Concurrent Xupdate problems

[Michael Watson <mb...@castlegate-tech.co.uk>]

I am attempting to write a multi-user application, where each user would act
as an
Xindice database client.  To this end my application needs to ensure that
records
correctly locked etc whilst updates are made.  Ideally, transaction
processing would
be helpful, but not essential.  I have succeeded in writing a small test
program to create
and update records in the database.  This program performs a mixture of
xpath queries,
document insertions, Sequencer increments and xupdates.  However, When I
attempt to
run two or more instances of the program concurrently from the same server,
the Xupdates on
all but one of the clients will crash causing a exception on the clients.
I have tried to identify the precise cause of the problem.  It is my belief
that the
fault lies entirely within the Xupdate tasks (all the other parts of the
program seem
to run OK if the Xupdates are disabled).
I have produces a small test program comprising Xupdates only.  This program
simply
attempts to rename a record and then rename it back again.  It is possible
to run the program
concurrently with itself knowing that each program instance will update
different records
so they should not interfere with each other.  However, this program
exhibits exactly
the same fault as the main program.

Here is the XML of one entry in the database:

<?xml version="1.0" encoding="UTF-8"?>

<version_managed_component>
    <component_identifier>23</component_identifier>
    <latest>
        <latest_created>
            <version_id>
                <l1>1</l1>
                <l2>3</l2>
            </version_id>
        </latest_created>
        <latest_created>
            <version_id>
                <l1>2</l1>
                <l2>6</l2>
            </version_id>
        </latest_created>
    </latest>
</version_managed_component>

Here is the source code of my test program:  It should be invoked with an
argument
matching a component_id in the database (a different one for each program
invocation).
/*
 * xupdatetest.java
 *
 * Created on 22 April 2002, 21:01
 */

package xupdatetest;

import org.xmldb.api.base.*;
import org.xmldb.api.modules.*;
import org.xmldb.api.*;
// For the dbXML specific CollectionManager service
import org.apache.xindice.client.xmldb.services.*;

/**
 *
 * @author  root
 * @version
 */
public class xupdatetest
{
    static org.xmldb.api.base.Collection col;
    static XUpdateQueryService update_service;

    /** Creates new xupdatetest */
    public xupdatetest()
    {
    }

    public static long update(String command_set)
        throws XMLDBException
    {
        long result;

        String xupdate =
             "<xu:modifications version=\"1.0\"\n"
           + "    xmlns:xu=\"http://www.xmldb.org/xupdate\"\n"
           + ">\n"
           + command_set
           + "</xu:modifications>";
        try
        {
            result = update_service.update(xupdate);
        }
        catch (XMLDBException e)
        {
            System.out.println("Update: Exception "+e.getMessage()
                               +" on Query "+xupdate);
            throw e;
        }
        return result;
   }


    /**
    * @param args the command line arguments
    */
    private static void init()
        throws ClassNotFoundException, InstantiationException,
               IllegalAccessException, XMLDBException
    {
        String driver = "org.apache.xindice.client.xmldb.DatabaseImpl";
        Class c = Class.forName(driver);

        Database database = (Database) c.newInstance();
        DatabaseManager.registerDatabase(database);

        col = DatabaseManager.getCollection("xmldb:xindice:///db/docs/xut");
        update_service =
            (XUpdateQueryService)
col.getService("XUpdateQueryService","1.0");
    }

    public static void main (String args[])
    {
        String id = args[0];
        long done;

        try
        {
            init();
            while  (true)
            {
                String lock_latest_version_record =
                      "    <xu:rename select =
\"/version_managed_component[component_identifier='"+id+"']/latest/latest_cr
eated\">"
                      + "locked_latest_created"
                      + "</xu:rename>\n";

                 done = update(lock_latest_version_record);
                 if (done == 0)
                 {
                     System.out.println("Cannot lock "+id);
                 }
                 else
                 {
                     System.out.println("locked "+id);
                 }
                 String unlock_latest_version_record =
                      "    <xu:rename select =
\"/version_managed_component[component_identifier='"+id+"']/latest/locked_la
test_created\">"
                      + "latest_created"
                      + "</xu:rename>\n";

                 done = update(unlock_latest_version_record);
                 if (done == 0)
                 {
                     System.out.println("Cannot unlock "+id);
                 }
                 else
                 {
                     System.out.println("unlocked "+id);
                 }
            }

       }
       catch (Exception e)
       {
           System.out.println("Exception "+e.getMessage());
       }
       finally
       {
           try
           {
               if (col != null)
                   col.close();
           }
           catch(Exception e)
           {
               System.out.println("Collection failed to close");
           }
       }
    }
}

The fault report is as follows:

org.apache.xindice.client.corba.db.APIException:
IDL:org/apache/xindice/client/corba/db/APIException:1.0
	at
org.apache.xindice.client.corba.db.APIExceptionHelper.read(APIExceptionHelpe
r.java:112)
	at
org.apache.xindice.client.corba.db._CollectionStub.queryCollection(_Collecti
onStub.java:834)
	at
org.apache.xindice.client.xmldb.services.XUpdateQueryServiceImpl.updateResul
t(XUpdateQueryServiceImpl.java:165)
	at
org.apache.xindice.client.xmldb.services.XUpdateQueryServiceImpl.update(XUpd
ateQueryServiceImpl.java:185)
	at xupdatetest.xupdatetest.update(xupdatetest.java:43)
	at xupdatetest.xupdatetest.main(xupdatetest.java:102)
Update: Exception Query Processing Error on Query <xu:modifications
version="1.0"
    xmlns:xu="http://www.xmldb.org/xupdate"
>
    <xu:rename select =
"/version_managed_component[component_identifier='0']/latest/locked_latest_c
reated">latest_created</xu:rename>
</xu:modifications>
Exception Query Processing Error

Could anyone please advise me of the status of Xindice in regard to
concurrent operation.
I am quite happy to prepare code for single user operation for now as long
as I know when
concurrent operation will be fully operational.

Regards,

Michael Watson