1 /*
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  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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  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.
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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 InstanceKlass;
 33 class Klass;
 34 class Thread;
 35 
 36 //------------------------------------------------------------------------------------------------------------------------
 37 // In order to preserve oops during garbage collection, they should be
 38 // allocated and passed around via Handles within the VM. A handle is
 39 // simply an extra indirection allocated in a thread local handle area.
 40 //
 41 // A handle is a value object, so it can be passed around as a value, can
 42 // be used as a parameter w/o using &-passing, and can be returned as a
 43 // return value.
 44 //
 45 // oop parameters and return types should be Handles whenever feasible.
 46 //
 47 // Handles are declared in a straight-forward manner, e.g.
 48 //
 49 //   oop obj = ...;
 50 //   Handle h2(thread, obj);      // allocate a new handle in thread
 51 //   Handle h3;                   // declare handle only, no allocation occurs
 52 //   ...
 53 //   h3 = h1;                     // make h3 refer to same indirection as h1
 54 //   oop obj2 = h2();             // get handle value
 55 //   h1->print();                 // invoking operation on oop
 56 //
 57 // Handles are specialized for different oop types to provide extra type
 58 // information and avoid unnecessary casting. For each oop type xxxOop
 59 // there is a corresponding handle called xxxHandle.
 60 
 61 //------------------------------------------------------------------------------------------------------------------------
 62 // Base class for all handles. Provides overloading of frequently
 63 // used operators for ease of use.
 64 
 65 class Handle {
 66  private:
 67   oop* _handle;
 68 
 69  protected:
 70   oop     obj() const                            { return _handle == NULL ? (oop)NULL : *_handle; }
 71   oop     non_null_obj() const                   { assert(_handle != NULL, "resolving NULL handle"); return *_handle; }
 72 
 73  public:
 74   // Constructors
 75   Handle()                                       { _handle = NULL; }
 76   inline Handle(Thread* thread, oop obj);
 77 
 78   // General access
 79   oop     operator () () const                   { return obj(); }
 80   oop     operator -> () const                   { return non_null_obj(); }
 81 
 82   bool operator == (oop o) const                 { return obj() == o; }
 83   bool operator != (oop o) const                 { return obj() != o; }
 84   bool operator == (const Handle& h) const       { return obj() == h.obj(); }
 85   bool operator != (const Handle& h) const       { return obj() != h.obj(); }
 86 
 87   // Null checks
 88   bool    is_null() const                        { return _handle == NULL; }
 89   bool    not_null() const                       { return _handle != NULL; }
 90 
 91   // Debugging
 92   void    print()                                { obj()->print(); }
 93 
 94   // Direct interface, use very sparingly.
 95   // Used by JavaCalls to quickly convert handles and to create handles static data structures.
 96   // Constructor takes a dummy argument to prevent unintentional type conversion in C++.
 97   Handle(oop *handle, bool dummy)                { _handle = handle; }
 98 
 99   // Raw handle access. Allows easy duplication of Handles. This can be very unsafe
100   // since duplicates is only valid as long as original handle is alive.
101   oop* raw_value() const                         { return _handle; }
102   static oop raw_resolve(oop *handle)            { return handle == NULL ? (oop)NULL : *handle; }
103 };
104 
105 // Specific Handles for different oop types
106 #define DEF_HANDLE(type, is_a)                   \
107   class type##Handle: public Handle {            \
108    protected:                                    \
109     type##Oop    obj() const                     { return (type##Oop)Handle::obj(); } \
110     type##Oop    non_null_obj() const            { return (type##Oop)Handle::non_null_obj(); } \
111                                                  \
112    public:                                       \
113     /* Constructors */                           \
114     type##Handle ()                              : Handle()                 {} \
115     inline type##Handle (Thread* thread, type##Oop obj); \
116     \
117     /* Operators for ease of use */              \
118     type##Oop    operator () () const            { return obj(); } \
119     type##Oop    operator -> () const            { return non_null_obj(); } \
120   };
121 
122 
123 DEF_HANDLE(instance         , is_instance_noinline         )
124 DEF_HANDLE(array            , is_array_noinline            )
125 DEF_HANDLE(objArray         , is_objArray_noinline         )
126 DEF_HANDLE(typeArray        , is_typeArray_noinline        )
127 
128 //------------------------------------------------------------------------------------------------------------------------
129 
130 // Metadata Handles.  Unlike oop Handles these are needed to prevent metadata
131 // from being reclaimed by RedefineClasses.
132 // Metadata Handles should be passed around as const references to avoid copy construction
133 // and destruction for parameters.
