loop over all instances to find a free one                                                                                                                                                                                                                                                                 
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                       instance exists?                                                                                                         
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                            free?                               
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                             yes
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                         reserve this instance                                                                                                                                                  
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                                                                                                                                                
                                                                                                                                                                                                       get next instance