[fpc-devel] volatile variables
JeLlyFish.software at gmx.net
Tue Jun 28 19:05:50 CEST 2011
On Tue, 28 Jun 2011 15:54:35 +0200, Michael Schnell <mschnell at lumino.de>
> But if you do the same with
> volatile static int x;
> the code will stay and another thread can watch x growing in a time
> sharing system.
No, it can't. "volatile" just ensures that accessing the variable results
actual memory accesses. That does not mean cache-coherence, so another core
may still see other (as in "older") values.
> I believe that inserting some ptherad_mutex... calls will not force the
> compiler to bother about some intermediate values of a non volatile
Well, then it's probably overly aggressive or buggy.
> I believe that with FPC global variables are assumed to be volatile and
> not optimized away or cashed in registers. But what about heap-variables
They are not volatile, I'd guess. And I don't see the need to assume they
are. You would always need proper synchronisation constructs here.
> Thus true for global variables, not necessary true for static variables
> as they can't be accessed by a function defined in another module (I
> don't know whether the C compiler makes a difference)
It should not. It can't possibly assume that a call to pthread_...()
result in a recursive call back to the caller... ;)
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