134 
135 // Specific Handles for different oop types
136 #define DEF_METADATA_HANDLE(name, type)          \
137   class name##Handle;                            \
138   class name##Handle : public StackObj {         \
139     type*     _value;                            \
140     Thread*   _thread;                           \
141    protected:                                    \
142     type*        obj() const                     { return _value; } \
143     type*        non_null_obj() const            { assert(_value != NULL, "resolving NULL _value"); return _value; } \
144                                                  \
145    public:                                       \
146     /* Constructors */                           \
147     name##Handle () : _value(NULL), _thread(NULL) {}   \
148     name##Handle (Thread* thread, type* obj);    \
149                                                  \
150     name##Handle (const name##Handle &h);        \
151     name##Handle& operator=(const name##Handle &s); \
152                                                  \
153     /* Destructor */                             \
154     ~name##Handle ();                            \
155     void remove();                               \
156                                                  \
157     /* Operators for ease of use */              \
158     type*        operator () () const            { return obj(); } \
159     type*        operator -> () const            { return non_null_obj(); } \
160                                                  \
161     bool    operator == (type* o) const          { return obj() == o; } \
162     bool    operator == (const name##Handle& h) const  { return obj() == h.obj(); } \
163                                                  \
164     /* Null checks */                            \
165     bool    is_null() const                      { return _value == NULL; } \
166     bool    not_null() const                     { return _value != NULL; } \
167   };
168 
169 
170 DEF_METADATA_HANDLE(method, Method)
171 DEF_METADATA_HANDLE(constantPool, ConstantPool)
172 
173 //------------------------------------------------------------------------------------------------------------------------
174 // Thread local handle area
175 class HandleArea: public Arena {
176   friend class HandleMark;
177   friend class NoHandleMark;
178   friend class ResetNoHandleMark;
179 #ifdef ASSERT
180   int _handle_mark_nesting;
181   int _no_handle_mark_nesting;
182 #endif
183   HandleArea* _prev;          // link to outer (older) area
184  public:
185   // Constructor
186   HandleArea(HandleArea* prev) : Arena(mtThread, Chunk::tiny_size) {
187     debug_only(_handle_mark_nesting    = 0);
188     debug_only(_no_handle_mark_nesting = 0);
189     _prev = prev;
190   }
191 
192   // Handle allocation
193  private:
194   oop* real_allocate_handle(oop obj) {
195     // Ignore UseMallocOnly by allocating only in arena.
196     oop* handle = (oop*)internal_amalloc(oopSize);
197     *handle = obj;
198     return handle;
199   }
200  public:
201 #ifdef ASSERT
202   oop* allocate_handle(oop obj);
203 #else
204   oop* allocate_handle(oop obj) { return real_allocate_handle(obj); }
205 #endif
206 
207   // Garbage collection support
208   void oops_do(OopClosure* f);
209 
210   // Number of handles in use
211   size_t used() const     { return Arena::used() / oopSize; }
212 
213   debug_only(bool no_handle_mark_active() { return _no_handle_mark_nesting > 0; })
214 };
215 
216 
217 //------------------------------------------------------------------------------------------------------------------------
218 // Handles are allocated in a (growable) thread local handle area. Deallocation
219 // is managed using a HandleMark. It should normally not be necessary to use
220 // HandleMarks manually.
221 //
222 // A HandleMark constructor will record the current handle area top, and the
223 // destructor will reset the top, destroying all handles allocated in between.
224 // The following code will therefore NOT work:
225 //
226 //   Handle h;
227 //   {
228 //     HandleMark hm(THREAD);
229 //     h = Handle(THREAD, obj);
230 //   }
231 //   h()->print();       // WRONG, h destroyed by HandleMark destructor.
232 //
233 // If h has to be preserved, it can be converted to an oop or a local JNI handle
234 // across the HandleMark boundary.
235 
236 // The base class of HandleMark should have been StackObj but we also heap allocate
237 // a HandleMark when a thread is created. The operator new is for this special case.
238 
239 class HandleMark {
240  private:
241   Thread *_thread;              // thread that owns this mark
242   HandleArea *_area;            // saved handle area
243   Chunk *_chunk;                // saved arena chunk
244   char *_hwm, *_max;            // saved arena info
245   size_t _size_in_bytes;        // size of handle area
246   // Link to previous active HandleMark in thread
247   HandleMark* _previous_handle_mark;
248 
249   void initialize(Thread* thread);                // common code for constructors
250   void set_previous_handle_mark(HandleMark* mark) { _previous_handle_mark = mark; }
251   HandleMark* previous_handle_mark() const        { return _previous_handle_mark; }
252 
253   size_t size_in_bytes() const { return _size_in_bytes; }
254   // remove all chunks beginning with the next
255   void chop_later_chunks();
256  public:
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 // ResetNoHandleMark is called in a context where there is an enclosing
289 // NoHandleMark. A thread in _thread_in_native must not create handles so
290 // this is used when transitioning via ThreadInVMfromNative.
291 class ResetNoHandleMark: public StackObj {
292   int _no_handle_mark_nesting;
293  public:
294 #ifdef ASSERT
295   ResetNoHandleMark();
296   ~ResetNoHandleMark();
297 #else
298   ResetNoHandleMark()  {}
299   ~ResetNoHandleMark() {}
300 #endif
301 };
302 
303 // The HandleMarkCleaner is a faster version of HandleMark.
304 // It relies on the fact that there is a HandleMark further
305 // down the stack (in JavaCalls::call_helper), and just resets
306 // to the saved values in that HandleMark.
307 
308 class HandleMarkCleaner: public StackObj {
309  private:
310   Thread* _thread;
311  public:
312   inline HandleMarkCleaner(Thread* thread);
313   inline ~HandleMarkCleaner();
314 };
315 
316 #endif // SHARE_RUNTIME_HANDLES_HPP