1 /*
  2  * Copyright (c) 2003, 2023, 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   void print_action_queue(outputStream* st) {
 86     SeenThread* seen = this;
 87     while (seen != nullptr) {
 88       seen->thread()->print_value_on(st);
 89       st->print(", ");
 90       seen = seen->next();
 91     }
 92   }
 93 };
 94 
 95 SeenThread* PlaceholderEntry::actionToQueue(PlaceholderTable::classloadAction action) {
 96   SeenThread* queuehead = nullptr;
 97   switch (action) {
 98     case PlaceholderTable::LOAD_INSTANCE:
 99        queuehead = _loadInstanceThreadQ;
100        break;
101     case PlaceholderTable::LOAD_SUPER:
102        queuehead = _superThreadQ;
103        break;
104     case PlaceholderTable::DEFINE_CLASS:
105        queuehead = _defineThreadQ;
106        break;
107     case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
108        queuehead = _inlineTypeFieldQ;
109        break;
110     default: Unimplemented();
111   }
112   return queuehead;
113 }
114 
115 void PlaceholderEntry::set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
116   switch (action) {
117     case PlaceholderTable::LOAD_INSTANCE:
118        _loadInstanceThreadQ = seenthread;
119        break;
120     case PlaceholderTable::LOAD_SUPER:
121        _superThreadQ = seenthread;
122        break;
123     case PlaceholderTable::DEFINE_CLASS:
124        _defineThreadQ = seenthread;
125        break;
126     case PlaceholderTable::PRIMITIVE_OBJECT_FIELD:
127        _inlineTypeFieldQ = seenthread;
128        break;
129     default: Unimplemented();
130   }
131   return;
132 }
133 
134 // Doubly-linked list of Threads per action for class/classloader pair
135 // Class circularity support: links in thread before loading superclass
136 // bootstrap loader support:  links in a thread before load_instance_class
137 // definers: use as queue of define requestors, including owner of
138 // define token. Appends for debugging of requestor order
139 void PlaceholderEntry::add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
140   assert_lock_strong(SystemDictionary_lock);
141   SeenThread* threadEntry = new SeenThread(thread);
142   SeenThread* seen = actionToQueue(action);
143 
144   if (seen == nullptr) {
145     set_threadQ(threadEntry, action);
146     return;
147   }
148   SeenThread* next;
149   while ((next = seen->next()) != nullptr) {
150     seen = next;
151   }
152   seen->set_next(threadEntry);
153   threadEntry->set_prev(seen);
154   return;
155 }
156 
157 bool PlaceholderEntry::check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
158   assert_lock_strong(SystemDictionary_lock);
159   SeenThread* threadQ = actionToQueue(action);
160   SeenThread* seen = threadQ;
161   while (seen) {
162     if (thread == seen->thread()) {
163       return true;
164     }
165     seen = seen->next();
166   }
167   return false;
168 }
169 
170 // returns true if seenthreadQ is now empty
171 // Note, caller must ensure probe still exists while holding
172 // SystemDictionary_lock
173 // ignores if cleanup has already been done
174 // if found, deletes SeenThread
175 bool PlaceholderEntry::remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action) {
176   assert_lock_strong(SystemDictionary_lock);
177   SeenThread* threadQ = actionToQueue(action);
178   SeenThread* seen = threadQ;
179   SeenThread* prev = nullptr;
180   while (seen) {
181     if (thread == seen->thread()) {
182       if (prev) {
183         prev->set_next(seen->next());
184       } else {
185         set_threadQ(seen->next(), action);
186       }
187       if (seen->next()) {
188         seen->next()->set_prev(prev);
189       }
190       delete seen;
191       break;
192     }
193     prev = seen;
194     seen = seen->next();
195   }
196   return (actionToQueue(action) == nullptr);
197 }
198 
199 
200 void PlaceholderEntry::set_supername(Symbol* supername) {
201   assert_locked_or_safepoint(SystemDictionary_lock);
202   assert(_supername == nullptr || _supername->refcount() > 1, "must be referenced also by the loader");
203   _supername = supername;
204 }
205 
206 // Placeholder objects represent classes currently being loaded.
207 // All threads examining the placeholder table must hold the
208 // SystemDictionary_lock, so we don't need special precautions
209 // on store ordering here.
210 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
211                             Symbol* supername){
212   assert_locked_or_safepoint(SystemDictionary_lock);
213   assert(class_name != nullptr, "adding nullptr obj");
214 
215   PlaceholderEntry entry;
216   entry.set_supername(supername);
217   PlaceholderKey key(class_name, loader_data);
218   bool created;
219   PlaceholderEntry* table_copy = _placeholders->put_if_absent(key, entry, &created);
220   assert(created, "better be absent");
221   return table_copy;
222 }
223 
224 // Remove a placeholder object.
