We will introduce some usage details of include* require*,
and from the perspective of PHP application and zend source code , to analyze the implementation and calling process of __autoload spl_autoload_register respectively.
The purpose of the analysis is to deepen your understanding of these details and further understand the Zend source code.
PHP 版本：`php-5.6` 核心方法：` spl_autoload_register`
Manual loading
__autoload
spl_autoload_register
Include:include include_once requice requice_one
The following documents also apply to require.
The included file is first searched according to the path given by the parameter. If no directory (only the file name) is given, it is searched according to the directory specified by include_path. If the file is not found under include_path, include will finally search in the directory where the calling script file is located and the current working directory. The include construct emits a warning if the file is not found at the end; this is different from require, which emits a fatal error.If a path is defined - whether it is an absolute path (starting with a drive letter or under Windows, starting with / under Unix/Linux) or a relative path to the current directory (starting with . or ..) - --include_path will be completely ignored. For example, if a file starts with ../, the parser will look for the file in the parent directory of the current directory.
Code example:
FILE: run.php
<?php
ini_set('display_errors', '1');
// 直接包含
$ret = include 'class.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();
// 包含不存在的文件
$ret1 = include './class1.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret1, gettype($ret1));
// 重复包含
$ret2 = include './class.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();FILE: class.php
Result: 
Conclusion:
include Success return value: 1, Failure return value: false
include Failure will result in warning, will not interrupt the process
include_onceThe behavior is similar to the include statement, the only difference is if This file has already been included and will not be included again.
Modify run.php as follows:
<?php
ini_set('display_errors', '1');
// 直接包含
$ret = include 'class.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();
// 重复包含
$ret2 = include_once './class.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();Result:
include_once When included repeatedly, 1 will be returned directly, and this inclusion operation will be ignored and continue to execute
Modifyrequire
is almost identical toinclude, butrequireis generated on errorE_COMPILE_ERRORlevel error. (The script will stop running)
run.php as follows:
<?php
ini_set('display_errors', '1');
// 直接包含
$ret = require 'class.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();
// 包含不存在的文件
$ret1 = require './class1.php';
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret1, gettype($ret1));
require Successful inclusion, same as include, return value: 1
require Contains failure, throws Fatal error directly, and the process terminates
##require_oncerun.phpstatement is exactly the same as the
Modifyrequirestatement. The only difference is thatPHPwill check whether the file has been included. If so, will not be included again.
as follows: <div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">ini_set(&#39;display_errors&#39;, &#39;1&#39;);
// 直接包含
$ret = require_once &#39;class.php&#39;;
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();
// 重复包含
$ret2 = require_once &#39;./class.php&#39;;
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret, gettype($ret));
Foo::getFoo();
// 包含不存在的文件
$ret1 = require_once &#39;./class1.php&#39;;
echo sprintf("include ret-value:%d,ret-type:%s\n", $ret1, gettype($ret1));</pre><div class="contentsignin">Copy after login</div></div>Result:
##Conclusion :
include_once requice requice_one When successful, 1 will be returned. The difference lies in the processing of failed inclusion and repeated inclusion __autoload
.Usage example:FILE:
PHP code explanation
foo.php<div class="code" style="position:relative; padding:0px; margin:0px;"><div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"><?php
class Foo
{
static public function getFoo()
{
echo "I am foo!\n";
}
}</pre><div class="contentsignin">Copy after login</div></div><div class="contentsignin">Copy after login</div></div>FILE:
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false"><?php
ini_set(&#39;display_errors&#39;, &#39;1&#39;);
function __autoload($classname)
{
$filename = "./". lcfirst($classname) .".php";
include_once($filename);
}
Foo::getFoo();</pre><div class="contentsignin">Copy after login</div></div>Result:
➜ load git:(master) ✗ php run.php I am foo!
