From 30b6bce74ee98480b72d4a23328c0b30c28b4566 Mon Sep 17 00:00:00 2001
From: Henning Baldersheim <balder@yahoo-inc.com>
Date: Thu, 2 Apr 2020 13:58:37 +0000
Subject: Improve thread visibility.

---
 vespalib/src/vespa/vespalib/util/gencnt.cpp | 2 +-
 vespalib/src/vespa/vespalib/util/gencnt.h   | 9 +++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/vespalib/src/vespa/vespalib/util/gencnt.cpp b/vespalib/src/vespa/vespalib/util/gencnt.cpp
index 5adbf14a757..ad82cf2e67c 100644
--- a/vespalib/src/vespa/vespalib/util/gencnt.cpp
+++ b/vespalib/src/vespa/vespalib/util/gencnt.cpp
@@ -58,7 +58,7 @@ GenCnt::distance(const GenCnt &other) const
 GenCnt &
 GenCnt::operator=(const GenCnt &src)
 {
-    _val = src._val;
+    _val = src.getAsInt();
     return *this;
 }
 
diff --git a/vespalib/src/vespa/vespalib/util/gencnt.h b/vespalib/src/vespa/vespalib/util/gencnt.h
index 7bfc5a7e49b..cac868a8adb 100644
--- a/vespalib/src/vespa/vespalib/util/gencnt.h
+++ b/vespalib/src/vespa/vespalib/util/gencnt.h
@@ -2,6 +2,7 @@
 #pragma once
 
 #include <cstdint>
+#include <atomic>
 
 namespace vespalib {
 
@@ -16,7 +17,7 @@ namespace vespalib {
 class GenCnt
 {
 private:
-    uint32_t _val;
+    std::atomic<uint32_t> _val;
 public:
 
     /**
@@ -31,12 +32,12 @@ public:
      **/
     GenCnt(uint32_t val) : _val(val) {}
 
-    GenCnt(const GenCnt &rhs) = default;
+    GenCnt(const GenCnt &rhs) : _val(rhs.getAsInt()) {}
 
     /**
      * @brief empty destructor
      **/
-    ~GenCnt() {}
+    ~GenCnt() = default;
 
     /**
      * @brief Increase the generation count held by this object
@@ -95,7 +96,7 @@ public:
      *
      * @return generation counter
      **/
-    uint32_t getAsInt() const { return _val; }
+    uint32_t getAsInt() const { return _val.load(std::memory_order_relaxed); }
 
     /**
      * @brief Set the generation counter from an integer
-- 
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