1 /*
2 * Copyright (c) 1997, 2009, 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 //------------------------------------------------------------------------------------------------------------------------
26 // In order to preserve oops during garbage collection, they should be
27 // allocated and passed around via Handles within the VM. A handle is
28 // simply an extra indirection allocated in a thread local handle area.
29 //
30 // A handle is a ValueObj, so it can be passed around as a value, can
31 // be used as a parameter w/o using &-passing, and can be returned as a
32 // return value.
33 //
34 // oop parameters and return types should be Handles whenever feasible.
35 //
36 // Handles are declared in a straight-forward manner, e.g.
37 //
38 // oop obj = ...;
39 // Handle h1(obj); // allocate new handle
40 // Handle h2(thread, obj); // faster allocation when current thread is known
41 // Handle h3; // declare handle only, no allocation occurs
42 // ...
43 // h3 = h1; // make h3 refer to same indirection as h1
44 // oop obj2 = h2(); // get handle value
45 // h1->print(); // invoking operation on oop
46 //
47 // Handles are specialized for different oop types to provide extra type
48 // information and avoid unnecessary casting. For each oop type xxxOop
49 // there is a corresponding handle called xxxHandle, e.g.
50 //
51 // oop Handle
52 // methodOop methodHandle
53 // instanceOop instanceHandle
54 //
55 // For klassOops, it is often useful to model the Klass hierarchy in order
56 // to get access to the klass_part without casting. For each xxxKlass there
57 // is a corresponding handle called xxxKlassHandle, e.g.
58 //
59 // klassOop Klass KlassHandle
60 // klassOop methodKlass methodKlassHandle
61 // klassOop instanceKlass instanceKlassHandle
62 //
63
64 //------------------------------------------------------------------------------------------------------------------------
65 // Base class for all handles. Provides overloading of frequently
66 // used operators for ease of use.
67
68 class Handle VALUE_OBJ_CLASS_SPEC {
69 private:
70 oop* _handle;
71
72 protected:
73 oop obj() const { return _handle == NULL ? (oop)NULL : *_handle; }
74 oop non_null_obj() const { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
75
76 public:
77 // Constructors
78 Handle() { _handle = NULL; }
79 Handle(oop obj);
80 #ifndef ASSERT
81 Handle(Thread* thread, oop obj);
82 #else
83 // Don't inline body with assert for current thread
84 Handle(Thread* thread, oop obj);
85 #endif // ASSERT
86
87 // General access
88 oop operator () () const { return obj(); }
89 oop operator -> () const { return non_null_obj(); }
90 bool operator == (oop o) const { return obj() == o; }
91 bool operator == (const Handle& h) const { return obj() == h.obj(); }
92
93 // Null checks
94 bool is_null() const { return _handle == NULL; }
95 bool not_null() const { return _handle != NULL; }
96
97 // Debugging
98 void print() { obj()->print(); }
99
100 // Direct interface, use very sparingly.
101 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
102 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
103 Handle(oop *handle, bool dummy) { _handle = handle; }
104
105 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
106 // since duplicates is only valid as long as original handle is alive.
107 oop* raw_value() { return _handle; }
108 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
109 };
110
111
112 //------------------------------------------------------------------------------------------------------------------------
113 // Base class for Handles containing klassOops. Provides overloading of frequently
114 // used operators for ease of use and typed access to the Klass part.
115 class KlassHandle: public Handle {
116 protected:
117 klassOop obj() const { return (klassOop)Handle::obj(); }
118 klassOop non_null_obj() const { return (klassOop)Handle::non_null_obj(); }
119 Klass* as_klass() const { return non_null_obj()->klass_part(); }
120
121 public:
122 // Constructors
123 KlassHandle () : Handle() {}
124 KlassHandle (oop obj) : Handle(obj) {
125 assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
126 }
127 KlassHandle (Klass* kl) : Handle(kl ? kl->as_klassOop() : (klassOop)NULL) {
128 assert(SharedSkipVerify || is_null() || obj()->is_klass(), "not a klassOop");
129 }
130
131 // Faster versions passing Thread
132 KlassHandle (Thread* thread, oop obj) : Handle(thread, obj) {
133 assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
134 }
135 KlassHandle (Thread *thread, Klass* kl)
136 : Handle(thread, kl ? kl->as_klassOop() : (klassOop)NULL) {
137 assert(is_null() || obj()->is_klass(), "not a klassOop");
138 }
139
140 // Direct interface, use very sparingly.
