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work_registries
 Post subject: nested lazy batchfetch cause ConcurrentModificationException
PostPosted: Thu Feb 11, 2010 8:17 pm 
Newbie

Joined: Mon Feb 01, 2010 1:04 pm
Posts: 6
I get java.util.ConcurrentModificationException due to nested lazy batch fetching:

Analysis of Problem:

It's not a multi-threading issue.

1. MyDataObject2.toString() results in lazy loading of MyDataObject2
2. during lazy loading of MyDataObject2, a org.hibernate.util.EqualsHelper.equals() is triggering lazy loading of MyDataObject1 while still inside of loop iterating over org.hibernate.engine.BatchFetchQueue.batchLoadableEntityKeys in org.hibernate.engine.BatchFetchQueue.getEntityBatch()
3. during lazy loading of MyDataObject1, org.hibernate.engine.BatchFetchQueue.removeBatchLoadableEntityKey modifies org.hibernate.engine.BatchFetchQueue.batchLoadableEntityKeys, will result in ConcurrentModificationException as soon as loop in org.hibernate.engine.BatchFetchQueue.getEntityBatch is continued

How can I prevent that and still use lazy / batch fetching?

Hibernate 3.2.4.sp1 (coming with jboss-4.2.3.GA)

Relevant mapping used (legacy DB + code to be accomodated):
Code:
   <class name="MyDataObject1" mutable="false">
      <composite-id name="MyDataObject1PK">
         <key-property name="MyDataObject1Nr">
         </key-property>
      </composite-id>
...
      <list name="MyDataObject2s">
         <key>
            <column name="MyDataObject1Nr" not-null="true"></column>
         </key>
         <list-index base="1">
            <column name="number" not-null="true"></column>
         </list-index>
         <one-to-many entity-name="MyDataObject2"/>
      </list>
...
   </class>

   <class name="MyDataObject2" mutable="false">
      <composite-id mapped="true">
         <key-many-to-one name="myDataObject1">
            <column name="MyDataObject1Nr" not-null="true"></column>
         </key-many-to-one>
         <key-property name="number">
         </key-property>
      </composite-id>
...
   </class>


