Do not left-trim arrays when concurrent sweeping is active.

src/mark-compact.cc

 // 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 4068 matching lines @@
   FreeList* free_list = space == heap()->old_pointer_space()
                             ? free_list_old_pointer_space_.get()
                             : free_list_old_data_space_.get();
   FreeList private_free_list(space);
   while (it.has_next()) {
     Page* p = it.next();
 
     if (p->TryParallelSweeping()) {
       SweepConservatively<SWEEP_IN_PARALLEL>(space, &private_free_list, p);
       free_list->Concatenate(&private_free_list);
+      p->set_parallel_sweeping(MemoryChunk::PARALLEL_SWEEPING_FINALIZE);
     }
   }
 }
 
 
 void MarkCompactCollector::SweepSpace(PagedSpace* space, SweeperType sweeper) {
   space->set_was_swept_conservatively(sweeper == CONSERVATIVE ||
                                       sweeper == LAZY_CONSERVATIVE ||
                                       sweeper == PARALLEL_CONSERVATIVE ||
                                       sweeper == CONCURRENT_CONSERVATIVE);
@@ skipping 178 matching lines @@
 
   // Deallocate evacuated candidate pages.
   ReleaseEvacuationCandidates();
 }
 
 
 void MarkCompactCollector::ParallelSweepSpaceComplete(PagedSpace* space) {
   PageIterator it(space);
   while (it.has_next()) {
     Page* p = it.next();
-    if (p->parallel_sweeping() == MemoryChunk::PARALLEL_SWEEPING_IN_PROGRESS) {
+    if (p->parallel_sweeping() == MemoryChunk::PARALLEL_SWEEPING_FINALIZE) {
       p->set_parallel_sweeping(MemoryChunk::PARALLEL_SWEEPING_DONE);
       p->MarkSweptConservatively();
     }
+    ASSERT(p->parallel_sweeping() == MemoryChunk::PARALLEL_SWEEPING_DONE);
   }
 }
 
 
 void MarkCompactCollector::ParallelSweepSpacesComplete() {
   ParallelSweepSpaceComplete(heap()->old_pointer_space());
   ParallelSweepSpaceComplete(heap()->old_data_space());
 }
 
 
@@ skipping 217 matching lines @@
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 
 
 } }  // namespace v8::internal