1 /*
   2  * Copyright (c) 2003, 2017, 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/placeholders.hpp"
  27 #include "classfile/systemDictionary.hpp"
  28 #include "oops/oop.inline.hpp"
  29 #include "runtime/fieldType.hpp"
  30 #include "utilities/hashtable.inline.hpp"
  31 
  32 // Placeholder methods
  33 
  34 PlaceholderEntry* PlaceholderTable::new_entry(int hash, Symbol* name,
  35                                               ClassLoaderData* loader_data,
  36                                               bool havesupername,
  37                                               Symbol* supername) {
  38   PlaceholderEntry* entry = (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::new_entry(hash, name);
  39   // Hashtable with Symbol* literal must increment and decrement refcount.
  40   name->increment_refcount();
  41   entry->set_loader_data(loader_data);
  42   entry->set_havesupername(havesupername);
  43   entry->set_supername(supername);
  44   entry->set_superThreadQ(NULL);
  45   entry->set_loadInstanceThreadQ(NULL);
  46   entry->set_defineThreadQ(NULL);
  47   entry->set_definer(NULL);
  48   entry->set_instance_klass(NULL);
  49   return entry;
  50 }
  51 
  52 void PlaceholderTable::free_entry(PlaceholderEntry* entry) {
  53   // decrement Symbol refcount here because Hashtable doesn't.
  54   entry->literal()->decrement_refcount();
  55   if (entry->supername() != NULL) entry->supername()->decrement_refcount();
  56   Hashtable<Symbol*, mtClass>::free_entry(entry);
  57 }
  58 
  59 
  60 // Placeholder objects represent classes currently being loaded.
  61 // All threads examining the placeholder table must hold the
  62 // SystemDictionary_lock, so we don't need special precautions
  63 // on store ordering here.
  64 void PlaceholderTable::add_entry(int index, unsigned int hash,
  65                                  Symbol* class_name, ClassLoaderData* loader_data,
  66                                  bool havesupername, Symbol* supername){
  67   assert_locked_or_safepoint(SystemDictionary_lock);
  68   assert(class_name != NULL, "adding NULL obj");
  69 
  70   // Both readers and writers are locked so it's safe to just
  71   // create the placeholder and insert it in the list without a membar.
  72   PlaceholderEntry* entry = new_entry(hash, class_name, loader_data, havesupername, supername);
  73   add_entry(index, entry);
  74 }
  75 
  76 
  77 // Remove a placeholder object.
  78 void PlaceholderTable::remove_entry(int index, unsigned int hash,
  79                                     Symbol* class_name,
  80                                     ClassLoaderData* loader_data) {
  81   assert_locked_or_safepoint(SystemDictionary_lock);
  82   PlaceholderEntry** p = bucket_addr(index);
  83   while (*p) {
  84     PlaceholderEntry *probe = *p;
  85     if (probe->hash() == hash && probe->equals(class_name, loader_data)) {
  86       // Delete entry
  87       *p = probe->next();
  88       free_entry(probe);
  89       return;
  90     }
  91     p = probe->next_addr();
  92   }
  93 }
  94 
  95 PlaceholderEntry* PlaceholderTable::get_entry(int index, unsigned int hash,
  96                                        Symbol* class_name,
  97                                        ClassLoaderData* loader_data) {
  98   assert_locked_or_safepoint(SystemDictionary_lock);
  99 
 100   for (PlaceholderEntry *place_probe = bucket(index);
 101                          place_probe != NULL;
 102                          place_probe = place_probe->next()) {
 103     if (place_probe->hash() == hash &&
 104         place_probe->equals(class_name, loader_data)) {
 105       return place_probe;
 106     }
 107   }
 108   return NULL;
 109 }
 110 
 111 Symbol* PlaceholderTable::find_entry(int index, unsigned int hash,
 112                                        Symbol* class_name,
 113                                        ClassLoaderData* loader_data) {
 114   PlaceholderEntry* probe = get_entry(index, hash, class_name, loader_data);
 115   return (probe? probe->klassname(): (Symbol*)NULL);
 116 }
 117 
 118   // find_and_add returns probe pointer - old or new
 119   // If no entry exists, add a placeholder entry
 120   // If entry exists, reuse entry
 121   // For both, push SeenThread for classloadAction
 122   // if havesupername: this is used for circularity for instanceklass loading
 123 PlaceholderEntry* PlaceholderTable::find_and_add(int index, unsigned int hash,
 124                                                  Symbol* name,
 125                                                  ClassLoaderData* loader_data,
 126                                                  classloadAction action,
 127                                                  Symbol* supername,
 128                                                  Thread* thread) {
