Light-weight threads

[Robert Jacques]

On Wed, 24 Feb 2010 04:15:03 -0500, Norbert Nemec  
<Norbert at nemec-online.de> wrote:

> Hi there,
>
> I just found that recent change in the language to make all global  
> variables thread-local by default. This makes me think of a major  
> performance problem: every thread creation will have to copy all the  
> thread-local variables. This makes it impossible to efficiently spawn  
> many light-weight threads even if they do not make use of the global  
> variables at all.
>
> I guess I am not the first one to spot this problem? I believe that  
> thread creation should come with as little overhead as possible. Maybe a  
> concept of light-weight threads based on side-effect free code could  
> complement the regular threads?
>
> Just a quick idea to throw into discussion...
>
> Greetings,
> Norbert

Norbert, you are confusing threads with fibers. OS Threads have never  
been, nor will ever be, "light-weight" in any sense of the word. If they  
were, no one would care about thread-pools and the like. Languages that  
feature light-weight threads, such as Erlang, are actually spawning  
fibers. The Erlang runtime, for example, only ever uses one D style thread  
to host millions of 'logical' threads.
Basic fiber support is already in druntime. Actually, it looks like the  
std.thread and std.concurrency updates will internally use either a thread  
pool or a fiber based back-end, so you might not have to worry about it.  
If you're simply looking for a task library, dsimcha has been working on  
one as have others (look in scrapple and for the blip project on dsource,  
IIRC)