1 /*
2 * Copyright (c) 1997, 2023, 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
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7 * published by the Free Software Foundation.
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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).
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24
25 #ifndef SHARE_RUNTIME_HANDLES_HPP
26 #define SHARE_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 class Thread;
35
36 //------------------------------------------------------------------------------------------------------------------------
37 // In order to preserve oops during garbage collection, they should be
38 // allocated and passed around via Handles within the VM. A handle is
39 // simply an extra indirection allocated in a thread local handle area.
40 //
41 // A handle is a value object, so it can be passed around as a value, can
42 // be used as a parameter w/o using &-passing, and can be returned as a
43 // return value.
44 //
45 // oop parameters and return types should be Handles whenever feasible.
46 //
47 // Handles are declared in a straight-forward manner, e.g.
48 //
49 // oop obj = ...;
50 // Handle h2(thread, obj); // allocate a new handle in thread
51 // Handle h3; // declare handle only, no allocation occurs
52 // ...
53 // h3 = h1; // make h3 refer to same indirection as h1
54 // oop obj2 = h2(); // get handle value
55 // h1->print(); // invoking operation on oop
56 //
57 // Handles are specialized for different oop types to provide extra type
58 // information and avoid unnecessary casting. For each oop type xxxOop
59 // there is a corresponding handle called xxxHandle.
60
61 //------------------------------------------------------------------------------------------------------------------------
62 // Base class for all handles. Provides overloading of frequently
63 // used operators for ease of use.
64
65 class Handle {
66 private:
67 oop* _handle;
68
69 protected:
70 oop obj() const { return _handle == nullptr ? (oop)nullptr : *_handle; }
71 oop non_null_obj() const { assert(_handle != nullptr, "resolving null handle"); return *_handle; }
72
73 public:
74 // Constructors
75 Handle() { _handle = nullptr; }
76 inline Handle(Thread* thread, oop obj);
77
78 // General access
79 oop operator () () const { return obj(); }
80 oop operator -> () const { return non_null_obj(); }
81
82 bool operator == (oop o) const { return obj() == o; }
83 bool operator != (oop o) const { return obj() != o; }
84 bool operator == (const Handle& h) const { return obj() == h.obj(); }
85 bool operator != (const Handle& h) const { return obj() != h.obj(); }
86
87 // Null checks
88 bool is_null() const { return _handle == nullptr; }
89 bool not_null() const { return _handle != nullptr; }
90
91 // Debugging
92 void print() { obj()->print(); }
93
94 // Direct interface, use very sparingly.
95 // Used by JavaCalls to quickly convert handles and to create handles static data structures.
96 // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
97 Handle(oop *handle, bool dummy) { _handle = handle; }
98
99 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
100 // since duplicates is only valid as long as original handle is alive.
101 oop* raw_value() const { return _handle; }
102 static oop raw_resolve(oop *handle) { return handle == nullptr ? (oop)nullptr : *handle; }
103
104 inline void replace(oop obj);
105 };
106
107 // Specific Handles for different oop types
108 #define DEF_HANDLE(type, is_a) \
109 class type##Handle: public Handle { \
110 protected: \
111 type##Oop obj() const { return (type##Oop)Handle::obj(); } \
112 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \
113 \
114 public: \
115 /* Constructors */ \
116 type##Handle () : Handle() {} \
117 inline type##Handle (Thread* thread, type##Oop obj); \
118 type##Handle (oop *handle, bool dummy) : Handle(handle, dummy) {} \
119 \
120 /* Operators for ease of use */ \
121 type##Oop operator () () const { return obj(); } \
122 type##Oop operator -> () const { return non_null_obj(); } \
123 };
124
125
126 DEF_HANDLE(instance , is_instance_noinline )
127 DEF_HANDLE(stackChunk , is_stackChunk_noinline )
128 DEF_HANDLE(array , is_array_noinline )
129 DEF_HANDLE(objArray , is_objArray_noinline )
130 DEF_HANDLE(typeArray , is_typeArray_noinline )
131
132 //------------------------------------------------------------------------------------------------------------------------
133
134 // Metadata Handles. Unlike oop Handles these are needed to prevent metadata
135 // from being reclaimed by RedefineClasses.
136 // Metadata Handles should be passed around as const references to avoid copy construction
137 // and destruction for parameters.
