Re: [TM4J-users] abitrary DuplicateObjectIDExceptions ?!

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Hi Kal,
Yes, this could be the reason for this strange behaviour. Indeed, the topicmaps
I am parsing are quite small. After Your mail, I put some debug messages in
XTMBuilder and the IDGeneratorImpl.
I have attached the output when parsing one(!) topicmap. As one can see, there
seem to be two IDGenerators active. What for ? Is one handling topics and the
other associations?
In fact, when parsing the TM after ID 8 was assigned, the second IDGenerator
starts its work and sometimes, the id-prefix remains the same (because
System.currentTimeMillis() returned the same
value) -> crash!
Anyways, I've solved the problem by using a static counter for creating the
base-id instead of the current time (code attached). Ok - static variables are
not really a clean way to solve problems in terms of OOP.
But it's ok for me ;-)
Thanks for the help,
kind regards,
Niko

XTMBuilder constructor
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// $Id: IDGeneratorImpl.java,v 1.4 2002/02/09 19:38:23 kal_ahmed Exp $

package org.tm4j.topicmap.utils;

/**
 * An alternative IDGenerator implementation.
 * This implementation returns a two-part, pseudo-unique ID. The first part of
 * the ID is the number of the created IDGenerator by this JVM,.
 * The second part of the ID is a simple incrementing
 * counter.
 * This class does not generate truely unique IDs, but the degree of uniqueness

 * should be sufficient for most applications.
 */
public class AlternativeIDGeneratorImpl implements IDGenerator
{
    protected String baseID;
    protected long counter;
    private static long genCounter = (long) 0;

    /**
     * Constructs a new IDGeneratorImpl object, with the
     * base part of the ID string set to the time of creation.
     */
    public AlternativeIDGeneratorImpl()
    {
        baseID = "x" + ( genCounter++ );
    }

    /**
     * Returns a pseudo-unique identifier as a concatenation of
     * the base identifier created in the object constructor
     * followed by a dash (-) and then a simple, incrementing
     * counter value (encoded in hexadecimal).
     */
    public String getID()
    {
        String id = baseID + "-" + Long.toString(counter++, 16);
        return id;
    }
}

Kal Ahmed wrote:

> Hi Niko,
>
> This seems a bit weird - the autogenerated IDs are created by an
> IDGenerator which is constructed by the XTMBuilder class when it is
> created. The default implementation of IDGenerator uses
> System.currentTimeMillis() to generate the base ID string in its
> constructor and then uses an incrementing counter as a suffix to generate
> individual ids (so you get "x<time at creation of IDGenerator>-<count>" as
> the id string). I was pretty sure that this should not cause a problem for
> most applications. If this algorithm is working as expected, I would expect
> that it would only be possible that you would see a duplicate ID being
> generated if the first topic map is small enough to be processed and loaded
> in the resolution of the system clock (usually currentTimeMillis() does not
> update every millisecond).
>
> One way to test if this is the case would be to insert a sleep() into the
> constructor for IDGeneratorImpl - If it was something like 300 to 700 ms,
> that **should** force a new value. Alternatively you could change the
> constructor to get an initial value and then to loop until it gets a new
> value different to the initial value - that should guarantee that two
> different IDGeneratorImpls created by the same thread will *always* have a
> unique base id.
>
> If you try one of these approaches and have some success perhaps you could
> post it back to me as a patch ?
>
> BTW, the IDGenerator implementation used is runtime configurable - use the
> system property org.tm4j.topicmap.idGenerator to define the name of the
> class to be loaded as the IDGenerator for topic map parsing - this class
> must implement org.tm4j.topicmap.utils.IDGenerator.
>
> Cheers,
>
> Kal
>
> At 15:31 02/04/2002 +0200, Niko Popitsch wrote:
> >Hi,
> >
> >I discovered a strange behaviour of tm4j 0.6.1 with loading topic maps.
> >I load multiple TMs from disk. the first load is ok. but then successive
> >loads throw DuplicateObjectIDExceptions !sometimes!. This really seems
> >to be abitrary behaviour.
> >I always create a new Saxparser,
> >         saxParser = new SAXParser();
> >a new TM Factory,
> >     TopicMapFactoryImpl tmfi = new TopicMapFactoryImpl();
> >a new Topic map,
> >     TopicMap tm = tmfi.createTopicMap( baseLocator );
> >a new XTM Builder
> >         XTMBuilder xtmBuilder = new XTMBuilder( tm );
> >a new XTM Parser
> >         XTMParser xtmParser  = new XTMParser( xtmBuilder );
> >and then i parse:
> >         saxParser.setContentHandler( xtmParser );
> >         saxParser.parse( src );
> >
> >what could this be ???
> >thanks,
> >Niko :)
> >
> >
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