On 9 June 2011 14:41, Mark Thomas <ma...@apache.org> wrote: > 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.
Note that System.identityHashCode() is not necessarily unique: https://issues.apache.org/jira/browse/LANG-459 Could of course use == to disambiguate such objects. > Mark > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > For additional commands, e-mail: dev-h...@commons.apache.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
