Re: [boost] [string] proposal

Subject: Re: [boost] [string] proposal
From: Dean Michael Berris (mikhailberis_at_[hidden])
Date: 2011-01-21 11:32:31

On Sat, Jan 22, 2011 at 12:19 AM, Peter Dimov <pdimov_at_[hidden]> wrote:
> Dean Michael Berris wrote:
>
>> 1. The overhead of maintaining that table of reference counts may be
>> significant if you have a lot of strings created in your application.
>
> No table is needed; the reference count is just placed before the string
> data in the allocated memory.
>

Interesting. That can work, although you'll run into all sorts of
load/store issues and alignment requirements. Of course much like
anything that needs to be shared across threads too, so it's not that
bad.

>> 3. The reference count almost always will be implemented with atomic
>> counters to be efficient. In cases where the hardware doesn't support these
>> (in embedded environments)
>
> ...
>
> Copying the string requires a memory allocation, which also grabs a lock.
> You're not likely to have a lock-free allocator if you don't have atomic
> operations.
>

Yeah, I agree. So never mind that limitation, it's going to be a
limitation anyway with anything that has to be synchronized. :)

>> 2. In the case that you do have strings copied around, consider the case
>> in multi-threaded applications where you have different threads running on
>> different cores.
>
> Copying the string data outweighs the reference count update because of the
> allocation.
>

Right.

So I guess I can be convinced that ref counting in strings would be just fine.

I can't wait to get that so that I can make cpp-netlib just use these
smart strings throughout. :D

-- 
Dean Michael Berris
about.me/deanberris