深入理解PHP之isset和array_key_exists对比

1、概述经常使用isset判断变量或数组中的键是否存在, 但是数组中可以使用array_key_exists这个函数, 那么这两个谁最优呢?官方文档对两者的定义-分类描述文档isset语言构造器检测变量是否已设置并且非 NULLhttp://php.net/manual/zh/function.isset.phparray_key_exists函数检查数组里是否有指定的键名或索引http://php.net/manual/zh/function.array-key-exists.phpisset() 对于数组中为 NULL 的值不会返回 TRUE，而 array_key_exists() 会。array_key_exists() 仅仅搜索第一维的键。 多维数组里嵌套的键不会被搜索到。要检查对象是否有某个属性，应该去用 property_exists()。2、测试2.1 测试环境OSPHPPHPUnitMacOS 10.13.6PHP 7.2.7 (cli)PHPUnit 6.5.72.2 单元测试class issetTest extends \PHPUnit\Framework\TestCase{ /** * @dataProvider dataArr / public function testName($arr) { $this->assertTrue(isset($arr[’name’])); $this->assertFalse(isset($arr[‘age’])); $this->assertTrue(isset($arr[‘sex’])); $this->assertTrue(array_key_exists(’name’, $arr)); $this->assertTrue(array_key_exists(‘age’, $arr)); $this->assertTrue(array_key_exists(‘sex’, $arr)); $this->assertFalse(empty($arr[’name’])); $this->assertTrue(empty($arr[‘age’])); $this->assertTrue(empty($arr[‘sex’])); } public function dataArr() { return [ [ [’name’ => 123, ‘age’ => null, ‘sex’ => 0] ] ]; }}/PHPUnit 6.5.7 by Sebastian Bergmann and contributors.. 1 / 1 (100%)Time: 113 ms, Memory: 8.00MBOK (1 test, 9 assertions)/2.3 性能-执行时间如上, php cli环境下, 执行10000000次, 测试代码和执行时间如下:<?php$arr = [ ’name’ => 123, ‘age’ => null];$max = 10000000;testFunc($arr, ’name’, $max);testFunc($arr, ‘age’, $max);function testFunc($arr, $key, $max = 1000){ echo ‘$arr[\'', $key, '\'] | - | -’, PHP_EOL; $startTime = microtime(true); for ($i = 0; $i <= $max; $i++) { isset($arr[$key]); } echo ‘^ | isset | ‘, microtime(true) - $startTime, PHP_EOL; $startTime = microtime(true); for ($i = 0; $i <= $max; $i++) { array_key_exists($key, $arr); } echo ‘^ | array_key_exists | ‘, microtime(true) - $startTime, PHP_EOL; $startTime = microtime(true); for ($i = 0; $i <= $max; $i++) { isset($arr[$key]) || array_key_exists($key, $arr); } echo ‘^ | isset or array_key_exists | ‘, microtime(true) - $startTime, PHP_EOL;}PHP 5.6-|函数|执行时间(s)$arr[’name’]–^isset0.64719796180725^array_key_exists2.5713651180267^isset or array_key_exists1.1359150409698$arr[‘age’]–^isset0.53988218307495^array_key_exists2.7240340709686^isset or array_key_exists2.9613540172577PHP 7.2.4-|函数|执行时间(s)$arr[’name’]–^isset0.24308800697327^array_key_exists0.3645191192627^isset or array_key_exists0.28933310508728$arr[‘age’]–^isset0.23279714584351^array_key_exists0.33850502967834^isset or array_key_exists0.549358129501342.4 性能-使用VLD查看opcode/usr/local/Cellar/php/7.2.7/bin/php -d vld.active=1 -dvld.verbosity=3 vld.php描述issetarray_key_existscode$arr = [’name’ => ’li’]; isset($arr[’name’]);$arr = [’name’ => ’li’]; array_key_exists(’name’, $arr);-dvld.active=1-dvld.verbosity=33、源码3.1 isset 源码分析Zend/zend_language_scanner.l (Scanning阶段)Scanning阶段，程序会扫描zend_language_scanner.l文件将代码文件转换成语言片段。<ST_IN_SCRIPTING>“isset” { RETURN_TOKEN(T_ISSET);}可见 isset 生成对应的token为 T_ISSET3.1.2 Zend/zend_language_parser.y (Parsing阶段)当执行PHP源码，会先进行语法分析，isset的yacc如下：接下来就到了Parsing阶段，这个阶段，程序将 T_ISSET 等Tokens转换成有意义的表达式，此时会做语法分析，Tokens的yacc保存在zend_language_parser.y文件中。