分析PHP内核中是如何实现 empty, isset 这些函数的
#### 叨叨几句本来这个问题是在oschina上提出的： <http://www.oschina.net/question/1179015_2140695>但一直没收到合适的答案，所以还是自己下功夫梳理了一下，如果有错误的地方，欢迎交流。通常的函数是通过ZEND_FUNCTION(xxx) 这种宏定义来实现的，这个规范很好理解，也很容易读懂源码。但empty(), isset() 准确的说不是函数，但PHP的Manual还是称之函数，类似的还有echo, eval等。#### 准备工作用于查看PHP的扩展vld，下载： <http://pecl.php.net/package/vld>PHP源码，分支 => remotes/origin/PHP-5.6.14 git clone http://git.php.net/repository/php-src.git -b PHP-5.6.14PHP opcode对应参考： <http://php.net/manual/en/internals2.opcodes.php>> PHP执行程序版本为 5.6.14 ，其他版本opcode可能会有细微差别。PHP 内核源码分析： <http://www.php-internals.com/book/>#### 开始分析示例代码 vld.php : <?php $a = 0; empty($a); isset($a);通过vld 查看opcode ，`php -d vld.active=1 vld.php` number of ops: 10 compiled vars: !0 = $a line #* E I O op fetch ext return operands ------------------------------------------------------------------------------------- 2 0 E > EXT_STMT 1 ASSIGN !0, 0 3 2 EXT_STMT 3 ISSET_ISEMPTY_VAR 293601280 ~1 !0 4 FREE ~1 4 5 EXT_STMT 6 ISSET_ISEMPTY_VAR 310378496 ~2 !0 7 FREE ~2 6 8 EXT_STMT 9 > RETURN 1 branch: # 0; line: 2- 6; sop: 0; eop: 9; out1: -2opcode中都出现了ZEND_ISSET_ISEMPTY_VAR，我们一步步分析。当执行PHP源码，会先进行语法分析，empty, isset的yacc如下：vim Zend/zend_language_parser.y +1265 1265 internal_functions_in_yacc: 1266 › › T_ISSET '(' isset_variables ')' { $$ = $3; } 1267 › |› T_EMPTY '(' variable ')'› { zend_do_isset_or_isempty(ZEND_ISEMPTY, &$$, &$3 TSRMLS_CC); } 1275 1276 isset_variables: 1277 › › isset_variable› › › { $$ = $1; } 1280 1281 isset_variable: 1282 › › variable› › › › { zend_do_isset_or_isempty(ZEND_ISSET, &$$, &$1 TSRMLS_CC); }最终都执行了zend_do_isset_or_isempty，继续查找： git grep -in "zend_do_isset_or_isempty" Zend/zend_compile.c:6287:void zend_do_isset_or_isempty(int type, znode *result, znode *variable TSRMLS_DC) /* {:{:{ */vi Zend/zend_compile.c +6287 6287 void zend_do_isset_or_isempty(int type, znode *result, znode *variable TSRMLS_DC) /* {{{ */ 6288 { 6289 › zend_op *last_op; 6290 6291 › zend_do_end_variable_parse(variable, BP_VAR_IS, 0 TSRMLS_CC); 6292 6293 › if (zend_is_function_or_method_call(variable)) { 6294 › › if (type == ZEND_ISEMPTY) { 6295 › › › /* empty(func()) can be transformed to !func() */ 6296 › › › zend_do_unary_op(ZEND_BOOL_NOT, result, variable TSRMLS_CC); 6297 › › } else { 6298 › › › zend_error_noreturn(E_COMPILE_ERROR, "Cannot use isset() on the result of a function call (you can use \"null !