1 /*
   2  * Copyright (c) 2013, 2015, Red Hat, Inc. and/or its affiliates.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.
   7  *
   8  * This code is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  11  * version 2 for more details (a copy is included in the LICENSE file that
  12  * accompanied this code).
  13  *
  14  * You should have received a copy of the GNU General Public License version
  15  * 2 along with this work; if not, write to the Free Software Foundation,
  16  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  17  *
  18  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  19  * or visit www.oracle.com if you need additional information or have any
  20  * questions.
  21  *
  22  */
  23 
  24 #ifndef SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP
  25 #define SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP
  26 
  27 #include "oops/oop.hpp"
  28 #include "utilities/globalDefinitions.hpp"
  29 #include "gc/shenandoah/shenandoahHeap.hpp"
  30 
  31 class BrooksPointer {
  32 
  33 public:
  34   static const uint BROOKS_POINTER_OBJ_SIZE = 1;
  35   static const int BYTE_OFFSET = -8;
  36 
  37 private:
  38 
  39   HeapWord** _heap_word;
  40 
  41   BrooksPointer(HeapWord** heap_word);
  42 
  43 public:
  44 
  45   bool check_forwardee_is_in_heap(oop forwardee);
  46 
  47   inline oop get_forwardee_raw() {
  48     return oop(*_heap_word);
  49   }
  50 
  51   inline oop get_forwardee() {
  52     oop forwardee;
  53 
  54 #ifdef ASSERT
  55     if (ShenandoahVerifyReadsToFromSpace) {
  56       ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  57       ShenandoahHeapRegion* hr = sh->heap_region_containing(_heap_word);
  58 
  59       {
  60         hr->memProtectionOff();
  61         forwardee = (oop) (*_heap_word);
  62         hr->memProtectionOn();
  63       }
  64     } else {
  65       forwardee = get_forwardee_raw();
  66     }
  67 #else
  68     forwardee = get_forwardee_raw();
  69 #endif
  70 
  71     assert(check_forwardee_is_in_heap(forwardee), "forwardee must be in heap");
  72     assert(forwardee->is_oop(), "forwardee must be valid oop");
  73     return forwardee;
  74   }
  75 
  76   void set_forwardee(oop forwardee);
  77   HeapWord* cas_forwardee(HeapWord* old, HeapWord* forwardee);
  78 
  79   static BrooksPointer get(oop obj);
  80 };
  81 
  82 #endif // SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP