Long polling + graceful shutdown

[gschuager]

Hi, I am implementing something like this https://outcompute.com/2019/05/26/latency-adaptive-real-time-with-reactive-caching-on-microsoft-orleans/ based on the samples from 3.x branch.

Is there any way to receive a notification in a grain that the silo is requested to be shut down? I would like to use this to cancel the long-poll async waiting task as soon as possible in order to let the grain be deactivated and the silo shut down quickly.

I understand that OnDeactivateAsync won't get called until pending requests are completed (I tested this and it makes sense) and in this case I have the long-poll one preventing that.

[JorgeCandeias]

Hi, post author here.

We can receive such notifications from the ApplicationStopping token of the IHostApplicationLifetime service we can request from DI. This token will be raised upon a graceful shutdown request from the host itself and can be used to swiftly cancel any long-running work in the app. It's not an orleans specific feature.

To protect any task with this, we can write await myTask.WaitAsync(_lifetime.ApplicationStopping).
In hindsight I should have added that to the samples as lack thereof can cause a grain to delay graceful deactivation.

That is quite the old post by the way. I suggest reading about support for IAsyncEnumerable<T> in Orleans v7+ here #8416
This performs long-polling behind the scenes but is far more comfortable to use and can be adapted in various ways.

I have a couple of examples here including usage as an async queue, broadcast or rewindable stream.

The original pattern is still more powerful yet it's now overkill for most use cases.

[gschuager]

Great! many thanks! will look into those topics

[gschuager]

I've been doing some experiments with IAsyncEnumerable and it seems to be a good fit to stream data from one grain to another, but as far as I can tell, I am missing the back-pressure handling part.

The context is that I eventually need to deliver state updates to a web application. I plan to use Signalr, and I see that it supports streaming via IAsyncEnumerable, but the sever would be pushing updates at its own peace instead of the client requesting them when it is ready to handle them.

Is there any way around this without using client initiated polling?