isset的yacc如下(T_ISSET)：internal_functions_in_yacc: T_ISSET ‘(’ isset_variables ‘)’ { $$ = $3; } | T_EMPTY ‘(’ expr ‘)’ { $$ = zend_ast_create(ZEND_AST_EMPTY, $3); } | T_INCLUDE expr { $$ = zend_ast_create_ex(ZEND_AST_INCLUDE_OR_EVAL, ZEND_INCLUDE, $2); } | T_INCLUDE_ONCE expr { $$ = zend_ast_create_ex(ZEND_AST_INCLUDE_OR_EVAL, ZEND_INCLUDE_ONCE, $2); } | T_EVAL ‘(’ expr ‘)’ { $$ = zend_ast_create_ex(ZEND_AST_INCLUDE_OR_EVAL, ZEND_EVAL, $3); } | T_REQUIRE expr { $$ = zend_ast_create_ex(ZEND_AST_INCLUDE_OR_EVAL, ZEND_REQUIRE, $2); } | T_REQUIRE_ONCE expr { $$ = zend_ast_create_ex(ZEND_AST_INCLUDE_OR_EVAL, ZEND_REQUIRE_ONCE, $2); };isset_variables: isset_variable { $$ = $1; } | isset_variables ‘,’ isset_variable { $$ = zend_ast_create(ZEND_AST_AND, $1, $3); };isset_variable: expr { $$ = zend_ast_create(ZEND_AST_ISSET, $1); };%%/ Zend/zend_ast.c */# zend_ast_export_excase ZEND_AST_EMPTY: FUNC_OP(“empty”);case ZEND_AST_ISSET: FUNC_OP(“isset”);最终执行了zend_ast_create(ZEND_AST_ISSET, $1);我们知道, PHP7开始, 语法解析过程的产物保存于CG(AST)，接着zend引擎会把AST进一步编译为 zend_op_array ，它是编译阶段最终的产物，也是执行阶段的输入3.1.3 Zend/zend_compile.c(将表达式编译成opcodes)将表达式编译成opcodes，可见isset对应的opcodes为ZEND_AST_ISSET。打开zend_compile.c文件# void zend_compile_expr(znode *result, zend_ast ast) / {{{ */ case ZEND_AST_ISSET:case ZEND_AST_EMPTY: zend_compile_isset_or_empty(result, ast); return;最终执行了zend_compile_isset_or_empty函数，在源码目录中查找, 可以发现，此函数也在 zend_compile.c 文件中定义。void zend_compile_isset_or_empty(znode *result, zend_ast ast) / {{{ */{ zend_ast *var_ast = ast->child[0]; znode var_node; zend_op opline = NULL; ZEND_ASSERT(ast->kind == ZEND_AST_ISSET || ast->kind == ZEND_AST_EMPTY); if (!zend_is_variable(var_ast) || zend_is_call(var_ast)) { if (ast->kind == ZEND_AST_EMPTY) { / empty(expr) can be transformed to !expr */ zend_ast not_ast = zend_ast_create_ex(ZEND_AST_UNARY_OP, ZEND_BOOL_NOT, var_ast); zend_compile_expr(result, not_ast); return; } else { zend_error_noreturn(E_COMPILE_ERROR, “Cannot use isset() on the result of an expression " “(you can use "null !== expression" instead)”); } } switch (var_ast->kind) { case ZEND_AST_VAR: if (is_this_fetch(var_ast)) { opline = zend_emit_op(result, ZEND_ISSET_ISEMPTY_THIS, NULL, NULL); } else if (zend_try_compile_cv(&var_node, var_ast) == SUCCESS) { opline = zend_emit_op(result, ZEND_ISSET_ISEMPTY_VAR, &var_node, NULL); opline->extended_value = ZEND_FETCH_LOCAL | ZEND_QUICK_SET; } else { opline = zend_compile_simple_var_no_cv(result, var_ast, BP_VAR_IS, 0); opline->opcode = ZEND_ISSET_ISEMPTY_VAR; } break; case ZEND_AST_DIM: opline = zend_compile_dim_common(result, var_ast, BP_VAR_IS); opline->opcode = ZEND_ISSET_ISEMPTY_DIM_OBJ; break; case ZEND_AST_PROP: opline = zend_compile_prop_common(result, var_ast, BP_VAR_IS); opline->opcode = ZEND_ISSET_ISEMPTY_PROP_OBJ; break; case ZEND_AST_STATIC_PROP: opline = zend_compile_static_prop_common(result, var_ast, BP_VAR_IS, 0); opline->opcode = ZEND_ISSET_ISEMPTY_STATIC_PROP; break; EMPTY_SWITCH_DEFAULT_CASE() } result->op_type = opline->result_type = IS_TMP_VAR; opline->extended_value |= ast->kind == ZEND_AST_ISSET ? ZEND_ISSET : ZEND_ISEMPTY;}/ }}} /从这个函数最后一行可以看出，最终执行的还是ZEND_ISSET, 根据不同的用法会使用不同的opcode处理, 此处以ZEND_ISSET_ISEMPTY_DIM_OBJ为例。3.1.4 Zend/zend_vm_execute.h (执行opcodes)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。zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CONST_CONST_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CONST_TMPVAR_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CONST_CV_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_CONST_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_TMPVAR_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_CV_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_CONST_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_TMPVAR_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_TMPVAR_CV_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CV_CONST_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CV_TMPVAR_HANDLER,zend_vm_execute.h: ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CV_CV_HANDLER, 我们看下 ZEND_ISSET_ISEMPTY_DIM_OBJ_SPEC_CV_CV_HANDLER 这个处理函数if (opline->extended_value & ZEND_ISSET) { / > IS_NULL means not IS_UNDEF and not IS_NULL / result = value != NULL && Z_TYPE_P(value) > IS_NULL && (!Z_ISREF_P(value) || Z_TYPE_P(Z_REFVAL_P(value)) != IS_NULL);} else / if (opline->extended_value & ZEND_ISEMPTY) */ { result = (value == NULL || !i_zend_is_true(value));}上面的 if … else 就是判断是isset，还是empty，然后做不同处理，Z_TYPE_P, i_zend_is_true 不同判断。可见，isset的最终实现是通过 Z_TYPE_P 获取变量类型，然后再进行判断的。函数的完整定义请查看Zend/zend_vm_execute.h，以下是 i_zend_is_true 和 Z_TYPE_P的定义：Zend/zend_operators.h 中的i_zend_is_true()Zend/zend_types.h 中的 Z_TYPE_P()3.2 array_key_exists 源码分析3.2.1 ext/standard/array.c (数组扩展中实现)array_key_exists是php内置函数，通过扩展方式实现的。打开php源码，ext/standard/目录下// ➜ standard git:(master) ✗ grep -r ‘PHP_FUNCTION(array_key_exists)’ array.c: PHP_FUNCTION(array_key_exists)php_array.h: PHP_FUNCTION(array_key_exists);具体实现如下：/ {{{ proto bool array_key_exists(mixed key, array search) Checks if the given key or index exists in the array */PHP_FUNCTION(array_key_exists){ zval key; / key to check for */ HashTable array; / array to check in /#ifndef FAST_ZPP if (zend_parse_parameters(ZEND_NUM_ARGS(), “zH”, &key, &array) == FAILURE) { return; }#else ZEND_PARSE_PARAMETERS_START(2, 2) Z_PARAM_ZVAL(key) Z_PARAM_ARRAY_OR_OBJECT_HT(array) ZEND_PARSE_PARAMETERS_END();#endif switch (Z_TYPE_P(key)) { case IS_STRING: if (zend_symtable_exists_ind(array, Z_STR_P(key))) { RETURN_TRUE; } RETURN_FALSE; case IS_LONG: if (zend_hash_index_exists(array, Z_LVAL_P(key))) { RETURN_TRUE; } RETURN_FALSE; case IS_NULL: if (zend_hash_exists_ind(array, ZSTR_EMPTY_ALLOC())) { RETURN_TRUE; } RETURN_FALSE; default: php_error_docref(NULL, E_WARNING, “The first argument should be either a string or an integer”); RETURN_FALSE; }}/ }}} /可以看到, 是通过 Z_TYPE_P 宏获取变量类型, 通过 zend_hash 相关函数判断 key 是否存在。以key为字符串为例，在Zend/zend_hash.h追踪具体实现：3.2.2 Zend/zend_hash.hZEND_API zval ZEND_FASTCALL zend_hash_find(const HashTable *ht, zend_string *key);…static zend_always_inline int zend_symtable_exists_ind(HashTable *ht, zend_string *key){ zend_ulong idx; if (ZEND_HANDLE_NUMERIC(key, idx)) { return zend_hash_index_exists(ht, idx); } else { return zend_hash_exists_ind(ht, key); }}static zend_always_inline int zend_hash_exists_ind(const HashTable *ht, zend_string key){ zval zv; zv = zend_hash_find(ht, key); return zv && (Z_TYPE_P(zv) != IS_INDIRECT || Z_TYPE_P(Z_INDIRECT_P(zv)) != IS_UNDEF);}再次先通过函数ZEND_HANDLE_NUMERIC对key做判断，看这个字符串是不是数字类型的, 当key为数字时执行 zend_hash_index_exists, 实现如下:3.2.3 Zend/zend_hash.c3.2.3.1 zend_hash_index_exists()/ * 这里有一个宏HASH_FLAG_PACKED，为真就代表当前数组的key都是系统生成的，也就是说是按从0到1，2，3等等按序排列的，所以判读键为key的是否存在，直接检查arData数组中第idx个元素是否有定义就行了，这里不涉及什么hash查找，冲突解决等一系列问题。 * * 但如果HASH_FLAG_PACKED为假，那么肯定就需要先计算idx的hash值，找到key为idx的数据应该在arData的第几位才行。这就要通过函数zend_hash_index_find_bucket了。 /ZEND_API zend_bool ZEND_FASTCALL zend_hash_index_exists(const HashTable ht, zend_ulong h){ Bucket p; IS_CONSISTENT(ht); if (ht->u.flags & HASH_FLAG_PACKED) { if (h < ht->nNumUsed) { if (Z_TYPE(ht->arData[h].val) != IS_UNDEF) { return 1; } } return 0; } p = zend_hash_index_find_bucket(ht, h); return p ? 1 : 0;}3.2.3.2 zend_hash_find()在Zend/zend_hash.c中有zend_hash_find()的实现, code如下:/++– zend_hash_find –++// Returns the hash table data if found and NULL if not. /ZEND_API zval ZEND_FASTCALL zend_hash_find(const HashTable *ht, zend_string *key){ Bucket *p; IS_CONSISTENT(ht); p = zend_hash_find_bucket(ht, key); return p ? &p->val : NULL;}3.2.3.3 zend_hash_index_find_bucket()static zend_always_inline Bucket *zend_hash_index_find_bucket(const HashTable *ht, zend_ulong h){ uint32_t nIndex; uint32_t idx; Bucket *p, *arData; arData = ht->arData; nIndex = h | ht->nTableMask; idx = HT_HASH_EX(arData, nIndex); while (idx != HT_INVALID_IDX) { ZEND_ASSERT(idx < HT_IDX_TO_HASH(ht->nTableSize)); p = HT_HASH_TO_BUCKET_EX(arData, idx); if (p->h == h && !p->key) { return p; } idx = Z_NEXT(p->val); } return NULL;}3.2.3.4 zend_hash_find_bucket()static zend_always_inline Bucket *zend_hash_find_bucket(const HashTable *ht, zend_string *key){ zend_ulong h; uint32_t nIndex; uint32_t idx; Bucket *p, arData; h = zend_string_hash_val(key); arData = ht->arData; nIndex = h | ht->nTableMask; idx = HT_HASH_EX(arData, nIndex); while (EXPECTED(idx != HT_INVALID_IDX)) { p = HT_HASH_TO_BUCKET_EX(arData, idx); if (EXPECTED(p->key == key)) { / check for the same interned string */ return p; } else if (EXPECTED(p->h == h) && EXPECTED(p->key) && EXPECTED(ZSTR_LEN(p->key) == ZSTR_LEN(key)) && EXPECTED(memcmp(ZSTR_VAL(p->key), ZSTR_VAL(key), ZSTR_LEN(key)) == 0)) { return p; } idx = Z_NEXT(p->val); } return NULL;}这里需要明白一点，数字的哈希值就等于他本身，所以才有不计算h的哈希值，就执行h | ht->nTableMask。然后处理一下冲突，最后得出key为idx的数据是否存在于数组中。如果idx确确实实是字符串，那么思路更简单一点，最后通过zen_hash_find_bucket来判断是否存在，与上面zend_hash_index_find_bucket不同的是，函数中要先计算字符串key的哈希值，然后再执行h | ht->nTableMask。如下, zend_symtable_exists_ind –>ZEND_HANDLE_NUMERIC{ZEND_HANDLE_NUMERIC} ZEND_HANDLE_NUMERIC –> zend_hash_index_exists ZEND_HANDLE_NUMERIC –> zend_hash_exists_ind zend_hash_index_exists–>zend_hash_index_find_bucket zend_hash_exists_ind–>zend_hash_find zend_hash_find–>zend_hash_find_bucket4、总结isset效率高于array_key_exists, PHP7之后有30%左右的提升, php5.6有将近70%的提升。isset是语法结构, array_key_exists是函数, 调用开销要小。isset通过 Z_TYPE_P 获取变量类型，然后再进行判断实现的; array_key_exists则是通过hash查找来实现的。对于数组，isset的性能要高于array_key_exists 所以，如果数组比较大，我们应该用如下方法保证性能和准确性 isset or array_key_exists。5、扩展阅读PHP源码PHP7内核剖析升级 php7 后 isset 不太对了[[PHP源码阅读]empty和isset函数](http://www.hoohack.me/2016/05…深入理解PHP内核PHP安装与使用VLD查看opcode代码array_key_exists官方文档isset官方文档