Do not dereference handles during relocation.

src/heap.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
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@@ skipping 1838 matching lines @@
       } else if (type == FIXED_ARRAY_TYPE) {
         ASSERT(sub_type <= LAST_FIXED_ARRAY_SUB_TYPE);
         object_counts_[FIRST_FIXED_ARRAY_SUB_TYPE + sub_type]++;
         object_sizes_[FIRST_FIXED_ARRAY_SUB_TYPE + sub_type] += size;
       }
     }
   }
 
   void CheckpointObjectStats();
 
+  // We don't use a ScopedLock here since we want to lock the heap
+  // only when FLAG_parallel_recompilation is true.
+  class RelocationLock {
+   public:
+    explicit RelocationLock(Heap* heap);
+
+    ~RelocationLock() {
+      if (FLAG_parallel_recompilation) {
+#ifdef DEBUG
+        heap_->relocation_mutex_locked_by_optimizer_thread_ = false;

[Hannes Payer (out of office), 2013/04/26 07:27:47]

Just set it to false if the destructor is called by the optimizing compiler
thread.

+#endif  // DEBUG
+        heap_->relocation_mutex_->Unlock();
+      }
+    }
+
+#ifdef DEBUG
+    static bool IsLockedByOptimizerThread(Heap* heap) {

[Hannes Payer (out of office), 2013/04/26 07:27:47]

I think you may want to avoid static methods since there may be multiple
optimizing compiler threads per process.

+      return heap->relocation_mutex_locked_by_optimizer_thread_;
+    }
+#endif  // DEBUG
+
+   private:
+    Heap* heap_;
+  };
+
  private:
   Heap();
 
   // This can be calculated directly from a pointer to the heap; however, it is
   // more expedient to get at the isolate directly from within Heap methods.
   Isolate* isolate_;
 
   Object* roots_[kRootListLength];
 
   intptr_t code_range_size_;
@@ skipping 454 matching lines @@
   bool configured_;
 
   ExternalStringTable external_string_table_;
 
   ErrorObjectList error_object_list_;
 
   VisitorDispatchTable<ScavengingCallback> scavenging_visitors_table_;
 
   MemoryChunk* chunks_queued_for_free_;
 
+  Mutex* relocation_mutex_;
+#ifdef DEBUG
+  bool relocation_mutex_locked_by_optimizer_thread_;
+#endif  // DEBUG;
+
   friend class Factory;
   friend class GCTracer;
   friend class DisallowAllocationFailure;
   friend class AlwaysAllocateScope;
   friend class Page;
   friend class Isolate;
   friend class MarkCompactCollector;
   friend class MarkCompactMarkingVisitor;
   friend class MapCompact;
 #ifdef VERIFY_HEAP
@@ skipping 685 matching lines @@
   AssertNoAllocation no_alloc;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_