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