"Concurrent Modification Exception" during an update?

Hibernate ORM
1

Problem

Im using hibernate 5.4.11 core and when i try to update large amounts of entities i run into that issue right here. It looks like an hibernate internal exception.

Update

I tested it with hibernate 5.4.23, the same exception occured. I also updated my “mysql connector” to the latest version “8.0.22” and it didnt worked either, the same exception.

Describtion

This is how i update my entities, it runs in another thread, which should not be the problem here… its basically a own thread for database operations, during that operation no other database operations are running.

        // Run the database operation for updating the entities async in a new thread, return updated entities once done
        return CompletableFuture.runAsync(() -> {

            var session = database.openSession();
            session.beginTransaction();

            try {

                // Save identities first
                for (var identity : identities)
                    session.update(identity);

                // Update components, each component-type
                for(var insertedClass : insertationOrder)
                    for (var hbc : componentsPerType.get(insertedClass))
                        session.update(hbc);

                session.flush();
                session.clear();

                session.getTransaction().commit();
            } catch (Exception e){

                var messageComposer = new ExceptionMessageComposer(e);
                GameExtension.getInstance().trace("Update : "+messageComposer.toString());
                session.getTransaction().rollback();
            }

            session.close();
        }).thenApply(v -> entities);

The class i try to save

@Entity
@Table(name = "chunk", uniqueConstraints = {@UniqueConstraint(columnNames={"x", "y"})}, indexes = {@Index(columnList = "x,y")})
@Access(value = AccessType.FIELD)
@SelectBeforeUpdate(false)
public class Chunk extends HibernateComponent{

    public int x;
    public int y;
    public Date createdOn;

    @OneToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "chunk_identity", joinColumns = @JoinColumn(name = "identity_id"), inverseJoinColumns = @JoinColumn(name = "id"), inverseForeignKey = @ForeignKey(ConstraintMode.NO_CONSTRAINT))
    @Fetch(FetchMode.JOIN)
    @BatchSize(size = 50)
    public Set<Identity> inChunk = new LinkedHashSet<>();

    @Transient
    public Set<ChunkLoader> loadedBy = new LinkedHashSet<>();

    public Chunk() {}
    public Chunk(int x, int y, Date createdOn) {
        this.x = x;
        this.y = y;
        this.createdOn = createdOn;
    }
}



@Entity
@Table(name = "location")
@Access(AccessType.FIELD)
public class Transform extends HibernateComponent {

    @Embedded
    public Vector2 position = new Vector2();

    @ManyToOne
    @JoinColumn(name = "chunk_id", referencedColumnName = "identity_id", updatable = false)
    @Fetch(FetchMode.JOIN)
    public Chunk chunk;

    @Transient
    public Vector2 previousPos = new Vector2();

    public Transform() {}
    public Transform(Vector2 position) { this.position = position; }
    public Transform(Vector2 position, Chunk chunk) { this.position = position; this.chunk = chunk; }
}

The exception i get

19:29:05,126 INFO  [ForkJoinPool.commonPool-worker-19] Extensions     - {Game}: Update : java.util.ConcurrentModificationException:
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Exception: java.util.ConcurrentModificationException
Message: *** Null ***
+--- --- ---+
Stack Trace:
+--- --- ---+
java.base/java.util.HashMap$HashIterator.nextNode(HashMap.java:1493)
java.base/java.util.HashMap$KeyIterator.next(HashMap.java:1516)
org.hibernate.persister.collection.AbstractCollectionPersister.insertRows(AbstractCollectionPersister.java:1555)
org.hibernate.action.internal.CollectionUpdateAction.execute(CollectionUpdateAction.java:89)
org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:604)
org.hibernate.engine.spi.ActionQueue.lambda$executeActions$1(ActionQueue.java:478)
java.base/java.util.LinkedHashMap.forEach(LinkedHashMap.java:684)
org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:475)
org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:348)
org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:40)
org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:102)
org.hibernate.internal.SessionImpl.doFlush(SessionImpl.java:1356)
org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1343)
com.parallelorigin.persistence.database.ECSDatabase.lambda$updateEntities$16(ECSDatabase.java:242)
java.base/java.util.concurrent.CompletableFuture$AsyncRun.run(CompletableFuture.java:1736)
java.base/java.util.concurrent.CompletableFuture$AsyncRun.exec(CompletableFuture.java:1728)
java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Anyone having an idea why hibernate throws that internal exception and what i could do to solve this issue ?

2

I think your question was sufficiently answered no StackOverflow already. https://stackoverflow.com/questions/64719951/concurrentmodificationexception-when-updating-my-entities/64726829#64726829