138
139 // Specific Handles for different oop types
140 #define DEF_METADATA_HANDLE(name, type) \
141 class name##Handle; \
142 class name##Handle : public StackObj { \
143 type* _value; \
144 Thread* _thread; \
145 protected: \
146 type* obj() const { return _value; } \
147 type* non_null_obj() const { assert(_value != nullptr, "resolving null _value"); return _value; } \
148 \
149 public: \
150 /* Constructors */ \
151 name##Handle () : _value(nullptr), _thread(nullptr) {} \
152 name##Handle (Thread* thread, type* obj); \
153 \
154 name##Handle (const name##Handle &h); \
155 name##Handle& operator=(const name##Handle &s); \
156 \
157 /* Destructor */ \
158 ~name##Handle (); \
159 void remove(); \
160 \
161 /* Operators for ease of use */ \
162 type* operator () () const { return obj(); } \
163 type* operator -> () const { return non_null_obj(); } \
164 \
165 bool operator == (type* o) const { return obj() == o; } \
166 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \
167 \
168 /* Null checks */ \
169 bool is_null() const { return _value == nullptr; } \
170 bool not_null() const { return _value != nullptr; } \
171 };
172
173
174 DEF_METADATA_HANDLE(method, Method)
175 DEF_METADATA_HANDLE(constantPool, ConstantPool)
176
177 //------------------------------------------------------------------------------------------------------------------------
178 // Thread local handle area
179 class HandleArea: public Arena {
180 friend class HandleMark;
181 friend class NoHandleMark;
182 friend class ResetNoHandleMark;
183 #ifdef ASSERT
184 int _handle_mark_nesting;
185 int _no_handle_mark_nesting;
186 #endif
187 HandleArea* _prev; // link to outer (older) area
188 public:
189 // Constructor
190 HandleArea(HandleArea* prev) : Arena(mtThread, Tag::tag_ha, Chunk::tiny_size) {
191 debug_only(_handle_mark_nesting = 0);
192 debug_only(_no_handle_mark_nesting = 0);
193 _prev = prev;
194 }
195
196 // Handle allocation
197 private:
198 oop* real_allocate_handle(oop obj) {
199 oop* handle = (oop*)internal_amalloc(oopSize);
200 *handle = obj;
201 return handle;
202 }
203 public:
204 #ifdef ASSERT
205 oop* allocate_handle(oop obj);
206 oop* allocate_null_handle();
207 #else
208 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
209 oop* allocate_null_handle() { return allocate_handle(nullptr); }
210 #endif
211
212 // Garbage collection support
213 void oops_do(OopClosure* f);
214
215 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
216 };
217
218
219 //------------------------------------------------------------------------------------------------------------------------
220 // Handles are allocated in a (growable) thread local handle area. Deallocation
221 // is managed using a HandleMark. It should normally not be necessary to use
222 // HandleMarks manually.
223 //
224 // A HandleMark constructor will record the current handle area top, and the
225 // destructor will reset the top, destroying all handles allocated in between.
226 // The following code will therefore NOT work:
227 //
228 // Handle h;
229 // {
230 // HandleMark hm(THREAD);
231 // h = Handle(THREAD, obj);
232 // }
233 // h()->print(); // WRONG, h destroyed by HandleMark destructor.
234 //
235 // If h has to be preserved, it can be converted to an oop or a local JNI handle
236 // across the HandleMark boundary.
237
238 // The base class of HandleMark should have been StackObj but we also heap allocate
239 // a HandleMark when a thread is created. The operator new is for this special case.
240
241 class HandleMark {
242 private:
243 Thread *_thread; // thread that owns this mark
244 HandleArea *_area; // saved handle area
245 Chunk *_chunk; // saved arena chunk
246 char *_hwm, *_max; // saved arena info
247 size_t _size_in_bytes; // size of handle area
248 // Link to previous active HandleMark in thread
249 HandleMark* _previous_handle_mark;
250
251 void initialize(Thread* thread); // common code for constructors
252 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
253 HandleMark* previous_handle_mark() const { return _previous_handle_mark; }
254
255 size_t size_in_bytes() const { return _size_in_bytes; }
256 // remove all chunks beginning with the next
257 void chop_later_chunks();
258 public:
259 HandleMark(Thread* thread) { initialize(thread); }
260 ~HandleMark();
261
262 // Functions used by HandleMarkCleaner
263 // called in the constructor of HandleMarkCleaner
264 void push();
265 // called in the destructor of HandleMarkCleaner
266 void pop_and_restore();
267 // overloaded operators
268 void* operator new(size_t size) throw();
269 void* operator new [](size_t size) throw();
270 void operator delete(void* p);
271 void operator delete[](void* p);
272 };
273
274 //------------------------------------------------------------------------------------------------------------------------
275 // A NoHandleMark stack object will verify that no handles are allocated
276 // in its scope. Enabled in debug mode only.
277
278 class NoHandleMark: public StackObj {
279 public:
280 #ifdef ASSERT
281 NoHandleMark();
282 ~NoHandleMark();
283 #else
284 NoHandleMark() {}
285 ~NoHandleMark() {}
286 #endif
287 };
288
289
290 // ResetNoHandleMark is called in a context where there is an enclosing
291 // NoHandleMark. A thread in _thread_in_native must not create handles so
292 // this is used when transitioning via ThreadInVMfromNative.
293 class ResetNoHandleMark: public StackObj {
294 int _no_handle_mark_nesting;
295 public:
296 #ifdef ASSERT
297 ResetNoHandleMark();
298 ~ResetNoHandleMark();
299 #else
300 ResetNoHandleMark() {}
301 ~ResetNoHandleMark() {}
302 #endif
303 };
304
305 // The HandleMarkCleaner is a faster version of HandleMark.
306 // It relies on the fact that there is a HandleMark further
307 // down the stack (in JavaCalls::call_helper), and just resets
308 // to the saved values in that HandleMark.
309
310 class HandleMarkCleaner: public StackObj {
311 private:
312 Thread* _thread;
313 public:
314 inline HandleMarkCleaner(Thread* thread);
315 inline ~HandleMarkCleaner();
316 };
317
318 #endif // SHARE_RUNTIME_HANDLES_HPP