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 ResourceHashtable<PlaceholderKey, PlaceholderEntry, _placeholder_table_size, AnyObj::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 = nullptr;
75 _stprev = nullptr;
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 != nullptr) {
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 = nullptr;
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 if (seen == nullptr) {
144 set_threadQ(threadEntry, action);
145 return;
146 }
147 SeenThread* next;
148 while ((next = seen->next()) != nullptr) {
149 seen = next;
150 }
151 seen->set_next(threadEntry);
152 threadEntry->set_prev(seen);
153 return;
154 }
155
156 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
157 assert_lock_strong(SystemDictionary_lock);
158 SeenThread* threadQ = actionToQueue(action);
159 SeenThread* seen = threadQ;
160 while (seen) {
161 if (thread == seen->thread()) {
162 return true;
163 }
164 seen = seen->next();
165 }
166 return false;
167 }
168
169 // returns true if seenthreadQ is now empty
170 // Note, caller must ensure probe still exists while holding
171 // SystemDictionary_lock
172 // ignores if cleanup has already been done
173 // if found, deletes SeenThread
174 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
175 assert_lock_strong(SystemDictionary_lock);
176 SeenThread* threadQ = actionToQueue(action);
177 SeenThread* seen = threadQ;
178 SeenThread* prev = nullptr;
179 while (seen) {
180 if (thread == seen->thread()) {
181 if (prev) {
182 prev->set_next(seen->next());
183 } else {
184 set_threadQ(seen->next(), action);
185 }
186 if (seen->next()) {
187 seen->next()->set_prev(prev);
188 }
189 delete seen;
190 break;
191 }
192 prev = seen;
193 seen = seen->next();
194 }
195 return (actionToQueue(action) == nullptr);
196 }
197
198
199 void PlaceholderEntry::set_supername(Symbol* supername) {
200 assert_locked_or_safepoint(SystemDictionary_lock);
201 assert(_supername == nullptr || _supername->refcount() > 1, "must be referenced also by the loader");
202 _supername = supername;
203 }
204
205 // Placeholder objects represent classes currently being loaded.
206 // All threads examining the placeholder table must hold the
207 // SystemDictionary_lock, so we don't need special precautions
208 // on store ordering here.
209 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
210 Symbol* supername){
211 assert_locked_or_safepoint(SystemDictionary_lock);
212 assert(class_name != nullptr, "adding nullptr obj");
213
214 PlaceholderEntry entry;
215 entry.set_supername(supername);
216 PlaceholderKey key(class_name, loader_data);
217 bool created;
218 PlaceholderEntry* table_copy = _placeholders.put_if_absent(key, entry, &created);
219 assert(created, "better be absent");
220 return table_copy;
221 }
222
223 // Remove a placeholder object.
224 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
225 assert_locked_or_safepoint(SystemDictionary_lock);
226
227 PlaceholderKey key(class_name, loader_data);
228 _placeholders.remove(key);
229 }
230
231
232 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
233 assert_locked_or_safepoint(SystemDictionary_lock);
234 PlaceholderKey key(class_name, loader_data);
235 return _placeholders.get(key);
236 }
237
238 static const char* action_to_string(PlaceholderTable::classloadAction action) {
239 switch (action) {
240 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
241 case PlaceholderTable::LOAD_SUPER: return "LOAD_SUPER";
242 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
243 case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD";
244 }
245 return "";
246 }
247
248 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
249 if (log_is_enabled(Debug, class, load, placeholders)) {
250 LogTarget(Debug, class, load, placeholders) lt;
251 ResourceMark rm;
252 LogStream ls(lt);
253 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
254 entry->print_on(&ls);
255 }
256 }
257
258 // find_and_add returns probe pointer - old or new
259 // If no entry exists, add a placeholder entry
260 // If entry exists, reuse entry
261 // For both, push SeenThread for classloadAction
262 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
263 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
264 ClassLoaderData* loader_data,
265 classloadAction action,
266 Symbol* supername,
267 JavaThread* thread) {
268 assert(action != LOAD_SUPER || supername != nullptr, "must have a super class name");
269 PlaceholderEntry* probe = get_entry(name, loader_data);
270 if (probe == nullptr) {
271 // Nothing found, add place holder
272 probe = add_entry(name, loader_data, supername);
273 } else {
274 if (action == LOAD_SUPER) {
275 probe->set_supername(supername);
276 }
277 }
278 probe->add_seen_thread(thread, action);
279 log(name, probe, "find_and_add", action);
280 return probe;
281 }
282
283
284 // placeholder is used to track class loading internal states
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 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
296 classloadAction action,
297 JavaThread* thread) {
298 assert_locked_or_safepoint(SystemDictionary_lock);
299 PlaceholderEntry* probe = get_entry(name, loader_data);
300 assert(probe != nullptr, "must find an entry");
301 log(name, probe, "find_and_remove", action);
302 probe->remove_seen_thread(thread, action);
303 if (probe->superThreadQ() == nullptr) {
304 probe->set_supername(nullptr);
305 }
306 // If no other threads using this entry, and this thread is not using this entry for other states
307 if ((probe->superThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr)
308 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)
309 && (probe->inlineTypeFieldQ() == nullptr)) {
310 remove_entry(name, loader_data);
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() != nullptr) {
322 st->print(", supername ");
323 supername()->print_value_on(st);
324 }
325 if (definer() != nullptr) {
326 st->print(", definer ");
327 definer()->print_value_on(st);
328 }
329 if (instance_klass() != nullptr) {
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); }