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     : Hashtable<Symbol*, mtClass>(table_size, sizeof(PlaceholderEntry)) {

   176 }

   177 

   178 void PlaceholderEntry::verify() const {

   179   guarantee(loader_data() != NULL, "Must have been setup.");

   180   guarantee(loader_data()->class_loader() == NULL || loader_data()->class_loader()->is_instance(),

   181             "checking type of _loader");

   182   guarantee(instance_klass() == NULL

   183             || instance_klass()->is_instance_klass(),

   184             "checking type of instance_klass result");

   185 }

   186 

   187 void PlaceholderTable::verify() {

   188   verify_table<PlaceholderEntry>("Placeholder Table");

   189 }

   190 

   191 

   192 // Note, doesn't append a cr

   193 // Can't call this print_on because HashtableEntry doesn't initialize its vptr

   194 // and print_on is a virtual function so the vptr call crashes.

   195 void PlaceholderEntry::print_entry(outputStream* st) const {

   196   klassname()->print_value_on(st);

   197   if (loader_data() != NULL) {

   198     st->print(", loader ");

   199     loader_data()->print_value_on(st);

   200   }

   201   if (supername() != NULL) {

   202     st->print(", supername ");

   203     supername()->print_value_on(st);

   204   }

   205   if (definer() != NULL) {

   206     st->print(", definer ");

   207     definer()->print_value_on(st);

   208   }

   209   if (instance_klass() != NULL) {

   210     st->print(", InstanceKlass ");

   211     instance_klass()->print_value_on(st);

   212   }

   213   st->cr();

   214   st->print("loadInstanceThreadQ threads:");

   215   loadInstanceThreadQ()->print_action_queue(st);

   216   st->cr();

   217   st->print("superThreadQ threads:");

   218   superThreadQ()->print_action_queue(st);

   219   st->cr();

   220   st->print("defineThreadQ threads:");

   221   defineThreadQ()->print_action_queue(st);

   222   st->cr();

   223 }

   224 

   225 void PlaceholderTable::print_on(outputStream* st) const {

   226   st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",

   227                 table_size(), number_of_entries());

   228   for (int pindex = 0; pindex < table_size(); pindex++) {

   229     for (PlaceholderEntry* probe = bucket(pindex);

   230                            probe != NULL;

   231                            probe = probe->next()) {

   232       st->print("%4d: placeholder ", pindex);

   233       probe->print_entry(st);

   234     }

   235   }

   236 }