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From Stefan Guggisberg <stefan.guggisb...@gmail.com>
Subject Re: Item cannot be saved because it has been modified externally: node /
Date Mon, 13 Dec 2010 21:04:42 GMT
2010/12/13 François Cassistat <f@maya-systems.com>:
> Re-hi,
>
> Thanks for your answers. I have tested with 2.3-SNAPSHOT and it still doesn't work...
Although, the exception message is better "property /test/property: the property cannot be
saved because it has been modified externally."
>
> I do not understand why it should be an wanted behavior.

because it prevents you from accidentally overwriting changes made by
other sessions.

just like a text editor application will warn you, that the document
you're about to
persist had been modified by somebody else after you've opened it for editing.

there are different ways to handle such situations, and i guess none
is the ultimate
'correct way'. it depends on the use case.

if your application must concurrently modify a specific property then you should
use locking. that's what locks are intended for.

cheers
stefan

> Does Jackrabbit is designed to work with Node locks and Transaction only? There is no
way to take the changes I've made in one Session and retry them? Based on my analysis :
> - Transaction would slow down the repository...
> - Locked nodes looks complicated and deadlock friendly since I need to modify properties
at many place in the repository at once.
> - Retrying to get a new session and remake the changes when there was an error at session.save()
looks like a dirty solution to me.
>
> Maybe there is something I did not understand with jackrabbit concurrency model. Any
pointers?
>
>
> François
>
>
>
> Le 2010-12-13 à 4:33 AM, Stefan Guggisberg a écrit :
>
>> On Sat, Dec 11, 2010 at 11:52 AM, Norman Maurer <norman@apache.org> wrote:
>>> Hi there,
>>>
>>> this is fixed in the upcomming jackrabbit 2.2.0 (which should be
>>> released within the next days). In the meantime you can grab a
>>> snapshot here:
>>>
>>> https://repository.apache.org/content/groups/snapshots/org/apache/jackrabbit/
>>>
>>> Version name is 2.2-SNAPSHOT.
>>
>> sorry, but i have to contradict norman.
>>
>> the following behavior is as per design:
>>
>> 1. sessionA modifies a property
>> 2. sessionB modifies the same property and saves its changes
>> 3. sessionA tries to save its changes but fails with a
>>  InvalidItemStateException because its changes have become stale
>>
>> this is the behavior as implemented in trunk.
>>
>> cheers
>> stefan
>>
>>>
>>> Bye,
>>> Norman
>>>
>>>
>>>
>>>
>>> 2010/12/11 François Cassistat <f@maya-systems.com>:
>>>> 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
>>>>>
>>>>
>>>>
>>>
>
>

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