1 /*
2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 *
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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,
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23 */
24
25 #ifndef SHARE_VM_RUNTIME_HANDLES_HPP
26 #define SHARE_VM_RUNTIME_HANDLES_HPP
27
28 #include "oops/klass.hpp"
29 #include "oops/klassOop.hpp"
30 #include "utilities/top.hpp"
31
32 //------------------------------------------------------------------------------------------------------------------------
33 // In order to preserve oops during garbage collection, they should be
34 // allocated and passed around via Handles within the VM. A handle is
35 // simply an extra indirection allocated in a thread local handle area.
36 //
37 // A handle is a ValueObj, so it can be passed around as a value, can
38 // be used as a parameter w/o using &-passing, and can be returned as a
39 // return value.
40 //
41 // oop parameters and return types should be Handles whenever feasible.
42 //
43 // Handles are declared in a straight-forward manner, e.g.
44 //
45 // oop obj = ...;
46 // Handle h1(obj); // allocate new handle
47 // Handle h2(thread, obj); // faster allocation when current thread is known
48 // Handle h3; // declare handle only, no allocation occurs
49 // ...
50 // h3 = h1; // make h3 refer to same indirection as h1
51 // oop obj2 = h2(); // get handle value
52 // h1->print(); // invoking operation on oop
53 //
54 // Handles are specialized for different oop types to provide extra type
55 // information and avoid unnecessary casting. For each oop type xxxOop
56 // there is a corresponding handle called xxxHandle, e.g.
57 //
58 // oop Handle
59 // methodOop methodHandle
60 // instanceOop instanceHandle
61 //
62 // For klassOops, it is often useful to model the Klass hierarchy in order
63 // to get access to the klass_part without casting. For each xxxKlass there
64 // is a corresponding handle called xxxKlassHandle, e.g.
65 //
66 // klassOop Klass KlassHandle
67 // klassOop methodKlass methodKlassHandle
68 // klassOop instanceKlass instanceKlassHandle
69 //
70
71 //------------------------------------------------------------------------------------------------------------------------
72 // Base class for all handles. Provides overloading of frequently
73 // used operators for ease of use.
74
75 class Handle VALUE_OBJ_CLASS_SPEC {
76 private:
77 oop* _handle;
78
79 protected:
80 oop obj() const { return _handle == NULL ? (oop)NULL : *_handle; }
81 oop non_null_obj() const { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
82
83 public:
84 // Constructors
85 Handle() { _handle = NULL; }
86 Handle(oop obj);
87 #ifndef ASSERT
88 Handle(Thread* thread, oop obj);
89 #else
90 // Don't inline body with assert for current thread
91 Handle(Thread* thread, oop obj);
92 #endif // ASSERT
93
94 // General access
95 oop operator () () const { return obj(); }
96 oop operator -> () const { return non_null_obj(); }
97 bool operator == (oop o) const { return obj() == o; }
98 bool operator == (const Handle& h) const { return obj() == h.obj(); }
99
100 // Null checks
101 bool is_null() const { return _handle == NULL; }
102 bool not_null() const { return _handle != NULL; }
103
104 // Debugging
105 void print() { obj()->print(); }
106
107 // Direct interface, use very sparingly.
108 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
109 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
110 Handle(oop *handle, bool dummy) { _handle = handle; }
111
112 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
113 // since duplicates is only valid as long as original handle is alive.
114 oop* raw_value() { return _handle; }
115 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; }
116 };
117
118
119 //------------------------------------------------------------------------------------------------------------------------
120 // Base class for Handles containing klassOops. Provides overloading of frequently
121 // used operators for ease of use and typed access to the Klass part.
122 class KlassHandle: public Handle {
123 protected:
124 klassOop obj() const { return (klassOop)Handle::obj(); }
125 klassOop non_null_obj() const { return (klassOop)Handle::non_null_obj(); }
126 Klass* as_klass() const { return non_null_obj()->klass_part(); }
127
128 public:
129 // Constructors
130 KlassHandle () : Handle() {}
131 KlassHandle (oop obj) : Handle(obj) {
132 assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
133 }
134 KlassHandle (Klass* kl) : Handle(kl ? kl->as_klassOop() : (klassOop)NULL) {
135 assert(SharedSkipVerify || is_null() || obj()->is_klass(), "not a klassOop");
136 }
137
138 // Faster versions passing Thread
139 KlassHandle (Thread* thread, oop obj) : Handle(thread, obj) {
140 assert(SharedSkipVerify || is_null() || obj->is_klass(), "not a klassOop");
141 }
142 KlassHandle (Thread *thread, Klass* kl)
143 : Handle(thread, kl ? kl->as_klassOop() : (klassOop)NULL) {
144 assert(is_null() || obj()->is_klass(), "not a klassOop");
145 }
146
147 // Direct interface, use very sparingly.
