Simultaneous access

[slad]

Hi all,

I am trying to imitate simultaneous access to data, using EJB 3.0 under JBoss 4.0.5GA.
Stateless session bean has following method:

@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
 public String fieldInc(int id) {
 EntityManager em = null;
 String result;

 try {
 InitialContext ctx = new InitialContext();
 EntityManagerFactory emf = (EntityManagerFactory) ctx.lookup("java:/EntityManagerFactory");
 em = emf.createEntityManager();
 Foo f = em.find(Foo.class, id); // Foo is Entity bean, it represents table in DB under MySQL 5.0.24a

 if(f == null) {
 em.close();
 return "No entity found by given id("+id+")";
 }

 f.setSomefield(f.getSomefield()+1);
 em.persist(f);
 result = "new field value: "+f.getSomefield();
 em.close();
 return result;
 } catch(Exception e) {
 if(em != null) {
 em.close();
 }
 return e.toString();
 }
 }

this code is called from servlet like:

for(int i=0;i<100;i++){
 sess.fieldInc(1);
}

so, when I start this servlet in 2 windows the field's value doesn't increases by 200, but only ~140. Is that annotation enough to start container managed transaction? Or maybe I should use User Transaction to make concurrent access for modifying data work properly?

thanks for any advise

[slad]

okay,

for(int i=0;i<100;i++){
 synchronized(SimultanServlet.class){
 sess.fieldInc(1);
 }
}

helped (don't know if it correct, but it works...)

the next question is - how to make it work in cluster - synchronized won't help...