Search Algorithms used by top engines? what are the top parallel search algorithms used by top engines ,and which one is the best ?
And is there a reference implementation of them in any programming language ? I know most of  the top engines are open source but they tend to be extremely complex and unsuitable for learning .
Best performing algorithms are YBWC and DTS. Lazy SMP is probably giving best performance/complexity ratio. You can read more about parallel search algorithms here (make sure to check referencies and links. 
As for reference realization, I haven't seen any, so I just used simpler engines with parallel search,  and, mostly, algorithms descriptions.