In an application we would like to support synchronous operations in the application layer, whereas operations below it are done with asynchronous operations. Callback handlers are not appropriate in this case, To make the example more clear, suppose you have a remote_vector which you would like to iterate through, remote_vector a(10); for( int i=0; i<10; ++i ) { std::cout << a[i] << std::endl; } here, a[i] will cause messages to be sent to retrieve the actual vector data before printing it. The network layer is hidden from the user. What is the best way to "emulate" synchronous behaviour with asio? The thread running this iteration should not block, but do other work (at the io_service?) until the requested results are received. Many thanks, Kind regards, Rutger ter Borg