[heap] Concurrently free empty slot set buckets.

src/heap/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HEAP_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include <list>
 #include <memory>
 #include <unordered_set>
@@ skipping 435 matching lines @@
 
   size_t size() const { return size_; }
   void set_size(size_t size) { size_ = size; }
 
   inline Heap* heap() const { return heap_; }
 
   inline SkipList* skip_list() { return skip_list_; }
 
   inline void set_skip_list(SkipList* skip_list) { skip_list_ = skip_list; }
 
-  inline SlotSet* old_to_new_slots() { return old_to_new_slots_; }
+  inline SlotSet* old_to_new_slots() { return old_to_new_slots_.Value(); }
   inline SlotSet* old_to_old_slots() { return old_to_old_slots_; }
   inline TypedSlotSet* typed_old_to_new_slots() {
     return typed_old_to_new_slots_.Value();
   }
   inline TypedSlotSet* typed_old_to_old_slots() {
     return typed_old_to_old_slots_;
   }
   inline LocalArrayBufferTracker* local_tracker() { return local_tracker_; }
 
   V8_EXPORT_PRIVATE void AllocateOldToNewSlots();
@@ skipping 179 matching lines @@
   // Used by the incremental marker to keep track of the scanning progress in
   // large objects that have a progress bar and are scanned in increments.
   int progress_bar_;
 
   // Count of bytes marked black on page.
   int live_byte_count_;
 
   // A single slot set for small pages (of size kPageSize) or an array of slot
   // set for large pages. In the latter case the number of entries in the array
   // is ceil(size() / kPageSize).
-  SlotSet* old_to_new_slots_;
+  base::AtomicValue<SlotSet*> old_to_new_slots_;
   SlotSet* old_to_old_slots_;
   base::AtomicValue<TypedSlotSet*> typed_old_to_new_slots_;
   TypedSlotSet* typed_old_to_old_slots_;
 
   SkipList* skip_list_;
 
   intptr_t write_barrier_counter_;
 
   // Assuming the initial allocation on a page is sequential,
   // count highest number of bytes ever allocated on the page.
@@ skipping 2280 matching lines @@
   PageIterator old_iterator_;
   PageIterator code_iterator_;
   PageIterator map_iterator_;
   LargePageIterator lo_iterator_;
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_SPACES_H_