When do I have to use boost::asio:strand

Question

Reading the document of boost::asio, it is still not clear when I need to use asio::strand. Suppose that I have one thread using io_service is it then safe to write on a s

Answer 1

Calling io_service::run() from only one thread will cause all event handlers to execute within the thread, regardless of how many threads are invoking Connection::write(...). Therefore, with no possible concurrent execution of handlers, it is safe. The documentation refers to this as an implicit strand.

On the other hand, if multiple threads are invoking io_service::run(), then a strand would become necessary. This answer covers strands in much more detail.