


It is recommended not to use include_once (require_once) as much as possible
This article is a detailed analysis and introduction to the reasons not to use (include/require)_once. Friends in need can refer to
About use include or include_once (hereinafter, all include require_once), this discussion has been long, and the conclusion has always been, that is, try to use include instead of include_once. In the past, the most common reason was, include_once needs to query the loaded file list, confirm whether it exists, and then load it again.
Admittedly, this reason is correct, but what I want to talk about today is another reason.
We know that to determine whether a file is loaded, PHP needs to get the open_path of the file, which means, for example:
Copy code The code is as follows:
<?php set_include_path ("/tmp/:/tmp2/"); include_once("2.php"); ?>
When PHP sees include_once "2.php", it does not know what the actual path of this file is, and it cannot go from the loaded file list Determine whether it has been loaded, so in the implementation of include_once, it will first try to parse the real path of the file (for ordinary files, this parsing is just like checking getcwd and the file path, so if it is a relative path, it will generally not succeed), if If the parsing is successful, search for EG (include_files). If it exists, it means it has been included and returns. Otherwise, open the file and get the opened_path of the file. For example, in the above example, this file exists in "/tmp2/2.php".
Then, after getting the opened_path, PHP goes to the loaded file list to find out whether it is included. If not, then compile directly, and open file is no longer needed.
1. Try to parse the absolute path of the file. If the parsing can be successful, check EG (included_files), return if it exists, and continue if it does not exist.
2. Open the file and get the open path of the file
3. Use the open path to search EG (included_files) to see if it exists. If it exists, return it. If it does not exist, continue.
4. Compile file (compile_file)
In most cases, Not a problem, but the problem is when you use APC...
When using APC, APC hijacks the compile_file pointer to the compiled file, thereby getting the compilation result directly from the cache, avoiding the need to modify the actual file open, avoiding the system call to open.
However, when you use include_once in your code, before compile_file, PHP has already tried to open the file, and then entered the compile file hijacked by APC In this way, an additional open operation will be generated. To solve this problem, APC introduces include_once_override. When include_once_override is turned on, APC will hijack PHP's ZEND_INCLUDE_OR_EVAL opcode handler and determine the file's size through stat. Absolute path, and then if it is found that it is not loaded, rewrite the opcode to include and make a tricky solution.
But, unfortunately, as I said, APC's include_once_override implementation has not been good, and there will be some Undefined problems, such as:
Copy code The code is as follows:
<?php set_include_path("/tmp"); function a($arg = array()) { include_once("b.php"); } a(); a(); ?>
Then, our b.php is placed in "/tmp/ b.php", the content is as follows:
The code is as follows:
<?php class B {} ?>
Then when apc.include_once_override is turned on, continuous access will get the following error:
Fatal error - include() : Cannot redeclare class b
Excluding these technical factors, I have always believed that we should use include instead of include_once, because we can completely plan a file by ourselves It is only loaded once. You can also use automatic loading to do this.
If you use include_once, it only proves that you have no confidence in your code.
So, I suggest everyone not to use include_once
The above is the detailed content of It is recommended not to use include_once (require_once) as much as possible. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

Magnet link is a link method for downloading resources, which is more convenient and efficient than traditional download methods. Magnet links allow you to download resources in a peer-to-peer manner without relying on an intermediary server. This article will introduce how to use magnet links and what to pay attention to. 1. What is a magnet link? A magnet link is a download method based on the P2P (Peer-to-Peer) protocol. Through magnet links, users can directly connect to the publisher of the resource to complete resource sharing and downloading. Compared with traditional downloading methods, magnetic

How to use mdf files and mds files With the continuous advancement of computer technology, we can store and share data in a variety of ways. In the field of digital media, we often encounter some special file formats. In this article, we will discuss a common file format - mdf and mds files, and introduce how to use them. First, we need to understand the meaning of mdf files and mds files. mdf is the extension of the CD/DVD image file, and the mds file is the metadata file of the mdf file.

CrystalDiskMark is a small HDD benchmark tool for hard drives that quickly measures sequential and random read/write speeds. Next, let the editor introduce CrystalDiskMark to you and how to use crystaldiskmark~ 1. Introduction to CrystalDiskMark CrystalDiskMark is a widely used disk performance testing tool used to evaluate the read and write speed and performance of mechanical hard drives and solid-state drives (SSD). Random I/O performance. It is a free Windows application and provides a user-friendly interface and various test modes to evaluate different aspects of hard drive performance and is widely used in hardware reviews

foobar2000 is a software that can listen to music resources at any time. It brings you all kinds of music with lossless sound quality. The enhanced version of the music player allows you to get a more comprehensive and comfortable music experience. Its design concept is to play the advanced audio on the computer The device is transplanted to mobile phones to provide a more convenient and efficient music playback experience. The interface design is simple, clear and easy to use. It adopts a minimalist design style without too many decorations and cumbersome operations to get started quickly. It also supports a variety of skins and Theme, personalize settings according to your own preferences, and create an exclusive music player that supports the playback of multiple audio formats. It also supports the audio gain function to adjust the volume according to your own hearing conditions to avoid hearing damage caused by excessive volume. Next, let me help you

NetEase Mailbox, as an email address widely used by Chinese netizens, has always won the trust of users with its stable and efficient services. NetEase Mailbox Master is an email software specially created for mobile phone users. It greatly simplifies the process of sending and receiving emails and makes our email processing more convenient. So how to use NetEase Mailbox Master, and what specific functions it has. Below, the editor of this site will give you a detailed introduction, hoping to help you! First, you can search and download the NetEase Mailbox Master app in the mobile app store. Search for "NetEase Mailbox Master" in App Store or Baidu Mobile Assistant, and then follow the prompts to install it. After the download and installation is completed, we open the NetEase email account and log in. The login interface is as shown below

After long pressing the play button of the speaker, connect to wifi in the software and you can use it. Tutorial Applicable Model: Xiaomi 12 System: EMUI11.0 Version: Xiaoai Classmate 2.4.21 Analysis 1 First find the play button of the speaker, and press and hold to enter the network distribution mode. 2 Log in to your Xiaomi account in the Xiaoai Speaker software on your phone and click to add a new Xiaoai Speaker. 3. After entering the name and password of the wifi, you can call Xiao Ai to use it. Supplement: What functions does Xiaoai Speaker have? 1 Xiaoai Speaker has system functions, social functions, entertainment functions, knowledge functions, life functions, smart home, and training plans. Summary/Notes: The Xiao Ai App must be installed on your mobile phone in advance for easy connection and use.

Cloud storage has become an indispensable part of our daily life and work nowadays. As one of the leading cloud storage services in China, Baidu Netdisk has won the favor of a large number of users with its powerful storage functions, efficient transmission speed and convenient operation experience. And whether you want to back up important files, share information, watch videos online, or listen to music, Baidu Cloud Disk can meet your needs. However, many users may not understand the specific use method of Baidu Netdisk app, so this tutorial will introduce in detail how to use Baidu Netdisk app. Users who are still confused can follow this article to learn more. ! How to use Baidu Cloud Network Disk: 1. Installation First, when downloading and installing Baidu Cloud software, please select the custom installation option.

Get started easily: How to use pip mirror source With the popularity of Python around the world, pip has become a standard tool for Python package management. However, a common problem that many developers face when using pip to install packages is slowness. This is because by default, pip downloads packages from Python official sources or other external sources, and these sources may be located on overseas servers, resulting in slow download speeds. In order to improve download speed, we can use pip mirror source. What is a pip mirror source? To put it simply, just