141 // Used by SystemDictionaryHandles to create handles on existing WKKs.
142 // The obj of such a klass handle may be null, because the handle is formed
143 // during system bootstrapping.
144 KlassHandle(klassOop *handle, bool dummy) : Handle((oop*)handle, dummy) {
145 assert(SharedSkipVerify || is_null() || obj() == NULL || obj()->is_klass(), "not a klassOop");
146 }
147
148 // General access
149 klassOop operator () () const { return obj(); }
150 Klass* operator -> () const { return as_klass(); }
151 };
152
153
154 //------------------------------------------------------------------------------------------------------------------------
155 // Specific Handles for different oop types
156 #define DEF_HANDLE(type, is_a) \
157 class type##Handle; \
158 class type##Handle: public Handle { \
159 protected: \
160 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
161 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
162 \
163 public: \
164 /* Constructors */ \
165 type##Handle () : Handle() {} \
166 type##Handle (type##Oop obj) : Handle((oop)obj) { \
167 assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(), \
168 "illegal type"); \
169 } \
170 type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \
171 assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(), "illegal type"); \
172 } \
173 \
174 /* Special constructor, use sparingly */ \
175 type##Handle (type##Oop *handle, bool dummy) : Handle((oop*)handle, dummy) {} \
176 \
177 /* Operators for ease of use */ \
178 type##Oop operator () () const { return obj(); } \
179 type##Oop operator -> () const { return non_null_obj(); } \
180 };
181
182
183 DEF_HANDLE(instance , is_instance )
184 DEF_HANDLE(method , is_method )
185 DEF_HANDLE(constMethod , is_constMethod )
186 DEF_HANDLE(methodData , is_methodData )
187 DEF_HANDLE(array , is_array )
188 DEF_HANDLE(constantPool , is_constantPool )
189 DEF_HANDLE(constantPoolCache, is_constantPoolCache)
190 DEF_HANDLE(objArray , is_objArray )
191 DEF_HANDLE(typeArray , is_typeArray )
192 DEF_HANDLE(symbol , is_symbol )
193
194 //------------------------------------------------------------------------------------------------------------------------
195 // Specific KlassHandles for different Klass types
196
197 #define DEF_KLASS_HANDLE(type, is_a) \
198 class type##Handle : public KlassHandle { \
199 public: \
200 /* Constructors */ \
201 type##Handle () : KlassHandle() {} \
202 type##Handle (klassOop obj) : KlassHandle(obj) { \
203 assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(), \
204 "illegal type"); \
205 } \
206 type##Handle (Thread* thread, klassOop obj) : KlassHandle(thread, obj) { \
207 assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(), \
208 "illegal type"); \
209 } \
210 \
211 /* Access to klass part */ \
212 type* operator -> () const { return (type*)obj()->klass_part(); } \
213 \
214 static type##Handle cast(KlassHandle h) { return type##Handle(h()); } \
215 \
216 };
217
218
219 DEF_KLASS_HANDLE(instanceKlass , oop_is_instance_slow )
220 DEF_KLASS_HANDLE(methodKlass , oop_is_method )
221 DEF_KLASS_HANDLE(constMethodKlass , oop_is_constMethod )
222 DEF_KLASS_HANDLE(klassKlass , oop_is_klass )
223 DEF_KLASS_HANDLE(arrayKlassKlass , oop_is_arrayKlass )
224 DEF_KLASS_HANDLE(objArrayKlassKlass , oop_is_objArrayKlass )
225 DEF_KLASS_HANDLE(typeArrayKlassKlass , oop_is_typeArrayKlass)
226 DEF_KLASS_HANDLE(arrayKlass , oop_is_array )
227 DEF_KLASS_HANDLE(typeArrayKlass , oop_is_typeArray_slow)
228 DEF_KLASS_HANDLE(objArrayKlass , oop_is_objArray_slow )
229 DEF_KLASS_HANDLE(symbolKlass , oop_is_symbol )
230 DEF_KLASS_HANDLE(constantPoolKlass , oop_is_constantPool )
231 DEF_KLASS_HANDLE(constantPoolCacheKlass, oop_is_constantPool )
232
233
