DetachContextMenuStrip pattern can lead to memory leaks

kirsan31 commented 4 days ago

.NET version

All up to .Net9.

Did it work in .NET Framework?

No

Did it work in any of the earlier releases of .NET Core or .NET 5+?

No.

Issue description

This null out ContextMenuStrip pattern:

private void DetachContextMenuStrip(object? sender, EventArgs e) => ContextMenuStrip = null;

// And ContextMenuStrip.Set` property:
EventHandler disposedHandler = new(DetachContextMenuStrip);

if (oldValue is not null)
{
    oldValue.Disposed -= disposedHandler;
}

if (value is not null)
{
    value.Disposed += disposedHandler;
}

Can lead to memory leaks. Using in 3 places:

Control https://github.com/dotnet/winforms/blob/d1986025b2dafdcc3aeda0505da37e580bb3d82e/src/System.Windows.Forms/src/System/Windows/Forms/Control.cs#L1232 More or less justified, since control in most cases lives either as long as the menu, or longer. But I didn't find a ContextMenuStrip.Disposed -= disposedHandler; code in Control.Dispose. So if ContextMenuStrip will outlive control (and user not null out ContextMenuStrip property) - we will have memory leak (control will remain in memory) at any case.
DataGridViewBand and DataGridViewCell https://github.com/dotnet/winforms/blob/1f2d238fe75b40408de8d3cd6ca363df3615132f/src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewBand.cs#L59 https://github.com/dotnet/winforms/blob/1f2d238fe75b40408de8d3cd6ca363df3615132f/src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewCell.cs#L117 Here it probably does more harm than good, since DataGridView elements in most cases live less than the menu and they never disposed.

My thots are:

At the very least we should add ContextMenuStrip.Disposed -= disposedHandler; code in Control.Dispose.
Ideally, to avoid making breaking changes we should use some implementation of weak events here. 🤔

Steps to reproduce

DetachContextMenuStripLeaks.zip

Use context menu on the DataGridView from the repro app, compare snapshots before and after:
"Refresh data" will leak DataGridView elements.
Every "Add Control" + "Remove Control" will leak one Control class.

elachlan commented 3 days ago

@LeafShi1 can your team please test this?

kirsan31 commented 3 days ago

@elachlan DataGridView case (point 2) was tested in #6859. I will adapt repro app to test also point 1...

---------------------UPD---------------------

Updated 1 post with repro app and instructions.

LeafShi1 commented 7 hours ago

@LeafShi1 can your team please test this?

This problem does exist

dotnet / winforms