1 /*
2 * Copyright (c) 1997, 2015, 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.
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23 */
24
25 #ifndef SHARE_VM_RUNTIME_HANDLES_HPP
26 #define SHARE_VM_RUNTIME_HANDLES_HPP
27
28 #include "oops/oop.hpp"
29 #include "oops/oopsHierarchy.hpp"
30
31 class InstanceKlass;
32 class Klass;
33
34 //------------------------------------------------------------------------------------------------------------------------
35 // In order to preserve oops during garbage collection, they should be
36 // allocated and passed around via Handles within the VM. A handle is
37 // simply an extra indirection allocated in a thread local handle area.
38 //
39 // A handle is a ValueObj, so it can be passed around as a value, can
40 // be used as a parameter w/o using &-passing, and can be returned as a
41 // return value.
42 //
43 // oop parameters and return types should be Handles whenever feasible.
44 //
45 // Handles are declared in a straight-forward manner, e.g.
46 //
47 // oop obj = ...;
48 // Handle h1(obj); // allocate new handle
49 // Handle h2(thread, obj); // faster allocation when current thread is known
50 // Handle h3; // declare handle only, no allocation occurs
51 // ...
52 // h3 = h1; // make h3 refer to same indirection as h1
53 // oop obj2 = h2(); // get handle value
54 // h1->print(); // invoking operation on oop
55 //
56 // Handles are specialized for different oop types to provide extra type
57 // information and avoid unnecessary casting. For each oop type xxxOop
58 // there is a corresponding handle called xxxHandle, e.g.
59 //
60 // oop Handle
61 // Method* methodHandle
62 // instanceOop instanceHandle
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 Handle(Thread* thread, oop obj);
81
82 // General access
83 oop operator () () const { return obj(); }
84 oop operator -> () const { return non_null_obj(); }
85 bool operator == (oop o) const { return obj() == o; }
86 bool operator == (const Handle& h) const { return obj() == h.obj(); }
87
88 // Null checks
89 bool is_null() const { return _handle == NULL; }
90 bool not_null() const { return _handle != NULL; }
91
92 // Debugging
93 void print() { obj()->print(); }
94
95 // Direct interface, use very sparingly.
96 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
97 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
98 Handle(oop *handle, bool dummy) { _handle = handle; }
99
100 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
101 // since duplicates is only valid as long as original handle is alive.
102 oop* raw_value() { return _handle; }
103 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
104 };
105
106 // Specific Handles for different oop types
107 #define DEF_HANDLE(type, is_a) \
108 class type##Handle: public Handle { \
109 protected: \
110 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
111 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
112 \
113 public: \
114 /* Constructors */ \
115 type##Handle () : Handle() {} \
116 type##Handle (type##Oop obj) : Handle((oop)obj) { \
117 assert(is_null() || ((oop)obj)->is_a(), \
118 "illegal type"); \
119 } \
120 type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \
121 assert(is_null() || ((oop)obj)->is_a(), "illegal type"); \
122 } \
123 \
124 /* Operators for ease of use */ \
125 type##Oop operator () () const { return obj(); } \
126 type##Oop operator -> () const { return non_null_obj(); } \
127 };
128
129
130 DEF_HANDLE(instance , is_instance_noinline )
131 DEF_HANDLE(array , is_array_noinline )
132 DEF_HANDLE(objArray , is_objArray_noinline )
133 DEF_HANDLE(typeArray , is_typeArray_noinline )
134
135 //------------------------------------------------------------------------------------------------------------------------
136
137 // Metadata Handles. Unlike oop Handles these are needed to prevent metadata
138 // from being reclaimed by RedefineClasses.
139
140 // Specific Handles for different oop types
141 #define DEF_METADATA_HANDLE(name, type) \
142 class name##Handle; \
143 class name##Handle : public StackObj { \
144 type* _value; \
145 Thread* _thread; \
146 protected: \
147 type* obj() const { return _value; } \
148 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \
149 \
150 public: \
151 /* Constructors */ \
152 name##Handle () : _value(NULL), _thread(NULL) {} \
153 name##Handle (type* obj); \
154 name##Handle (Thread* thread, type* obj); \
155 \
156 name##Handle (const name##Handle &h); \
157 name##Handle& operator=(const name##Handle &s); \
158 \
159 /* Destructor */ \
160 ~name##Handle (); \
161 void remove(); \
162 \
163 /* Operators for ease of use */ \
164 type* operator () () const { return obj(); } \
165 type* operator -> () const { return non_null_obj(); } \
166 \
167 bool operator == (type* o) const { return obj() == o; } \
168 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \
169 \
170 /* Null checks */ \
171 bool is_null() const { return _value == NULL; } \
172 bool not_null() const { return _value != NULL; } \
173 };
174
175
176 DEF_METADATA_HANDLE(method, Method)
177 DEF_METADATA_HANDLE(constantPool, ConstantPool)
178
179 // Writing this class explicitly, since DEF_METADATA_HANDLE(klass) doesn't
180 // provide the necessary Klass* <-> Klass* conversions. This Klass
181 // could be removed when we don't have the Klass* typedef anymore.
