PHP garbage collection mechanism reference counter concept analysis_PHP tutorial

If you have xdebug installed, you can use xdebug_debug_zval() to display "zval" information. As follows:

Copy code The code is as follows:

$str = "jb51.net";
xdebug_debug_zval('str');

Result:

str:
(refcount=1, is_ref=0),
string 'jb51.net' (length=10)

Only when the variable container is destroyed when "refcount" becomes 0. When you unset() a variable, the refcount in the desired "zval" will be reduced by 1. Let's talk about what we encountered a few days ago. unset reference problem:

Copy code The code is as follows:

$a = "aaa";
$ b = & $a;
unset($a);
//echo $b; //aaa will still be output here, you will know why if you print it with xdebug_debug_zval
xdebug_debug_zval("b");

Result:

b:
(refcount=1, is_ref=0), string 'aaa' (length=3)
Continuing to talk about the reference counter issue, the situation is different for array and object types:

Copy code The code is as follows:

$arr = array( 'a' => 'aaa', 'b' => "bbb" );
xdebug_debug_zval( 'arr' );
$arr['aaa'] = $arr['a'];
xdebug_debug_zval( ' arr' );
?>

Result:

arr:
(refcount=1, is_ref=0),
array
'a' => (refcount=1, is_ref=0), string 'aaa' (length=3)
'b' => (refcount=1, is_ref=0),string 'bbb' (length=3)
arr:
(refcount=1, is_ref=0),
array
'a' => (refcount=2, is_ref=0),string 'aaa' (length=3)
'b' => (refcount=1, is_ref=0),string 'bbb ' (length=3)
'aaa' => (refcount=2, is_ref=0),string 'aaa' (length=3)

You can see that the original array elements and the newly added array elements are associated with the same zval variable container of "refcount" 2. Here I am just trying to inspire others.

For details about PHP reference counters, please refer to the manual: http://php.net/manual/zh/features.gc.refcounting-basics.php

http://www.bkjia.com/PHPjc/327870.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/327870.htmlTechArticleIf you have xdebug installed, you can use xdebug_debug_zval() to display "zval" information. As follows: Copy the code The code is as follows: ?php $str = "jb51.net"; xdebug_debug_zval('str'); Result:...