RFR: 7902982: jcstress: Add samples for some mutex algorithms [v8]

[Aleksey Shipilev]

On Tue, 29 Jun 2021 15:04:51 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:
> 
>   replaced approach with taken1 and taken2 by the approach of using non atomic int increments

Very close to the final form.

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_01_NoAlgorithm.java line 2:

> 1: /*
> 2:  * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.

Here and later: the year is 2021. :)

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_01_NoAlgorithm.java line 52:

> 50:  * If one actor after another enters the critical section,
> 51:  * the first actor will read 0 for v and increment v to 1 for its result
> 52:  * the second actor will read 1 for v and increment v to 2 for its result.

Yeah, I don't think this explanation is necessary. You can just say something like: "All samples for mutex algorithms use the non-atomic increment example from API_01_Sample."

And yes, it is true that we don't actually need this test, as we have API_01_Sample -- we can just go ahead and start testing the mutexes.

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_01_NoAlgorithm.java line 55:

> 53:  */
> 54: @JCStressTest
> 55: @Outcome(expect = ACCEPTABLE, desc = "Both actors have entered the critical section whenever they wanted")

Here and later, let's list the outcomes, though, in case there are some completely surprising ones:


@Outcome(id = {"1, 2", "2, 1"}, expect = ACCEPTABLE, desc = "Sequential execution.")
@Outcome(id = "1, 1", expect = ACCEPTABLE_INTERESTING, desc = "Both actors came up with the same value: lock failure.")

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_02_PetersonAlgorithm.java line 62:

> 60:         flagForActor1 = true;
> 61:         turn = 2;
> 62:         while (flagForActor2 && turn == 2) ;

Suggestion:

        while (flagForActor2 && turn == 2); // wait

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_02_PetersonAlgorithm.java line 73:

> 71:         flagForActor2 = true;
> 72:         turn = 1;
> 73:         while (flagForActor1 && turn == 1) ;

Suggestion:

        while (flagForActor1 && turn == 1); // wait

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_04_AtomicBoolean.java line 32:

> 30: import org.openjdk.jcstress.annotations.State;
> 31: import org.openjdk.jcstress.infra.results.II_Result;
> 32: import org.openjdk.jcstress.infra.results.ZZ_Result;

Here and other places, `ZZ_Result` is not needed anymore?

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_04_AtomicBoolean.java line 53:

> 51: @State
> 52: public class Mutex_04_AtomicBoolean {
> 53:     private final AtomicBoolean canEnterCriticalSection = new AtomicBoolean(true);

Invert and call it `taken`?

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_04_AtomicBoolean.java line 58:

> 56:     @Actor
> 57:     public void actor1(II_Result r) {
> 58:         while(!canEnterCriticalSection.compareAndSet(true, false)) ;

Suggestion:

        while (!canEnterCriticalSection.compareAndSet(true, false)); // spin

jcstress-samples/src/main/java/org/openjdk/jcstress/samples/concurreny/mutex/Mutex_04_AtomicBoolean.java line 67:

> 65:     @Actor
> 66:     public void actor2(II_Result r) {
> 67:         while(!canEnterCriticalSection.compareAndSet(true, false)) ;

Suggestion:

        while (!canEnterCriticalSection.compareAndSet(true, false)); // spin

-------------

Changes requested by shade (Committer).

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