Introduce --job-based-sweeping flag and use individual jobs for sweeping if set

src/mark-compact.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 726 matching lines @@
 
   // Mark the global table which maps weak objects to dependent code without
   // marking its contents.
   void MarkWeakObjectToCodeTable();
 
   // Special case for processing weak references in a full collection. We need
   // to artifically keep AllocationSites alive for a time.
   void MarkAllocationSite(AllocationSite* site);
 
  private:
+  class SweeperTask;
+
   explicit MarkCompactCollector(Heap* heap);
   ~MarkCompactCollector();
 
   bool MarkInvalidatedCode();
   bool WillBeDeoptimized(Code* code);
   void RemoveDeadInvalidatedCode();
   void ProcessInvalidatedCode(ObjectVisitor* visitor);
 
   void UnlinkEvacuationCandidates();
   void ReleaseEvacuationCandidates();
@@ skipping 27 matching lines @@
 
   // True if we are collecting slots to perform evacuation from evacuation
   // candidates.
   bool compacting_;
 
   bool was_marked_incrementally_;
 
   // True if concurrent or parallel sweeping is currently in progress.
   bool sweeping_pending_;
 
+  Semaphore pending_sweeper_jobs_semaphore_;
+
   bool sequential_sweeping_;
 
   // A pointer to the current stack-allocated GC tracer object during a full
   // collection (NULL before and after).
   GCTracer* tracer_;
 
   SlotsBufferAllocator slots_buffer_allocator_;
 
   SlotsBuffer* migration_slots_buffer_;
 
@@ skipping 218 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 
 } }  // namespace v8::internal
 
 #endif  // V8_MARK_COMPACT_H_