In-depth understanding of PHP principles and execution cycle analysis, in-depth understanding of php_PHP tutorial

In-depth understanding of the execution cycle analysis of PHP principles, in-depth understanding of php

This article describes the execution cycle of PHP principles. Share it with everyone for your reference, the details are as follows:

The execution cycle of PHP, from the initial PHP script we wrote -> to the final script being executed -> getting the execution result, this process can actually be divided into the following stages:

First, Zend Engine (ZE) calls the lexical analyzer (generated by Lex, the source file is in Zend/zend_language_sanner.l), removes spaces and comments from the PHP source file we want to execute, and divides it into tokens one by one. .

Then, ZE will forward the obtained token to the syntax analyzer (generated by yacc, the source file is in Zend/zend_language_parser.y), and generate opcodes one by one. The opcodes generally exist in the form of op array, which is executed by PHP. intermediate language.

Finally, ZE calls zend_executor to execute the op array and output the results. (That is, convert the source file into machine language and then run it on a virtual machine.)

ZE is a virtual machine. It is precisely because of its existence that we can write PHP scripts without considering the type of operating system. This is the reason for PHP's portability. ZE is a CISC (Complex Instruction Processor), which supports 150 instructions (specific instructions are in Zend/zend_vm_opcodes.h), including the simplest ZEND_ECHO (echo) to the complex ZEND_INCLUDE_OR_EVAL (include, require), All the PHP we write will eventually be processed into a sequence of these 150 instructions (op code), and will eventually be executed .

PHP is a scripting language, that is to say, the PHP code written by the user will eventually be interpreted and executed by the PHP interpreter. All PHP codes written will be translated into virtual instructions (OPCODES) of the PHP virtual machine ZE to execute.

So what is our PHP script ultimately "translated" into? In other words, what does the op code look like? Opcode is an intermediate language compiled from PHP scripts.

There is already such a module in PECL, utilizing the VLD (Vulcan Logic Dissassembler) module developed by Derick Rethans. You only need to download this module and load it into PHP, and you can get the result of script translation through simple settings.

Installation and application of VLD module:

[root@localhost software]# tar zxvf vld-0.9.1.tgz.gz
[root@localhost vld-0.9.1]# /usr/local/php/bin/phpize
[root@localhost vld-0.9.1]# ./configure --with-php-config=/usr/local/php/bin/php-config
[root@localhost vld-0.9.1]# make install //不需要make

Edit the php.ini file and activate the vld extension.

Example:

Create a file, such as: hello.php

<&#63;php
  echo 'hello, world.';
&#63;>

Execution:

[root@localhost html]# /usr/local/php/bin/php -dvld.active=1 hello.php
Branch analysis from position: 0
Return found
filename:    /var/www/html/hello.php
function name: (null)
number of ops: 3
compiled vars: none
line   # op              fetch     ext return operands
-------------------------------------------------------------------------------
  2   0 ECHO                           'hello%2C+world.'
  4   1 RETURN                          1
     2* ZEND_HANDLE_EXCEPTION
hello, world.

Watch another one:

[root@localhost html]# vi vld.php
<&#63;php
  $i = "This is a string";
  //I am comments
  echo $i. ' that has been echoed on screen';
&#63;>

Execution:

[root@localhost html]# /usr/local/php/bin/php -dvld.active=1 vld.php
Branch analysis from position: 0
Return found
filename:    /var/www/html/vld.php
function name: (null)
number of ops: 5
compiled vars: !0 = $i
line   # op              fetch     ext return operands
-------------------------------------------------------------------------------
  3   0 ASSIGN                          !0, 'This+is+a+string'
  7   1 CONCAT                      ~1  !0, '+that+has+been+echoed+on+screen'
     2 ECHO                           ~1
 10  3 RETURN                          1
     4* ZEND_HANDLE_EXCEPTION
This is a string that has been echoed on screen

Note: ZEND_HANDLE_EXCEPTION is the 149th instruction in Zend/zend_vm_opcodes.h

compiled vars: !0 = $i Here is the variable name "i" obtained from !0 (*zval).
#0 Assign the string "this is a string" (ASSIGN) to !0
#1 String concatenation
#2 Show

These intermediate codes will be executed directly by Zend VM (Zend Virtual Machine). The function actually responsible for execution is: zend_execute (zend_execute.h).

Readers who are interested in more PHP-related content can check out the special topics on this site: "Summary of PHP mathematical operation skills", "Summary of PHP operating office document skills (including word, excel, access, ppt)", "PHP array ( Array) operating skills collection", "php sorting algorithm summary", "php common traversal algorithms and techniques summary", "php data structure and algorithm tutorial", "php programming algorithm summary", "php regular expression usage summary", "Summary of PHP operations and operator usage", "Summary of PHP string usage" and "Summary of common PHP database operation skills"

I hope this article will be helpful to everyone in PHP programming.

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