1 /*
2 * Copyright (c) 2003, 2025, 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 "classfile/classLoaderData.inline.hpp"
26 #include "classfile/placeholders.hpp"
27 #include "logging/log.hpp"
28 #include "logging/logTag.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/symbolHandle.hpp"
32 #include "runtime/javaThread.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "utilities/resourceHash.hpp"
35
36 class PlaceholderKey {
37 SymbolHandle _name;
38 ClassLoaderData* _loader_data;
39 public:
40 PlaceholderKey(Symbol* name, ClassLoaderData* l) : _name(name), _loader_data(l) {}
41
42 static bool equals(PlaceholderKey const& k1, PlaceholderKey const& k2) {
43 return (k1._name == k2._name && k1._loader_data == k2._loader_data);
44 }
45 static unsigned hash(PlaceholderKey const& k) {
46 return (unsigned) k._name->identity_hash() ^ (int)((intptr_t)k._loader_data >> 3);
47 }
48 void print_on(outputStream* st) const;
49 };
50
51 const int _placeholder_table_size = 503; // Does this really have to be prime?
52 using InternalPlaceholderTable = ResourceHashtable<PlaceholderKey, PlaceholderEntry, _placeholder_table_size, AnyObj::C_HEAP, mtClass,
53 PlaceholderKey::hash, PlaceholderKey::equals>;
54 static InternalPlaceholderTable* _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 class SeenThread: public CHeapObj<mtInternal> {
65 private:
66 JavaThread* _thread;
67 SeenThread* _stnext;
68 SeenThread* _stprev;
69 public:
70 SeenThread(JavaThread* thread) {
71 _thread = thread;
72 _stnext = nullptr;
73 _stprev = nullptr;
74 }
75 JavaThread* thread() const { return _thread;}
76 void set_thread(JavaThread* thread) { _thread = thread; }
77
78 SeenThread* next() const { return _stnext;}
79 void set_next(SeenThread* seen) { _stnext = seen; }
80 void set_prev(SeenThread* seen) { _stprev = seen; }
81
82 static void print_action_queue(SeenThread* seen, outputStream* st) {
83 while (seen != nullptr) {
84 seen->thread()->print_value_on(st);
85 st->print(", ");
86 seen = seen->next();
87 }
88 }
89 };
90
91 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) {
92 SeenThread* queuehead = nullptr;
93 switch (action) {
94 case PlaceholderTable::LOAD_INSTANCE:
95 queuehead = _loadInstanceThreadQ;
96 break;
97 case PlaceholderTable::DETECT_CIRCULARITY:
98 queuehead = _circularityThreadQ;
99 break;
100 case PlaceholderTable::DEFINE_CLASS:
101 queuehead = _defineThreadQ;
102 break;
103 default: Unimplemented();
104 }
105 return queuehead;
106 }
107
108 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
109 switch (action) {
110 case PlaceholderTable::LOAD_INSTANCE:
111 _loadInstanceThreadQ = seenthread;
112 break;
113 case PlaceholderTable::DETECT_CIRCULARITY:
114 _circularityThreadQ = seenthread;
115 break;
116 case PlaceholderTable::DEFINE_CLASS:
117 _defineThreadQ = seenthread;
118 break;
119 default: Unimplemented();
120 }
121 return;
122 }
123
124 // Doubly-linked list of Threads per action for class/classloader pair
125 // Class circularity support: links in thread before loading superclass
126 // bootstrap loader support: links in a thread before load_instance_class
127 // definers: use as queue of define requestors, including owner of
128 // define token. Appends for debugging of requestor order
129 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
130 assert_lock_strong(SystemDictionary_lock);
131 SeenThread* threadEntry = new SeenThread(thread);
132 SeenThread* seen = actionToQueue(action);
133
134 if (seen == nullptr) {
135 set_threadQ(threadEntry, action);
136 return;
137 }
138 SeenThread* next;
139 while ((next = seen->next()) != nullptr) {
140 seen = next;
141 }
142 seen->set_next(threadEntry);
143 threadEntry->set_prev(seen);
144 return;
145 }
146
147 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
148 assert_lock_strong(SystemDictionary_lock);
149 SeenThread* threadQ = actionToQueue(action);
150 SeenThread* seen = threadQ;
151 while (seen) {
152 if (thread == seen->thread()) {
153 return true;
154 }
155 seen = seen->next();
156 }
157 return false;
158 }
159
160 // returns true if seenthreadQ is now empty
161 // Note, caller must ensure probe still exists while holding
162 // SystemDictionary_lock
163 // ignores if cleanup has already been done
164 // if found, deletes SeenThread
165 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
166 assert_lock_strong(SystemDictionary_lock);
167 SeenThread* threadQ = actionToQueue(action);
168 SeenThread* seen = threadQ;
169 SeenThread* prev = nullptr;
170 while (seen) {
171 if (thread == seen->thread()) {
172 if (prev) {
173 prev->set_next(seen->next());
174 } else {
175 set_threadQ(seen->next(), action);
176 }
177 if (seen->next()) {
178 seen->next()->set_prev(prev);
179 }
180 delete seen;
181 break;
182 }
183 prev = seen;
184 seen = seen->next();
185 }
186 return (actionToQueue(action) == nullptr);
187 }
188
189
190 void PlaceholderEntry::set_next_klass_name(Symbol* next_klass_name) {
191 assert_locked_or_safepoint(SystemDictionary_lock);
192 assert(_next_klass_name == nullptr || _next_klass_name->refcount() > 1, "must be referenced also by the loader");
193 _next_klass_name = next_klass_name;
194 }
195
196 // Placeholder objects represent classes currently being loaded.
