1 /*
2 * Copyright (c) 1997, 2018, 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 #ifndef SHARE_VM_RUNTIME_HANDLES_HPP
26 #define SHARE_VM_RUNTIME_HANDLES_HPP
27
28 #include "memory/arena.hpp"
29 #include "oops/oop.hpp"
30 #include "oops/oopsHierarchy.hpp"
31
32 class InstanceKlass;
33 class Klass;
34
35 //------------------------------------------------------------------------------------------------------------------------
36 // In order to preserve oops during garbage collection, they should be
37 // allocated and passed around via Handles within the VM. A handle is
38 // simply an extra indirection allocated in a thread local handle area.
39 //
40 // A handle is a value object, so it can be passed around as a value, can
41 // be used as a parameter w/o using &-passing, and can be returned as a
42 // return value.
43 //
44 // oop parameters and return types should be Handles whenever feasible.
45 //
46 // Handles are declared in a straight-forward manner, e.g.
47 //
48 // oop obj = ...;
49 // Handle h2(thread, obj); // allocate a new handle in thread
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.
59
60 //------------------------------------------------------------------------------------------------------------------------
61 // Base class for all handles. Provides overloading of frequently
62 // used operators for ease of use.
63
64 class Handle {
65 private:
66 oop* _handle;
67
68 protected:
69 oop obj() const { return _handle == NULL ? (oop)NULL : *_handle; }
70 oop non_null_obj() const { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
71
72 public:
73 // Constructors
74 Handle() { _handle = NULL; }
75 inline Handle(Thread* thread, oop obj);
76
77 // General access
78 oop operator () () const { return obj(); }
79 oop operator -> () const { return non_null_obj(); }
80 bool operator == (oop o) const { return obj() == o; }
81 bool operator == (const Handle& h) const { return obj() == h.obj(); }
82
83 // Null checks
84 bool is_null() const { return _handle == NULL; }
85 bool not_null() const { return _handle != NULL; }
86
87 // Debugging
88 void print() { obj()->print(); }
89
90 // Direct interface, use very sparingly.
91 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
92 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
93 Handle(oop *handle, bool dummy) { _handle = handle; }
94
95 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
96 // since duplicates is only valid as long as original handle is alive.
97 oop* raw_value() { return _handle; }
98 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
99 };
100
101 // Specific Handles for different oop types
102 #define DEF_HANDLE(type, is_a) \
103 class type##Handle: public Handle { \
104 protected: \
105 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
106 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
107 \
108 public: \
109 /* Constructors */ \
110 type##Handle () : Handle() {} \
111 inline type##Handle (Thread* thread, type##Oop obj); \
112 \
113 /* Operators for ease of use */ \
114 type##Oop operator () () const { return obj(); } \
115 type##Oop operator -> () const { return non_null_obj(); } \
116 };
117
118
119 DEF_HANDLE(instance , is_instance_noinline )
120 DEF_HANDLE(array , is_array_noinline )
121 DEF_HANDLE(objArray , is_objArray_noinline )
122 DEF_HANDLE(typeArray , is_typeArray_noinline )
123
124 //------------------------------------------------------------------------------------------------------------------------
125
126 // Metadata Handles. Unlike oop Handles these are needed to prevent metadata
127 // from being reclaimed by RedefineClasses.
128 // Metadata Handles should be passed around as const references to avoid copy construction
129 // and destruction for parameters.
