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| C Z6.0+pooncerelease+poacquirerelease+fencembonceonce
|
| (*
| * Result: Sometimes
| *
| * This litmus test shows that a release-acquire chain, while sufficient
| * when there is but one non-reads-from (AKA non-rf) link, does not suffice
| * if there is more than one. Of the three processes, only P1() reads from
| * P0's write, which means that there are two non-rf links: P1() to P2()
| * is a write-to-write link (AKA a "coherence" or just "co" link) and P2()
| * to P0() is a read-to-write link (AKA a "from-reads" or just "fr" link).
| * When there are two or more non-rf links, you typically will need one
| * full barrier for each non-rf link. (Exceptions include some cases
| * involving locking.)
| *)
|
| {}
|
| P0(int *x, int *y)
| {
| WRITE_ONCE(*x, 1);
| smp_store_release(y, 1);
| }
|
| P1(int *y, int *z)
| {
| int r0;
|
| r0 = smp_load_acquire(y);
| smp_store_release(z, 1);
| }
|
| P2(int *x, int *z)
| {
| int r1;
|
| WRITE_ONCE(*z, 2);
| smp_mb();
| r1 = READ_ONCE(*x);
| }
|
| exists (1:r0=1 /\ z=2 /\ 2:r1=0)
|
|
