Double Checked Locking

[Jonathan M Davis]

On Saturday, December 17, 2011 22:16:38 Michel Fortin wrote:
> On 2011-12-17 23:10:19 +0000, Andrei Alexandrescu
> 
> <SeeWebsiteForEmail at erdani.org> said:
> > On 12/17/11 5:03 PM, Jonathan M Davis wrote:
> >> Well, you learn something new every day I guess. I'd never even heard
> >> of
> >> double-checked locking before this. I came up with it on my own in an
> >> attempt to reduce how much the mutex was used. Is the problem with it
> >> that the write isn't actually atomic? Wikipedia makes it sound like
> >> the problem might be that the object might be partially initialized
> >> but not fully initialized, which I wouldn't have thought possible,
> >> since I would have thought that the object would be fully initialized
> >> and _then_ the reference would be assigned to it. And it's my
> >> understanding that a pointer assignment like that would be atomic. Or
> >> is there more going on than that, making it so that the assignment
> >> itself really isn't atomic?
> > 
> > There so much going on about double-checked locking, it's not even
> > funny. Atomic assignments have the least to do with it. Check this out:
> > http://goo.gl/f0VQG
> 
> Shouldn't a properly implemented double-checked locking pattern be part
> of the standard library? This way people will have a better chance of
> not screwing up. I think the pattern is common enough to warrant it.

Well, from the sounds of it, the basic double-checked locking pattern would 
work just fine with a shared variable if shared were fully implemented, but 
since it's not, it doesn't work right now. So, I don't know that we need to do 
anything other than finish implementing shared.

- Jonathan M Davis