Re: [xwiki-devs] XWikiDocuments not thread safe added to XWikiCacheStore

Hi Thomas Thanks for responding and thanks for supporting the suggested solution. I understand the doc.Key-issue that you mentioned. Yet, I think this is

a XWikiCacheStore#loadXWikDoc concern. In my understanding the expected document to load is defined by the document-reference and the language. Thus the Hibernate-Store must be concerned in setting the context database

to the Wiki-Reference before loading the document. This is acctually

done in the XWiki#getDocument call. I agree that this might be the wrong place to do it. Thus, I would suggest to fix this issue in the XWikiHibernateStore on a seperate jira-issue.

Maybe this could be combined with a significant performance improvment in loading the documents with fewer sql-queries per loading action. With XWIKI-13623 I try to tackle the issue about randomly loosing

data because of an not thread safe construction and publication of XWikiDocument java objects in XWikiCacheStore. Because this issue gave us a big

in production multiple times, I solved it in our project in the way

If the xwiki-dev team supports the suggested solution, I would be willing to proceed and prepare a pull request for an adapted XWikiCacheStore fix. Kind regards, Fabian 2016-08-08 12:07 GMT+02:00 Thomas Mortagne <thomas.mortagne(a)xwiki.com>om>: > XWikiCacheStore#loadXWikiDoc is actually a bit tricker than that right > now for retro compatibility and laziness (really need to rewrite this > whole store API) reasons and before applying what you propose the way > it deals with document uid should be modified a bit. > > Hibernate store is always loading the document from the wiki indicated > in the context completely ignoring the wiki in the XWikiDocument > object. That means that doc.getKey() may be different than the key of > the document that will actually come from the hibernate store. So > before adding DocumentLoader jingling a first thing to do is generate > the initial cache key with a mix of the wiki id located in the context > and the XWikiDocument reference. > > Then what you propose sounds good. > > On Mon, Aug 8, 2016 at 8:53 AM, Fabian Pichler > <fabian.pichler(a)synventis.com> wrote: > > Hi devs > > > > http://jira.xwiki.org/browse/XWIKI-13623 > > I would like to discuss the suggested solution, before I start > implementing > > it: > > > > *I suggest the following solution:* > > Introducing a nested DocumentLoader class which loads the document > calling > > the basestore loadXWikiDoc in a synchronized getDocOrLoad method. The > > DocumentLoader objects gets instantiated in the cacheStore on a cache > miss. > > It then gets stored in a ConcurrentHashMap using the same key which is > used > > for the document cache (DocumentReference including language). Using > > putIfAbsent to insert the DocumentLoader and calling the synchronized > load > > method on the object in the map solves the memory visibility issue and > > moreover ensures that the same XWikiDocument is not loaded multiple

> > concurrently from the database. It is still possible to load different > > documents in parallel. A DocumentLoader will load the XWikiDocument

> > once and the returns the identical document object on any following

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