Here is the code,hoping this can help you :

public static final void main(String[] args) {

        try {

            // load up the knowledge base

            KnowledgeBase kbase = readKnowledgeBase();

            StatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();

            StatefulKnowledgeSession ksession2 = kbase.newStatefulKnowledgeSession();

            KnowledgeRuntimeLogger logger = KnowledgeRuntimeLoggerFactory.newThreadedFileLogger(ksession, "test", 1000);

            ksession.getWorkItemManager().registerWorkItemHandler("Human Task", new WSHumanTaskHandler());

            ksession2.getWorkItemManager().registerWorkItemHandler("Human Task", new WSHumanTaskHandler());

            // start a new process instance

            Map<String, Object> params = new HashMap<String, Object>();

            params.put("employee", "krisv");

            ksession.startProcess("com.sample.evaluation", params);

            ksession2.startProcess("com.sample.evaluation", params);

            //logger.close();

        } catch (Throwable t) {

            t.printStackTrace();

        }

    }

    private static KnowledgeBase readKnowledgeBase() throws Exception {

        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();

        kbuilder.add(ResourceFactory.newClassPathResource("Evaluation.bpmn"), ResourceType.BPMN2);

        return kbuilder.newKnowledgeBase();

    }

I created two session here,when i run it ,two processinstance was created,and there are two tasks for user "krisv"

i can complete the first task successfully,and the continued tasks was created too like this:

[2011:05:149 14:05:344:debug] Arguments : [org.jbpm.task.Task@b1e211a8]

[2011:05:149 14:05:423:debug] Message receieved on client : AddTaskResponse

[2011:05:149 14:05:423:debug] Arguments : [3]

[2011:05:149 14:05:423:debug] Message receieved on client : AddTaskResponse

[2011:05:149 14:05:423:debug] Arguments : [4]

however,when i complete the second task in the above picture,the result is like this:

[2011:05:149 14:05:357:debug] Message receieved on client : GetTaskResponse

[2011:05:149 14:05:357:debug] Arguments : [org.jbpm.task.Task@ce8b1e7d]

[2011:05:149 14:05:420:debug] Message receieved on client : GetTaskResponse

[2011:05:149 14:05:420:debug] Arguments : [org.jbpm.task.Task@ce8b1e7d]

[2011:05:149 14:05:421:debug] Message receieved on client : GetTaskResponse

[2011:05:149 14:05:421:debug] Arguments : [org.jbpm.task.Task@ce8b1e7d]

[2011:05:149 14:05:421:debug] Message receieved on client : GetTaskResponse

[2011:05:149 14:05:421:debug] Arguments : [org.jbpm.task.Task@ce8b1e7d]

there are no AddTaskResponse,and the continued tasks can not be created.

Thank you very much for your response!The human task server is started in another class ,so i didn't get errors in this part.

Can you give me more advice if i want to achive that different users start their own process instance of one process in different place and different time,or i can say in different class.

So in order to achive the requirement above,different session will be ok,or i have to use the same session to start different processinstance?

By the way,when you say the session persistence configurations do you mean the sessioninfo table in the database?

I finished the persistence configurations according to the user guide of jbpm5.And my database has the sessioninfo,processinstanceinfo tables ,etc.Below is my test code:

public static void main(String[] args){

        try {

            PoolingDataSource ds = new PoolingDataSource();

            ds.setUniqueName("jdbc/testDS");

            ds.setClassName("com.mysql.jdbc.jdbc2.optional.MysqlXADataSource");

            ds.setMaxPoolSize(3);

            ds.setAllowLocalTransactions(true);

            ds.getDriverProperties().put("user", "root");

            ds.getDriverProperties().put("password", "root");

            ds.getDriverProperties().put("URL", "jdbc:mysql://localhost:3306/jbpm5");

            ds.init();

            // load up the knowledge base

            KnowledgeBase kbase = readKnowledgeBase();

            // start a new process instance

            EntityManagerFactory emf = Persistence

                    .createEntityManagerFactory("org.jbpm.persistence.jpa");

            Environment env = KnowledgeBaseFactory.newEnvironment();

            env.set(EnvironmentName.ENTITY_MANAGER_FACTORY,

                    emf);

            env.set(EnvironmentName.TRANSACTION_MANAGER,

                    TransactionManagerServices.getTransactionManager());

            // create a new knowledge session that uses JPA to store the runtime

            // state

            StatefulKnowledgeSession ksession=null;

            ksession= JPAKnowledgeService.newStatefulKnowledgeSession(

                    kbase,

                    null,

                    env);

            JPAWorkingMemoryDbLogger logger = new JPAWorkingMemoryDbLogger(ksession);

            ksession.getWorkItemManager().registerWorkItemHandler("Human Task", new WSHumanTaskHandler());

            // start a new process instance

            Map<String, Object> params = new HashMap<String, Object>();

            params.put("employee", "krisv");

            ksession.startProcess("com.sample.evaluation", params);

           logger.dispose();

        } catch (Throwable t) {

            t.printStackTrace();

        }

    }

    private static KnowledgeBase readKnowledgeBase() throws Exception {

        KnowledgeBuilder kbuilder = KnowledgeBuilderFactory

                .newKnowledgeBuilder();

        kbuilder.add(ResourceFactory.newClassPathResource("Evaluation.bpmn"),

                ResourceType.BPMN2);

        return kbuilder.newKnowledgeBase();

    }

The first time i run the code,the processinstance and the tasks are created successfully.But when i run it second time ,exception was occured just like this:

javax.persistence.PersistenceException: [PersistenceUnit: org.jbpm.persistence.jpa] Unable to build EntityManagerFactory

    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:677)

    at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:126)

    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:83)

    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:60)

    at com.sample.ProcessTest.main(ProcessTest.java:67)

Caused by: org.hibernate.HibernateException: Could not obtain BTM transaction manager instance

    at org.hibernate.transaction.BTMTransactionManagerLookup.getTransactionManager(BTMTransactionManagerLookup.java:50)

    at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:357)

    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1327)

    at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:867)

    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:669)

    ... 4 more

Caused by: java.lang.reflect.InvocationTargetException

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

    at java.lang.reflect.Method.invoke(Method.java:597)

    at org.hibernate.transaction.BTMTransactionManagerLookup.getTransactionManager(BTMTransactionManagerLookup.java:47)

    ... 8 more

Caused by: bitronix.tm.utils.InitializationException: cannot open disk journal

    at bitronix.tm.BitronixTransactionManager.<init>(BitronixTransactionManager.java:59)

    at bitronix.tm.TransactionManagerServices.getTransactionManager(TransactionManagerServices.java:43)

    ... 13 more

Caused by: java.io.IOException:The process cannot access the file because another process has locked a portion of the file

    at java.io.RandomAccessFile.read(Native Method)

    at java.io.RandomAccessFile.readInt(RandomAccessFile.java:720)

    at bitronix.tm.journal.TransactionLogHeader.<init>(TransactionLogHeader.java:77)

    at bitronix.tm.journal.TransactionLogAppender.<init>(TransactionLogAppender.java:50)

    at bitronix.tm.journal.DiskJournal.open(DiskJournal.java:132)

    at bitronix.tm.BitronixTransactionManager.<init>(BitronixTransactionManager.java:46)

    ... 14 more

I do not know what happened above,can you help me out?Waiting for your response,thank you!!