Re: Caching question

Hi Carlos.

I have not tried anything of this but the first thing that comes to my 
mind is something like this:

Change the FinderCachingAdvice so that the HashMap holding the caches is 
static.

private static Map cache = new StaticBucketMap(1000);

Add a method to the advice similar to this:

public static void remove(final String uuid) {
     // removes the object with the uuid from the cache
}

Then if f.e. your Folder have some methods like 
create/remove/update/move or so then you could create an Advice that 
advises those methods and transparently removes the Folder from the 
cache when these methods are called:

// some advice, that f.e advises the remove or move methods on Folder
...
     public Object execute(final JoinPoint joinPoint) throws Throwable {
	final Object result = joinPoint.proceed();

         MethodJoinPoint jp = (MethodJoinPoint)joinPoint;
         String uuid = ((Identifiable)jp.getTargetObject()).getUuid(); 

         FinderCachingAdvice.remove(uuid); // or look it up through some 
Registry

         return result;
     }
...

As I said this is the first thing that comes to my mind, might not work, 
I'll have to think some more about this.
Pretty interesting problem.

Sincerely, Jonas.


Carlos Villela wrote:
> Hi folks!
> 
> After reading about AOP being extremely good for caching objects, I've 
> decided I should give it a try on some expensive O(n^2) methods I have 
> here. It's a very AOP-newbie question, I'll understand if you want to 
> ignore it or just tell me to RTFM :) - but here comes an important 
> problem: how to invalidate the cache in some scenarios? Here's some code 
> (i've removed some assertions to clear things out a little):
> 
>    /** Iterates over the root folder, and if the folder is not found, 
> recurses through subfolders to find the uuid */
>    public static Folder findFolder(String uuid) {
>        Folder root = ((HasRootFolder) new EntryPoint()).getRootFolder();
> 
>        Folder f = findFolder(uuid, root);
>        if (f == null) {
>            List folders = ((HasFolders) root).getFolders();
>            if (folders == null)
>                return null;
> 
>            for (Iterator i = folders.iterator(); i.hasNext();) {
>                f = findFolder(uuid, (Folder) i.next());
>                if (f != null)
>                    break;
>            }
>        }
>        return f;
>    }
> 
>    /** Recurses through subfolders to find a Folder with a given uuid */
>    public static Folder findFolder(String uuid, Folder folder) {
>        List folders = ((HasFolders) folder).getFolders();
> 
>        if (folders == null)
>            return null;
> 
>        for (Iterator i = folders.iterator(); i.hasNext();) {
>            Folder f = (Folder) i.next();
>            if (((Identifiable) f).getUuid().equals(uuid)) {
>                return f;
>            }
>        }
>        return null;
>    }
> 
> Ok, I can cache these methods with a simple advice (again, assertions 
> removed):
> 
> public class FinderCachingAdvice extends MethodAdvice {
> 
>    private Map cache = new StaticBucketMap(1000);
> 
>    public Object execute(final JoinPoint joinPoint) throws Throwable {
>     String uuid = (MethodJoinPoint) 
> joinPoint.getParameters()[0].toString();
>        final Long hash = new Long.parseLong(uuid);
> 
>        final Object cachedResult = cache.get(hash);
> 
>        // if we have a cached result; return the cache
>        if (cachedResult != null) return cachedResult;
> 
>        // else, proceed with the method invocation and store the result 
> in the cache
>        final Object result = joinPoint.proceed();
>        cache.put(hash, result);
> 
>        return result;
>    }
> }
> 
> Then, I get to the problem: when do I know I need to invalidate the 
> cache for a given UUID? When the object is moved in the folder structure 
> or it's deleted, sure. But how do to it with aspects? Any enlightening 
> ideas? :)
> 
> []'s
> -cv
> 
> 
> 
> 
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-- 
Jonas
http://freeroller.net/page/jboner





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