Add ItemDropped callback to ChannelOptionsBase

[Prunkles]

There is no way to detect when an event is dropped due to BufferOptions.BoundedChannelFullMode being set to drop.

Starting with some version of System.Threading.Channels, an itemDropped callback was added to the BoundedChannel. So I added a BufferItemDropped callback to the ChannelOptionsBase.

This callback would fit better in the BufferOptions, but because it requires a TEvent, it would also need to be added to the BufferOptions. I am not sure if it is affordable, because of how many things depend on BufferOptions being without generic parameters.

[cla-checker-service]

💚 CLA has been signed

[Prunkles]

I guess I've signed the CLA, but I haven't received any confirmation

[Prunkles]

Oh, never mind, it updated when I commented

[stevejgordon]

Sorry for the delay, @Prunkles . Thanks for contributing this PR. In principle, it's okay and something we should add, but I'd like to consider where we should include this option a bit further.

[Prunkles]

@stevejgordon

I'd like to consider where we should include this option a bit further.

This decision was made based on the Channel.CreateBounded(BoundedChannelOptions options, Action<T>? itemDropped) itself: as we can see, it takes itemDropped separately from other options as well. I guess it is for the same reason I wrote above (to avoid making the Options type generic)

This callback would fit better in the BufferOptions.

Also, I thought about it a bit more, and I think I was wrong, at least because that itemDropped option is clearly intended for the BCL Channel type, so it should be in the corresponding ChannelBufferOptions, and not just BufferOptions which does not have any "channel" semantics

So I think the current placement is the most appropriate