I am trying to understand both of these items and how they are executing in our code, so I made a small demo to debug through. 1) Why can't I pass boost::io_service by reference in the call, boost::thread workerThread(DoWork, 1, ioService); with a function signature of void DoWork (const unsigned int threadNum, boost::asio::io_service * ioService) ? I changed it to a pointer and it works, but I don't know why I can't do it by reference. 2) If boost::thread is not copyable, how can I store a collection of "thread handles" or boost::thread objects like the variable workerThread? I can't use the std collections I would usually use... 3) When stepping through the code, the debugger jumps between the main thread, the worker thread, and a call stack in the depths of boost code where one item points to the line where the call to ioService->run() is. The first two make sense. I don't understand the latter. The call stack looks very much like one we get in production code and is all I have to go on in trying to debug a problem. The challenge is trying to determing who created the thread and find that line in source, because the production code is keeps creating threads until the program crashes. #include <iostream> #include #include #include #include //-------------------------------------------------------------------------­---- /// This function is the entry point for each worker thread void DoWork(const unsigned int threadNum, boost::asio::io_service * ioService) { std::cout << "Doing work in worker thread: " << threadNum << "\n"; // Perform the work // Multiple threads may call io_service::run() to set up a pool // of threads from which completion handlers may be invoked. ioService->run(); } //-------------------------------------------------------------------------­---- /// This function gets called when the asynchronous operation completes /// Guarantee - A completion handler will only get called from the same thread that called boost::asio::io_service::run() void OnCompletion(const boost::system::error_code & e, const unsigned * itemNum) { std::cout << "Completed item # " << *itemNum << " has completed. \n"; } //-------------------------------------------------------------------------­---- int main() { boost::asio::io_service ioService; boost::asio::deadline_timer timer(ioService, boost::posix_time::seconds(5)); const unsigned maxItems = 5; // Queue up some work for(unsigned int itemNum = 0; itemNum < maxItems; ++itemNum) { // The work to do is an asynchronous wait timer.async_wait(boost::bind(OnCompletion, // Method to callback boost::asio::placeholders::error, // &itemNum)); // Arg 1 to pass } // Create a thread to do the work boost::thread workerThread(DoWork, 1, &ioService); // Do other stuff in the main thread for(unsigned i = 0; i < 100; ++i) { std::cout << "Doing other work in main thread\n"; } // Done return 0; }