GC, Multithreading, Heap(s)

[Steven Schveighoffer]

"g012" wrote
> Hello,
>
> I'm not yet programming seriously in D, but I've been lurking on it since
> quite some years now, and I have some questions about its current (or
> future ?) features related to memory that need answers before the decisive
> jump.
>
> In the context of a multithreaded program, I'd like to know if it's
> possible to do the following in D (if a feature is not currently 
> supported,
> can you indicate if it's planned for a future release):
>
> . replacing the default heap allocator with a multithread optimized one,
> like nedmalloc. I saw I can overload new and delete in a class / struct,
> but I'd like to do the overload on the generic new / delete. If it's not
> possible, does the default allocator already support multithreaded heap
> allocations without locking systematically ?

With the new druntime, the garbage collector is completely replacable (this 
was always the case with Tango).  So you can do whatever you want ;)

> . is the GC multithreaded, ie when it pauses all the threads to run, does
> it run multithreaded itself, with one thread per hardware thread ?

No

> . if a thread has data to be collected that only itself is referencing,
> will a dedicated GC thread run in parallel of the other threads 
> (themselves
> running as normal, unpaused, simultaneously to the thread-local GC) ? If
> no, is there a way to declare that a variable will be referenced only in
> the current thread, and to have a thread-specific collector that does not
> imply to pause other threads to run ? The idea is to collect thread-local
> variables by a thread-locale GC, and shared variables by the global GC. 
> And
> if it is possible, can we disable temporarily thread-local GC similarly to
> the global GC ?
>
> If anything that can optimize heap usage in threads better than the above
> points is already implemented (or planned to) in D, please explain it to 
> me
> :)

See this article on a future enhancement planned for D.  Specifically make 
sure you read the last paragraph.

http://bartoszmilewski.wordpress.com/2008/07/30/sharing-in-d/

-Steve