When encountering an uncontained class,
__autoload# will be triggered ## Load, if there is no such class in all loading rules,Fatal error
. <h3>Zend 代码解释</h3><p>下面，我们来看一下 <code>Zend 引擎是如何触发 __autoload 调用的。
利用 vld 来查看刚才执行过程中产生的 opcode，结果如下：
我们看到，PHP 运行到第 10 行时，所生成的 opcode 为：INIT_STATIC_METHOD_CALL，两个操作数都为常量（CONST）。
根据 opcode 的处理函数对应规则，我们利用 命名法 可以确定，
处理函数为：ZEND_INIT_STATIC_METHOD_CALL_SPEC_CONST_CONST_HANDLER
源码位置为：vim Zend/zend_vm_execute.h +3819
源码如下：
static int ZEND_FASTCALL ZEND_INIT_STATIC_METHOD_CALL_SPEC_CONST_CONST_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
USE_OPLINE
zval *function_name;
zend_class_entry *ce;
call_slot *call = EX(call_slots) + opline->result.num;
SAVE_OPLINE();
if (IS_CONST == IS_CONST) {
/* no function found. try a static method in class */
if (CACHED_PTR(opline->op1.literal->cache_slot)) {
ce = CACHED_PTR(opline->op1.literal->cache_slot);
} else {
ce = zend_fetch_class_by_name(Z_STRVAL_P(opline->op1.zv), Z_STRLEN_P(opline->op1.zv), opline->op1.literal + 1, opline->extended_value TSRMLS_CC);
if (UNEXPECTED(EG(exception) != NULL)) {
HANDLE_EXCEPTION();
}
if (UNEXPECTED(ce == NULL)) {
zend_error_noreturn(E_ERROR, "Class '%s' not found", Z_STRVAL_P(opline->op1.zv));
}
CACHE_PTR(opline->op1.literal->cache_slot, ce);
}
call->called_scope = ce;
} else {
ce = EX_T(opline->op1.var).class_entry;
if (opline->extended_value == ZEND_FETCH_CLASS_PARENT || opline->extended_value == ZEND_FETCH_CLASS_SELF) {
call->called_scope = EG(called_scope);
} else {
call->called_scope = ce;
}
}
if (IS_CONST == IS_CONST &&
IS_CONST == IS_CONST &&
CACHED_PTR(opline->op2.literal->cache_slot)) {
call->fbc = CACHED_PTR(opline->op2.literal->cache_slot);
} else if (IS_CONST != IS_CONST &&
IS_CONST == IS_CONST &&
(call->fbc = CACHED_POLYMORPHIC_PTR(opline->op2.literal->cache_slot, ce))) {
/* do nothing */
} else if (IS_CONST != IS_UNUSED) {
char *function_name_strval = NULL;
int function_name_strlen = 0;
if (IS_CONST == IS_CONST) {
function_name_strval = Z_STRVAL_P(opline->op2.zv);
function_name_strlen = Z_STRLEN_P(opline->op2.zv);
} else {
function_name = opline->op2.zv;
if (UNEXPECTED(Z_TYPE_P(function_name) != IS_STRING)) {
if (UNEXPECTED(EG(exception) != NULL)) {
HANDLE_EXCEPTION();
}
zend_error_noreturn(E_ERROR, "Function name must be a string");
} else {
function_name_strval = Z_STRVAL_P(function_name);
function_name_strlen = Z_STRLEN_P(function_name);
}
}
if (function_name_strval) {
if (ce->get_static_method) {
call->fbc = ce->get_static_method(ce, function_name_strval, function_name_strlen TSRMLS_CC);
} else {
call->fbc = zend_std_get_static_method(ce, function_name_strval, function_name_strlen, ((IS_CONST == IS_CONST) ? (opline->op2.literal + 1) : NULL) TSRMLS_CC);
}
if (UNEXPECTED(call->fbc == NULL)) {
zend_error_noreturn(E_ERROR, "Call to undefined method %s::%s()", ce->name, function_name_strval);
}
if (IS_CONST == IS_CONST &&
EXPECTED(call->fbc->type <= ZEND_USER_FUNCTION) &&
