变量赋值(引用) php内核的实现(二）
<?php
$a=1;
$b=&$a;
$c=2;
$a=&$c;
echo $a."\n";
echo $b;
2
1
结论:
首先保存 左值的内存地址， 因这个内存地址会被再次被赋值
1)右值是引用
进入2.2 2.3 2.4步骤
例子：
<?php $a=1;
$c=2; $b=&$a; //执行到这里时，属于第2种情况 $c=&$a; //执行到这里时，属于第1种情况,
2)右值不是引用，右值的refcount_gc减1
2.1)如果refcount_gc减1，大于0 ，说明有别的变量也共同使用了zval,需要单独分配内存给右值
2.2）将右值（内存地址）赋值给左值
2.3）refcount_gc 加1，并设置 is_ref=1
2.4)销毁左值
2.3.1）将上面保存的左值的zval的refcount_gc减1
2.3.1.1）上面值为0，则zval_dtor
2.3.1.2)上面值大于0，则进入GC buffer, 但zval类型必须为 object或 array
可以发现$a,$b,$c全是CV变量
当php解释器执行到$b=&$a时，会执行到下面的handler
static int ZEND_FASTCALL ZEND_ASSIGN_REF_SPEC_CV_CV_HANDLER(ZEND_OPCODE_HANDLER_ARGS) { USE_OPLINE zend_free_op free_op2; zval **variable_ptr_ptr; zval **value_ptr_ptr; SAVE_OPLINE(); value_ptr_ptr = _get_zval_ptr_ptr_cv_BP_VAR_W(EX_CVs(), opline->op2.var TSRMLS_CC); if (IS_CV == IS_VAR && value_ptr_ptr && !Z_ISREF_PP(value_ptr_ptr) && opline->extended_value == ZEND_RETURNS_FUNCTION && !EX_T(opline->op2.var).var.fcall_returned_reference) { if (free_op2.var == NULL) { PZVAL_LOCK(*value_ptr_ptr); /* undo the effect of get_zval_ptr_ptr() */ } zend_error(E_STRICT, "Only variables should be assigned by reference"); if (UNEXPECTED(EG(exception) != NULL)) { HANDLE_EXCEPTION(); } return ZEND_ASSIGN_SPEC_CV_CV_HANDLER(ZEND_OPCODE_HANDLER_ARGS_PASSTHRU); } else if (IS_CV == IS_VAR && opline->extended_value == ZEND_RETURNS_NEW) { PZVAL_LOCK(*value_ptr_ptr); } if (IS_CV == IS_VAR && UNEXPECTED(EX_T(opline->op1.var).var.ptr_ptr == &EX_T(opline->op1.var).var.ptr)) { zend_error_noreturn(E_ERROR, "Cannot assign by reference to overloaded object"); } variable_ptr_ptr = _get_zval_ptr_ptr_cv_BP_VAR_W(EX_CVs(), opline->op1.var TSRMLS_CC); if ((IS_CV == IS_VAR && UNEXPECTED(value_ptr_ptr == NULL)) || (IS_CV == IS_VAR && UNEXPECTED(variable_ptr_ptr == NULL))) { zend_error_noreturn(E_ERROR, "Cannot create references to/from string offsets nor overloaded objects"); } zend_assign_to_variable_reference(variable_ptr_ptr, value_ptr_ptr TSRMLS_CC); //在这里执行分配的操作 if (IS_CV == IS_VAR && opline->extended_value == ZEND_RETURNS_NEW) { Z_DELREF_PP(variable_ptr_ptr); } if (RETURN_VALUE_USED(opline)) { PZVAL_LOCK(*variable_ptr_ptr); AI_SET_PTR(&EX_T(opline->result.var), *variable_ptr_ptr); } CHECK_EXCEPTION(); ZEND_VM_NEXT_OPCODE(); }
