Subj : Re: Can C++ local static objects be made thread safe?
To   : comp.programming.threads
From : Alexander Terekhov
Date : Fri Feb 04 2005 10:08 am


Marcin 'Qrczak' Kowalczyk wrote:
> 
> Giancarlo Niccolai <searchforme@ingoogle.com> writes:
> 
> >> Because it would change various instances of code written with no
> >> threads in mind from unsafe to safe to use with threads.
> >
> > That is utterly impossible.
> 
> It is possible. Consider this function:
> 
> char32_t lookup_unicode_char_by_name(const string &name) {
>    static map<string, char32_t> database =
>       read_unicode_database_from_file();
>    map<string, char32_t>::iterator it = database.find(name);

You probably mean

   static const map<string, char32_t> database(
      read_unicode_database_from_file());
   map<string, char32_t>::const_iterator it = database.find(name);

>    return it == database.end() ? it->second : (char32_t)-1;
> }

The thing is that not all local statics are immutable and/or 
need thread-safe init provided by implementation to begin with.

regards,
alexander.

.