Fix data race in v8::internal::UnboundQueue

src/unbound-queue-inl.h

 // Copyright 2010 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 50 matching lines @@
 
 template<typename Record>
 void UnboundQueue<Record>::DeleteFirst() {
   Node* tmp = first_;
   first_ = tmp->next;
   delete tmp;
 }
 
 
 template<typename Record>
-void UnboundQueue<Record>::Dequeue(Record* rec) {
-  ASSERT(divider_ != last_);
+bool UnboundQueue<Record>::Dequeue(Record* rec) {
+  if (divider_ == Acquire_Load(&last_)) return false;
   Node* next = reinterpret_cast<Node*>(divider_)->next;
   *rec = next->value;
   Release_Store(&divider_, reinterpret_cast<AtomicWord>(next));
+  return true;
 }
 
 
 template<typename Record>
 void UnboundQueue<Record>::Enqueue(const Record& rec) {
   Node*& next = reinterpret_cast<Node*>(last_)->next;
   next = new Node(rec);
   Release_Store(&last_, reinterpret_cast<AtomicWord>(next));
-  while (first_ != reinterpret_cast<Node*>(divider_)) DeleteFirst();
+
+  while (first_ != reinterpret_cast<Node*>(Acquire_Load(&divider_))) {
+    DeleteFirst();
+  }
 }
 
 
 template<typename Record>
-Record* UnboundQueue<Record>::Peek() {
-  ASSERT(divider_ != last_);
+bool UnboundQueue<Record>::IsEmpty() const {
+  return NoBarrier_Load(&divider_) == NoBarrier_Load(&last_);
+}
+
+
+template<typename Record>
+Record* UnboundQueue<Record>::Peek() const {
+  if (divider_ == Acquire_Load(&last_)) return NULL;
   Node* next = reinterpret_cast<Node*>(divider_)->next;
   return &next->value;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_UNBOUND_QUEUE_INL_H_