148 // Used by SystemDictionaryHandles to create handles on existing WKKs.
149 // The obj of such a klass handle may be null, because the handle is formed
150 // during system bootstrapping.
151 KlassHandle(klassOop *handle, bool dummy) : Handle((oop*)handle, dummy) {
152 assert(SharedSkipVerify || is_null() || obj() == NULL || obj()->is_klass(), "not a klassOop");
153 }
154
155 // General access
156 klassOop operator () () const { return obj(); }
157 Klass* operator -> () const { return as_klass(); }
158 };
159
160
161 //------------------------------------------------------------------------------------------------------------------------
162 // Specific Handles for different oop types
163 #define DEF_HANDLE(type, is_a) \
164 class type##Handle; \
165 class type##Handle: public Handle { \
166 protected: \
167 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
168 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
169 \
170 public: \
171 /* Constructors */ \
172 type##Handle () : Handle() {} \
173 type##Handle (type##Oop obj) : Handle((oop)obj) { \
174 assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(), \
175 "illegal type"); \
176 } \
177 type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \
178 assert(SharedSkipVerify || is_null() || ((oop)obj)->is_a(), "illegal type"); \
179 } \
180 \
181 /* Special constructor, use sparingly */ \
182 type##Handle (type##Oop *handle, bool dummy) : Handle((oop*)handle, dummy) {} \
183 \
184 /* Operators for ease of use */ \
185 type##Oop operator () () const { return obj(); } \
186 type##Oop operator -> () const { return non_null_obj(); } \
187 };
188
189
190 DEF_HANDLE(instance , is_instance )
191 DEF_HANDLE(method , is_method )
192 DEF_HANDLE(constMethod , is_constMethod )
193 DEF_HANDLE(methodData , is_methodData )
194 DEF_HANDLE(array , is_array )
195 DEF_HANDLE(constantPool , is_constantPool )
196 DEF_HANDLE(constantPoolCache, is_constantPoolCache)
197 DEF_HANDLE(objArray , is_objArray )
198 DEF_HANDLE(typeArray , is_typeArray )
199 DEF_HANDLE(symbol , is_symbol )
200
201 //------------------------------------------------------------------------------------------------------------------------
202 // Specific KlassHandles for different Klass types
203
204 #define DEF_KLASS_HANDLE(type, is_a) \
205 class type##Handle : public KlassHandle { \
206 public: \
207 /* Constructors */ \
208 type##Handle () : KlassHandle() {} \
209 type##Handle (klassOop obj) : KlassHandle(obj) { \
210 assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(), \
211 "illegal type"); \
212 } \
213 type##Handle (Thread* thread, klassOop obj) : KlassHandle(thread, obj) { \
214 assert(SharedSkipVerify || is_null() || obj->klass_part()->is_a(), \
215 "illegal type"); \
216 } \
217 \
218 /* Access to klass part */ \
219 type* operator -> () const { return (type*)obj()->klass_part(); } \
220 \
221 static type##Handle cast(KlassHandle h) { return type##Handle(h()); } \
222 \
223 };
224
225
226 DEF_KLASS_HANDLE(instanceKlass , oop_is_instance_slow )
227 DEF_KLASS_HANDLE(methodKlass , oop_is_method )
228 DEF_KLASS_HANDLE(constMethodKlass , oop_is_constMethod )
229 DEF_KLASS_HANDLE(klassKlass , oop_is_klass )
230 DEF_KLASS_HANDLE(arrayKlassKlass , oop_is_arrayKlass )
231 DEF_KLASS_HANDLE(objArrayKlassKlass , oop_is_objArrayKlass )
232 DEF_KLASS_HANDLE(typeArrayKlassKlass , oop_is_typeArrayKlass)
233 DEF_KLASS_HANDLE(arrayKlass , oop_is_array )
234 DEF_KLASS_HANDLE(typeArrayKlass , oop_is_typeArray_slow)
235 DEF_KLASS_HANDLE(objArrayKlass , oop_is_objArray_slow )
236 DEF_KLASS_HANDLE(symbolKlass , oop_is_symbol )
237 DEF_KLASS_HANDLE(constantPoolKlass , oop_is_constantPool )
238 DEF_KLASS_HANDLE(constantPoolCacheKlass, oop_is_constantPool )
239
240
241 //------------------------------------------------------------------------------------------------------------------------
