session.getDataHashCode not equals Arrays.hashCode( attributesData ) when session attributes whithout changes by msm-kryo-serializer

[51037405]

final ConcurrentMap<String, Object> attributes = _session.getAttributesFiltered();
            final byte[] attributesData = serializeAttributes( _session, attributes );
            final int hashCode = Arrays.hashCode( attributesData );
            //<editor-fold desc="additional logs">
            if ( _log.isDebugEnabled() ) {
                _log.debug( "attributesData  " + new String(attributesData) );
                _log.debug( "Arrays.hashCode " + hashCode + ",Session.getDataHashCode " + _session.getDataHashCode() );
            }
            final BackupResult result;
            //</editor-fold>
            if ( _session.getDataHashCode() != hashCode
                    || _force
                    || _session.authenticationChanged() ) {

                _session.setLastBackupTime( System.currentTimeMillis() );
                final byte[] data = _transcoderService.serialize( _session, attributesData );

                result = doBackupSession( _session, data, attributesData );
                if ( result.isSuccess() ) {
                    _session.setDataHashCode( hashCode );
                }
            } else {
                result = new BackupResult( BackupResultStatus.SKIPPED );
            }

session will be backup when _session.getDataHashCode != Arrays.hashCode( attributesData ) ,sometiems, session attributes without any changes, but attributesData has changed .
For example:
put two attributes into session, (iccid = 1234 , cityCode = heibei )
first access log:

Jan 19, 2017 4:11:53 PM de.javakaffee.web.msm.BackupSessionTask call FINE: attributesData  cityCod�heibe�icci�123� 
Jan 19, 2017 4:11:53 PM de.javakaffee.web.msm.BackupSessionTask call FINE: Arrays.hashCode -1759883946,Session.getDataHashCode 1744582514 Jan 19, 2017 4:11:53 PM 

second access log

Jan 19, 2017 4:11:55 PM de.javakaffee.web.msm.BackupSessionTask call FINE: attributesData icci�123�cityCod�heibe� 
Jan 19, 2017 4:11:55 PM de.javakaffee.web.msm.BackupSessionTask call FINE: Arrays.hashCode 1744582514,Session.getDataHashCode -1759883946 Jan 19, 2017 4:11:55 PM 

in this case, session will be covered in concurrent requests even if the attributes have not changes.

If Req_A is a get request, just read session attributes ,Req_B is a post request ,modify session attributes .
Session will be covered when Req_A finished.
So, i will get the attribute from session that is set by Req_B is null in the next request.
How to solve this question?

[51037405]

version info:
msm : 2.1.1
kryo : 4.0.0
kryo-serializers : 0.41
minlog : 1.2
objenesis: 2.2
reflectasm: 1.11.3
asm: 5.0.4
setting:

<Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager"  
		memcachedNodes="n1:172.16.50.65:11211"            
		requestUriIgnorePattern=".*\.(png|gif|jpg|css|js)$"  
		sticky="false"
		sessionBackupAsync="false"
		sessionBackupTimeout="1800000"  
		copyCollectionsForSerialization="false"  
		transcoderFactoryClass="de.javakaffee.web.msm.serializer.kryo.KryoTranscoderFactory"/>

[magro]

Thanks for this detailed report! AFAICS the two request logs show a different order of the attributes (attributesData), which most probably explains the different hashcode. Therefore we'd have to sort attributes before computing the hashcode. WDYT?
Do you want to submit a pull request?

[51037405]

Thanks for the reply!
Now we get hashcode by the attributesData(the attributes has been serialized).
If sort attributes before computing the hashcode , we'll get hashcode by the attributes has been ordered instead of the attributesData, right?
Or we sort attributes before serialize attributes?

[magro]

Right, I meant to sort the attributes (the result of _session.getAttributesFiltered()).

[51037405]

Thank you very much! I got the same hashcode when the attributes been sorted.