From 4710e1f93dacca4898d6a3f69e4e36ed34c51b0f Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Mon, 23 Jul 2018 15:44:05 +0200
Subject: [PATCH] Fix the conflict between <CGAL/atomic.h> and <CGAL/thread.h>

Before this commit, they were both defining
`CGAL::cpp11::atomic`. Now, `<CGAL/thread.h>` includes
`<CGAL/atomic.h>`, and it only defined `CGAL::cpp11::atomic`, using
the TBB implementation, if `CGAL_NO_ATOMIC` was defined by
`<CGAL/atomic.h>`.

@sgiraudot Please have a look.
---
 STL_Extension/include/CGAL/thread.h | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/STL_Extension/include/CGAL/thread.h b/STL_Extension/include/CGAL/thread.h
index a777d7e7286..737105e1a8b 100644
--- a/STL_Extension/include/CGAL/thread.h
+++ b/STL_Extension/include/CGAL/thread.h
@@ -55,10 +55,11 @@
 
 #if !CGAL_USE_TBB_THREADS
 #  include <thread>
-#  include <atomic>
 #  include <chrono>
 #endif
 
+#include <CGAL/atomic.h> // for CGAL::cpp11::atomic
+
 namespace CGAL {
 
 namespace cpp11 {
@@ -66,7 +67,6 @@ namespace cpp11 {
 #if CGAL_USE_TBB_THREADS
   
   using std::thread; // std::thread is declared by TBB if TBB_IMPLEMENT_CPP0X == 1
-  using tbb::atomic;
 
   inline void sleep_for (double seconds)
   {
@@ -75,10 +75,9 @@ namespace cpp11 {
     std::this_thread::sleep_for(tbb::tick_count::interval_t(seconds));
   }
   
-#else
+#else // C++11 implementation
 
   using std::thread;
-  using std::atomic;
 
   inline void sleep_for (double seconds)
   {
@@ -91,6 +90,12 @@ namespace cpp11 {
 
 #endif
 
+#if defined(CGAL_NO_ATOMIC) && defined(CGAL_LINKED_WITH_TBB)
+  // If <CGAL/atomic.h> did not defined CGAL::cpp11::atomic, then use
+  // tbb::atomic as a fallback.
+  using tbb::atomic;
+#endif
+
 } // cpp11