1 /* 2 * Copyright (c) 2003, 2018, 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 #include "precompiled.hpp" 26 #include "classfile/classLoaderData.inline.hpp" 27 #include "classfile/placeholders.hpp" 28 #include "classfile/systemDictionary.hpp" 29 #include "oops/oop.inline.hpp" 30 #include "runtime/fieldType.hpp" 31 #include "utilities/hashtable.inline.hpp" 32 33 // Placeholder methods 34 35 PlaceholderEntry* PlaceholderTable::new_entry(int hash, Symbol* name, 36 ClassLoaderData* loader_data, 37 bool havesupername, 38 Symbol* supername) { 39 PlaceholderEntry* entry = (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::new_entry(hash, name); 40 // Hashtable with Symbol* literal must increment and decrement refcount. 41 name->increment_refcount(); 42 entry->set_loader_data(loader_data); 43 entry->set_havesupername(havesupername); 44 entry->set_supername(supername); 45 entry->set_superThreadQ(NULL); 46 entry->set_loadInstanceThreadQ(NULL); 47 entry->set_defineThreadQ(NULL); 48 entry->set_definer(NULL); 49 entry->set_instance_klass(NULL); 50 return entry; 51 } 52 53 void PlaceholderTable::free_entry(PlaceholderEntry* entry) { 54 // decrement Symbol refcount here because Hashtable doesn't. 55 entry->literal()->decrement_refcount(); 56 if (entry->supername() != NULL) entry->supername()->decrement_refcount(); 57 Hashtable<Symbol*, mtClass>::free_entry(entry); 58 } 59 60 61 // Placeholder objects represent classes currently being loaded. 62 // All threads examining the placeholder table must hold the 63 // SystemDictionary_lock, so we don't need special precautions 64 // on store ordering here. 65 void PlaceholderTable::add_entry(int index, unsigned int hash, 66 Symbol* class_name, ClassLoaderData* loader_data, 67 bool havesupername, Symbol* supername){ 68 assert_locked_or_safepoint(SystemDictionary_lock); 69 assert(class_name != NULL, "adding NULL obj"); 70 71 // Both readers and writers are locked so it's safe to just 72 // create the placeholder and insert it in the list without a membar. 73 PlaceholderEntry* entry = new_entry(hash, class_name, loader_data, havesupername, supername); 74 add_entry(index, entry); 75 } 76 77 78 // Remove a placeholder object. 79 void PlaceholderTable::remove_entry(int index, unsigned int hash, 80 Symbol* class_name, 81 ClassLoaderData* loader_data) { 82 assert_locked_or_safepoint(SystemDictionary_lock); 83 PlaceholderEntry** p = bucket_addr(index); 84 while (*p) { 85 PlaceholderEntry *probe = *p; 86 if (probe->hash() == hash && probe->equals(class_name, loader_data)) { 87 // Delete entry 88 *p = probe->next(); 89 free_entry(probe); 90 return; 91 } 92 p = probe->next_addr(); 93 } 94 } 95 96 PlaceholderEntry* PlaceholderTable::get_entry(int index, unsigned int hash, 97 Symbol* class_name, 98 ClassLoaderData* loader_data) { 99 assert_locked_or_safepoint(SystemDictionary_lock); 100 101 for (PlaceholderEntry *place_probe = bucket(index); 102 place_probe != NULL; 103 place_probe = place_probe->next()) { 104 if (place_probe->hash() == hash && 105 place_probe->equals(class_name, loader_data)) { 106 return place_probe; 107 } 108 } 109 return NULL; 110 } 111 112 Symbol* PlaceholderTable::find_entry(int index, unsigned int hash, 113 Symbol* class_name, 114 ClassLoaderData* loader_data) { 115 PlaceholderEntry* probe = get_entry(index, hash, class_name, loader_data); 116 return (probe? probe->klassname(): (Symbol*)NULL); 117 } 118 119 // find_and_add returns probe pointer - old or new 120 // If no entry exists, add a placeholder entry 121 // If entry exists, reuse entry 122 // For both, push SeenThread for classloadAction 123 // if havesupername: this is used for circularity for instanceklass loading 124 PlaceholderEntry* PlaceholderTable::find_and_add(int index, unsigned int hash, 125 Symbol* name, 126 ClassLoaderData* loader_data, 127 classloadAction action, 128 Symbol* supername, 129 Thread* thread) { 130 PlaceholderEntry* probe = get_entry(index, hash, name, loader_data); 131 if (probe == NULL) { 132 // Nothing found, add place holder 133 add_entry(index, hash, name, loader_data, (action == LOAD_SUPER), supername); 134 probe = get_entry(index, hash, name, loader_data); 135 } else { 136 if (action == LOAD_SUPER) { 137 probe->set_havesupername(true); 138 probe->set_supername(supername); 139 } 140 } 141 if (probe) probe->add_seen_thread(thread, action); 142 return probe; 143 } 144 145 146 // placeholder is used to track class loading internal states 147 // placeholder existence now for loading superclass/superinterface 148 // superthreadQ tracks class circularity, while loading superclass/superinterface 149 // loadInstanceThreadQ tracks load_instance_class calls 150 // definer() tracks the single thread that owns define token 151 // defineThreadQ tracks waiters on defining thread's results 152 // 1st claimant creates placeholder 153 // find_and_add adds SeenThread entry for appropriate queue 154 // All claimants remove SeenThread after completing action 155 // On removal: if definer and all queues empty, remove entry 156 // Note: you can be in both placeholders and systemDictionary 157 // Therefore - must always check SD first 158 // Ignores the case where entry is not found 159 void PlaceholderTable::find_and_remove(int index, unsigned int hash, 160 Symbol* name, ClassLoaderData* loader_data, 161 classloadAction action, 162 Thread* thread) { 163 assert_locked_or_safepoint(SystemDictionary_lock); 164 PlaceholderEntry *probe = get_entry(index, hash, name, loader_data); 165 if (probe != NULL) { 166 probe->remove_seen_thread(thread, action); 167 // If no other threads using this entry, and this thread is not using this entry for other states 168 if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL) 169 && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)) { 170 remove_entry(index, hash, name, loader_data); 171 } 172 } 173 } 174 175 PlaceholderTable::PlaceholderTable(int table_size) 176 : Hashtable<Symbol*, mtClass>(table_size, sizeof(PlaceholderEntry)) { 177 } 178 179 void PlaceholderEntry::verify() const { 180 guarantee(loader_data() != NULL, "Must have been setup."); 181 guarantee(loader_data()->class_loader() == NULL || loader_data()->class_loader()->is_instance(), 182 "checking type of _loader"); 183 guarantee(instance_klass() == NULL 184 || instance_klass()->is_instance_klass(), 185 "checking type of instance_klass result"); 186 } 187 188 void PlaceholderTable::verify() { 189 verify_table<PlaceholderEntry>("Placeholder Table"); 190 } 191 192 193 // Note, doesn't append a cr 194 // Can't call this print_on because HashtableEntry doesn't initialize its vptr 195 // and print_on is a virtual function so the vptr call crashes. 196 void PlaceholderEntry::print_entry(outputStream* st) const { 197 klassname()->print_value_on(st); 198 if (loader_data() != NULL) { 199 st->print(", loader "); 200 loader_data()->print_value_on(st); 201 } 202 if (supername() != NULL) { 203 st->print(", supername "); 204 supername()->print_value_on(st); 205 } 206 if (definer() != NULL) { 207 st->print(", definer "); 208 definer()->print_value_on(st); 209 } 210 if (instance_klass() != NULL) { 211 st->print(", InstanceKlass "); 212 instance_klass()->print_value_on(st); 213 } 214 st->cr(); 215 st->print("loadInstanceThreadQ threads:"); 216 loadInstanceThreadQ()->print_action_queue(st); 217 st->cr(); 218 st->print("superThreadQ threads:"); 219 superThreadQ()->print_action_queue(st); 220 st->cr(); 221 st->print("defineThreadQ threads:"); 222 defineThreadQ()->print_action_queue(st); 223 st->cr(); 224 } 225 226 void PlaceholderTable::print_on(outputStream* st) const { 227 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)", 228 table_size(), number_of_entries()); 229 for (int pindex = 0; pindex < table_size(); pindex++) { 230 for (PlaceholderEntry* probe = bucket(pindex); 231 probe != NULL; 232 probe = probe->next()) { 233 st->print("%4d: placeholder ", pindex); 234 probe->print_entry(st); 235 } 236 } 237 }