Sharing Ref Counted Containers

[Andrei Alexandrescu]

Michel Fortin wrote:
> On 2010-08-04 21:55:33 -0400, Jonathan M Davis <jmdavisprog at gmail.com> 
> said:
> 
>> I would have thought that sharing pretty much _any_ type more complex 
>> than a
>> primitive type without it being synchronized would be a bad idea. And 
>> since the
>> standard containers obviously aren't going to be synchronized, I would 
>> expect
>> you to have to wrap them in a class or struct which is synchronized.
> 
> You're exactly right Jonathan. The problem is that 'synchronized' only 
> protects what's directly inside the class and doesn't protect anything 
> beyond an indirection. The container and its reference counter is beyond 
> an indirection, so it is not protected by 'synchronized' and is thus 
> 'shared' according to the type system.
> 
> So that's what the type system tells you. You can cast your way around 
> that undesired 'shared', and it's the only way to use a container in a 
> synchronized class. I think that's the reason dsimcha wants the 
> documentation to be clearer. Because using a container inside a 
> synchronized class is probably going to be a common thing, what you 
> should and should not do with the container should be documented for 
> when you cast your way around the type system.
> 
> Personally, I'd say that not being able to use a container inside a 
> synchronized class without subverting the type system looks like a 
> failure of the type system.

How about an insufficiency of the container library?

Andrei