D and multicore

[sybrandy]

> Sean, sybrandy, don, fawzi, tobias, gary, dsimcha, bearophile, russel, trass3r, dennis, and simen clearly have ideas how to work with parallel problems.

Ideas: Yes.
Expert: No.  I haven't exercised it much as I haven't been able to do it 
at work.  Others here have shown that they have more knowledge than I.

> Sean mentioned:
>
> "In the long term there may turn out to be better models, but I don't know of one today."
>
> So he's basically saying that those others listed in the wikipedia pages are totally unsuitable for real world tasks? Only Erlang style message passing works?

It's the easiest to understand for the most part as it's very similar to 
how the real world works.  Think about a coffee shop: two 
processes/people, let's call them Alice (customer) and Bob (barrista), 
are in the coffee shop.  Alice is ordering coffee and Bob is making 
coffee.  Alice tells Bob that she wants a 
super-duper-extra-foamy-mocha-hazel-choco-latte.  E.g. she sends a 
message to Bob.  Bob then does his magic and sends a message to Alice by 
handing her overpriced coffee.

So, from an understandability standpoint, it's very simple to 
understand.  There are also other benefits that are best expressed in 
Joe Armstrong's thesis, which you can easily find online.  He is one of 
the creators of Erlang and his thesis describes many of the benefits of 
the architecture.

Is it the best for all problems?  No.  For example, there are better 
tools for parallelizing loops.  The Actor Model, which is what Erlang 
uses, doesn't work very well for this.  There are other methods as well, 
but outside of auto parellelization and the actor model, they are harder 
to implement correctly, IIRC.  There may be a couple I don't really know 
about.

Now, will any of these provide you with instant benefits in your apps? 
Probably not.  Most software today was designed to run on one core and 
therefore doesn't use multiple cores very well.  Firefox (3.6 and 
later), Chrome, IE 9, and I think the latest version of Opera all use 
multiple threads now mainly to keep certain pages/plugins from killing 
the entire browser, though you may notice some speedups just from that.

However, this does not mean that multiple cores are not benefiting you 
much.  The OS is (should be) smart enough to distribute multiple apps 
across the cores, so you can have your browser and your word processor 
working hard and not have either one prevent the other one from getting 
any CPU time.  The problem is that most of us don't have more than 2-4 
apps working hard at any time, so past 4 cores you probably won't be 
getting much benefit in this respect.  As threading becomes more popular 
and threaded apps are better designed, we should see a trend of better 
CPU usage on the desktop.

Casey