EXPECTED((call->fbc->common.fn_flags & (ZEND_ACC_CALL_VIA_HANDLER|ZEND_ACC_NEVER_CACHE)) == 0)) {
if (IS_CONST == IS_CONST) {
CACHE_PTR(opline->op2.literal->cache_slot, call->fbc);
} else {
CACHE_POLYMORPHIC_PTR(opline->op2.literal->cache_slot, ce, call->fbc);
}
}
}
if (IS_CONST != IS_CONST) {
}
} else {
if (UNEXPECTED(ce->constructor == NULL)) {
zend_error_noreturn(E_ERROR, "Cannot call constructor");
}
if (EG(This) && Z_OBJCE_P(EG(This)) != ce->constructor->common.scope && (ce->constructor->common.fn_flags & ZEND_ACC_PRIVATE)) {
zend_error_noreturn(E_ERROR, "Cannot call private %s::__construct()", ce->name);
}
call->fbc = ce->constructor;
}
if (call->fbc->common.fn_flags & ZEND_ACC_STATIC) {
call->object = NULL;
} else {
if (EG(This) &&
Z_OBJ_HT_P(EG(This))->get_class_entry &&
!instanceof_function(Z_OBJCE_P(EG(This)), ce TSRMLS_CC)) {
/* We are calling method of the other (incompatible) class,
but passing $this. This is done for compatibility with php-4. */
if (call->fbc->common.fn_flags & ZEND_ACC_ALLOW_STATIC) {
zend_error(E_DEPRECATED, "Non-static method %s::%s() should not be called statically, assuming $this from incompatible context", call->fbc->common.scope->name, call->fbc->common.function_name);
} else {
/* An internal function assumes $this is present and won't check that. So PHP would crash by allowing the call. */
zend_error_noreturn(E_ERROR, "Non-static method %s::%s() cannot be called statically, assuming $this from incompatible context", call->fbc->common.scope->name, call->fbc->common.function_name);
}
}
if ((call->object = EG(This))) {
Z_ADDREF_P(call->object);
call->called_scope = Z_OBJCE_P(call->object);
}
}
call->num_additional_args = 0;
call->is_ctor_call = 0;
EX(call) = call;
CHECK_EXCEPTION();
ZEND_VM_NEXT_OPCODE();
}通过以上源码，我们发现关键方法为 zend_fetch_class_by_name，跟进此方法：
zend_class_entry *zend_fetch_class_by_name(const char *class_name, uint class_name_len, const zend_literal *key, int fetch_type TSRMLS_DC) /* {{{ */
{
zend_class_entry **pce;
int use_autoload = (fetch_type & ZEND_FETCH_CLASS_NO_AUTOLOAD) == 0;
if (zend_lookup_class_ex(class_name, class_name_len, key, use_autoload, &pce TSRMLS_CC) == FAILURE) {
if (use_autoload) {
if ((fetch_type & ZEND_FETCH_CLASS_SILENT) == 0 && !EG(exception)) {
if ((fetch_type & ZEND_FETCH_CLASS_MASK) == ZEND_FETCH_CLASS_INTERFACE) {
zend_error(E_ERROR, "Interface '%s' not found", class_name);
} else if ((fetch_type & ZEND_FETCH_CLASS_MASK) == ZEND_FETCH_CLASS_TRAIT) {
zend_error(E_ERROR, "Trait '%s' not found", class_name);
} else {
zend_error(E_ERROR, "Class '%s' not found", class_name);
}
}
}
return NULL;
}
return *pce;
}我们发现是通过 zend_lookup_class_ex 来获取类，继续跟进：
ZEND_API int zend_lookup_class_ex(const char *name, int name_length, const zend_literal *key, int use_autoload, zend_class_entry ***ce TSRMLS_DC) /* {{{ */
{
...
/* 注意：在 类的符号表 中没有找到示例中调用的类 foo */
if (zend_hash_quick_find(EG(class_table), lc_name, lc_length, hash, (void **) ce) == SUCCESS) {
if (!key) {
free_alloca(lc_free, use_heap);
}
return SUCCESS;
}
...
