第22章-vtable和itable的重新初始化

这个函数的调用流程是

init.cpp->init_globals()

universe.cpp->universe_post_init()

bool universe_post_init() {// 防止二次初始化assert(!is_init_completed(), "Error: initialization not yet completed!");Universe::_fully_initialized = true;EXCEPTION_MARK;{ ResourceMark rm;// 解释器初始化Interpreter::initialize();      // needed for interpreter entry pointsif (!UseSharedSpaces) {HandleMark hm(THREAD);// 获取Object klass的句柄KlassHandle ok_h(THREAD, SystemDictionary::Object_klass());// 对vtable进行重新初始化，细节看`章节22.1`Universe::reinitialize_vtable_of(ok_h, CHECK_false);// 对itable重新进行初始化：vtable我们在`章节20.1 20.2`中已经讲过，itable就是针对Java接口方法的实现方法，只有普通类才有，Interface本身没有itableUniverse::reinitialize_itables(CHECK_false);}}HandleMark hm(THREAD);Klass* k;instanceKlassHandle k_h;// 创建一个空 java.lang.Class 数组Universe::_the_empty_class_klass_array = oopFactory::new_objArray(SystemDictionary::Class_klass(), 0, CHECK_false);// 解析 OutOfMemoryError 类k = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_OutOfMemoryError(), true, CHECK_false);// 生成句柄k_h = instanceKlassHandle(THREAD, k);// 分配空间存放 OutOfMemoryError 内存溢出时各对应属性字段Universe::_out_of_memory_error_java_heap = k_h->allocate_instance(CHECK_false);Universe::_out_of_memory_error_metaspace = k_h->allocate_instance(CHECK_false);Universe::_out_of_memory_error_class_metaspace = k_h->allocate_instance(CHECK_false);Universe::_out_of_memory_error_array_size = k_h->allocate_instance(CHECK_false);Universe::_out_of_memory_error_gc_overhead_limit =k_h->allocate_instance(CHECK_false);Universe::_out_of_memory_error_realloc_objects = k_h->allocate_instance(CHECK_false);// 解析 NullPointerException 类及设置对应属性字段k = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_NullPointerException(), true, CHECK_false);Universe::_null_ptr_exception_instance = InstanceKlass::cast(k)->allocate_instance(CHECK_false);// 解析 ArithmeticException 类及设置对应属性字段k = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_ArithmeticException(), true, CHECK_false);Universe::_arithmetic_exception_instance = InstanceKlass::cast(k)->allocate_instance(CHECK_false);//  解析虚拟机错误 VirtualMachineError 类及设置对应属性字段k = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_VirtualMachineError(), true, CHECK_false);bool linked = InstanceKlass::cast(k)->link_class_or_fail(CHECK_false);if (!linked) {tty->print_cr("Unable to link/verify VirtualMachineError class");return false; // initialization failed}Universe::_virtual_machine_error_instance =InstanceKlass::cast(k)->allocate_instance(CHECK_false);Universe::_vm_exception = InstanceKlass::cast(k)->allocate_instance(CHECK_false);if (!DumpSharedSpaces) {// 创建各错误/异常抛出时需要设置的 msg 信息Handle msg = java_lang_String::create_from_str("Java heap space", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_java_heap, msg());msg = java_lang_String::create_from_str("Metaspace", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_metaspace, msg());msg = java_lang_String::create_from_str("Compressed class space", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_class_metaspace, msg());msg = java_lang_String::create_from_str("Requested array size exceeds VM limit", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_array_size, msg());msg = java_lang_String::create_from_str("GC overhead limit exceeded", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_gc_overhead_limit, msg());msg = java_lang_String::create_from_str("Java heap space: failed reallocation of scalar replaced objects", CHECK_false);java_lang_Throwable::set_message(Universe::_out_of_memory_error_realloc_objects, msg());msg = java_lang_String::create_from_str("/ by zero", CHECK_false);java_lang_Throwable::set_message(Universe::_arithmetic_exception_instance, msg());// Setup the array of errors that have preallocated backtracek = Universe::_out_of_memory_error_java_heap->klass();assert(k->name() == vmSymbols::java_lang_OutOfMemoryError(), "should