[
https://issues.apache.org/jira/browse/JCR-1552?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12592076#action_12592076
]
Thomas Mueller commented on JCR-1552:
-------------------------------------
Jackrabbit should either always or never throw an exception. When concurrently
updating or adding properties, that is. 'Never throw an exception' seems
easier. Also the implementation is faster, that's why I would prefer that.
If we decide to 'always throw', then the algorithm could be as follows:
whenever a session reads, re-reads, transiently modifies, or adds a property,
remember the old version (timestamp or data). When calling save, check if the
current persistent state matches the old timestamp or data.
When concurrently updating or adding nodes (so far I was talking about
properties only), the same algorithm can be used. One problem is the following
use case:
Node b = a.hasNode(x) ? a.getNode(x) : a.addNode(x);
With multiple threads / sessions you end up with same name siblings sometimes.
That's probably not what the user wants. This is not an issue for properties as
there is no 'addProperty' method. I don't know if there is a solution for nodes
without using locks. For SQL databases, one solution is using the MERGE
statement (sometimes called UPSERT from INSERT or UPDATE).
> Concurrent conflicting property creation sometimes doesn't fail
> ---------------------------------------------------------------
>
> Key: JCR-1552
> URL: https://issues.apache.org/jira/browse/JCR-1552
> Project: Jackrabbit
> Issue Type: Bug
> Components: jackrabbit-core
> Affects Versions: core 1.4.2
> Reporter: Thomas Mueller
> Assignee: Stefan Guggisberg
> Fix For: 1.5
>
>
> The following test prints "Success":
> Session s1 = ...
> Session s2 = ...
> s1.getRootNode().setProperty("b", "0"); // init with zero
> s1.getRootNode().setProperty("b", (String) null); // delete
> s1.save();
> s1.getRootNode().setProperty("b", "1");
> s2.getRootNode().setProperty("b", "2");
> s1.save();
> s2.save();
> System.out.println("Success");
> However if the line marked "... // delete" is commented out,
> it fails with the following exception:
> javax.jcr.InvalidItemStateException:
> cafebabe-cafe-babe-cafe-babecafebabe/{}b: the item cannot be saved
> because it has been modified externally.
> at
> org.apache.jackrabbit.core.ItemImpl.getTransientStates(ItemImpl.java:246)
> at org.apache.jackrabbit.core.ItemImpl.save(ItemImpl.java:928)
> at org.apache.jackrabbit.core.SessionImpl.save(SessionImpl.java:849)
> It should fail in all cases. If we decide it shouldn't fail, it needs to be
> documented.
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
