Introduction to php life cycle

PHP operating mode:

The two operating modes of PHP are WEB mode and CLI mode. Regardless of the mode, PHP works the same, running as a SAPI.

1. When we type the php command in the terminal, it uses the CLI.

It is like a web server to support php to complete the request. After the request is completed, control is returned to the terminal.

2. When using Apache or another web server as the host, when a request comes, PHP will support the completion of the request. Generally:

• Multiple processes (usually compiled as apache module to handle PHP requests)

• Multi-threaded mode

Brief execution process:

1. PHP runs with the startup of Apache;

2. PHP is connected to Apache through the mod_php5.so module (specifically It is SAPI (Server Application Programming Interface);

3. PHP has three modules in total: kernel, Zend engine, and extension layer;

4. PHP kernel is used to process requests. File streams, error handling and other related operations;

5. Zend Engine (ZE) is used to convert source files into machine language and then run it on a virtual machine;

6. Extension layer Is a set of functions, libraries, and streams that PHP uses to perform specific operations. For example, we need the MySQL extension to connect to the MySQL database;

7. When ZE executes the program, it may need to connect to several extensions. At this time, ZE will hand over control to the extension and return it after processing the specific task;

8. Finally, ZE returns the program running results to the PHP kernel, which then transmits the results to the SAPI layer and finally outputs them to the browser.

Several stages of running PHP:

SAPI runs PHP through the following stages:

1. Module Initialization phase (Module init):

That is to call the method in PHP_MINIT_FUNCTION in each extension source code to initialize the module, apply for some variables required by the module, allocate memory, etc.

2. Request initialization phase (Request init):

After receiving the client's request, the method in each extended PHP_RINIT_FUNCTION is called to initialize the execution environment of the PHP script.

3. Execute PHP script

4. Request Shutdown:

At this time, the PHP_RSHUTDOWN_FUNCTION method of each extension is called to clean up the request site, and ZE starts to recycle variables and memory.

5. Module shutdown:

The PHP_MSHUTDOWN_FUNCTION method in the extension source code will be called when the web server exits or the command line script is executed.

SAPI life cycle under various circumstances

1. Single-process SAPI life cycle. (CGI)

CLI/CGI mode PHP belongs to the single-process SAPI mode. This type of request is closed after processing the request once. That is to say, each request will repeat these steps: start - request start - request close - end. You can see that the initialization of the extension consumes a lot of resources.

2. Multi-process SAPI life cycle. (MPM's perfork method)

Usually PHP is compiled into a module of apache to handle PHP requests (mod_php). Apache generally adopts multi-process mode. After Apache is started, it will fork out multiple child processes (apache can specify the number of processes to start forking out). The memory space of each process is independent, and each child process will go through the start and end stages as soon as it is focked.

3. Multi-threaded SAPI life cycle. (Single process in FastCGI or MPM work mode)

Multi-threaded mode is similar to a process in multi-process. In this mode, only one server process is running, but many will be running at the same time. Threads can reduce some resource overhead. Module init and Module shutdown only need to be run once. Some global variables only need to be initialized once. Because of the unique characteristics of threads, it is convenient to share some data between requests. possible.

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