Hi, I'm trying to find a method of solving the problem detailed below using Boost (or an alternative: 1 - I have to send a series of messages to a hardware device to query its internal parameter values at application load-time. This I can do; 2 - I have a callback that receives responses from the hardware, though I get some replies go missing due to saturation; 3 * The hardware manufacturer tells me that I should send 1 query then wait for the response before sending the next query. I could use Sleep, but this depends on a specific wait time and I'm not sure if it suspends all processing, including my callback, so this doesn't look satisfactory. What I'm looking for is a "wait until response" kind of thing, but I haven't found such a thing so far, though I have found several wait routines for handling multiple threads. I'd appreciate any guidance as to what to look for, as my searches are obviously not asking the right questions. Best wishes. Tim Burgess Raised Bar Ltd. E: <mailto:tim@raisedbar.net> tim@raisedbar.net M: +44 (0)7989 486976