242 // Thread local handle area
243
244 class HandleArea: public Arena {
245 friend class HandleMark;
246 friend class NoHandleMark;
247 friend class ResetNoHandleMark;
248 #ifdef ASSERT
249 int _handle_mark_nesting;
250 int _no_handle_mark_nesting;
251 #endif
252 HandleArea* _prev; // link to outer (older) area
253 public:
254 // Constructor
255 HandleArea(HandleArea* prev) {
256 debug_only(_handle_mark_nesting = 0);
257 debug_only(_no_handle_mark_nesting = 0);
258 _prev = prev;
259 }
260
261 // Handle allocation
262 private:
263 oop* real_allocate_handle(oop obj) {
264 #ifdef ASSERT
265 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
266 #else
267 oop* handle = (oop*) Amalloc_4(oopSize);
268 #endif
269 *handle = obj;
270 return handle;
271 }
272 public:
273 #ifdef ASSERT
274 oop* allocate_handle(oop obj);
275 #else
276 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
277 #endif
278
279 // Garbage collection support
280 void oops_do(OopClosure* f);
281
282 // Number of handles in use
283 size_t used() const { return Arena::used() / oopSize; }
284
285 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
286 };
287
288
289 //------------------------------------------------------------------------------------------------------------------------
290 // Handles are allocated in a (growable) thread local handle area. Deallocation
291 // is managed using a HandleMark. It should normally not be necessary to use
292 // HandleMarks manually.
293 //
294 // A HandleMark constructor will record the current handle area top, and the
295 // desctructor will reset the top, destroying all handles allocated in between.
296 // The following code will therefore NOT work:
297 //
298 // Handle h;
299 // {
300 // HandleMark hm;
301 // h = Handle(obj);
302 // }
303 // h()->print(); // WRONG, h destroyed by HandleMark destructor.
304 //
305 // If h has to be preserved, it can be converted to an oop or a local JNI handle
306 // across the HandleMark boundary.
307
308 // The base class of HandleMark should have been StackObj but we also heap allocate
309 // a HandleMark when a thread is created.
310
311 class HandleMark {
312 private:
313 Thread *_thread; // thread that owns this mark
314 HandleArea *_area; // saved handle area
315 Chunk *_chunk; // saved arena chunk
316 char *_hwm, *_max; // saved arena info
317 NOT_PRODUCT(size_t _size_in_bytes;) // size of handle area
318 // Link to previous active HandleMark in thread
319 HandleMark* _previous_handle_mark;
320
321 void initialize(Thread* thread); // common code for constructors
322 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
323 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
324
325 public:
326 HandleMark(); // see handles_inline.hpp
327 HandleMark(Thread* thread) { initialize(thread); }
328 ~HandleMark();
329
330 // Functions used by HandleMarkCleaner
331 // called in the constructor of HandleMarkCleaner
332 void push();
333 // called in the destructor of HandleMarkCleaner
334 void pop_and_restore();
335 };
336
337 //------------------------------------------------------------------------------------------------------------------------
338 // A NoHandleMark stack object will verify that no handles are allocated
339 // in its scope. Enabled in debug mode only.
340
341 class NoHandleMark: public StackObj {
342 public:
343 #ifdef ASSERT
344 NoHandleMark();
345 ~NoHandleMark();
346 #else
347 NoHandleMark() {}
348 ~NoHandleMark() {}
349 #endif
350 };
351
352
353 class ResetNoHandleMark: public StackObj {
354 int _no_handle_mark_nesting;
355 public:
356 #ifdef ASSERT
357 ResetNoHandleMark();
358 ~ResetNoHandleMark();
359 #else
360 ResetNoHandleMark() {}
361 ~ResetNoHandleMark() {}
362 #endif
363 };
364
365 #endif // SHARE_VM_RUNTIME_HANDLES_HPP