1 /*
2 * Copyright (c) 2003, 2021, 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 "runtime/mutexLocker.hpp"
33 #include "runtime/thread.hpp"
34 #include "utilities/hashtable.inline.hpp"
35
36 // SeenThread objects represent list of threads that are
37 // currently performing a load action on a class.
38 // For class circularity, set before loading a superclass.
39 // For bootclasssearchpath, set before calling load_instance_class.
40 // Defining must be single threaded on a class/classloader basis
41 // For DEFINE_CLASS, the head of the queue owns the
42 // define token and the rest of the threads wait to return the
43 // result the first thread gets.
44 class SeenThread: public CHeapObj<mtInternal> {
45 private:
46 JavaThread* _thread;
47 SeenThread* _stnext;
48 SeenThread* _stprev;
49 public:
50 SeenThread(JavaThread* thread) {
51 _thread = thread;
52 _stnext = NULL;
53 _stprev = NULL;
54 }
55 JavaThread* thread() const { return _thread;}
56 void set_thread(JavaThread* thread) { _thread = thread; }
57
58 SeenThread* next() const { return _stnext;}
59 void set_next(SeenThread* seen) { _stnext = seen; }
60 void set_prev(SeenThread* seen) { _stprev = seen; }
61
62 void print_action_queue(outputStream* st) {
63 SeenThread* seen = this;
64 while (seen != NULL) {
65 seen->thread()->print_value_on(st);
66 st->print(", ");
67 seen = seen->next();
68 }
69 }
70 };
71
72 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) {
73 SeenThread* queuehead = NULL;
74 switch (action) {
75 case PlaceholderTable::LOAD_INSTANCE:
76 queuehead = _loadInstanceThreadQ;
77 break;
78 case PlaceholderTable::LOAD_SUPER:
79 queuehead = _superThreadQ;
80 break;
81 case PlaceholderTable::DEFINE_CLASS:
82 queuehead = _defineThreadQ;
83 break;
84 default: Unimplemented();
85 }
86 return queuehead;
87 }
88
89 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
90 switch (action) {
91 case PlaceholderTable::LOAD_INSTANCE:
92 _loadInstanceThreadQ = seenthread;
93 break;
94 case PlaceholderTable::LOAD_SUPER:
95 _superThreadQ = seenthread;
96 break;
97 case PlaceholderTable::DEFINE_CLASS:
98 _defineThreadQ = seenthread;
99 break;
100 default: Unimplemented();
101 }
102 return;
103 }
104
105 // Doubly-linked list of Threads per action for class/classloader pair
106 // Class circularity support: links in thread before loading superclass
107 // bootstrap loader support: links in a thread before load_instance_class
108 // definers: use as queue of define requestors, including owner of
109 // define token. Appends for debugging of requestor order
110 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
111 assert_lock_strong(SystemDictionary_lock);
112 SeenThread* threadEntry = new SeenThread(thread);
113 SeenThread* seen = actionToQueue(action);
114
115 assert(action != PlaceholderTable::LOAD_INSTANCE || seen == NULL,
116 "Only one LOAD_INSTANCE allowed at a time");
117
118 if (seen == NULL) {
119 set_threadQ(threadEntry, action);
120 return;
121 }
122 SeenThread* next;
123 while ((next = seen->next()) != NULL) {
124 seen = next;
125 }
126 seen->set_next(threadEntry);
127 threadEntry->set_prev(seen);
128 return;
129 }
130
131 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
132 assert_lock_strong(SystemDictionary_lock);
133 SeenThread* threadQ = actionToQueue(action);
134 SeenThread* seen = threadQ;
135 while (seen) {
136 if (thread == seen->thread()) {
137 return true;
138 }
139 seen = seen->next();
140 }
141 return false;
142 }
143
144 // returns true if seenthreadQ is now empty
145 // Note, caller must ensure probe still exists while holding
146 // SystemDictionary_lock
147 // ignores if cleanup has already been done
148 // if found, deletes SeenThread
149 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
150 assert_lock_strong(SystemDictionary_lock);
151 SeenThread* threadQ = actionToQueue(action);
152 SeenThread* seen = threadQ;
153 SeenThread* prev = NULL;
154 while (seen) {
155 if (thread == seen->thread()) {
156 if (prev) {
157 prev->set_next(seen->next());
158 } else {
159 set_threadQ(seen->next(), action);
160 }
161 if (seen->next()) {
162 seen->next()->set_prev(prev);
163 }
164 delete seen;
165 break;
166 }
167 prev = seen;
168 seen = seen->next();
169 }
170 return (actionToQueue(action) == NULL);
171 }
172
173
174 // Placeholder methods
175
176 PlaceholderEntry* PlaceholderTable::new_entry(int hash, Symbol* name,
177 ClassLoaderData* loader_data,
178 Symbol* supername) {
179 PlaceholderEntry* entry = (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::new_entry(hash, name);
180 // Hashtable with Symbol* literal must increment and decrement refcount.
