Re: question re. usage of "static" within static member functions of a class

From:

"Chris M. Thomasson" <no@spam.invalid>

Newsgroups:

comp.lang.c++

Date:

Sat, 12 Sep 2009 02:29:35 -0700

Message-ID:

<h8fpjp$1ad2$1@news.ett.com.ua>

"James Kanze" <james.kanze@gmail.com> wrote in message
news:edee09a7-fbc2-41fd-84b4-dcdae859b12e@a21g2000yqc.googlegroups.com...
[...]

The problem is that C++ (up through the 2003 standard) simply
lacks memory barriers. Double-checked locking is one example
of code that _needs_ a memory barrier to work correctly -- but
it's only one example of many.

It can be made to work with thread local storage as well,
without memory barriers.

Indeed; something along the lines of:

<pseudo-code typed in newsreader>
___________________________________________________________________
template<typename T, unsigned T_id = 0>
struct non_destroying_singleton
{
    static T& instance()
    {
        __thread T* l_instance = NULL;

        if (! l_instance)
        {
            static T* g_instance = NULL;

            static pthread_mutex_t g_mutex = PTHREAD_MUTEX_INITIALIZER;

            lock_guard lock(g_mutex);

            if (! (l_instance = g_instance))
            {
                l_instance = g_instance = new T();
            }
        }

        return *l_instance;
    }
};
___________________________________________________________________

No memory barriers required! Yeah!

;^)

[...]