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20.5 字典表创建和基础类预加载
20.5.1 systemDictionary.cpp/hpp
20.5.1.1 SystemDictionary::initialize
void SystemDictionary::initialize(TRAPS) {// Allocate arraysassert(dictionary() == NULL,"SystemDictionary should only be initialized once");_sdgeneration = 0;// 创建字典（就是Hash Table）_dictionary = new Dictionary(calculate_systemdictionary_size(PredictedLoadedClassCount));// 创建占位符表（就是Hash Table）_placeholders = new PlaceholderTable(_nof_buckets);_number_of_modifications = 0;// 创建约束表（就是Hash Table）_loader_constraints = new LoaderConstraintTable(_loader_constraint_size);// 创建解析错误表（就是Hash Table）_resolution_errors = new ResolutionErrorTable(_resolution_error_size);// 创建调用方法符号表（就是Hash Table）_invoke_method_table = new SymbolPropertyTable(_invoke_method_size);// 分配一个数组来存放系统类加载锁_system_loader_lock_obj = oopFactory::new_intArray(0, CHECK);// 初始化基础类，细节继续看`章节20.5.1.2`initialize_preloaded_classes(CHECK);
#if INCLUDE_JFRjfr_event_handler_proxy = SymbolTable::new_permanent_symbol("jdk/jfr/proxy/internal/EventHandlerProxy", CHECK);
#endif // INCLUDE_JFR
}
20.5.1.2 initialize_preloaded_classes
这一部分也用到了很多宏定义，咱们先把宏展开后再来讲解
class SystemDictionary : AllStatic {friend class VMStructs;friend class SystemDictionaryHandles;public:enum WKID {NO_WKID = 0,#define WK_KLASS_ENUM(name, symbol, ignore_o) WK_KLASS_ENUM_NAME(name), WK_KLASS_ENUM_NAME(symbol) = WK_KLASS_ENUM_NAME(name),WK_KLASSES_DO(WK_KLASS_ENUM)#undef WK_KLASS_ENUMWKID_LIMIT,FIRST_WKID = NO_WKID + 1};
}
// ==============第1块宏：枚举=================
// 宏展开前
#define WK_KLASS_ENUM(name, symbol, ignore_o) WK_KLASS_ENUM_NAME(name), WK_KLASS_ENUM_NAME(symbol) = WK_KLASS_ENUM_NAME(name),WK_KLASSES_DO(WK_KLASS_ENUM)
// 宏展开后
// 第1步WK_KLASS_ENUM(String_klass,java_lang_String,Pre)WK_KLASS_ENUM_NAME(String_klass), WK_KLASS_ENUM_NAME(java_lang_String) = WK_KLASS_ENUM_NAME(String_klass),
// 第2步// 前置宏定义#define WK_KLASS_ENUM_NAME(kname) kname##_knumString_klass_knum,java_lang_String_knum=String_klass_knum
// 最终 enum WKID 宏展开后enum WKID {NO_WKID = 0,Object_klass_knum, java_lang_Object_knum = Object_klass_knum, \String_klass_knum, java_lang_String_knum = String_klass_knum, \Class_klass_knum, java_lang_Class_knum = Class_klass_knum, \Cloneable_klass_knum, java_lang_Cloneable_knum = Cloneable_klass_knum, \ClassLoader_klass_knum, java_lang_ClassLoader_knum = ClassLoader_klass_knum, \Serializable_klass_knum, java_io_Serializable_knum = Serializable_klass_knum, \System_klass_knum, java_lang_System_knum = System_klass_knum, \...WKID_LIMIT,FIRST_WKID = NO_WKID + 1}; // ==============第2块宏：函数=================
// 方法的宏展开前
#define WK_KLASS_DECLARE(name, symbol, option) \static Klass* name() { return check_klass_##option(_well_known_klasses[WK_KLASS_ENUM_NAME(name)]); } \static Klass** name##_addr() { \return &SystemDictionary::_well_known_klasses[SystemDictionary::WK_KLASS_ENUM_NAME(name)]; \}WK_KLASSES_DO(WK_KLASS_DECLARE);#undef WK_KLASS_DECLARE
// 方法的宏展开后，这里以 Object_klass为例，其他的类推static Klass* Object_klass() { return check_klass_pre(_well_known_klasses[Object_klass_knum]); } static Klass** Object_klass_addr() { return &SystemDictionary::_well_known_klasses[SystemDictionary::Object_klass_knum]; }// ==============第3块宏：wk_init_info数组=================
// 宏展开前
static const short wk_init_info[] = {#define WK_KLASS_INIT_INFO(name, symbol, option) \( ((int)vmSymbols::VM_SYMBOL_ENUM_NAME(symbol) \<< SystemDictionary::CEIL_LG_OPTION_LIMIT) \| (int)SystemDictionary::option ),WK_KLASSES_DO(WK_KLASS_INIT_INFO)#undef WK_KLASS_INIT_INFO0
};
// 宏展开后，这里还是以 Object_klass 为例，其他的类推
static const short wk_init_info[] = {( ((int)vmSymbols::java_lang_Object_enum << SystemDictionary::CEIL_LG_OPTION_LIMIT) | (int)SystemDictionary::Pre ),0
};
要使用的宏已经展开了，下面接着讲正题
