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bind backend: pthread_mutex_t should be inited and destroyed and not be copied #8350

To make our live easier, use a native C++ mutex.

Fixes #8161

https://github.com/PowerDNS/pdns/pull/8350

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--- modules/bindbackend/bindbackend2.cc.orig	2019-11-29 15:11:44 UTC

+++ modules/bindbackend/bindbackend2.cc

@@ -80,6 +80,9 @@ pthread_mutex_t Bind2Backend::s_supermaster_config_loc

 pthread_mutex_t Bind2Backend::s_startup_lock=PTHREAD_MUTEX_INITIALIZER;

 string Bind2Backend::s_binddirectory;  

+template <typename T>

+std::mutex LookButDontTouch<T>::s_lock;

+

 BB2DomainInfo::BB2DomainInfo()

 {

   d_loaded=false;

--- modules/bindbackend/bindbackend2.hh.orig	2019-11-29 15:11:44 UTC

+++ modules/bindbackend/bindbackend2.hh

@@ -29,6 +29,7 @@

 #include <pthread.h>

 #include <time.h>

 #include <fstream>

+#include <mutex>

 #include <boost/utility.hpp>

 #include <boost/tuple/tuple.hpp>

@@ -103,22 +104,18 @@ template <typename T>

 class LookButDontTouch //  : public boost::noncopyable

 {

 public:

-  LookButDontTouch() 

+  LookButDontTouch()

   {

-    pthread_mutex_init(&d_lock, 0);

-    pthread_mutex_init(&d_swaplock, 0);

   }

   LookButDontTouch(shared_ptr<T> records) : d_records(records)

   {

-    pthread_mutex_init(&d_lock, 0);

-    pthread_mutex_init(&d_swaplock, 0);

   }

   shared_ptr<const T> get()

   {

     shared_ptr<const T> ret;

     {

-      Lock l(&d_lock);

+      std::lock_guard<std::mutex> lock(s_lock);

       ret = d_records;

     }

     return ret;

@@ -128,22 +125,14 @@ class LookButDontTouch //  : public boost::noncopyable

   {

     shared_ptr<T> ret;

     {

-      Lock l(&d_lock);

+      std::lock_guard<std::mutex> lock(s_lock);

       ret = d_records;

     }

     return ret;

   }

-

-  void swap(shared_ptr<T> records)

-  {

-    Lock l(&d_lock);

-    Lock l2(&d_swaplock);

-    d_records.swap(records);

-  }

-  pthread_mutex_t d_lock;

-  pthread_mutex_t d_swaplock;

 private:

+  static std::mutex s_lock;

   shared_ptr<T> d_records;

 };