Subj : Re: Memory Barriers, Compiler Optimizations, etc.
To   : comp.programming.threads
From : SenderX
Date : Thu Feb 03 2005 06:28 pm

>> loads: the consumer-side barrier is usually executed "AFTER" the load.
>>
>> movl %(eax), %ecx
>> ; consumer-side barrier
>
>> stores: the producer-side barrier is usually executed "BEFORE" the store.
>>
>> ; consumer-side barrier
^^^^^^^^^^^^^^^^^^

Thats suppose to be producer-side.

>> movl %ecx, %(eax)
>




> Are you sure that it's not the opposite?

Yes, I'm sure. Here is why:


/* example of correct code */

/* processor A - executes producer-barrier "before" the store to shared */
object_t *local = create_object( . );
ac_cpu_mb_producer();
shared = local;


/* processor B - executes consumer-barrier "after" the load from shared */
object_t *local = shared;
ac_cpu_mb_consumer_dep();
if ( local ) { use_object( local ); }




If you reverse that logic, you break the hell of it:


/* example of busted code */

/* processor A */
object_t *local = create_object( . );
shared = local;
ac_cpu_mb_producer(); /* no, no */


/* processor B */
ac_cpu_mb_consumer_dep(); /* no, no */
object_t *local = shared;
if ( local ) { use_object( local ); }



Understand now?


;)

.