> as I said, I was assuming I could garuntee testset was an *atomic*
> function... i.e. indivisible and possibly smaller than the timeslice
> of a scheduler... like a few i/o functions...
Speed doesn't guarantee anything. A timer interrupt can reschedule you
anytime, anywhere. Also, reschedules happen on system call exit, so any
system call you use is going to make you more vulnerable to unexpected
rescheduling.
> I'd probably have to look over the SMP kernel source and see what they
> use for semaphores...
What you really want is SysV semaphores. man semop, semctl, and semget. If
semaphores are not suitable (you mentioned possibly needing lots of them), I
would rethink your locking, and maybe make it less granular. If that's no
good, you can get atomic ops in user-mode on IA32 with the xchg intruction and
the lock prefix. Alpha has the load-locked/store-conditional instructions...
BTW this is the kernel semaphore down proc (from include/asm-i386/semaphore.h).
Probably not what you are after...
extern inline void down(struct semaphore * sem)
{
#if WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
__asm__ __volatile__(
"# atomic down operation\n\t"
#ifdef __SMP__
"lock ; "
#endif
"decl (%0)\n\t" /* --sem->count */
"js 2f\n"
"1:\n"
".section .text.lock,\"ax\"\n"
"2:\tcall __down_failed\n\t"
"jmp 1b\n"
".previous"
:/* no outputs */
:"c" (sem)
:"memory");
}
Jeff
************
[EMAIL PROTECTED] http://www.linuxchix.org
