jbpm process instance save

Question

Hi all i am new to JBPM. i am using jbpm4.4 this is my basic example code:

    ProcessEngine processEngine = new Configuration()
           .buildProcessEngine();
      NewDeployment deployment=processEngine.getRepositoryService().createDeployment().addResourceFromClasspath("com/pardis/jpdl/test.jpdl.xml");
      String deploymentId = deployment.deploy();
      Map<String,Object> variables = new HashMap<String,Object>();
      variables.put("customer", "John Doe");
      variables.put("type", "Accident");
      variables.put("amount", new Float(763.74));
      ProcessInstance processInstance = processEngine.getExecutionService().startProcessInstanceByKey("iran",variables,"doops");
processEngine.getExecutionService().signalExecutionById(processInstance.getId());

and this is my process definition:

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

<process key="iran" name="test" xmlns="http://jbpm.org/4.4/jpdl"&gt;
   <start g="388,85,48,48" name="start1">
      <transition g="-49,-18" name="to state1" to="state1"/>
   </start>
   <end g="519,310,48,48" name="end1"/>
   <java class="test.TestAction" g="278,173,92,52" method="pr" name="java1">
      <arg> <object expr="#{type}"/> </arg>
      <arg> <object expr="#{customer}"/> </arg>
      <arg> <object expr="#{amount}"/> </arg>
      <transition name="to state2" to="state2" g="-49,-18"/>
   </java>
   <state g="89,151,92,52" name="state1">
      <transition g="-45,-18" name="to java1" to="java1"/>
   </state>
   <state name="state2" g="500,205,92,52">
      <transition name="to end1" to="end1" g="-42,-18"/>
   </state>
</process>

i have a question about it:

1. suppose that the execution of process is halted on some state, how could i persist the execution and resume it again? i want to run a process for multiple users and keep tracks of executions.

i think that JBPM documentation is very poor! so could you suggest a useful resource to me? thanks in advance