/*
* ZVAL_STRINGL 为 zval （即 PHP 类型的实现基础 zvalue_value）赋值宏，
* 此处实现了 把 ZEND_AUTOLOAD_FUNC_NAME 值 赋给 autoload_function
* #define ZEND_AUTOLOAD_FUNC_NAME "__autoload"
*/
ZVAL_STRINGL(&autoload_function, ZEND_AUTOLOAD_FUNC_NAME, sizeof(ZEND_AUTOLOAD_FUNC_NAME) - 1, 0);
...
fcall_info.size = sizeof(fcall_info);
fcall_info.function_table = EG(function_table);
fcall_info.function_name = &autoload_function;
fcall_info.symbol_table = NULL;
fcall_info.retval_ptr_ptr = &retval_ptr;
fcall_info.param_count = 1;
fcall_info.params = args;
fcall_info.object_ptr = NULL;
fcall_info.no_separation = 1;
fcall_cache.initialized = EG(autoload_func) ? 1 : 0;
fcall_cache.function_handler = EG(autoload_func); /* 留意此处 */
fcall_cache.calling_scope = NULL;
fcall_cache.called_scope = NULL;
fcall_cache.object_ptr = NULL;
...
retval = zend_call_function(&fcall_info, &fcall_cache TSRMLS_CC); /* 调用自动加载函数 */
...
EG(autoload_func) = fcall_cache.function_handler;
zval_ptr_dtor(&class_name_ptr);
zend_hash_quick_del(EG(in_autoload), lc_name, lc_length, hash);
...
}我们发现是通过 zend_call_function 出发了自动加载函数，而且看到了加载方法的名字 __autoload （宏：ZEND_AUTOLOAD_FUNC_NAME）
zend_call_function 中会做一下检测并调用等，而且我们看到 zend_lookup_class_ex 的返回结果即为 zend_call_function 的返回结果。
接下来我们逐步退出函数调用栈：
假设 zend_call_function 调用失败，返回 FALSE，
则 zend_lookup_class_ex 返回 FALSE；
则 zend_fetch_class_by_name 返回 NULL；
则 ZEND_INIT_STATIC_METHOD_CALL_SPEC_CONST_CONST_HANDLER 抛出异常 Class ** not found，如下图所示：
至此，我们通过 PHP 代码 Zend 源码 了解了 __autoload 的调用过程。
我们知道 __autoload 现在已并不推荐使用，
它的缺点也很明显，不支持多个自动加载函数。
将函数注册到SPL __autoload函数队列中。如果该队列中的函数尚未激活，则激活它们。如果在你的程序中已经实现了__autoload()函数，它必须显式注册到__autoload()队列中。
使用示例：
FILE:foo.php
(同上 __autoload)
FILE:foo2.class.php
<?php
class Foo2
{
static public function getFoo2()
{
echo "I am foo2!\n";
}
}FILE:run.php
<?php
ini_set('display_errors', '1');
$my_autoload1 = function ($classname)
{
echo "entry my_autoload1 \n";
$filename = "./". lcfirst($classname) .".php";
include_once($filename);
};
$my_autoload2 = function ($classname)
{
echo "entry my_autoload2 \n";
$filename = "./". lcfirst($classname) .".class.php";
include_once($filename);
};
spl_autoload_register($my_autoload1);
spl_autoload_register($my_autoload2);
Foo::getFoo();
Foo2::getFoo2();结果如下：
我们看到，调用 getFoo2 时，会先调用第一个注册的 autoload 方法，如果没找到对应的类，会产生 warning 并继续调用后边注册的 autoload 方法。
说明了 PHP 内核中为通过 spl_autoload_register 注册的 autoload 方法维护了一个队列，当前文件为包含调用类，便会触发此队列，并依次调用，直到队列结束 或者 找到对应类。
首先，我们看一下 PHP 文件生成的 opcode
我们发现，其方法调用所生成的 opcode 跟 __autoload 一样，
但是我们之前调用了 `spl_autoload_register，
那么，看一下 spl_autoload_register 的源码：
FILE: ext/spl/php_spl.c*
PHP_FUNCTION(spl_autoload_register)
{
char *func_name, *error = NULL;
int func_name_len;
char *lc_name = NULL;
zval *zcallable = NULL;
zend_bool do_throw = 1;
zend_bool prepend = 0;
zend_function *spl_func_ptr;
autoload_func_info alfi;
zval *obj_ptr;
zend_fcall_info_cache fcc;
if (zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET, ZEND_NUM_ARGS() TSRMLS_CC, "|zbb", &zcallable, &do_throw, &prepend) == FAILURE) {
return;
}
if (ZEND_NUM_ARGS()) {
if (Z_TYPE_P(zcallable) == IS_STRING) {
if (Z_STRLEN_P(zcallable) == sizeof("spl_autoload_call") - 1) {
