php处理包含文件

Question

This question has to do with the internal mechanics of the PHP engine. I'm asking it in an effort to understand the file include process.

Say, you got a 20,000 lines include file ( something like "functions_library.php" ) that gets included on all your php scripts.

Does PHP check/verify if that include file is syntactically correct every single time one of your php scripts load that file? Does this process happen at each page load over and over and over again?

Or...

Does PHP pay attention to the file's last modification date? If it turns out that there were no changes to it since the last check, does it simply ignore the checking?

Answer 1

On a default installation, the file will be parsed every single time. However, any production installation of PHP is recommended to have a bytecode cache, such as APC or many others . When bytecode cache is used, the script is parsed the first time and the interpreted code will be stored in memory.

Different configurations may alter how often file modifications are checked. Under some configurations, for very high performance, manual flushing or restarting the web server may be required.

Answer 2

如果包含该文件，PHP将需要每次都解释它。

Answer 3

PHP will re-interpret the file every time you call include() .

This can be tested visually with the use of variables. If you have something like this:

otherScript.php:
   <?php echo $foo; ?>

script.php:
    <?php
    $foo = 1;
    include("otherScript.php");
    $foo = 2;
    include("otherScript.php");
    ?>

The output will be:

12

This is a poor example, but it should demonstrate the PHP will need to include the contents of the file each time. It is a pretty good guess to state that the PHP interpreter won't keep a copy of the included file in memory for each reference - there can be hundreds of includes per application.

To deal with this specific ideal, however, they provide a method include_once() that will, as the name implies, only include the file one time and prevent it from being included any additional times.