8259862: MutableSpace's end should be atomic

Make _end volatile and use atomic access

Reviewed-by: ayang, tschatzl

Author: Kim Barrett

src/hotspot/share/gc/parallel/mutableSpace.hpp

@@ -28,6 +28,7 @@
 #include "memory/allocation.hpp"
 #include "memory/iterator.hpp"
 #include "memory/memRegion.hpp"
+#include "runtime/atomic.hpp"
 #include "utilities/copy.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/macros.hpp"
@@ -42,9 +43,6 @@ class WorkGang;
 // page allocation time by having the memory pretouched (with
 // AlwaysPretouch) and for optimizing page placement on NUMA systems
 // by make the underlying region interleaved (with UseNUMA).
-//
-// Invariant: bottom() <= top() <= end()
-// top() and end() are exclusive.
 
 class MutableSpaceMangler;
 
@@ -56,9 +54,11 @@ class MutableSpace: public CHeapObj<mtGC> {
   // The last region which page had been setup to be interleaved.
   MemRegion _last_setup_region;
   size_t _alignment;
-  HeapWord* _bottom;
-  HeapWord* volatile _top;
-  HeapWord* _end;
+  // Supports CAS-based allocation.
+  // Invariant: bottom() <= top() <= end()
+  HeapWord* _bottom;            // Start of the region.
+  HeapWord* volatile _top;      // Current allocation pointer.
+  HeapWord* volatile _end;      // Current allocation limit.  expand() advances.
 
   MutableSpaceMangler* mangler() { return _mangler; }
 
@@ -67,21 +67,22 @@ class MutableSpace: public CHeapObj<mtGC> {
   void set_last_setup_region(MemRegion mr) { _last_setup_region = mr;   }
   MemRegion last_setup_region() const      { return _last_setup_region; }
 
+ protected:
+  HeapWord* volatile* top_addr()           { return &_top; }
+  HeapWord* volatile* end_addr()           { return &_end; }
+
  public:
   virtual ~MutableSpace();
   MutableSpace(size_t page_size);
 
   // Accessors
   HeapWord* bottom() const                 { return _bottom; }
-  HeapWord* top() const                    { return _top;    }
-  HeapWord* end() const                    { return _end; }
+  HeapWord* top() const                    { return Atomic::load(&_top); }
+  HeapWord* end() const                    { return Atomic::load(&_end); }
 
   void set_bottom(HeapWord* value)         { _bottom = value; }
-  virtual void set_top(HeapWord* value)    { _top = value;   }
-  void set_end(HeapWord* value)            { _end = value; }
-
-  HeapWord* volatile* top_addr()           { return &_top; }
-  HeapWord** end_addr()                    { return &_end; }
+  virtual void set_top(HeapWord* value)    { Atomic::store(&_top, value); }
+  void set_end(HeapWord* value)            { Atomic::store(&_end, value); }
 
   size_t alignment()                       { return _alignment; }
 

src/hotspot/share/gc/parallel/parallelScavengeHeap.hpp

@@ -200,9 +200,6 @@ class ParallelScavengeHeap : public CollectedHeap {
 
   bool supports_inline_contig_alloc() const { return !UseNUMA; }
 
-  HeapWord* volatile* top_addr() const { return !UseNUMA ? young_gen()->top_addr() : (HeapWord* volatile*)-1; }
-  HeapWord** end_addr() const { return !UseNUMA ? young_gen()->end_addr() : (HeapWord**)-1; }
-
   void ensure_parsability(bool retire_tlabs);
   void resize_all_tlabs();
 

src/hotspot/share/gc/parallel/psYoungGen.hpp

@@ -133,9 +133,6 @@ class PSYoungGen : public CHeapObj<mtGC> {
     return result;
   }
 
-  HeapWord* volatile* top_addr() const   { return eden_space()->top_addr(); }
-  HeapWord** end_addr() const   { return eden_space()->end_addr(); }
-
   // Iteration.
   void oop_iterate(OopIterateClosure* cl);
   void object_iterate(ObjectClosure* cl);

src/hotspot/share/gc/parallel/vmStructs_parallelgc.hpp

@@ -46,7 +46,7 @@
   nonstatic_field(PSVirtualSpace,              _committed_high_addr,                          char*)                                 \
                                                                                                                                      \
   nonstatic_field(MutableSpace,                _bottom,                                       HeapWord*)                             \
-  nonstatic_field(MutableSpace,                _end,                                          HeapWord*)                             \
+  volatile_nonstatic_field(MutableSpace,       _end,                                          HeapWord*)                             \
   volatile_nonstatic_field(MutableSpace,       _top,                                          HeapWord*)                             \
                                                                                                                                      \
   nonstatic_field(PSYoungGen,                  _reserved,                                     MemRegion)                             \