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 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::LOAD_SUPER:
 99        queuehead = _superThreadQ;
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::LOAD_SUPER:
115        _superThreadQ = 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_supername(Symbol* supername) {
192   assert_locked_or_safepoint(SystemDictionary_lock);
193   assert(_supername == nullptr || _supername->refcount() > 1, "must be referenced also by the loader");
194   _supername = supername;
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 PlaceholderEntry* add_entry(Symbol* class_name, ClassLoaderData* loader_data,
202                             Symbol* supername){
203   assert_locked_or_safepoint(SystemDictionary_lock);
204   assert(class_name != nullptr, "adding nullptr obj");
205 
206   PlaceholderEntry entry;
207   entry.set_supername(supername);
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 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::LOAD_SUPER:    return "LOAD_SUPER";
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 LOAD_SUPER, 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* supername,
258                                                  JavaThread* thread) {
259   assert(action != LOAD_SUPER || supername != nullptr, "must have a super class name");
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, supername);
264   } else {
265     if (action == LOAD_SUPER) {
266       probe->set_supername(supername);
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->superThreadQ() == nullptr) {
299     probe->set_supername(nullptr);
300   }
301   // If no other threads using this entry, and this thread is not using this entry for other states
302   if ((probe->superThreadQ() == 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 (supername() != nullptr) {
316     st->print(", supername ");
317     supername()->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("superThreadQ threads:");
332   SeenThread::print_action_queue(superThreadQ(), 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); }
--- EOF ---