225 void remove_entry(Symbol* class_name, ClassLoaderData* loader_data) {
226   assert_locked_or_safepoint(SystemDictionary_lock);
227 
228   PlaceholderKey key(class_name, loader_data);
229   _placeholders->remove(key);
230 }
231 
232 
233 PlaceholderEntry* PlaceholderTable::get_entry(Symbol* class_name, ClassLoaderData* loader_data) {
234   assert_locked_or_safepoint(SystemDictionary_lock);
235   PlaceholderKey key(class_name, loader_data);
236   return _placeholders->get(key);
237 }
238 
239 static const char* action_to_string(PlaceholderTable::classloadAction action) {
240   switch (action) {
241   case PlaceholderTable::LOAD_INSTANCE: return "LOAD_INSTANCE";
242   case PlaceholderTable::LOAD_SUPER:    return "LOAD_SUPER";
243   case PlaceholderTable::DEFINE_CLASS:  return "DEFINE_CLASS";
244   case PlaceholderTable::PRIMITIVE_OBJECT_FIELD: return "PRIMITIVE_OBJECT_FIELD";
245  }
246  return "";
247 }
248 
249 inline void log(Symbol* name, PlaceholderEntry* entry, const char* function, PlaceholderTable::classloadAction action) {
250   if (log_is_enabled(Debug, class, load, placeholders)) {
251     LogTarget(Debug, class, load, placeholders) lt;
252     ResourceMark rm;
253     LogStream ls(lt);
254     ls.print("entry %s : %s %s ", name->as_C_string(), function, action_to_string(action));
255     entry->print_on(&ls);
256   }
257 }
258 
259 // find_and_add returns probe pointer - old or new
260 // If no entry exists, add a placeholder entry
261 // If entry exists, reuse entry
262 // For both, push SeenThread for classloadAction
263 // If LOAD_SUPER, this is used for circularity detection for instanceklass loading.
264 PlaceholderEntry* PlaceholderTable::find_and_add(Symbol* name,
265                                                  ClassLoaderData* loader_data,
266                                                  classloadAction action,
267                                                  Symbol* supername,
268                                                  JavaThread* thread) {
269   assert(action != LOAD_SUPER || supername != nullptr, "must have a super class name");
270   PlaceholderEntry* probe = get_entry(name, loader_data);
271   if (probe == nullptr) {
272     // Nothing found, add place holder
273     probe = add_entry(name, loader_data, supername);
274   } else {
275     if (action == LOAD_SUPER) {
276       probe->set_supername(supername);
277     }
278   }
279   probe->add_seen_thread(thread, action);
280   log(name, probe, "find_and_add", action);
281   return probe;
282 }
283 
284 void PlaceholderTable::initialize(){
285   _placeholders = new (mtClass) InternalPlaceholderTable();
286 }
287 
288 
289 // placeholder is used to track class loading internal states
290 // superthreadQ tracks class circularity, while loading superclass/superinterface
291 // loadInstanceThreadQ tracks load_instance_class calls
292 // definer() tracks the single thread that owns define token
293 // defineThreadQ tracks waiters on defining thread's results
294 // 1st claimant creates placeholder
295 // find_and_add adds SeenThread entry for appropriate queue
296 // All claimants remove SeenThread after completing action
297 // On removal: if definer and all queues empty, remove entry
298 // Note: you can be in both placeholders and systemDictionary
299 // Therefore - must always check SD first
300 void PlaceholderTable::find_and_remove(Symbol* name, ClassLoaderData* loader_data,
301                                        classloadAction action,
302                                        JavaThread* thread) {
303   assert_locked_or_safepoint(SystemDictionary_lock);
304   PlaceholderEntry* probe = get_entry(name, loader_data);
305   assert(probe != nullptr, "must find an entry");
306   log(name, probe, "find_and_remove", action);
307   probe->remove_seen_thread(thread, action);
308   if (probe->superThreadQ() == nullptr) {
309     probe->set_supername(nullptr);
310   }
311   // If no other threads using this entry, and this thread is not using this entry for other states
312   if ((probe->superThreadQ() == nullptr) && (probe->loadInstanceThreadQ() == nullptr)
313       && (probe->defineThreadQ() == nullptr) && (probe->definer() == nullptr)
314       && (probe->inlineTypeFieldQ() == nullptr)) {
315     remove_entry(name, loader_data);
316   }
317 }
318 
319 void PlaceholderKey::print_on(outputStream* st) const {
320   _name->print_value_on(st);
321   st->print(", loader ");
322   _loader_data->print_value_on(st);
323 }
324 
325 void PlaceholderEntry::print_on(outputStream* st) const {
326   if (supername() != nullptr) {
327     st->print(", supername ");
328     supername()->print_value_on(st);
329   }
330   if (definer() != nullptr) {
331     st->print(", definer ");
332     definer()->print_value_on(st);
333   }
334   if (instance_klass() != nullptr) {
335     st->print(", InstanceKlass ");
336     instance_klass()->print_value_on(st);
337   }
338   st->cr();
339   st->print("loadInstanceThreadQ threads:");
340   loadInstanceThreadQ()->print_action_queue(st);
341   st->cr();
342   st->print("superThreadQ threads:");
343   superThreadQ()->print_action_queue(st);
344   st->cr();
345   st->print("defineThreadQ threads:");
346   defineThreadQ()->print_action_queue(st);
347   st->cr();
348   st->print("inlineTypeFieldQ threads:");
349   inlineTypeFieldQ()->print_action_queue(st);
350   st->cr();
351 }
352 
353 void PlaceholderTable::print_on(outputStream* st) {
354   auto printer = [&] (PlaceholderKey& key, PlaceholderEntry& entry) {
355       st->print("placeholder ");
356       key.print_on(st);
357       entry.print_on(st);
358       return true;
359   };
360   st->print_cr("Placeholder table (table_size=%d, placeholders=%d)",
361                 _placeholders->table_size(), _placeholders->number_of_entries());
362   _placeholders->iterate(printer);
363 }
364 
365 void PlaceholderTable::print() { return print_on(tty); }