1 /*
2 * Copyright (c) 2003, 2024, 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 static void print_action_queue(SeenThread* seen, outputStream* st) {
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::DETECT_CIRCULARITY:
101 queuehead = _circularityThreadQ;
102 break;
103 case PlaceholderTable::DEFINE_CLASS:
104 queuehead = _defineThreadQ;
105 break;
106 default: Unimplemented();
107 }
108 return queuehead;
109 }
110
111 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
112 switch (action) {
113 case PlaceholderTable::LOAD_INSTANCE:
114 _loadInstanceThreadQ = seenthread;
115 break;
116 case PlaceholderTable::DETECT_CIRCULARITY:
117 _circularityThreadQ = seenthread;
118 break;
119 case PlaceholderTable::DEFINE_CLASS:
120 _defineThreadQ = seenthread;
121 break;
122 default: Unimplemented();
123 }
124 return;
125 }
126
127 // Doubly-linked list of Threads per action for class/classloader pair
128 // Class circularity support: links in thread before loading superclass
129 // bootstrap loader support: links in a thread before load_instance_class
130 // definers: use as queue of define requestors, including owner of
131 // define token. Appends for debugging of requestor order
132 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
133 assert_lock_strong(SystemDictionary_lock);
134 SeenThread* threadEntry = new SeenThread(thread);
135 SeenThread* seen = actionToQueue(action);
136
137 if (seen == nullptr) {
138 set_threadQ(threadEntry, action);
139 return;
140 }
141 SeenThread* next;
142 while ((next = seen->next()) != nullptr) {
143 seen = next;
144 }
145 seen->set_next(threadEntry);
146 threadEntry->set_prev(seen);
147 return;
148 }
149
150 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
151 assert_lock_strong(SystemDictionary_lock);
152 SeenThread* threadQ = actionToQueue(action);
153 SeenThread* seen = threadQ;
154 while (seen) {
155 if (thread == seen->thread()) {
156 return true;
157 }
158 seen = seen->next();
159 }
160 return false;
161 }
162
163 // returns true if seenthreadQ is now empty
164 // Note, caller must ensure probe still exists while holding
165 // SystemDictionary_lock
166 // ignores if cleanup has already been done
167 // if found, deletes SeenThread
168 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
169 assert_lock_strong(SystemDictionary_lock);
170 SeenThread* threadQ = actionToQueue(action);
171 SeenThread* seen = threadQ;
172 SeenThread* prev = nullptr;
173 while (seen) {
174 if (thread == seen->thread()) {
175 if (prev) {
176 prev->set_next(seen->next());
177 } else {
178 set_threadQ(seen->next(), action);
179 }
180 if (seen->next()) {
181 seen->next()->set_prev(prev);
182 }
183 delete seen;
184 break;
185 }
186 prev = seen;
187 seen = seen->next();
188 }
189 return (actionToQueue(action) == nullptr);
190 }
191
192
193 void PlaceholderEntry::set_next_klass_name(Symbol* next_klass_name) {
194 assert_locked_or_safepoint(SystemDictionary_lock);
195 assert(_next_klass_name == nullptr || _next_klass_name->refcount() > 1, "must be referenced also by the loader");
196 _next_klass_name = next_klass_name;
197 }
198
199 // Placeholder objects represent classes currently being loaded.
200 // All threads examining the placeholder table must hold the
201 // SystemDictionary_lock, so we don't need special precautions
202 // on store ordering here.
203 static PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
204 Symbol* next_klass_name){
205 assert_locked_or_safepoint(SystemDictionary_lock);
206 assert(class_name != nullptr, "adding nullptr obj");
207
208 PlaceholderEntry entry;
209 entry.set_next_klass_name(next_klass_name);
210 PlaceholderKey key(class_name, loader_data);
211 bool created;
212 PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created);
213 assert(created, "better be absent");
214 return table_copy;
215 }
216
217 // Remove a placeholder object.
