Re: [Proxool-developer] CodeReview - AbstractListenerContainer

[<chr...@em...>]

Good :)

Thats my piece of verbose code. Have Bill given you commit rights yet? 
If so feel free to replace it with what you suggest.

CHR


Bertrand Renuart wrote:

> I had a look at the AbstractListenerContainer... and found it much 
> complex for what it is supposed to do.
>  
> Let's recap the (supposed) requirements:
> - fast access to the list of registered listeners - frequent (read);
> - must support concurrency;
> - add/remove can be slower and are less frequent (update)
>  
>  
> The following implementation makes use of an object array to store the 
> reference to registered listeners.
> Every time add/remove is called, a new array is created with the new 
> state - the original is *not modified* but *replaced* by a new one. 
> This behavior is important since it guarantees that once you got the 
> array, you know it will *never been modified while you play with it*. 
> Thanks to this trick, no need for read/write locks and a fast access 
> to the list ;-)
>  
> The only precaution now is to make sure that only one thread can 
> access add/remove at a time. This code is protected by synchronized 
> statement - which is not a penality since modifications are not frequent.
>  
>  
> Classes extending this container can get access to the list of 
> registered listener by calling the protected /getListeners()/ method 
> that returns a reference to the array.
> It is now enough to iterate through the array with a simple for loop. 
> That's another benefit: no need to construct an iterator every time we 
> have to deliver an event...
>  
>  
> All this is definitly less expensive than the current implementation 
> that makes heavy use of synchronized statements :(
>  
>  
> The (new) code is below.
> Feel free to send any comments :)
>  
>
> public abstract class AbstractFastListenerContainer implements 
> ListenerContainerIF
> {
>     static final Log LOG = 
> LogFactory.getLog(AbstractFastListenerContainer.class);
>    
>     private Object[] listeners = EMPTY_LISTENERS;
>     private static final Object[] EMPTY_LISTENERS = new Object[]{};
>
>     /**
>      * @see ListenerContainerIF#addListener(Object)
>      */
>     public synchronized void addListener(Object listener)
>     {
>         // create a new array
>         Object[] newListeners = new Object[listeners.length];
>        
>         // copy listeners currently registered
>         System.arraycopy(listeners, 0, newListeners, 0, listeners.length);
>        
>         // add the new one
>         newListeners[listeners.length] = listener;
>        
>         // commit changes
>         listeners = newListeners;
>     }
>    
>    
>     /**
>      * @see ListenerContainerIF#removeListener(Object)
>      */
>     public synchronized boolean removeListener(Object listener)
>     {
>         // find listener to remove in the list
>         int index=-1;
>         for(int i=0; i<listeners.length; i++) {
>             if( listeners[i]==listener ) {
>                 index = i;
>                 break;
>             }
>         }
>        
>         // not found ?
>         if( index==-1 )
>             return false;
>        
>         // create a new array of the right size
>         Object[] newListeners = new Object[listeners.length-1];
>        
>         // copy registered listeners minus the one to remove
>         if( index > 0 )
>             System.arraycopy(listeners, 0, newListeners, 0, index);
>        
>         if( index < listeners.length-1 )
>             System.arraycopy(listeners, index+1, newListeners, index, 
> listeners.length-index-1);
>        
>         // commit
>         listeners = newListeners;
>         return true;
>     }
>
>    
>     /**
>      * Get a reference to the array containing registered listeners
>      */
>     protected Object[] getListeners() {
>         return listeners;
>     }
>
>
>     /**
>      * @see ListenerContainerIF#isEmpty()
>      */
>     public boolean isEmpty() {
>         return listeners.length==0;
>     }
> }
>
>  
>
>  
>