Database with multiple thread

[Surajkumar]

Hi,
I want to access the database from 2 different threads and i am establishing the connection of database within the threads, but still when i access dartabase i get error as follows:
QSqlQuery:repare: database not open

My code snippet is as follows:
In constructor i am starting the 2 threads

pthread_create(&hd1, NULL, a, NULL);
   pthread_create(&hd2, NULL, b, NULL);
   pthread_join(hd1,NULL);
   pthread_join(hd2,NULL);

pthread_create(&hd1, NULL, a, NULL);
   pthread_create(&hd2, NULL, b, NULL);
   pthread_join(hd1,NULL);
   pthread_join(hd2,NULL);

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The below are Thread functions:

void *a(void *arg)
{
    db = QSqlDatabase::addDatabase("QPSQL","con1");
    db.setDatabaseName("abc");
    db.setHostName("127.0.0.1");
    db.setUserName("root");
    db.setPassword("123456");
    db.open();
 
while(1)
{
        printf("In Thd1\n");
          QSqlQuery qry2;
        qry2.prepare("SELECT max(msgid) from tx_msg");
        qry2.exec();
        while(qry2.next())
        {
            printf("MSGID:%d",qry2.value(0).toInt()) ;
        }
          usleep(1000);
}
pthread_exit(NULL);
}

void *a(void *arg)
{
    db = QSqlDatabase::addDatabase("QPSQL","con1");
    db.setDatabaseName("abc");
    db.setHostName("127.0.0.1");
    db.setUserName("root");
    db.setPassword("123456");
    db.open();

while(1)
{
        printf("In Thd1\n");
          QSqlQuery qry2;
        qry2.prepare("SELECT max(msgid) from tx_msg");
        qry2.exec();
        while(qry2.next())
        {
            printf("MSGID:%d",qry2.value(0).toInt()) ;
        }
          usleep(1000);
}
pthread_exit(NULL);
}

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2nd thread :

void *b(void *arg)
{
    db1 = QSqlDatabase::addDatabase("QPSQL","con2");
    db1.setDatabaseName("abc");
    db1.setHostName("127.0.0.1");
    db1.setUserName("root");
    db1.setPassword("123456");
    db1.open();
while(1)
{
        printf("In Thd2\n");
        QSqlQuery qry1;
        qry1.prepare("SELECT max(msgid) from tx_msg");
        qry1.exec();
        while(qry1.next())
        {
            printf("MSGID:%d",qry1.value(0).toInt()) ;
        }
        usleep(1000);
}
pthread_exit(NULL);
}

void *b(void *arg)
{
    db1 = QSqlDatabase::addDatabase("QPSQL","con2");
    db1.setDatabaseName("abc");
    db1.setHostName("127.0.0.1");
    db1.setUserName("root");
    db1.setPassword("123456");
    db1.open();
while(1)
{
        printf("In Thd2\n");
        QSqlQuery qry1;
        qry1.prepare("SELECT max(msgid) from tx_msg");
        qry1.exec();
        while(qry1.next())
        {
            printf("MSGID:%d",qry1.value(0).toInt()) ;
        }
        usleep(1000);
}
pthread_exit(NULL);
}

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How can i access same database from different threads?