Re: Help Needed with Connection Pooling for Java Swing Based - Mailing list pgsql-jdbc

Pardon my inaccuracy.  I should have said "Realizing" instead of
instantiating.  "Realizing" is the name that the AWT developers gave to
the process  (which is encapsulated in the AWT's component
implementation) of actually allocating the system resources needed to
display the GUI widgets.  Typically, it happens when you call pack or
setVisible(true) on a Window, Frame or Dialog. When a component is
realized, it checks to see if the dispatcher thread is running, and if
not, starts it.  Depending on what you're using, it may also start other
threads to support features like the Pluggable Look and Feel and so on.
As far as I know, it's only possible to have one AWT Event Dispatch thread.

Bringing us back to the original topic, Once the AWT threads are
running, it's basically hit-or-miss whether the app will stop unless
System.exit is explicitly called or you set the default close operation
on your frame to EXIT_ON_CLOSE (which just calls System.exit for you),
so this has nothing to do with JDBC or PostgreSQL's driver.

Scot P. Floess wrote:

> Derek:
>
> Are you sure instantiating a Swing component launches a new thread?
> Simply instantiating 2 JButtons will launch 2 threads?  I don't think
> that is the case.
>
> Derek S wrote:
>
>> Instantiating any Swing component does in fact start a new thread -
>> the AWT Event Dispatch thread.  My experience with it has been that
>> this thread quite often doesn't terminate the way you might expect
>> when the main method ends.  This is a well known issue that Swing and
>> AWT programmers simply have to deal with and has absolutely nothing
>> to do with JDBC.  Generally speaking, all Swing/AWT based
>> applications call System.exit when they are finished doing whatever
>> it is they do in order to ensure that the AWT Event Dispatch thread
>> shuts down properly.
>>
>> Barry Lind wrote:
>>
>>> I just ran your test case and everything seems to be working
>>> correctly as far as I can tell.  The program creates one and only
>>> one connection to the database.  I don't see multiple connections
>>> created as you are reporting.
>>>
>>> I don't know anything about swing, but it is clear that the code for
>>> swing you have below isn't correct.  Because with this swing call
>>> the program doesn't exit.  It seems the swing code is starting some
>>> other threads that are running and thus the main program doesn't
>>> exit until those threads stop running (and I don't know what swing
>>> calls are necessary to stop the swing threads from running).
>>>
>>> So with the swing call in place I have to ctrl-C to stop the app
>>> from running, but from the jdbc side of things everything seems to
>>> be working correctly.
>>>
>>> Perhaps I don't understand the problem you are seeing?
>>>
>>> thanks,
>>> --Barry
>>>
>>>
>>> Shanmugasundaram Doraisamy wrote:
>>>
>>>> Dear group,
>>>>
>>>> We are having some problems when using JDBC Connection Pool using
>>>> Postgrsql Jdbc3PoolingDataSource.
>>>>
>>>> The Pool behaves fine if there is no Swing Component in the Program.
>>>> If there is a swing Component ,then the connection seems to be not
>>>> returning to the pool and calling for an additional instance of the
>>>> class leeds to the creation of fresh Connection objects ,at times
>>>> it even exceeds the maximum number allowed in the pool.
>>>> If we go for System.exit(0);(Killing) then only the Connection is
>>>> returned .
>>>>
>>>> But if we comment the swing component line (here in the attached
>>>> Program a JOptionPane is Used) then the pool behaves fine.
>>>>
>>>>
>>>> Herewith Iam attaching a Program which is behaving as detailed.
>>>>
>>>> Any Help is Welcome.
>>>>
>>>> ##################################################################
>>>>
>>>>
>>>> ##################################################################
>>>>
>>>> /*
>>>>  * ConPool.java
>>>>  *
>>>>  * Created on 26 March 2003, 11:54
>>>>  */
>>>>
>>>> /**
>>>>  *
>>>>  * @author  naks from vpsd,Erode
>>>>  *   */
>>>> import org.postgresql.jdbc3.*;
>>>> import java.sql.*;
>>>>
>>>> public class ConPool {
>>>>        Jdbc3PoolingDataSource source = null;
>>>>     private Connection conn = null;
>>>>        /** Creates a new instance of ConPool */
>>>>     public ConPool() {
>>>>            }
>>>>        /** Setting the Pool which intializes the Pool to 2. */
>>>>     public void setPool() {
>>>>         // DataSource initialization
>>>>         System.out.println("setPool()");
>>>>         try {
>>>>             System.out.println("setting pool");
>>>>             // constructs a pool only when source is not assigned.
>>>>             // this will prevent problems if the same pool is set
>>>> more than
>>>>             // one time
>>>>             if (source == null) {
>>>>                 source = new Jdbc3PoolingDataSource();
>>>>                 // DataSource configuration.
>>>>                       source.setServerName("192.168.0.51");
>>>>         source.setDatabaseName("kec_test_pool");
>>>>         source.setUser("venbro");
>>>>         source.setPassword("venbro");
>>>>         source.setMaxConnections(2);
>>>>                                } else {
>>>>                 System.out.println("pool is set");
>>>>                 return;
>>>>             }
>>>>         } catch (Exception loException) {
>>>>             // logger.logToFile(loException);
>>>>             loException.printStackTrace();
>>>>         }
>>>>
>>>>     } //End of setPool method
>>>>           /**
>>>>      * Method inserts data to a table "test" which is like
>>>>      * create table test (param1 varchar(2),param2 varchar(2)) ;
>>>>          */
>>>>      public int insertDatas(){
>>>>            int count=-1;
>>>>              try{
>>>>                conn=source.getConnection();
>>>>
>>>>       PreparedStatement st = conn.prepareStatement("INSERT INTO
>>>> test values('P1','P2')");
>>>>            count = st.executeUpdate();
>>>>
>>>>       st.close();
>>>>            conn.commit();
>>>>       conn.close();
>>>>          }
>>>>     catch (SQLException ex) {
>>>>        count=0;
>>>>       ex.printStackTrace();
>>>>     }
>>>>        return count;
>>>>     }//End of Insert Method
>>>>               public static void main(String args[]){
>>>>                       ConPool cp=new ConPool();
>>>>         cp. setPool();
>>>>         int sucess_flag=cp.insertDatas();
>>>>         System.out.println("Sucess"+sucess_flag);
>>>>                /**
>>>>           * Upto this level the Connection pooling is working fine .
>>>>           * But if this Swing Component is added then it creates
>>>> new Connection
>>>>           * which is even more than the intial connection of the
>>>> pool..
>>>>          *  We have to kill the application (System.exit(0))to
>>>> remove the Connection
>>>>          ** But on commenting line :105 "Swingline " the Pool is
>>>> working fine..
>>>>                  */
>>>>
>>>> javax.swing.JOptionPane.showMessageDialog(null,"VENBRO-ERODE","MESSAGE",1);//
>>>> Swing line 105
>>>>                 }
>>>>
>>>> }//End of the class
>>>> ##########################################################################################
>>>>
>>>> ###########################################################################################
>>>>
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