PHP源码分析之变量的存储过程分解

Z时代
2024-01-10
分类：综合

PHP代码如下：

$php_var = 1;

对应C的代码是：

zval* c_var;    //定义PHP变量指针  
MAKE_STD_ZVAL(c_var);  //初始化PHP变量  
ZVAL_LONG(c_var,1) ;//赋值  
ZEND_SET_SYMBL( EG(active_symbol_table), " php_var ", c_var);//注册到全局变量符号表

一．首先看第一行： zval* c_var;//申明一个zval指针c_var； zval的结构如下：


struct _zval_struct {  
    /* Variable information */  
    zvalue_value value;     /* 变量的值 */  
    zend_uint refcount;     /* 引用计数,垃圾回收的时候用到 */  
    zend_uchar type;        /* 变量类型 */  
    zend_uchar is_ref;      /* 是否为引用变量 */  
};  
typedef struct _zval_struct zval;

其中值zvalue_value的结构如下：


typedef union _zvalue_value {  
    long lval;              /* 长整形*/  
    double dval;            /* 双精度类型 */  
    struct {                  /* 字符串类型的值 */  
        char *val;              
        int len;  
    } str;  
    HashTable *ht;              /* 数组类型的值 */  
    zend_object_value obj;     /*对象类型的值*/  
} zvalue_value;

二．接下来看第二行: MAKE_STD_ZVAL(new_val);//变量初始化相关宏如下： //初始化


#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)->is_ref = 0;

展开后为：


(c_var) = (zval *) emalloc(sizeof(zval));  //分配内存  
(c_var)-> refcount = 1;  //引用计数初始化  
(c_var)-> is_ref = 0; //是否引用

可以看到其作用就是分配内存，初始化refcount，is_ref

三．下面看第三行 ZVAL_LONG(c_var,1) 相关宏为：


//定义值  
#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

展开后为：


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

四：接下来看第四行： ZEND_SET_SYMBOL( EG(active_symbol_table), “php_var”, c_var); 首先说明下PHP的变量是存在一个hashtable里的


struct _zend_executor_globals {    
        ….  
        HashTable symbol_table;//全局变量的符号表    
        HashTable *active_symbol_table;//局部变量的符号表    
        …..  
    };

Hashtable的Key为变量的名称，即php_var，值为指向PHP变量的指针，即c_var指针；相关宏为：


#define ZEND_SET_SYMBOL(symtable, name, var)          \   {                                                     \  
        char *_name = (name);                         \  
        ZEND_SET_SYMBOL_WITH_LENGTH(symtable, _name, strlen(_name)+1, var, 1, 0);   \  
}  
//主要的实现为下面这个函数：  
#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)->is_ref = 1;                                \  
            if (_refcount) {                                      \  
                (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);                                                           \  
        }                                                  \  
    }