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/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 }