Great stuff David. Either you can just mail the patches to the list and someone will commit them, or I can give you CVS access if you wish to modify CVS directly?
James ------- http://radio.weblogs.com/0112098/ ----- Original Message ----- From: "David D. Lucas" <[EMAIL PROTECTED]> To: "Jim Brain" <[EMAIL PROTECTED]> Cc: "Dennis Sosnoski" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; "David Hooker" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Wednesday, October 23, 2002 2:56 AM Subject: Re: [dom4j-user] Re: [dom4j-dev] RE: Thread Safety > First off, my posts are not making it into sourceforge.net due to my > remote location (I think). So, this is for those who can get my > response. :-) > > I have a version of DOM4J that uses ThreadLocal in the DocumentFactory > and DOMDocumentFactory as well as some tweaks to NamespaceCache, QName, > and QNameCache. It fixes my problem and basically sets up a singleton > of dom4j for each thread. There will be some initial startup propogated > to each thread, but the safety looks a lot better. No exceptions. > > Our testing has gone all day with this change and it is working great! > Performance does not seem to be to have been lost or gained, pretty much > a wash. I did notice some XPath stuff we may be able to cache also. > > Not sure how to get my changes into the main tree, but we want them in > soon so we do not fragment the code base. > > Let me know if you want a copy of my changes. > > Thanks, > Dave > > > Jim Brain wrote: > > In the case I have, we are doing: > > > > public static Element doThis() { > > Element e=DocumentHelper.createElement("Jim"); > > e.addElement("Fred"); > > return e; > > } > > > > According to Java rules, multiple threads calling doThis should get an > > instance of Element on the local heap, and no two threads are using the > > same Element. However, under the covers, the ELement are using a > > singleton documentFactory (createElement sets that up). I guess I could > > create my own documentFactory for each thread (threadlocal storage), but > > I hesitate to go there just yet. > > > > Jim > > > > > > Dennis Sosnoski wrote: > > > >> Actually, on looking at this in more detail it looks like the > >> NamespaceCache already handles the multiple threads with separate > >> documents case properly, with synchronized methods. QNameCache just > >> needs the same type of change. I don't know why this was addressed in > >> NamespaceCache but not in QNameCache - James, are you out there for > >> comment? > >> > >> - Dennis > >> > >> Dennis Sosnoski wrote: > >> > >>> In the simple case where multiple threads are building separate > >>> documents simultaneously you only need to change the static data > >>> structures: QNameCache and NamespaceCache that I know of. Using > >>> non-threadsafe code for these static data structures is a true bug in > >>> the current dom4j implementation, and should be fixed. > >>> > >>> If you actually want to support multiple threads accessing a writable > >>> document (even if only one is doing the writing) the problems go far > >>> beyond HashMap. You'd need to synchronize *all* calls (including > >>> read-only access calls to elements and such, since another thread > >>> could be modifying the data at the same time as your reader is > >>> accessing it). In order to avoid deadlock problems you'd probably > >>> want to use the document root object for all the synchronizations. > >>> The cleanest way of implementing this is by doing it in your own > >>> code, wrapping the dom4j calls with a synchronize on the document > >>> object. > >>> > >>> - Dennis > >>> > >>> David Hooker wrote: > >>> > >>>> I second this (or is it third?) also. I've seen some weird exceptions > >>>> coming out of DOM4J on SMP (multi-cpu) machines. While I can't > >>>> definitively blame Dom4J, it would at least lessen the risk in this > >>>> area. > >>>> > >>>> -----Original Message----- > >>>> From: [EMAIL PROTECTED] > >>>> [mailto:dom4j-dev-admin@;lists.sourceforge.net] On Behalf Of Brain, Jim > >>>> Sent: Tuesday, October 22, 2002 10:59 AM > >>>> To: 'David D. Lucas'; [EMAIL PROTECTED]; > >>>> [EMAIL PROTECTED] > >>>> Cc: Brain, Jim > >>>> Subject: [dom4j-dev] RE: Thread Safety > >>>> > >>>> > >>>> I also echo a need to resolve this. We are currently having this issue > >>>> in > >>>> production on a mission critical (probably everyone says that, but > >>>> it is > >>>> an > >>>> app entry system for an insurance carrier, so I hope that qualifies) > >>>> application running on IBM OS/390 (ye old mainframe). Before I pull > >>>> the > >>>> HashTable version, I'd like to hear what the longer term plans are, > >>>> since > >>>> there is a considerable ramp time on getting new cuts of code through > >>>> our > >>>> integration management process. > >>>> > >>>> Jim > >>>> > >>>> > >>>> Jim Brain, [EMAIL PROTECTED] > >>>> "Researching tomorrow's decisions today." > >>>> (319) 369-2070 (work) > >>>> SYSTEMS ARCHITECT, ITS, AEGON FINANCIAL PARTNERS > >>>> > >>>> -----Original Message----- > >>>> From: David D. Lucas [mailto:ddlucas@;lse.com] Sent: Tuesday, > >>>> October 22, 2002 9:34 AM > >>>> To: [EMAIL PROTECTED]; > >>>> [EMAIL PROTECTED] > >>>> Cc: Brain, Jim > >>>> Subject: Thread Safety > >>>> > >>>> Sorry for the cross post, but I have not seen any feedback on the > >>>> thread > >>>> > >>>> safety issues. I have taken the stock CVS and changed all the > >>>> HashMaps to Hashtables to get things to work in our server environment. > >>>> > >>>> I would like to know what the long term direction is for thread > >>>> safety and if anyone would like my changes? > >>>> > >>>> Basically I took all the classes in org.dom4j.* and org.dom4j.tree.* > >>>> and > >>>> > >>>> changed them to use Hashtable. The methods out there with > >>>> synchronization are probably no longer needed now that we have a > >>>> Hashtable. I am looking at an alternative approach to keep the > >>>> HashMap and performance without having thread related failures. > >>>> > >>>> All this came from the QNameCache getting corrupted when two threads > >>>> hit > >>>> > >>>> it at the same time. It appears that one did a put while another > >>>> did a get and resulted in a null coming back. > >>>> > >>>> Please let me know what I should do next with the code. If you want > >>>> I can post it or check it in (given access to development CVS). > >>>> > >>>> Thanks in advance, > >>>> Dave > >>>> > >>>> > >>>> > >>> > >>> > >>> > >>> ------------------------------------------------------- > >>> This sf.net emial is sponsored by: Influence the future of Java(TM) > >>> technology. Join the Java Community Process(SM) (JCP(SM)) program > >>> now. > >>> http://ad.doubleclick.net/clk;4699841;7576301;v?http://www.sun.com/javavote > >>> > >>> _______________________________________________ > >>> dom4j-dev mailing list > >>> [EMAIL PROTECTED] > >>> https://lists.sourceforge.net/lists/listinfo/dom4j-dev > >>> > >> > >> > >> > >> ------------------------------------------------------- > >> This sf.net emial is sponsored by: Influence the future of Java(TM) > >> technology. Join the Java Community Process(SM) (JCP(SM)) program now. > >> http://ad.doubleclick.net/clk;4699841;7576301;v?http://www.sun.com/javavote > >> > >> _______________________________________________ > >> dom4j-user mailing list > >> [EMAIL PROTECTED] > >> https://lists.sourceforge.net/lists/listinfo/dom4j-user > >> > >> . > >> > > > > > -- > > +------------------------------------------------------------+ > | David Lucas mailto:ddlucas@;lse.com | > | Lucas Software Engineering, Inc. 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