1 /*
2 * Copyright (c) 2003, 2021, 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.
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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
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23 */
24
25 #ifndef SHARE_CLASSFILE_PLACEHOLDERS_HPP
26 #define SHARE_CLASSFILE_PLACEHOLDERS_HPP
27
28 #include "utilities/hashtable.hpp"
29
30 class PlaceholderEntry;
31 class Thread;
32 class ClassLoaderData;
33 class Symbol;
34
35 // Placeholder objects. These represent classes currently
36 // being loaded, as well as arrays of primitives.
37 //
38
39 class PlaceholderTable : public Hashtable<Symbol*, mtClass> {
40
41 public:
42 PlaceholderTable(int table_size);
43
44 PlaceholderEntry* new_entry(int hash, Symbol* name, ClassLoaderData* loader_data, Symbol* supername);
45 void free_entry(PlaceholderEntry* entry);
46
47 PlaceholderEntry* bucket(int i) const {
48 return (PlaceholderEntry*)Hashtable<Symbol*, mtClass>::bucket(i);
49 }
50
51 PlaceholderEntry** bucket_addr(int i) {
52 return (PlaceholderEntry**)Hashtable<Symbol*, mtClass>::bucket_addr(i);
53 }
54
55 PlaceholderEntry* add_entry(unsigned int hash, Symbol* name,
56 ClassLoaderData* loader_data,
57 Symbol* supername);
58
59 // This returns a Symbol* to match type for SystemDictionary
60 Symbol* find_entry(unsigned int hash,
61 Symbol* name, ClassLoaderData* loader_data);
62
63 PlaceholderEntry* get_entry(unsigned int hash,
64 Symbol* name, ClassLoaderData* loader_data);
65
66 // caller to create a placeholder entry must enumerate an action
67 // caller claims ownership of that action
68 // For parallel classloading:
69 // multiple LOAD_INSTANCE threads can proceed in parallel
70 // multiple LOAD_SUPER threads can proceed in parallel
71 // LOAD_SUPER needed to check for class circularity
72 // DEFINE_CLASS: ultimately define class must be single threaded
73 // on a class/classloader basis
74 // so the head of that queue owns the token
75 // and the rest of the threads return the result the first thread gets
76 enum classloadAction {
77 LOAD_INSTANCE = 1, // calling load_instance_class
78 LOAD_SUPER = 2, // loading superclass for this class
79 DEFINE_CLASS = 3 // find_or_define class
80 };
81
82 // find_and_add returns probe pointer - old or new
83 // If no entry exists, add a placeholder entry and push SeenThread for classloadAction
84 // If entry exists, reuse entry and push SeenThread for classloadAction
85 PlaceholderEntry* find_and_add(unsigned int hash,
86 Symbol* name, ClassLoaderData* loader_data,
87 classloadAction action, Symbol* supername,
88 JavaThread* thread);
89
90 void remove_entry(unsigned int hash,
91 Symbol* name, ClassLoaderData* loader_data);
92
93 // find_and_remove first removes SeenThread for classloadAction
94 // If all queues are empty and definer is null, remove the PlacheholderEntry completely
95 void find_and_remove(unsigned int hash,
96 Symbol* name, ClassLoaderData* loader_data,
97 classloadAction action, JavaThread* thread);
98
99 void print_on(outputStream* st) const;
100 void print() const;
101 void verify();
102 };
103
104 class SeenThread;
105
106 // Placeholder objects represent classes currently being loaded.
107 // All threads examining the placeholder table must hold the
108 // SystemDictionary_lock, so we don't need special precautions
109 // on store ordering here.
110 // The system dictionary is the only user of this class.
111
112 class PlaceholderEntry : public HashtableEntry<Symbol*, mtClass> {
113
114 friend class PlaceholderTable;
115
116 private:
117 ClassLoaderData* _loader_data; // initiating loader
118 Symbol* _supername;
119 JavaThread* _definer; // owner of define token
120 InstanceKlass* _instanceKlass; // InstanceKlass from successful define
121 SeenThread* _superThreadQ; // doubly-linked queue of Threads loading a superclass for this class
122 SeenThread* _loadInstanceThreadQ; // loadInstance thread
123 // This can't be multiple threads since class loading waits for
124 // this token to be removed.
125
126 SeenThread* _defineThreadQ; // queue of Threads trying to define this class
127 // including _definer
128 // _definer owns token
129 // queue waits for and returns results from _definer
130
131 SeenThread* actionToQueue(PlaceholderTable::classloadAction action);
132 void set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action);
133 void add_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
134 bool remove_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
135
136 public:
137 // Simple accessors, used only by SystemDictionary
138 Symbol* klassname() const { return literal(); }
139
140 ClassLoaderData* loader_data() const { return _loader_data; }
141 void set_loader_data(ClassLoaderData* loader_data) { _loader_data = loader_data; }
142
143 Symbol* supername() const { return _supername; }
144 void set_supername(Symbol* supername) {
145 _supername = supername;
146 if (_supername != NULL) _supername->increment_refcount();
147 }
148
149 JavaThread* definer() const {return _definer; }
150 void set_definer(JavaThread* definer) { _definer = definer; }
151
152 InstanceKlass* instance_klass() const {return _instanceKlass; }
153 void set_instance_klass(InstanceKlass* ik) { _instanceKlass = ik; }
154
155 SeenThread* superThreadQ() const { return _superThreadQ; }
156 void set_superThreadQ(SeenThread* SeenThread) { _superThreadQ = SeenThread; }
157
158 SeenThread* loadInstanceThreadQ() const { return _loadInstanceThreadQ; }
159 void set_loadInstanceThreadQ(SeenThread* SeenThread) { _loadInstanceThreadQ = SeenThread; }
160
161 SeenThread* defineThreadQ() const { return _defineThreadQ; }
162 void set_defineThreadQ(SeenThread* SeenThread) { _defineThreadQ = SeenThread; }
163
164 PlaceholderEntry* next() const {
165 return (PlaceholderEntry*)HashtableEntry<Symbol*, mtClass>::next();
166 }
167
168 PlaceholderEntry** next_addr() {
169 return (PlaceholderEntry**)HashtableEntry<Symbol*, mtClass>::next_addr();
170 }
171
172 // Test for equality
173 // Entries are unique for class/classloader name pair
174 bool equals(Symbol* class_name, ClassLoaderData* loader) const {
175 return (klassname() == class_name && loader_data() == loader);
176 }
177
178 bool super_load_in_progress() {
179 return (_superThreadQ != NULL);
180 }
181
182 bool instance_load_in_progress() {
183 return (_loadInstanceThreadQ != NULL);
184 }
185
186 bool define_class_in_progress() {
187 return (_defineThreadQ != NULL);
188 }
189
190 // Used for ClassCircularityError checking
191 bool check_seen_thread(JavaThread* thread, PlaceholderTable::classloadAction action);
192
193 // Print method doesn't append a cr
194 void print_entry(outputStream* st) const;
195 void verify() const;
196 };
197
198 #endif // SHARE_CLASSFILE_PLACEHOLDERS_HPP