[gnome-shell] background: don't load the same image more than once concurrently

[Ray Strode <halfline src gnome org>]

commit bed3bb45f7cb55ed6a2d88fd54f29d9ed502e901
Author: Ray Strode <rstrode redhat com>
Date:   Mon Mar 25 15:03:48 2013 -0400

    background: don't load the same image more than once concurrently
    
    If a background gets requested from the cache while it's still
    being loaded from an earlier call, then there will be two concurrent
    loads of the same file.
    
    That concurrency is mitigates the effectiveness of the cache and
    also causes leaks.
    
    This commit consolidates file loads so that concurrency doesn't
    happen.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=696157

 js/ui/background.js |   92 ++++++++++++++++++++++++++++++++++++++++-----------
 1 files changed, 72 insertions(+), 20 deletions(-)
---
diff --git a/js/ui/background.js b/js/ui/background.js
index cacdffb..2625452 100644
--- a/js/ui/background.js
+++ b/js/ui/background.js
@@ -38,6 +38,7 @@ const BackgroundCache = new Lang.Class({
     _init: function() {
        this._patterns = [];
        this._images = [];
+       this._pendingFileLoads = [];
        this._fileMonitors = {};
     },
 
@@ -128,6 +129,73 @@ const BackgroundCache = new Lang.Class({
         this._removeContent(this._images, content);
     },
 
+    _loadImageContent: function(params) {
+        params = Params.parse(params, { monitorIndex: 0,
+                                        style: null,
+                                        filename: null,
+                                        effects: Meta.BackgroundEffects.NONE,
+                                        cancellable: null,
+                                        onFinished: null });
+
+        for (let i = 0; i < this._pendingFileLoads.length; i++) {
+            if (this._pendingFileLoads[i].filename == params.filename &&
+                this._pendingFileLoads[i].style == params.style) {
+                this._pendingFileLoads[i].callers.push({ shouldCopy: true,
+                                                         monitorIndex: params.monitorIndex,
+                                                         effects: params.effects,
+                                                         onFinished: params.onFinished });
+                return;
+            }
+        }
+
+        this._pendingFileLoads.push({ filename: params.filename,
+                                      style: params.style,
+                                      callers: [{ shouldCopy: false,
+                                                  monitorIndex: params.monitorIndex,
+                                                  effects: params.effects,
+                                                  onFinished: params.onFinished }] });
+
+        let content = new Meta.Background({ meta_screen: global.screen,
+                                            monitor: params.monitorIndex,
+                                            effects: params.effects });
+
+        content.load_file_async(params.filename,
+                                params.style,
+                                params.cancellable,
+                                Lang.bind(this,
+                                          function(object, result) {
+                                              try {
+                                                  content.load_file_finish(result);
+
+                                                  this._monitorFile(params.filename);
+                                                  this._images.push(content);
+                                              } catch(e) {
+                                                  content = null;
+                                              }
+
+                                              for (let i = 0; i < this._pendingFileLoads.length; i++) {
+                                                  let pendingLoad = this._pendingFileLoads[i];
+                                                  if (pendingLoad.filename != params.filename ||
+                                                      pendingLoad.style != params.style)
+                                                      continue;
+
+                                                  for (let j = 0; j < pendingLoad.callers.length; j++) {
+                                                      if (pendingLoad.callers[j].onFinished) {
+                                                          if (content && pendingLoad.callers[j].shouldCopy) {
+                                                              content = 
object.copy(pendingLoad.callers[j].monitorIndex,
+                                                                                    
pendingLoad.callers[j].effects);
+
+                                                          }
+
+                                                          pendingLoad.callers[j].onFinished(content);
+                                                      }
+                                                  }
+
+                                                  this._pendingFileLoads.splice(i, 1);
+                                              }
+                                          }));
+    },
+
     getImageContent: function(params) {
         params = Params.parse(params, { monitorIndex: 0,
                                         style: null,
@@ -171,27 +239,11 @@ const BackgroundCache = new Lang.Class({
             if (params.onFinished)
                 params.onFinished(content);
         } else {
-            content = new Meta.Background({ meta_screen: global.screen,
-                                            monitor: params.monitorIndex,
-                                            effects: params.effects });
-
-            content.load_file_async(params.filename,
-                                    params.style,
-                                    params.cancellable,
-                                    Lang.bind(this,
-                                              function(object, result) {
-                                                  try {
-                                                      content.load_file_finish(result);
-
-                                                      this._monitorFile(params.filename);
-                                                      this._images.push(content);
-                                                  } catch(e) {
-                                                       content = null;
-                                                  }
+            this._loadImageContent({ filename: params.filename,
+                                     style: params.style,
+                                     cancellable: params.cancellable,
+                                     onFinished: params.onFinished });
 
-                                                  if (params.onFinished)
-                                                      params.onFinished(content);
-                                              }));
         }
     },