Memory Leak related to ChromiumWebBrowser.CleanupElement on tab opening/closing

[dmitry...@gmail.com]

Hi CefSharp group!

I've discovered that ChromiumWebBrowser control object is not garbage collected after tab closing in CefSharp.Wpf.Example project.
The version of CefSharp I use is CefSharp-33.0.2.
I've investigated it using JetBrains DotMemory and WinDbg and found out the following:

File: CefSharp.Wpf\ChromiumWebBrowser.cs

1. By default, CleanupElement is a Window that hosts CefSharp control:

        private void OnLoaded(object sender, RoutedEventArgs routedEventArgs)
        {
            if (CleanupElement == null)
            {
                CleanupElement = Window.GetWindow(this);
            }

            AddSourceHookIfNotAlreadyPresent();
        }

2. Then, we subscribe to Unloaded event of CleanupElement and never unsubscribe:

        protected virtual void OnCleanupElementChanged(FrameworkElement oldValue, FrameworkElement newValue)
        {
            if (oldValue != null)
            {
                oldValue.Unloaded -= OnCleanupElementUnloaded;
            }

            if (newValue != null)
            {
                newValue.Unloaded -= OnCleanupElementUnloaded;
                newValue.Unloaded += OnCleanupElementUnloaded;
            }
        }


This makes Window to hold a reference to ChromiumWebBrowser control through FrameworkElement.Unloaded event subscription.

The solution that I use is to add the following code to Dispose method:

            if(CleanupElement != null)
            {
                CleanupElement.Unloaded -= OnCleanupElementUnloaded;
            }


Dmitry

[Jørn Hansen]

Hi Dmitry,

Thanks for digging into this and sharing your findings. That's much appreciated! Quite recently a PR was merged to `master` that will in hopefully not to long go out as our 39.0.0 release:
https://github.com/cefsharp/CefSharp/pull/786

If you still have DotMemory etc. in hand :-) it would be very welcome if you could check out if that PR fixes the issue or we still have the leak for the scenario you describe.

You can either grab the latest CI build at https://www.myget.org/F/cefsharp/ or build master from source.

--
Thanks,
JornH

[Alex Maitland]

Quick look using the WPF example and I'm not sure if `OnCleanupElementUnloaded ` actually gets called, so the whole feature may need a rethink.

Short term, I think we should unhook the event handler. Long term we may need to evaluate.

Dmitry: Any chance you could submit a PR to our github project?

[dmitry...@gmail.com]

Hi Alex
Ok, let me try to submit PR.

[dmitry...@gmail.com]

Hi Jorn

I've just checked this scenario on CefSharp-39.0.0-pre02 and I can still see the memory leak and DotMemory shows the same reason - ChromiumWebBrowser object is held by RoutedEventHandler, which is  a subscription to Window.Unloaded routed event.

Dmitry

[dmitry...@gmail.com]

Hi guys,
Here's my pull request: https://github.com/cefsharp/CefSharp/pull/827.
I'm new to github so please correct me if I've done something not the way that it's supposed to be done.

Dmitry