Concurrency issues

sylvain75 · **Joined:** Mon Apr 04, 2011 1:03 pm **Posts:** 2

Hi All,

I have been struggling with a concurency issue for the last couple of days and I have to admit that it is starting to drive me crazy. I am using Spring 3 along with Hibernate.

I have the following controller (in the MVC layer) :

Code:

@RequestMapping("/smppMTDS")
public ModelAndView handleRequest(HttpServletRequest request,
         HttpServletResponse response) throws Exception {
         
   String returnStr = receivedMTManager.getUnsentDSReceivedMT();
      
   response.setContentType("text");
   PrintWriter out = response.getWriter();
   if(null!=returnStr)
   {
      out.println(returnStr);
   }
         
   return null;
}

This method is called by another server several times per second.
"getUnsentDSReceivedMT" is in the service layer, its content is the following :

Code:

@Transactional(isolation=Isolation.SERIALIZABLE)
public String getUnsentDSReceivedMT()
{
   ReceivedMT receivedMT =  receivedMTDao.getUnsentDSReceivedMT();
      
   if(receivedMT!=null)
   {
      receivedMT.setDsSentTime(new Date());
      receivedMTDao.update(receivedMT);
                  
      return("Id="+receivedMT.getMessageId()+";Status="+receivedMT.getDs()+";");
         
   }
   return null;
}

I need "receivedMTDao.getUnsentDSReceivedMT()" to return 2 different objects when 2 requests come in simultaneously. Otherwise the other server gets twice the same data and causes problems. Unfortunately, when 2 requests come in quickly, this happens:"receivedMTDao.getUnsentDSReceivedMT()" returns twice the same data. This is bewildering as I was assuming that a read lock was used when data are read from the DB with this isolation level.

If anyone could help me out with this, I would be really grateful. Any idea ?

Note: I am using MySQL INNODB.

Note : "getUnsentDSReceivedMT" is in the dao layer. Here it is :

Code:

public ReceivedMT getUnsentDSReceivedMT() {
      
   StringBuilder stringQuery = new StringBuilder("");
   stringQuery.append(" FROM ReceivedMT ");
   stringQuery.append(" WHERE dsSentTime is null ");      
   Query query = sessionFactory.getCurrentSession().createQuery(stringQuery.toString()).setMaxResults(1);
         
   return (ReceivedMT) query.uniqueResult();
      
}

Sylvain

burroinquieto · **Joined:** Sat Sep 24, 2005 11:04 pm **Posts:** 21

Try setting an explicit lock mode for your query:

Code:

public ReceivedMT getUnsentDSReceivedMT() {
   return (ReceivedMT)sessionFactory.getCurrentSession().createQuery(
      "select mt from ReceivedMT mt where dsSentTime is null")
      .setLockMode("mt", LockMode.PESSIMISTIC_WRITE)
      .setMaxResults(1)
      .uniqueResult();
} 

niks23 · **Joined:** Mon Apr 04, 2011 3:31 am **Posts:** 41

hi Read this ...

http://www.roseindia.net/hibernate/firstexample.shtml