Fix data race in SamplingCircularQueue

src/circular-queue-inl.h

 // Copyright 2011 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 17 matching lines @@
 #ifndef V8_CIRCULAR_QUEUE_INL_H_
 #define V8_CIRCULAR_QUEUE_INL_H_
 
 #include "circular-queue.h"
 
 namespace v8 {
 namespace internal {
 
 
 void* SamplingCircularQueue::Enqueue() {
-  WrapPositionIfNeeded(&producer_pos_->enqueue_pos);
+  if (producer_pos_->enqueue_pos == producer_pos_->next_chunk_pos) {
+    if (producer_pos_->enqueue_pos == buffer_ + buffer_size_) {
+      producer_pos_->next_chunk_pos = buffer_;
+      producer_pos_->enqueue_pos = buffer_;
+    }
+    Acquire_Store(producer_pos_->next_chunk_pos, kEnqueueStarted);
+    // Skip marker.
+    producer_pos_->enqueue_pos += 1;
+    producer_pos_->next_chunk_pos += chunk_size_;
+  }
   void* result = producer_pos_->enqueue_pos;
   producer_pos_->enqueue_pos += record_size_;
   return result;
 }
 
 
 void SamplingCircularQueue::WrapPositionIfNeeded(
     SamplingCircularQueue::Cell** pos) {
-  if (**pos == kEnd) *pos = buffer_;
+  if (*pos == buffer_ + buffer_size_) *pos = buffer_;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_CIRCULAR_QUEUE_INL_H_