io_context object's event processing
loop to execute at most one handler.
function blocks until one handler has been dispatched, or until the
has been stopped.
The number of handlers that were executed. A zero return value implies
io_context object is stopped
Subsequent calls to
poll_one() will return immediately unless there
is a prior call to
function from a thread that is currently calling one of
on the same
io_context object may introduce
the potential for deadlock. It is the caller's reponsibility to avoid