[QUIC] Finalize QUIC dispose model

[scalablecory]

Socket currently has a behavior of throwing SocketError.OperationAborted for outstanding operations when Dispose() is called.

We need to decide how Dispose() will trigger outstanding operations:

• QuicListener -- outstanding AcceptConnection() calls.
• QuicConnection -- outstanding Connect(), AcceptStream(), Close() calls. Plus any already open streams.
• QuicStream -- outstanding Read(), Write(), Shutdown(), Abort() calls.

The current model throws an OperationAbortedException, mimicing the Socket API; We should look at how consistent we want to be here, and if we want to adjust for usability/perf reasons, such as having AcceptConnection() or having AcceptStream() return null rather than throwing.

We should also consider how this interacts with a user-initiated connection/stream abort, and with a server-initiated connection/stream abort. In sockets, a variety of error codes can be thrown for these, one of them being SocketError.OperationAborted.

[GSPP]

What would this do if Dispose is called right before an operation is started? Would this throw ObjectDisposedException? If yes, this would cause an inherent race condition. For example, a caller of Socket.Accept cannot know whether he will receive SocketError.OperationAborted or an ODE. That makes the SocketError.OperationAborted not useful for handling this condition.

This is a thorny issue for Socket and it seems to apply just as much to QUIC. There has been some extensive discussion which might be useful to take note of: https://github.com/dotnet/corefx/issues/5749

Having an orderly was for shutting down is quite important as essentially any application must shut down eventually. This issue affects many users of Socket and QUIC.

[geoffkizer]

I think from a usability point of view, returning null from AcceptConnection or AcceptStream when a local close has happened is the best behavior, even though it's different than the behavior of Socket.Accept.

AcceptStream can also fail because of a remote close, either graceful or abortive; I'm less sure what should happen in this case. I think you can make an argument that graceful remote close should result in null from AcceptStream. Abortive remote close probably shouldn't.

[geoffkizer]

What would this do if Dispose is called right before an operation is started? Would this throw ObjectDisposedException? If yes, this would cause an inherent race condition.

Agreed, this is a good issue.

[geoffkizer]

I think QuicStream issues are covered under #756.

Let's use this issue specifically for QuicConnection and QuicListener. (Or maybe we should open issues for each...)

Edit: I do think the AcceptConnection and AcceptStream issues are very similar; we should be consistent here. I think the only other issue then, is Dispose during Connect. Am I missing anything here?