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PHP5+引进$GLOBALS延迟初始化概念_PHP教程

时间:2021-07-01 10:21:17 帮助过:5人阅读

今天在使用$GLOBALS['_SERVER']来替代$_SERVER来访问相关的环境变量,总是会报“_SERVER undefined”错误。如下用例:

用例1:
print_r($GLOBALS);
此时输出中并没有_SERVER相关信息:
Array

[GLOBALS] => Array
*RECURSION*
[_POST] => Array


[_GET] => Array


[_COOKIE] => Array


[_FILES] => Array



用例2:
print_r($GLOBALS);
print_r($_SERVER);
此时输出中含有_SERVER相关信息:
Array

[GLOBALS] => Array
*RECURSION*
[_POST] => Array


[_GET] => Array


[_COOKIE] => Array


[_FILES] => Array


[_SERVER] => Array



查了下PHP手册关于$GLOBALS描述,引用therandshow at gmail dot com的评论:
therandshow at gmail dot com
As of PHP 5.4 $GLOBALS is now initialized just-in-time. This means there now is an advantage to not use
the $GLOBALS variable as you can avoid the overhead of initializing it. How much of an advantage that is
I'm not sure, but I've never liked $GLOBALS much anyways.
追根数源,发现PHP5Changelog更新日志的描述:
Unordered List ItemImproved Zend Engine, performance tweaks and optimizations
Unordered List ItemChanged $GLOBALS into a JIT autoglobal, so it's initialized only if used. (this may affect opcode caches!)www.2cto.com
718 ; When enabled, the SERVER and ENV variables are created when they're first
719 ; used (Just In Time) instead of when the script starts. If these variables
720 ; are not used within a script, having this directive on will result in a
721 ; performance gain. The PHP directives register_globals, register_long_arrays,
722 ; and register_argc_argv must be disabled for this directive to have any affect.
723 ; http://php.com/auto-globals-jit
724 auto_globals_jit = On
终于弄明白了,PHP5+中在开启auto_globals_jit = On情况下,$_SERVER变量和$_ENV变量不会在脚本启动时就创建,而是会在第一次使用$SERVER和$ENV时才会创建。所以就会出现上述两个用例的情况。


备注:
实测结论:
auto_globals_jit setting is also affecting $_REQUEST superglobal in 5.3 It is not explicitly stated in documentation.
至少5.3.13版本中开启auto_globals_jit = On情况下,$_REQUEST也只会在第一次使用时才会创建。

www.bkjia.comtruehttp://www.bkjia.com/PHPjc/735083.htmlTechArticle今天在使用$GLOBALS[_SERVER]来替代$_SERVER来访问相关的环境变量,总是会报_SERVER undefined错误。如下用例: 用例1: ?php print_r($GLOBALS); 此时...

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