Fix data race in SamplingCircularQueue

src/circular-queue-inl.h

Index: src/circular-queue-inl.h
diff --git a/src/circular-queue-inl.h b/src/circular-queue-inl.h
index 373bf6092a95f40e7aaa01bb835436b312bf2703..b48070ab5d24a064e4f8a91a72020e80d8f02954 100644
--- a/src/circular-queue-inl.h
+++ b/src/circular-queue-inl.h
@@ -35,7 +35,16 @@ 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;
@@ -44,7 +53,7 @@ void* SamplingCircularQueue::Enqueue() {
 
 void SamplingCircularQueue::WrapPositionIfNeeded(
     SamplingCircularQueue::Cell** pos) {
-  if (**pos == kEnd) *pos = buffer_;
+  if (*pos == buffer_ + buffer_size_) *pos = buffer_;
 }