On Jan 25, 2009, at 9:28 PM, Mck wrote:
>
>> Can anyone figure out what might go wrong in the original version of
>> the class?
>
> I have no idea how something here can result in a 404.
> Do multiple instances create cause the 404?
>
I can see no other explanation. But I fail to see why.
> As far as the locking i wonder if because INSTANCES in a HashMap and
> not
> meant to be used concurrently that this introduces the need to have
> the
> second check. But replacing the HashMap with a ConcurrentHashMap is
> only
> useful when having multiples instances isn't a problem.
>
>
> On a separate note would the following work as an base implementation
> that all our SiteKeyedFactories could use:
>
>
Yes. Looks good!
> static <T> T instanceOf(
> final Site site,
> final Map<Site,T> instances,
> final ReentrantReadWriteLock instancesLock,
> final FactoryConstructor<T> constructor){
>
> try {
> instancesLock.readLock().lock();
> if (!instances.containsKey(site)) {
> // It is not possible to upgrade a read lock...
> instancesLock.readLock().unlock();
> instancesLock.writeLock().lock();
> try {
> // ...so check the condition again.
> if (!instances.containsKey(site)) {
> instances.put(site, constructor.construct());
> }
> } catch (SiteKeyedFactoryInstantiationException e) {
> LOG.error(ERR_DOC_BUILDER_CREATION, e);
> } finally {
> // Downgrade to a read lock.
> instancesLock.readLock().lock();
> instancesLock.writeLock().unlock();
> }
> }
> return instances.get(site);
> } finally {
> // Finally release the read lock.
> instancesLock.readLock().unlock();
> }
> }
>
> interface FactoryConstructor<T>{
> T construct() throws SiteKeyedFactoryInstantiationException;
> }
>
>
> ~mck
>
> --
> "Physics is to math what sex is to masturbation." Richard Feynman
> | semb.wever.org | sesat.no | sesam.no |
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