Vector -- how do i use it??

[Derick Potgieter]

Hi,

I`m busy with my lock method.

long cookie = getNewCookie();  //produces a new cookie
lockedList.add(recNo); //adds the record no to the static lockedlist vector
map.put(new Integer(recNo),new Long(cookie)); //adds both to a HashMap for tracking
return cookie;

but my problem is in my unlock method nl.

  
public void unlock(int recNo, long cookie) throws RecordNotFoundException,
  .....
  if(test that cookies are the same){
    lockedList.remove(recNo); //-----------here is my problem
    map.remove(new Integer(recNo));
    lockedList.notifyAll();
  }
 

how can i remove the recno that i locked from the vector, i`m specifying
the location to remove, but i only have the record no to work with??

Any suggestions?? the reason for the vector is because it is thread safe, and i`m syncronizing on it.

Thanks
Derick

[Denis Spirin]

Hi Derick

Why do you need lockedList? You store locked record number in HashMap, why to duplicate it in Vector?

You may make HashMap as static instance, and I see no problems with synchronization here.
[ June 02, 2004: Message edited by: Denis Spirin ]

[Vishwa Kumba]

Derick,
Vector also has another remove method. Did you try that?

Object remove(int index)
boolean remove(Object o)

You can remove the same way you removed the rec number object from the map.
Moreover, you can only add objects to Vector. I think you are trying to add
a primitive type to the Vector in your locking method.

lockedList.add(recNo)

Just curious, why are you using 2 collection classes for your locking design?

[Dmitry Gavrilov]

Hi Derick
I think that You can do so...

 
Map map = new HashMap();
 
long lock(int recNo) .... {
    synchronized(map)
    Integer recRef = new Integer(recNo);
    while(map.get(recRef) != null) 
       try { 
         wait();
       } catch (InterruptedException e){ /* do nothing */ }
    Long result = getNewCookie();
    map.put(recRef, result);
    return result.longValue();
  }
}
 
void unlock(int recNo, long cookie)... {
   syncronized(map) {
      Integer recNoRef = new Integer(recNo);
      Long cookies = (Long)map.get(recNoRef);
      if(cookies.longValue() != cookie)
         throw new SecurityException ....
      map.remove(recNoRef);
      notifyAll();
   }
}

But I think that the better decision is to create a LockManager.class.
[ June 04, 2004: Message edited by: Dmitry Gavrilov ]

[Denis Spirin]

In fact, if you access collection from sync block, you dont need to care about if this collection is sync or not.