234 //------------------------------------------------------------------------------------------------------------------------
235 // Thread local handle area
236
237 class HandleArea: public Arena {
238 friend class HandleMark;
239 friend class NoHandleMark;
240 friend class ResetNoHandleMark;
241 #ifdef ASSERT
242 int _handle_mark_nesting;
243 int _no_handle_mark_nesting;
244 #endif
245 HandleArea* _prev; // link to outer (older) area
246 public:
247 // Constructor
248 HandleArea(HandleArea* prev) {
249 debug_only(_handle_mark_nesting = 0);
250 debug_only(_no_handle_mark_nesting = 0);
251 _prev = prev;
252 }
253
254 // Handle allocation
255 private:
256 oop* real_allocate_handle(oop obj) {
257 #ifdef ASSERT
258 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
259 #else
260 oop* handle = (oop*) Amalloc_4(oopSize);
261 #endif
262 *handle = obj;
263 return handle;
264 }
265 public:
266 #ifdef ASSERT
267 oop* allocate_handle(oop obj);
268 #else
269 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
270 #endif
271
272 // Garbage collection support
273 void oops_do(OopClosure* f);
274
275 // Number of handles in use
276 size_t used() const { return Arena::used() / oopSize; }
277
278 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
279 };
280
281
282 //------------------------------------------------------------------------------------------------------------------------
283 // Handles are allocated in a (growable) thread local handle area. Deallocation
284 // is managed using a HandleMark. It should normally not be necessary to use
285 // HandleMarks manually.
286 //
287 // A HandleMark constructor will record the current handle area top, and the
288 // desctructor will reset the top, destroying all handles allocated in between.
289 // The following code will therefore NOT work:
290 //
291 // Handle h;
292 // {
293 // HandleMark hm;
294 // h = Handle(obj);
295 // }
296 // h()->print(); // WRONG, h destroyed by HandleMark destructor.
297 //
298 // If h has to be preserved, it can be converted to an oop or a local JNI handle
299 // across the HandleMark boundary.
300
301 // The base class of HandleMark should have been StackObj but we also heap allocate
302 // a HandleMark when a thread is created.
303
304 class HandleMark {
305 private:
306 Thread *_thread; // thread that owns this mark
307 HandleArea *_area; // saved handle area
308 Chunk *_chunk; // saved arena chunk
309 char *_hwm, *_max; // saved arena info
310 NOT_PRODUCT(size_t _size_in_bytes;) // size of handle area
311 // Link to previous active HandleMark in thread
312 HandleMark* _previous_handle_mark;
313
314 void initialize(Thread* thread); // common code for constructors
315 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
316 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
317
318 public:
319 HandleMark(); // see handles_inline.hpp
320 HandleMark(Thread* thread) { initialize(thread); }
321 ~HandleMark();
322
323 // Functions used by HandleMarkCleaner
324 // called in the constructor of HandleMarkCleaner
325 void push();
326 // called in the destructor of HandleMarkCleaner
327 void pop_and_restore();
328 };
329
330 //------------------------------------------------------------------------------------------------------------------------
331 // A NoHandleMark stack object will verify that no handles are allocated
332 // in its scope. Enabled in debug mode only.
333
334 class NoHandleMark: public StackObj {
335 public:
336 #ifdef ASSERT
337 NoHandleMark();
338 ~NoHandleMark();
339 #else
340 NoHandleMark() {}
341 ~NoHandleMark() {}
342 #endif
343 };
344
345
346 class ResetNoHandleMark: public StackObj {
347 int _no_handle_mark_nesting;
348 public:
349 #ifdef ASSERT
350 ResetNoHandleMark();
351 ~ResetNoHandleMark();
352 #else
353 ResetNoHandleMark() {}
354 ~ResetNoHandleMark() {}
355 #endif
356 };