be out of memory error");k_h = instanceKlassHandle(THREAD, k);int len = (StackTraceInThrowable) ? (int)PreallocatedOutOfMemoryErrorCount : 0;Universe::_preallocated_out_of_memory_error_array = oopFactory::new_objArray(k_h(), len, CHECK_false);for (int i=0; i<len; i++) {oop err = k_h->allocate_instance(CHECK_false);Handle err_h = Handle(THREAD, err);java_lang_Throwable::allocate_backtrace(err_h, CHECK_false);Universe::preallocated_out_of_memory_errors()->obj_at_put(i, err_h());}Universe::_preallocated_out_of_memory_error_avail_count = (jint)len;}// 对 Finalizer 类的处理InstanceKlass::cast(SystemDictionary::Finalizer_klass())->link_class(CHECK_false);Method* m = InstanceKlass::cast(SystemDictionary::Finalizer_klass())->find_method(vmSymbols::register_method_name(),vmSymbols::register_method_signature());if (m == NULL || !m->is_static()) {tty->print_cr("Unable to link/verify Finalizer.register method");return false; // initialization failed (cannot throw exception yet)}Universe::_finalizer_register_cache->init(SystemDictionary::Finalizer_klass(), m);// 对 Unsafe 类的处理InstanceKlass::cast(SystemDictionary::misc_Unsafe_klass())->link_class(CHECK_false);m = InstanceKlass::cast(SystemDictionary::misc_Unsafe_klass())->find_method(vmSymbols::throwIllegalAccessError_name(),vmSymbols::void_method_signature());if (m != NULL && !m->is_static()) {// Note null is okay; this method is used in itables, and if it is null,// then AbstractMethodError is thrown instead.tty->print_cr("Unable to link/verify Unsafe.throwIllegalAccessError method");return false; // initialization failed (cannot throw exception yet)}Universe::_throw_illegal_access_error_cache->init(SystemDictionary::misc_Unsafe_klass(), m);// 对 ClassLoader 类的处理InstanceKlass::cast(SystemDictionary::ClassLoader_klass())->link_class(CHECK_false);m = InstanceKlass::cast(SystemDictionary::ClassLoader_klass())->find_method(vmSymbols::addClass_name(), vmSymbols::class_void_signature());if (m == NULL || m->is_static()) {tty->print_cr("Unable to link/verify ClassLoader.addClass method");return false; // initialization failed (cannot throw exception yet)}Universe::_loader_addClass_cache->init(SystemDictionary::ClassLoader_klass(), m);// 对 ProtectionDomain 类的处理InstanceKlass::cast(SystemDictionary::ProtectionDomain_klass())->link_class(CHECK_false);m = InstanceKlass::cast(SystemDictionary::ProtectionDomain_klass())->find_method(vmSymbols::impliesCreateAccessControlContext_name(),vmSymbols::void_boolean_signature());// Allow NULL which should only happen with bootstrapping.if (m != NULL) {if (m->is_static()) {// NoSuchMethodException doesn't actually work because it tries to run the// <init> function before java_lang_Class is linked. Print error and exit.tty->print_cr("ProtectionDomain.impliesCreateAccessControlContext() has the wrong linkage");return false; // initialization failed}Universe::_pd_implies_cache->init(SystemDictionary::ProtectionDomain_klass(), m);}// The folowing is initializing converter functions for serialization in// JVM.cpp. If we clean up the StrictMath code above we may want to find// a better solution for this as well.initialize_converter_functions();// This needs to be done before the first scavenge/gc, since// it's an input to soft ref clearing policy.{MutexLocker x(Heap_lock);Universe::update_heap_info_at_gc();}// ("weak") refs processing infrastructure initializationUniverse::heap()->post_initialize();// Initialize performance counters for metaspacesMetaspaceCounters::initialize_performance_counters();CompressedClassSpaceCounters::initialize_performance_counters();MemoryService::add_metaspace_memory_pools();MemoryService::set_universe_heap(Universe::_collectedHeap);
#if INCLUDE_CDSif (UseSharedSpaces) {SharedClassUtil::initialize(CHECK_false);}
#endifreturn true;
}

