Subj : Re: Consistency of a byte shared variable
To   : comp.programming.threads
From : SenderX
Date : Mon Jan 31 2005 11:49 pm

DOH, Sorry for the last post!. Anyway...


>> POSIX,
>
>    POSIX requires locks around all accesses to shared variables. See the 
> POSIX memory visibility rules.


Does POSIX guarantee that the following scenario will be correct?


// shared vars
int s1 = 0;
int s2 = 0;
int s3 = 0;
int s4 = 0;
int s5 = 0;


// shared semaphore
sem_t flag; /* val = 0 */




// Thread A
A1: s1 = 1;
A2: s2 = 2;
A3: s3 = 3;
A4: s4 = 4;
A5: s5 = 5;
sem_post( &flag );


// Thread B
B1: sem_wait( &flag );
B2: int test = s1 + s2 + s3 + s4 + s5;
B3: if ( test != 15 ) { abort(); }



Could the example "ever" abort in B3 under the POSIX memory visibility 
rules?

.