65 // knows how to get the G1 heap and how to use the bitmap
  66 // in the concurrent marker used by G1 to filter remembered
  67 // sets.
  68 
  69 class HeapRegionDCTOC : public DirtyCardToOopClosure {
  70 private:
  71   HeapRegion* _hr;
  72   G1ParPushHeapRSClosure* _rs_scan;
  73   G1CollectedHeap* _g1;
  74 
  75   // Walk the given memory region from bottom to (actual) top
  76   // looking for objects and applying the oop closure (_cl) to
  77   // them. The base implementation of this treats the area as
  78   // blocks, where a block may or may not be an object. Sub-
  79   // classes should override this to provide more accurate
  80   // or possibly more efficient walking.
  81   void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
  82 
  83 public:
  84   HeapRegionDCTOC(G1CollectedHeap* g1,
  85                   HeapRegion* hr, G1ParPushHeapRSClosure* cl,

  86                   CardTableModRefBS::PrecisionStyle precision);
  87 };
  88 
  89 // The complicating factor is that BlockOffsetTable diverged
  90 // significantly, and we need functionality that is only in the G1 version.
  91 // So I copied that code, which led to an alternate G1 version of
  92 // OffsetTableContigSpace.  If the two versions of BlockOffsetTable could
  93 // be reconciled, then G1OffsetTableContigSpace could go away.
  94 
  95 // The idea behind time stamps is the following. We want to keep track of
  96 // the highest address where it's safe to scan objects for each region.
  97 // This is only relevant for current GC alloc regions so we keep a time stamp
  98 // per region to determine if the region has been allocated during the current
  99 // GC or not. If the time stamp is current we report a scan_top value which
 100 // was saved at the end of the previous GC for retained alloc regions and which is
 101 // equal to the bottom for all other regions.
 102 // There is a race between card scanners and allocating gc workers where we must ensure
 103 // that card scanners do not read the memory allocated by the gc workers.
 104 // In order to enforce that, we must not return a value of _top which is more recent than the
 105 // time stamp. This is due to the fact that a region may become a gc alloc region at

  65 // knows how to get the G1 heap and how to use the bitmap
  66 // in the concurrent marker used by G1 to filter remembered
  67 // sets.
  68 
  69 class HeapRegionDCTOC : public DirtyCardToOopClosure {
  70 private:
  71   HeapRegion* _hr;
  72   G1ParPushHeapRSClosure* _rs_scan;
  73   G1CollectedHeap* _g1;
  74 
  75   // Walk the given memory region from bottom to (actual) top
  76   // looking for objects and applying the oop closure (_cl) to
  77   // them. The base implementation of this treats the area as
  78   // blocks, where a block may or may not be an object. Sub-
  79   // classes should override this to provide more accurate
  80   // or possibly more efficient walking.
  81   void walk_mem_region(MemRegion mr, HeapWord* bottom, HeapWord* top);
  82 
  83 public:
  84   HeapRegionDCTOC(G1CollectedHeap* g1,
  85                   HeapRegion* hr,
  86                   G1ParPushHeapRSClosure* cl,
  87                   CardTableModRefBS::PrecisionStyle precision);
  88 };
  89 
  90 // The complicating factor is that BlockOffsetTable diverged
  91 // significantly, and we need functionality that is only in the G1 version.
  92 // So I copied that code, which led to an alternate G1 version of
  93 // OffsetTableContigSpace.  If the two versions of BlockOffsetTable could
  94 // be reconciled, then G1OffsetTableContigSpace could go away.
  95 
  96 // The idea behind time stamps is the following. We want to keep track of
  97 // the highest address where it's safe to scan objects for each region.
  98 // This is only relevant for current GC alloc regions so we keep a time stamp
  99 // per region to determine if the region has been allocated during the current
 100 // GC or not. If the time stamp is current we report a scan_top value which
 101 // was saved at the end of the previous GC for retained alloc regions and which is
 102 // equal to the bottom for all other regions.
 103 // There is a race between card scanners and allocating gc workers where we must ensure
 104 // that card scanners do not read the memory allocated by the gc workers.
 105 // In order to enforce that, we must not return a value of _top which is more recent than the
 106 // time stamp. This is due to the fact that a region may become a gc alloc region at