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 ValueObj, 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 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 type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \ 112 assert(is_null() || ((oop)obj)->is_a(), "illegal type"); \ 113 } \ 114 \ 115 /* Operators for ease of use */ \ 116 type##Oop operator () () const { return obj(); } \ 117 type##Oop operator -> () const { return non_null_obj(); } \ 118 }; 119 120 121 DEF_HANDLE(instance , is_instance_noinline ) 122 DEF_HANDLE(array , is_array_noinline ) 123 DEF_HANDLE(objArray , is_objArray_noinline ) 124 DEF_HANDLE(typeArray , is_typeArray_noinline ) 125 126 //------------------------------------------------------------------------------------------------------------------------ 127 128 // Metadata Handles. Unlike oop Handles these are needed to prevent metadata 129 // from being reclaimed by RedefineClasses. 130 // Metadata Handles should be passed around as const references to avoid copy construction 131 // and destruction for parameters. 132 133 // Specific Handles for different oop types 134 #define DEF_METADATA_HANDLE(name, type) \ 135 class name##Handle; \ 136 class name##Handle : public StackObj { \ 137 type* _value; \ 138 Thread* _thread; \ 139 protected: \ 140 type* obj() const { return _value; } \ 141 type* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; } \ 142 \ 143 public: \ 144 /* Constructors */ \ 145 name##Handle () : _value(NULL), _thread(NULL) {} \ 146 name##Handle (type* obj); \ 147 name##Handle (Thread* thread, type* obj); \ 148 \ 149 name##Handle (const name##Handle &h); \ 150 name##Handle& operator=(const name##Handle &s); \ 151 \ 152 /* Destructor */ \ 153 ~name##Handle (); \ 154 void remove(); \ 155 \ 156 /* Operators for ease of use */ \ 157 type* operator () () const { return obj(); } \ 158 type* operator -> () const { return non_null_obj(); } \ 159 \ 160 bool operator == (type* o) const { return obj() == o; } \ 161 bool operator == (const name##Handle& h) const { return obj() == h.obj(); } \ 162 \ 163 /* Null checks */ \ 164 bool is_null() const { return _value == NULL; } \ 165 bool not_null() const { return _value != NULL; } \ 166 }; 167 168 169 DEF_METADATA_HANDLE(method, Method) 170 DEF_METADATA_HANDLE(constantPool, ConstantPool) 171 172 //------------------------------------------------------------------------------------------------------------------------ 173 // Thread local handle area 174 class HandleArea: public Arena { 175 friend class HandleMark; 176 friend class NoHandleMark; 177 friend class ResetNoHandleMark; 178 #ifdef ASSERT 179 int _handle_mark_nesting; 180 int _no_handle_mark_nesting; 181 #endif 182 HandleArea* _prev; // link to outer (older) area 183 public: 184 // Constructor 185 HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) { 186 debug_only(_handle_mark_nesting = 0); 187 debug_only(_no_handle_mark_nesting = 0); 188 _prev = prev; 189 } 190 191 // Handle allocation 192 private: 193 oop* real_allocate_handle(oop obj) { 194 #ifdef ASSERT 195 oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize)); 196 #else 197 oop* handle = (oop*) Amalloc_4(oopSize); 198 #endif 199 *handle = obj; 200 return handle; 201 } 202 public: 203 #ifdef ASSERT 204 oop* allocate_handle(oop obj); 205 #else 206 oop* allocate_handle(oop obj) { return real_allocate_handle(obj); } 207 #endif 208 209 // Garbage collection support 210 void oops_do(OopClosure* f); 211 212 // Number of handles in use 213 size_t used() const { return Arena::used() / oopSize; } 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; 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 public: 257 HandleMark(); // see handles_inline.hpp 258 HandleMark(Thread* thread) { initialize(thread); } 259 ~HandleMark(); 260 261 // Functions used by HandleMarkCleaner 262 // called in the constructor of HandleMarkCleaner 263 void push(); 264 // called in the destructor of HandleMarkCleaner 265 void pop_and_restore(); 266 // overloaded operators 267 void* operator new(size_t size) throw(); 268 void* operator new [](size_t size) throw(); 269 void operator delete(void* p); 270 void operator delete[](void* p); 271 }; 272 273 //------------------------------------------------------------------------------------------------------------------------ 274 // A NoHandleMark stack object will verify that no handles are allocated 275 // in its scope. Enabled in debug mode only. 276 277 class NoHandleMark: public StackObj { 278 public: 279 #ifdef ASSERT 280 NoHandleMark(); 281 ~NoHandleMark(); 282 #else 283 NoHandleMark() {} 284 ~NoHandleMark() {} 285 #endif 286 }; 287 288 289 class ResetNoHandleMark: public StackObj { 290 int _no_handle_mark_nesting; 291 public: 292 #ifdef ASSERT 293 ResetNoHandleMark(); 294 ~ResetNoHandleMark(); 295 #else 296 ResetNoHandleMark() {} 297 ~ResetNoHandleMark() {} 298 #endif 299 }; 300 301 #endif // SHARE_VM_RUNTIME_HANDLES_HPP