Mac Forum / Programming / Mac Programming / April 2006

I just got done reading Apple's documentation of Cocoa multithreading,
but I didn't find an answer to this basic question:

Are local variables re-created automatically for each thread?  In other
words, if I have an object method, or for that matter a plain, old, C
function, that gets called by one of my threads, are its local
variables created uniquely for that thread?  For example:

int q=0;

double calc(double a, double b) {

 double c;

 a*=a; b*=b; c=a+b;
 c=5./a/c/q;

 if (c<10.) q++;
 return c; }

In the above function, a, b, and c are all locals.  If multiple threads
are running this function simultaneously, does each thread have its
own, private variables for a, b, and c, not shared with the other
threads?

(I am assuming that the variable q would be shared by all threads since
it is defined outside the function.)

And while we're on the subject of multithreading -- is there a way to
ask the OS if any processor cores are free to execute a new thread?  I
didn't see anything about that in Apple's documentation either, and in
the project on which I am working it would be pretty pointless to
create a new thread if there is no unused processor core to execute it.

Any help is appreciated!

Thanks,
Darel

<DarelRex@gmail.com>