Re: [boost] Thread-safe singleton (was [FSM] Review library versionupdate)

From: Moshe Matitya (Moshe.Matitya_at_[hidden])
Date: 2007-02-08 04:42:26

On Tuesday, February 06, 2007 8:09 PM, Andrey Semashev wrote:
> 
> Tuesday, February 6, 2007, 1:34:50 AM, you wrote:
> 
> > ...
> >
> > What kind of solutions have you come up with for lazily initializing
> > singletons in a thread-safe manner?
> 
> In most cases I tried not to create the singleton lazily but
> initialize it as soon as possible. The perfect time is on executable
> module load which, AFAIK, is always done in single thread on
> platforms I have faced yet. Such approach was quite sufficient for me
> since it solves the key problem of the singleton creation.

I don't see how such an assumption can be made.  What if a thread is
started in the constructor or initializer of a global object?  I.e.:

    void thread_func()
    {
        // This may be called before, or concurrently with,
        // your singleton early-initialization function
        singleton::instance()->do_something();
    }

    class foo
    {
        foo()
        {
            boost::thread my_thread (&thread_func);
        }
    };

    // Constructed on module load
    foo global_foo;

Then there's the issue of singletons located in shared libraries (on
*nix platforms) or DLL's (on Windows).  If these modules are loaded
dynamically, there may already be multiple threads running.

Moshe