Finalizer crashes because of FileSystemWatcher Dispose exception in FileSystemWatcher_mobile.cs

[snakefoot]

Steps to Reproduce

1. Create FileSystemWatcher from NetStandard-library.
2. FileSystemWatcher constructor fails with NotImplementedException
3. Finalizer thread attempts to cleanup afterwards and calls FileSystemWatcher.Dispose that fails with NotImplementedException (Unhandled exception)

See also NLog/NLog#1946 (comment)

Could be nice that FileSystemWatcher.Dispose did not throw exceptions, since it is already protected by FileSystemWatcher-constructor throwing NotImplementedException .

Strange that Finalizer-thread runs naked, and can take down the entire application if cleaning up an object that has a bad Dispose-method.

Current Behavior

Crashes with unhandled exception:

Unhandled Exception: System.NotImplementedException: The method or operation is not implemented. at System.IO.FileSystemWatcher.Dispose (System.Boolean disposing) [0x00000] in /Library/Frameworks/Xamarin.Mac.framework/Versions/4.0.0.216/src/mono/mcs/class/System/System.IO/FileSystemWatcher_mobile.cs:62
at System.ComponentModel.Component.Finalize () [0x00000] in /Library/Frameworks/Xamarin.Mac.framework/Versions/4.0.0.216/src/mono/mcs/class/referencesource/System/compmod/system/componentmodel/Component.cs:35

Expected Behavior

Doesn't crash

On which platforms did you notice this

[ x] macOS
[ ] Linux
[ ] Windows

Version Used:

Xamarin.Mac.framework/Versions/4.0.0.216

Stacktrace

Unhandled Exception: System.NotImplementedException: The method or operation is not implemented. at System.IO.FileSystemWatcher.Dispose (System.Boolean disposing) [0x00000] in /Library/Frameworks/Xamarin.Mac.framework/Versions/4.0.0.216/src/mono/mcs/class/System/System.IO/FileSystemWatcher_mobile.cs:62
at System.ComponentModel.Component.Finalize () [0x00000] in /Library/Frameworks/Xamarin.Mac.framework/Versions/4.0.0.216/src/mono/mcs/class/referencesource/System/compmod/system/componentmodel/Component.cs:35

[akoeplinger]

I agree we should remove the exception from Dispose().

@marek-safar any thoughts on enabling FSW for Xamarin.Mac?

[marek-safar]

We should have FSW everywhere as it's included in netstandard

[akoeplinger]

Filed #7371 for tracking enabling FSW on more platforms.

[ArgusMagnus]

I ran into the same problem today with an app which was previously working. I was able to work around this by deriving from the FileSystemWatcher and override the Dispose method:

static bool CanHaveFileSources { get; } = false;

sealed class FileSystemWatcherTest : FileSystemWatcher
{
	protected override void Dispose(bool disposing)
	{
		try { base.Dispose(disposing); }
		catch { }
	}
}
// ...
try
{
	using (var tmp = new FileSystemWatcherTest())
	{
		CanHaveFileSources = true;
	}
}
catch { CanHaveFileSources = false; }