1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
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  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  *
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 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 InlineKlass;
 33 class InstanceKlass;
 34 class Klass;
 35 class Thread;
 36 
 37 //------------------------------------------------------------------------------------------------------------------------
 38 // In order to preserve oops during garbage collection, they should be
 39 // allocated and passed around via Handles within the VM. A handle is
 40 // simply an extra indirection allocated in a thread local handle area.
 41 //
 42 // A handle is a value object, so it can be passed around as a value, can
 43 // be used as a parameter w/o using &-passing, and can be returned as a
 44 // return value.
 45 //
 46 // oop parameters and return types should be Handles whenever feasible.
 47 //
 48 // Handles are declared in a straight-forward manner, e.g.
 49 //
 50 //   oop obj = ...;
 51 //   Handle h2(thread, obj);      // allocate a new handle in thread
 52 //   Handle h3;                   // declare handle only, no allocation occurs
 53 //   ...
 54 //   h3 = h1;                     // make h3 refer to same indirection as h1
 55 //   oop obj2 = h2();             // get handle value
 56 //   h1->print();                 // invoking operation on oop
 57 //
 58 // Handles are specialized for different oop types to provide extra type
 59 // information and avoid unnecessary casting. For each oop type xxxOop
 60 // there is a corresponding handle called xxxHandle.
 61 
 62 //------------------------------------------------------------------------------------------------------------------------
 63 // Base class for all handles. Provides overloading of frequently
 64 // used operators for ease of use.
 65 
 66 class Handle {
 67  private:
 68   oop* _handle;
 69 
 70  protected:
 71   oop     obj() const                            { return _handle == NULL ? (oop)NULL : *_handle; }
 72   oop     non_null_obj() const                   { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
 73 
 74  public:
 75   // Constructors
 76   Handle()                                       { _handle = NULL; }
 77   inline Handle(Thread* thread, oop obj);
 78 
 79   // General access
 80   oop     operator () () const                   { return obj(); }
 81   oop     operator -> () const                   { return non_null_obj(); }
 82 
 83   bool operator == (oop o) const                 { return obj() == o; }
 84   bool operator != (oop o) const                 { return obj() != o; }
 85   bool operator == (const Handle& h) const       { return obj() == h.obj(); }
 86   bool operator != (const Handle& h) const       { return obj() != h.obj(); }
 87 
 88   // Null checks
 89   bool    is_null() const                        { return _handle == NULL; }
 90   bool    not_null() const                       { return _handle != NULL; }
 91 
 92   // Debugging
 93   void    print()                                { obj()->print(); }
 94 
 95   // Direct interface, use very sparingly.
 96   // Used by JavaCalls to quickly convert handles and to create handles static data structures.
 97   // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
 98   Handle(oop *handle, bool dummy)                { _handle = handle; }
 99 
100   // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
101   // since duplicates is only valid as long as original handle is alive.
102   oop* raw_value() const                         { return _handle; }
103   static oop raw_resolve(oop *handle)            { return handle == NULL ? (oop)NULL : *handle; }
104 };
105 
106 // Specific Handles for different oop types
107 #define DEF_HANDLE(type, is_a)                   \
108   class type##Handle: public Handle {            \
109    protected:                                    \
110     type##Oop    obj() const                     { return (type##Oop)Handle::obj(); } \
111     type##Oop    non_null_obj() const            { return (type##Oop)Handle::non_null_obj(); } \
112                                                  \
113    public:                                       \
114     /* Constructors */                           \
115     type##Handle ()                              : Handle()                 {} \
116     inline type##Handle (Thread* thread, type##Oop obj); \
117     \
118     /* Operators for ease of use */              \
119     type##Oop    operator () () const            { return obj(); } \
120     type##Oop    operator -> () const            { return non_null_obj(); } \
121   };
122 
123 
124 DEF_HANDLE(instance         , is_instance_noinline         )
125 DEF_HANDLE(array            , is_array_noinline            )
126 DEF_HANDLE(objArray         , is_objArray_noinline         )
127 DEF_HANDLE(typeArray        , is_typeArray_noinline        )
128 DEF_HANDLE(flatArray        , is_flatArray_noinline        )
129 
130 //------------------------------------------------------------------------------------------------------------------------
131 
132 // Metadata Handles.  Unlike oop Handles these are needed to prevent metadata
133 // from being reclaimed by RedefineClasses.
134 // Metadata Handles should be passed around as const references to avoid copy construction
135 // and destruction for parameters.
136 
137 // Specific Handles for different oop types
138 #define DEF_METADATA_HANDLE(name, type)          \
139   class name##Handle;                            \
140   class name##Handle : public StackObj {         \
141     type*     _value;                            \
142     Thread*   _thread;                           \
143    protected:                                    \
144     type*        obj() const                     { return _value; } \
145     type*        non_null_obj() const            { assert(_value != NULL, "resolving NULL _value"); return _value; } \
146                                                  \
147    public:                                       \
148     /* Constructors */                           \
149     name##Handle () : _value(NULL), _thread(NULL) {}   \
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 //------------------------------------------------------------------------------------------------------------------------
176 // Thread local handle area
177 class HandleArea: public Arena {
178   friend class HandleMark;
179   friend class NoHandleMark;
180   friend class ResetNoHandleMark;
181 #ifdef ASSERT
182   int _handle_mark_nesting;
183   int _no_handle_mark_nesting;
184 #endif
185   HandleArea* _prev;          // link to outer (older) area
186  public:
187   // Constructor
188   HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
189     debug_only(_handle_mark_nesting    = 0);
190     debug_only(_no_handle_mark_nesting = 0);
191     _prev = prev;
192   }
193 
194   // Handle allocation
195  private:
196   oop* real_allocate_handle(oop obj) {
197     // Ignore UseMallocOnly by allocating only in arena.
198     oop* handle = (oop*)internal_amalloc(oopSize);
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(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