1 /*
2 * Copyright (c) 2003, 2019, 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 "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 // FLATTENABLE_FIELD: needed to check for value type flattenable fields circularity
78 enum classloadAction {
79 LOAD_INSTANCE = 1, // calling load_instance_class
80 LOAD_SUPER = 2, // loading superclass for this class
81 DEFINE_CLASS = 3, // find_or_define class
82 FLATTENABLE_FIELD = 4 // flattenable value type fields
83 };
84
85 // find_and_add returns probe pointer - old or new
86 // If no entry exists, add a placeholder entry and push SeenThread for classloadAction
87 // If entry exists, reuse entry and push SeenThread for classloadAction
88 PlaceholderEntry* find_and_add(int index, unsigned int hash,
89 Symbol* name, ClassLoaderData* loader_data,
90 classloadAction action, Symbol* supername,
91 Thread* thread);
92
93 void remove_entry(int index, unsigned int hash,
94 Symbol* name, ClassLoaderData* loader_data);
95
96 // find_and_remove first removes SeenThread for classloadAction
97 // If all queues are empty and definer is null, remove the PlacheholderEntry completely
98 void find_and_remove(int index, unsigned int hash,
99 Symbol* name, ClassLoaderData* loader_data,
100 classloadAction action, Thread* thread);
101
102 void print_on(outputStream* st) const;
103 void verify();
104 };
105
106 // SeenThread objects represent list of threads that are
107 // currently performing a load action on a class.
108 // For class circularity, set before loading a superclass.
109 // For bootclasssearchpath, set before calling load_instance_class.
110 // Defining must be single threaded on a class/classloader basis
111 // For DEFINE_CLASS, the head of the queue owns the
112 // define token and the rest of the threads wait to return the
113 // result the first thread gets.
114 // For FLATTENABLE_FIELD, set when loading value type fields for
115 // class circularity checking.
116 class SeenThread: public CHeapObj<mtInternal> {
117 private:
118 Thread *_thread;
119 SeenThread* _stnext;
120 SeenThread* _stprev;
121 public:
122 SeenThread(Thread *thread) {
123 _thread = thread;
124 _stnext = NULL;
125 _stprev = NULL;
126 }
127 Thread* thread() const { return _thread;}
128 void set_thread(Thread *thread) { _thread = thread; }
129
130 SeenThread* next() const { return _stnext;}
131 void set_next(SeenThread *seen) { _stnext = seen; }
132 void set_prev(SeenThread *seen) { _stprev = seen; }
133
134 void print_action_queue(outputStream* st) {
135 SeenThread* seen = this;
136 while (seen != NULL) {
137 seen->thread()->print_value_on(st);
138 st->print(", ");
139 seen = seen->next();
140 }
141 }
142 };
143
144 // Placeholder objects represent classes currently being loaded.
145 // All threads examining the placeholder table must hold the
146 // SystemDictionary_lock, so we don't need special precautions
147 // on store ordering here.
148 // The system dictionary is the only user of this class.
149
150 class PlaceholderEntry : public HashtableEntry<Symbol*, mtClass> {
151
152 private:
153 ClassLoaderData* _loader_data; // initiating loader
154 bool _havesupername; // distinguish between null supername, and unknown
155 Symbol* _supername;
156 Thread* _definer; // owner of define token
157 InstanceKlass* _instanceKlass; // InstanceKlass from successful define
158 SeenThread* _superThreadQ; // doubly-linked queue of Threads loading a superclass for this class
159 SeenThread* _loadInstanceThreadQ; // loadInstance thread
160 // can be multiple threads if classloader object lock broken by application
161 // or if classloader supports parallel classloading
162
163 SeenThread* _defineThreadQ; // queue of Threads trying to define this class
164 // including _definer
165 // _definer owns token
166 // queue waits for and returns results from _definer
167 SeenThread* _flattenableFieldQ; // queue of value types for circularity checking
168
169 public:
170 // Simple accessors, used only by SystemDictionary
171 Symbol* klassname() const { return literal(); }
172
173 ClassLoaderData* loader_data() const { return _loader_data; }
174 void set_loader_data(ClassLoaderData* loader_data) { _loader_data = loader_data; }
175
176 bool havesupername() const { return _havesupername; }
177 void set_havesupername(bool havesupername) { _havesupername = havesupername; }
178
179 Symbol* supername() const { return _supername; }
180 void set_supername(Symbol* supername) {
181 _supername = supername;
182 if (_supername != NULL) _supername->increment_refcount();
183 }
184
185 Thread* definer() const {return _definer; }
186 void set_definer(Thread* definer) { _definer = definer; }
187
188 InstanceKlass* instance_klass() const {return _instanceKlass; }
189 void set_instance_klass(InstanceKlass* ik) { _instanceKlass = ik; }
