1 /*
   2  * Copyright (c) 1997, 2014, 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/klass.hpp"
  29 
  30 //------------------------------------------------------------------------------------------------------------------------
  31 // In order to preserve oops during garbage collection, they should be
  32 // allocated and passed around via Handles within the VM. A handle is
  33 // simply an extra indirection allocated in a thread local handle area.
  34 //
  35 // A handle is a ValueObj, so it can be passed around as a value, can
  36 // be used as a parameter w/o using &-passing, and can be returned as a
  37 // return value.
  38 //
  39 // oop parameters and return types should be Handles whenever feasible.
  40 //
  41 // Handles are declared in a straight-forward manner, e.g.
  42 //
  43 //   oop obj = ...;
  44 //   Handle h1(obj);              // allocate new handle
  45 //   Handle h2(thread, obj);      // faster allocation when current thread is known
  46 //   Handle h3;                   // declare handle only, no allocation occurs
  47 //   ...
  48 //   h3 = h1;                     // make h3 refer to same indirection as h1
  49 //   oop obj2 = h2();             // get handle value
  50 //   h1->print();                 // invoking operation on oop
  51 //
  52 // Handles are specialized for different oop types to provide extra type
  53 // information and avoid unnecessary casting. For each oop type xxxOop
  54 // there is a corresponding handle called xxxHandle, e.g.
  55 //
  56 //   oop           Handle
  57 //   Method*       methodHandle
  58 //   instanceOop   instanceHandle
  59 
  60 //------------------------------------------------------------------------------------------------------------------------
  61 // Base class for all handles. Provides overloading of frequently
  62 // used operators for ease of use.
  63 
  64 class Handle VALUE_OBJ_CLASS_SPEC {
  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(oop obj);
  76   Handle(Thread* thread, oop obj);
  77 
  78   // General access
  79   oop     operator () () const                   { return obj(); }
  80   oop     operator -> () const                   { return non_null_obj(); }
  81   bool    operator == (oop o) const              { return obj() == o; }
  82   bool    operator == (const Handle& h) const          { return obj() == h.obj(); }
  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     type##Handle (type##Oop obj) : Handle((oop)obj) {                         \
 113       assert(is_null() || ((oop)obj)->is_a(),                                 \
 114              "illegal type");                                                 \
 115     }                                                                         \
 116     type##Handle (Thread* thread, type##Oop obj) : Handle(thread, (oop)obj) { \
 117       assert(is_null() || ((oop)obj)->is_a(), "illegal type");                \
 118     }                                                                         \
 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         )
 127 DEF_HANDLE(array            , is_array            )
 128 DEF_HANDLE(objArray         , is_objArray         )
 129 DEF_HANDLE(typeArray        , is_typeArray        )
 130 
 131 //------------------------------------------------------------------------------------------------------------------------
 132 
 133 // Metadata Handles.  Unlike oop Handles these are needed to prevent metadata
 134 // from being reclaimed by RedefineClasses.
 135 
 136 // Specific Handles for different oop types
 137 #define DEF_METADATA_HANDLE(name, type)          \
 138   class name##Handle;                            \
 139   class name##Handle : public StackObj {         \
 140     type*     _value;                            \
 141     Thread*   _thread;                           \
 142    protected:                                    \
 143     type*        obj() const                     { return _value; } \
 144     type*        non_null_obj() const            { assert(_value != NULL, "resolving NULL _value"); return _value; } \
 145                                                  \
 146    public:                                       \
 147     /* Constructors */                           \
 148     name##Handle () : _value(NULL), _thread(NULL) {}   \
 149     name##Handle (type* obj);                    \
 150     name##Handle (Thread* thread, type* obj);    \
 151                                                  \
 152     name##Handle (const name##Handle &h);        \
 153     name##Handle& operator=(const name##Handle &s); \
 154                                                  \
 155     /* Destructor */                             \
 156     ~name##Handle ();                            \
 157     void remove();                               \
 158                                                  \
 159     /* Operators for ease of use */              \
 160     type*        operator () () const            { return obj(); } \
 161     type*        operator -> () const            { return non_null_obj(); } \
 162                                                  \
 163     bool    operator == (type* o) const          { return obj() == o; } \
 164     bool    operator == (const name##Handle& h) const  { return obj() == h.obj(); } \
 165                                                  \
 166     /* Null checks */                            \
 167     bool    is_null() const                      { return _value == NULL; } \
 168     bool    not_null() const                     { return _value != NULL; } \
 169   };
 170 
 171 
 172 DEF_METADATA_HANDLE(method, Method)
 173 DEF_METADATA_HANDLE(constantPool, ConstantPool)
 174 
 175 // Writing this class explicitly, since DEF_METADATA_HANDLE(klass) doesn't
 176 // provide the necessary Klass* <-> Klass* conversions. This Klass
 177 // could be removed when we don't have the Klass* typedef anymore.
