java - RxJava computation explosion -

i'm facing tricky issue combinelatest. i'm building huge chain of combinelatest , starting second item main observable, there explosion of computation.

import org.testng.annotations.test; import rx.observable; import rx.observers.testsubscriber; import rx.subjects.publishsubject; import rx.subjects.subject;  import java.util.list; import java.util.concurrent.atomic.atomicinteger;  public class rxtest {      private atomicinteger ai = new atomicinteger(0);     private atomicinteger ai2 = new atomicinteger(0);      @test     public void explosion() {         subject<integer, integer> sub = publishsubject.create();         observable<integer> ret = getobservable(2, sub);          testsubscriber<integer> testsubscriber = new testsubscriber<integer>();         ret.subscribe(testsubscriber);          sub.onnext(1);         sub.onnext(2); // may commented         sub.oncompleted();          testsubscriber.assertnoerrors();          list<integer> numbers = testsubscriber.getonnextevents();          system.out.println(numbers.size());         system.out.println(ai);         system.out.println(ai2);     }      private observable<integer> getobservable(int depth, observable<integer> source) {         if (depth == 0) {             return source;         } else {             observable<integer> o = getobservable(depth - 1, source);             (int = 0; < 300; ++i) {                 ai2.incrementandget();                 o = observable.combinelatest(                         o,                         getobservable(depth - 1, source).map((a) -> {                             ai.incrementandget();                             return a;                         }),                         (a, b) -> + b                 );             }             return o;         }     } } 

with 1 item, have:

1 90600 90600 

with two:

90602  271200 90600 

it seems normal behaviour of rx. i'm trying know if possible avoid kind of explosion. goal have kind of output (like recreate chain each value)

2  181200 90600 

this code example of problem not real use case.

i'm facing fact building observable quick(and having first value observable) if i'm changing "leaf" observable, it's not.

thanks