void SystemDictionary::initialize_preloaded_classes(TRAPS) {assert(WK_KLASS(Object_klass) == NULL, "preloaded classes should only be initialized once");// Preload commonly used klassesWKID scan = FIRST_WKID;// first do Object, then String, Classif (UseSharedSpaces) {initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(Object_klass), scan, CHECK);// Initialize the constant pool for the Object_classInstanceKlass* ik = InstanceKlass::cast(Object_klass());ik->constants()->restore_unshareable_info(CHECK);initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(Class_klass), scan, CHECK);} else {// 直接看这一步，这个的实现往后看，完成后，那些基础的类就被加载进来了，现在知道为啥我们在Java代码时，基础类（Object/Class/String等）都是不需要额外加载和import进来的，原因就在这initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(Class_klass), scan, CHECK);}// 计算String 和 Class 类的字段偏移java_lang_String::compute_offsets();java_lang_Class::compute_offsets();// 给8个基础类型创建它们的Class类型对象（在虚拟机中就是InstanceMirrorKlass）Universe::initialize_basic_type_mirrors(CHECK);// 修正mirrorUniverse::fixup_mirrors(CHECK);// 接下来都是继续加载基础类initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(Reference_klass), scan, CHECK);// Preload ref klasses and set reference typesInstanceKlass::cast(WK_KLASS(Reference_klass))->set_reference_type(REF_OTHER);InstanceRefKlass::update_nonstatic_oop_maps(WK_KLASS(Reference_klass));initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(Cleaner_klass), scan, CHECK);InstanceKlass::cast(WK_KLASS(SoftReference_klass))->set_reference_type(REF_SOFT);InstanceKlass::cast(WK_KLASS(WeakReference_klass))->set_reference_type(REF_WEAK);InstanceKlass::cast(WK_KLASS(FinalReference_klass))->set_reference_type(REF_FINAL);InstanceKlass::cast(WK_KLASS(PhantomReference_klass))->set_reference_type(REF_PHANTOM);InstanceKlass::cast(WK_KLASS(Cleaner_klass))->set_reference_type(REF_CLEANER);initialize_wk_klasses_through(WK_KLASS_ENUM_NAME(ReferenceQueue_klass), scan, CHECK);// JSR 292 classesWKID jsr292_group_start = WK_KLASS_ENUM_NAME(MethodHandle_klass);WKID jsr292_group_end = WK_KLASS_ENUM_NAME(VolatileCallSite_klass);initialize_wk_klasses_until(jsr292_group_start, scan, CHECK);if (EnableInvokeDynamic) {initialize_wk_klasses_through(jsr292_group_end, scan, CHECK);} else {// Skip the JSR 292 classes, if not enabled.scan = WKID(jsr292_group_end + 1);}initialize_wk_klasses_until(WKID_LIMIT, scan, CHECK);// 基础类型的包装类的Klass_box_klasses[T_BOOLEAN] = WK_KLASS(Boolean_klass);_box_klasses[T_CHAR] = WK_KLASS(Character_klass);_box_klasses[T_FLOAT] = WK_KLASS(Float_klass);_box_klasses[T_DOUBLE] = WK_KLASS(Double_klass);_box_klasses[T_BYTE] = WK_KLASS(Byte_klass);_box_klasses[T_SHORT] = WK_KLASS(Short_klass);_box_klasses[T_INT] = WK_KLASS(Integer_klass);_box_klasses[T_LONG] = WK_KLASS(Long_klass);//_box_klasses[T_OBJECT] = WK_KLASS(object_klass);//_box_klasses[T_ARRAY] = WK_KLASS(object_klass);{ // 计算加载类时应该使用 loadClass 还是 loadClassInternalMethod* method = InstanceKlass::cast(ClassLoader_klass())->find_method(vmSymbols::loadClassInternal_name(), vmSymbols::string_class_signature());_has_loadClassInternal = (method != NULL);}{// 计算要不要用 checkPackageAccess 方法Method* method = InstanceKlass::cast(ClassLoader_klass())->find_method(vmSymbols::checkPackageAccess_name(), vmSymbols::class_protectiondomain_signature());_has_checkPackageAccess = (method != NULL);}
}
SystemDictionary::initialize_wk_klasses_until
void SystemDictionary::initialize_wk_klasses_until(WKID limit_id, WKID &start_id, TRAPS) {assert((int)start_id <= (int)limit_id, "IDs are out of order!");// 这里就是遍历 WKID 枚举，把基础类都加载一遍，看本章节前面对宏展开的那块for (int id = (int)start_id; id < (int)limit_id; id++) {assert(id >= (int)FIRST_WKID && id < (int)WKID_LIMIT, "oob");int info = wk_init_info[id - FIRST_WKID];int sid = (info >> CEIL_LG_OPTION_LIMIT);int opt = (info & right_n_bits(CEIL_LG_OPTION_LIMIT));// 直接看这，这一步完成后，就对基础加载完成了，继续往后看initialize_wk_klass((WKID)id, opt, CHECK);}// 下一次开始的位置换到本次limit的位置start_id = limit_id;
}
SystemDictionary::initialize_wk_klass
bool SystemDictionary::initialize_wk_klass(WKID id, int init_opt, TRAPS) {assert(id >= (int)FIRST_WKID && id < (int)WKID_LIMIT, "oob");int info = wk_init_info[id - FIRST_WKID];int sid = (info >> CEIL_LG_OPTION_LIMIT);// 拿到对应的符号Symbol* symbol = vmSymbols::symbol_at((vmSymbols::SID)sid);// 从数组 _well_known_klasses 中拿到已加载的类Klass** klassp = &_well_known_klasses[id];bool must_load = (init_opt < SystemDictionary::Opt);if ((*klassp) == NULL) { // 初始klassp肯定是null// 下面就是真正类加载的环节了，这个先不讲，留待后续类加载一章来讲if (must_load) {(*klassp) = resolve_or_fail(symbol, true, CHECK_0); // 加载必须的类} else {(*klassp) = resolve_or_null(symbol, CHECK_0); // 加载可选的类}}return ((*klassp) != NULL);
}
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