Java: Synchronizing on primitives?

Question

In our system, we have a method that will do some work when it\'s called with a certain ID:

public void doWork(long id) { /* ... */ }

Now, this

Answer 1

You could create a list or set of active ids and use wait and notify:

List working;
public void doWork(long id) {
synchronized(working)
{
   while(working.contains(id))
   {
      working.wait();
   }
   working.add(id)//lock
}
//do something
synchronized(working)
{
    working.remove(id);//unlock
    working.notifyAll();
}
}

Problems solved:

• Only threads with same id's wait, all others are concurrent
• No memory Leak as the "locks" (Long) will be removed on unlock
• Works with autoboxing

Problems there:

• while/notifyAll may cause some performance loss with high number of threads
• Not reentrant