Re: [boost] Strings and thread safety

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-09-08 11:20:02

Philippe Vaucher wrote:
>> lexical_cast was NEVER thread safe to
>> start -- not one word in the docs indicates that it is thread-safe, and
>> the
>> implementation clearly isn't because of several things that are used.  So
>> clients using lexical_cast from multiple threads should beware...
>>
> 
> There's something I want to clear out, lexical_cast is reentrant and only
> uses "stacked" variables no ? 

So what?  Those stack types are free to reference global data. And in the case 
of stringstream, in combination with operators<< and operator>>, they most 
certainly do access global data in the form of locales and facets.

> It looks like the "thread-dangerosity" you're
> speaking about is like the same we would have by used two different
> stringstream objects in two different threads...

Yep.

> Enlighten me if I missed something.

Well again, please show me in the lexical_cast documentation the line that 
indicates that it is a 'thread-safe' operation.  You won't find it because it 
isn't.  You have the issues of both the internal implementation and the types 
being converted to/from (eg: string) using global data in their 
implementation.  Since lexical_cast is generic, it has no way of controlling 
the thread safety of user defined types and their associated operator>> and 
operator<<.

The real problem here, is that lexical_cast *will work* most of the time in an 
MT environment without difficulty. But that's not good enough to declare it 
'thread-safe'...which is the entire assumption in this thread.  Actually, as 
this whole discussion illustrates, it's probably enough to make it 
'thread-dangerous' ;-)

Jeff