how to safe update

[sergiu72]

hello

I want to know what settings should have for safe updates using stateless beans (if it is possible), when have concurrency. I try to test using this code:

//this code is from Runnable objects (I have many objects of this type):

 for(int i=0;i<UPDATE_NO;i++){
 int amount = ran.nextInt(1000);
 amountSum +=amount;
 testSessionC.adjust2Balance(balance.getId(),amount);
 }

//stateless bean:

@Stateless
@Remote(TestSessionC.class)
@Local(TestSessionC.class)
public class TestSessionCBean implements TestSessionC{

 @PersistenceContext(unitName = "...")
 EntityManager em;

 public void adjust2Balance(long id, int amount) {
 Balance b = em.find(Balance.class, id);
 em.lock(b, LockModeType.WRITE);
 float old = b.getAmount();
 b.setAmount(old+amount);
 em.merge(b);
 }

}

my Balance entity use version control:

 @Version
 @Column(name = "OPTLOCK")
 public int getVersion() {
 return version;
 }

thanks for any ideea