.NET 6 Blazor server app not Disposing razor pages on browser tab close

[jeffraska]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When IDisposable is implemented in razor page and browser tab is closed by user, the Dispose method is called after few minutes and not immediately after tab close.
The very first thing I'd mention is that disposing of razor pages worked correctly in .NET 5 so apparently it's a bug in .NET 6 (or ASP.NET Core Runtime). Problem started to appear after I've upgraded my project to .NET 6.

This problem was discused previously in https://github.com/dotnet/aspnetcore/issues/38147 but solution in answer does not solve this problem - .NET knows about tab being closed but just do not call Dispose.

Expected Behavior

When browser tab is closed .NET should dispose all razor pages that existed in this session.

Steps To Reproduce

1. Create Blazor server app according to https://dotnet.microsoft.com/en-us/learn/aspnet/blazor-tutorial/create
2. Implement IDisposable in Counter.razor and set breakpoint in Dispose method
3. Add HubFilter using builder.Services.Configure<HubOptions>(O => O.AddFilter<HubFilter>()); and set breakpoint in OnDisconnectedAsync
4. Start app and navigate to /counter
5. Close tab
6. OnDisconnectedAsync is called but Dispose is not.

Exceptions (if any)

No response

.NET Version

6.0.101

Anything else?

No response

[jeffraska]

I studied problem further and it looks like problem appear in Vivaldi and Firefox but not in Google Chrome. So it's somehow browser issue.

[TanayParikh]

Hello @jeffraska thanks for contacting us. Blazor server disconnects the circuit based on the page unload event.

aspnetcore/src/Components/Web.JS/src/Boot.Server.ts

Lines 68 to 80 in e973236

	let disconnectSent = false;
	const cleanup = () => {
	if (!disconnectSent) {
	const data = new FormData();
	const circuitId = circuit.circuitId!;
	data.append('circuitId', circuitId);
	disconnectSent = navigator.sendBeacon('_blazor/disconnect', data);
	}
	};
	Blazor.disconnect = cleanup;
	window.addEventListener('unload', cleanup, { capture: false, once: true });

I studied problem further and it looks like problem appear in Vivaldi and Firefox but not in Google Chrome. So it's somehow browser issue.

Hmm I see, thanks for pointing that out. While Vivaldi isn't a supported browser, Firefox is. I have a feeling this may be a Firefox browser quirk to do with when/if the unload event is called.

[TanayParikh]

Hmm based on the usage notes for unload, it doesn't seem like that's the recommended way to do things anymore.

We may want to consider updating this to utilize the visibilitychange event, however it may not have full support in Safari (will need to do some testing).

[javiercn]

Our notification mechanism is a best effort not a guaranteed outcome, since the browser doesn't guarantee that the event is fired. Even in that case, this is a "performance" optimization to eagerly terminate the circuit when we know it won't be used any longer.

In this scenario dispose gets called after around 3 minutes (by default) when we detect the connection has been lost and the client doesn't re-connect as part of disposing the entire circuit.

[javiercn]

Created a separate issue #39409 to track the suggestions from @TanayParikh

[ghost]

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