Remove NetworkService::write_notification

[tomaka]

The API of the write_notification method doesn't permit back-pressure to be propagated to the code that emits notifications.
For this reason, NetworkService now has a replacement notification_sender method.

The write_notification isn't marked as #[deprecated] because we have a policy against that, but it should very much be considered as deprecated.

This issue consists in removing the usage of write_notification from the sc-network-gossip crate (the only crate that uses it).
It is unclear to me how difficult it is to do so, but I know that it is certainly not trivial.

[rphmeier]

This issue consists in removing the usage of write_notification from the sc-network-gossip crate (the only crate that uses it).

We also make heavy use of this API in Polkadot at the moment, so that is also a blocker for removal.

[tomaka]

Polkadot should actually not be that difficult because its code is very asynchronous. The notification_sender replacement should therefore be rather easy to use, and the difficulty IMO is mostly about figuring out what to do exactly when buffers are full.

When it comes to GrandPa, however, we still use manual polling, and replacing a synchronous function call with an asynchronous call can require a big amount of refactoring.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[rphmeier]

Yep, still very important.