PHP7 Core Development Principles Explained: From Basics to Advanced PHP Kernel Mechanisms

1. Introduction to PHP7 Core Development Principles

PHP7 is one of the most widely used PHP versions, but many developers have a vague understanding of PHP's core development principles. In this article, we will start from scratch and explain the design and implementation principles of the PHP kernel, helping you gain a deeper understanding of the PHP internals.

2. PHP Kernel Encapsulation

In the development of PHP7, the PHP kernel adopts an object-oriented encapsulation approach, grouping related functionality into respective PHP classes. Developers simply instantiate these classes and call the provided APIs to use the corresponding features.

2.1 String Encapsulation

Strings in PHP are composed of multiple characters, and here is an example of creating a string:

$str = 'Hello World';

In the PHP kernel, string encapsulation is handled by the zend_string structure. Here is the definition of the zend_string structure:

struct _zend_string {
    zend_refcounted_h gc;
    zend_ulong        h;
    size_t            len;
    char              val[1];
};
        

The zend_string structure implements automatic memory management, greatly reducing the burden on developers.

2.2 Array Encapsulation

Arrays are a very commonly used data structure in PHP, used to store multiple elements of the same type. In PHP7, arrays are implemented using HashTable. Here is an example of using an array in PHP:

$arr = array('apple', 'banana', 'orange');

In the PHP kernel, the HashTable is a structure that stores key-value pairs, where both keys and values can be of any type. The definition of the HashTable structure is as follows:

typedef struct _hashtable {
    uint32_t               nTableSize;       /* Table size */
    uint32_t               nTableMask;       /* Used for traversing the existing hash table, must be a power of 2 */
    uint32_t               nNumOfElements;   /* Current number of elements in the hash table */
    uint32_t               nNextFreeElement; /* The smallest unused index */
    Bucket                *pInternalPointer; /* Pointer to the current element */
    Bucket                 *pListHead;       /* Points to the first doubly linked list of the Bucket array */
    Bucket                 *pListTail;       /* Points to the last doubly linked list of the Bucket array */
    Bucket                **arBuckets;       /* Hash table */
    dtor_func_t            pDestructor;      /* Destructor function pointer */
    zend_bool              persistent;        /* Persistence */
    unsigned char          nApplyCount;       /* Recursive counter */
    zend_bool              bApplyProtection; /* Prevent modifications during hash table traversal */
    zend_bitset            *pInternalPointerMap; /* Mapping for pInternalPointer */
    unsigned char          nIteratorsCount;   /* Number of iterators */
} HashTable;
        

Using the Bucket array in HashTable, developers can access the key-value pairs of each element, and insertions and deletions are handled via the provided API.

3. PHP Kernel Memory Management Mechanisms

PHP's memory management primarily involves two mechanisms:

3.1 zend_mm Mechanism

The zend_mm mechanism is a commonly used and mature memory management technique in the PHP kernel, aimed at reducing memory allocation frequency. Reusable memory is cached in zend_mm for future use.

3.2 GC Garbage Collection Mechanism

PHP implements its own GC garbage collection mechanism, based on reference counting, which reduces the overhead of manual memory management. This automatic memory management is implemented within the Zend Engine, easing the developers' burden.

4. PHP7 Module Development

PHP's kernel supports modular development, and custom modules can be developed using dynamic link libraries. The typical steps for developing PHP modules are as follows:

4.1 Defining a Module

The first step in module development is to define the module's basic properties. The module information can be defined using the zend_module_entry structure, as shown below:

zend_module_entry mytest_module_entry = {
    STANDARD_MODULE_HEADER,
    PHP_MYTEST_EXTNAME,
    NULL,   /* Functions */
    NULL,   /* MINIT */
    NULL,   /* MSHUTDOWN */
    NULL,   /* RINIT */
    NULL,   /* RSHUTDOWN */
    NULL,   /* MINFO */
    PHP_MYTEST_VERSION,
    STANDARD_MODULE_PROPERTIES
};
        

4.2 Defining PHP Functions

Once a module is loaded, its functions can be called. Functions are defined using the zend_function_entry structure, as shown below:

const zend_function_entry mytest_functions[] = {
    PHP_FE(mytest_hello, NULL)
    PHP_FE_END
};
        

4.3 Compiling and Installing a Module

After module development, it needs to be compiled into a .so library and installed into the PHP module directory. PHP provides tools such as phpize and configure to compile and install modules.

5. Conclusion

In this article, we explored the core principles of PHP's internal development, covering zend_string, HashTable encapsulation, zend_mm mechanism, GC garbage collection, and module development. We hope this article helps you gain a deeper understanding of PHP's internals and assists you in applying these concepts in your real-world development.