Working with m_TransferMap has become thread-safe.

src/TransferImpl.cpp

@@ -109,7 +109,7 @@ void LibUSB::TransferImpl::Start()
 	}
 
 	// 3. Ensure that the callback can reach this transfer.
-	m_TransferMap.insert(make_pair(this, shared_from_this()));
+	InsertTransfer(make_pair(this, shared_from_this()));
 
 	// 4. Submit the transfer
 	int Result = libusb_submit_transfer(m_pTransfer.get());
@@ -225,7 +225,8 @@ void LibUSB::TransferImpl::AsyncTransferCallback( libusb_transfer* pTransfer )
 	TransferImpl* index = (TransferImpl*) pTransfer->user_data;
 
 	/// Obtain the transfer's shared_ptr
-	m_TransferMap[index].lock()->NotifyComplete();
+	auto transfer = GetTransfer(index);
+	transfer.lock()->NotifyComplete();
 
 
 }
@@ -248,7 +249,7 @@ void LibUSB::TransferImpl::NotifyComplete()
 
 
 	// Remove the TransferMap entry.
-	m_TransferMap.erase(this);
+	EraseTransfer(this);
 }
 
 void LibUSB::TransferImpl::Reset()
@@ -462,7 +463,8 @@ LibUSB::TransferResult_t LibUSB::TransferImpl::Result() const
 }
 
 
-std::map<LibUSB::TransferImpl*, std::weak_ptr<LibUSB::TransferImpl>> LibUSB::TransferImpl::m_TransferMap;
+LibUSB::TransferImpl::TransferStorage LibUSB::TransferImpl::m_TransferMap;
+std::mutex LibUSB::TransferImpl::m_TransferMap_mutex;
 
 
 // **********************************

src/TransferImpl.hpp

@@ -137,9 +137,29 @@ namespace LibUSB
 
 	private:
 
-
 		/// Weak pointers to all active transfer objects
-		static std::map<TransferImpl*, std::weak_ptr<TransferImpl>> m_TransferMap;
+		using TransferStorage = std::map<TransferImpl*, std::weak_ptr<TransferImpl>>;
+		static TransferStorage m_TransferMap;
+		static std::mutex m_TransferMap_mutex;
+
+		/// Adding a new transfer object to the storage.
+		template<class T>
+		inline static std::pair<TransferStorage::iterator, bool> InsertTransfer(T&& value) {
+			std::lock_guard<std::mutex> lk(m_TransferMap_mutex);
+			return m_TransferMap.insert(std::move(value));
+		}
+
+		/// Deleting an transfer object from storage.
+		inline static size_t EraseTransfer(TransferImpl* index) {
+			std::lock_guard<std::mutex> lk(m_TransferMap_mutex);
+			return m_TransferMap.erase(index);
+		}
+
+		/// Retrieving an transfer object from storage.
+		inline static std::weak_ptr<TransferImpl> GetTransfer(TransferImpl* index) {
+			std::lock_guard<std::mutex> lk(m_TransferMap_mutex);
+			return m_TransferMap[index];
+		}
 
 		/// Pointer to the Parent Transfer object
 		std::weak_ptr<Transfer> m_pParentTransfer;