From 006adf321ad4af7b1681e617c73308c5b4e811c4 Mon Sep 17 00:00:00 2001
From: Otto Moerbeek <otto.moerbeek@open-xchange.com>
Date: Fri, 10 May 2019 13:45:00 +0200
Subject: [PATCH] Minimal fix to avoid busy looping. The condition_variable
 varant showed spurious failures on travis so go for the minimial fix.

---
 pdns/communicator.cc       | 24 +++++++++++++++---------
 pdns/communicator.hh       |  4 +---
 pdns/mastercommunicator.cc |  2 +-
 pdns/slavecommunicator.cc  |  4 ++--
 4 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/pdns/communicator.cc b/pdns/communicator.cc
index 836f07e59..be8af6172 100644
--- a/pdns/communicator.cc
+++ b/pdns/communicator.cc
@@ -113,21 +113,24 @@ void CommunicatorClass::mainloop(void)
     d_tickinterval=::arg().asNum("slave-cycle-interval");
     makeNotifySockets();
 
+    int rc;
+    time_t next, tick;
+
     for(;;) {
       slaveRefresh(&P);
       masterUpdateCheck(&P);
+      tick=doNotifications(); // this processes any notification acknowledgements and actually send out our own notifications
+      
+      tick = min (tick, d_tickinterval); 
+      
+      next=time(0)+tick;
 
-      time_t tick = doNotifications(); // this processes any notification acknowledgements and actually send out our own notifications
-      tick = min(tick, d_tickinterval);
-      time_t next = time(0) + tick;
-
-      while (time(0) < next) {
-        std::unique_lock<std::mutex> lk(d_any_mutex);
-        auto rc = d_any_condvar.wait_for(lk, std::chrono::seconds(1));
-        lk.unlock();
+      while(time(0) < next) {
+        rc=d_any_sem.tryWait();
 
-        if (rc == std::cv_status::timeout) {
+        if(rc) {
           bool extraSlaveRefresh = false;
+          Utility::sleep(1);
           {
             Lock l(&d_lock);
             if (d_tocheck.size())
@@ -137,6 +140,9 @@ void CommunicatorClass::mainloop(void)
             slaveRefresh(&P);
         }
         else {
+          // eat up extra posts to avoid busy looping if many posts were done
+          while (d_any_sem.tryWait() == 0) {
+          }
           break; // something happened
         }
         // this gets executed at least once every second
diff --git a/pdns/communicator.hh b/pdns/communicator.hh
index d7d7178a7..c63534dc2 100644
--- a/pdns/communicator.hh
+++ b/pdns/communicator.hh
@@ -25,7 +25,6 @@
 #include <pthread.h>
 #include <string>
 #include <semaphore.h>
-#include <condition_variable>
 #include <queue>
 #include <list>
 #include <limits>
@@ -206,8 +205,7 @@ private:
   set<DNSName> d_inprogress;
   
   Semaphore d_suck_sem;
-  std::condition_variable d_any_condvar;
-  std::mutex d_any_mutex;
+  Semaphore d_any_sem;
   time_t d_tickinterval;
   set<DomainInfo> d_tocheck;
   struct cmp {
diff --git a/pdns/mastercommunicator.cc b/pdns/mastercommunicator.cc
index 5d6c97459..048034749 100644
--- a/pdns/mastercommunicator.cc
+++ b/pdns/mastercommunicator.cc
@@ -303,5 +303,5 @@ void CommunicatorClass::makeNotifySockets()
 void CommunicatorClass::notify(const DNSName &domain, const string &ip)
 {
   d_nq.add(domain, ip);
-  d_any_condvar.notify_one();
+  d_any_sem.post();
 }
diff --git a/pdns/slavecommunicator.cc b/pdns/slavecommunicator.cc
index 50cf01c0b..190488faf 100644
--- a/pdns/slavecommunicator.cc
+++ b/pdns/slavecommunicator.cc
@@ -727,7 +727,7 @@ void CommunicatorClass::addSlaveCheckRequest(const DomainInfo& di, const ComboAd
   }
   d_tocheck.erase(di);
   d_tocheck.insert(ours);
-  d_any_condvar.notify_one(); // kick the loop!
+  d_any_sem.post(); // kick the loop!
 }
 
 void CommunicatorClass::addTrySuperMasterRequest(DNSPacket *p)
@@ -735,7 +735,7 @@ void CommunicatorClass::addTrySuperMasterRequest(DNSPacket *p)
   Lock l(&d_lock);
   DNSPacket ours = *p;
   if(d_potentialsupermasters.insert(ours).second)
-    d_any_condvar.notify_one(); // kick the loop!
+    d_any_sem.post(); // kick the loop!
 }
 
 void CommunicatorClass::slaveRefresh(PacketHandler *P)
-- 
2.40.0