From e919ecedfc18d1e2007711ddf2dc0f641f689528 Mon Sep 17 00:00:00 2001
From: sdong <siying.d@fb.com>
Date: Tue, 27 Jan 2015 13:57:44 -0800
Subject: [PATCH] SuperVersion::Unref() to use sequential consistency to
 decrease ref counting

Summary: I'm not sure the expected results of std::atomic::fetch_sub() when using memory_order_relaxed, and I suspect TSAN complains.

Test Plan: make all check

Reviewers: rven, yhchiang, igor

Reviewed By: igor

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D32259
---
 db/column_family.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/db/column_family.cc b/db/column_family.cc
index e6e75aad9..be01a2993 100644
--- a/db/column_family.cc
+++ b/db/column_family.cc
@@ -181,7 +181,7 @@ SuperVersion* SuperVersion::Ref() {
 
 bool SuperVersion::Unref() {
   // fetch_sub returns the previous value of ref
-  uint32_t previous_refs = refs.fetch_sub(1, std::memory_order_relaxed);
+  uint32_t previous_refs = refs.fetch_sub(1);
   assert(previous_refs > 0);
   return previous_refs == 1;
 }