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.