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background: Fix cancellable issues

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If we have the following sequence:

    cache.getImageContent({ filename: "foo", cancellable: cancellable1 });
    cache.getImageContent({ filename: "foo", cancellable: cancellable2 });
    cancellable1.cancel();

Then the second load will complete with "null" as its content, even though
it was never cancelled, and we'll see a blank image. Meanwhile, since the
second load simply appends to the list of callers for the second load,
cancellable2 does absolutely nothing: cancelling it won't stop the load,
and it will still receive onFinished handling.

To prevent this from happening, give the actual load operation its own
Gio.Cancellable, which is "ref-counted" -- only cancel it when all the other
possible callers cancel.

Additionally, clean up the large nested loops by splitting out duplicated
code and other stuff.

https://bugzilla.gnome.org/show_bug.cgi?id=722149
This commit is contained in:
Jasper St. Pierre 2014-01-13 18:42:32 -05:00
parent 2fba8e29e0
commit a2e4153fa0
1 changed files with 64 additions and 54 deletions
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118
js/ui/background.js
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@ -132,6 +132,46 @@ const BackgroundCache = new Lang.Class({
this._removeContent(this._images, content);
},
_loadImageContentInternal: function(filename, style) {
let cancellable = new Gio.Cancellable();
let content = new Meta.Background({ meta_screen: global.screen });
let info = { filename: filename,
style: style,
cancellable: cancellable,
callers: [] };
content.load_file_async(filename, style, cancellable, Lang.bind(this, function(object, result) {
if (cancellable.is_cancelled())
return;
try {
content.load_file_finish(result);
} catch(e) {
content = null;
}
if (content) {
this._monitorFile(filename);
info.callers.forEach(Lang.bind(this, function(caller) {
let newContent = content.copy(caller.monitorIndex, caller.effects);
this._images.push(newContent);
caller.onFinished(newContent);
}));
} else {
info.callers.forEach(Lang.bind(this, function(caller) {
caller.onFinished(null);
}));
}
let idx = this._pendingFileLoads.indexOf(info);
this._pendingFileLoads.splice(idx, 1);
}));
this._pendingFileLoads.push(info);
return info;
},
_loadImageContent: function(params) {
params = Params.parse(params, { monitorIndex: 0,
style: null,
@ -140,67 +180,38 @@ const BackgroundCache = new Lang.Class({
cancellable: null,
onFinished: null });
let caller = { monitorIndex: params.monitorIndex,
effects: params.effects,
cancellable: params.cancellable,
onFinished: params.onFinished };
let info = 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;
let pendingLoad = this._pendingFileLoads[i];
if (pendingLoad.filename == params.filename && pendingLoad.style == params.style) {
info = pendingLoad;
break;
}
}
this._pendingFileLoads.push({ filename: params.filename,
style: params.style,
callers: [{ shouldCopy: false,
monitorIndex: params.monitorIndex,
effects: params.effects,
onFinished: params.onFinished }] });
if (!info)
info = this._loadImageContentInternal(params.filename, params.style);
let content = new Meta.Background({ meta_screen: global.screen,
monitor: params.monitorIndex,
effects: params.effects });
info.callers.push(caller);
content.load_file_async(params.filename,
params.style,
params.cancellable,
Lang.bind(this,
function(object, result) {
try {
content.load_file_finish(result);
if (caller.cancellable) {
caller.cancellable.connect(Lang.bind(this, function() {
let idx = info.callers.indexOf(caller);
info.callers.splice(idx, 1);
this._monitorFile(params.filename);
this._images.push(content);
} catch(e) {
content = null;
}
if (info.callers.length == 0) {
info.cancellable.cancel();
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) {
let newContent;
if (content && pendingLoad.callers[j].shouldCopy) {
newContent = content.copy(pendingLoad.callers[j].monitorIndex,
pendingLoad.callers[j].effects);
this._images.push(newContent);
} else {
newContent = content;
}
pendingLoad.callers[j].onFinished(newContent);
}
}
this._pendingFileLoads.splice(i, 1);
}
}));
let idx = this._pendingFileLoads.indexOf(info);
this._pendingFileLoads.splice(idx, 1);
}
}));
}
},
getImageContent: function(params) {
@ -250,7 +261,6 @@ const BackgroundCache = new Lang.Class({
monitorIndex: params.monitorIndex,
cancellable: params.cancellable,
onFinished: params.onFinished });
}
},