_DefaultTabControllerState should dispose all created TabContoller instances. [prod-leak-fix] #136608
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| /// | ||
| /// This instance of [TabController] must not be used anymore and has to be | ||
| /// disposed since [AnimationController] was injected into the new | ||
| /// [TabController]. |
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Is this true? May be it is up to invoker if the instance can be used or not?
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To be honest, usage of the TabController after the removal of AnimationController from it (after the call of _copyWith) is impossible because we have several “bang operators” which will throw:
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This method does not do anything with the original instance, that makes it unusable, so it should not have opinion about what to do with it.
I suggest:
- Move
_animationController = null;out of this method to the invokers, because the methods name does not assume any updates like this. - Revert update do the comment.
How does it sound?
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@polina-c, thanks for the suggestions. According to what you suggested, here is the new code:
@override
void didUpdateWidget(DefaultTabController oldWidget) {
super.didUpdateWidget(oldWidget);
if (oldWidget.length != widget.length) {
...
final TabController newController = _controller._copyWith...
_controller._animationController = null;
_controller.dispose();
_controller = newController;
}
if (oldWidget.animationDuration != widget.animationDuration) {
final TabController newController = _controller._copyWith...
_controller._animationController = null;
_controller.dispose();
_controller = newController;
}
}What do you think?
Does explicit nulling of the private member look good to you?
polina-c
added
the
a: leak tracking
| _controller.dispose(); | ||
| _controller = newController; | ||
| } | ||
|
|
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How about making it more readable:
TabController newController = _controller;
if (oldWidget.length != widget.length) {
newController = newController._copyWith...
}
if (oldWidget.animationDuration != widget.animationDuration) {
newController = newController._copyWith...
}
if (newController != _controller) {
_controller.dispose();
_controller = newController;
_animationController = null;
}
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@polina-c, thanks a lot for your suggestion, it looks much cleaner. But if we do it in such a way, then we will lose the reference to the first new TabController if the length and animationDuration are changed at the same time.
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Really? Both _copyWith are invoked for newController, not for _controller. so, nothing is lost.
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Maybe I am missing something, but here is how I see the flow in case both length and animationDuration was updated:
// newController = TabController0
TabController newController = _controller;
if (oldWidget.length != widget.length) {
// newController = TabController1
newController = newController._copyWith...
}
if (oldWidget.animationDuration != widget.animationDuration) {
// newController = TabController2
newController = newController._copyWith...
}
if (newController != _controller) {
_controller._animationController = null;
// TabController0.dispose()
_controller.dispose();
// _controller = TabController2
_controller = newController;
// TabController1 is lost
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Oh, I see now.
You are right.
Thanks for explanation.
Then the only question is about _animationController = null;:
- Why we need it? Old controller is not referenced and is disposed, so what's the point to null _animationController?
- If it is needed, (1) it does not seem
_copyWithis right method to do it and (2) there should be comment that explains why it is needed.
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Thanks for the review.
Under the hood, _copyWith transfers AnimationController from one TabController to another.
/// Creates a new [TabController] with `index`, `previousIndex`, `length`, and
/// `animationDuration` if they are non-null.
///
/// This method is used by [DefaultTabController].
///
/// When [DefaultTabController.length] is updated, this method is called to
/// create a new [TabController] without creating a new [AnimationController].
TabController _copyWith({
...
}) {
...
return TabController._(
...
animationController: _animationController,
....
);
}In dispose method of the TabController we have disposal of the AnimationController.
@override
void dispose() {
_animationController?.dispose();
_animationController = null;
super.dispose();
}We can't hold the same AnimationController in both TabControllers because it will cause double disposal in the future. So, to not dispose recently injected AnimationController in the old TabController, we need to null it. It will be disposed in the new TabController in the future.
This explains why I added nulling of the _animationController in the _copyWith method and added this comment:
/// This instance of [TabController] must not be used anymore and has to be
/// disposed since [AnimationController] was injected into the new
/// [TabController].
What can you suggest to improve or change?
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Got it. Thanks.
Then _copyWith is now doing way more than just copying.
How about renaming _copyWith to _copyWithAndDispose, and making it fully disposing the original instance?
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Great suggestion, thanks!
Pushed the new version.
|
@polina-c, thanks for help and review! |
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…oller instances. (flutter#136608)" This reverts commit 9fa9fd3.
…oller instances. (#136608)" (#144579) This reverts commit 9fa9fd3. Fixes #144087. Fixes #138588. This crash has been reported previously from a customer in google3 in #138588, but we weren't able to track it down. Thankfully, a repro was now provided in #144087 (comment) which traced the crash down to a change made in #136608. This PR reverts that change to fix that crash for now. I will post a new PR shortly that will add a test to cover the use case that caused the crash with #136608 to make sure we don't re-introduce the crash in the future.
polina-c
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Description
Tests
material/tabs_test.dartto usetestWidgetsWithLeakTracking.Pre-launch Checklist
///).