182 class KlassHandle : public StackObj {
183 Klass* _value;
184 protected:
185 Klass* obj() const { return _value; }
186 Klass* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; }
187
188 public:
189 KlassHandle() : _value(NULL) {}
190 KlassHandle(const Klass* obj) : _value(const_cast<Klass *>(obj)) {};
191 KlassHandle(Thread* thread, const Klass* obj) : _value(const_cast<Klass *>(obj)) {};
192
193 Klass* operator () () const { return obj(); }
194 Klass* operator -> () const { return non_null_obj(); }
195
196 bool operator == (Klass* o) const { return obj() == o; }
197 bool operator == (const KlassHandle& h) const { return obj() == h.obj(); }
198
199 bool is_null() const { return _value == NULL; }
200 bool not_null() const { return _value != NULL; }
201 };
202
203 class instanceKlassHandle : public KlassHandle {
204 public:
205 /* Constructors */
206 instanceKlassHandle () : KlassHandle() {}
207 instanceKlassHandle (const Klass* k) : KlassHandle(k) {
208 assert(k == NULL || is_instanceKlass(k), "illegal type");
209 }
210 instanceKlassHandle (Thread* thread, const Klass* k) : KlassHandle(thread, k) {
211 assert(k == NULL || is_instanceKlass(k), "illegal type");
212 }
213 /* Access to klass part */
214 InstanceKlass* operator () () const { return (InstanceKlass*)obj(); }
215 InstanceKlass* operator -> () const { return (InstanceKlass*)obj(); }
216
217 debug_only(bool is_instanceKlass(const Klass* k));
218 };
219
220
221 //------------------------------------------------------------------------------------------------------------------------
222 // Thread local handle area
223 class HandleArea: public Arena {
224 friend class HandleMark;
225 friend class NoHandleMark;
226 friend class ResetNoHandleMark;
227 #ifdef ASSERT
228 int _handle_mark_nesting;
229 int _no_handle_mark_nesting;
230 #endif
231 HandleArea* _prev; // link to outer (older) area
232 public:
233 // Constructor
234 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
235 debug_only(_handle_mark_nesting = 0);
236 debug_only(_no_handle_mark_nesting = 0);
237 _prev = prev;
238 }
239
240 // Handle allocation
241 private:
242 oop* real_allocate_handle(oop obj) {
243 #ifdef ASSERT
244 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
245 #else
246 oop* handle = (oop*) Amalloc_4(oopSize);
247 #endif
248 *handle = obj;
249 return handle;
250 }
251 public:
252 #ifdef ASSERT
253 oop* allocate_handle(oop obj);
254 #else
255 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
256 #endif
257
258 // Garbage collection support
259 void oops_do(OopClosure* f);
260
261 // Number of handles in use
262 size_t used() const { return Arena::used() / oopSize; }
263
264 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
265 };
266
267
268 //------------------------------------------------------------------------------------------------------------------------
269 // Handles are allocated in a (growable) thread local handle area. Deallocation
270 // is managed using a HandleMark. It should normally not be necessary to use
271 // HandleMarks manually.
272 //
273 // A HandleMark constructor will record the current handle area top, and the
274 // destructor will reset the top, destroying all handles allocated in between.
275 // The following code will therefore NOT work:
276 //
277 // Handle h;
278 // {
279 // HandleMark hm;
280 // h = Handle(obj);
281 // }
282 // h()->print(); // WRONG, h destroyed by HandleMark destructor.
283 //
284 // If h has to be preserved, it can be converted to an oop or a local JNI handle
285 // across the HandleMark boundary.
286
287 // The base class of HandleMark should have been StackObj but we also heap allocate
288 // a HandleMark when a thread is created. The operator new is for this special case.
289
290 class HandleMark {
291 private:
292 Thread *_thread; // thread that owns this mark
293 HandleArea *_area; // saved handle area
294 Chunk *_chunk; // saved arena chunk
295 char *_hwm, *_max; // saved arena info
296 size_t _size_in_bytes; // size of handle area
297 // Link to previous active HandleMark in thread
298 HandleMark* _previous_handle_mark;
299
300 void initialize(Thread* thread); // common code for constructors
301 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
302 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
303
304 size_t size_in_bytes() const { return _size_in_bytes; }
305 public:
306 HandleMark(); // see handles_inline.hpp
307 HandleMark(Thread* thread) { initialize(thread); }
308 ~HandleMark();
309
310 // Functions used by HandleMarkCleaner
311 // called in the constructor of HandleMarkCleaner
312 void push();
313 // called in the destructor of HandleMarkCleaner
314 void pop_and_restore();
315 // overloaded operators
316 void* operator new(size_t size) throw();
317 void* operator new [](size_t size) throw();
318 void operator delete(void* p);
319 void operator delete[](void* p);
320 };
321
322 //------------------------------------------------------------------------------------------------------------------------
323 // A NoHandleMark stack object will verify that no handles are allocated
324 // in its scope. Enabled in debug mode only.
325
326 class NoHandleMark: public StackObj {
327 public:
328 #ifdef ASSERT
329 NoHandleMark();
330 ~NoHandleMark();
331 #else
332 NoHandleMark() {}
333 ~NoHandleMark() {}
334 #endif
335 };
336
337
338 class ResetNoHandleMark: public StackObj {
339 int _no_handle_mark_nesting;
340 public:
341 #ifdef ASSERT
342 ResetNoHandleMark();
343 ~ResetNoHandleMark();
344 #else
345 ResetNoHandleMark() {}
346 ~ResetNoHandleMark() {}
347 #endif
348 };
349
350 #endif // SHARE_VM_RUNTIME_HANDLES_HPP