1 /*

     2  * Copyright (c) 2003, 2017, 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 #ifndef SHARE_VM_CLASSFILE_PLACEHOLDERS_HPP

    26 #define SHARE_VM_CLASSFILE_PLACEHOLDERS_HPP

    27 

    28 #include "runtime/thread.hpp"

    29 #include "utilities/hashtable.hpp"

    30 

    31 class PlaceholderEntry;

    32 

    33 // Placeholder objects. These represent classes currently

    34 // being loaded, as well as arrays of primitives.

    35 //

    36 

    37 class PlaceholderTable : public Hashtable<Symbol*, mtClass> {

    38 

    39 public:

    40   PlaceholderTable(int table_size);

    41 

    42   PlaceholderEntry* new_entry(int hash, Symbol* name, ClassLoaderData* loader_data, bool havesupername, Symbol* supername);

    43   void free_entry(PlaceholderEntry* entry);

    44 

    45   PlaceholderEntry* bucket(int i) const {

    46     return (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::bucket(i);

    47   }

    48 

    49   PlaceholderEntry** bucket_addr(int i) {

    50     return (PlaceholderEntry**)Hashtable<Symbol*, mtClass>::bucket_addr(i);

    51   }

    52 

    53   void add_entry(int index, PlaceholderEntry* new_entry) {

    54     Hashtable<Symbol*, mtClass>::add_entry(index, (HashtableEntry<Symbol*, mtClass>*)new_entry);

    55   }

    56 

    57   void add_entry(int index, unsigned int hash, Symbol* name,

    58                 ClassLoaderData* loader_data, bool havesupername, Symbol* supername);

    59 

    60   // This returns a Symbol* to match type for SystemDictionary

    61   Symbol* find_entry(int index, unsigned int hash,

    62                        Symbol* name, ClassLoaderData* loader_data);

    63 

    64   PlaceholderEntry* get_entry(int index, unsigned int hash,

    65                        Symbol* name, ClassLoaderData* loader_data);

    66 

    67 // caller to create a placeholder entry must enumerate an action

    68 // caller claims ownership of that action

    69 // For parallel classloading:

    70 // multiple LOAD_INSTANCE threads can proceed in parallel

    71 // multiple LOAD_SUPER threads can proceed in parallel

    72 // LOAD_SUPER needed to check for class circularity

    73 // DEFINE_CLASS: ultimately define class must be single threaded

    74 // on a class/classloader basis

    75 // so the head of that queue owns the token

    76 // and the rest of the threads return the result the first thread gets

    77  enum classloadAction {

    78     LOAD_INSTANCE = 1,             // calling load_instance_class

    79     LOAD_SUPER = 2,                // loading superclass for this class

    80     DEFINE_CLASS = 3               // find_or_define class

    81  };

    82 

    83   // find_and_add returns probe pointer - old or new

    84   // If no entry exists, add a placeholder entry and push SeenThread for classloadAction

    85   // If entry exists, reuse entry and push SeenThread for classloadAction

    86   PlaceholderEntry* find_and_add(int index, unsigned int hash,

    87                                  Symbol* name, ClassLoaderData* loader_data,

    88                                  classloadAction action, Symbol* supername,

    89                                  Thread* thread);

    90 

    91   void remove_entry(int index, unsigned int hash,

    92                     Symbol* name, ClassLoaderData* loader_data);

    93 

    94   // find_and_remove first removes SeenThread for classloadAction

    95   // If all queues are empty and definer is null, remove the PlacheholderEntry completely

    96   void find_and_remove(int index, unsigned int hash,

    97                        Symbol* name, ClassLoaderData* loader_data,

    98                        classloadAction action, Thread* thread);

    99 

   100   void print_on(outputStream* st) const;

   101   void verify();

   102 };

   103 

   104 // SeenThread objects represent list of threads that are

   105 // currently performing a load action on a class.

   106 // For class circularity, set before loading a superclass.

   107 // For bootclasssearchpath, set before calling load_instance_class.

   108 // Defining must be single threaded on a class/classloader basis

   109 // For DEFINE_CLASS, the head of the queue owns the

   110 // define token and the rest of the threads wait to return the

   111 // result the first thread gets.