if (!zend_binary_strcasecmp(Z_STRVAL_P(zcallable), sizeof("spl_autoload_call"), "spl_autoload_call", sizeof("spl_autoload_call"))) {
if (do_throw) {
zend_throw_exception_ex(spl_ce_LogicException, 0 TSRMLS_CC, "Function spl_autoload_call() cannot be registered");
}
RETURN_FALSE;
}
}
}
if (!zend_is_callable_ex(zcallable, NULL, IS_CALLABLE_STRICT, &func_name, &func_name_len, &fcc, &error TSRMLS_CC)) {
alfi.ce = fcc.calling_scope;
alfi.func_ptr = fcc.function_handler;
obj_ptr = fcc.object_ptr;
if (Z_TYPE_P(zcallable) == IS_ARRAY) {
if (!obj_ptr && alfi.func_ptr && !(alfi.func_ptr->common.fn_flags & ZEND_ACC_STATIC)) {
if (do_throw) {
zend_throw_exception_ex(spl_ce_LogicException, 0 TSRMLS_CC, "Passed array specifies a non static method but no object (%s)", error);
}
if (error) {
efree(error);
}
efree(func_name);
RETURN_FALSE;
}
else if (do_throw) {
zend_throw_exception_ex(spl_ce_LogicException, 0 TSRMLS_CC, "Passed array does not specify %s %smethod (%s)", alfi.func_ptr ? "a callable" : "an existing", !obj_ptr ? "static " : "", error);
}
if (error) {
efree(error);
}
efree(func_name);
RETURN_FALSE;
} else if (Z_TYPE_P(zcallable) == IS_STRING) {
if (do_throw) {
zend_throw_exception_ex(spl_ce_LogicException, 0 TSRMLS_CC, "Function '%s' not %s (%s)", func_name, alfi.func_ptr ? "callable" : "found", error);
}
if (error) {
efree(error);
}
efree(func_name);
RETURN_FALSE;
} else {
if (do_throw) {
zend_throw_exception_ex(spl_ce_LogicException, 0 TSRMLS_CC, "Illegal value passed (%s)", error);
}
if (error) {
efree(error);
}
efree(func_name);
RETURN_FALSE;
}
}
alfi.closure = NULL;
alfi.ce = fcc.calling_scope;
alfi.func_ptr = fcc.function_handler;
obj_ptr = fcc.object_ptr;
if (error) {
efree(error);
}
lc_name = safe_emalloc(func_name_len, 1, sizeof(long) + 1);
zend_str_tolower_copy(lc_name, func_name, func_name_len);
efree(func_name);
if (Z_TYPE_P(zcallable) == IS_OBJECT) {
alfi.closure = zcallable;
Z_ADDREF_P(zcallable);
lc_name = erealloc(lc_name, func_name_len + 2 + sizeof(zend_object_handle));
memcpy(lc_name + func_name_len, &Z_OBJ_HANDLE_P(zcallable),
sizeof(zend_object_handle));
func_name_len += sizeof(zend_object_handle);
lc_name[func_name_len] = '\0';
}
if (SPL_G(autoload_functions) && zend_hash_exists(SPL_G(autoload_functions), (char*)lc_name, func_name_len+1)) {
if (alfi.closure) {
Z_DELREF_P(zcallable);
}
goto skip;
}
if (obj_ptr && !(alfi.func_ptr->common.fn_flags & ZEND_ACC_STATIC)) {
/* add object id to the hash to ensure uniqueness, for more reference look at bug #40091 */
lc_name = erealloc(lc_name, func_name_len + 2 + sizeof(zend_object_handle));
memcpy(lc_name + func_name_len, &Z_OBJ_HANDLE_P(obj_ptr), sizeof(zend_object_handle));
func_name_len += sizeof(zend_object_handle);
lc_name[func_name_len] = '\0';
alfi.obj = obj_ptr;
Z_ADDREF_P(alfi.obj);
} else {
alfi.obj = NULL;
}
if (!SPL_G(autoload_functions)) {
ALLOC_HASHTABLE(SPL_G(autoload_functions));
zend_hash_init(SPL_G(autoload_functions), 1, NULL, (dtor_func_t) autoload_func_info_dtor, 0);
}
zend_hash_find(EG(function_table), "spl_autoload", sizeof("spl_autoload"), (void **) &spl_func_ptr);
