Re: [boost] [lexical_cast] optimization commited to HEAD

From: John Maddock (john_at_[hidden])
Date: 2006-08-31 09:03:10

Caleb Epstein wrote:
> On 8/31/06, John Maddock <john_at_[hidden]> wrote:
>
>> In any case all the implementations I'm aware of are minimally
>> thread safe these days, if that's not the case I'd certainly like to
>> hear about it.  BTW implementations that used copy-on-write in the
>> early days almost all (all?) switched away from that precisely
>> because of threading issues.
>
> Even the latest libstdc++ (GNU's Standard C++ library) uses a
> refcounted std::string.

Darn, I hadn't realised that :-(

> One needs to be careful when sharing strings across thread boundaries.
> See these bug reports for a detailed discussion:
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10350
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21334

Very interesting stuff!

I'm not sure that it's relevent in this case though: if you're 
lexical_cast'ing *to* a string then these issues shouldn't arise, whether 
there are other threads getting involved or not.  If you're casting *from* a 
string, then it appears that you need a mutex if you know the string is 
likely to be visible to other threads, even if all accesses to it are 
non-mutating.

Have I got that right?

Thanks, John.