Stacktrace of modCount modification responsible for ConcurrentModificationException later on:
Code:
Daemon Thread [Thread-1581] (Suspended (modification of field modCount in org.apache.commons.collections.SequencedHashMap))   
   org.apache.commons.collections.SequencedHashMap.removeImpl(java.lang.Object) line: 472   
   org.apache.commons.collections.SequencedHashMap.remove(java.lang.Object) line: 460   
   org.hibernate.engine.BatchFetchQueue.removeBatchLoadableEntityKey(org.hibernate.engine.EntityKey) line: 130   
   org.hibernate.engine.StatefulPersistenceContext.addEntity(org.hibernate.engine.EntityKey, java.lang.Object) line: 314   
   org.hibernate.engine.StatefulPersistenceContext.addEntity(java.lang.Object, org.hibernate.engine.Status, java.lang.Object[], org.hibernate.engine.EntityKey, java.lang.Object, org.hibernate.LockMode, boolean, org.hibernate.persister.entity.EntityPersister, boolean, boolean) line: 408   
   org.hibernate.engine.TwoPhaseLoad.addUninitializedEntity(org.hibernate.engine.EntityKey, java.lang.Object, org.hibernate.persister.entity.EntityPersister, org.hibernate.LockMode, boolean, org.hibernate.engine.SessionImplementor) line: 240   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).loadFromResultSet(java.sql.ResultSet, int, java.lang.Object, java.lang.String, org.hibernate.engine.EntityKey, java.lang.String, org.hibernate.LockMode, org.hibernate.persister.entity.Loadable, org.hibernate.engine.SessionImplementor) line: 1366   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).instanceNotYetLoaded(java.sql.ResultSet, int, org.hibernate.persister.entity.Loadable, java.lang.String, org.hibernate.engine.EntityKey, org.hibernate.LockMode, org.hibernate.engine.EntityKey, java.lang.Object, java.util.List, org.hibernate.engine.SessionImplementor) line: 1308   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).getRow(java.sql.ResultSet, org.hibernate.persister.entity.Loadable[], org.hibernate.engine.EntityKey[], java.lang.Object, org.hibernate.engine.EntityKey, org.hibernate.LockMode[], java.util.List, org.hibernate.engine.SessionImplementor) line: 1206   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).getRowFromResultSet(java.sql.ResultSet, org.hibernate.engine.SessionImplementor, org.hibernate.engine.QueryParameters, org.hibernate.LockMode[], org.hibernate.engine.EntityKey, java.util.List, org.hibernate.engine.EntityKey[], boolean) line: 580   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).doQuery(org.hibernate.engine.SessionImplementor, org.hibernate.engine.QueryParameters, boolean) line: 701   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).doQueryAndInitializeNonLazyCollections(org.hibernate.engine.SessionImplementor, org.hibernate.engine.QueryParameters, boolean) line: 236   
   org.hibernate.loader.entity.EntityLoader(org.hibernate.loader.Loader).loadEntityBatch(org.hibernate.engine.SessionImplementor, java.io.Serializable[], org.hibernate.type.Type, java.lang.Object, java.lang.String, java.io.Serializable, org.hibernate.persister.entity.EntityPersister) line: 1955   
   org.hibernate.loader.entity.BatchingEntityLoader.load(java.io.Serializable, java.lang.Object, org.hibernate.engine.SessionImplementor) line: 69   
   org.hibernate.persister.entity.SingleTableEntityPersister(org.hibernate.persister.entity.AbstractEntityPersister).load(java.io.Serializable, java.lang.Object, org.hibernate.LockMode, org.hibernate.engine.SessionImplementor) line: 3044   
   org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 395   
   org.hibernate.event.def.DefaultLoadEventListener.doLoad(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 375   
   org.hibernate.event.def.DefaultLoadEventListener.load(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 139   
   org.hibernate.event.def.DefaultLoadEventListener.onLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 98   
   org.hibernate.impl.SessionImpl.fireLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 878   
   org.hibernate.impl.SessionImpl.immediateLoad(java.lang.String, java.io.Serializable) line: 836   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).initialize() line: 66   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).getImplementation() line: 111   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(java.lang.Object, java.lang.reflect.Method, java.lang.reflect.Method, java.lang.Object[]) line: 166   
   MyDataObject1_$$_javassist_153.equals(java.lang.Object) line: not available   
   org.hibernate.util.EqualsHelper.equals(java.lang.Object, java.lang.Object) line: 10   
   org.hibernate.type.ManyToOneType(org.hibernate.type.AbstractType).isEqual(java.lang.Object, java.lang.Object, org.hibernate.EntityMode) line: 108   
   org.hibernate.type.EmbeddedComponentType(org.hibernate.type.ComponentType).isEqual(java.lang.Object, java.lang.Object, org.hibernate.EntityMode) line: 125   
   org.hibernate.engine.BatchFetchQueue.getEntityBatch(org.hibernate.persister.entity.EntityPersister, java.io.Serializable, int, org.hibernate.EntityMode) line: 226   
   org.hibernate.loader.entity.BatchingEntityLoader.load(java.io.Serializable, java.lang.Object, org.hibernate.engine.SessionImplementor) line: 60   
   org.hibernate.persister.entity.SingleTableEntityPersister(org.hibernate.persister.entity.AbstractEntityPersister).load(java.io.Serializable, java.lang.Object, org.hibernate.LockMode, org.hibernate.engine.SessionImplementor) line: 3044   
   org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 395   
   org.hibernate.event.def.DefaultLoadEventListener.doLoad(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 375   
   org.hibernate.event.def.DefaultLoadEventListener.load(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 139   
   org.hibernate.event.def.DefaultLoadEventListener.onLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 98   
   org.hibernate.impl.SessionImpl.fireLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 878   
   org.hibernate.impl.SessionImpl.immediateLoad(java.lang.String, java.io.Serializable) line: 836   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).initialize() line: 66   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).getImplementation() line: 111   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(java.lang.Object, java.lang.reflect.Method, java.lang.reflect.Method, java.lang.Object[]) line: 166   
   MyDataObject2_$$_javassist_146.toString() line: not available   
   java.lang.String.valueOf(java.lang.Object) line: 2615   
   java.lang.StringBuilder.append(java.lang.Object) line: 116   
   MyDataObject2.toString() line: 592   
   java.lang.String.valueOf(java.lang.Object) line: 2615   
   java.lang.StringBuilder.append(java.lang.Object) line: 116   


