From 594cc987af2e0af6417c4ac2b947ee8cdad59e5e Mon Sep 17 00:00:00 2001
From: costan <costan@google.com>
Date: Fri, 9 Mar 2018 16:10:08 -0800
Subject: [PATCH] Bypass OSMemoryBarrier() warning on Mac.

This is a stopgap for removing warnings on Mac builds, so -Werror can be
turned on. C++11 will be required in the nearby future, which guarantees
<atomic> support. Once that happens, the simplified version of this will
match https://github.com/google/leveldb/pull/503

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=188553251
---
 port/atomic_pointer.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/port/atomic_pointer.h b/port/atomic_pointer.h
index 54f0885..43dab2a 100644
--- a/port/atomic_pointer.h
+++ b/port/atomic_pointer.h
@@ -21,13 +21,12 @@
 #include <stdint.h>
 #ifdef LEVELDB_ATOMIC_PRESENT
 #include <atomic>
+#elif defined(__APPLE__)
+#include <libkern/OSAtomic.h>
 #endif
 #ifdef OS_WIN
 #include <windows.h>
 #endif
-#ifdef __APPLE__
-#include <libkern/OSAtomic.h>
-#endif
 
 #if defined(_M_X64) || defined(__x86_64__)
 #define ARCH_CPU_X86_FAMILY 1
@@ -56,7 +55,11 @@ namespace port {
 // Mac OS
 #elif defined(__APPLE__)
 inline void MemoryBarrier() {
+#if defined(LEVELDB_ATOMIC_PRESENT)
+  std::atomic_thread_fence(std::memory_order_seq_cst);
+#else
   OSMemoryBarrier();
+#endif  // defined(LEVELDB_ATOMIC_PRESENT)
 }
 #define LEVELDB_HAVE_MEMORY_BARRIER