Handler.post() only If not already on main thread?

[ursusursus]

Hi,
Id like to ask, if its possible for HandlerScheduler to check wether it "needs to change threads", i.e. avoid posting if already on main thread. unnecessarily

This can manifest it self, when using observable mapped to Started, Success, Error events, and UI (main thread) subscribes to the observable (and Started is created via startWith()), which then posts the Started emit for no reason.

I know you can do this by rearranging the operators like

fooObservable.
.map( __ -> Success)
.onErrorReturn(t -> Error(t))
.observeOn(AndroidSchedulers.mainThread)
.startWith(Started))

But that ties it to main thread from from within of the api. I think in this case the subscriber should decide, (which we already do most of the time - which leaves the Started to be posted). Say if that was a network observable, and you want to compose 2 of them some how, which gives them implicit scheduler unneccesarily)

[JakeWharton]

Dupe of #228. The answer is yes, it needs to post.