[Feature request]: Make 'PipelineDisposed' event available on ResiliencePipelineProvider

[Damien Honeyford]

Is your feature request related to a specific problem? Or an existing feature?

For long-lived services with a reference to an existing ResiliencePipeline to be able to respond to that pipeline having been disposed due to a configuration change (when EnableReloads is used) they need a way of knowing that the pipeline has been disposed.

Currently it requires some 'acrobatics' to forward the notification provided by the OnPipelineDisposed callback on ConfigureBuilderContext<TKey> or AddResiliencePipelineContext<TKey> to the consumer of a ResiliencePipeline so that they can fetch an updated instance of the ResiliencePipeline they're using.

Describe the solution you'd like

Add an event or callback to ResiliencePipelineProvider that can be used by a long-lived service to fetch an updated ResiliencePipeline instance.

public class MyLongLivedService : IDisposable
{
    private readonly ResiliencePipelineProvider<string> _provider;
    private ResiliencePipeline _pipeline;

    public MyLongLivedService(ResiliencePipelineProvider<string> resiliencePipelineProvider)
    {
        _provider = resiliencePipelineProvider;
        _provider.PipelineDisposed += ReloadPipeline;
        _pipeline = _provder.GetPipeline("my-pipeline");
    }

    private void ReloadPipeline()
    {
        _pipeline = _provder.GetPipeline("my-pipeline");
    }

    public void Dispose()
    {
        _pipeline.PipelineDisposed -= ReloadPipeline;
    }
}

Additional context

I'm not sure whether Microsoft have moved away from events as most of their newer code seems to favour callbacks from what I've seen.

[martintmk]

Hey @damienhoneyford, the MyLongLivedService is not necessary, because Polly already does the reload transparently automatically.

When you enable the reloads, Polly returns a wrapper pipeline that is aware of reloads and it does something very similar than your example. Additionally, it also disposes the old pipeline.

Effectively those means that you can retrieve the pipeline once and keep it for that rest of application lifetime even when reloads are enabled.