Re: [boost] [Boost.utility]

Subject: Re: [boost] [Boost.utility]
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-01-27 17:03:27

AMDG

Andrew Chinkoff wrote:
> Ok, I see. I would try to explain.
>
> Let us look at pseudo code:
>
> *** BEGIN PSEUDO CODE ***
> static int* my_int = 0;
> static Mutex mutex;
>
> void CreateInt()
> {
> 	if(!my_int)
> 	{
> 		Locker locker(mutex);
> 		if(!my_int)
> 			my_int = new int(100);
> 	}
> }
>
> void thread_func()
> {
> 	boost::call_once(CreateInt, flag);
> 	printf("[%d]", *my_int);
> }
>
> void main()
> {
> 		th1 = create_thread(thread_func);
> 		th2 = create_thread(thread_func);
> 		while(1)
> 		{
> 			// Prints "[0][100]", or "[100][0]", or "[100][100]" - hm... undefined!
> 		}
> }
> *** END OF PSEUDO CODE ***
>   

There is no race in this code.
It will always print [100][100].

In fact, the code would work equally well if you said:

void CreateInt() {
    my_int = new int(100);
}

In Christ,
Steven Watanabe