== func()\" instead)"); 6299 › › } 6300 6301 › › return; 6302 › } 6303 6304 › if (variable->op_type == IS_CV) { 6305 › › last_op = get_next_op(CG(active_op_array) TSRMLS_CC); 6306 › › last_op->opcode = ZEND_ISSET_ISEMPTY_VAR;最后一行 6306，ZEND_ISSET_ISEMPTY_VAR 这个opcode 出来了，IS_CV 判断参数是否为变量。注意zend_is_function_or_method_call(variable)，当isset(fun($a))，函数参数写法会报错，empty在5.5版本开始支持函数参数，低版本不支持。opcode 是由 zend_execute 执行的，最终会对应处理函数的查找，这个是核心，请参阅： <http://www.php-internals.com/book/?p=chapt02/02-03-03-from-opcode-to-handler>opcode 对应处理函数的命名规律： ZEND_[opcode]_SPEC_(变量类型1)_(变量类型2)_HANDLER变量类型1和变量类型2是可选的，如果同时存在，那就是左值和右值，归纳有下几类： VAR TMP CV UNUSED CONST 这样可以根据相关的执行场景来判定。所以 ZEND_ISSET_ISEMPTY_VAR 对应的handler如下： Zend/zend_vm_execute.h:44233: ZEND_ISSET_ISEMPTY_VAR_SPEC_CONST_CONST_HANDLER, Zend/zend_vm_execute.h:44235: ZEND_ISSET_ISEMPTY_VAR_SPEC_CONST_VAR_HANDLER, Zend/zend_vm_execute.h:44236: ZEND_ISSET_ISEMPTY_VAR_SPEC_CONST_UNUSED_HANDLER, Zend/zend_vm_execute.h:44238: ZEND_ISSET_ISEMPTY_VAR_SPEC_TMP_CONST_HANDLER, Zend/zend_vm_execute.h:44240: ZEND_ISSET_ISEMPTY_VAR_SPEC_TMP_VAR_HANDLER, Zend/zend_vm_execute.h:44241: ZEND_ISSET_ISEMPTY_VAR_SPEC_TMP_UNUSED_HANDLER, Zend/zend_vm_execute.h:44243: ZEND_ISSET_ISEMPTY_VAR_SPEC_VAR_CONST_HANDLER, Zend/zend_vm_execute.h:44245: ZEND_ISSET_ISEMPTY_VAR_SPEC_VAR_VAR_HANDLER, Zend/zend_vm_execute.h:44246: ZEND_ISSET_ISEMPTY_VAR_SPEC_VAR_UNUSED_HANDLER, Zend/zend_vm_execute.h:44253: ZEND_ISSET_ISEMPTY_VAR_SPEC_CV_CONST_HANDLER, Zend/zend_vm_execute.h:44255: ZEND_ISSET_ISEMPTY_VAR_SPEC_CV_VAR_HANDLER, Zend/zend_vm_execute.h:44256: ZEND_ISSET_ISEMPTY_VAR_SPEC_CV_UNUSED_HANDLER,我们看下 ZEND_ISSET_ISEMPTY_VAR_SPEC_CV_VAR_HANDLER 这个处理函数：vim Zend/zend_vm_execute.h +37946 38013 › if (opline->extended_value & ZEND_ISSET) { 38014 › › if (isset && Z_TYPE_PP(value) != IS_NULL) { 38015 › › › ZVAL_BOOL(&EX_T(opline->result.var).tmp_var, 1); 38016 › › } else { 38017 › › › ZVAL_BOOL(&EX_T(opline->result.var).tmp_var, 0); 38018 › › } 38019 › } else /* if (opline->extended_value & ZEND_ISEMPTY) */ { 38020 › › if (!isset || !i_zend_is_true(*value)) { 38021 › › › ZVAL_BOOL(&EX_T(opline->result.var).tmp_var, 1); 38022 › › } else { 38023 › › › ZVAL_BOOL(&EX_T(opline->result.var).tmp_var, 0); 38024 › › }上面的 if ... else 就是判断是isset，还是empty，然后做不同处理，Z_TYPE_PP, i_zend_is_true 不同判断。echo 等处理类似，自己按照流程具体去分析。关键是根据映射表找到对应的handler处理函数。了解这些处理流程后，相信会对PHP语句的性能分析更熟悉。原文出自[老刺猬](http://www.yinqisen.cn)，<http://www.yinqisen.cn/blog-680.html>
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