Added Observable.window(count, skip) operator

[amihusb]

As part of #411

Feels like i don't cover all cases in tests. Too complicated operator.

WindowSized is the appropriate name?

I'm embarrassed for the long wait, relocated to another city this month.

[arkivanov]

Thanks for the PR, I will check when I have time. From the first sight, looks like you can avoid using the Serializer, since there is only one stream - the upstream. Serializer is needed when there are multiple concurrent data streams. The upstream is guaranteed to produce items sequentially.

[amihusb]

Oh, yes, i can avoid serializer, thanks. Then i need an atomic counter of active windows.

I don't miss anything: upstream is guaranteed to produce items sequentially by library operators/factories, but we can create "unstable" upstream by observableUnsafe { ...creating threads and call observer.onNext... }, right?

Will update implementation today.

[arkivanov]

Sequential streams are guaranteed by the Rx contract. Every stream is allowed to produce events on different threads but always sequentially. You can break the contract of course, but operators should not cover such cases.

[amihusb]

@arkivanov thanks for the clarification. Updated PR.

[arkivanov]

Sorry, let's use two counters. Otherwise looks good!

[arkivanov]

@amihusb Thanks for your contribution!