   112 class SeenThread: public CHeapObj<mtInternal> {

   113 private:

   114    Thread *_thread;

   115    SeenThread* _stnext;

   116    SeenThread* _stprev;

   117 public:

   118    SeenThread(Thread *thread) {

   119        _thread = thread;

   120        _stnext = NULL;

   121        _stprev = NULL;

   122    }

   123    Thread* thread()                const { return _thread;}

   124    void set_thread(Thread *thread) { _thread = thread; }

   125 

   126    SeenThread* next()              const { return _stnext;}

   127    void set_next(SeenThread *seen) { _stnext = seen; }

   128    void set_prev(SeenThread *seen) { _stprev = seen; }

   129 

   130   void print_action_queue(outputStream* st) {

   131     SeenThread* seen = this;

   132     while (seen != NULL) {

   133       seen->thread()->print_value_on(st);

   134       st->print(", ");

   135       seen = seen->next();

   136     }

   137   }

   138 };

   139 

   140 // Placeholder objects represent classes currently being loaded.

   141 // All threads examining the placeholder table must hold the

   142 // SystemDictionary_lock, so we don't need special precautions

   143 // on store ordering here.

   144 // The system dictionary is the only user of this class.

   145 

   146 class PlaceholderEntry : public HashtableEntry<Symbol*, mtClass> {

   147 

   148  private:

   149   ClassLoaderData*  _loader_data;   // initiating loader

   150   bool              _havesupername; // distinguish between null supername, and unknown

   151   Symbol*           _supername;

   152   Thread*           _definer;       // owner of define token

   153   InstanceKlass*    _instanceKlass; // InstanceKlass from successful define

   154   SeenThread*       _superThreadQ;  // doubly-linked queue of Threads loading a superclass for this class

   155   SeenThread*       _loadInstanceThreadQ;  // loadInstance thread

   156                                     // can be multiple threads if classloader object lock broken by application

   157                                     // or if classloader supports parallel classloading

   158 

   159   SeenThread*       _defineThreadQ; // queue of Threads trying to define this class

   160                                     // including _definer

   161                                     // _definer owns token

   162                                     // queue waits for and returns results from _definer

   163 

   164  public:

   165   // Simple accessors, used only by SystemDictionary

   166   Symbol*            klassname()           const { return literal(); }

   167 

   168   ClassLoaderData*   loader_data()         const { return _loader_data; }

   169   void               set_loader_data(ClassLoaderData* loader_data) { _loader_data = loader_data; }

   170 

   171   bool               havesupername()       const { return _havesupername; }

   172   void               set_havesupername(bool havesupername) { _havesupername = havesupername; }

   173 

   174   Symbol*            supername()           const { return _supername; }

   175   void               set_supername(Symbol* supername) {

   176     _supername = supername;

   177     if (_supername != NULL) _supername->increment_refcount();

   178   }

   179 

   180   Thread*            definer()             const {return _definer; }

   181   void               set_definer(Thread* definer) { _definer = definer; }

   182 

   183   InstanceKlass*     instance_klass()      const {return _instanceKlass; }

   184   void               set_instance_klass(InstanceKlass* ik) { _instanceKlass = ik; }

   185 

   186   SeenThread*        superThreadQ()        const { return _superThreadQ; }

   187   void               set_superThreadQ(SeenThread* SeenThread) { _superThreadQ = SeenThread; }

   188 

   189   SeenThread*        loadInstanceThreadQ() const { return _loadInstanceThreadQ; }

   190   void               set_loadInstanceThreadQ(SeenThread* SeenThread) { _loadInstanceThreadQ = SeenThread; }

   191 

   192   SeenThread*        defineThreadQ()        const { return _defineThreadQ; }

   193   void               set_defineThreadQ(SeenThread* SeenThread) { _defineThreadQ = SeenThread; }

   194 

   195   PlaceholderEntry* next() const {

   196     return (PlaceholderEntry*)HashtableEntry<Symbol*, mtClass>::next();

   197   }

   198 

   199   PlaceholderEntry** next_addr() {

   200     return (PlaceholderEntry**)HashtableEntry<Symbol*, mtClass>::next_addr();

