Transaction Test

Question

Hi ,
I am conducting a test wherein I am initiating 5 threads and each thread is
carrying out a query and an update on a transaction.
I am not able to do that. I get an exception saying "Transaction is active"
Does this mean that I can have only one transaction active at any point of
time. Can I not have mulitple transactions for the same PM?
Is it a limitation on the JDO specs?
Thanks,
Sushanto
The test is as below:
import User;
import javax.jdo.Transaction;
import javax.jdo.Extent;
import javax.jdo.Query;
import javax.jdo.PersistenceManager;
import java.util.Collection;
public class TestThread extends Thread{
public static void main(String args[]) {
try {
for(int i =0; i < 5; i++) {
PersistenceManager gPm = Database.getPM("db1");
T2 t = new T2(gPm);
} catch (Exception e) {
e.printStackTrace();
class T2 extends Thread {
PersistenceManager gPm = null;
public T2(PersistenceManager pm) {
this.gPm = pm;
start();
public void run() {
try {
long memId = 0;
Transaction tm = gPm.currentTransaction();
tm.begin();
Class classObj = Class.forName("com.yodlee.yde.persistence.user.User");
Extent gExtent = gPm.getExtent(classObj, false);
Query q = gPm.newQuery(classObj, gExtent, "memId == 1");
Collection results = (Collection)q.execute();
User u = (User) results.iterator().next();
System.out.println("threadid:" + this + " :memId:" + u) ;
u.setLoginName("Sushi");
u.setLoginNameAsucase("SUSHI");
gPm.makePersistent(u);
tm.commit();
} catch (Exception e) {
e.printStackTrace() ;
System.out.println("exception");

Answer 1

"Sushanto" <[email protected]> writes:
Hi ,
I am conducting a test wherein I am initiating 5 threads and each thread is
carrying out a query and an update on a transaction.
I am not able to do that. I get an exception saying "Transaction is active"
Does this mean that I can have only one transaction active at any point of
time. Can I not have mulitple transactions for the same PM?
Is it a limitation on the JDO specs?According to the spec, there is a one-to-one relation between PM and
Transaction. So, you can only have a single transaction per PM.
In fact, Kodo's PM implementation is also a transaction --
pm.currentTransaction() just returns 'this'.
So, you should re-write your test to create a new PM from a common
factory for each thread.
-Patrick
Patrick Linskey [email protected]
SolarMetric Inc. http://www.solarmetric.com