I've managed to make some basic case that throws the error every time.

import org.apache.jackrabbit.core.TransientRepository;

import javax.jcr.*;

public class JCRConcurrency
{
    public static void main(String[] args) throws RepositoryException
    {
        Repository repo;
        if (args.length >= 2)
            repo = new TransientRepository(args[0], args[1]);
        else
            repo = new TransientRepository();
        SimpleCredentials simpleCredentials = new SimpleCredentials("username", "password".toCharArray());
        Session sessionInit = repo.login(simpleCredentials);

        // initialization
        Node root = sessionInit.getRootNode();
        Node test;
        if (root.hasNode("test"))
            test = root.getNode("test");
        else
            test = root.addNode("test");
        if (!test.hasProperty("property"))
            test.setProperty("property", 0);
        sessionInit.save();
        String testIdentifier = test.getIdentifier();

        // session 1
        Session session1 = repo.login(simpleCredentials);
        Node test1 = session1.getNodeByIdentifier(testIdentifier);
        System.out.println(test1.getProperty("property").getLong());
        test1.setProperty("property", 1);

        // session 2 is doing some other things at the same time
        Session session2 = repo.login(simpleCredentials);
        Node test2 = session2.getNodeByIdentifier(testIdentifier);
        test2.setProperty("property", 2);

        // session 2 saves first
        session2.save();
        session2.logout();

        // session 1 saves
        session1.save();
        session1.logout();

        sessionInit.logout();

        System.exit(0);
    }
}




Le 2010-12-10 à 6:12 PM, François Cassistat a écrit :

> Hi list !
> 
> I've got some concurrency problem while saving. My application use distinct Sessions object and when two processes are trying to modify the same property of the same node at the same time. I've get the exception below :
> javax.jcr.InvalidItemStateException: Item cannot be saved because it has been modified externally: node /
>        at org.apache.jackrabbit.core.ItemImpl.getTransientStates(ItemImpl.java:249)
>        at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:981)
>        at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:920)
>        at com.myproject.MyProject.save(MyProject.java:1525)
>        ...
> 
> 
> I have tried saving this way :
> synchronized (this)
> {
>    session.refresh(true);
>    session.save();
> }
> 
> 
> Is there any way around or only locks and transactions can prevent that ?
> 
> 
> Thanks !
> 
> 
> François
>