D and multicore

[Gary Whatmore]

parallel noob Wrote:

> Hello
> 
> Intro: people with pseudonyms are often considered trolls here, but this is a really honest question by a sw engineer now writing mostly sequential web applications.  (I write "parallel" web apps, but the logic goes that you write sequential applications for each http query, the frontend distributes queries among backend http processes, and the database "magically" ensures proper locking. There's hardly ever any locks in my code.)
> 
> D is touted as the next gen of multicore languages. I pondered between D and D.learn, where to ask this. It just strikes me odd that there isn't any kind of documentation explaining how I should write (parallel) code for multicore in D. If D is much different, the general guidelines for PHP web applications, Java, or Erlang might don't work. From what I've gathered from these discussions, there are:
> 
>  - array operations and auto-parallelization of loops
>  - mmx/sse intrinsics via library
>  - transactional memory (requires hardware support? doesn't work?)
>  - "erlang style" concurrency? == process functions in Phobos 2?
>  - threads, locks, and synchronization primitives
> 
> Sean, sybrandy, don, fawzi, tobias, gary, dsimcha, bearophile, russel, trass3r, dennis, and simen clearly have ideas how to work with parallel problems. 
> 
> A quick look at wikipedia gave http://en.wikipedia.org/wiki/Parallel_computing and http://en.wikipedia.org/wiki/Parallel_programming_model
> 
> I fail to map these concepts discussed here with the things listed on those pages. I found MPI, POSIX Threads, TBB, Erlang, OpenMP, and OpenCL there.
> 
> 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?
> 
> The next machine I buy comes with 12 or 16 cores or even more -- this one has 4 cores. The typical applications I use take advantage of 1-2 threads. For example a cd ripper starts a new process for each mp3 encoder. The program runs at most 3 threads (the gui, the mp3 encoder, the cd ripper). More and more applications run in the browser. The browser actively uses one thread + one thread per applet. I can't even utilize more than 50% of the power of the current gen!
> 
> The situation is different with GPUs. My Radeon 5970 has 3200 cores. When the core count doubles, the FPS rating in games almost doubles. They definitely are not running Erlang style processes (one for GUI, one for sounds, one for physics, one for network). That would leave 3150 cores unused.

This question would have been more appropriate in D.learn. I started my journey with http://www.amazon.com/Java-Concurrency-Practice-Brian-Goetz/dp/0321349601

The GPU is a different kind of beast. GPU uses CUDA/OpenCL.