1 /*
2 * Copyright (c) 2003, 2022, 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 "logging/log.hpp"
29 #include "logging/logTag.hpp"
30 #include "logging/logStream.hpp"
31 #include "memory/resourceArea.hpp"
32 #include "oops/symbolHandle.hpp"
33 #include "runtime/javaThread.hpp"
34 #include "runtime/mutexLocker.hpp"
35 #include "utilities/resourceHash.hpp"
36
37 class PlaceholderKey {
38 SymbolHandle _name;
39 ClassLoaderData* _loader_data;
40 public:
41 PlaceholderKey(Symbol* name, ClassLoaderData* l) : _name(name), _loader_data(l) {}
42
43 static bool equals(PlaceholderKey const& k1, PlaceholderKey const& k2) {
44 return (k1._name == k2._name && k1._loader_data == k2._loader_data);
45 }
46 static unsigned hash(PlaceholderKey const& k) {
47 return (unsigned) k._name->identity_hash() ^ (int)((intptr_t)k._loader_data >> 3);
48 }
49 void print_on(outputStream* st) const;
50 };
51
52 const int _placeholder_table_size = 503; // Does this really have to be prime?
53 ResourceHashtable<PlaceholderKey, PlaceholderEntry, _placeholder_table_size, ResourceObj::C_HEAP, mtClass,
54 PlaceholderKey::hash, PlaceholderKey::equals> _placeholders;
55
56 // SeenThread objects represent list of threads that are
57 // currently performing a load action on a class.
58 // For class circularity, set before loading a superclass.
59 // For bootclasssearchpath, set before calling load_instance_class.
60 // Defining must be single threaded on a class/classloader basis
61 // For DEFINE_CLASS, the head of the queue owns the
62 // define token and the rest of the threads wait to return the
63 // result the first thread gets.
64 // For INLINE_FIELD, set when loading inline type fields for
65 // class circularity checking.
66 class SeenThread: public CHeapObj<mtInternal> {
67 private:
68 JavaThread* _thread;
69 SeenThread* _stnext;
70 SeenThread* _stprev;
71 public:
72 SeenThread(JavaThread* thread) {
73 _thread = thread;
74 _stnext = NULL;
75 _stprev = NULL;
76 }
77 JavaThread* thread() const { return _thread;}
78 void set_thread(JavaThread* thread) { _thread = thread; }
79
80 SeenThread* next() const { return _stnext;}
81 void set_next(SeenThread* seen) { _stnext = seen; }
82 void set_prev(SeenThread* seen) { _stprev = seen; }
83
84 void print_action_queue(outputStream* st) {
85 SeenThread* seen = this;
86 while (seen != NULL) {
87 seen->thread()->print_value_on(st);
88 st->print(", ");
89 seen = seen->next();
90 }
91 }
92 };
93
94 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) {
95 SeenThread* queuehead = NULL;
96 switch (action) {
97 case PlaceholderTable::LOAD_INSTANCE:
98 queuehead = _loadInstanceThreadQ;
99 break;
100 case PlaceholderTable::LOAD_SUPER:
101 queuehead = _superThreadQ;
102 break;
103 case PlaceholderTable::DEFINE_CLASS:
104 queuehead = _defineThreadQ;
105 break;
106 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
107 queuehead = _inlineTypeFieldQ;
108 break;
109 default: Unimplemented();
110 }
111 return queuehead;
112 }
113
114 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
115 switch (action) {
116 case PlaceholderTable::LOAD_INSTANCE:
117 _loadInstanceThreadQ = seenthread;
118 break;
119 case PlaceholderTable::LOAD_SUPER:
120 _superThreadQ = seenthread;
121 break;
122 case PlaceholderTable::DEFINE_CLASS:
123 _defineThreadQ = seenthread;
124 break;
125 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
126 _inlineTypeFieldQ = seenthread;
127 break;
128 default: Unimplemented();
129 }
130 return;
131 }
132
133 // Doubly-linked list of Threads per action for class/classloader pair
134 // Class circularity support: links in thread before loading superclass
135 // bootstrap loader support: links in a thread before load_instance_class
136 // definers: use as queue of define requestors, including owner of
137 // define token. Appends for debugging of requestor order
138 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
139 assert_lock_strong(SystemDictionary_lock);
140 SeenThread* threadEntry = new SeenThread(thread);
141 SeenThread* seen = actionToQueue(action);
142
143 assert(action != PlaceholderTable::LOAD_INSTANCE || seen == NULL,
144 "Only one LOAD_INSTANCE allowed at a time");
145
146 if (seen == NULL) {
147 set_threadQ(threadEntry, action);
148 return;
149 }
150 SeenThread* next;
151 while ((next = seen->next()) != NULL) {
152 seen = next;
153 }
154 seen->set_next(threadEntry);
155 threadEntry->set_prev(seen);
156 return;
157 }
158
159 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
160 assert_lock_strong(SystemDictionary_lock);
161 SeenThread* threadQ = actionToQueue(action);
162 SeenThread* seen = threadQ;
163 while (seen) {
164 if (thread == seen->thread()) {
165 return true;
166 }
167 seen = seen->next();
168 }
169 return false;
170 }
171
172 // returns true if seenthreadQ is now empty
173 // Note, caller must ensure probe still exists while holding
174 // SystemDictionary_lock
175 // ignores if cleanup has already been done
176 // if found, deletes SeenThread
177 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
178 assert_lock_strong(SystemDictionary_lock);
179 SeenThread* threadQ = actionToQueue(action);
180 SeenThread* seen = threadQ;
181 SeenThread* prev = NULL;
182 while (seen) {
183 if (thread == seen->thread()) {
184 if (prev) {
185 prev->set_next(seen->next());
186 } else {
187 set_threadQ(seen->next(), action);
188 }
189 if (seen->next()) {
190 seen->next()->set_prev(prev);
191 }
192 delete seen;
193 break;
194 }
195 prev = seen;
196 seen = seen->next();
197 }
198 return (actionToQueue(action) == NULL);
199 }
200
201
202 // Placeholder methods
203
204 // Placeholder objects represent classes currently being loaded.
