io_service to invoke the given
handler and return immediately.
template< typename CompletionHandler> void post( CompletionHandler handler);
guarantees that the handler will only be called in a thread in which the
member functions is currently being invoked.
The handler to be called. The
io_service will make a copy
of the handler object as required. The function signature of the
handler must be:
This function throws an exception only if:
throws an exception.