How RXJava Scheduler/Threading works for different operator?

Question

Can anyone please help me to explain which scheduler are running below code?

Completable.complete()                 
.subscribeOn(http://Schedulers.io  ())                 
.observeOn(AndroidSchedulers.mainThread())                 
.delay(5000, TimeUnit.MILLISECONDS)                 
.doOnComplete(() -> liveDataState.postValue(""))                 
.subscribe()

My question is which schedulers are delay(), doOnComplete() and subscribe() are using io or mainThread?

what is state. also you can log to see on which thread you are on with Thread.currentThread().getName() — Raghunandan, Dec 31 '18 at 05:25
Each operator's documentation specifies which scheduler it works on. For example, that [delay](http://reactivex.io/RxJava/2.x/javadoc/io/reactivex/Completable.html#delay-long-java.util.concurrent.TimeUnit-) runs on the computation scheduler. — akarnokd, Dec 31 '18 at 15:26

score 3 · Answer 1 · answered Jan 01 '19 at 18:52

After digging into RxJava threading last two days found the rule of thumbs for handling RxJava Threading/Scheduling:

observeOn works only downstream operator
subscribeOn works for both downstream and upstream operator
Consecutive/Multiple subscribeOn do not change the thread
Consequent observeOn do change the thread for downstream oerator
Unlike with subscribeOn(), we can use observeOn() multiple times for seamless thread switching
Operator like delay(), interval() have default scheduler and can change the downstream scheduler as well

So, for my case:

Completable.complete()   // IO scheduler based on subscribeOn scheduler           
.subscribeOn(http://Schedulers.io  ())                 
.observeOn(AndroidSchedulers.mainThread())                 
.delay(5000, TimeUnit.MILLISECONDS)   // Default Computation scheduler              
.doOnComplete(() -> liveDataState.postValue(""))  // Computation scheduler by delay scheduler             
.subscribe()  // Computation scheduler by delay as well

Also, you can look into the marble diagram for more understanding:

How RXJava Scheduler/Threading works for different operator?

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