205 // All threads examining the placeholder table must hold the
206 // SystemDictionary_lock, so we don't need special precautions
207 // on store ordering here.
208 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
209 Symbol* supername){
210 assert_locked_or_safepoint(SystemDictionary_lock);
211 assert(class_name != NULL, "adding NULL obj");
212
213 PlaceholderEntry entry;
214 entry.set_supername(supername);
215 PlaceholderKey key(class_name, loader_data);
216 bool created;
217 PlaceholderEntry* table_copy = _placeholders.put_if_absent(key, entry, &created);
218 assert(created, "better be absent");
219 return table_copy;
220 }
221
222 // Remove a placeholder object.
223 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
224 assert_locked_or_safepoint(SystemDictionary_lock);
225
226 PlaceholderKey key(class_name, loader_data);
227 _placeholders.remove(key);
228 }
229
230
231 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
232 assert_locked_or_safepoint(SystemDictionary_lock);
233 PlaceholderKey key(class_name, loader_data);
234 return _placeholders.get(key);
235 }
236
237 static const char* action_to_string(PlaceholderTable::classloadAction action) {
238 switch (action) {
239 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
240 case PlaceholderTable::LOAD_SUPER: return "LOAD_SUPER";
241 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
242 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD";
243 }
244 return "";
245 }
246
247 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
248 if (log_is_enabled(Debug, class, load, placeholders)) {
249 LogTarget(Debug, class, load, placeholders) lt;
250 ResourceMark rm;
251 LogStream ls(lt);
252 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
253 entry->print_on(&ls);
254 }
255 }
256
257 // find_and_add returns probe pointer - old or new
258 // If no entry exists, add a placeholder entry
259 // If entry exists, reuse entry
260 // For both, push SeenThread for classloadAction
261 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
262 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
263 ClassLoaderData* loader_data,
264 classloadAction action,
265 Symbol* supername,
266 JavaThread* thread) {
267 assert(action != LOAD_SUPER || supername != NULL, "must have a super class name");
268 PlaceholderEntry* probe = get_entry(name, loader_data);
269 if (probe == NULL) {
270 // Nothing found, add place holder
271 probe = add_entry(name, loader_data, supername);
272 } else {
273 if (action == LOAD_SUPER) {
274 probe->set_supername(supername);
275 }
276 }
277 probe->add_seen_thread(thread, action);
278 log(name, probe, "find_and_add", action);
279 return probe;
280 }
281
282
283 // placeholder is used to track class loading internal states
284 // placeholder existence now for loading superclass/superinterface
285 // superthreadQ tracks class circularity, while loading superclass/superinterface
286 // loadInstanceThreadQ tracks load_instance_class calls
287 // definer() tracks the single thread that owns define token
288 // defineThreadQ tracks waiters on defining thread's results
289 // 1st claimant creates placeholder
290 // find_and_add adds SeenThread entry for appropriate queue
291 // All claimants remove SeenThread after completing action
292 // On removal: if definer and all queues empty, remove entry
293 // Note: you can be in both placeholders and systemDictionary
294 // Therefore - must always check SD first
295 // Ignores the case where entry is not found
296 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
297 classloadAction action,
298 JavaThread* thread) {
299 assert_locked_or_safepoint(SystemDictionary_lock);
300 PlaceholderEntry* probe = get_entry(name, loader_data);
301 if (probe != NULL) {
302 log(name, probe, "find_and_remove", action);
303 probe->remove_seen_thread(thread, action);
304 // If no other threads using this entry, and this thread is not using this entry for other states
305 if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
306 && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)
307 && (probe->inlineTypeFieldQ() == NULL)) {
308 probe->clear_supername();
309 remove_entry(name, loader_data);
310 }
311 }
312 }
313
314 void PlaceholderKey::print_on(outputStream* st) const {
315 _name->print_value_on(st);
316 st->print(", loader ");
317 _loader_data->print_value_on(st);
318 }
319
320 void PlaceholderEntry::print_on(outputStream* st) const {
321 if (supername() != NULL) {
322 st->print(", supername ");
323 supername()->print_value_on(st);
324 }
325 if (definer() != NULL) {
326 st->print(", definer ");
327 definer()->print_value_on(st);
328 }
329 if (instance_klass() != NULL) {
330 st->print(", InstanceKlass ");
331 instance_klass()->print_value_on(st);
332 }
333 st->cr();
334 st->print("loadInstanceThreadQ threads:");
335 loadInstanceThreadQ()->print_action_queue(st);
336 st->cr();
337 st->print("superThreadQ threads:");
338 superThreadQ()->print_action_queue(st);
339 st->cr();
340 st->print("defineThreadQ threads:");
341 defineThreadQ()->print_action_queue(st);
342 st->cr();
343 st->print("inlineTypeFieldQ threads:");
344 inlineTypeFieldQ()->print_action_queue(st);
345 st->cr();
346 }
347
348 void PlaceholderTable::print_on(outputStream* st) {
349 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) {
350 st->print("placeholder ");
351 key.print_on(st);
352 entry.print_on(st);
353 return true;
354 };
355 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
356 _placeholders.table_size(), _placeholders.number_of_entries());
357 _placeholders.iterate(printer);
358 }
359
360 void PlaceholderTable::print() { return print_on(tty); }