A few steps later:
Code:
this: org.hibernate.engine.BatchFetchQueue.batchLoadableEntityKeys of currents session batch fetch queue

this   SequencedHashMap$OrderedIterator  (id=1753)   
   expectedModCount   27970   
   pos   SequencedHashMap$Entry  (id=1755)   
   returnType   0   
   this$0   SequencedHashMap  (id=1278)   
      entries   HashMap<K,V>  (id=1286)   
      modCount   27975   
      sentinel   SequencedHashMap$Entry  (id=1301)   

Daemon Thread [Thread-1581] (Suspended (exception java.util.ConcurrentModificationException))   
   org.apache.commons.collections.SequencedHashMap$OrderedIterator.next() line: 757   
   org.hibernate.engine.BatchFetchQueue.getEntityBatch(org.hibernate.persister.entity.EntityPersister, java.io.Serializable, int, org.hibernate.EntityMode) line: 220   
   org.hibernate.loader.entity.BatchingEntityLoader.load(java.io.Serializable, java.lang.Object, org.hibernate.engine.SessionImplementor) line: 60   
   org.hibernate.persister.entity.SingleTableEntityPersister(org.hibernate.persister.entity.AbstractEntityPersister).load(java.io.Serializable, java.lang.Object, org.hibernate.LockMode, org.hibernate.engine.SessionImplementor) line: 3044   
   org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 395   
   org.hibernate.event.def.DefaultLoadEventListener.doLoad(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 375   
   org.hibernate.event.def.DefaultLoadEventListener.load(org.hibernate.event.LoadEvent, org.hibernate.persister.entity.EntityPersister, org.hibernate.engine.EntityKey, org.hibernate.event.LoadEventListener$LoadType) line: 139   
   org.hibernate.event.def.DefaultLoadEventListener.onLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 98   
   org.hibernate.impl.SessionImpl.fireLoad(org.hibernate.event.LoadEvent, org.hibernate.event.LoadEventListener$LoadType) line: 878   
   org.hibernate.impl.SessionImpl.immediateLoad(java.lang.String, java.io.Serializable) line: 836   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).initialize() line: 66   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer(org.hibernate.proxy.AbstractLazyInitializer).getImplementation() line: 111   
   org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(java.lang.Object, java.lang.reflect.Method, java.lang.reflect.Method, java.lang.Object[]) line: 166   
   MyDataObject2_$$_javassist_146.toString() line: not available   
   java.lang.String.valueOf(java.lang.Object) line: 2615   
   java.lang.StringBuilder.append(java.lang.Object) line: 116   
   MyDataObject2.toString() line: 592   
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work_registries
 Post subject: Re: nested lazy batchfetch cause ConcurrentModificationException
PostPosted: Thu Feb 11, 2010 8:36 pm 
Newbie

Joined: Mon Feb 01, 2010 1:04 pm
Posts: 6
Ok, a simple lazy="false" prevents the ConcurrentModificationException.

But I still believe it to be a strange behaviour by Hibernate. Should react more robustly, or issue a warning or something. Or even be able to handle the lazy="true" case properly as well.

Code:
   <class name="MyDataObject2" mutable="false">
      <composite-id mapped="true">
         <key-many-to-one name="myDataObject1" lazy="false">
            <column name="MyDataObject1Nr" not-null="true"></column>
         </key-many-to-one>
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