1 /* 2 * Copyright (c) 1997, 2017, 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 "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 h2(thread, obj); // allocate a new handle in thread 49 // Handle h3; // declare handle only, no allocation occurs 50 // ... 51 // h3 = h1; // make h3 refer to same indirection as h1 52 // oop obj2 = h2(); // get handle value 53 // h1->print(); // invoking operation on oop 54 // 55 // Handles are specialized for different oop types to provide extra type 56 // information and avoid unnecessary casting. For each oop type xxxOop 57 // there is a corresponding handle called xxxHandle. 58 59 //------------------------------------------------------------------------------------------------------------------------ 60 // Base class for all handles. Provides overloading of frequently 61 // used operators for ease of use. 62 63 class Handle VALUE_OBJ_CLASS_SPEC { 64 private: 65 oop* _handle; 66 67 protected: 68 oop obj() const { return _handle == NULL ? (oop)NULL : *_handle; } 69 oop non_null_obj() const { assert(_handle != NULL, "resolving NULL handle"); return *_handle; } 70 71 public: 72 // Constructors 73 Handle() { _handle = NULL; } 74 Handle(Thread* thread, oop obj); 75 76 // General access 77 oop operator () () const { return obj(); } 78 oop operator -> () const { return non_null_obj(); } 79 bool operator == (oop o) const { return obj() == o; } 80 bool operator == (const Handle& h) const { return obj() == h.obj(); } 81 82 // Null checks 83 bool is_null() const { return _handle == NULL; } 84 bool not_null() const { return _handle != NULL; } 85 86 // Debugging 87 void print() { obj()->print(); } 88 89 // Direct interface, use very sparingly. 90 // Used by JavaCalls to quickly convert handles and to create handles static data structures. 91 // Constructor takes a dummy argument to prevent unintentional type conversion in C++. 92 Handle(oop *handle, bool dummy) { _handle = handle; } 93 94 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe 95 // since duplicates is only valid as long as original handle is alive. 96 oop* raw_value() { return _handle; } 97 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; } 98 }; 99 100 // Specific Handles for different oop types 101 #define DEF_HANDLE(type, is_a) \ 102 class type##Handle: public Handle { \ 103 protected: \ 104 type##Oop obj() const { return (type##Oop)Handle::obj(); } \ 105 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \ 106 \ 107 public: \ 108 /* Constructors */ \ 109 type##Handle () : Handle() {} \ 110 type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \ 111 assert(is_null() || ((oop)obj)->is_a(), "illegal type"); \ 112 } \ 113 \ 114 /* Operators for ease of use */ \ 115 type##Oop operator () () const { return obj(); } \ 116 type##Oop operator -> () const { return non_null_obj(); } \ 117 }; 118 119 120 DEF_HANDLE(instance , is_instance_noinline ) 121 DEF_HANDLE(array , is_array_noinline ) 122 DEF_HANDLE(objArray , is_objArray_noinline ) 123 DEF_HANDLE(typeArray , is_typeArray_noinline ) 124 125 //------------------------------------------------------------------------------------------------------------------------ 126 127 // Metadata Handles. Unlike oop Handles these are needed to prevent metadata 128 // from being reclaimed by RedefineClasses. 129 130 // Specific Handles for different oop types 131 #define DEF_METADATA_HANDLE(name, type) \ 132 class name##Handle; \ 133 class name##Handle : public StackObj { \ 134 type* _value; \ 135 Thread* _thread; \ 136 protected: \ 137 type* obj() const { return _value; } \ 138 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \ 139 \ 140 public: \ 141 /* Constructors */ \ 142 name##Handle () : _value(NULL), _thread(NULL) {} \ 143 name##Handle (type* obj); \ 144 name##Handle (Thread* thread, type* obj); \ 145 \ 146 name##Handle (const name##Handle &h); \ 147 name##Handle& operator=(const name##Handle &s); \ 148 \ 149 /* Destructor */ \ 150 ~name##Handle (); \ 151 void remove(); \ 152 \ 153 /* Operators for ease of use */ \ 154 type* operator () () const { return obj(); } \ 155 type* operator -> () const { return non_null_obj(); } \ 156 \ 157 bool operator == (type* o) const { return obj() == o; } \ 158 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \ 159 \ 160 /* Null checks */ \ 161 bool is_null() const { return _value == NULL; } \ 162 bool not_null() const { return _value != NULL; } \ 163 }; 164 165 166 DEF_METADATA_HANDLE(method, Method) 167 DEF_METADATA_HANDLE(constantPool, ConstantPool) 168 169 //------------------------------------------------------------------------------------------------------------------------ 170 // Thread local handle area 171 class HandleArea: public Arena { 172 friend class HandleMark; 173 friend class NoHandleMark; 174 friend class ResetNoHandleMark; 175 #ifdef ASSERT 176 int _handle_mark_nesting; 177 int _no_handle_mark_nesting; 178 #endif 179 HandleArea* _prev; // link to outer (older) area 180 public: 181 // Constructor 182 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) { 183 debug_only(_handle_mark_nesting = 0); 184 debug_only(_no_handle_mark_nesting = 0); 185 _prev = prev; 186 } 187 188 // Handle allocation 189 private: 190 oop* real_allocate_handle(oop obj) { 191 #ifdef ASSERT 192 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize)); 193 #else 194 oop* handle = (oop*) Amalloc_4(oopSize); 195 #endif 196 *handle = obj; 197 return handle; 198 } 199 public: 200 #ifdef ASSERT 201 oop* allocate_handle(oop obj); 202 #else 203 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); } 204 #endif 205 206 // Garbage collection support 207 void oops_do(OopClosure* f); 208 209 // Number of handles in use 210 size_t used() const { return Arena::used() / oopSize; } 211 212 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; }) 213 }; 214 215 216 //------------------------------------------------------------------------------------------------------------------------ 217 // Handles are allocated in a (growable) thread local handle area. Deallocation 218 // is managed using a HandleMark. It should normally not be necessary to use 219 // HandleMarks manually. 220 // 221 // A HandleMark constructor will record the current handle area top, and the 222 // destructor will reset the top, destroying all handles allocated in between. 223 // The following code will therefore NOT work: 224 // 225 // Handle h; 226 // { 227 // HandleMark hm; 228 // h = Handle(THREAD, obj); 229 // } 230 // h()->print(); // WRONG, h destroyed by HandleMark destructor. 231 // 232 // If h has to be preserved, it can be converted to an oop or a local JNI handle 233 // across the HandleMark boundary. 234 235 // The base class of HandleMark should have been StackObj but we also heap allocate 236 // a HandleMark when a thread is created. The operator new is for this special case. 237 238 class HandleMark { 239 private: 240 Thread *_thread; // thread that owns this mark 241 HandleArea *_area; // saved handle area 242 Chunk *_chunk; // saved arena chunk 243 char *_hwm, *_max; // saved arena info 244 size_t _size_in_bytes; // size of handle area 245 // Link to previous active HandleMark in thread 246 HandleMark* _previous_handle_mark; 247 248 void initialize(Thread* thread); // common code for constructors 249 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; } 250 HandleMark* previous_handle_mark() const { return _previous_handle_mark; } 251 252 size_t size_in_bytes() const { return _size_in_bytes; } 253 public: 254 HandleMark(); // see handles_inline.hpp 255 HandleMark(Thread* thread) { initialize(thread); } 256 ~HandleMark(); 257 258 // Functions used by HandleMarkCleaner 259 // called in the constructor of HandleMarkCleaner 260 void push(); 261 // called in the destructor of HandleMarkCleaner 262 void pop_and_restore(); 263 // overloaded operators 264 void* operator new(size_t size) throw(); 265 void* operator new [](size_t size) throw(); 266 void operator delete(void* p); 267 void operator delete[](void* p); 268 }; 269 270 //------------------------------------------------------------------------------------------------------------------------ 271 // A NoHandleMark stack object will verify that no handles are allocated 272 // in its scope. Enabled in debug mode only. 273 274 class NoHandleMark: public StackObj { 275 public: 276 #ifdef ASSERT 277 NoHandleMark(); 278 ~NoHandleMark(); 279 #else 280 NoHandleMark() {} 281 ~NoHandleMark() {} 282 #endif 283 }; 284 285 286 class ResetNoHandleMark: public StackObj { 287 int _no_handle_mark_nesting; 288 public: 289 #ifdef ASSERT 290 ResetNoHandleMark(); 291 ~ResetNoHandleMark(); 292 #else 293 ResetNoHandleMark() {} 294 ~ResetNoHandleMark() {} 295 #endif 296 }; 297 298 #endif // SHARE_VM_RUNTIME_HANDLES_HPP --- EOF ---