   201   }

   202 

   203   // Test for equality

   204   // Entries are unique for class/classloader name pair

   205   bool equals(Symbol* class_name, ClassLoaderData* loader) const {

   206     return (klassname() == class_name && loader_data() == loader);

   207   }

   208 

   209   SeenThread* actionToQueue(PlaceholderTable::classloadAction action) {

   210     SeenThread* queuehead = NULL;

   211     switch (action) {

   212       case PlaceholderTable::LOAD_INSTANCE:

   213          queuehead = _loadInstanceThreadQ;

   214          break;

   215       case PlaceholderTable::LOAD_SUPER:

   216          queuehead = _superThreadQ;

   217          break;

   218       case PlaceholderTable::DEFINE_CLASS:

   219          queuehead = _defineThreadQ;

   220          break;

   221       default: Unimplemented();

   222     }

   223     return queuehead;

   224   }

   225 

   226   void set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {

   227     switch (action) {

   228       case PlaceholderTable::LOAD_INSTANCE:

   229          _loadInstanceThreadQ = seenthread;

   230          break;

   231       case PlaceholderTable::LOAD_SUPER:

   232          _superThreadQ = seenthread;

   233          break;

   234       case PlaceholderTable::DEFINE_CLASS:

   235          _defineThreadQ = seenthread;

   236          break;

   237       default: Unimplemented();

   238     }

   239     return;

   240   }

   241 

   242   bool super_load_in_progress() {

   243      return (_superThreadQ != NULL);

   244   }

   245 

   246   bool instance_load_in_progress() {

   247     return (_loadInstanceThreadQ != NULL);

   248   }

   249 

   250   bool define_class_in_progress() {

   251     return (_defineThreadQ != NULL);

   252   }

   253 

   254 // Doubly-linked list of Threads per action for class/classloader pair

   255 // Class circularity support: links in thread before loading superclass

   256 // bootstrapsearchpath support: links in a thread before load_instance_class

   257 // definers: use as queue of define requestors, including owner of

   258 // define token. Appends for debugging of requestor order

   259   void add_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {

   260     assert_lock_strong(SystemDictionary_lock);

   261     SeenThread* threadEntry = new SeenThread(thread);

   262     SeenThread* seen = actionToQueue(action);

   263 

   264     if (seen == NULL) {

   265       set_threadQ(threadEntry, action);

   266       return;

   267     }

   268     SeenThread* next;

   269     while ((next = seen->next()) != NULL) {

   270       seen = next;

   271     }

   272     seen->set_next(threadEntry);

   273     threadEntry->set_prev(seen);

   274     return;

   275   }

   276 

   277   bool check_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {

   278     assert_lock_strong(SystemDictionary_lock);

   279     SeenThread* threadQ = actionToQueue(action);

   280     SeenThread* seen = threadQ;

   281     while (seen) {

   282       if (thread == seen->thread()) {

   283         return true;

   284       }

   285       seen = seen->next();

   286     }

   287     return false;

   288   }

   289 

   290   // returns true if seenthreadQ is now empty

   291   // Note, caller must ensure probe still exists while holding

   292   // SystemDictionary_lock

   293   // ignores if cleanup has already been done

   294   // if found, deletes SeenThread

   295   bool remove_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {

   296     assert_lock_strong(SystemDictionary_lock);

   297     SeenThread* threadQ = actionToQueue(action);

   298     SeenThread* seen = threadQ;

   299     SeenThread* prev = NULL;

   300     while (seen) {

   301       if (thread == seen->thread()) {

   302         if (prev) {

   303           prev->set_next(seen->next());

   304         } else {

   305           set_threadQ(seen->next(), action);

   306         }

   307         if (seen->next()) {

   308           seen->next()->set_prev(prev);

   309         }

   310         delete seen;

   311         break;

   312       }

   313       prev = seen;

   314       seen = seen->next();

   315     }

   316     return (actionToQueue(action) == NULL);

   317   }

   318 

   319   // Print method doesn't append a cr

   320   void print_entry(outputStream* st) const;

   321   void verify() const;

   322 };

   323 

   324 #endif // SHARE_VM_CLASSFILE_PLACEHOLDERS_HPP