深入理解PHP之OpCode原理详解

本文实例讲述了PHP中OpCode的原理。分享给大家供大家参考，具体如下：

OpCode是一种PHP脚本编译后的中间语言，就像Java的ByteCode,或者.NET的MSL。 此文主要基于《 Understanding OPcode》和 网络，根据个人的理解和修改，特记录下来 ：

PHP代码：

<?php  echo "Hello World";  $a = 1 + 1;  echo $a;?>

PHP执行这段代码会经过如下4个步骤：

1. Scanning (Lexing) ,将PHP代码转换为语言片段(Tokens)
2. Parsing , 将Tokens转换成简单而有意义的表达式
3. Compilation , 将表达式编译成Opocdes
4. Execution , 顺次执行Opcodes，每次一条，从而实现PHP脚本的功能。

注：现在有的Cache比如：APC ，可以使得PHP缓存Opcodes ，这样，每次有请求来临的时候，就不需要重复执行前面3步，从而能大幅的提高PHP的执行速度。

首先，Zend/zend_language_scanner.c 会根据Zend/zend_language_scanner.l(Lex文件)，来对输入的 PHP代码进行词法分析，从而得到一个一个的“词”，PHP4.2+开始提供了一个函数叫token_get_all ，这个函数就可以讲一段PHP代码 Scanning成Tokens；

<?php$tokens = token_get_all('<?php  echo "Hello World";  $a = 1 + 1;  echo $a;?>');print_r($tokens);?>

将会得到如下结果：

Array(  [0] => Array    (      [0] => 367      [1] => <?php      [2] => 1    )  [1] => Array    (      [0] => 370      [1] =>      [2] => 2    )  [2] => Array    (      [0] => 316      [1] => echo      [2] => 2    )  [3] => Array    (      [0] => 370      [1] =>      [2] => 2    )  [4] => Array    (      [0] => 315      [1] => "Hello World"      [2] => 2    )  [5] => ;  [6] => Array    (      [0] => 370      [1] =>      [2] => 2    )  [7] => Array    (      [0] => 309      [1] => $a      [2] => 3    )  [8] => Array    (      [0] => 370      [1] =>      [2] => 3    )  [9] => =  [10] => Array    (      [0] => 370      [1] =>      [2] => 3    )  [11] => Array    (      [0] => 305      [1] => 1      [2] => 3    )  [12] => Array    (      [0] => 370      [1] =>      [2] => 3    )  [13] => +  [14] => Array    (      [0] => 370      [1] =>      [2] => 3    )  [15] => Array    (      [0] => 305      [1] => 1      [2] => 3    )  [16] => ;  [17] => Array    (      [0] => 370      [1] =>      [2] => 3    )  [18] => Array    (      [0] => 316      [1] => echo      [2] => 4    )  [19] => Array    (      [0] => 370      [1] =>      [2] => 4    )  [20] => Array    (      [0] => 309      [1] => $a      [2] => 4    )  [21] => ;  [22] => Array    (      [0] => 370      [1] =>      [2] => 4    )  [23] => Array    (      [0] => 369      [1] => ?>      [2] => 5    ))