Mac 10.13 warning: 'OSMemoryBarrier' is deprecated

[tofutim]

Describe the issue

When compiling for Mac, a warning....

./port/atomic_pointer.h:55:3: warning: 'OSMemoryBarrier' is deprecated: first deprecated in macOS 10.12 - Use
      std::atomic_thread_fence() from <atomic> instead [-Wdeprecated-declarations]
  OSMemoryBarrier();
  ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.13.sdk/usr/include/libkern/OSAtomicDeprecated.h:749:9: note: 
      'OSMemoryBarrier' has been explicitly marked deprecated here
void    OSMemoryBarrier( void );

May also want to look here where they deal with it google/leveldb#422

Can you reliably reproduce the issue?

If so, please list the steps to reproduce below:

1. autogen
2. configure
3. make!

Expected behavior

No warnings...

Actual behavior

Warnings

Machine specs:

• OS: OSX 10.13

[Fuzzbawls]

need to see further up in your compile log

[sabhiram]

This is a warning that got patched into OSX 10.12 and above (I think), which nudges the user to move to std::atomic in place of the OSMemoryBarrier().

Fixing this needs some cross platform insight as it might affect different platforms differently.

[mochfauz]

no update ?

Found elsewhere (can't recall where), contributed en passant, prolly best published as a patch.

diff --git a/src/leveldb/port/atomic_pointer.h b/src/leveldb/port/atomic_pointer.h
index 9bf091f75..d1698ef30 100644
--- a/src/leveldb/port/atomic_pointer.h
+++ b/src/leveldb/port/atomic_pointer.h
@@ -52,7 +52,10 @@ namespace port {
 // Mac OS
 #elif defined(OS_MACOSX)
 inline void MemoryBarrier() {
-  OSMemoryBarrier();
+#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