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