Wait for concurrent unmapping tasks in GC prologue.

src/heap/mark-compact.cc

 // Copyright 2012 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.
 
 #include "src/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 532 matching lines @@
     SweepInParallel(heap()->paged_space(CODE_SPACE), 0);
     SweepInParallel(heap()->paged_space(MAP_SPACE), 0);
   }
 
   if (heap()->concurrent_sweeping_enabled()) {
     pending_sweeper_jobs_semaphore_.Wait();
     pending_sweeper_jobs_semaphore_.Wait();
     pending_sweeper_jobs_semaphore_.Wait();
   }
 
-  heap()->WaitUntilUnmappingOfFreeChunksCompleted();
-
   ParallelSweepSpacesComplete();
   sweeping_in_progress_ = false;
   RefillFreeList(heap()->paged_space(OLD_SPACE));
   RefillFreeList(heap()->paged_space(CODE_SPACE));
   RefillFreeList(heap()->paged_space(MAP_SPACE));
   heap()->paged_space(OLD_SPACE)->ResetUnsweptFreeBytes();
   heap()->paged_space(CODE_SPACE)->ResetUnsweptFreeBytes();
   heap()->paged_space(MAP_SPACE)->ResetUnsweptFreeBytes();
 
 #ifdef VERIFY_HEAP
@@ skipping 240 matching lines @@
   state_ = PREPARE_GC;
 #endif
 
   DCHECK(!FLAG_never_compact || !FLAG_always_compact);
 
   if (sweeping_in_progress()) {
     // Instead of waiting we could also abort the sweeper threads here.
     EnsureSweepingCompleted();
   }
 
+  // If concurrent unmapping tasks are still running, we should wait for
+  // them here.
+  heap()->WaitUntilUnmappingOfFreeChunksCompleted();
+
   // Clear marking bits if incremental marking is aborted.
   if (was_marked_incrementally_ && heap_->ShouldAbortIncrementalMarking()) {
     heap()->incremental_marking()->Stop();
     ClearMarkbits();
     AbortWeakCollections();
     AbortWeakCells();
     AbortCompaction();
     was_marked_incrementally_ = false;
   }
 
@@ skipping 3917 matching lines @@
   SlotsBuffer* buffer = *buffer_address;
   while (buffer != NULL) {
     SlotsBuffer* next_buffer = buffer->next();
     DeallocateBuffer(buffer);
     buffer = next_buffer;
   }
   *buffer_address = NULL;
 }
 }  // namespace internal
 }  // namespace v8