RFR: 7902982: jcstress: Add samples for some mutex algorithms [v3]

[Vladimir Sitnikov]

On Tue, 29 Jun 2021 12:46:42 GMT, mmirwaldt for openjdk <github.com+86246875+mmirwaldt-openjdk at openjdk.org> wrote:

>> I have implemented 3 more samples:
>> *) the NoAlgorithm sample should show users of JCStress how they can define a critical section in a simple way
>> *) one sample for the Peterson's algorithm 
>> *) one sample for the Dekker's algorithm 
>> I have translated the pseudo code implementations of the English wikipedia articles into Java.
>> I have also tried out those examples: they compile and they run without any problems.
>
> mmirwaldt for openjdk has updated the pull request incrementally with one additional commit since the last revision:
> 
>   removed ids for forbidden outcomes

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_02_PetersonAlgorithm.java line 49:

> 47:  */
> 48: @JCStressTest
> 49: @Outcome(id = {"false, false"}, expect = ACCEPTABLE, desc = "Both actors have entered the critical section one after another")

What do you think of `Each actor observes another one as 'outside of the critical section'`?

It would help if you could add a comment describing what the outcome really means.
It looks like every actor records if it observes another actor in the same critical section, however, that is not really clear from the code ��

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_02_PetersonAlgorithm.java line 65:

> 63:         taken1 = true;
> 64:         r.r1 = taken2;
> 65:         taken1 = false;

What do you think of adding comments that show where the critical section starts and where it ends?
It turns out that here only 1 or 8 lines are inside the critical section, so adding begin-end comments would help.

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PR: https://git.openjdk.java.net/jcstress/pull/85