130
131 // Specific Handles for different oop types
132 #define DEF_METADATA_HANDLE(name, type) \
133 class name##Handle; \
134 class name##Handle : public StackObj { \
135 type* _value; \
136 Thread* _thread; \
137 protected: \
138 type* obj() const { return _value; } \
139 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \
140 \
141 public: \
142 /* Constructors */ \
143 name##Handle () : _value(NULL), _thread(NULL) {} \
144 name##Handle (type* obj); \
145 name##Handle (Thread* thread, type* obj); \
146 \
147 name##Handle (const name##Handle &h); \
148 name##Handle& operator=(const name##Handle &s); \
149 \
150 /* Destructor */ \
151 ~name##Handle (); \
152 void remove(); \
153 \
154 /* Operators for ease of use */ \
155 type* operator () () const { return obj(); } \
156 type* operator -> () const { return non_null_obj(); } \
157 \
158 bool operator == (type* o) const { return obj() == o; } \
159 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \
160 \
161 /* Null checks */ \
162 bool is_null() const { return _value == NULL; } \
163 bool not_null() const { return _value != NULL; } \
164 };
165
166
167 DEF_METADATA_HANDLE(method, Method)
168 DEF_METADATA_HANDLE(constantPool, ConstantPool)
169
170 //------------------------------------------------------------------------------------------------------------------------
171 // Thread local handle area
172 class HandleArea: public Arena {
173 friend class HandleMark;
174 friend class NoHandleMark;
175 friend class ResetNoHandleMark;
176 #ifdef ASSERT
177 int _handle_mark_nesting;
178 int _no_handle_mark_nesting;
179 #endif
180 HandleArea* _prev; // link to outer (older) area
181 public:
182 // Constructor
183 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
184 debug_only(_handle_mark_nesting = 0);
185 debug_only(_no_handle_mark_nesting = 0);
186 _prev = prev;
187 }
188
189 // Handle allocation
190 private:
191 oop* real_allocate_handle(oop obj) {
192 #ifdef ASSERT
193 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
194 #else
195 oop* handle = (oop*) Amalloc_4(oopSize);
196 #endif
197 *handle = obj;
198 return handle;
199 }
200 public:
201 #ifdef ASSERT
202 oop* allocate_handle(oop obj);
203 #else
204 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
205 #endif
206
207 // Garbage collection support
208 void oops_do(OopClosure* f);
209
210 // Number of handles in use
211 size_t used() const { return Arena::used() / oopSize; }
212
213 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
214 };
215
216
217 //------------------------------------------------------------------------------------------------------------------------
218 // Handles are allocated in a (growable) thread local handle area. Deallocation
219 // is managed using a HandleMark. It should normally not be necessary to use
220 // HandleMarks manually.
221 //
222 // A HandleMark constructor will record the current handle area top, and the
223 // destructor will reset the top, destroying all handles allocated in between.
224 // The following code will therefore NOT work:
225 //
226 // Handle h;
227 // {
228 // HandleMark hm;
229 // h = Handle(THREAD, obj);
230 // }
231 // h()->print(); // WRONG, h destroyed by HandleMark destructor.
232 //
233 // If h has to be preserved, it can be converted to an oop or a local JNI handle
234 // across the HandleMark boundary.
235
236 // The base class of HandleMark should have been StackObj but we also heap allocate
237 // a HandleMark when a thread is created. The operator new is for this special case.
238
239 class HandleMark {
240 private:
241 Thread *_thread; // thread that owns this mark
242 HandleArea *_area; // saved handle area
243 Chunk *_chunk; // saved arena chunk
244 char *_hwm, *_max; // saved arena info
245 size_t _size_in_bytes; // size of handle area
246 // Link to previous active HandleMark in thread
247 HandleMark* _previous_handle_mark;
248
249 void initialize(Thread* thread); // common code for constructors
250 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
251 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
252
253 size_t size_in_bytes() const { return _size_in_bytes; }
254 public:
255 HandleMark(); // see handles_inline.hpp
256 HandleMark(Thread* thread) { initialize(thread); }
257 ~HandleMark();
258
259 // Functions used by HandleMarkCleaner
260 // called in the constructor of HandleMarkCleaner
261 void push();
262 // called in the destructor of HandleMarkCleaner
263 void pop_and_restore();
264 // overloaded operators
265 void* operator new(size_t size) throw();
266 void* operator new [](size_t size) throw();
267 void operator delete(void* p);
268 void operator delete[](void* p);
269 };
270
271 //------------------------------------------------------------------------------------------------------------------------
272 // A NoHandleMark stack object will verify that no handles are allocated
273 // in its scope. Enabled in debug mode only.
274
275 class NoHandleMark: public StackObj {
276 public:
277 #ifdef ASSERT
278 NoHandleMark();
279 ~NoHandleMark();
280 #else
281 NoHandleMark() {}
282 ~NoHandleMark() {}
283 #endif
284 };
285
286
287 class ResetNoHandleMark: public StackObj {
288 int _no_handle_mark_nesting;
289 public:
290 #ifdef ASSERT
291 ResetNoHandleMark();
292 ~ResetNoHandleMark();
293 #else
294 ResetNoHandleMark() {}
295 ~ResetNoHandleMark() {}
296 #endif
297 };
298
299 // The HandleMarkCleaner is a faster version of HandleMark.
300 // It relies on the fact that there is a HandleMark further
301 // down the stack (in JavaCalls::call_helper), and just resets
302 // to the saved values in that HandleMark.
303
304 class HandleMarkCleaner: public StackObj {
305 private:
306 Thread* _thread;
307 public:
308 inline HandleMarkCleaner(Thread* thread);
309 inline ~HandleMarkCleaner();
310 };
311
312 #endif // SHARE_VM_RUNTIME_HANDLES_HPP