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unset a reference of property object

php.internals

Glash Gnome

4 years ago

Hello,

I am developing a PHP extension. I can't reproduce the behavior of
references of Zend/PHP.

Here is some Code illustrating Zend's behavior:
<?php
class Foo { public $baz = array(1);}
$foo = new Foo();
$ref = &$foo->baz;
$foo->baz = [123];//set array has reference
var_dump($foo);

Output ------------------------
object(Foo)#1 (1) {
["baz"]=>
&array(1) { [0]=> int(123) }
}
--------------------------------
Note the symbol ( &) output from the var_dump();


Now I add unset($ref) in my code
<?php
class Foo { public $baz = array(1);}
$foo = new Foo();
$ref = &$foo->baz;
//unset($ref);// kill reference
$foo->baz = [123];// set array has reference
unset($ref) ;// kill reference
var_dump($foo);
------------------------
object(Foo)#1 (1) {
["baz"]=>
array(1) { [0]=> int(123) }
}
--------------------------------

Note that the symbol (&) has disappeared from the output of var_dump();

I would like to reproduce this behavior but I don't know which method of
zend_object_handlers allows to remove( Z_UNREF) the reference.

Thank you for your help

Glash Gnome

4 years ago

Out of politeness I answer myself,


PHP_FUNCTION(var_dump)
-> php_var_dump()
-> zend_std_get_properties_for() //                     Zend
object handler get_properties_for
-> obj->handlers->get_debug_info(obj, &is_temp); // Zend
object handler get_debug_info
-> zend_std_get_properties();//                 Zend
object handler get_properties
-> rebuild_object_properties()
-> _zend_hash_append_ind()
=> ZVAL_INDIRECT(&p->val, ptr); // do the
trick( Z_TYPE change)
TODO: Find out how to manage the IS_INDIRECT

So to reproduce the default php behavior I can implement the
get_debug_info handler.

I'm still trying to figure out how to modify this line :
void my_get_debug_info() {
// ...
// Z_REFCOUNT(intern->data)==1
// Z_TYPE(intern->data)==IS_REFERENCE
// Z_TYPE(Z_REF(intern->data)->val)==IS_ARRAY
zval zdata; ZVAL_COPY(&zdata, &intern->data);// Why do I have to
hide that it's a reference ?
zend_hash_str_update(debug_info, "data", sizeof("data")-1, &zdata);
// ...
return debug_info;
}

my_handlers.get_debug_info = my_get_debug_info;


struct _my {// intern structure
zval data;// array of unsigned int
zend_object std;
};

Le sam. 9 avr. 2022 à 15:42, Glash Gnome <glash.gnome@gmail.com> a écrit :

Glash Gnome

4 years ago

Q1: "how to modify this line to reproduce the behavior of PHP"

A1:

/* {{{ vendor_my_get_debug_info */

static HashTable*

vendor_my_get_debug_info(zend_object *object, int *is_temp)

{

vendor_my *intern = ZOBJ_TO_VENDOR_MY(object);

HashTable   *debug_info=NULL, *std_props=NULL;

*is_temp = 1;

std_props = zend_std_get_properties(object);

debug_info = zend_array_dup(std_props);

zval zdata;

if (Z_ISREF(intern->data) && Z_REFCOUNT(intern->data)<2) {// If
the reference is no longer used by the PHP-user

ZVAL_COPY(&zdata, &Z_REF(intern->data)->val);// hide reference
(for compatibility)

} else {

ZVAL_COPY(&zdata, &intern->data);// show reference (for debugging ???)

}

zend_hash_str_update(debug_info, "data", sizeof("data")-1, &zdata);

return debug_info;

} /* }}} */

Q2: "Why do I have to hide that it's a reference ?"
A2: For historical( debugging) raison, see :
https://github.com/php/php-src/blob/master/ext/standard/var.c#L202
I think it's a bad idea to show & but it doesn't really matter.

In my case I think it's best never to show the reference :
zval zdata; ZVAL_COPY(&zdata, Z_ISREF(intern->data) ?
&Z_REF(intern->data)->val : &intern->data);
zend_hash_str_update(debug_info, "data", sizeof("data")-1, &zdata);
If I need to debug references/refcount it is better to use gdb's
pretty-print feature but no var_dump()

Le sam. 9 avr. 2022 à 17:51, Glash Gnome <glash.gnome@gmail.com> a écrit :