[PHP-DEV] Weak references in PHP
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
Re: [PHP-DEV] Weak references in PHP
Can anybody tell me if such features are available in PHP (I failed to find them myself). Look at __destruct method for classes in ZE2. They wopn't tell you the reference count, but the do get called when the ref count goes to 0. -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re: [PHP-DEV] Weak references in PHP
Hi, I don't quite understand. If you are thinking of implementing something similar to JDO then your persistent object manager will only hold the objects which are retrieve by the script. At the end of the request it'll persist the changes and will free the objects. Why would you want them to be destroyed during the request? Andi 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 -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re[2]: [PHP-DEV] Weak references in PHP
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, Konstantinmailto:[EMAIL PROTECTED] -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re[2]: [PHP-DEV] Weak references in PHP
Hello George, Friday, February 28, 2003, 5:46:18 PM, you wrote: Can anybody tell me if such features are available in PHP (I failed to find them myself). GS Look at __destruct method for classes in ZE2. They wopn't tell you the GS reference count, but the do get called when the ref count goes to 0. Sorry, I am dummy in PHP world:( Can you explain more precisely what is ZE2 and where should I look for __destruct method. I didn't find any reference to such method neither in PHP manual neither in PHP sources i have downloaded. -- Best regards, Konstantinmailto:[EMAIL PROTECTED] -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re: Re[2]: [PHP-DEV] Weak references 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. It's in ZE2 have a look at Zend/ZEND_CHANGES in the source tree for details (you'll need to be running php5/HEAD). And it's a userland method, so the cache can be implemented in PHP. -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re: Re[2]: [PHP-DEV] Weak references in PHP
ZE2 == Zend Engine 2, which will be replacing the current Zend Engine in PHP 5. Amoung other things, one of it's main features is a more roboust OOP framework, which includes class destructors. J Konstantin Knizhnik wrote: Hello George, Friday, February 28, 2003, 5:46:18 PM, you wrote: Can anybody tell me if such features are available in PHP (I failed to find them myself). GS Look at __destruct method for classes in ZE2. They wopn't tell you the GS reference count, but the do get called when the ref count goes to 0. Sorry, I am dummy in PHP world:( Can you explain more precisely what is ZE2 and where should I look for __destruct method. I didn't find any reference to such method neither in PHP manual neither in PHP sources i have downloaded. -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
Re[2]: [PHP-DEV] Weak references in PHP
At 08:00 PM 2/28/2003 +0300, Konstantin Knizhnik wrote: 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. If you need to go over a list of million objects you are doing something wrong :) 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. I disagree. JDO performs well and doesn't cache the objects as usually pessimistic locking is used with it. Of course, if you want to use optimistic locking and the nature of your application allows you to do so efficiently the caching might make sense (or it's mainly a read-only app). 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. I don't quite understand why you need __destruct() as other systems in Java don't use this but I might be completely misunderstanding what you want to do. Yes, you'll need to do this with a C extension. Anyway, good luck. I hope the Engine 2 solves some of your problems (such as object handles which allow you to always access the same DB object). Andi -- PHP Development Mailing List http://www.php.net/ To unsubscribe, visit: http://www.php.net/unsub.php
