cgi php-cgi, the underlying principles of PHP

一 Concept:

cgi

cgi (common gateway interface), common gateway interface. The protocol used when interacting between web servers (such as nginx) and script parsers (such as php-cgi). It specifies the format in which data such as the requested URL, http header, and post data should be passed to the script parser, and the format in which the script parser should return the http response.

fastcgi

fastcgi is an upgraded version of cgi protocol. Standard cgi will parse the configuration file of the corresponding script (such as php.ini) for each request, load the configuration and extensions, and initialize the execution environment. The performance is very poor. fastcgi adopts master-worker mode and resident memory strategy to improve response speed.

php-cgi

php's fastcgi implementation also serves as a php script parser responsible for running php scripts; the disadvantage is that process management and scheduling are poor.

php-fpm

is used to manage and schedule php-cgi processes, similar to spawn-fcgi

Two principles

First understand the workflow of ordinary cgi:
The web server receives the user request and Submit the request to the cgi program, the cgi program processes the parameters submitted in the request accordingly, and then outputs a standard html statement and returns it to the web server, and the web server returns it to the client. This is the working principle of ordinary cgi.
From the above, what cgi wants to achieve is nothing more than dynamic web pages. The characteristic of this processing method is that every time it receives a request, the web server has to fork out a separate cgi program process to process it. This way The advantage is that the web server is separated from specific program processing, with a clear structure and strong controllability. At the same time, the disadvantage is that if there is high access demand, the cgi process fork will become a huge server burden. Imagine the data You will understand if hundreds of concurrent requests cause the server to fork hundreds of processes. This is why cgi has always been notorious for low performance and high resource consumption.
There are solutions for corresponding problems. The currently popular solution is to use module design. Basically, the current web server has a corresponding module mechanism to expand its functions. As long as the module is designed according to its design specifications, It can be inserted into the process processing of the web server itself, so the performance is greatly improved, such as IIS's isapi and apache's dso. However, this method is not without its shortcomings. For example, different web servers must be developed according to different standards, and web server independence cannot be achieved; for example, this transfers the input verification work to the web server, and there is no way to handle it freely; for example, Once a problem occurs, it will affect the entire web Server processing flow; for example, the insertion of the web server process results in the inability to run as a multi-user label, the inability to process virtual host permissions, etc.
Fortunately, we have another choice, which is fastcgi. Fastcgi is an extension based on the CGI architecture. Its core idea is to establish an intelligent and sustainable middle layer between the web server and the specific CGI program to manage the operation of the CGI program, so that the web server only needs to submit requests to this layer. This layer then derives several reusable cgi program instances, and then distributes requests to these instances. These instances are controllable, sustainable, and reusable. Therefore, on the one hand, it avoids repeated forking of the process. On the other hand, the control and detection mechanism of the middle layer can be used to monitor the running status of these instances, and the instances can be forked or recycled according to different conditions to achieve both flexibility and stability. The underlying working principle of PHP ://www.nowamagic .net/librarys/veda/detail/102/

The above introduces cgi php-cgi, the underlying principles of PHP, including aspects of it. I hope it will be helpful to friends who are interested in PHP tutorials.