本篇文章给大家介绍《解析PHP8底层内核源码-数组（四）》。有一定的参考价值，有需要的朋友可以参考一下，希望对大家有所帮助。

相关文章推荐：《解析PHP8底层内核源码-数组（一）》《解析PHP8底层内核源码-数组（二）》《解析PHP8底层内核源码-数组（三）》

在Runningprocess 里已经知道代码需要经过词法分析 语法分析 编译 执行 四大步骤

• 《深入解析PHP底层之Running process》

PHP 8会在编译阶段（将AST抽象语法树编译成opcode时）就创建一个数组常量。这个数组常量和数字常量、字符串常量一样，是在编译阶段就确定并分配内存的。因此数组的初始化发生在编译阶段。

PHP的数组初始化代码 部分如下

//如果开启zend_debug 
#if !ZEND_DEBUG && defined(HAVE_BUILTIN_CONSTANT_P)
# define zend_new_array(size) \
(__builtin_constant_p(size) ? \
((((uint32_t)(size)) <= HT_MIN_SIZE) ? \
_zend_new_array_0() \
//走 _zend_new_array_0
: \
_zend_new_array((size)) \
) \
: \
_zend_new_array((size)) \
)
#else
//没有开启 也就是一般模式 走 _zend_new_array
# define zend_new_array(size) \
_zend_new_array(size)
#endif
ZEND_API void ZEND_FASTCALL _zend_hash_init(HashTable *ht, uint32_t nSize, dtor_func_t pDestructor, zend_bool persistent)
{
_zend_hash_init_int(ht, nSize, pDestructor, persistent);
}
ZEND_API HashTable* ZEND_FASTCALL _zend_new_array_0(void)
{        //分配内存空间
HashTable *ht = emalloc(sizeof(HashTable));
         //初始化
_zend_hash_init_int(ht, HT_MIN_SIZE, ZVAL_PTR_DTOR, 0);
return ht;
}
//初始化方法
static zend_always_inline void _zend_hash_init_int(HashTable *ht, uint32_t nSize, dtor_func_t pDestructor, zend_bool persistent)
{
GC_SET_REFCOUNT(ht, 1);
GC_TYPE_INFO(ht) = GC_ARRAY | (persistent ? ((GC_PERSISTENT|GC_NOT_COLLECTABLE) << GC_FLAGS_SHIFT) : 0);
HT_FLAGS(ht) = HASH_FLAG_UNINITIALIZED;
ht->nTableMask = HT_MIN_MASK;
HT_SET_DATA_ADDR(ht, &uninitialized_bucket);
ht->nNumUsed = 0;
ht->nNumOfElements = 0;
ht->nInternalPointer = 0;
ht->nNextFreeElement = ZEND_LONG_MIN;
ht->pDestructor = pDestructor;
ht->nTableSize = zend_hash_check_size(nSize);
}
//初始化 bucket 也就是 ardata
ZEND_API void ZEND_FASTCALL zend_hash_real_init(HashTable *ht, zend_bool packed)
{
IS_CONSISTENT(ht);
HT_ASSERT_RC1(ht);
//调用 zend_hash_real_init_ex方法
zend_hash_real_init_ex(ht, packed);
}
//zend_hash_real_init_ex方法
static zend_always_inline void zend_hash_real_init_ex(HashTable *ht, bool packed)
{
HT_ASSERT_RC1(ht);
ZEND_ASSERT(HT_FLAGS(ht) & HASH_FLAG_UNINITIALIZED);
if (packed) {
//如果是packed_array 
zend_hash_real_init_packed_ex(ht);
} else {
//如果是 hash_array
zend_hash_real_init_mixed_ex(ht);
}
}
//paced_array 初始化bucket 的代码
static zend_always_inline void zend_hash_real_init_packed_ex(HashTable *ht)
{
void *data;
if (UNEXPECTED(GC_FLAGS(ht) & IS_ARRAY_PERSISTENT)) {
data = pemalloc(HT_SIZE_EX(ht->nTableSize, HT_MIN_MASK), 1);
} else if (EXPECTED(ht->nTableSize == HT_MIN_SIZE)) {
data = emalloc(HT_SIZE_EX(HT_MIN_SIZE, HT_MIN_MASK));
} else {
data = emalloc(HT_SIZE_EX(ht->nTableSize, HT_MIN_MASK));
}
HT_SET_DATA_ADDR(ht, data);
/* Don't overwrite iterator count. */
ht->u.v.flags = HASH_FLAG_PACKED | HASH_FLAG_STATIC_KEYS;
HT_HASH_RESET_PACKED(ht);
}
//hash_array 初始化bucket的代码
static zend_always_inline void zend_hash_real_init_mixed_ex(HashTable *ht)
{
void *data;
uint32_t nSize = ht->nTableSize;
if (UNEXPECTED(GC_FLAGS(ht) & IS_ARRAY_PERSISTENT)) {
data = pemalloc(HT_SIZE_EX(nSize, HT_SIZE_TO_MASK(nSize)), 1);
} else if (EXPECTED(nSize == HT_MIN_SIZE)) {
data = emalloc(HT_SIZE_EX(HT_MIN_SIZE, HT_SIZE_TO_MASK(HT_MIN_SIZE)));
ht->nTableMask = HT_SIZE_TO_MASK(HT_MIN_SIZE);
HT_SET_DATA_ADDR(ht, data);
/* Don't overwrite iterator count. */
ht->u.v.flags = HASH_FLAG_STATIC_KEYS;
#ifdef __SSE2__
do {
__m128i xmm0 = _mm_setzero_si128();
xmm0 = _mm_cmpeq_epi8(xmm0, xmm0);
_mm_storeu_si128((__m128i*)&HT_HASH_EX(data,  0), xmm0);
