Duplicate of bug #33487.

This not the same situation as #33487
Here, it's not a question of local variable within a method.
And we actually unset the created object.
If I do the same with $this->backtrace = str_pad(' ', 2300); then the memory is not eaten up.
This occurs only if debug_backtrace() result is affected to a property of the test object.

Backtrace information that is returned from debug_backtrace() contains reference to $this object. So this examle creates circular data structure.

PHP cannot free circular structures at runtime and does free them on request shutdown.

So this bug is the same as bug #33595 (recursive references leak memory).

OK, nice, that explains the difference to php4.
unset($res) is not sufficient ... obviously,

<?php
class test
{
    var $backtrace            = null;
    function test()
    {
        $this->backtrace = debug_backtrace();
        unset($this->backtrace[0]['object']);
    }
}
set_time_limit(0);
for($i = 0; $i <= 500000; $i++) {
    $ret = &new test();
    unset($ret);
} 
?> 

does not break anymore.

However, this circular reference is due to the new 'object' returned by debug_backtrace() which is not documented.
It merits a *big* warning.

Also, it had been nice to be able to do it by __destruct() , but it's not called by unset() ...

I report back to pear , thanks !

__destruct() is not called because object is not destroyed (it is still referenced from inside). unset() just destroy reference to object from variable $ret;

We need add information about 'object' field into  debug_backtrace() documentation.

'object' already documented.