How to address thread-safety of service data used for maintaining static local variables in C++?

Question

Consider the following scenario. We have a C++ function with a static local variable:

void function()
{
    static int variable = obtain();
    //blahblablah         


        

Answer 1

C++ says that your static variable should only be initialized once - however C++ doesn't deal with threads(yet).

gcc(atleast on *nix systems) does the proper magic to safely guard multiple threads initializing such a static variable. According to http://social.msdn.microsoft.com/Forums/en/vcgeneral/thread/12f8e2c7-d94d-4904-8c79-a0b0d1088e0b , msvc does not - and in such a case you'll have to lock the initialization yourself.

Guarding the initialization with a critical section should protect all this - i.e. your functionThreadSafe() is ok - (unless obtain() itself calls functionThreadSafe()

http://blogs.msdn.com/b/oldnewthing/archive/2004/03/08/85901.aspx is worth a read in this regard.

Personally, to avoid surprises I'd try to rewrite this so you can initialize variable yourself, once, before you create any threads - e.g.

static int variable = 0;
void init_variable() //call this once, at the start of main()
{
  variable = obtain();
}

void function() 
{
  //use variable, lock if you write to it
}