Hi,
Would this also be an issue with ODMG? I am using ODMG in a web application
and have just one shared instance of my ODMG implementation (ie
OJB.getInstance()) in the application scope. When interacting with the
database then I simply create new transactions from this ODMG instance and
use those. Is this thread safe?
Thanks as always
Fiona
----- Original Message -----
From: "Armin Waibel" <[EMAIL PROTECTED]>
To: "OJB Users List" <[EMAIL PROTECTED]>
Sent: Tuesday, August 17, 2004 12:42 PM
Subject: Re: ConcurrentModification!!!
> Tino Sch�llhorn wrote:
>
> > Hi Armin,
> >
> > how do I make sure that different threads get different connections?
>
> Each PB instance use its own connection, so if you use a PB instance per
> thread, OJB automatic use its own connection instance per PB instance.
>
> > I
> > get my PB instances form a helper method:
> >
> > public static PersistenceBroker getPBFromAlias(String jcdAlias) {
>
> ===>????
> > MetadataManager mm = MetadataManager.getInstance();
> > ConnectionRepository cr = mm.connectionRepository();
> >
> > PBKey pbKey = cr.getStandardPBKeyForJcdAlias(jcdAlias);
> >
> > if (pbKey == null) {
> > throw new RuntimeException(
> > "Konnte keinen PersistenceBroker zu alias '" + jcdAlias + "'
> > finden!"
> > );
> > }
> ===>????
>
> Why not simply:
>
> PBKey pbKey = new PBKey(jcdAlias);
> PersistenceBroker res =
> PersistenceBrokerFactory.createPersistenceBroker(pbKey);
>
> or
>
> PersistenceBroker res =
> PersistenceBrokerFactory.createPersistenceBroker(jcdAlias, null, null);
>
> >
> > return res;
> > }
> >
>
> regards,
> Armin
>
>
> >
> > I am invoking this method in different threads? Do I have to synchronize
> > this method?
> >
> > Tino
> >
> > Armin Waibel wrote:
> >
> >> Hi Tino,
> >>
> >> are you sure that the used PB instance was not shared across different
> >> threads? The PB itself is not threadsafe, each thread has to use its
> >> own instance of PB obtained from the PBF.
> >>
> >> >> java.util.ConcurrentModificationException
> >> >> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:782)
> >> >> at java.util.HashMap$KeyIterator.next(HashMap.java:818)
> >> >> at
> >> >> org.apache.ojb.broker.cache.InternalCache.pushToRealCache(Unknown
> >> Source)
> >>
> >>
> >> <snip>
> >> private void pushToRealCache()
> >> {
> >> Iterator it = localCache.keySet().iterator();
> >> Identity oid;
> >> while (it.hasNext())
> >> {
> >> oid = (Identity) it.next();
> >> realCache.cache(oid, localCache.get(oid));
> >> }
> >> localCache.clear();
> >> }
> >> </snip>
> >>
> >> You can see from the code snip that a ConcurrentModificationException
> >> can occur when different threads using the same PB instance (each PB
> >> has an own instance of InternalCache).
> >>
> >> regards,
> >> Armin
> >>
> >>
> >> Tino Sch�llhorn wrote:
> >>
> >>> I forgot to mention that we are using OJB 1.0 !
> >>>
> >>> Tino Sch�llhorn wrote:
> >>>
> >>>> Hi,
> >>>>
> >>>> we are using OJB in a Tomcat-Application and are greatly satisfied.
> >>>> Now we are moving our application to a windows 2003 server with 2
> >>>> processors and we encounter some problems. One is the following:
> >>>>
> >>>> We implemented a DownloadServlet which is responsible for delivering
> >>>> Streams of previously uploaded files. But on this machine we get
> >>>> errors when downloading some files (the thing is: sometimes it is
> >>>> ok, sometimes it is not). Here is the Stacktrace which I think could
> >>>> be responsible to this problem:
> >>>>
> >>>> java.util.ConcurrentModificationException
> >>>> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:782)
> >>>> at java.util.HashMap$KeyIterator.next(HashMap.java:818)
> >>>> at
> >>>> org.apache.ojb.broker.cache.InternalCache.pushToRealCache(Unknown
> >>>> Source)
> >>>> at
> >>>>
org.apache.ojb.broker.cache.InternalCache.disableMaterializationCache(Unknow
n
> >>>> Source)
> >>>> at
> >>>>
org.apache.ojb.broker.accesslayer.RsIterator.getObjectFromResultSet(Unknown
> >>>> Source)
> >>>> at org.apache.ojb.broker.accesslayer.RsIterator.next(Unknown
> >>>> Source)
> >>>> at
> >>>>
org.apache.ojb.broker.core.PersistenceBrokerImpl.getObjectByQuery(Unknown
> >>>> Source)
> >>>> at
> >>>>
org.apache.ojb.broker.core.DelegatingPersistenceBroker.getObjectByQuery(Unkn
own
> >>>> Source)
> >>>> at
> >>>>
org.apache.ojb.broker.core.DelegatingPersistenceBroker.getObjectByQuery(Unkn
own
> >>>> Source)
> >>>> at kos.generator.DataObject.getObjectById(DataObject.java:368)
> >>>> at kos.wnetz.om.base.File.getFileById(File.java:156)
> >>>> at
> >>>> kos.wnetz.modules.fs2.DownloadServlet.doGet(DownloadServlet.java:34)
> >>>> at javax.servlet.http.HttpServlet.service(HttpServlet.java:743)
> >>>> at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
> >>>>
> >>>>
> >>>> Do you have any ideas how this error could be prevented? Is this a
> >>>> synchronization-problem of OJB? I will try to synchonize our
> >>>> DownloadServlet - but due to performance-reasons this is not our
> >>>> preferred solution (;-))
> >>>>
> >>>> With regards
> >>>> Tino
> >>>
> >>>
> >>>
> >>>
> >>>
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> >>>
> >>>
> >>>
> >
> >
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> >
> >
>
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