Detailed explanation of the operating mechanism and implementation principles of PHP core

PHP is a popular open source server-side scripting language that is heavily used for web development. It can handle dynamic data and control HTML output, but how to achieve this? Then, this article will introduce the core operating mechanism and implementation principles of PHP, and use specific code examples to further illustrate its operating process.

PHP source code interpretation

PHP source code is a program written in C language. After compilation, the executable file php.exe is generated. For PHP used in Web development, it is generally executed during execution. Run through a web server such as Apache or Nginx. Among the files executed by PHP, the core is Zend Engine. Zend Engine is the core manager of PHP, which is responsible for converting PHP source code into machine code that the operating system can understand.

Zend Engine mainly consists of two parts, namely Zend Compiler and Zend Executor. Zend Compiler is used to compile PHP code into an intermediate code called opcode. Zend Executor is an interpreter of PHP code, which can run opcode on the local computer.

After writing PHP code, it will first be compiled into bytecode by Zend Compiler, and this bytecode is stored directly in memory. From a performance perspective, this compilation method is more efficient. Because before the file is compiled into opcode, we can use Zend Compiler to optimize the code to achieve higher execution efficiency. For developers who write open source libraries or frameworks, this is a very effective way to greatly improve code execution efficiency while ensuring security and scalability.

PHP runtime mechanism

After the PHP code is compiled, Zend Engine will execute opcode. For a local computer, it does not understand what opcode is, so it needs Zend Engine to parse and execute it. We may wonder, how is the execution of opcode implemented?

Zend Engine will parse the opcode into a function call corresponding to the C language. In this process, some Zend virtual machine data types will be used, such as zval, HashTable, zend_class_entry, etc. These data types are Zend's internal data types and are used to represent different PHP syntax structures and variable types. During this process, Zend Engine will convert some data types into data types that the local computer can directly operate, such as long, double, char, etc. This approach optimizes efficiency throughout the entire process.

The built-in functions in PHP are built based on structures such as zend_function_entry. Developers can also use this method to quickly build their own built-in functions when developing PHP extensions or modules.

The execution process of PHP code can be observed through debugging tools. Using debugging tools like XDebug, you can perform breakpoint debugging, single-step execution, etc. during the execution of PHP code.

If you want to learn more about the internal implementation of PHP, please take a look at the code example below.

Code example

// example1.php
$a = 1;
$b = 2;
$c = $a $b;
echo $c;

The above code will be compiled into the following opcode by Zend Compiler.

number of ops: 5
compiled vars: !0 = $a, !1 = $b, !2 = $c

line #* E I O op fetch ext return operands

3 0 E > ASSIGN !0, 1
4 1 ASSIGN !1, 2
5 2 ADD !2, !0, !1
6 3 ECHO !2
7 4 > RETURN 1

In the above opcode, there are some mark bits that describe the execution process of the opcode. For example, "E" indicates that this opcode will produce side effects and so on. For a description of these flag bits, you can view PHP's official documentation.

You can use the following command to convert the above code into opcode.

php -dextension=opcache.so -dvld.active=1 -dvld.execute=0 example1.php

You can use VLD (VLD is Zend’s opcode interpretation plug-in, which can convert PHP code The opcode is forwarded and displayed) plug-in to view the generated opcode:

$ php -dextension=vld.so example1.php
Finding entry points
Branch analysis from position: 0
Return found
filename: /home/user/example1.php
function name: (null)
number of ops: 5
compiled vars: !0 = $a, !1 = $b, !2 = $c

#line #* E I O op fetch ext return operands

3 0 E > ASSIGN !0, 1
4 1 ASSIGN !1, 2
5 2 ADD ! 2, !0, !1
6 3 ECHO !2

     4      > RETURN        1

$

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