code: public static <T1, T2, T3, T4, T5, T6, T7, T8> Func8<T1, T2, T3, T4, T5, T6, T7, T8, Observable<Void>> toAsync(Action8<? super T1, ? super T2, ? super T3, ? super T4, ? super T5, ? super T6, ? super T7, ? super T8> action) {
          return toAsync(action, Schedulers.computation());
      }
docs: Convert a synchronous action call into an asynchronous function call through an Observable.
  <p>
  <img width="640" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/toAsync.an.png" alt="">
  
  @param <T1> the first parameter type
  @param <T2> the second parameter type
  @param <T3> the third parameter type
  @param <T4> the fourth parameter type
  @param <T5> the fifth parameter type
  @param <T6> the sixth parameter type
  @param <T7> the seventh parameter type
  @param <T8> the eighth parameter type
  @param action the action to convert
  @return a function that returns an Observable that executes the {@code action} and emits {@code null}
  @see <a href="https://github.com/ReactiveX/RxJava/wiki/Async-Operators#wiki-toasync-or-asyncaction-or-asyncfunc">RxJava Wiki: toAsync()</a>
  @see <a href="http://msdn.microsoft.com/en-us/library/hh228993.aspx">MSDN: Observable.ToAsync</a>