Forces the buffered output of the stream Stream to be sent to the associated device.
Sends the current buffered output of an output
stream Stream to the actual output device, which is usually
a disk or a tty device.
flush_output/1 fails if Stream
does not permit flushing or the bottom layer flushing function
of Stream is not properly defined.
Stream errors (see ref-iou-sfh-est), plus:
If the host operating system, such as UNIX,
buffers an output file stream, the output may be written to the disk
some time after