Local static variables and multithreading

[Marcin Kalicinski]

I'm trying to write platform-independent code that will work correctly in
multithreaded environment. I know C++ standard says nothing about threads,
but I still think my question is not entirely off-topic here:

int f()
{
static int n = g();
return n;
}

If I call the above function from multiple threads, can I still assume that
g() will only be called once? Or is it platform dependent?

thank you,
Marcin

 

[John Carson]

I'm trying to write platform-independent code that will work
correctly in multithreaded environment. I know C++ standard says
nothing about threads, but I still think my question is not entirely
off-topic here:
int f()
{
static int n = g();
return n;
}

If I call the above function from multiple threads, can I still
assume that g() will only be called once?

No.

http://blogs.msdn.com/oldnewthing/archive/2004/03/08/85901.aspx

Or is it platform dependent?

I suspect the answer is no on any multithreaded platform.

 

[abelikoff]

In order to guarantee the above, the compiler would need to be aware of
threads. It would actually need to generate code to handle that
assignment inside a mutex or a critical section. C++ doesn't do that
(yet).

The code above can exhibit a number of nasty bugs: from duplicate
invocation of g() to use of partially initialized n.

-- Sasha