I'm starting using Boost::Asio. I tried to write a simple class to send and receive asynchronously UDP datagrams, following the boost::asio tutorial. The class compiles fine, but it's not working and comes out with an exception about a mutex (which shouldn't be involved I guess). Basically there are two methods: one starts an async_receive_from and the other send packets asynchronously. I first start the receiver, then I try to send a packet to localhost (127.0.0.1). But nothing happens. Here is the code, maybe you may know what's wrong. With the following class the header: namespace msgSrv { class endPoint { public: asio::ip::udp::endpoint ep; endPoint(std::string ip, int port); }; class msgSrv { private: asio::ip::udp::socket *asioSocket; asio::io_service *asioIoService; int listenPort; boost::array rcvBuff; asio::ip::udp::endpoint lastRcvdPcktEndp; char * sbuff; public: boost::condition_variable cond; boost::mutex mut; msgSrv(int listenPort); virtual ~msgSrv(); void start(); void pckRcvd(const asio::error_code& error, std::size_t bytes_transferred); void sendTo(const char* buff, int len, endPoint ep); void sendHnd(const asio::error_code& error, std::size_t bytes_transferred); }; } the .cpp #include "msgSrv.h" namespace msgSrv { endPoint::endPoint(const std::string ip, int port) { asio::ip::address addr = asio::ip::address::from_string(ip); ep = asio::ip::udp::endpoint(addr, port); } msgSrv::msgSrv(int listenPort) { // TODO Auto-generated constructor stub this->listenPort = listenPort; try { asioIoService = new asio::io_service(); asioSocket = new asio::ip::udp::socket(*asioIoService, asio::ip::udp::endpoint(asio::ip::udp::v4(), listenPort)); //new asio::ip::udp::socket_(*asioIoService, udp::endpoint(udp::v4(), listenPort)); } catch (std::exception &e) { std::cerr << "Error initializing ioservice or socket:" << e.what(); } asioIoService->run(); } msgSrv::~msgSrv() { // TODO Auto-generated destructor stub delete asioIoService; delete asioSocket; } void msgSrv::start() { asioSocket->async_receive_from(asio::buffer(rcvBuff), lastRcvdPcktEndp, boost::bind(&msgSrv::pckRcvd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::pckRcvd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Rcvd! " << lastRcvdPcktEndp.address().to_string() << ":" << lastRcvdPcktEndp.port() << "\n"; } void msgSrv::sendTo(const char* buff, int len, endPoint ep) { sbuff = new char[len]; mempcpy(sbuff, buff, len); asioSocket->async_send_to(asio::buffer(sbuff, len), ep.ep, boost::bind( &msgSrv::sendHnd, this, asio::placeholders::error, asio::placeholders::bytes_transferred)); } void msgSrv::sendHnd(const asio::error_code& error, std::size_t bytes_transferred) { std::cout << "Snt!\n"; delete sbuff; } } and the following "main" file: int main() { msgSrv::msgSrv aa(4450); aa.start(); msgSrv::endPoint ep("127.0.0.1", 4450); std::string a("Prova!"); int len = a.length(); aa.sendTo(a.c_str(), len, ep); std::cout << "sent...\n"; std::cout << "notified...\n"; } all I get is: terminate called after throwing an instance of 'asio::system_error' what(): mutex: Invalid argument sent... notified... What's wrong?? I tried even to put a while(1) in the main, to see if something happens... I even tried to put a condition in the main that is unlocked by the receive handler... all remains locked... So what??? No idea!