1 /*
  2  * Copyright (c) 2003, 2022, 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, ResourceObj::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 = NULL;
 75        _stprev = NULL;
 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 != NULL) {
 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 = NULL;
 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   assert(action != PlaceholderTable::LOAD_INSTANCE || seen == NULL,
144          "Only one LOAD_INSTANCE allowed at a time");
145 
146   if (seen == NULL) {
147     set_threadQ(threadEntry, action);
148     return;
149   }
150   SeenThread* next;
151   while ((next = seen->next()) != NULL) {
152     seen = next;
153   }
154   seen->set_next(threadEntry);
155   threadEntry->set_prev(seen);
156   return;
157 }
158 
159 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
160   assert_lock_strong(SystemDictionary_lock);
161   SeenThread* threadQ = actionToQueue(action);
162   SeenThread* seen = threadQ;
163   while (seen) {
164     if (thread == seen->thread()) {
165       return true;
166     }
167     seen = seen->next();
168   }
169   return false;
170 }
171 
172 // returns true if seenthreadQ is now empty
173 // Note, caller must ensure probe still exists while holding
174 // SystemDictionary_lock
175 // ignores if cleanup has already been done
176 // if found, deletes SeenThread
177 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
178   assert_lock_strong(SystemDictionary_lock);
179   SeenThread* threadQ = actionToQueue(action);
180   SeenThread* seen = threadQ;
181   SeenThread* prev = NULL;
182   while (seen) {
183     if (thread == seen->thread()) {
184       if (prev) {
185         prev->set_next(seen->next());
186       } else {
187         set_threadQ(seen->next(), action);
188       }
189       if (seen->next()) {
190         seen->next()->set_prev(prev);
191       }
192       delete seen;
193       break;
194     }
195     prev = seen;
196     seen = seen->next();
197   }
198   return (actionToQueue(action) == NULL);
199 }
200 
201 
202 // Placeholder methods
203 
204 // Placeholder objects represent classes currently being loaded.
205 // All threads examining the placeholder table must hold the
206 // SystemDictionary_lock, so we don't need special precautions
207 // on store ordering here.
208 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
209                             Symbol* supername){
210   assert_locked_or_safepoint(SystemDictionary_lock);
211   assert(class_name != NULL, "adding NULL obj");
212 
213   PlaceholderEntry entry;
214   entry.set_supername(supername);
215   PlaceholderKey key(class_name, loader_data);
216   bool created;
217   PlaceholderEntry* table_copy = _placeholders.put_if_absent(key, entry, &created);
218   assert(created, "better be absent");
219   return table_copy;
220 }
221 
222 // Remove a placeholder object.
223 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
224   assert_locked_or_safepoint(SystemDictionary_lock);
225 
226   PlaceholderKey key(class_name, loader_data);
227   _placeholders.remove(key);
228 }
229 
230 
231 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
232   assert_locked_or_safepoint(SystemDictionary_lock);
233   PlaceholderKey key(class_name, loader_data);
234   return _placeholders.get(key);
235 }
236 
237 static const char* action_to_string(PlaceholderTable::classloadAction action) {
238   switch (action) {
239   case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
240   case PlaceholderTable::LOAD_SUPER:    return "LOAD_SUPER";
241   case PlaceholderTable::DEFINE_CLASS:  return "DEFINE_CLASS";
242   case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD";
243  }
244  return "";
245 }
246 
247 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
248   if (log_is_enabled(Debug, class, load, placeholders)) {
249     LogTarget(Debug, class, load, placeholders) lt;
250     ResourceMark rm;
251     LogStream ls(lt);
252     ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
253     entry->print_on(&ls);
254   }
255 }
256 
257 // find_and_add returns probe pointer - old or new
258 // If no entry exists, add a placeholder entry
259 // If entry exists, reuse entry
260 // For both, push SeenThread for classloadAction
261 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
262 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
263                                                  ClassLoaderData* loader_data,
264                                                  classloadAction action,
265                                                  Symbol* supername,
266                                                  JavaThread* thread) {
267   assert(action != LOAD_SUPER || supername != NULL, "must have a super class name");
268   PlaceholderEntry* probe = get_entry(name, loader_data);
269   if (probe == NULL) {
270     // Nothing found, add place holder
271     probe = add_entry(name, loader_data, supername);
272   } else {
273     if (action == LOAD_SUPER) {
274       probe->set_supername(supername);
275     }
276   }
277   probe->add_seen_thread(thread, action);
278   log(name, probe, "find_and_add", action);
279   return probe;
280 }
281 
282 
283 // placeholder is used to track class loading internal states
284 // placeholder existence now for loading superclass/superinterface
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 // Ignores the case where entry is not found
296 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
297                                        classloadAction action,
298                                        JavaThread* thread) {
299   assert_locked_or_safepoint(SystemDictionary_lock);
300   PlaceholderEntry* probe = get_entry(name, loader_data);
301   if (probe != NULL) {
302     log(name, probe, "find_and_remove", action);
303     probe->remove_seen_thread(thread, action);
304     // If no other threads using this entry, and this thread is not using this entry for other states
305     if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
306         && (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)
307         && (probe->inlineTypeFieldQ() == NULL)) {
308       probe->clear_supername();
309       remove_entry(name, loader_data);
310     }
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() != NULL) {
322     st->print(", supername ");
323     supername()->print_value_on(st);
324   }
325   if (definer() != NULL) {
326     st->print(", definer ");
327     definer()->print_value_on(st);
328   }
329   if (instance_klass() != NULL) {
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); }