181 name->increment_refcount();
182 entry->set_loader_data(loader_data);
183 entry->set_supername(supername);
184 entry->set_superThreadQ(NULL);
185 entry->set_loadInstanceThreadQ(NULL);
186 entry->set_defineThreadQ(NULL);
187 entry->set_definer(NULL);
188 entry->set_instance_klass(NULL);
189 return entry;
190 }
191
192 void PlaceholderTable::free_entry(PlaceholderEntry* entry) {
193 // decrement Symbol refcount here because Hashtable doesn't.
194 entry->literal()->decrement_refcount();
195 if (entry->supername() != NULL) entry->supername()->decrement_refcount();
196 BasicHashtable<mtClass>::free_entry(entry);
197 }
198
199
200 // Placeholder objects represent classes currently being loaded.
201 // All threads examining the placeholder table must hold the
202 // SystemDictionary_lock, so we don't need special precautions
203 // on store ordering here.
204 PlaceholderEntry* PlaceholderTable::add_entry(unsigned int hash,
205 Symbol* class_name, ClassLoaderData* loader_data,
206 Symbol* supername){
207 assert_locked_or_safepoint(SystemDictionary_lock);
208 assert(class_name != NULL, "adding NULL obj");
209
210 // Both readers and writers are locked so it's safe to just
211 // create the placeholder and insert it in the list without a membar.
212 PlaceholderEntry* entry = new_entry(hash, class_name, loader_data, supername);
213 int index = hash_to_index(hash);
214 Hashtable<Symbol*, mtClass>::add_entry(index, entry);
215 return entry;
216 }
217
218
219 // Remove a placeholder object.
220 void PlaceholderTable::remove_entry(unsigned int hash,
221 Symbol* class_name,
222 ClassLoaderData* loader_data) {
223 assert_locked_or_safepoint(SystemDictionary_lock);
224 int index = hash_to_index(hash);
225 PlaceholderEntry** p = bucket_addr(index);
226 while (*p != NULL) {
227 PlaceholderEntry *probe = *p;
228 if (probe->hash() == hash && probe->equals(class_name, loader_data)) {
229 // Delete entry
230 *p = probe->next();
231 free_entry(probe);
232 return;
233 }
234 p = probe->next_addr();
235 }
236 }
237
238 PlaceholderEntry* PlaceholderTable::get_entry(unsigned int hash,
239 Symbol* class_name,
240 ClassLoaderData* loader_data) {
241 assert_locked_or_safepoint(SystemDictionary_lock);
242
243 int index = hash_to_index(hash);
244 for (PlaceholderEntry *place_probe = bucket(index);
245 place_probe != NULL;
246 place_probe = place_probe->next()) {
247 if (place_probe->hash() == hash &&
248 place_probe->equals(class_name, loader_data)) {
249 return place_probe;
250 }
251 }
252 return NULL;
253 }
254
255 Symbol* PlaceholderTable::find_entry(unsigned int hash,
256 Symbol* class_name,
257 ClassLoaderData* loader_data) {
258 PlaceholderEntry* probe = get_entry(hash, class_name, loader_data);
259 return (probe != NULL ? probe->klassname() : NULL);
260 }
261
262 static const char* action_to_string(PlaceholderTable::classloadAction action) {
263 switch (action) {
264 case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
265 case PlaceholderTable::LOAD_SUPER: return "LOAD_SUPER";
266 case PlaceholderTable::DEFINE_CLASS: return "DEFINE_CLASS";
267 }
268 return "";
269 }
270
271 inline void log(PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
272 if (log_is_enabled(Debug, class, load, placeholders)) {
273 LogTarget(Debug, class, load, placeholders) lt;
274 ResourceMark rm;
275 LogStream ls(lt);
276 ls.print("%s %s ", function, action_to_string(action));
277 entry->print_entry(&ls);
278 }
279 }
280
281 // find_and_add returns probe pointer - old or new
282 // If no entry exists, add a placeholder entry
283 // If entry exists, reuse entry
284 // For both, push SeenThread for classloadAction
285 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
286 PlaceholderEntry* PlaceholderTable::find_and_add(unsigned int hash,
287 Symbol* name,
288 ClassLoaderData* loader_data,
289 classloadAction action,
290 Symbol* supername,
291 JavaThread* thread) {
292 assert(action != LOAD_SUPER || supername != NULL, "must have a super class name");
293 PlaceholderEntry* probe = get_entry(hash, name, loader_data);