_mm_storeu_si128((__m128i*)&HT_HASH_EX(data,  4), xmm0);
_mm_storeu_si128((__m128i*)&HT_HASH_EX(data,  8), xmm0);
_mm_storeu_si128((__m128i*)&HT_HASH_EX(data, 12), xmm0);
} while (0);
#elif defined(__aarch64__)
do {
int32x4_t t = vdupq_n_s32(-1);
vst1q_s32((int32_t*)&HT_HASH_EX(data,  0), t);
vst1q_s32((int32_t*)&HT_HASH_EX(data,  4), t);
vst1q_s32((int32_t*)&HT_HASH_EX(data,  8), t);
vst1q_s32((int32_t*)&HT_HASH_EX(data, 12), t);
} while (0);
#else
HT_HASH_EX(data,  0) = -1;
HT_HASH_EX(data,  1) = -1;
HT_HASH_EX(data,  2) = -1;
HT_HASH_EX(data,  3) = -1;
HT_HASH_EX(data,  4) = -1;
HT_HASH_EX(data,  5) = -1;
HT_HASH_EX(data,  6) = -1;
HT_HASH_EX(data,  7) = -1;
HT_HASH_EX(data,  8) = -1;
HT_HASH_EX(data,  9) = -1;
HT_HASH_EX(data, 10) = -1;
HT_HASH_EX(data, 11) = -1;
HT_HASH_EX(data, 12) = -1;
HT_HASH_EX(data, 13) = -1;
HT_HASH_EX(data, 14) = -1;
HT_HASH_EX(data, 15) = -1;
#endif
return;
} else {
data = emalloc(HT_SIZE_EX(nSize, HT_SIZE_TO_MASK(nSize)));
}
ht->nTableMask = HT_SIZE_TO_MASK(nSize);
HT_SET_DATA_ADDR(ht, data);
HT_FLAGS(ht) = HASH_FLAG_STATIC_KEYS;
HT_HASH_RESET(ht);
}
//数组赋值和更新值
static zend_always_inline zval *_zend_hash_index_add_or_update_i(HashTable *ht, zend_ulong h, zval *pData, uint32_t flag)
{
uint32_t nIndex;
uint32_t idx;
Bucket *p;
IS_CONSISTENT(ht);
HT_ASSERT_RC1(ht);
if ((flag & HASH_ADD_NEXT) && h == ZEND_LONG_MIN) {
h = 0;
}
if (HT_FLAGS(ht) & HASH_FLAG_PACKED) {
if (h < ht->nNumUsed) {
p = ht->arData + h;
if (Z_TYPE(p->val) != IS_UNDEF) {
replace:
if (flag & HASH_ADD) {
return NULL;
}
if (ht->pDestructor) {
ht->pDestructor(&p->val);
}
ZVAL_COPY_VALUE(&p->val, pData);
return &p->val;
} else { /* we have to keep the order :( */
goto convert_to_hash;
}
} else if (EXPECTED(h < ht->nTableSize)) {
add_to_packed:
p = ht->arData + h;
/* incremental initialization of empty Buckets */
if ((flag & (HASH_ADD_NEW|HASH_ADD_NEXT)) != (HASH_ADD_NEW|HASH_ADD_NEXT)) {
if (h > ht->nNumUsed) {
Bucket *q = ht->arData + ht->nNumUsed;
while (q != p) {
ZVAL_UNDEF(&q->val);
q++;
}
}
}
ht->nNextFreeElement = ht->nNumUsed = h + 1;
goto add;
} else if ((h >> 1) < ht->nTableSize &&
           (ht->nTableSize >> 1) < ht->nNumOfElements) {
zend_hash_packed_grow(ht);
goto add_to_packed;
} else {
if (ht->nNumUsed >= ht->nTableSize) {
ht->nTableSize += ht->nTableSize;
}
convert_to_hash:
zend_hash_packed_to_hash(ht);
}
} else if (HT_FLAGS(ht) & HASH_FLAG_UNINITIALIZED) {
if (h < ht->nTableSize) {
zend_hash_real_init_packed_ex(ht);
goto add_to_packed;
}
zend_hash_real_init_mixed(ht);
} else {
if ((flag & HASH_ADD_NEW) == 0 || ZEND_DEBUG) {
p = zend_hash_index_find_bucket(ht, h);
if (p) {
ZEND_ASSERT((flag & HASH_ADD_NEW) == 0);
goto replace;
}
}
ZEND_HASH_IF_FULL_DO_RESIZE(ht);/* If the Hash table is full, resize it */
}
idx = ht->nNumUsed++;
nIndex = h | ht->nTableMask;
p = ht->arData + idx;
Z_NEXT(p->val) = HT_HASH(ht, nIndex);
HT_HASH(ht, nIndex) = HT_IDX_TO_HASH(idx);
if ((zend_long)h >= ht->nNextFreeElement) {
ht->nNextFreeElement = (zend_long)h < ZEND_LONG_MAX ? h + 1 : ZEND_LONG_MAX;
}
add:
ht->nNumOfElements++;
p->h = h;
p->key = NULL;
ZVAL_COPY_VALUE(&p->val, pData);
return &p->val;
}

_zend_hash_init_int 流程图如下

在PHP 8中，数组的初始化其实是分两步的。

第1步：分配HashTable结构体内存

第2步: 初始化HashTable结构体各个字段

第3步：分配bucket数组内存，修改一些字段值。

对于第3步，并不是每次都进行。比如像“$a = array()”这种写法，由于数组为空，PHP 不会额外申请bucket数组内存。而对于“$a = array(1, 2, 3)”这种写法，由于数组非空，因此PHP 需要执行第3步 分配bucket数组内存，修改一些字段值。