[boost] singleton and thread safety

From: Jason Hise (chaos_at_[hidden])
Date: 2005-07-31 20:35:20

I need to ensure that certain objects (specifically the policy bundles 
which manage singleton instances) are created in a thread-safe manner.  
First question:  Can two threads both initialize the same static 
variable if they pass through the same function at the same time?  Ex:

void foo (  )
{
    static Thing t;
}

Can t's constructor be called twice by two threads executing foo?

If so, I feel that I need to construct my policy bundles before 
execution enters main, a time when it is pretty much guaranteed that the 
application is operating in a single-threaded context.  I thought that 
this would be simple to do:  just write a class that calls the function 
with the static variable in its constructor and create a global instance 
of that class.  However, the standard appears to say that initialization 
of such global variables can happen after main is entered, so long as it 
happens before the global variable is used.  If the program starts 
spawning threads before the global variable is constructed I would still 
have the same problem.

How can I ensure that initialization is performed before main is 
entered?  If I cannot, is there some other way to make initialization of 
static variables thread-safe?  I cannot lock a mutex to manage this, 
because the mutex lives inside the threading policy instance and the 
threading policy instance lives in the policy bundle that I am trying to 
create in the first place.

-Jason