What is PHP garbage collection mechanism
The whole reason for implementing a garbage collection mechanism is to save memory usage by cleaning up circularly referenced variables.
-
Reference count: php variables exist in a variable container called "zval". A zval variable container, in addition to the type and value of the variable, also includes two bytes of additional information: is_ref and refcount. is_ref is a bool value, used to identify whether this variable belongs to a reference collection, so that the PHP engine can distinguish ordinary variables from reference variables; refcount is used to represent the number of variables pointing to this zval variable container. When refcount = 0, it means that the Variables can be cleared or recycled
<?php $a = array( 'meaning' => 'life', 'number' => 42 ); $a['life'] = $a['meaning']; xdebug_debug_zval( 'a' ); ?>
Copy after loginThe output of the above routine is as follows:
a: (refcount=1, is_ref=0)=array ( 'meaning' => (refcount=2, is_ref=0)='life', 'number' => (refcount=1, is_ref=0)=42, 'life' => (refcount=2, is_ref=0)='life' )
Copy after loginThe output of The results are as follows:
<?php $a = array( 'one' ); $a[] =& $a; xdebug_debug_zval( 'a' ); unset($a); xdebug_debug_zval( 'a' ); ?>
Copy after login
In the above example, although there is no longer any symbol in a scope pointing to this variable container, since the array element "1" still points to the array itself, this container cannot Cleared. Because there is no other symbol pointing to it, the user has no way to clear the structure, resulting in a memory leak. PHP will clear this data structure at the end of script execution, but before PHP clears it, it will consume a lot of memoryRecycling cycle: Can be used to deal with memory leaks caused by circular references. If the reference count of a variable container increases, it will continue to be used and of course will no longer be in the garbage; if the reference count decreases to zero, the variable container will be cleared (free). That is to say, a garbage cycle will occur only when the reference count is reduced to a non-zero value; secondly, in a garbage cycle, by checking whether the reference count is reduced by 1 (simulation), and checking which variable containers have references The number of times is zero, to find out which part is garbage
-
Turn on and off the garbage collection mechanism: In addition to modifying the configuration
zend.enable_gc , you can also turn on and off the garbage collection mechanism by calling the gc_enable() and - gc_disable() functions respectively. In addition,
Possible roots are recorded even when the garbage collection mechanism is unavailable, so that every time a possible root is found, it is not checked whether the garbage collection mechanism is turned on, and the recording operation is faster. Call the gc_collect_cycles() function to force cycle recycling.
In the above example, although there is no longer any symbol in a scope pointing to this variable container, since the array element "1" still points to the array itself, this container cannot Cleared. Because there is no other symbol pointing to it, the user has no way to clear the structure, resulting in a memory leak. PHP will clear this data structure at the end of script execution, but before PHP clears it, it will consume a lot of memoryThe above is the detailed content of What is PHP garbage collection mechanism. 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
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
1667
14
1426
52
1328
25
1273
29
1255
24
PHP: A Key Language for Web Development
Apr 13, 2025 am 12:08 AM
PHP is a scripting language widely used on the server side, especially suitable for web development. 1.PHP can embed HTML, process HTTP requests and responses, and supports a variety of databases. 2.PHP is used to generate dynamic web content, process form data, access databases, etc., with strong community support and open source resources. 3. PHP is an interpreted language, and the execution process includes lexical analysis, grammatical analysis, compilation and execution. 4.PHP can be combined with MySQL for advanced applications such as user registration systems. 5. When debugging PHP, you can use functions such as error_reporting() and var_dump(). 6. Optimize PHP code to use caching mechanisms, optimize database queries and use built-in functions. 7
PHP and Python: Comparing Two Popular Programming Languages
Apr 14, 2025 am 12:13 AM
PHP and Python each have their own advantages, and choose according to project requirements. 1.PHP is suitable for web development, especially for rapid development and maintenance of websites. 2. Python is suitable for data science, machine learning and artificial intelligence, with concise syntax and suitable for beginners.
PHP vs. Python: Understanding the Differences
Apr 11, 2025 am 12:15 AM
PHP and Python each have their own advantages, and the choice should be based on project requirements. 1.PHP is suitable for web development, with simple syntax and high execution efficiency. 2. Python is suitable for data science and machine learning, with concise syntax and rich libraries.
PHP in Action: Real-World Examples and Applications
Apr 14, 2025 am 12:19 AM
PHP is widely used in e-commerce, content management systems and API development. 1) E-commerce: used for shopping cart function and payment processing. 2) Content management system: used for dynamic content generation and user management. 3) API development: used for RESTful API development and API security. Through performance optimization and best practices, the efficiency and maintainability of PHP applications are improved.
The Enduring Relevance of PHP: Is It Still Alive?
Apr 14, 2025 am 12:12 AM
PHP is still dynamic and still occupies an important position in the field of modern programming. 1) PHP's simplicity and powerful community support make it widely used in web development; 2) Its flexibility and stability make it outstanding in handling web forms, database operations and file processing; 3) PHP is constantly evolving and optimizing, suitable for beginners and experienced developers.
PHP vs. Other Languages: A Comparison
Apr 13, 2025 am 12:19 AM
PHP is suitable for web development, especially in rapid development and processing dynamic content, but is not good at data science and enterprise-level applications. Compared with Python, PHP has more advantages in web development, but is not as good as Python in the field of data science; compared with Java, PHP performs worse in enterprise-level applications, but is more flexible in web development; compared with JavaScript, PHP is more concise in back-end development, but is not as good as JavaScript in front-end development.
PHP and Python: Different Paradigms Explained
Apr 18, 2025 am 12:26 AM
PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.
PHP and Python: Code Examples and Comparison
Apr 15, 2025 am 12:07 AM
PHP and Python have their own advantages and disadvantages, and the choice depends on project needs and personal preferences. 1.PHP is suitable for rapid development and maintenance of large-scale web applications. 2. Python dominates the field of data science and machine learning.
