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PHP源代码数组统计count分析

Jun 13, 2016 pm 12:06 PM
count php zend keep analyze go variable character array Way source code of structure statistics

zend给php的所有变量都用结构的方式去保存,而字符串的保存和数组的保存也是不同的,数组采用的是hash表的方式去保存(大家知道hash保存的地址有效的减少冲突-hash散列表的概念你懂的),而在php中的结构体上表现如下:

复制代码 代码如下:


//文件1:zend/zend.h
/*
* zval
*/
typedef struct _zval_struct zval;
...
typedef union _zvalue_value {
long lval; /* long value */
double dval; /* double value */
struct {
char *val;
int len;
} str;
HashTable *ht; /* hash table value */
zend_object_value obj;
} zvalue_value;

struct _zval_struct {
/* Variable information */
zvalue_value value; /* value */
zend_uint refcount__gc;
zend_uchar type; /* active type */
zend_uchar is_ref__gc;
};
//hash表的结构如下
//文件2:zend/zend_hash.h
typedef struct _hashtable {
uint nTableSize;
uint nTableMask;
uint nNumOfElements;
ulong nNextFreeElement;
Bucket *pInternalPointer; /* Used for element traversal */
Bucket *pListHead;
Bucket *pListTail;
Bucket **arBuckets;
dtor_func_t pDestructor;
zend_bool persistent;
unsigned char nApplyCount;
zend_bool bApplyProtection;
#if ZEND_DEBUG
int inconsistent;
#endif
}
HashTable;


一般的变量(字符串)在使用strlen获取长度的时候,其实获取的就是zvalue_value.str这个结构中的len属性,效率上O(1)次,特别说明的一点是:strlen在php中并没有核心的实现,而是在使用了zend中的宏定义来获取:

复制代码 代码如下:


//文件3:zend/zend_operators.php
#define Z_STRLEN(zval) (zval).value.str.len
...
#define Z_STRLEN_P(zval_p) Z_STRLEN(*zval_p)
...
#define Z_STRLEN_PP(zval_pp) Z_STRLEN(**zval_pp)


而对于数组的count操作,其实有两种结果,在count 的api中也提到了第二个参数mode《http://www.php.net/manual/en/function.count.php》,这个mode参数指明了,是否需要重新统计,而它的重新统计将会遍历一次数组,效率上是O(N)[N:长度],默认情况下是不重新统计,那这个时候将会直接输出hashtable中的nNumOfElements,此时的效率也是O(1)次:count代码如下:

复制代码 代码如下:


//文件4:ext/standard/array.c
PHP_FUNCTION(count)
{
zval *array;
long mode = COUNT_NORMAL;

if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "z|l", &array, &mode) == FAILURE) {
return;
}

switch (Z_TYPE_P(array)) {
case IS_NULL:
RETURN_LONG(0);
break;
case IS_ARRAY:
RETURN_LONG (php_count_recursive (array, mode TSRMLS_CC));
break;
.....

//php_count_recursive的实现
static int php_count_recursive(zval *array, long mode TSRMLS_DC) /* {{{ */
{
long cnt = 0;
zval **element;

if (Z_TYPE_P(array) == IS_ARRAY) {
//错误处理
if (Z_ARRVAL_P(array)->nApplyCount > 1) {
php_error_docref(NULL TSRMLS_CC, E_WARNING, "recursion detected");
return 0;
}
//通过zend_hash_num_elements直接获得长度
cnt = zend_hash_num_elements(Z_ARRVAL_P(array));

//如果指定了需要重新统计,则会进入一次循环统计
if (mode == COUNT_RECURSIVE) {
HashPosition pos;

for (zend_hash_internal_pointer_reset_ex(Z_ARRVAL_P(array), &pos);
zend_hash_get_current_data_ex(Z_ARRVAL_P(array), (void **) &element, &pos) == SUCCESS;
zend_hash_move_forward_ex(Z_ARRVAL_P(array), &pos)
) {
Z_ARRVAL_P(array)->nApplyCount++;
cnt += php_count_recursive(*element, COUNT_RECURSIVE TSRMLS_CC);
Z_ARRVAL_P(array)->nApplyCount--;
}
}
}

return cnt;
}

//文件5:zend/zend_hash.c
//zend_hash_num_elements的实现
ZEND_API int zend_hash_num_elements(const HashTable *ht)
{
IS_CONSISTENT(ht);

return ht->nNumOfElements;
}

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