crowd-pulse pipeline

pipeline

+-----------------+                           
|                 |                           
|  Observable<A>  |                           
|                 |                           
+--------+--------+                           
         |                                    
         |                                    
+--------v--------+                           
|                 |                           
|  Observable<A>  |                           
|                 |                           
+--------+--------+                           
         |                                    
         |                                    
+--------v--------+                           
|                 |                           
|  Observable<A>  +-----------------+         
|                 |                 |         
+--------+--------+                 |         
this is  |                 +--------v--------+
.cache() |                 |                 |
         |                 |  Observable<B>  |
         |                 |                 |
         |                 +--------+--------+
         |                          |         
         |                          |         
         |                 +--------v--------+
         |                 |                 |
         |                 |  Observable<B>  |
         |                 |                 |
         |                 +--------+--------+
         |                 this is  |         
         |                 .cache() |         
         |                          |         
         |                          |         
         | which operator to wait   |         
         | for Observable<B> and    |         
         | then emit Observable<A>? |         
         |                          |         
         |    +-----------------+   |         
         |    |                 |   |         
         +---->  Observable<A>  <---+         
              |                 |             
              +-----------------+             
                                              
            items have to be emitted          
            only when Observable<B>           
            has completed