Home > php教程 > php手册 > body text

PHP垃圾回收机制引用计数器概念分析

WBOY
Release: 2016-06-13 11:45:20
Original
1304 people have browsed it

如果你安装了xdebug,就可以用xdebug_debug_zval()显示“zval”的信息了。如下:

复制代码 代码如下:


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

结果:

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

只有当变量容器在”refcount“变成0时就被销毁.当你unset()一个变量时,想要的“zval”中refcount就会减1,再来说说前几天遇到的unset引用问题:

复制代码 代码如下:


$a = "aaa";
$b = & $a;
unset($a);
//echo $b; //这里依然会输出aaa,用xdebug_debug_zval打印你就知道为什么了
xdebug_debug_zval("b");

结果:

b:
(refcount=1, is_ref=0),string 'aaa' (length=3)
继续说引用计数器问题,对于array和object符合类型情况又不一样了:

复制代码 代码如下:


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

结果:

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)

可以看到看到原有的数组元素和新添加的数组元素关联到同一个"refcount"2的zval变量容器.这里我也只是起到抛砖引玉的作用。

具体关于PHP引用计数器可以参照手册:http://php.net/manual/zh/features.gc.refcounting-basics.php

source:php.cn
Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Popular Recommendations
Popular Tutorials
More>
Latest Downloads
More>
Web Effects
Website Source Code
Website Materials
Front End Template