 178 class KlassHandle : public StackObj {
 179   Klass* _value;
 180  protected:
 181    Klass* obj() const          { return _value; }
 182    Klass* non_null_obj() const { assert(_value != NULL, "resolving NULL _value"); return _value; }
 183 
 184  public:
 185    KlassHandle()                                 : _value(NULL) {}
 186    KlassHandle(const Klass* obj)                 : _value(const_cast<Klass *>(obj)) {};
 187    KlassHandle(Thread* thread, const Klass* obj) : _value(const_cast<Klass *>(obj)) {};
 188 
 189    Klass* operator () () const { return obj(); }
 190    Klass* operator -> () const { return non_null_obj(); }
 191 
 192    bool operator == (Klass* o) const             { return obj() == o; }
 193    bool operator == (const KlassHandle& h) const { return obj() == h.obj(); }
 194 
 195     bool is_null() const  { return _value == NULL; }
 196     bool not_null() const { return _value != NULL; }
 197 };
 198 
 199 class instanceKlassHandle : public KlassHandle {
 200  public:
 201   /* Constructors */
 202   instanceKlassHandle () : KlassHandle() {}
 203   instanceKlassHandle (const Klass* k) : KlassHandle(k) {
 204     assert(k == NULL || k->oop_is_instance(),
 205            "illegal type");
 206   }
 207   instanceKlassHandle (Thread* thread, const Klass* k) : KlassHandle(thread, k) {
 208     assert(k == NULL || k->oop_is_instance(),
 209            "illegal type");
 210   }
 211   /* Access to klass part */
 212   InstanceKlass*       operator () () const { return (InstanceKlass*)obj(); }
 213   InstanceKlass*       operator -> () const { return (InstanceKlass*)obj(); }
 214 };
 215 
 216 
 217 //------------------------------------------------------------------------------------------------------------------------
 218 // Thread local handle area
 219 class HandleArea: public Arena {
 220   friend class HandleMark;
 221   friend class NoHandleMark;
 222   friend class ResetNoHandleMark;
 223 #ifdef ASSERT
 224   int _handle_mark_nesting;
 225   int _no_handle_mark_nesting;
 226 #endif
 227   HandleArea* _prev;          // link to outer (older) area
 228  public:
 229   // Constructor
 230   HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
 231     debug_only(_handle_mark_nesting    = 0);
 232     debug_only(_no_handle_mark_nesting = 0);
 233     _prev = prev;
 234   }
 235 
 236   // Handle allocation
 237  private:
 238   oop* real_allocate_handle(oop obj) {
 239 #ifdef ASSERT
 240     oop* handle = (oop*) (UseMallocOnly ? internal_malloc_4(oopSize) : Amalloc_4(oopSize));
 241 #else
 242     oop* handle = (oop*) Amalloc_4(oopSize);
 243 #endif
 244     *handle = obj;
 245     return handle;
 246   }
 247  public:
 248 #ifdef ASSERT
 249   oop* allocate_handle(oop obj);
 250 #else
 251   oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
 252 #endif
 253 
 254   // Garbage collection support
 255   void oops_do(OopClosure* f);
 256 
 257   // Number of handles in use
 258   size_t used() const     { return Arena::used() / oopSize; }
 259 
 260   debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
 261 };
 262 
 263 
 264 //------------------------------------------------------------------------------------------------------------------------
 265 // Handles are allocated in a (growable) thread local handle area. Deallocation
 266 // is managed using a HandleMark. It should normally not be necessary to use
 267 // HandleMarks manually.
 268 //
 269 // A HandleMark constructor will record the current handle area top, and the
 270 // destructor will reset the top, destroying all handles allocated in between.
 271 // The following code will therefore NOT work:
 272 //
 273 //   Handle h;
 274 //   {
 275 //     HandleMark hm;
 276 //     h = Handle(obj);
 277 //   }
 278 //   h()->print();       // WRONG, h destroyed by HandleMark destructor.
 279 //
 280 // If h has to be preserved, it can be converted to an oop or a local JNI handle
 281 // across the HandleMark boundary.
 282 
 283 // The base class of HandleMark should have been StackObj but we also heap allocate
 284 // a HandleMark when a thread is created. The operator new is for this special case.
 285 
 286 class HandleMark {
 287  private:
 288   Thread *_thread;              // thread that owns this mark
 289   HandleArea *_area;            // saved handle area
 290   Chunk *_chunk;                // saved arena chunk
 291   char *_hwm, *_max;            // saved arena info
 292   size_t _size_in_bytes;        // size of handle area
 293   // Link to previous active HandleMark in thread
 294   HandleMark* _previous_handle_mark;
 295 
 296   void initialize(Thread* thread);                // common code for constructors
 297   void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
 298   HandleMark* previous_handle_mark() const        { return _previous_handle_mark; }
 299 
 300   size_t size_in_bytes() const { return _size_in_bytes; }
 301  public:
 302   HandleMark();                            // see handles_inline.hpp
 303   HandleMark(Thread* thread)                      { initialize(thread); }
 304   ~HandleMark();
 305 
 306   // Functions used by HandleMarkCleaner
 307   // called in the constructor of HandleMarkCleaner
 308   void push();
 309   // called in the destructor of HandleMarkCleaner
 310   void pop_and_restore();
 311   // overloaded operators
 312   void* operator new(size_t size) throw();
 313   void* operator new [](size_t size) throw();
 314   void operator delete(void* p);
 315   void operator delete[](void* p);
 316 };
 317 
 318 //------------------------------------------------------------------------------------------------------------------------
 319 // A NoHandleMark stack object will verify that no handles are allocated
 320 // in its scope. Enabled in debug mode only.
 321 
 322 class NoHandleMark: public StackObj {
 323  public:
 324 #ifdef ASSERT
 325   NoHandleMark();
 326   ~NoHandleMark();
 327 #else
 328   NoHandleMark()  {}
 329   ~NoHandleMark() {}
 330 #endif
 331 };
 332 
 333 
 334 class ResetNoHandleMark: public StackObj {
 335   int _no_handle_mark_nesting;
 336  public:
 337 #ifdef ASSERT
 338   ResetNoHandleMark();
 339   ~ResetNoHandleMark();
 340 #else
 341   ResetNoHandleMark()  {}
 342   ~ResetNoHandleMark() {}
 343 #endif
 344 };
 345 
 346 #endif // SHARE_VM_RUNTIME_HANDLES_HPP