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