;
 
         this._ibus = IBus.Bus.new_async();
         this._ibus.connect('connected', Lang.bind(this, this._onConnected));
@@ -176,5 +195,27 @@ const IBusManager = new Lang.Class({
         this._ibus.set_global_engine_async(id, this._MAX_INPUT_SOURCE_ACTIVATION_TIME,
                                            null, callback);
     },
+
+    preloadEngines: function(ids) {
+        if (!IBus || !this._ibus || ids.length == 0)
+            return;
+
+        if (this._preloadEnginesId != 0) {
+            Mainloop.source_remove(this._preloadEnginesId);
+            this._preloadEnginesId = 0;
+        }
+
+        this._preloadEnginesId =
+            Mainloop.timeout_add_seconds(this._PRELOAD_ENGINES_DELAY_TIME,
+                                         Lang.bind(this, function() {
+                                             this._ibus.preload_engines_async(
+                                                 ids,
+                                                 -1,
+                                                 null,
+                                                 null);
+                                             this._preloadEnginesId = 0;
+                                             return GLib.SOURCE_REMOVE;
+                                         }));
+    },
 });
 Signals.addSignalMethods(IBusManager.prototype);

js/ui/status/keyboard.js

@@ -381,6 +381,10 @@ const InputSourceManager = new Lang.Class({
 
         if (this._mruSources.length > 0)
             this._mruSources[0].activate();
+
+        // All ibus engines are preloaded here to reduce the launching time
+        // when users switch the input sources.
+        this._ibusManager.preloadEngines(Object.keys(this._ibusSources));
     },
 
     _makeEngineShortName: function(engineDesc) {