HibernateCursorItemReader thread safety

[danieln]

Hi,

I have a multi-threaded chunk step that uses HibernateCursorItemReader to read items from a MySQL DB.
As HibernateCursorItemReader is not thread-safe, i wrapped it in another class, overriding the read() method and declared it synchronized.
In the step configuration, i defined the reader in the chunk to be the wrapper reader, and the inner reader (HibernateCursorItemReader) is defined as a stream so that its lifecycle methods are called properly.

I am on Hibernate 3.5.3 and use stateful session in the reader.

Problem is that 5% of the reads fail with the following exceptions:

 ERROR org.hibernate.AssertionFailure - an assertion failure occured (this may indicate a bug in Hibernate
, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: possible non-threadsafe access to the session
        at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:124)
        at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:898)
        at org.hibernate.loader.Loader.doQuery(Loader.java:773)
        at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:270)
        at org.hibernate.loader.Loader.loadEntity(Loader.java:1933)
        at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:86)
        at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:76)
        at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3270)
        at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:496)
        at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:477)
        at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:227)
        at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:285)
        at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:152)
        at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:1080)
        at org.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1028)
        at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:623)
        at org.hibernate.type.EntityType.resolve(EntityType.java:431)
        at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:140)
        at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:898)
        at org.hibernate.loader.Loader.loadSingleRow(Loader.java:327)
        at org.hibernate.impl.ScrollableResultsImpl.prepareCurrentRow(ScrollableResultsImpl.java:254)
        at org.hibernate.impl.ScrollableResultsImpl.next(ScrollableResultsImpl.java:123)
        at org.springframework.batch.item.database.HibernateCursorItemReader.doRead(HibernateCursorItemReader.java:154)
        at org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader.read(AbstractItemCountingItemStreamItemReader.java:85)
        at sun.reflect.GeneratedMethodAccessor89.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)

 ERROR org.hibernate.AssertionFailure - an assertion failure occured (this may indicate a bug in Hibernate, but is more likely due to unsafe use of the session)
org.hibernate.AssertionFailure: possible non-threadsafe access to the session
        at org.hibernate.event.def.DefaultPostLoadEventListener.onPostLoad(DefaultPostLoadEventListener.java:51)
        at org.hibernate.engine.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:234)
        at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:898)
        at org.hibernate.loader.Loader.loadSingleRow(Loader.java:327)
        at org.hibernate.impl.ScrollableResultsImpl.prepareCurrentRow(ScrollableResultsImpl.java:254)
        at org.hibernate.impl.ScrollableResultsImpl.next(ScrollableResultsImpl.java:123)
        at org.springframework.batch.item.database.HibernateCursorItemReader.doRead(HibernateCursorItemReader.java:154)
        at org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader.read(AbstractItemCountingItemStreamItemReader.java:85)
        at sun.reflect.GeneratedMethodAccessor89.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy90.read(Unknown Source)
        at com.muzicall.rbt4all.massactivation.reader.StopAwareStagingItemReader.read(StopAwareStagingItemReader.java:89)
        at sun.reflect.GeneratedMethodAccessor89.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
        at $Proxy91.read(Unknown Source)

Any clue?

Thanks

Daniel

[danieln]

if i synchronize also the update() method of the wrapper, the problem is solved.
Reason is that i use stateful session, which get cleared in the update() method. This interferes with another thread in the read() method.