js/src/gc/RelocationOverlay.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /*
   8  * GC-internal definition of relocation overlay used while moving cells.
   9  */
  10
  11 #ifndef gc_RelocationOverlay_h
  12 #define gc_RelocationOverlay_h
  13
  14 #include "mozilla/Assertions.h"
  15
  16 #include <stdint.h>
  17
  18 #include "gc/Cell.h"
  19
  20 namespace js {
  21 namespace gc {
  22
  23 /*
  24  * This structure overlays a Cell that has been moved and provides a way to find
  25  * its new location. It's used during generational and compacting GC.
  26  */
  27 class RelocationOverlay : public Cell {
  28  public:
  29   /* The location the cell has been moved to, stored in the cell header. */
  30   Cell* forwardingAddress() const {
  31     MOZ_ASSERT(isForwarded());
  32     return reinterpret_cast<Cell*>(header_.getForwardingAddress());
  33   }
  34
  35  protected:
  36   /* A list entry to track all relocated things. */
  37   RelocationOverlay* next_;
  38
  39   explicit RelocationOverlay(Cell* dst);
  40
  41  public:
  42   static const RelocationOverlay* fromCell(const Cell* cell) {
  43     return static_cast<const RelocationOverlay*>(cell);
  44   }
  45
  46   static RelocationOverlay* fromCell(Cell* cell) {
  47     return static_cast<RelocationOverlay*>(cell);
  48   }
  49
  50   static RelocationOverlay* forwardCell(Cell* src, Cell* dst);
  51
  52   void setNext(RelocationOverlay* next) {
  53     MOZ_ASSERT(isForwarded());
  54     next_ = next;
  55   }
  56
  57   RelocationOverlay* next() const {
  58     MOZ_ASSERT(isForwarded());
  59     return next_;
  60   }
  61 };
  62
  63 }  // namespace gc
  64 }  // namespace js
  65
  66 #endif /* gc_RelocationOverlay_h */