From e214d500b82ce0ac82f1880dc1dc54c244329bee Mon Sep 17 00:00:00 2001
From: Romain Geissler <romain.geissler@amadeus.com>
Date: Thu, 8 Dec 2022 16:00:14 +0000
Subject: [PATCH] Use std::atomic::fetch_add in modern C++.

---
 core/src/gauge.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/core/src/gauge.cc b/core/src/gauge.cc
index 251fba27..a52d103a 100644
--- a/core/src/gauge.cc
+++ b/core/src/gauge.cc
@@ -17,11 +17,16 @@ void Gauge::Decrement(const double value) { Change(-1.0 * value); }
 void Gauge::Set(const double value) { value_.store(value); }
 
 void Gauge::Change(const double value) {
-  // C++ 20 will add std::atomic::fetch_add support for floating point types
+#if __cpp_lib_atomic_float >= 201711L
+  value_.fetch_add(value);
+#else
+  // Pre-C++ 20 fallback: busy loop (which might be more expansive than using
+  // fetch_add).
   auto current = value_.load();
   while (!value_.compare_exchange_weak(current, current + value)) {
     // intentionally empty block
   }
+#endif
 }
 
 void Gauge::SetToCurrentTime() {