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 
  36 private:
  37 
  38   HeapWord** _heap_word;
  39 
  40   BrooksPointer(HeapWord** heap_word);
  41 
  42 public:
  43 
  44   bool check_forwardee_is_in_heap(oop forwardee);
  45 
  46   inline oop get_forwardee_raw() {
  47     return oop(*_heap_word);
  48   }
  49 
  50   inline oop get_forwardee() {
  51     oop forwardee;
  52 
  53 #ifdef ASSERT
  54     if (ShenandoahVerifyReadsToFromSpace) {
  55       ShenandoahHeap* sh = (ShenandoahHeap*) Universe::heap();
  56       ShenandoahHeapRegion* hr = sh->heap_region_containing(_heap_word);
  57 
  58       {
  59         hr->memProtectionOff();
  60         forwardee = (oop) (*_heap_word);
  61         hr->memProtectionOn();
  62       }
  63     } else {
  64       forwardee = get_forwardee_raw();
  65     }
  66 #else
  67     forwardee = get_forwardee_raw();
  68 #endif
  69 
  70     assert(check_forwardee_is_in_heap(forwardee), "forwardee must be in heap");
  71     assert(forwardee->is_oop(), "forwardee must be valid oop");
  72     return forwardee;
  73   }
  74 
  75   void set_forwardee(oop forwardee);
  76   HeapWord* cas_forwardee(HeapWord* old, HeapWord* forwardee);
  77 
  78   static BrooksPointer get(oop obj);
  79 };
  80 
  81 #endif // SHARE_VM_GC_SHENANDOAH_BROOKSPOINTER_HPP