1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
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  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).
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 24 
 25 #ifndef SHARE_CLASSFILE_PLACEHOLDERS_HPP
 26 #define SHARE_CLASSFILE_PLACEHOLDERS_HPP
 27 
 28 class PlaceholderEntry;
 29 class Thread;
 30 class ClassLoaderData;
 31 class Symbol;
 32 
 33 // Placeholder objects. These represent classes currently
 34 // being loaded, as well as arrays of primitives.
 35 //
 36 
 37 class PlaceholderTable : public AllStatic {
 38  public:
 39   // caller to create a placeholder entry must enumerate an action
 40   // caller claims ownership of that action
 41   // For parallel classloading:
 42   // multiple LOAD_INSTANCE threads can proceed in parallel
 43   // multiple LOAD_SUPER threads can proceed in parallel
 44   // LOAD_SUPER needed to check for class circularity
 45   // DEFINE_CLASS: ultimately define class must be single threaded
 46   // on a class/classloader basis
 47   // so the head of that queue owns the token
 48   // and the rest of the threads return the result the first thread gets
 49   // PRIMITIVE_OBJECT_FIELD: needed to check for inline type fields circularity
 50   enum classloadAction {
 51     LOAD_INSTANCE = 1,             // calling load_instance_class
 52     LOAD_SUPER = 2,                // loading superclass for this class
 53     DEFINE_CLASS = 3,              // find_or_define class
 54     PRIMITIVE_OBJECT_FIELD = 4     // primitive object fields
 55  };
 56 
 57   static PlaceholderEntry* get_entry(Symbol* name, ClassLoaderData* loader_data);
 58 
 59   // find_and_add returns probe pointer - old or new
 60   // If no entry exists, add a placeholder entry and push SeenThread for classloadAction
 61   // If entry exists, reuse entry and push SeenThread for classloadAction
 62   static PlaceholderEntry* find_and_add(Symbol* name, ClassLoaderData* loader_data,
 63                                         classloadAction action, Symbol* supername,
 64                                         JavaThread* thread);
 65 
 66   // find_and_remove first removes SeenThread for classloadAction
 67   // If all queues are empty and definer is null, remove the PlacheholderEntry completely
 68   static void find_and_remove(Symbol* name, ClassLoaderData* loader_data,
 69                        classloadAction action, JavaThread* thread);
 70 
 71   static void print_on(outputStream* st);
 72   static void print();
 73 };
 74 
 75 class SeenThread;
 76 
 77 // Placeholder objects represent classes currently being loaded.
 78 // All threads examining the placeholder table must hold the
 79 // SystemDictionary_lock, so we don't need special precautions
 80 // on store ordering here.
 81 // The system dictionary is the only user of this class.
 82 class PlaceholderEntry {
 83   friend class PlaceholderTable;
 84  private:
 85   Symbol*           _supername;
 86   JavaThread*       _definer;       // owner of define token
 87   InstanceKlass*    _instanceKlass; // InstanceKlass from successful define
 88   SeenThread*       _superThreadQ;  // doubly-linked queue of Threads loading a superclass for this class
 89   SeenThread*       _loadInstanceThreadQ;  // loadInstance thread
 90                                     // This can't be multiple threads since class loading waits for
 91                                     // this token to be removed.
 92 
 93   SeenThread*       _defineThreadQ; // queue of Threads trying to define this class
 94                                     // including _definer
 95                                     // _definer owns token
 96                                     // queue waits for and returns results from _definer
 97   SeenThread*       _inlineTypeFieldQ;  // queue of inline types for circularity checking
 98 
 99   SeenThread* actionToQueue(PlaceholderTable::classloadAction action);
100   void set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action);
101   void add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
102   bool remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
103 
104  public:
105   PlaceholderEntry() :
106      _supername(nullptr), _definer(nullptr), _instanceKlass(nullptr),
107      _superThreadQ(nullptr), _loadInstanceThreadQ(nullptr), _defineThreadQ(nullptr),
108      _inlineTypeFieldQ(nullptr) { }
109 
110   Symbol*            supername()           const { return _supername; }
111   void               set_supername(Symbol* supername) {
112     Symbol::maybe_decrement_refcount(_supername);
113     _supername = supername;
114     Symbol::maybe_increment_refcount(_supername);
115   }
116   void               clear_supername() {
117     Symbol::maybe_decrement_refcount(_supername);
118     _supername = nullptr;
119   }
120 
121   JavaThread*        definer()             const {return _definer; }
122   void               set_definer(JavaThread* definer) { _definer = definer; }
123 
124   InstanceKlass*     instance_klass()      const {return _instanceKlass; }
125   void               set_instance_klass(InstanceKlass* ik) { _instanceKlass = ik; }
126 
127   SeenThread*        superThreadQ()        const { return _superThreadQ; }
128   void               set_superThreadQ(SeenThread* SeenThread) { _superThreadQ = SeenThread; }
129 
130   SeenThread*        loadInstanceThreadQ() const { return _loadInstanceThreadQ; }
131   void               set_loadInstanceThreadQ(SeenThread* SeenThread) { _loadInstanceThreadQ = SeenThread; }
132 
133   SeenThread*        defineThreadQ()       const { return _defineThreadQ; }
134   void               set_defineThreadQ(SeenThread* SeenThread) { _defineThreadQ = SeenThread; }
135 
136   SeenThread*        inlineTypeFieldQ()    const { return _inlineTypeFieldQ; }
137   void               set_inlineTypeFieldQ(SeenThread* SeenThread) { _inlineTypeFieldQ = SeenThread; }
138 
139   bool super_load_in_progress() {
140      return (_superThreadQ != NULL);
141   }
142 
143   bool instance_load_in_progress() {
144     return (_loadInstanceThreadQ != NULL);
145   }
146 
147   bool define_class_in_progress() {
148     return (_defineThreadQ != NULL);
149   }
150 
151   bool inline_type_field_in_progress() {
152     return (_inlineTypeFieldQ != NULL);
153   }
154 
155   // Used for ClassCircularityError checking
156   bool check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
157 
158   void print_on(outputStream* st) const;
159 };
160 
161 #endif // SHARE_CLASSFILE_PLACEHOLDERS_HPP