PHP source code analysis: stored procedure decomposition of variables_PHP tutorial

The PHP code is as follows:

Copy code The code is as follows:

$php_var = 1;

The corresponding code for C is:

Copy code The code is as follows:

zval* c_var; //Define PHP variable pointer
MAKE_STD_ZVAL(c_var); //Initialize PHP variables
ZVAL_LONG(c_var,1);//Assignment
ZEND_SET_SYMBL( EG(active_symbol_table), " php_var ", c_var);//Register to the global variable symbol table

1. First look at the first line: zval* c_var;//Declare a zval pointer c_var; The structure of zval is as follows:

Copy code The code is as follows:

struct _zval_struct {
/* Variable information */
zvalue_value value; /* The value of the variable */
zend_uint refcount; /* Reference counting, used during garbage collection */
zend_uchar type; /* Variable type */
zend_uchar is_ref; /* Is it a reference variable? */
};
typedef struct _zval_struct zval;

The structure of the value zvalue_value is as follows:

Copy code The code is as follows:

typedef union _zvalue_value {
long lval; /* Long shaping*/
Double dval; /* Double precision type */
struct { struct { /* string type value */
char *val; char *val;
int len;
} str;
HashTable *ht; /* Array type value */
zend_object_value obj; /*Value of object type*/
} zvalue_value;

2. Next, look at the second line: MAKE_STD_ZVAL(new_val);//Variable initialization. The relevant macros are as follows: //Initialization

Copy code The code is as follows:

#define MAKE_STD_ZVAL(zv)                                                           ALLOC_ZVAL(zv);
INIT_PZVAL(zv);

#define ALLOC_ZVAL(z)
ZEND_FAST_ALLOC(z, zval, ZVAL_CACHE_LIST)

#define ZEND_FAST_ALLOC(p, type, fc_type)
(p) = (type *) emalloc(sizeof(type))

#define INIT_PZVAL(z)
(z)->refcount = 1; (z)->refcount = 1;
(z)->is_ref = 0;

After expansion:

Copy code The code is as follows:

(c_var) = (zval *) emalloc(sizeof(zval)); //Allocate memory
(c_var)-> refcount = 1; //Reference count initialization
(c_var)-> is_ref = 0; //Whether to quote

You can see that its function is to allocate memory, initialize refcount, is_ref

3. Let’s look at the third line ZVAL_LONG(c_var,1). The related macro is:

Copy code The code is as follows:

//Define value
#define ZVAL_LONG(z, l) {                                                                       Z_TYPE_P(z) = IS_LONG;
​​Z_LVAL_P(z) = l; ​​ ​  
}
#define Z_TYPE_P(zval_p) Z_TYPE(*zval_p)
#define Z_TYPE(zval) (zval).type
#define Z_LVAL_P(zval_p) Z_LVAL(*zval_p)
#define Z_LVAL(zval) (zval).value.lval

Expanded to:

Copy code The code is as follows:

(* c_var).type = IS_LONG;
(* c_var).value = 1;

Four: Next, look at the fourth line: ZEND_SET_SYMBOL( EG(active_symbol_table), “php_var”, c_var); First, let’s explain that PHP variables are stored in a hashtable

Copy code The code is as follows:

struct _zend_executor_globals {
….
HashTable symbol_table;//Symbol table of global variables
HashTable *active_symbol_table;//Symbol table of local variables
…..
};  

The key of Hashtable is the name of the variable, that is, php_var, and the value is the pointer to the PHP variable, that is, the c_var pointer; the relevant macros are:

Copy code The code is as follows:

#define ZEND_SET_SYMBOL(symtable, name, var)                                              char *_name = (name); char *_name = (name); ZEND_SET_SYMBOL_WITH_LENGTH(symtable, _name, strlen(_name)+1, var, 1, 0);
}
//The main implementation is the following function:
#define ZEND_SET_SYMBOL_WITH_LENGTH(symtable, name, name_length, var, _refcount, _is_ref)                                                           {                                                                              zval **orig_var; If (zend_hash_find(symtable, (name), (name_length), (void **) &orig_var)==SUCCESS                                                       && PZVAL_IS_REF(*orig_var)) {                                                       (var)->refcount = (*orig_var)->refcount; (var)->refcount; (var)->refcount; (var)->is_ref = 1; (var)->is_ref = 1;                if (_refcount) {                                            (var)->refcount += _refcount-1; (var)->refcount += _refcount-1;
                                                                                                             zval_dtor(*orig_var);              **orig_var = *(var);                                                                            FREE_ZVAL(var);                                
        } else {                                               
            (var)->is_ref = _is_ref;                               
            if (_refcount) {                                       
                (var)->refcount = _refcount;                       
            }                                              
            zend_hash_update(symtable, (name), (name_length), &(var), sizeof(zval *), NULL);                                                            
        }                                                   
    }            

该函数的功能是：
1. 如果全局符号表已经存在该变量且是引用类型，则

a. 将原来变量的引用计数refcount，is_ref信息赋给c_var;
b. 释放掉原来变量zvalue的值，比如原来其值指向的是一个mysql连接资源，则释放该资源。
c. 将c_var指向的变量赋值给原来的变量 d. 释放c_var的内存空间 这样保证了，如果变量被应用，值一起改变。比如如果前面有$b=&a;

2. 如果全局符号表不存在该变量或者存在该变量但不是引用变量，则直接改变其值。

http://www.bkjia.com/PHPjc/824657.htmlwww.bkjia.comtruehttp://www.bkjia.com/PHPjc/824657.htmlTechArticlePHP代码如下： 复制代码 代码如下: $php_var = 1; 对应C的代码是： 复制代码 代码如下: zval* c_var; //定义PHP变量指针 MAKE_STD_ZVAL(c_var); //初始化...