PHP Kernel Research Static Variables_PHP Tutorial-PHP Tutorial-php.cn

PHP Kernel Research Static Variables_PHP Tutorial

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Release： 2016-07-14 10:08:23

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static variable

It can be a static global variable. If unset is not called, then this static variable will always exist and will be released by Zend memory management until the program exits

It can be a static local variable: defined in a function, the static variable will not disappear after the function is executed

It can be a static member variable: defined in a class, it can be shared among objects of all classes

For example

function test(){

static $a=1;

$a++;

}

test(); //$a=2

test();//$a=3

test();//$a=4

Finally $a=4..

Let’s analyze it from the kernel

static is not a function, it is a keyword, so it can only be found from LEX syntax analysis

Open zend/zend_language_scanner.l and find static

Code found

"static" {

return T_STATIC;

}

is a macro

Open zend/zend_language_pareser.l

Search T_STATIC

Code found

T_STATIC static_var_list ';'

Follow up static_var_list

Code found

static_var_list:

static_var_list ',' T_VARIABLE { zend_do_fetch_static_variable(&$3, NULL, ZEND_FETCH_STATIC TSRMLS_CC); }

| | static_var_list ',' T_VARIABLE '=' static_scalar { zend_do_fetch_static_variable(&$3, &$5, ZEND_FETCH_STATIC TSRMLS_CC); }

| | T_VARIABLE { zend_do_fetch_static_variable(&$1, NULL, ZEND_FETCH_STATIC TSRMLS_CC); }

| | T_VARIABLE '=' static_scalar { zend_do_fetch_static_variable(&$1, &$3, ZEND_FETCH_STATIC TSRMLS_CC); }

;

That’s it.. It is parsed into the above code by PHP’s syntax parser

zend_do_fetch_static_variable is the function

It is defined in zend/zend_compile.c

The code is as follows

void zend_do_fetch_static_variable(znode *varname, const znode *static_assignment, int fetch_type TSRMLS_DC)

{

zval *tmp; //A temporary variable

zend_op *opline;

znode lval;

znode result;

ALLOC_ZVAL(tmp); //Apply for a piece of memory

if (static_assignment) {

*tmp = static_assignment->u.constant;

} else {

INIT_ZVAL(*tmp);

} }

if (!CG(active_op_array)->static_variables) {//Initialize the HASH key value of static variables

ALLOC_HASHTABLE(CG(active_op_array)->static_variables);

// Initialize HASH value

zend_hash_init(CG(active_op_array)->static_variables, 2, NULL, ZVAL_PTR_DTOR, 0);

} }

zend_hash_update(CG(active_op_array)->static_variables, varname->u.constant.value.str.val, varname->u.constant.value.str.len+1, &tmp, sizeof(zval * ), NULL);

if (varname->op_type == IS_CONST) {

if (Z_TYPE(varname->u.constant) != IS_STRING) {

convert_to_string(&varname->u.constant);

}

opline = get_next_op(CG(active_op_array) TSRMLS_CC);

opline->result.op_type = IS_VAR;

opline->result.u.EA.type = 0;

opline->result.u.var = get_temporary_variable(CG(active_op_array));

opline->op1 = *varname;

SET_UNUSED(opline->op2);

opline->op2.u.EA.type = ZEND_FETCH_STATIC;

result = opline->result;