 129   PlaceholderEntry* probe = get_entry(index, hash, name, loader_data);
 130   if (probe == NULL) {
 131     // Nothing found, add place holder
 132     add_entry(index, hash, name, loader_data, (action == LOAD_SUPER), supername);
 133     probe = get_entry(index, hash, name, loader_data);
 134   } else {
 135     if (action == LOAD_SUPER) {
 136       probe->set_havesupername(true);
 137       probe->set_supername(supername);
 138     }
 139   }
 140   if (probe) probe->add_seen_thread(thread, action);
 141   return probe;
 142 }
 143 
 144 
 145 // placeholder is used to track class loading internal states
 146 // placeholder existence now for loading superclass/superinterface
 147 // superthreadQ tracks class circularity, while loading superclass/superinterface
 148 // loadInstanceThreadQ tracks load_instance_class calls
 149 // definer() tracks the single thread that owns define token
 150 // defineThreadQ tracks waiters on defining thread's results
 151 // 1st claimant creates placeholder
 152 // find_and_add adds SeenThread entry for appropriate queue
 153 // All claimants remove SeenThread after completing action
 154 // On removal: if definer and all queues empty, remove entry
 155 // Note: you can be in both placeholders and systemDictionary
 156 // Therefore - must always check SD first
 157 // Ignores the case where entry is not found
 158 void PlaceholderTable::find_and_remove(int index, unsigned int hash,
 159                                        Symbol* name, ClassLoaderData* loader_data,
 160                                        classloadAction action,
 161                                        Thread* thread) {
 162     assert_locked_or_safepoint(SystemDictionary_lock);
 163     PlaceholderEntry *probe = get_entry(index, hash, name, loader_data);
 164     if (probe != NULL) {
 165        probe->remove_seen_thread(thread, action);
 166        // If no other threads using this entry, and this thread is not using this entry for other states
 167        if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
 168           && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)) {
 169          remove_entry(index, hash, name, loader_data);
 170        }
 171     }
 172   }
 173 
 174 PlaceholderTable::PlaceholderTable(int table_size)
 175     : TwoOopHashtable<Symbol*, mtClass>(table_size, sizeof(PlaceholderEntry)) {
 176 }
 177 
 178 #ifndef PRODUCT
 179 // Note, doesn't append a cr
 180 void PlaceholderEntry::print() const {
 181   klassname()->print_value();
 182   if (loader_data() != NULL) {
 183     tty->print(", loader ");
 184     loader_data()->print_value();
 185   }
 186   if (supername() != NULL) {
 187     tty->print(", supername ");
 188     supername()->print_value();
 189   }
 190   if (definer() != NULL) {
 191     tty->print(", definer ");
 192     definer()->print_value();
 193   }
 194   if (instance_klass() != NULL) {
 195     tty->print(", InstanceKlass ");
 196     instance_klass()->print_value();
 197   }
 198   tty->print("\n");
 199   tty->print("loadInstanceThreadQ threads:");
 200   loadInstanceThreadQ()->printActionQ();
 201   tty->print("\n");
 202   tty->print("superThreadQ threads:");
 203   superThreadQ()->printActionQ();
 204   tty->print("\n");
 205   tty->print("defineThreadQ threads:");
 206   defineThreadQ()->printActionQ();
 207   tty->print("\n");
 208 }
 209 #endif
 210 
 211 void PlaceholderEntry::verify() const {
 212   guarantee(loader_data() != NULL, "Must have been setup.");
 213   guarantee(loader_data()->class_loader() == NULL || loader_data()->class_loader()->is_instance(),
 214             "checking type of _loader");
 215   guarantee(instance_klass() == NULL
 216             || instance_klass()->is_instance_klass(),
 217             "checking type of instance_klass result");
 218 }
 219 
 220 void PlaceholderTable::verify() {
 221   int element_count = 0;
 222   for (int pindex = 0; pindex < table_size(); pindex++) {
 223     for (PlaceholderEntry* probe = bucket(pindex);
 224                            probe != NULL;
 225                            probe = probe->next()) {
 226       probe->verify();
 227       element_count++;  // both klasses and place holders count
 228     }
 229   }
 230   guarantee(number_of_entries() == element_count,
 231             "Verify of system dictionary failed");
 232 }
 233 
 234 
 235 #ifndef PRODUCT
 236 void PlaceholderTable::print() {
 237   for (int pindex = 0; pindex < table_size(); pindex++) {
 238     for (PlaceholderEntry* probe = bucket(pindex);
 239                            probe != NULL;
 240                            probe = probe->next()) {
 241       if (Verbose) tty->print("%4d: ", pindex);
 242       tty->print(" place holder ");
 243 
 244       probe->print();
 245       tty->cr();
 246     }
 247   }
 248 }
 249 #endif