Hello Andi, The problem is that script can fetch very large number of objects and all of them doesn't fit in the memory. Lets say we have very large list of objects (several millions objects or more). And our script traverse the list and fetch objects one by one and do some calculations (for example calculates total sum). So at each moment of time only one persistent object is actually needed. But without weak references we will have to keep all these millions of objects in memory.
Also performance of OODBBS greatly depends on efficient caching of objects. If we throw away all objects after each request and has to reload them from the server for each request, then performance will we awful. It is very significant to be able to cache most frequently used objects. LRU or some other discipline can be used for it. But any not depending from the discipline we use we need some mechanism which allows to map OPIDs to instances and do not prevent GC from collecting the objects. That is why almost all languages with implicit memory deallocation have some kind of weak references. And I was wondered when do not find such facility in PHP. Using __destruct method (thanks to George) it may be possible to implement what I need, but only if object cache is implemented in C (and so is not visible for PHP garbage collector). So no pure PHP solution exits. Unfortunately I didn't fins any reference to __destruct method in PHP manual and do not understand how it works. If I just declare __destruct method in class, it is not invoked when object is destructed. Friday, February 28, 2003, 6:29:21 PM, you wrote: AG> Hi, AG> I don't quite understand. If you are thinking of implementing something AG> similar to JDO then your persistent object manager will only hold the AG> objects which are retrieve by the script. At the end of the request it'll AG> persist the changes and will free the objects. Why would you want them to AG> be destroyed during the request? AG> Andi AG> At 02:39 PM 2/28/2003 +0300, Konstantin Knizhnik wrote: >>To be able to implmenet interface of object-oriented database to PHP I need >>to >>have object cache which will map persistent object identifier (OPID) to >>loaded instance of the object. This cache should be "weak", i.e. it should >>not prevent garbage collection from deallocating unused instances of >>peristent object (otherwise all database will be soon loaded in memory).. >> >>As far as I understand, PHP uses GC bases on refernce couters. Also I do not >>find something like weak reference in language manual. There are two other >>ways how to solve the problem >>without weak references: >>1. Be able to check valye of reference counter (so I can check the it is >>equal to 1 and if so remove this object from object cache) >>2. Be able to detect the moment when object is removed by GC (in this case I >>can make object cache invisible for GC and when object is deleted, it will >>be also unlinked frmo object cache). >> >>Can anybody tell me if such features are available in PHP (I failed to find >>them myself). >>Or may be there is some other way to solve the problem? >> >>Thanks in advance >>Konstantin >> >> >> >>-- >>PHP Development Mailing List <http://www.php.net/> >>To unsubscribe, visit: http://www.php.net/unsub.php -- Best regards, Konstantin mailto:[EMAIL PROTECTED] -- PHP Development Mailing List <http://www.php.net/> To unsubscribe, visit: http://www.php.net/unsub.php
