1 /* 2 * Copyright (c) 2003, 2021, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_CLASSFILE_PLACEHOLDERS_HPP 26 #define SHARE_CLASSFILE_PLACEHOLDERS_HPP 27 28 #include "utilities/hashtable.hpp" 29 30 class PlaceholderEntry; 31 class Thread; 32 class ClassLoaderData; 33 class Symbol; 34 35 // Placeholder objects. These represent classes currently 36 // being loaded, as well as arrays of primitives. 37 // 38 39 class PlaceholderTable : public Hashtable<Symbol*, mtClass> { 40 41 public: 42 PlaceholderTable(int table_size); 43 44 PlaceholderEntry* new_entry(int hash, Symbol* name, ClassLoaderData* loader_data, Symbol* supername); 45 void free_entry(PlaceholderEntry* entry); 46 47 PlaceholderEntry* bucket(int i) const { 48 return (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::bucket(i); 49 } 50 51 PlaceholderEntry** bucket_addr(int i) { 52 return (PlaceholderEntry**)Hashtable<Symbol*, mtClass>::bucket_addr(i); 53 } 54 55 PlaceholderEntry* add_entry(unsigned int hash, Symbol* name, 56 ClassLoaderData* loader_data, 57 Symbol* supername); 58 59 // This returns a Symbol* to match type for SystemDictionary 60 Symbol* find_entry(unsigned int hash, 61 Symbol* name, ClassLoaderData* loader_data); 62 63 PlaceholderEntry* get_entry(unsigned int hash, 64 Symbol* name, ClassLoaderData* loader_data); 65 66 // caller to create a placeholder entry must enumerate an action 67 // caller claims ownership of that action 68 // For parallel classloading: 69 // multiple LOAD_INSTANCE threads can proceed in parallel 70 // multiple LOAD_SUPER threads can proceed in parallel 71 // LOAD_SUPER needed to check for class circularity 72 // DEFINE_CLASS: ultimately define class must be single threaded 73 // on a class/classloader basis 74 // so the head of that queue owns the token 75 // and the rest of the threads return the result the first thread gets 76 enum classloadAction { 77 LOAD_INSTANCE = 1, // calling load_instance_class 78 LOAD_SUPER = 2, // loading superclass for this class 79 DEFINE_CLASS = 3 // find_or_define class 80 }; 81 82 // find_and_add returns probe pointer - old or new 83 // If no entry exists, add a placeholder entry and push SeenThread for classloadAction 84 // If entry exists, reuse entry and push SeenThread for classloadAction 85 PlaceholderEntry* find_and_add(unsigned int hash, 86 Symbol* name, ClassLoaderData* loader_data, 87 classloadAction action, Symbol* supername, 88 JavaThread* thread); 89 90 void remove_entry(unsigned int hash, 91 Symbol* name, ClassLoaderData* loader_data); 92 93 // find_and_remove first removes SeenThread for classloadAction 94 // If all queues are empty and definer is null, remove the PlacheholderEntry completely 95 void find_and_remove(unsigned int hash, 96 Symbol* name, ClassLoaderData* loader_data, 97 classloadAction action, JavaThread* thread); 98 99 void print_on(outputStream* st) const; 100 void print() const; 101 void verify(); 102 }; 103 104 class SeenThread; 105 106 // Placeholder objects represent classes currently being loaded. 107 // All threads examining the placeholder table must hold the 108 // SystemDictionary_lock, so we don't need special precautions 109 // on store ordering here. 110 // The system dictionary is the only user of this class. 111 112 class PlaceholderEntry : public HashtableEntry<Symbol*, mtClass> { 113 114 friend class PlaceholderTable; 115 116 private: 117 ClassLoaderData* _loader_data; // initiating loader 118 Symbol* _supername; 119 JavaThread* _definer; // owner of define token 120 InstanceKlass* _instanceKlass; // InstanceKlass from successful define 121 SeenThread* _superThreadQ; // doubly-linked queue of Threads loading a superclass for this class 122 SeenThread* _loadInstanceThreadQ; // loadInstance thread 123 // This can't be multiple threads since class loading waits for 124 // this token to be removed. 125 126 SeenThread* _defineThreadQ; // queue of Threads trying to define this class 127 // including _definer 128 // _definer owns token 129 // queue waits for and returns results from _definer 130 131 SeenThread* actionToQueue(PlaceholderTable::classloadAction action); 132 void set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action); 133 void add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action); 134 bool remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action); 135 136 public: 137 // Simple accessors, used only by SystemDictionary 138 Symbol* klassname() const { return literal(); } 139 140 ClassLoaderData* loader_data() const { return _loader_data; } 141 void set_loader_data(ClassLoaderData* loader_data) { _loader_data = loader_data; } 142 143 Symbol* supername() const { return _supername; } 144 void set_supername(Symbol* supername) { 145 _supername = supername; 146 if (_supername != NULL) _supername->increment_refcount(); 147 } 148 149 JavaThread* definer() const {return _definer; } 150 void set_definer(JavaThread* definer) { _definer = definer; } 151 152 InstanceKlass* instance_klass() const {return _instanceKlass; } 153 void set_instance_klass(InstanceKlass* ik) { _instanceKlass = ik; } 154 155 SeenThread* superThreadQ() const { return _superThreadQ; } 156 void set_superThreadQ(SeenThread* SeenThread) { _superThreadQ = SeenThread; } 157 158 SeenThread* loadInstanceThreadQ() const { return _loadInstanceThreadQ; } 159 void set_loadInstanceThreadQ(SeenThread* SeenThread) { _loadInstanceThreadQ = SeenThread; } 160 161 SeenThread* defineThreadQ() const { return _defineThreadQ; } 162 void set_defineThreadQ(SeenThread* SeenThread) { _defineThreadQ = SeenThread; } 163 164 PlaceholderEntry* next() const { 165 return (PlaceholderEntry*)HashtableEntry<Symbol*, mtClass>::next(); 166 } 167 168 PlaceholderEntry** next_addr() { 169 return (PlaceholderEntry**)HashtableEntry<Symbol*, mtClass>::next_addr(); 170 } 171 172 // Test for equality 173 // Entries are unique for class/classloader name pair 174 bool equals(Symbol* class_name, ClassLoaderData* loader) const { 175 return (klassname() == class_name && loader_data() == loader); 176 } 177 178 bool super_load_in_progress() { 179 return (_superThreadQ != NULL); 180 } 181 182 bool instance_load_in_progress() { 183 return (_loadInstanceThreadQ != NULL); 184 } 185 186 bool define_class_in_progress() { 187 return (_defineThreadQ != NULL); 188 } 189 190 // Used for ClassCircularityError checking 191 bool check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action); 192 193 // Print method doesn't append a cr 194 void print_entry(outputStream* st) const; 195 void verify() const; 196 }; 197 198 #endif // SHARE_CLASSFILE_PLACEHOLDERS_HPP