if (EG(autoload_func) == spl_func_ptr) { /* registered already, so we insert that first */
autoload_func_info spl_alfi;
spl_alfi.func_ptr = spl_func_ptr;
spl_alfi.obj = NULL;
spl_alfi.ce = NULL;
spl_alfi.closure = NULL;
zend_hash_add(SPL_G(autoload_functions), "spl_autoload", sizeof("spl_autoload"), &spl_alfi, sizeof(autoload_func_info), NULL);
if (prepend && SPL_G(autoload_functions)->nNumOfElements > 1) {
/* Move the newly created element to the head of the hashtable */
HT_MOVE_TAIL_TO_HEAD(SPL_G(autoload_functions));
}
}
if (zend_hash_add(SPL_G(autoload_functions), lc_name, func_name_len+1, &alfi.func_ptr, sizeof(autoload_func_info), NULL) == FAILURE) {
if (obj_ptr && !(alfi.func_ptr->common.fn_flags & ZEND_ACC_STATIC)) {
Z_DELREF_P(alfi.obj);
}
if (alfi.closure) {
Z_DELREF_P(alfi.closure);
}
}
if (prepend && SPL_G(autoload_functions)->nNumOfElements > 1) {
/* Move the newly created element to the head of the hashtable */
HT_MOVE_TAIL_TO_HEAD(SPL_G(autoload_functions));
}
skip:
efree(lc_name);
}
if (SPL_G(autoload_functions)) {
zend_hash_find(EG(function_table), "spl_autoload_call", sizeof("spl_autoload_call"), (void **) &EG(autoload_func)); /* 注意此处 */
} else {
zend_hash_find(EG(function_table), "spl_autoload", sizeof("spl_autoload"), (void **) &EG(autoload_func));
}
RETURN_TRUE;
} /* }}} */通过分析源码，我们发现 spl_autoload_register 会把注册的自动加载函数添加到 autoload_functions 中，最后将 autoload_functions 赋值给 EG(autoload_func) （上方源码倒数第一个 if 判断逻辑中）。
而有印象的同学会发现，EG(autoload_func) 在分析 __autoload 调用源码时出现过（可以划到之前的分析查看），它是执行环境全局结构体中的成员，出现调用大概源码如下：
ZEND_API int zend_lookup_class_ex(const char *name, int name_length, const zend_literal *key, int use_autoload, zend_class_entry ***ce TSRMLS_DC)
{
...
fcall_info.size = sizeof(fcall_info);
fcall_info.function_table = EG(function_table);
fcall_info.function_name = &autoload_function;
fcall_info.symbol_table = NULL;
fcall_info.retval_ptr_ptr = &retval_ptr;
fcall_info.param_count = 1;
fcall_info.params = args;
fcall_info.object_ptr = NULL;
fcall_info.no_separation = 1;
fcall_cache.initialized = EG(autoload_func) ? 1 : 0;
fcall_cache.function_handler = EG(autoload_func); /* 注意这里 */
fcall_cache.calling_scope = NULL;
fcall_cache.called_scope = NULL;
fcall_cache.object_ptr = NULL;
zend_exception_save(TSRMLS_C);
retval = zend_call_function(&fcall_info, &fcall_cache TSRMLS_CC);
zend_exception_restore(TSRMLS_C);
...
return retval;
}分析到这里，我们已经知道了，spl_autoload_register 注册的函数是如何在 PHP 代码调用时被触发的。
感兴趣的同学可以继续查看一下 zend_call_function 的源码，了解具体的调用方式。
Register the autoload function through spl_autoload_register, which will maintain a autoload queue in the Zend engine, and you can add multiple autoload function, and trigger the call of autoload_func when PHP calls a class unknown to the current file.
At the same time, careful students will also find from the spl_autoload_register source code that when the method passed in during registration cannot be called, if there is an implementation spl_autoload, it will also Be registered in the autoload queue.
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