Support Semaphores

[michaelAlvarino]

Describe the bug
EqualsVerifier fails verification tests for classes using Semaphores due to recursive datastructures.

To Reproduce
Create the class/test below and run.

Code that triggers the behavior

package experiment;

import java.util.concurrent.Semaphore;

public class TestEqVerifier {
    private final Semaphore sem = new Semaphore(1);
}

package experiment;

import nl.jqno.equalsverifier.EqualsVerifier;
import org.junit.Test;

public class TestEqVerifierTest {
    @Test
    public void test() {
        EqualsVerifier.forClass(TestEqVerifier.class).verify();
    }
}

Error message

EqualsVerifier found a problem in class experiment.TestEqVerifier.
-> Recursive datastructure.
Add prefab values for one of the following types: Semaphore, Sync, Node.

For more information, go to: http://www.jqno.nl/equalsverifier/errormessages
java.lang.AssertionError: EqualsVerifier found a problem in class experiment.TestEqVerifier.
-> Recursive datastructure.
Add prefab values for one of the following types: Semaphore, Sync, Node.

For more information, go to: http://www.jqno.nl/equalsverifier/errormessages
	at nl.jqno.equalsverifier.api.SingleTypeEqualsVerifierApi.verify(SingleTypeEqualsVerifierApi.java:306)
	at experiment.TestEqVerifierTest.test(TestEqVerifierTest.java:9)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.runTestClass(JUnitTestClassExecutor.java:110)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:58)
	at org.gradle.api.internal.tasks.testing.junit.JUnitTestClassExecutor.execute(JUnitTestClassExecutor.java:38)
	at org.gradle.api.internal.tasks.testing.junit.AbstractJUnitTestClassProcessor.processTestClass(AbstractJUnitTestClassProcessor.java:62)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.processTestClass(SuiteTestClassProcessor.java:51)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
	at com.sun.proxy.$Proxy2.processTestClass(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.processTestClass(TestWorker.java:118)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:175)
	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:157)
	at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:404)
	at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
	at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
	at java.lang.Thread.run(Thread.java:748)
Caused by: nl.jqno.equalsverifier.internal.exceptions.RecursionException
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.createTuple(PrefabValues.java:145)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.realizeCacheFor(PrefabValues.java:138)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.traverseFields(FallbackFactory.java:88)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.createValues(FallbackFactory.java:39)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.createTuple(PrefabValues.java:155)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.realizeCacheFor(PrefabValues.java:138)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.traverseFields(FallbackFactory.java:88)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.createValues(FallbackFactory.java:39)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.createTuple(PrefabValues.java:155)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.realizeCacheFor(PrefabValues.java:138)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.traverseFields(FallbackFactory.java:88)
	at nl.jqno.equalsverifier.internal.prefabvalues.factories.FallbackFactory.createValues(FallbackFactory.java:39)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.createTuple(PrefabValues.java:155)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.realizeCacheFor(PrefabValues.java:138)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.giveTuple(PrefabValues.java:79)
	at nl.jqno.equalsverifier.internal.prefabvalues.PrefabValues.giveOther(PrefabValues.java:102)
	at nl.jqno.equalsverifier.internal.reflection.FieldModifier.lambda$changeField$2(FieldModifier.java:97)
	at nl.jqno.equalsverifier.internal.reflection.FieldModifier.lambda$change$3(FieldModifier.java:113)
	at nl.jqno.equalsverifier.internal.util.Rethrow.lambda$rethrow$0(Rethrow.java:47)
	at nl.jqno.equalsverifier.internal.util.Rethrow.rethrow(Rethrow.java:30)
	at nl.jqno.equalsverifier.internal.util.Rethrow.rethrow(Rethrow.java:45)
	at nl.jqno.equalsverifier.internal.util.Rethrow.rethrow(Rethrow.java:55)
	at nl.jqno.equalsverifier.internal.reflection.FieldModifier.change(FieldModifier.java:113)
	at nl.jqno.equalsverifier.internal.reflection.FieldModifier.changeField(FieldModifier.java:100)
	at nl.jqno.equalsverifier.internal.reflection.InPlaceObjectAccessor.scramble(InPlaceObjectAccessor.java:52)
	at nl.jqno.equalsverifier.internal.reflection.ClassAccessor.getRedAccessor(ClassAccessor.java:174)
	at nl.jqno.equalsverifier.internal.reflection.ClassAccessor.getRedObject(ClassAccessor.java:163)
	at nl.jqno.equalsverifier.internal.util.Configuration.ensureUnequalExamples(Configuration.java:198)
	at nl.jqno.equalsverifier.internal.util.Configuration.build(Configuration.java:98)
	at nl.jqno.equalsverifier.api.SingleTypeEqualsVerifierApi.buildConfig(SingleTypeEqualsVerifierApi.java:373)
	at nl.jqno.equalsverifier.api.SingleTypeEqualsVerifierApi.performVerification(SingleTypeEqualsVerifierApi.java:359)
	at nl.jqno.equalsverifier.api.SingleTypeEqualsVerifierApi.verify(SingleTypeEqualsVerifierApi.java:304)
	... 48 more


experiment.TestEqVerifierTest > test FAILED
    java.lang.AssertionError at TestEqVerifierTest.java:9
        Caused by: nl.jqno.equalsverifier.internal.exceptions.RecursionException at TestEqVerifierTest.java:9
1 test completed, 1 failed

Expected behavior
Node is definitely a recursive class, but using a Semaphore for some internal implementation should not concern customers using my library as long as I have implemented equals and hashcode properly.

Version
What version of EqualsVerifier are you using?
3.7

Additional context
Add any other context about the problem here.
I think this is also a problem with CompletableFutures due to the Completion class.

[jqno]

Thanks for letting me know about this one. I've made a fix, and I'll let you know when I make a release.
Until then, you can add .withPrefabValues(Semaphore.class, new Semaphore(1), new Semaphore(2)) as a workaround.

EqualsVerifier already has prefab values, so that shouldn't be a problem. But if they are, please let me know!

[michaelAlvarino]

Whoops, closed a bit early. We should probably wait for the release.

[jqno]

I've just released version 3.7.1. I'll close the issue now 😉