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PHP5+引进$GLOBALS延迟初始化概念

时间:2013-01-28 14:56:00

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:
    <?php
    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 $GLOBALS into a JIT autoglobal, so it's initialized only if used. (this may affect opcode caches!)www.2cto.com
    718 ; When enabled, the SERVER and ENV variables are created when they're first
    719 ; used (Just In Time) instead of when the script starts. If these variables
    720 ; are not used within a script, having this directive on will result in a
    721 ; performance gain. The PHP directives register_globals, register_long_arrays,
    722 ; and register_argc_argv must be disabled for this directive to have any affect.
    723 ; http://php.net/auto-globals-jit
    724 auto_globals_jit = On
    终于弄明白了,PHP5+中在开启auto_globals_jit = On情况下,$_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。

 

来源:PHPchina

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