regarding isolation between threads

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От Surabhi Ahuja
Тема regarding isolation between threads
Дата
Msg-id CE5C48E227F8ED4990FAC4332100ADC621B55D@EVS.iiitb.ac.in
обсуждение исходный текст
Ответы Re: regarding isolation between threads
Re: regarding isolation between threads
Re: regarding isolation between threads
Список pgsql-general
Дерево обсуждения
void *connect(void* threadid)
{
    char command[100];
    int *id_ptr, taskid;
    id_ptr = (int *) threadid;
    taskid = *id_ptr;
    if(taskid == 0)
        strcpy(command, "select insert (1)");
    else if(taskid == 1)
        strcpy(command, "select insert (1)");
    else if(taskid == 2)
        strcpy(command, "select insert (3)");
    else if(taskid == 3)
        strcpy(command, "select insert (4)");
    else if(taskid == 4)
        strcpy(command, "select insert (5)");
 
   PGconn *conn = connect("dbname=x host=y user=z");
   pgresult res;
   res = pqexec (conn, "begin transaction");
   res = pqexec (conn, command);
   res = pqexec (conn, "commit");
   pqfinish (conn);
 
   pthread_exit(NULL);
}
int main()
{
    pthread_t threads[NUM_THREADS];
    int rc;
    int *taskids[NUM_THREADS];
    for(int t=0; t<NUM_THREADS; t++)
    {
        taskids[t] = (int *) malloc(sizeof(int));
        *taskids[t] = t;
        rc = pthread_create(&threads[t], NULL, connect, (void *) taskids[t]);
        if (rc)
        {
            printf("ERROR; return code from pthread_create() is %d\n", rc);
            exit(-1);
        }
    }
    for(int t=0; t<NUM_THREADS; t++)
    {
        delete taskids[t];
    }
    pthread_exit(NULL);
}
 
 
the stored procedure (just the pseudo code)
 table x has a primary key k
insert(integer)
{
     select from table if k =  $1
     if not found
        insert into x ($1);
    else
       insert into some_other_table($1);
    end if
}
 
the kind of output i am expecting is:
 
table x: 1 3 4 5
table a: 1
and no error message
 
but the output is something like
 
table x : 1 3 4 5
table some_other_table :
it has nothing
and error message is displayed : "error in stored proc "insert(..... primary key violation .."
this error is because
 
two threads are simultaneoulsy trying to insert the values "1" each and thats where they interfere with each other.
 
thanks
surabhi ahuja

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