1 /*
2 * Copyright (c) 2003, 2023, 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 using InternalPlaceholderTable = ResourceHashtable<PlaceholderKey, PlaceholderEntry, _placeholder_table_size, AnyObj::C_HEAP, mtClass,
54 PlaceholderKey::hash, PlaceholderKey::equals>;
55 static InternalPlaceholderTable* _placeholders;
56
57 // SeenThread objects represent list of threads that are
58 // currently performing a load action on a class.
59 // For class circularity, set before loading a superclass.
60 // For bootclasssearchpath, set before calling load_instance_class.
61 // Defining must be single threaded on a class/classloader basis
62 // For DEFINE_CLASS, the head of the queue owns the
63 // define token and the rest of the threads wait to return the
64 // result the first thread gets.
65 // For INLINE_FIELD, set when loading inline type fields for
66 // class circularity checking.
67 class SeenThread: public CHeapObj<mtInternal> {
68 private:
69 JavaThread* _thread;
70 SeenThread* _stnext;
71 SeenThread* _stprev;
72 public:
73 SeenThread(JavaThread* thread) {
74 _thread = thread;
75 _stnext = nullptr;
76 _stprev = nullptr;
77 }
78 JavaThread* thread() const { return _thread;}
79 void set_thread(JavaThread* thread) { _thread = thread; }
80
81 SeenThread* next() const { return _stnext;}
82 void set_next(SeenThread* seen) { _stnext = seen; }
83 void set_prev(SeenThread* seen) { _stprev = seen; }
84
85 void print_action_queue(outputStream* st) {
86 SeenThread* seen = this;
87 while (seen != nullptr) {
88 seen->thread()->print_value_on(st);
89 st->print(", ");
90 seen = seen->next();
91 }
92 }
93 };
94
95 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) {
96 SeenThread* queuehead = nullptr;
97 switch (action) {
98 case PlaceholderTable::LOAD_INSTANCE:
99 queuehead = _loadInstanceThreadQ;
100 break;
101 case PlaceholderTable::LOAD_SUPER:
102 queuehead = _superThreadQ;
103 break;
104 case PlaceholderTable::DEFINE_CLASS:
105 queuehead = _defineThreadQ;
106 break;
107 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
108 queuehead = _inlineTypeFieldQ;
109 break;
110 default: Unimplemented();
111 }
112 return queuehead;
113 }
114
115 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
116 switch (action) {
117 case PlaceholderTable::LOAD_INSTANCE:
118 _loadInstanceThreadQ = seenthread;
119 break;
120 case PlaceholderTable::LOAD_SUPER:
121 _superThreadQ = seenthread;
122 break;
123 case PlaceholderTable::DEFINE_CLASS:
124 _defineThreadQ = seenthread;
125 break;
126 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
127 _inlineTypeFieldQ = seenthread;
128 break;
129 default: Unimplemented();
130 }
131 return;
132 }
133
134 // Doubly-linked list of Threads per action for class/classloader pair
135 // Class circularity support: links in thread before loading superclass
136 // bootstrap loader support: links in a thread before load_instance_class
137 // definers: use as queue of define requestors, including owner of
138 // define token. Appends for debugging of requestor order
139 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
140 assert_lock_strong(SystemDictionary_lock);
141 SeenThread* threadEntry = new SeenThread(thread);
142 SeenThread* seen = actionToQueue(action);
143
144 if (seen == nullptr) {
145 set_threadQ(threadEntry, action);
146 return;
147 }
148 SeenThread* next;
149 while ((next = seen->next()) != nullptr) {
150 seen = next;
151 }
152 seen->set_next(threadEntry);
153 threadEntry->set_prev(seen);
154 return;
155 }
156
157 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
158 assert_lock_strong(SystemDictionary_lock);
159 SeenThread* threadQ = actionToQueue(action);
160 SeenThread* seen = threadQ;
161 while (seen) {
162 if (thread == seen->thread()) {
163 return true;
164 }
165 seen = seen->next();
166 }
167 return false;
168 }
169
170 // returns true if seenthreadQ is now empty
171 // Note, caller must ensure probe still exists while holding
172 // SystemDictionary_lock
173 // ignores if cleanup has already been done
174 // if found, deletes SeenThread
175 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
176 assert_lock_strong(SystemDictionary_lock);
177 SeenThread* threadQ = actionToQueue(action);
178 SeenThread* seen = threadQ;
179 SeenThread* prev = nullptr;
180 while (seen) {
181 if (thread == seen->thread()) {
182 if (prev) {
183 prev->set_next(seen->next());
184 } else {
185 set_threadQ(seen->next(), action);
186 }
187 if (seen->next()) {
188 seen->next()->set_prev(prev);
189 }
190 delete seen;
191 break;
192 }
193 prev = seen;
194 seen = seen->next();
195 }
196 return (actionToQueue(action) == nullptr);
197 }
198
199
200 void PlaceholderEntry::set_supername(Symbol* supername) {
201 assert_locked_or_safepoint(SystemDictionary_lock);
202 assert(_supername == nullptr || _supername->refcount() > 1, "must be referenced also by the loader");
203 _supername = supername;
204 }
205
206 // Placeholder objects represent classes currently being loaded.
207 // All threads examining the placeholder table must hold the
208 // SystemDictionary_lock, so we don't need special precautions
209 // on store ordering here.
