In-depth understanding of the underlying development principles of PHP: memory management and garbage collection mechanism

In-depth understanding of the underlying development principles of PHP: memory management and garbage collection mechanism

Introduction:

PHP, as a high-level programming language, is widely used in Web development. Many developers are familiar with PHP's syntax and features, but may have relatively little understanding of PHP's underlying development principles. This article will deeply explore the memory management and garbage collection mechanisms in the underlying development principles of PHP to help readers better understand the operating mechanism of PHP.

1. PHP’s memory management

1. Memory allocation and release

The memory management in PHP is handled by the Zend engine. During PHP execution, the Zend engine dynamically allocates memory as needed and releases the corresponding memory when it is no longer in use.

In PHP, memory allocation is usually achieved through the malloc() function, and memory release is achieved through the free() function. When more memory is needed during PHP execution, the Zend engine will call the malloc() function to allocate memory space for variables and data structures. When a variable or data structure is no longer used, the Zend engine will call the free() function to release the corresponding memory.

2. Memory Allocator

In PHP, the Zend engine uses a tool called a memory allocator to manage memory allocation and release. The role of the memory allocator is to allocate memory to different variables and data structures on demand, as well as return the memory to the system when it is no longer used.

There are two common memory allocators: heap and stack. The heap refers to the memory space dynamically allocated when the program is running, while the stack refers to the memory space allocated for functions, local variables, etc. during program execution.

In PHP, the Zend engine manages the allocation and release of heap memory through the memory allocator. When PHP needs to allocate more memory during execution, the memory allocator will allocate a large enough space from the heap for variables and data structures. When a variable or data structure is no longer used, the memory allocator returns the corresponding memory space to the heap.

2. PHP’s garbage collection mechanism

1. Reference counting method

PHP uses reference counting method for garbage collection. The reference counting method means that PHP maintains a reference counter for a variable and records the number of times the variable is referenced. When a variable is referenced, the reference counter is incremented by 1; conversely, when a reference is canceled, the reference counter is decremented by 1. When the reference counter reaches 0, it means that the variable is no longer referenced and can be recycled.

The reference counting method is a simple and efficient garbage collection mechanism, but there are also some problems. For example, when there is a circular reference, that is, two objects refer to each other, the reference counter will never be 0, causing a memory leak.

2. Mark-clear method

In order to solve the memory leak problem caused by circular references, PHP also introduced the mark-clear method for garbage collection. The mark-clear method means that when PHP performs garbage collection, it first finds all active objects through the root node, and then marks these active objects; then it traverses all objects in the heap and clears the unmarked objects.

The mark-clear method is more complex than the reference counting method, but it is also more comprehensive. Through the mark-sweep method, PHP can accurately determine which objects are not referenced and recycle them.

3. PHP optimization skills

1. Reduce memory usage

In PHP development, rational use of variables, data structures and garbage collection mechanisms can effectively reduce memory usage. Memory usage. For example, timely release variables and data structures that are no longer used to avoid memory leaks; use references appropriately to reduce unnecessary memory allocation, etc.

2. Use cache

The cache is used in PHP to store and reuse calculated results, reducing repeated calculations and thus improving performance. Common caching technologies include: memory cache, file cache, database cache, etc.

3. Optimization algorithm and query

When developing PHP, optimizing the core algorithm and database query statements can greatly improve the performance of PHP. For example, use appropriate data structures and algorithms to avoid unnecessary loops and recursions; use indexes and optimize database query statements, etc.

Conclusion:

This article provides an in-depth understanding of the memory management and garbage collection mechanisms in the underlying development principles of PHP, and introduces techniques on how to optimize PHP programs. Understanding and mastering PHP's memory management and garbage collection mechanisms can help developers make better use of PHP's features and functions to develop efficient and reliable Web applications. At the same time, through optimization techniques and methods, the performance and stability of PHP applications can be improved to meet user needs.

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