src/hotspot/share/gc/g1/g1ConcurrentMark.inline.hpp

rev 49944 : imported patch 8201492-properly-implement-non-contiguous-reference-processing
rev 49945 : imported patch 8201492-stefanj-review

*** 37,60 ****
  #include "gc/shared/suspendibleThreadSet.hpp"
  #include "gc/shared/taskqueue.inline.hpp"
  #include "utilities/bitMap.inline.hpp"
  
  inline bool G1CMIsAliveClosure::do_object_b(oop obj) {
!   if (obj == NULL) {
!     return false;
!   }
!   assert(_g1h->is_in_reserved(obj), "Asked for liveness of oop " PTR_FORMAT " outside of reserved heap.", p2i(obj));
!   // Young regions have nTAMS == bottom(), i.e. all objects there are implicitly live,
!   // so we do not need to explicitly check for region type.
!   bool result = !_g1h->is_obj_ill(obj, _g1h->heap_region_containing(obj));
!   assert(_g1h->heap_region_containing(obj)->is_old_or_humongous() || result,
!          "Oop " PTR_FORMAT " in young region %u (%s) should be live",
!          p2i(obj), _g1h->addr_to_region((HeapWord*)obj), _g1h->heap_region_containing(obj)->get_short_type_str());
!   return result;
  }
  
  inline bool G1CMSubjectToDiscoveryClosure::do_object_b(oop obj) {
    if (obj == NULL) {
      return false;
    }
    assert(_g1h->is_in_reserved(obj), "Trying to discover obj " PTR_FORMAT " not in heap", p2i(obj));
    return _g1h->heap_region_containing(obj)->is_old_or_humongous();
--- 37,54 ----
  #include "gc/shared/suspendibleThreadSet.hpp"
  #include "gc/shared/taskqueue.inline.hpp"
  #include "utilities/bitMap.inline.hpp"
  
  inline bool G1CMIsAliveClosure::do_object_b(oop obj) {
!   return !_g1h->is_obj_ill(obj);
  }
  
  inline bool G1CMSubjectToDiscoveryClosure::do_object_b(oop obj) {
+   // Re-check whether the passed object is null. With ReferentBasedDiscovery the
+   // mutator may have changed the referent's value (i.e. cleared it) between the
+   // time the referent was determined to be potentially alive and calling this
+   // method.
    if (obj == NULL) {
      return false;
    }
    assert(_g1h->is_in_reserved(obj), "Trying to discover obj " PTR_FORMAT " not in heap", p2i(obj));
    return _g1h->heap_region_containing(obj)->is_old_or_humongous();