[boost] [asio] inefficiency in the polling

The current run/poll_one does polling regardless if there's task in the queue. If there's task in the queue, polling is just a waste of system call, since there's already a job to do. Also, my common use case is "wait and consume all work", which is not covered efficiently by current design. (run_one+poll takes two system calls) Side note: on Windows asio performs even worse, it only retrieve one event per syscall... Not sure if it's intended. Friendly note: please use "Reply to All" when replying to me.