PHP5+ introduces the concept of $GLOBALS delayed initialization

Today I was sorting out the code and wanted to use $GLOBALS['_SERVER'] instead of $_SERVER to access related environment variables, but the "_SERVER undefined" error was always reported. The following use cases:

Use Case 1:

print_r($GLOBALS);

There is no _SERVER related information in the output at this time:

Array

(

[GLOBALS] => Array

*RECURSION*

[_POST] => Array

(

)

[_GET] => Array

(

)

[_COOKIE] => Array

(

)

[_FILES] => Array

(

)

Use Case 2:

print_r($GLOBALS);

print_r($_SERVER);

The output now contains _SERVER related information:

Array

(

[GLOBALS] => Array

*RECURSION*

[_POST] => Array

(

)

[_GET] => Array

(

)

[_COOKIE] => Array

(

)

[_FILES] => Array

(

)

[_SERVER] => Array

(

)

Check the description of $GLOBALS in the PHP manual and quote the comment of therandshow at gmail dot com:

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.

Chasing the source, I found the description of the PHP5Changelog update log:

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

Finally figured it out, in PHP5+, when auto_globals_jit = On is turned on, the $_SERVER variable and $_ENV variable will not be created when the script starts, but will be created when $SERVER and $ENV are used for the first time. create. So the above two use cases will appear.

Remarks:

Actual measurement conclusion:

auto_globals_jit setting is also affecting $_REQUEST superglobal in 5.3 It is not explicitly stated in documentation.

When auto_globals_jit = On is enabled in at least version 5.3.13, $_REQUEST will only be created the first time it is used.

Related labels：

server code use initialization Delay tidy concept of

source：php.cn

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