294 if (probe == NULL) {
295 // Nothing found, add place holder
296 probe = add_entry(hash, name, loader_data, supername);
297 } else {
298 if (action == LOAD_SUPER) {
299 probe->set_supername(supername);
300 }
301 }
302 probe->add_seen_thread(thread, action);
303 log(probe, "find_and_add", action);
304 return probe;
305 }
306
307
308 // placeholder is used to track class loading internal states
309 // placeholder existence now for loading superclass/superinterface
310 // superthreadQ tracks class circularity, while loading superclass/superinterface
311 // loadInstanceThreadQ tracks load_instance_class calls
312 // definer() tracks the single thread that owns define token
313 // defineThreadQ tracks waiters on defining thread's results
314 // 1st claimant creates placeholder
315 // find_and_add adds SeenThread entry for appropriate queue
316 // All claimants remove SeenThread after completing action
317 // On removal: if definer and all queues empty, remove entry
318 // Note: you can be in both placeholders and systemDictionary
319 // Therefore - must always check SD first
320 // Ignores the case where entry is not found
321 void PlaceholderTable::find_and_remove(unsigned int hash,
322 Symbol* name, ClassLoaderData* loader_data,
323 classloadAction action,
324 JavaThread* thread) {
325 assert_locked_or_safepoint(SystemDictionary_lock);
326 PlaceholderEntry *probe = get_entry(hash, name, loader_data);
327 if (probe != NULL) {
328 log(probe, "find_and_remove", action);
329 probe->remove_seen_thread(thread, action);
330 // If no other threads using this entry, and this thread is not using this entry for other states
331 if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
332 && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)) {
333 remove_entry(hash, name, loader_data);
334 }
335 }
336 }
337
338 PlaceholderTable::PlaceholderTable(int table_size)
339 : Hashtable<Symbol*, mtClass>(table_size, sizeof(PlaceholderEntry)) {
340 }
341
342 void PlaceholderEntry::verify() const {
343 guarantee(loader_data() != NULL, "Must have been setup.");
344 guarantee(loader_data()->class_loader() == NULL || loader_data()->class_loader()->is_instance(),
345 "checking type of _loader");
346 guarantee(instance_klass() == NULL
347 || instance_klass()->is_instance_klass(),
348 "checking type of instance_klass result");
349 }
350
351 void PlaceholderTable::verify() {
352 verify_table<PlaceholderEntry>("Placeholder Table");
353 }
354
355
356 // Note, doesn't append a cr
357 // Can't call this print_on because HashtableEntry doesn't initialize its vptr
358 // and print_on is a virtual function so the vptr call crashes.
359 void PlaceholderEntry::print_entry(outputStream* st) const {
360 klassname()->print_value_on(st);
361 if (loader_data() != NULL) {
362 st->print(", loader ");
363 loader_data()->print_value_on(st);
364 }
365 if (supername() != NULL) {
366 st->print(", supername ");
367 supername()->print_value_on(st);
368 }
369 if (definer() != NULL) {
370 st->print(", definer ");
371 definer()->print_value_on(st);
372 }
373 if (instance_klass() != NULL) {
374 st->print(", InstanceKlass ");
375 instance_klass()->print_value_on(st);
376 }
377 st->cr();
378 st->print("loadInstanceThreadQ threads:");
379 loadInstanceThreadQ()->print_action_queue(st);
380 st->cr();
381 st->print("superThreadQ threads:");
382 superThreadQ()->print_action_queue(st);
383 st->cr();
384 st->print("defineThreadQ threads:");
385 defineThreadQ()->print_action_queue(st);
386 st->cr();
387 }
388
389 void PlaceholderTable::print_on(outputStream* st) const {
390 st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
391 table_size(), number_of_entries());
392 for (int pindex = 0; pindex < table_size(); pindex++) {
393 for (PlaceholderEntry* probe = bucket(pindex);
394 probe != NULL;
395 probe = probe->next()) {
396 st->print("%4d: placeholder ", pindex);
397 probe->print_entry(st);
398 }
399 }
400 }
401
402 void PlaceholderTable::print() const { return print_on(tty); }