Concurrency in D and Active Objects

[Robert Fraser]

Yigal Chripun wrote:
> Active Objects were mentioned in a thread on the NG, so I've looked
> around and found the following file which explains the idea in a very
> clear way. it also outline a possible implementation for C#.
> 
> http://blog.gurock.com/wp-content/uploads/2008/01/activeobjects.pdf
> 
> Since D is way better than Java/C#/C++ (all mentioned in the above
> article) it seems to me that such a useful abstraction could be
> implemented in D and probably would be simpler to do that than the other
> languages mentioned above.
> What are the benefits of D's approach of implementing a functional
> subset with pure functions compared to the above abstraction of Active
> Objects?

For low-level tasks (i.e. mapping a function to every element of an 
array), it's easier to write and a better solution using D's model (pure 
functions).

For high-level tasks (i.e. processing a SQL query in large database 
engine), active objects are _MUCH_ easier to work with, since they allow 
state (automatic state within functions doesn't cut it here, fellows). I 
think this is where the future of parallelization lies, not in forcing 
the user to worry about immutability and pure functions (which is not 
easy for the average programmer, I _hated_ learning FP in school).

*puts on flame-retardant vest* Maybe my mind is just too focused on 
database and web programming, but from working with an event-based 
parallelization technique (SEDA, but AO is quite similar in its 
approach, albiet more OO and by a different name), is that it's a lot 
easier to grasp for the programmer. All data outside the event needs to 
be synchronized on, of course, but a good event model uses very little 
global data.

OTOH, D's model is compiler-checkable (i.e. the compiler can guarantee 
you no sync issues), while an event/active object model is not (since 
you can access global state).

> Also, to make D's functional subset run Concurrently doesn't D need a
> special runtime that parallelizes the code (which D currently doesn't have)?

Yes, but that can be done. Active objects would need one, too.

> --Yigal