22.1 vtable重新初始化

22.1.1 universe.cpp

22.1.1.1 reinitialize_vtable_of

void Universe::reinitialize_vtable_of(KlassHandle k_h, TRAPS) {// 从句柄中取出Object KlassKlass* ko = k_h();// 从Object Klass 中取出vtableklassVtable* vt = ko->vtable();// 对 Object klass 本身vtable重新初始化，继续看`章节22.1.2.1`if (vt) vt->initialize_vtable(false, CHECK);// 如果是普通对象实例，那就继续处理子类的vtableif (ko->oop_is_instance()) {InstanceKlass* ik = (InstanceKlass*)ko;// 拿到子类for (KlassHandle s_h(THREAD, ik->subklass());s_h() != NULL;// next_sibling() 沿着兄弟子类继续找s_h = KlassHandle(THREAD, s_h()->next_sibling())) {// 层层子类 vtable 重新初始化，递归reinitialize_vtable_of(s_h, CHECK);}}
}

22.1.2 klassVtable.cpp

22.1.2.1 initialize_vtable

void klassVtable::initialize_vtable(bool checkconstraints, TRAPS) {// Java的super类，那还是Object，也就是说，这里还是取的Object Klass句柄KlassHandle super (THREAD, klass()->java_super());int nofNewEntries = 0;// 判断是否共享bool is_shared = _klass->is_shared();if (PrintVtables && !klass()->oop_is_array()) {ResourceMark rm(THREAD);tty->print_cr("Initializing: %s", _klass->name()->as_C_string());}#ifdef ASSERT// 对象的限制地址oop* end_of_obj = (oop*)_klass() + _klass()->size();// vtable的限制地址oop* end_of_vtable = (oop*)&table()[_length];// vtable的限制地址 必须小于等于  对象的限制地址，`章节20.1`中有画图描述assert(end_of_vtable <= end_of_obj, "vtable extends beyond end");
#endif// 当上面的_klass 是Object klass的时候，这里就是 trueif (Universe::is_bootstrapping()) {assert(!is_shared, "sanity");// 遍历清空vtable的值for (int i = 0; i < _length; i++) table()[i].clear();return;}// 当上面的_klass 不是Object Klass，是其他普通类的 klass时，走下面的逻辑// 这一步是取出超类的vtable的长度int super_vtable_len = initialize_from_super(super);// klass不能是数组类型的，因为数组没有函数if (klass()->oop_is_array()) {assert(super_vtable_len == _length, "arrays shouldn't introduce new methods");} else {assert(_klass->oop_is_instance(), "must be InstanceKlass");// 当前 klass的方法数组Array<Method*>* methods = ik()->methods();// 当前 klass的方法数组的长度int len = methods->length();// 超类的vtable长度int initialized = super_vtable_len;// Check each of this class's methods against super;// if override, replace in copy of super vtable, otherwise append to end// 对照超类的vtable中的方法，比较当前 klass 的方法，看看有没有覆盖（重写），如果有覆盖的，那么就要在super vtable的副本中替换，否则追加到末尾for (int i = 0; i < len; i++) {// update_inherited_vtable can stop for gc - ensure using handlesHandleMark hm(THREAD);assert(methods->at(i)->is_method(), "must be a Method*");methodHandle mh(THREAD, methods->at(i));// 这里就是判断有没有覆盖（重写），返回true，就是要新建，并追加到末尾bool needs_new_entry = update_inherited_vtable(ik(), mh, super_vtable_len, -1, checkconstraints, CHECK);if (needs_new_entry) {// 放到数组末尾put_method_at(mh(), initialized);// 设置当前vtable indexmh()->set_vtable_index(initialized); // set primary vtable indexinitialized++;}}// 用默认的方法更新vtable，逻辑跟上面的一样，也是遍历并比较覆盖，默认方法的讲解，在后续类加载时会具体讲Array<Method*>* default_methods = ik()->default_methods();if (default_methods != NULL) {len = default_methods->length();if (len > 0) {Array<int>* def_vtable_indices = NULL;if ((def_vtable_indices = ik()->default_vtable_indices()) == NULL) {assert(!is_shared, "shared class def_vtable_indices does not exist");def_vtable_indices = ik()->create_new_default_vtable_indices(len, CHECK);} else {assert(def_vtable_indices->length() == len, "reinit vtable len?");}for (int i = 0; i < len; i++) {HandleMark hm(THREAD);assert(default_methods->at(i)->is_method(), "must be a Method*");methodHandle mh(THREAD, default_methods->at(i));bool needs_new_entry = update_inherited_vtable(ik(), mh, super_vtable_len, i, checkconstraints, CHECK);// needs new entryif (needs_new_entry) {put_method_at(mh(), initialized);if (is_preinitialized_vtable()) {// At runtime initialize_vtable is rerun for a shared class// (loaded by the non-boot loader) as part of link_class_impl().// The dumptime vtable index should be the same as the runtime index.assert(def_vtable_indices->at(i) == initialized,"dump time vtable index is different from runtime index");} else {def_vtable_indices->at_put(i, initialized); //set vtable index}initialized++;}}}}// 所谓 miranda methods 就是 Java Interface/abstract 接口方法，这一步就是把接口类方法添加进去if (!ik()->is_interface()) {initialized = fill_in_mirandas(initialized);}assert(initialized <= _length, "vtable initialization failed");// vtable数组长度默认最大是256，这里如果实际存在的函数不足_length，那剩下的坑位就设置为NULLfor(;initialized < _length; initialized++) {put_method_at(NULL, initialized);}NOT_PRODUCT(verify(tty, true));}
}