Implements fs2.concurrent.Topic with fs2.concurrent.Queue

[vladimir-popov]

Implementation of the fs2.concurrent.Topic with fs2.concurrent.Queue as subscriptions. Read more in this issue #1406 .

[pchlupacek]

Just a quick comment on this. If we wont manage to get perfromance correct, there may be also ather combinators affected. So instead of getting this as quick solution only for topic I would like to go through pubsub, and make sure that

• this cannot be solved with pubsub
• if this cannot be solved with pubsub make sure that no other combinators using the pubsub (i.e. broadcast) are not affected by this too
• fix all the other combinators, if this will be pubsub design flaw.

[SystemFw]

I agree with @pchlupacek viewpoint on this: we actually already have a battle tested implementation of Topic using Queue - the pre PubSub one.

I'd rather see if we can fix it with PubSub though, cause it's much more flexible while at the same time abstracting away a lot of complicated and potentially unsafe synchronisation logic.

[vladimir-popov]

Ok. I understand your point. Now I’ll close this PR, but we will continue use it as temporary workaround.

[pchlupacek]

Thats completely fine @vladimir-popov