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 81 bool operator == (oop o) const; 82 bool operator == (const Handle& h) const; 83 84 // Null checks 85 bool is_null() const { return _handle == NULL; } 86 bool not_null() const { return _handle != NULL; } 87 88 // Debugging 89 void print() { obj()->print(); } 90 91 // Direct interface, use very sparingly. 92 // Used by JavaCalls to quickly convert handles and to create handles static data structures. 93 // Constructor takes a dummy argument to prevent unintentional type conversion in C++. 94 Handle(oop *handle, bool dummy) { _handle = handle; } 95 96 // Raw handle access. Allows easy duplication of Handles. This can be very unsafe 97 // since duplicates is only valid as long as original handle is alive. 98 oop* raw_value() { return _handle; } 99 static oop raw_resolve(oop *handle) { return handle == NULL ? (oop)NULL : *handle; } 100 }; 101 102 // Specific Handles for different oop types 103 #define DEF_HANDLE(type, is_a) \ 104 class type##Handle: public Handle { \ 105 protected: \ 106 type##Oop obj() const { return (type##Oop)Handle::obj(); } \ 107 type##Oop non_null_obj() const { return (type##Oop)Handle::non_null_obj(); } \ 108 \ 109 public: \ 110 /* Constructors */ \ 111 type##Handle () : Handle() {} \ 112 inline type##Handle (Thread* thread, type##Oop obj); \ 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 // Metadata Handles should be passed around as const references to avoid copy construction 130 // and destruction for parameters. 131 132 // Specific Handles for different oop types 133 #define DEF_METADATA_HANDLE(name, type) \ 134 class name##Handle; \ 135 class name##Handle : public StackObj { \ 136 type* _value; \ 137 Thread* _thread; \ 138 protected: \ 139 type* obj() const { return _value; } \ 140 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \ 141 \ 142 public: \ 143 /* Constructors */ \ 144 name##Handle () : _value(NULL), _thread(NULL) {} \ 145 name##Handle (type* obj); \ 146 name##Handle (Thread* thread, type* obj); \ 147 \ 148 name##Handle (const name##Handle &h); \ 149 name##Handle& operator=(const name##Handle &s); \ 150 \ 151 /* Destructor */ \ 152 ~name##Handle (); \ 153 void remove(); \ 154 \ 155 /* Operators for ease of use */ \ 156 type* operator () () const { return obj(); } \ 157 type* operator -> () const { return non_null_obj(); } \ 158 \ 159 bool operator == (type* o) const { return obj() == o; } \ 160 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \ 161 \ 162 /* Null checks */ \ 163 bool is_null() const { return _value == NULL; } \ 164 bool not_null() const { return _value != NULL; } \ 165 }; 166 167 168 DEF_METADATA_HANDLE(method, Method) 169 DEF_METADATA_HANDLE(constantPool, ConstantPool) 170 171 //------------------------------------------------------------------------------------------------------------------------ 172 // Thread local handle area 173 class HandleArea: public Arena { 174 friend class HandleMark; 175 friend class NoHandleMark; 176 friend class ResetNoHandleMark; 177 #ifdef ASSERT 178 int _handle_mark_nesting; 179 int _no_handle_mark_nesting; 180 #endif 181 HandleArea* _prev; // link to outer (older) area 182 public: 183 // Constructor 184 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) { 185 debug_only(_handle_mark_nesting = 0); 186 debug_only(_no_handle_mark_nesting = 0); 187 _prev = prev; 188 } 189 190 // Handle allocation 191 private: 192 oop* real_allocate_handle(oop obj) { 193 #ifdef ASSERT 194 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize)); 195 #else 196 oop* handle = (oop*) Amalloc_4(oopSize); 197 #endif 198 *handle = obj; 199 return handle; 200 } 201 public: 202 #ifdef ASSERT 203 oop* allocate_handle(oop obj); 204 #else 205 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); } 206 #endif 207 208 // Garbage collection support 209 void oops_do(OopClosure* f); 210 211 // Number of handles in use 212 size_t used() const { return Arena::used() / oopSize; } 213 214 debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; }) 215 }; 216 217 218 //------------------------------------------------------------------------------------------------------------------------ 219 // Handles are allocated in a (growable) thread local handle area. Deallocation 220 // is managed using a HandleMark. It should normally not be necessary to use 221 // HandleMarks manually. 222 // 223 // A HandleMark constructor will record the current handle area top, and the 224 // destructor will reset the top, destroying all handles allocated in between. 225 // The following code will therefore NOT work: 226 // 227 // Handle h; 228 // { 229 // HandleMark hm; 230 // h = Handle(THREAD, obj); 231 // } 232 // h()->print(); // WRONG, h destroyed by HandleMark destructor. 233 // 234 // If h has to be preserved, it can be converted to an oop or a local JNI handle 235 // across the HandleMark boundary. 236 237 // The base class of HandleMark should have been StackObj but we also heap allocate 238 // a HandleMark when a thread is created. The operator new is for this special case. 239 240 class HandleMark { 241 private: 242 Thread *_thread; // thread that owns this mark 243 HandleArea *_area; // saved handle area 244 Chunk *_chunk; // saved arena chunk 245 char *_hwm, *_max; // saved arena info 246 size_t _size_in_bytes; // size of handle area 247 // Link to previous active HandleMark in thread 248 HandleMark* _previous_handle_mark; 249 250 void initialize(Thread* thread); // common code for constructors 251 void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; } 252 HandleMark* previous_handle_mark() const { return _previous_handle_mark; } 253 254 size_t size_in_bytes() const { return _size_in_bytes; } 255 public: 256 HandleMark(); // see handles_inline.hpp 257 HandleMark(Thread* thread) { initialize(thread); } 258 ~HandleMark(); 259 260 // Functions used by HandleMarkCleaner 261 // called in the constructor of HandleMarkCleaner 262 void push(); 263 // called in the destructor of HandleMarkCleaner 264 void pop_and_restore(); 265 // overloaded operators 266 void* operator new(size_t size) throw(); 267 void* operator new [](size_t size) throw(); 268 void operator delete(void* p); 269 void operator delete[](void* p); 270 }; 271 272 //------------------------------------------------------------------------------------------------------------------------ 273 // A NoHandleMark stack object will verify that no handles are allocated 274 // in its scope. Enabled in debug mode only. 275 276 class NoHandleMark: public StackObj { 277 public: 278 #ifdef ASSERT 279 NoHandleMark(); 280 ~NoHandleMark(); 281 #else 282 NoHandleMark() {} 283 ~NoHandleMark() {} 284 #endif 285 }; 286 287 288 class ResetNoHandleMark: public StackObj { 289 int _no_handle_mark_nesting; 290 public: 291 #ifdef ASSERT 292 ResetNoHandleMark(); 293 ~ResetNoHandleMark(); 294 #else 295 ResetNoHandleMark() {} 296 ~ResetNoHandleMark() {} 297 #endif 298 }; 299 300 // The HandleMarkCleaner is a faster version of HandleMark. 301 // It relies on the fact that there is a HandleMark further 302 // down the stack (in JavaCalls::call_helper), and just resets 303 // to the saved values in that HandleMark. 304 305 class HandleMarkCleaner: public StackObj { 306 private: 307 Thread* _thread; 308 public: 309 inline HandleMarkCleaner(Thread* thread); 310 inline ~HandleMarkCleaner(); 311 }; 312 313 #endif // SHARE_VM_RUNTIME_HANDLES_HPP