title: RxJava with vertx: can't have multiple subscriptions exception
body: <p>I'm trying avoid vertx callback hell with RxJava.
  But I have "<code>rx.exceptions.OnErrorNotImplementedException: Cannot have multiple subscriptions</code>". What's wrong here?</p>
  
  <pre><code>public class ShouldBeBetterSetter extends AbstractVerticle {
      @Override
      public void start(Future&lt;Void&gt; startFuture) throws Exception {
          Func1&lt;AsyncMap&lt;String,Long&gt;, Observable&lt;Void&gt;&gt; obtainAndPutValueToMap = stringLongAsyncMap -&gt; {
              Long value = System.currentTimeMillis();
              return stringLongAsyncMap.putObservable("timestamp", value)
                  .doOnError(Throwable::printStackTrace)
                  .doOnNext(aVoid -&gt; System.out.println("succesfully putted"));
          };
  
          Observable&lt;AsyncMap&lt;String,Long&gt;&gt; clusteredMapObservable =
                  vertx.sharedData().&lt;String,Long&gt;getClusterWideMapObservable("mymap")
                          .doOnError(Throwable::printStackTrace);
  
          vertx.periodicStream(3000).toObservable()
                  .flatMap(l-&gt; clusteredMapObservable.flatMap(obtainAndPutValueToMap))
                  .forEach(o -&gt; {
                      System.out.println("just printing.");
                  });
      }
  }
  </code></pre>
  
  <p>Working Verticle (without Rx) can be found here:
  <a href="https://gist.github.com/IvanZelenskyy/9d50de8980b7bdf1e959e19593f7ce4a" rel="nofollow">https://gist.github.com/IvanZelenskyy/9d50de8980b7bdf1e959e19593f7ce4a</a></p>