


Analysis of Strange PHP Reference Efficiency Issues_PHP Tutorial
The function is as follows:
function update_timelist(&$arr,$timestamp,$threshold){
$timequeue = &$arr['timequeue'];
while(!empty($timequeue[0])&&($timestamp-$timequeue[0])>$threshold){
array_shift( $timequeue);
}
array_push($timequeue, $timestamp);
if($arr['count']
}
}
Do you see any problems with this function? In fact, there is a big problem in the function:
$timequeue = &$arr['timequeue'];
This line causes the program to read 22M data and generate a time node linked list It took nearly 40 seconds, but deleting the line and using $arr['timequeue'] directly shortened the time by 30 seconds. It only took about 10 seconds to process 22M.
function update_timelist(&$arr,$timestamp,$threshold){
while (!empty($arr['timequeue'][0])&&($timestamp-$arr['timequeue'][0])>$threshold){
array_shift($arr['timequeue']) ;
}
array_push($arr['timequeue'], $timestamp);
if($arr['count']
}
Do you see what the problem is? The problem is with the count function, I didn’t think of it. PHP marks the real content space pointed by the variable as reference type and non-reference type, like the following code:
$a = 'jb51.net';
$b = $a;
$c = $b;
Only one copy of the actual memory space is occupied because PHP's zend engine uses the copy on writing mechanism. It will only copy 'jb51.net' when $b and $c are modified. At this time, the content space type of 'jb51.net' is a non-reference type. If Change to the following code:
$a = 'jb51.net';
$b = $a;
$c = &$a;
What will happen to this? Is it still a memory space to store 'jb51.net'? No, because $c is a reference to $a, and the storage space pointed to by $a needs to be marked as a reference type, then a separate copy of 'jb51.net' must be made for $b, because $b points to a non-reference type. .
We can understand it this way, $c is now a reference to $a. If $b still executes the space of $a, then modifying $c will cause $b to be modified as well. Therefore, once a reference appears at this time, even if there is no write operation, it must Made a copy. It can also be understood that PHP has only two types of memory space pointed to by variables: non-reference and reference. The two types cannot be mixed or transferred. If you need to change the state of the memory space somewhere, you need to make a copy.
The following explains why adding $timequeue = &$arr['timequeue'] will cause count to slow down. Do you remember the calling process of the c function? In fact, the parameters we pass in need to be copied and passed in. The same is true for PHP. However, due to the copy on writing mechanism, count will not actually be copied when passing in non-reference types, but $timequeue = &$arr['timequeue '] specifies the memory space of $timequeue as a reference type, and count requires a non-reference type, which causes count to need to copy a copy of $arr['timequeue']. Why is there no problem if I pass $arr['timequeue'] directly? Of course count uses the copy on writing mechanism. What about array_shift and array_push? They are passed in references. Don't worry, this is not modifying the type of $arr['timequeue'] but actually passing in an alias of $arr['timequeue'].
I have just started learning PHP. The above analysis may not be correct or comprehensive. You can send emails and leave messages on my homepage to communicate with me.

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

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

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

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

If you are an experienced PHP developer, you might have the feeling that you’ve been there and done that already.You have developed a significant number of applications, debugged millions of lines of code, and tweaked a bunch of scripts to achieve op

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.
