fixed potential race condition

Garlic.cpp

@@ -650,6 +650,8 @@ namespace garlic
 			}
 		}
 		// delivery status sessions
+		{	
+			std::unique_lock<std::mutex> l(m_DeliveryStatusSessionsMutex);
 			for (auto it = m_DeliveryStatusSessions.begin (); it != m_DeliveryStatusSessions.end (); )
 			{
 				if (it->second->GetOwner () != this)
@@ -658,29 +660,38 @@ namespace garlic
 					++it;
 			}
 		}	
+	}
 
 	void GarlicDestination::RemoveDeliveryStatusSession (uint32_t msgID)
 	{
+		std::unique_lock<std::mutex> l(m_DeliveryStatusSessionsMutex);
 		m_DeliveryStatusSessions.erase (msgID);
 	}
 
 	void GarlicDestination::DeliveryStatusSent (GarlicRoutingSessionPtr session, uint32_t msgID)
 	{
+		std::unique_lock<std::mutex> l(m_DeliveryStatusSessionsMutex);
 		m_DeliveryStatusSessions[msgID] = session;
 	}
 
 	void GarlicDestination::HandleDeliveryStatusMessage (std::shared_ptr<I2NPMessage> msg)
 	{
 		uint32_t msgID = bufbe32toh (msg->GetPayload ());
+		GarlicRoutingSessionPtr session;
 		{
+			std::unique_lock<std::mutex> l(m_DeliveryStatusSessionsMutex);
 			auto it = m_DeliveryStatusSessions.find (msgID);
 			if (it != m_DeliveryStatusSessions.end ())
 			{
-				it->second->MessageConfirmed (msgID);
+				session = it->second;
 				m_DeliveryStatusSessions.erase (it);
-				LogPrint (eLogDebug, "Garlic: message ", msgID, " acknowledged");
 			}
 		}
+		if (session)
+		{
+			session->MessageConfirmed (msgID);
+			LogPrint (eLogDebug, "Garlic: message ", msgID, " acknowledged");
+		}
 	}
 
 	void GarlicDestination::SetLeaseSetUpdated ()

Garlic.h

@@ -195,6 +195,7 @@ namespace garlic
 			// incoming
 			std::map<SessionTag, std::shared_ptr<i2p::crypto::CBCDecryption>> m_Tags;
 			// DeliveryStatus
+			std::mutex m_DeliveryStatusSessionsMutex;
 			std::map<uint32_t, GarlicRoutingSessionPtr> m_DeliveryStatusSessions; // msgID -> session
 			
 		public: