[pdg-group] Meeting

[Xiong Ming]

Great! Thanks,  I'll definitely read the book. It's getting more 
intersting now. And hope more guys will join our discussion ( the group 
is getting smaller & smaller now), since this really get your something 
to learn.

Thanks

Don Hinton wrote:

>Hi Ming:
>
>On Sat, 20 Mar 2004, Xiong Ming wrote:
>
>  
>
>>Hi, Don:
>>    Thanks!  Your reply makes perfect sense to me. Would you mind if I 
>>ask some further questions? I wouldn't let go the opporutnity to get
>> a little more in-depth on this issue, because you are soooo familiar 
>>with this Active Object pattern, ;-). Please see below
>>    
>>
>
>You're welcome...
>
><snip>
>
>  
>
>>>Anyway, when MQ_Scheduler's ctor calls the Thread_Manager::spawn method,
>>>it passes the address of the svc_run function, and "this," a pointer to
>>>itself, as a void*.  svc_run, then dynamic_cast's void *arg back to a
>>>MQ_Scheduler* and invokes dispach() on it. 
>>>
>>>      
>>>
>>Yes, the dispatch () method basiclly runs a for loop (in a separate 
>>thread) that continuely iterate the Activation list to see if a certain 
>>method request
>>is runnable. When the can_run () (or guard ()) of a method request 
>>returns true,  it will execute the request via its actual servant 
>>(MQ_Servant).
>>
>>On the other hand,  the client thread uses MQ_Proxy to respond to 
>>request. As we know, MQ_Proxy maintains a pointer scheduler_ that points 
>>to the instance of the MQ_Scheduler, which is now running the dispatch 
>>() in a separate thread.  When here comes a new request, e.g., get (), 
>>the client thread will create a new method requst object and insert it 
>>to the activation list by invoking scheduler_.enqueue (method_request). 
>>Here comes a issue of concurrency. When we invoke scheduler_.enqueue (), 
>>is it going to affect the running of dispatch (), considering the fact 
>>that the two methods are running at the same time in separate threads 
>>but are invoked on the same object?  Or a better question is, will the 
>>scheduler_.enqueue () in the client thread make a contact with dispatch 
>>() in the seperate thread to sort of let dispatch () stop for a while to 
>>process scheduler_.enqueue ()? This is kind of complex, if i didn't make 
>>myself clear enough, you can think of it  as a question like: Is it 
>>possible for a object to process two methods simutaneously if the two 
>>methods are running on different threads?
>>    
>>
>
>Access to the internal list or queue must be synchronized, but that's
>sorta implicit in the design.  The book mentions this on page 383 but
>doesn't go into detail.  I think Doug's suggestion of looking at chapter 6
>in C++NPv2, the ACE_Task Framework (which implements the Active Object
>Pattern), would be a good idea, since it goes into detail about how to do
>this.  You can also just look at the ACE_Task implementation, i.e,
>ACE_wrappers/ace/Task*.
>
>If you don't have access to C++NPv1 and C++NPv2, you can borrow mine...
>
>hth...
>don
>
>  
>