when using native i/o take care to use it in nonblocking manner. if it would block use libmill's fdwait() to wait while the file descriptor is unblocked. in cas

when using native i/o take care to use it in nonblocking manner. if it would block use libmill's fdwait() to wait while the file descriptor is unblocked. in case of long computations call yield() once in a while to give other coroutines a chance to run.