JCStress arbiter question

[Семухин Дмитрий]

Hello all,

During my implementation of some tests using JCStress I have noticed
peculiar behaviour.

Simplified test:

@JCStressTest
@Outcome(id = "0", expect = Expect.ACCEPTABLE_INTERESTING, desc = "Both
results not visible")
@Outcome(id = "1", expect = Expect.ACCEPTABLE_INTERESTING, desc = "Single
result only visible")
@Outcome(id = "2", expect = Expect.ACCEPTABLE, desc = "Normal outcome")
@State
public class UnsafeCountingFactorizerTest {
    private UnsafeCountingFactorizer toTest = new
UnsafeCountingFactorizer();

    @Actor
    public void actor1() {
        toTest.service();
    }

    @Actor
    public void actor2() {
        toTest.service();
    }

    @Arbiter
    public void arbiter(J_Result r) {
        r.r1 = toTest.getCount();
    }

    public class UnsafeCountingFactorizer  {
        private long count = 0;

        public long getCount() {
            return count;
        }

        public void service() {
            count++;
        }
    }
}

Test results are only outcome=1 and outcome=2 but outcome=0 is valid in
JMM. Therefore I had a theory that threads are being reused during test
operatins which has a chance for us not to see outcome=0. I decided to
write this test:

@JCStressTest
@State
public class UnsafeCountingFactorizerTest {
    @Actor
    public void actor1(JJJ_Result r) {
        r.r1 = Thread.currentThread().getId();
    }

    @Actor
    public void actor2(JJJ_Result r) {
        r.r2 = Thread.currentThread().getId();
    }

    @Arbiter
    public void arbiter(JJJ_Result r) {
        r.r3 = Thread.currentThread().getId();
    }
}

Obviously it failed with forbidden outcome but I noticed the only 2 classes
of outcome are x,y,x and x,y,y. This is one of the evidences that arbiter
logic is executed in one of the threads already used by actors.

After all of the above I understood that without some config magic I will
not get all JMM-valid outcomes but failed to find such and therefore wrote
this email.

Possible straight-forward solution:

Create a setting in arbiter @interface (boolean guaranteeNoThreadReuse) and
if set to true - init thread before all others and make it busy spin until
the actors have done their thing.

Question section:

1)Am I doing something totally wrong?
2)Was such behaviour encountered before?
3)If not - should I implement this or any other solution you can think of?

Best regards, Dmitry.

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