On 09/06/2011 10:01, Julien Aymé wrote: > 2011/6/9 Mark Thomas <ma...@apache.org>: >> On 09/06/2011 04:39, Phil Steitz wrote: >>> Code in trunk now does not work when distinct pooled instances are >>> equal - i.e., if a factory produces instances A and B and >>> A.equals(B), this causes problems. I think this situation should >>> be allowed - i.e. it is an unacceptable restriction to put on object >>> factories that distinct the poolable objects they produce be >>> distinguishable under equals. This would be a new requirement for >>> [pool] and I don't think we should require it. What do others think? >> >> As I start to answer this, I can see a very long response developing. I >> will do my best to keep it short. That may mean I gloss over some aspects. >> >> The requirement that objects obtained from the factories meet >> A.equals(B) == false greatly simplifies the implementation of a number >> of requirements. Let me explain by using a single requirement although >> there are a number of other requirements that have very similar >> consequences. >> >> The Requirement: >> It shall not be possible to return an object to the pool more than once. >> >> The pool maintains a list of idle objects. The simplest implementation >> of the above requirement is to test if any returned object already >> exists in the pool. This doesn't catch all scenarios but it is a start. >> >> If we know that for objects obtained from the factories A.equals(B) == >> false then we can use a HashSet to store idle instances and it is very >> easy to determine if the object being returned exists in the set of idle >> objects. This makes determining if the object is being returned twice >> relatively inexpensive. It also makes a reasonable multi-threaded >> implementation possible. > > </snip> > > And what about using an IdentityHashSet (or IdentityHashMap) to store > idle objects. > This would meet the Requirement without having to enforce A.equals(B) == > false.
That would be one of the aspects I glossed over. They aren't always maps/sets and they need to support concurrent access by multiple threads. A wrapper for pooled objects that uses System.identityHashCode(Object) may be a possible solution that isn't too complex. It would add a requirement for the pool to unwrap/wrap objects on borrow/return. I can look at this if folks think the new restriction on factories is unacceptable. Mark --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
