diff --git a/ixwebsocket/IXDNSLookup.cpp b/ixwebsocket/IXDNSLookup.cpp
index 5e922088..9bdd78c7 100644
--- a/ixwebsocket/IXDNSLookup.cpp
+++ b/ixwebsocket/IXDNSLookup.cpp
@@ -17,6 +17,7 @@ namespace ix
     std::atomic<uint64_t> DNSLookup::_nextId(0);
     std::set<uint64_t> DNSLookup::_activeJobs;
     std::mutex DNSLookup::_activeJobsMutex;
+    std::mutex DNSLookup::_resMutex;
 
     DNSLookup::DNSLookup(const std::string& hostname, int port, int64_t wait) :
         _hostname(hostname),
@@ -36,7 +37,8 @@ namespace ix
         _activeJobs.erase(_id);
     }
 
-    struct addrinfo* DNSLookup::getAddrInfo(const std::string& hostname,
+    // we want hostname to be copied, not passed as a const reference
+    struct addrinfo* DNSLookup::getAddrInfo(std::string hostname,
                                             int port,
                                             std::string& errMsg)
     {
@@ -135,6 +137,7 @@ namespace ix
             return nullptr;
         }
 
+        std::unique_lock<std::mutex> rlock(_resMutex);
         return _res;
     }
 
@@ -156,7 +159,10 @@ namespace ix
         }
 
         // Copy result into the member variables
-        _res = res;
+        {
+            std::unique_lock<std::mutex> rlock(_resMutex);
+            _res = res;
+        }
         _errMsg = errMsg;
         _condition.notify_one();
         _done = true;
diff --git a/ixwebsocket/IXDNSLookup.h b/ixwebsocket/IXDNSLookup.h
index 9c83c92d..28f5adcb 100644
--- a/ixwebsocket/IXDNSLookup.h
+++ b/ixwebsocket/IXDNSLookup.h
@@ -39,7 +39,7 @@ namespace ix
         struct addrinfo* resolveBlocking(std::string& errMsg,
                                          const CancellationRequest& isCancellationRequested);
 
-        static struct addrinfo* getAddrInfo(const std::string& hostname,
+        static struct addrinfo* getAddrInfo(std::string hostname,
                                             int port,
                                             std::string& errMsg);
 
@@ -50,6 +50,7 @@ namespace ix
         int64_t _wait;
         std::string _errMsg;
         struct addrinfo* _res;
+        static std::mutex _resMutex;
 
         std::atomic<bool> _done;
         std::thread _thread;
diff --git a/ixwebsocket/IXSocketServer.cpp b/ixwebsocket/IXSocketServer.cpp
index 40abbbba..f72f363e 100644
--- a/ixwebsocket/IXSocketServer.cpp
+++ b/ixwebsocket/IXSocketServer.cpp
@@ -144,8 +144,7 @@ namespace ix
     {
         while (true)
         {
-            closeTerminatedThreads();
-            if (_connectionsThreads.empty()) break;
+            if (closeTerminatedThreads()) break;
 
             // wait 10ms and try again later.
             // we could have a timeout, but if we exit of here
@@ -176,8 +175,9 @@ namespace ix
     // field becomes true, and we can use that to know that we can join that thread
     // and remove it from our _connectionsThreads data structure (a list).
     //
-    void SocketServer::closeTerminatedThreads()
+    bool SocketServer::closeTerminatedThreads()
     {
+        std::lock_guard<std::mutex> lock(_connectionsThreadsMutex);
         auto it = _connectionsThreads.begin();
         auto itEnd  = _connectionsThreads.end();
 
@@ -195,6 +195,8 @@ namespace ix
             if (thread.joinable()) thread.join();
             it = _connectionsThreads.erase(it);
         }
+
+        return _connectionsThreads.empty();
     }
 
     void SocketServer::run()
@@ -278,6 +280,7 @@ namespace ix
             if (_stop) return;
 
             // Launch the handleConnection work asynchronously in its own thread.
+            std::lock_guard<std::mutex> lock(_conditionVariableMutex);
             _connectionsThreads.push_back(std::make_pair(
                     connectionState,
                     std::thread(&SocketServer::handleConnection,
diff --git a/ixwebsocket/IXSocketServer.h b/ixwebsocket/IXSocketServer.h
index 79d2c153..d5dfb492 100644
--- a/ixwebsocket/IXSocketServer.h
+++ b/ixwebsocket/IXSocketServer.h
@@ -77,6 +77,7 @@ namespace ix
 
         // the list of (connectionState, threads) for each connections
         ConnectionThreads _connectionsThreads;
+        std::mutex _connectionsThreadsMutex;
 
         // used to have the main control thread for a server
         // wait for a 'terminate' notification without busy polling
@@ -92,6 +93,7 @@ namespace ix
                                       std::shared_ptr<ConnectionState> connectionState) = 0;
         virtual size_t getConnectedClientsCount() = 0;
 
-        void closeTerminatedThreads();
+        // Returns true if all connection threads are joined
+        bool closeTerminatedThreads();
     };
 }