php原理 - 风雪之隅

深入理解PHP内存管理之谁动了我的内存

Published on 4 March 2011 by laruence

首先让我们看一个问题: 如下代码的输出,

var_dump(memory_get_usage());
$a = "laruence";
var_dump(memory_get_usage());
unset($a);
var_dump(memory_get_usage());

输出(在我的个人电脑上, 可能会因为系统,PHP版本,载入的扩展不同而不同):

int(90440)
int(90640)
int(90472)

注意到 90472-90440=32, 于是就有了各种的结论, 有的人说PHP的unset并不真正释放内存, 有的说, PHP的unset只是在释放大变量(大量字符串, 大数组)的时候才会真正free内存, 更有人说, 在PHP层面讨论内存是没有意义的.
那么, 到底unset会不会释放内存? 这32个字节跑哪里去了?

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深入理解PHP内存管理之一个低概率Core的分析

Published on 27 January 2011 by laruence

一个同事forward过来一个, 公司某产品线遇到的一个低概率, 但长时间出现了几次的Core的bt信息, 找我帮忙分析下原因.
bt栈如下(路径信息以*代替):

#0  0x00000000004a75e5 in _zend_mm_alloc_int (heap=0xd61260, size=79)
at /*/php-5.2.6/Zend/zend_alloc.c:1879
#1  0x000000000048d3cd in vspprintf (pbuf=0x7fbffe9cd8, max_len=1024, format=Variable "format" is not available.
)
    at /*/php-5.2.6/main/spprintf.c:224
#2  0x0000000000489747 in php_error_cb (type=1, error_filename=0x2a9a787ee8 "/*/application/helpers/util.php",
    error_lineno=1149, format=Variable "format" is not available.
) at /*/php-5.2.6/main/main.c:799
#3  0x000000000061db35 in soap_error_handler (error_num=1,
    error_filename=0x2a9a787ee8 "/*/application/helpers/util.php", error_lineno=1149,
    format=0x7b9cb8 "Maximum execution time of %d second%s exceeded", args=0x7fbffea3b0)
    at /*/php-5.2.6/ext/soap/soap.c:2178
#4  0x00000000004c2576 in zend_error (type=1, format=0x7b9cb8 "Maximum execution time of %d second%s exceeded")
    at /*/php-5.2.6/Zend/zend.c:976
#5  <signal handler called>
#6  0x00000000004a720f in _zend_mm_free_int (heap=0xd61260, p=Variable "p" is not available.
) at /*/php-5.2.6/Zend/zend_alloc.c:844
...以下省略

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