From: Remi Gacogne <remi.gacogne@powerdns.com>
Date: Tue, 1 Aug 2017 08:39:16 +0000 (+0200)
Subject: rec: Guard `registerAllStats()` with an atomic flag instead of a bool
X-Git-Tag: auth-4.1.0-rc1~8^2
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F5567%2Fhead;p=thirdparty%2Fpdns.git

rec: Guard `registerAllStats()` with an atomic flag instead of a bool

Unlikely as it seems, I just got hit by a race where three threads
were trying to register the stats at the same time, causing my
starting recursor to stay stuck while consuming a lot of CPU.
---

diff --git a/pdns/rec_channel_rec.cc b/pdns/rec_channel_rec.cc
index 2d086f1ed4..e79dd250e7 100644
--- a/pdns/rec_channel_rec.cc
+++ b/pdns/rec_channel_rec.cc
@@ -775,10 +775,9 @@ extern ResponseStats g_rs;
 
 void registerAllStats()
 {
-  static bool s_init = false;
-  if(s_init)
+  static std::atomic_flag s_init = ATOMIC_FLAG_INIT;
+  if(s_init.test_and_set())
     return;
-  s_init=true;
 
   addGetStat("questions", &g_stats.qcounter);
   addGetStat("ipv6-questions", &g_stats.ipv6qcounter);