From 905869ca1831211332e84f21913cc470957a95d8 Mon Sep 17 00:00:00 2001
From: Tor Egge <Tor.Egge@online.no>
Date: Sun, 5 Dec 2021 01:35:55 +0100
Subject: Ensure that moved b-tree node is visible for readers before updating
 reference in parent node.

---
 vespalib/src/vespa/vespalib/btree/btreeiterator.hpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/vespalib/src/vespa/vespalib/btree/btreeiterator.hpp b/vespalib/src/vespa/vespalib/btree/btreeiterator.hpp
index 2348e770e9d..042779f1b1b 100644
--- a/vespalib/src/vespa/vespalib/btree/btreeiterator.hpp
+++ b/vespalib/src/vespa/vespalib/btree/btreeiterator.hpp
@@ -983,6 +983,7 @@ moveFirstLeafNode(BTreeNode::Ref rootRef)
             InternalNodeTypeRefPair iPair = allocator.moveInternalNode(node);
             nodeRef = iPair.ref;
             node = iPair.data;
+            std::atomic_thread_fence(std::memory_order_release);
             pnode->setChild(0, nodeRef);
             moved = true;
         }
@@ -994,6 +995,7 @@ moveFirstLeafNode(BTreeNode::Ref rootRef)
         LeafNodeTypeRefPair
             lPair(allocator.moveLeafNode(_leaf.getNode()));
         _leaf.setNode(lPair.data);
+        std::atomic_thread_fence(std::memory_order_release);
         node->setChild(0, lPair.ref);
         moved = true;
     }
-- 
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