Concurrency and Safety and Uniqueness Types

[Sean Kelly]

Check out core.thread.Fiber. No fiber-local storage yet, but it's something I've considered and seems relatively important for writing a correct D program with fibers. 

Sent from my iPhone

On Sep 28, 2011, at 2:03 AM, Chris Dew <cmsdew at gmail.com> wrote:

> Warning: I've written multi-threaded code in C, Haskell and Java, but
> only single threaded code in D.
> 
> I'll use the word 'fibre' for a job which may take some time to run,
> and may be blocked from time to time.  It may mean the same as 'task'
> in D, but I'm not sure.  Greenlets, lightweightthreads or possibly
> cooroutines may be other names which have some bearing here.
> 
> In order to run N fibers efficiently I'm making a big assumption that
> we need to map them to a pool of M threads, where M is ~= NumCores (+
> num blocked threads?) and then use some form of 'select' or 'epoll' in
> the runtime to swap them in and out of threads, when they are really
> to run again.
> 
> What I think I want is fibre local storage, by default.  Thread local
> storage by default sounds fine for low-level work, but I don't want to
> think about, or manually implement, how my fibres are mapped onto
> threads efficiently.
> 
> As fibres can be moved between threads by the runtime, does that mean
> that their storage must be 'shared', with all the inefficiency that
> brings?
> 
> Are there Uniqueness Types in D?  They could be used to move the
> fibre's storage between threads as the fibre moves, without
> compromising safety.
> 
> If not, how do you currently implement storage for a fibre (task?), to
> make it migrateable when the runtime moves the fibre between threads?
> 
> Thanks,
> 
> Chris.