218 static void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
219 assert_locked_or_safepoint(SystemDictionary_lock);
220
221 PlaceholderKey key(class_name, loader_data);
222 _placeholders->remove(key);
223 }
224
225
226 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
227 assert_locked_or_safepoint(SystemDictionary_lock);
228 PlaceholderKey key(class_name, loader_data);
229 return _placeholders->get(key);
230 }
231
232 static const char* action_to_string(PlaceholderTable::classloadAction action) {
233 switch (action) {
234 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
235 case PlaceholderTable::DETECT_CIRCULARITY: return "DETECT_CIRCULARITY";
236 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
237 }
238 return "";
239 }
240
241 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
242 if (log_is_enabled(Debug, class, load, placeholders)) {
243 LogTarget(Debug, class, load, placeholders) lt;
244 ResourceMark rm;
245 LogStream ls(lt);
246 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
247 entry->print_on(&ls);
248 }
249 }
250
251 // find_and_add returns probe pointer - old or new
252 // If no entry exists, add a placeholder entry
253 // If entry exists, reuse entry
254 // For both, push SeenThread for classloadAction
255 // If DETECT_CIRCULARITY, this is used for circularity detection for instanceklass loading.
256 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
257 ClassLoaderData* loader_data,
258 classloadAction action,
259 Symbol* next_klass_name,
260 JavaThread* thread) {
261 assert(action != DETECT_CIRCULARITY || next_klass_name != nullptr,
262 "must have a class name for the next step in the class resolution recursion");
263 PlaceholderEntry* probe = get_entry(name, loader_data);
264 if (probe == nullptr) {
265 // Nothing found, add place holder
266 probe = add_entry(name, loader_data, next_klass_name);
267 } else {
268 if (action == DETECT_CIRCULARITY) {
269 probe->set_next_klass_name(next_klass_name);
270 }
271 }
272 probe->add_seen_thread(thread, action);
273 log(name, probe, "find_and_add", action);
274 return probe;
275 }
276
277 void PlaceholderTable::initialize(){
278 _placeholders = new (mtClass) InternalPlaceholderTable();
279 }
280
281
282 // placeholder is used to track class loading internal states
283 // superthreadQ tracks class circularity, while loading superclass/superinterface
284 // loadInstanceThreadQ tracks load_instance_class calls
285 // definer() tracks the single thread that owns define token
286 // defineThreadQ tracks waiters on defining thread's results
287 // 1st claimant creates placeholder
288 // find_and_add adds SeenThread entry for appropriate queue
289 // All claimants remove SeenThread after completing action
290 // On removal: if definer and all queues empty, remove entry
291 // Note: you can be in both placeholders and systemDictionary
292 // Therefore - must always check SD first
293 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
294 classloadAction action,
295 JavaThread* thread) {
296 assert_locked_or_safepoint(SystemDictionary_lock);
297 PlaceholderEntry* probe = get_entry(name, loader_data);
298 assert(probe != nullptr, "must find an entry");
299 log(name, probe, "find_and_remove", action);
300 probe->remove_seen_thread(thread, action);
301 if (probe->circularityThreadQ() == nullptr) {
302 probe->set_next_klass_name(nullptr);
303 }
304 // If no other threads using this entry, and this thread is not using this entry for other states
305 if ((probe->circularityThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr)
306 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)) {
307 remove_entry(name, loader_data);
308 }
309 }
310
311 void PlaceholderKey::print_on(outputStream* st) const {
312 _name->print_value_on(st);
313 st->print(", loader ");
314 _loader_data->print_value_on(st);
315 }
316
317 void PlaceholderEntry::print_on(outputStream* st) const {
318 if (next_klass_name() != nullptr) {
319 st->print(", next_klass_name ");
320 next_klass_name()->print_value_on(st);
321 }
322 if (definer() != nullptr) {
323 st->print(", definer ");
324 definer()->print_value_on(st);
325 }
326 if (instance_klass() != nullptr) {
327 st->print(", InstanceKlass ");
328 instance_klass()->print_value_on(st);
329 }
330 st->cr();
331 st->print("loadInstanceThreadQ threads:");
332 SeenThread::print_action_queue(loadInstanceThreadQ(), st);
333 st->cr();
334 st->print("circularityThreadQ threads:");
335 SeenThread::print_action_queue(circularityThreadQ(), st);
336 st->cr();
337 st->print("defineThreadQ threads:");
338 SeenThread::print_action_queue(defineThreadQ(), st);
339 st->cr();
340 }
341
342 void PlaceholderTable::print_on(outputStream* st) {
343 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) {
344 st->print("placeholder ");
345 key.print_on(st);
346 entry.print_on(st);
347 return true;
348 };
349 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
350 _placeholders->table_size(), _placeholders->number_of_entries());
351 _placeholders->iterate(printer);
352 }
353
354 void PlaceholderTable::print() { return print_on(tty); }