8028710: G1 does not retire allocation buffers after reference processing work

Summary: G1 does not retire allocation buffers after reference processing work when -XX:+ParallelRefProcEnabled is enabled. This causes wrong calculation of PLAB sizes, as the amount of space wasted is not updated correctly.
Reviewed-by: brutisso

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -4571,7 +4571,7 @@ HeapWord* G1CollectedHeap::par_allocate_during_gc(GCAllocPurpose purpose,
 }
 
 G1ParGCAllocBuffer::G1ParGCAllocBuffer(size_t gclab_word_size) :
-  ParGCAllocBuffer(gclab_word_size), _retired(false) { }
+  ParGCAllocBuffer(gclab_word_size), _retired(true) { }
 
 G1ParScanThreadState::G1ParScanThreadState(G1CollectedHeap* g1h, uint queue_num, ReferenceProcessor* rp)
   : _g1h(g1h),
@@ -4935,8 +4935,6 @@ void G1ParEvacuateFollowersClosure::do_void() {
       pss->trim_queue();
     }
   } while (!offer_termination());
-
-  pss->retire_alloc_buffers();
 }
 
 class G1KlassScanClosure : public KlassClosure {
@@ -5776,10 +5774,8 @@ void G1CollectedHeap::process_discovered_references(uint no_of_gc_workers) {
   }
 
   _gc_tracer_stw->report_gc_reference_stats(stats);
-  // We have completed copying any necessary live referent objects
-  // (that were not copied during the actual pause) so we can
-  // retire any active alloc buffers
-  pss.retire_alloc_buffers();
+
+  // We have completed copying any necessary live referent objects.
   assert(pss.refs()->is_empty(), "both queue and overflow should be empty");
 
   double ref_proc_time = os::elapsedTime() - ref_proc_start;

src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp

@@ -1691,15 +1691,19 @@ private:
 
 public:
   G1ParGCAllocBuffer(size_t gclab_word_size);
+  virtual ~G1ParGCAllocBuffer() {
+    guarantee(_retired, "Allocation buffer has not been retired");
+  }
 
-  void set_buf(HeapWord* buf) {
+  virtual void set_buf(HeapWord* buf) {
     ParGCAllocBuffer::set_buf(buf);
     _retired = false;
   }
 
-  void retire(bool end_of_gc, bool retain) {
-    if (_retired)
+  virtual void retire(bool end_of_gc, bool retain) {
+    if (_retired) {
       return;
+    }
     ParGCAllocBuffer::retire(end_of_gc, retain);
     _retired = true;
   }
@@ -1769,6 +1773,7 @@ public:
   G1ParScanThreadState(G1CollectedHeap* g1h, uint queue_num, ReferenceProcessor* rp);
 
   ~G1ParScanThreadState() {
+    retire_alloc_buffers();
     FREE_C_HEAP_ARRAY(size_t, _surviving_young_words_base, mtGC);
   }
 
@@ -1879,6 +1884,7 @@ public:
     return _surviving_young_words;
   }
 
+private:
   void retire_alloc_buffers() {
     for (int ap = 0; ap < GCAllocPurposeCount; ++ap) {
       size_t waste = _alloc_buffers[ap]->words_remaining();
@@ -1888,8 +1894,8 @@ public:
                                                  false /* retain */);
     }
   }
-private:
-  #define G1_PARTIAL_ARRAY_MASK 0x2
+
+#define G1_PARTIAL_ARRAY_MASK 0x2
 
   inline bool has_partial_array_mask(oop* ref) const {
     return ((uintptr_t)ref & G1_PARTIAL_ARRAY_MASK) == G1_PARTIAL_ARRAY_MASK;

src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp

@@ -60,6 +60,7 @@ public:
   // Initializes the buffer to be empty, but with the given "word_sz".
   // Must get initialized with "set_buf" for an allocation to succeed.
   ParGCAllocBuffer(size_t word_sz);
+  virtual ~ParGCAllocBuffer() {}
 
   static const size_t min_size() {
     return ThreadLocalAllocBuffer::min_size();
@@ -113,7 +114,7 @@ public:
   }
 
   // Sets the space of the buffer to be [buf, space+word_sz()).
-  void set_buf(HeapWord* buf) {
+  virtual void set_buf(HeapWord* buf) {
     _bottom   = buf;
     _top      = _bottom;
     _hard_end = _bottom + word_sz();
@@ -158,7 +159,7 @@ public:
   // Fills in the unallocated portion of the buffer with a garbage object.
   // If "end_of_gc" is TRUE, is after the last use in the GC.  IF "retain"
   // is true, attempt to re-use the unused portion in the next GC.
-  void retire(bool end_of_gc, bool retain);
+  virtual void retire(bool end_of_gc, bool retain);
 
   void print() PRODUCT_RETURN;
 };
@@ -238,14 +239,14 @@ public:
 
   void undo_allocation(HeapWord* obj, size_t word_sz);
 
-  void set_buf(HeapWord* buf_start) {
+  virtual void set_buf(HeapWord* buf_start) {
     ParGCAllocBuffer::set_buf(buf_start);
     _true_end = _hard_end;
     _bt.set_region(MemRegion(buf_start, word_sz()));
     _bt.initialize_threshold();
   }
 
-  void retire(bool end_of_gc, bool retain);
+  virtual void retire(bool end_of_gc, bool retain);
 
   MemRegion range() {
     return MemRegion(_top, _true_end);