190
191 SeenThread* superThreadQ() const { return _superThreadQ; }
192 void set_superThreadQ(SeenThread* SeenThread) { _superThreadQ = SeenThread; }
193
194 SeenThread* loadInstanceThreadQ() const { return _loadInstanceThreadQ; }
195 void set_loadInstanceThreadQ(SeenThread* SeenThread) { _loadInstanceThreadQ = SeenThread; }
196
197 SeenThread* defineThreadQ() const { return _defineThreadQ; }
198 void set_defineThreadQ(SeenThread* SeenThread) { _defineThreadQ = SeenThread; }
199
200 SeenThread* flattenableFieldQ() const { return _flattenableFieldQ; }
201 void set_flattenableFieldQ(SeenThread* SeenThread) { _flattenableFieldQ = SeenThread; }
202
203 PlaceholderEntry* next() const {
204 return (PlaceholderEntry*)HashtableEntry<Symbol*, mtClass>::next();
205 }
206
207 PlaceholderEntry** next_addr() {
208 return (PlaceholderEntry**)HashtableEntry<Symbol*, mtClass>::next_addr();
209 }
210
211 // Test for equality
212 // Entries are unique for class/classloader name pair
213 bool equals(Symbol* class_name, ClassLoaderData* loader) const {
214 return (klassname() == class_name && loader_data() == loader);
215 }
216
217 SeenThread* actionToQueue(PlaceholderTable::classloadAction action) {
218 SeenThread* queuehead = NULL;
219 switch (action) {
220 case PlaceholderTable::LOAD_INSTANCE:
221 queuehead = _loadInstanceThreadQ;
222 break;
223 case PlaceholderTable::LOAD_SUPER:
224 queuehead = _superThreadQ;
225 break;
226 case PlaceholderTable::DEFINE_CLASS:
227 queuehead = _defineThreadQ;
228 break;
229 case PlaceholderTable::FLATTENABLE_FIELD:
230 queuehead = _flattenableFieldQ;
231 break;
232 default: Unimplemented();
233 }
234 return queuehead;
235 }
236
237 void set_threadQ(SeenThread* seenthread, PlaceholderTable::classloadAction action) {
238 switch (action) {
239 case PlaceholderTable::LOAD_INSTANCE:
240 _loadInstanceThreadQ = seenthread;
241 break;
242 case PlaceholderTable::LOAD_SUPER:
243 _superThreadQ = seenthread;
244 break;
245 case PlaceholderTable::DEFINE_CLASS:
246 _defineThreadQ = seenthread;
247 break;
248 case PlaceholderTable::FLATTENABLE_FIELD:
249 _flattenableFieldQ = seenthread;
250 break;
251 default: Unimplemented();
252 }
253 return;
254 }
255
256 bool super_load_in_progress() {
257 return (_superThreadQ != NULL);
258 }
259
260 bool instance_load_in_progress() {
261 return (_loadInstanceThreadQ != NULL);
262 }
263
264 bool define_class_in_progress() {
265 return (_defineThreadQ != NULL);
266 }
267
268 bool flattenable_field_in_progress() {
269 return (_flattenableFieldQ != NULL);
270 }
271
272 // Doubly-linked list of Threads per action for class/classloader pair
273 // Class circularity support: links in thread before loading superclass
274 // bootstrapsearchpath support: links in a thread before load_instance_class
275 // definers: use as queue of define requestors, including owner of
276 // define token. Appends for debugging of requestor order
277 void add_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {
278 assert_lock_strong(SystemDictionary_lock);
279 SeenThread* threadEntry = new SeenThread(thread);
280 SeenThread* seen = actionToQueue(action);
281
282 if (seen == NULL) {
283 set_threadQ(threadEntry, action);
284 return;
285 }
286 SeenThread* next;
287 while ((next = seen->next()) != NULL) {
288 seen = next;
289 }
290 seen->set_next(threadEntry);
291 threadEntry->set_prev(seen);
292 return;
293 }
294
295 bool check_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {
296 assert_lock_strong(SystemDictionary_lock);
297 SeenThread* threadQ = actionToQueue(action);
298 SeenThread* seen = threadQ;
299 while (seen) {
300 if (thread == seen->thread()) {
301 return true;
302 }
303 seen = seen->next();
304 }
305 return false;
306 }
307
308 // returns true if seenthreadQ is now empty
309 // Note, caller must ensure probe still exists while holding
310 // SystemDictionary_lock
311 // ignores if cleanup has already been done
312 // if found, deletes SeenThread
313 bool remove_seen_thread(Thread* thread, PlaceholderTable::classloadAction action) {
314 assert_lock_strong(SystemDictionary_lock);
315 SeenThread* threadQ = actionToQueue(action);
316 SeenThread* seen = threadQ;
317 SeenThread* prev = NULL;
318 while (seen) {
319 if (thread == seen->thread()) {
320 if (prev) {
321 prev->set_next(seen->next());
322 } else {
323 set_threadQ(seen->next(), action);
324 }
325 if (seen->next()) {
326 seen->next()->set_prev(prev);
327 }
328 delete seen;
329 break;
330 }
331 prev = seen;
332 seen = seen->next();
333 }
334 return (actionToQueue(action) == NULL);
335 }
336
337 // Print method doesn't append a cr
338 void print_entry(outputStream* st) const;
339 void verify() const;
340 };
341
342 #endif // SHARE_CLASSFILE_PLACEHOLDERS_HPP