static void zend_assign_to_variable_reference(zval **variable_ptr_ptr, zval **value_ptr_ptr TSRMLS_DC) { zval *variable_ptr = *variable_ptr_ptr; zval *value_ptr = *value_ptr_ptr; if (variable_ptr == &EG(error_zval) || value_ptr == &EG(error_zval)) { variable_ptr_ptr = &EG(uninitialized_zval_ptr); } else if (variable_ptr != value_ptr) { if (!PZVAL_IS_REF(value_ptr)) { //此时右值不是一个引用 /* break it away */ Z_DELREF_P(value_ptr); //refcount_gc减1 的作用 是看 是否还有其他变量也使用了valu_ptr_ptr对应的zval,如果有，则重新分配zval if (Z_REFCOUNT_P(value_ptr)>0) { ALLOC_ZVAL(*value_ptr_ptr); ZVAL_COPY_VALUE(*value_ptr_ptr, value_ptr); value_ptr = *value_ptr_ptr; zendi_zval_copy_ctor(*value_ptr); } Z_SET_REFCOUNT_P(value_ptr, 1); //因为上面减1了，所以这里要加1， Z_SET_ISREF_P(value_ptr);//设置 is_ref为1 } *variable_ptr_ptr = value_ptr; //将variable_ptr_ptr这个地址指针内容 为 1 的地址 Z_ADDREF_P(value_ptr); //还要将 refcount_gc加1 zval_ptr_dtor(&variable_ptr); //根据情况释放内存
} else if (!Z_ISREF_P(variable_ptr)) { if (variable_ptr_ptr == value_ptr_ptr) { SEPARATE_ZVAL(variable_ptr_ptr); } else if (variable_ptr==&EG(uninitialized_zval) || Z_REFCOUNT_P(variable_ptr)>2) { /* we need to separate */ Z_SET_REFCOUNT_P(variable_ptr, Z_REFCOUNT_P(variable_ptr) - 2); ALLOC_ZVAL(*variable_ptr_ptr); ZVAL_COPY_VALUE(*variable_ptr_ptr, variable_ptr); zval_copy_ctor(*variable_ptr_ptr); *value_ptr_ptr = *variable_ptr_ptr; Z_SET_REFCOUNT_PP(variable_ptr_ptr, 2); } Z_SET_ISREF_PP(variable_ptr_ptr); } }
//zend_variables.c ZEND_API void _zval_copy_ctor_func(zval *zvalue ZEND_FILE_LINE_DC) { switch (Z_TYPE_P(zvalue) & IS_CONSTANT_TYPE_MASK) { case IS_RESOURCE: { TSRMLS_FETCH(); zend_list_addref(zvalue->value.lval); } break; case IS_BOOL: case IS_LONG: case IS_NULL: break; case IS_CONSTANT: case IS_STRING: CHECK_ZVAL_STRING_REL(zvalue); if (!IS_INTERNED(zvalue->value.str.val)) { zvalue->value.str.val = (char *) estrndup_rel(zvalue->value.str.val, zvalue->value.str.len); } break; case IS_ARRAY: case IS_CONSTANT_ARRAY: { zval *tmp; HashTable *original_ht = zvalue->value.ht; HashTable *tmp_ht = NULL; TSRMLS_FETCH(); if (zvalue->value.ht == &EG(symbol_table)) { return; /* do nothing */ } ALLOC_HASHTABLE_REL(tmp_ht); zend_hash_init(tmp_ht, zend_hash_num_elements(original_ht), NULL, ZVAL_PTR_DTOR, 0); zend_hash_copy(tmp_ht, original_ht, (copy_ctor_func_t) zval_add_ref, (void *) &tmp, sizeof(zval *)); zvalue->value.ht = tmp_ht; } break; case IS_OBJECT: { TSRMLS_FETCH(); Z_OBJ_HT_P(zvalue)->add_ref(zvalue TSRMLS_CC); } break; } }
//zend_API.h #define CHECK_ZVAL_STRING_REL(z) \ if (Z_STRVAL_P(z)[ Z_STRLEN_P(z) ] != '\0') { zend_error(E_WARNING, "String is not zero-terminated (%s) (source: %s:%d)", Z_STRVAL_P(z) ZEND_FILE_LINE_RELAY_CC); }
//zend_alloc.h #define estrndup_rel(s, length) _estrndup((s), (length) ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_CC)
