src/main/java/io/reactivex/disposables/Disposables.java
@NonNull
    public static Disposable fromAction(@NonNull Action run) {
        ObjectHelper.requireNonNull(run, "run is null");
        return new ActionDisposable(run);
    }
@NonNull
    public static Disposable fromAction(@NonNull Action run) {
        ObjectHelper.requireNonNull(run, "run is null");
        return new ActionDisposable(run);
    }
Construct a Disposable by wrapping a Action that is
executed exactly once when the Disposable is disposed.
@param run the Action to wrap
@return the new Disposable instance