use a write lock for sync so it can be recursive

libraries/networking/src/udt/Connection.cpp

@@ -146,6 +146,9 @@ void Connection::sync() {
         auto sinceLastReceive = duration_cast<microseconds>(high_resolution_clock::now() - _lastReceiveTime);
         
         if (sinceLastReceive.count() >= NUM_TIMEOUTS_FOR_EXPIRY * estimatedTimeout()) {
+            qDebug() << "Connection to" << _destination << "has not received any new data for"
+                 << NUM_TIMEOUTS_FOR_EXPIRY << "timeouts. It is now considered inactive and will be cleaned up.";
+            
             // connection inactive - emit a signal so we will be cleaned up
             emit connectionInactive(_destination);
             

libraries/networking/src/udt/Socket.cpp

@@ -254,14 +254,14 @@ void Socket::connectToSendSignal(const HifiSockAddr& destinationAddr, QObject* r
 
 void Socket::rateControlSync() {
     
-    QReadLocker readLocker(&_connectionsMutex);
+    QWriteLocker writeLocker(&_connectionsMutex);
     
     // enumerate our list of connections and ask each of them to send off periodic ACK packet for rate control
     for (auto& connection : _connectionsHash) {
         connection.second->sync();
     }
     
-    readLocker.unlock();
+    writeLocker.unlock();
     
     if (_synTimer.interval() != _synInterval) {
         // if the _synTimer interval doesn't match the current _synInterval (changes when the CC factory is changed)

libraries/networking/src/udt/Socket.h

@@ -94,7 +94,7 @@ private:
     std::unordered_map<HifiSockAddr, SequenceNumber> _unreliableSequenceNumbers;
     std::unordered_map<HifiSockAddr, std::unique_ptr<Connection>> _connectionsHash;
     
-    QReadWriteLock _connectionsMutex; // guards concurrent access to connections hashs
+    QReadWriteLock _connectionsMutex { QReadWriteLock::Recursive }; // guards concurrent access to connections hashs
     
     int _synInterval = 10; // 10ms
     QTimer _synTimer;