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.
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  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