src/hotspot/share/oops/oop.inline.hpp

*** 81,21 ***
  markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
    return AtomicAccess::cmpxchg(&_mark, old_mark, new_mark, order);
  }
  
  markWord oopDesc::prototype_mark() const {
!   if (UseCompactObjectHeaders) {
      return klass()->prototype_header();
    } else {
      return markWord::prototype();
    }
  }
  
  void oopDesc::init_mark() {
    set_mark(prototype_mark());
  }
  
  Klass* oopDesc::klass() const {
    switch (ObjLayout::klass_mode()) {
      case ObjLayout::Compact:
        return mark().klass();
      case ObjLayout::Compressed:
--- 81,34 ---
  markWord oopDesc::cas_set_mark(markWord new_mark, markWord old_mark, atomic_memory_order order) {
    return AtomicAccess::cmpxchg(&_mark, old_mark, new_mark, order);
  }
  
  markWord oopDesc::prototype_mark() const {
!   if (UseCompactObjectHeaders || EnableValhalla) {
      return klass()->prototype_header();
    } else {
      return markWord::prototype();
    }
  }
  
  void oopDesc::init_mark() {
    set_mark(prototype_mark());
  }
  
+ // This is specifically for Parallel GC. The other collectors need klass()->prototype_header()
+ // even without using Compact Object Headers. The issue is that this operation is unsafe
+ // using Parallel, as there are multiple concurrent GC workers that could access it.
+ // In practice, this has lead to relatively frequent crashes.
+ // More work needs to be done in the future to consolidate reinit_mark with init_mark.
+ void oopDesc::reinit_mark() {
+   if (UseCompactObjectHeaders) {
+     set_mark(klass()->prototype_header());
+   } else {
+     set_mark(markWord::prototype());
+   }
+ }
+ 
  Klass* oopDesc::klass() const {
    switch (ObjLayout::klass_mode()) {
      case ObjLayout::Compact:
        return mark().klass();
      case ObjLayout::Compressed:

*** 238,11 ***
--- 251,28 ---
  bool oopDesc::is_instance()    const { return klass()->is_instance_klass();             }
  bool oopDesc::is_instanceRef() const { return klass()->is_reference_instance_klass();   }
  bool oopDesc::is_stackChunk()  const { return klass()->is_stack_chunk_instance_klass(); }
  bool oopDesc::is_array()       const { return klass()->is_array_klass();                }
  bool oopDesc::is_objArray()    const { return klass()->is_objArray_klass();             }
+ bool oopDesc::is_refArray()    const { return klass()->is_refArray_klass();             }
  bool oopDesc::is_typeArray()   const { return klass()->is_typeArray_klass();            }
+ bool oopDesc::is_refined_objArray() const { return klass()->is_refined_objArray_klass(); }
+ 
+ bool oopDesc::is_inline_type() const { return mark().is_inline_type(); }
+ #ifdef _LP64
+ bool oopDesc::is_flatArray() const {
+   markWord mrk = mark();
+   return (mrk.is_unlocked()) ? mrk.is_flat_array() : klass()->is_flatArray_klass();
+ }
+ bool oopDesc::is_null_free_array() const {
+   markWord mrk = mark();
+   return (mrk.is_unlocked()) ? mrk.is_null_free_array() : klass()->is_null_free_array_klass();
+ }
+ #else
+ bool oopDesc::is_flatArray()       const { return klass()->is_flatArray_klass(); }
+ bool oopDesc::is_null_free_array() const { return klass()->is_null_free_array_klass(); }
+ #endif
  
  template<typename T>
  T*       oopDesc::field_addr(int offset)     const { return reinterpret_cast<T*>(cast_from_oop<intptr_t>(as_oop()) + offset); }
  
  template <typename T>