Thread monitoring for database query

Question

Hi,
I need to be able to store a database query in a thread. This means that the entire query from executing to return should take place in this thread (as well as connection etc). I would then like to know when it have finished its work so i can carry on some more porcessing.
I tried doing this with two threads, one to do the work and the other to 'watch' and then tell me when is is done. However, i errors 'every now and again' to which i can attribute to my thread structure not working properly. I am using a synchronised class and code post the code if anyone wishes to see it, however, i would appreciate it if someone could give me a basic structure to how i can go about this so that i do not get these 'random' errors.
Thanks Rudy

Answer 1

Okay -
I have an idea. Withut fully implementing your code, mind you.
If looks like you're having problems with concurrent access to your Vector.
A Vector is, of course, a Collection and a List (interfaces) - these are not thread safe. To make them thread safe, you need to "wrap" them.
<lifted from JavaDocs>
public static Collection synchronizedCollection(Collection c)
    Returns a synchronized (thread-safe) collection backed by the specified collection. In order to guarantee
serial access, it is critical that all access to the backing collection is accomplished through the returned
collection.
    It is imperative that the user manually synchronize on the returned collection when iterating over it:
  Collection c = Collections.synchronizedCollection(myCollection);
  synchronized(c) {
      Iterator i = c.iterator(); // Must be in the synchronized block
      while (i.hasNext())
         foo(i.next());
    Failure to follow this advice may result in non-deterministic behavior.
    The returned collection does not pass the hashCode and equals operations through to the backing
collection, but relies on Object's equals and hashCode methods. This is necessary to preserve the
contracts of these operations in the case that the backing collection is a set or a list.
    The returned collection will be serializable if the specified collection is serializable.
    Parameters:
        c - the collection to be "wrapped" in a synchronized collection.
    Returns:
        a synchronized view of the specified collection.</lifted from JavaDocs>
Give your Vector a wrapper and see if that solves your problem.
+M