//zend_alloc.c ZEND_API char *_estrndup(const char *s, uint length ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) { char *p; #ifdef ZEND_SIGNALS TSRMLS_FETCH(); #endif HANDLE_BLOCK_INTERRUPTIONS(); p = (char *) _emalloc(length+1 ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC); if (UNEXPECTED(p == NULL)) { HANDLE_UNBLOCK_INTERRUPTIONS(); return p; } memcpy(p, s, length); p[length] = 0; HANDLE_UNBLOCK_INTERRUPTIONS(); return p; }
//zend_execute_API.c
ZEND_API void _zval_ptr_dtor(zval **zval_ptr ZEND_FILE_LINE_DC) /* {{{ */ { #if DEBUG_ZEND>=2 printf("Reducing refcount for %x (%x): %d->%d\n", *zval_ptr, zval_ptr, Z_REFCOUNT_PP(zval_ptr), Z_REFCOUNT_PP(zval_ptr) - 1); #endif Z_DELREF_PP(zval_ptr); if (Z_REFCOUNT_PP(zval_ptr) == 0) { TSRMLS_FETCH(); if (*zval_ptr != &EG(uninitialized_zval)) { GC_REMOVE_ZVAL_FROM_BUFFER(*zval_ptr); zval_dtor(*zval_ptr); efree_rel(*zval_ptr); } } else { TSRMLS_FETCH(); if (Z_REFCOUNT_PP(zval_ptr) == 1) { Z_UNSET_ISREF_PP(zval_ptr); } GC_ZVAL_CHECK_POSSIBLE_ROOT(*zval_ptr); } }
//zend_variables.c ZEND_API void _zval_dtor_func(zval *zvalue ZEND_FILE_LINE_DC) { switch (Z_TYPE_P(zvalue) & IS_CONSTANT_TYPE_MASK) { case IS_STRING: case IS_CONSTANT: CHECK_ZVAL_STRING_REL(zvalue); STR_FREE_REL(zvalue->value.str.val); break; case IS_ARRAY: case IS_CONSTANT_ARRAY: { TSRMLS_FETCH(); if (zvalue->value.ht && (zvalue->value.ht != &EG(symbol_table))) { /* break possible cycles */ Z_TYPE_P(zvalue) = IS_NULL; zend_hash_destroy(zvalue->value.ht); FREE_HASHTABLE(zvalue->value.ht); } } break; case IS_OBJECT: { TSRMLS_FETCH(); Z_OBJ_HT_P(zvalue)->del_ref(zvalue TSRMLS_CC); } break; case IS_RESOURCE: { TSRMLS_FETCH(); /* destroy resource */ zend_list_delete(zvalue->value.lval); } break; case IS_LONG: case IS_DOUBLE: case IS_BOOL: case IS_NULL: default: return; break; } }
//zend.h #define STR_FREE_REL(ptr) if (ptr && !IS_INTERNED(ptr)) { efree_rel(ptr); } #define efree_rel(ptr) _efree((ptr) ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_CC) //zend_alloc.c ZEND_API void _efree(void *ptr ZEND_FILE_LINE_DC ZEND_FILE_LINE_ORIG_DC) { TSRMLS_FETCH(); if (UNEXPECTED(!AG(mm_heap)->use_zend_alloc)) { AG(mm_heap)->_free(ptr); return; } _zend_mm_free_int(AG(mm_heap), ptr ZEND_FILE_LINE_RELAY_CC ZEND_FILE_LINE_ORIG_RELAY_CC); }
#include <stdio.h> #include <stdlib.h> int main() { char *variable="abc"; char **variable_ptr_ptr=variable; char *variable_ptr=*variable_ptr_ptr; char *value="def"; char **value_ptr_ptr=value; char *value_ptr=*value_ptr_ptr; *variable_ptr_ptr=value_ptr; return 0; }