197 // All threads examining the placeholder table must hold the
198 // SystemDictionary_lock, so we don't need special precautions
199 // on store ordering here.
200 static PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
201 Symbol* next_klass_name){
202 assert_locked_or_safepoint(SystemDictionary_lock);
203 assert(class_name != nullptr, "adding nullptr obj");
204
205 PlaceholderEntry entry;
206 entry.set_next_klass_name(next_klass_name);
207 PlaceholderKey key(class_name, loader_data);
208 bool created;
209 PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created);
210 assert(created, "better be absent");
211 return table_copy;
212 }
213
214 // Remove a placeholder object.
215 static void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
216 assert_locked_or_safepoint(SystemDictionary_lock);
217
218 PlaceholderKey key(class_name, loader_data);
219 _placeholders->remove(key);
220 }
221
222
223 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
224 assert_locked_or_safepoint(SystemDictionary_lock);
225 PlaceholderKey key(class_name, loader_data);
226 return _placeholders->get(key);
227 }
228
229 static const char* action_to_string(PlaceholderTable::classloadAction action) {
230 switch (action) {
231 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
232 case PlaceholderTable::DETECT_CIRCULARITY: return "DETECT_CIRCULARITY";
233 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
234 }
235 return "";
236 }
237
238 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
239 if (log_is_enabled(Debug, class, load, placeholders)) {
240 LogTarget(Debug, class, load, placeholders) lt;
241 ResourceMark rm;
242 LogStream ls(lt);
243 ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
244 entry->print_on(&ls);
245 }
246 }
247
248 // find_and_add returns probe pointer - old or new
249 // If no entry exists, add a placeholder entry
250 // If entry exists, reuse entry
251 // For both, push SeenThread for classloadAction
252 // If DETECT_CIRCULARITY, this is used for circularity detection for instanceklass loading.
253 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
254 ClassLoaderData* loader_data,
255 classloadAction action,
256 Symbol* next_klass_name,
257 JavaThread* thread) {
258 assert(action != DETECT_CIRCULARITY || next_klass_name != nullptr,
259 "must have a class name for the next step in the class resolution recursion");
260 PlaceholderEntry* probe = get_entry(name, loader_data);
261 if (probe == nullptr) {
262 // Nothing found, add place holder
263 probe = add_entry(name, loader_data, next_klass_name);
264 } else {
265 if (action == DETECT_CIRCULARITY) {
266 probe->set_next_klass_name(next_klass_name);
267 }
268 }
269 probe->add_seen_thread(thread, action);
270 log(name, probe, "find_and_add", action);
271 return probe;
272 }
273
274 void PlaceholderTable::initialize(){
275 _placeholders = new (mtClass) InternalPlaceholderTable();
276 }
277
278
279 // placeholder is used to track class loading internal states
280 // superthreadQ tracks class circularity, while loading superclass/superinterface
281 // loadInstanceThreadQ tracks load_instance_class calls
282 // definer() tracks the single thread that owns define token
283 // defineThreadQ tracks waiters on defining thread's results
284 // 1st claimant creates placeholder
285 // find_and_add adds SeenThread entry for appropriate queue
286 // All claimants remove SeenThread after completing action
287 // On removal: if definer and all queues empty, remove entry
288 // Note: you can be in both placeholders and systemDictionary
289 // Therefore - must always check SD first
290 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
291 classloadAction action,
292 JavaThread* thread) {
293 assert_locked_or_safepoint(SystemDictionary_lock);
294 PlaceholderEntry* probe = get_entry(name, loader_data);
295 assert(probe != nullptr, "must find an entry");
296 log(name, probe, "find_and_remove", action);
297 probe->remove_seen_thread(thread, action);
298 if (probe->circularityThreadQ() == nullptr) {
299 probe->set_next_klass_name(nullptr);
300 }
301 // If no other threads using this entry, and this thread is not using this entry for other states
302 if ((probe->circularityThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr)
303 && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)) {
304 remove_entry(name, loader_data);
305 }
306 }
307
308 void PlaceholderKey::print_on(outputStream* st) const {
309 _name->print_value_on(st);
310 st->print(", loader ");
311 _loader_data->print_value_on(st);
312 }
313
314 void PlaceholderEntry::print_on(outputStream* st) const {
315 if (next_klass_name() != nullptr) {
316 st->print(", next_klass_name ");
317 next_klass_name()->print_value_on(st);
318 }
319 if (definer() != nullptr) {
320 st->print(", definer ");
321 definer()->print_value_on(st);
322 }
323 if (instance_klass() != nullptr) {
324 st->print(", InstanceKlass ");
325 instance_klass()->print_value_on(st);
326 }
327 st->cr();
328 st->print("loadInstanceThreadQ threads:");
329 SeenThread::print_action_queue(loadInstanceThreadQ(), st);
330 st->cr();
331 st->print("circularityThreadQ threads:");
332 SeenThread::print_action_queue(circularityThreadQ(), st);
333 st->cr();
334 st->print("defineThreadQ threads:");
335 SeenThread::print_action_queue(defineThreadQ(), st);
336 st->cr();
337 }
338
339 void PlaceholderTable::print_on(outputStream* st) {
340 auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) {
341 st->print("placeholder ");
342 key.print_on(st);
343 entry.print_on(st);
344 return true;
345 };
346 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
347 _placeholders->table_size(), _placeholders->number_of_entries());
348 _placeholders->iterate(printer);
349 }
350
351 void PlaceholderTable::print() { return print_on(tty); }