210 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
211 Symbol* supername){
212 assert_locked_or_safepoint(SystemDictionary_lock);
213 assert(class_name != nullptr, "adding nullptr obj");
214
215 PlaceholderEntry entry;
216 entry.set_supername(supername);
217 PlaceholderKey key(class_name, loader_data);
218 bool created;
219 PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created);
220 assert(created, "better be absent");
221 return table_copy;
222 }
223
224 // Remove a placeholder object.
225 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
226 assert_locked_or_safepoint(SystemDictionary_lock);
227
228 PlaceholderKey key(class_name, loader_data);
229 _placeholders->remove(key);
230 }
231
232
233 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
234 assert_locked_or_safepoint(SystemDictionary_lock);
235 PlaceholderKey key(class_name, loader_data);
236 return _placeholders->get(key);
237 }
238
239 static const char* action_to_string(PlaceholderTable::classloadAction action) {
240 switch (action) {
241 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
242 case PlaceholderTable::LOAD_SUPER: return "LOAD_SUPER";
243 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
244 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD";
245 }
246 return "";
247 }
248
249 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
250 if (log_is_enabled(Debug, class, load, placeholders)) {
251 LogTarget(Debug, class, load, placeholders) lt;
252 ResourceMark rm;
253 LogStream ls(lt);
254 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
255 entry->print_on(&ls);
256 }
257 }
258
259 // find_and_add returns probe pointer - old or new
260 // If no entry exists, add a placeholder entry
261 // If entry exists, reuse entry
262 // For both, push SeenThread for classloadAction
263 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
264 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
265 ClassLoaderData* loader_data,
266 classloadAction action,
267 Symbol* supername,
268 JavaThread* thread) {
269 assert(action != LOAD_SUPER || supername != nullptr, "must have a super class name");
270 PlaceholderEntry* probe = get_entry(name, loader_data);
271 if (probe == nullptr) {
272 // Nothing found, add place holder
273 probe = add_entry(name, loader_data, supername);
274 } else {
275 if (action == LOAD_SUPER) {
276 probe->set_supername(supername);
277 }
278 }
279 probe->add_seen_thread(thread, action);
280 log(name, probe, "find_and_add", action);
281 return probe;
282 }
283
284 void PlaceholderTable::initialize(){
285 _placeholders = new (mtClass) InternalPlaceholderTable();
286 }
287
288
289 // placeholder is used to track class loading internal states
290 // superthreadQ tracks class circularity, while loading superclass/superinterface
291 // loadInstanceThreadQ tracks load_instance_class calls
292 // definer() tracks the single thread that owns define token
293 // defineThreadQ tracks waiters on defining thread's results
294 // 1st claimant creates placeholder
295 // find_and_add adds SeenThread entry for appropriate queue
296 // All claimants remove SeenThread after completing action
297 // On removal: if definer and all queues empty, remove entry
298 // Note: you can be in both placeholders and systemDictionary
299 // Therefore - must always check SD first
300 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
301 classloadAction action,
302 JavaThread* thread) {
303 assert_locked_or_safepoint(SystemDictionary_lock);
304 PlaceholderEntry* probe = get_entry(name, loader_data);
305 assert(probe != nullptr, "must find an entry");
306 log(name, probe, "find_and_remove", action);
307 probe->remove_seen_thread(thread, action);
308 if (probe->superThreadQ() == nullptr) {
309 probe->set_supername(nullptr);
310 }
311 // If no other threads using this entry, and this thread is not using this entry for other states
312 if ((probe->superThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr)
313 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)
314 && (probe->inlineTypeFieldQ() == nullptr)) {
315 remove_entry(name, loader_data);
316 }
317 }
318
319 void PlaceholderKey::print_on(outputStream* st) const {
320 _name->print_value_on(st);
321 st->print(", loader ");
322 _loader_data->print_value_on(st);
323 }
324
325 void PlaceholderEntry::print_on(outputStream* st) const {
326 if (supername() != nullptr) {
327 st->print(", supername ");
328 supername()->print_value_on(st);
329 }
330 if (definer() != nullptr) {
331 st->print(", definer ");
332 definer()->print_value_on(st);
333 }
334 if (instance_klass() != nullptr) {
335 st->print(", InstanceKlass ");
336 instance_klass()->print_value_on(st);
337 }
338 st->cr();
339 st->print("loadInstanceThreadQ threads:");
340 loadInstanceThreadQ()->print_action_queue(st);
341 st->cr();
342 st->print("superThreadQ threads:");
343 superThreadQ()->print_action_queue(st);
344 st->cr();
345 st->print("defineThreadQ threads:");
346 defineThreadQ()->print_action_queue(st);
347 st->cr();
348 st->print("inlineTypeFieldQ threads:");
349 inlineTypeFieldQ()->print_action_queue(st);
350 st->cr();
351 }
352
353 void PlaceholderTable::print_on(outputStream* st) {
354 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) {
355 st->print("placeholder ");
356 key.print_on(st);
357 entry.print_on(st);
358 return true;
359 };
360 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
361 _placeholders->table_size(), _placeholders->number_of_entries());
362 _placeholders->iterate(printer);
363 }
364
365 void PlaceholderTable::print() { return print_on(tty); }