HybridDekkerTest, for your consideration

[Andrew Haley]

I needed a couple of tests like this for AArch64 testing.  They test
that varHandles are sequentially consistent when combined with
volatile variables.  Is this a good idea for jcstress itself, or
are there already some other tests which handle this?

@JCStressTest
@Description("Tests Dekker-lock-style idioms")
@Outcome(id = {"0, 1", "1, 0", "1, 1"}, expect = ACCEPTABLE, desc = "Trivial under sequential consistency")
@Outcome(id = "0, 0",                   expect = FORBIDDEN,  desc = "Violates sequential consistency")
@State
public class HybridDekkerTest {

    static final VarHandle VH_A, VH_B;

    static {
        try {
            VH_A = MethodHandles.lookup().findVarHandle(HybridDekkerTest.class, "a", int.class);
            VH_B = MethodHandles.lookup().findVarHandle(HybridDekkerTest.class, "b", int.class);
        } catch (NoSuchFieldException | IllegalAccessException e) {
            throw new IllegalStateException(e);
        }
    }

    volatile int a;
    volatile int b;

    @Actor
    public void actor1(IntResult2 r) {
        a = 1;
        r.r1 = (int) VH_B.getVolatile(this);
    }

    @Actor
    public void actor2(IntResult2 r) {
        b = 1;
        r.r2 = (int) VH_A.getVolatile(this);
    }
}

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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