The tcdrain() function shall block until all output written to the object
referred to by fildes is transmitted. The fildes argument is an
open file descriptor associated with a terminal.
Any attempts to use tcdrain() from a process which is a member of a
background process group on a fildes associated with its controlling
terminal, shall cause the process group to be sent a SIGTTOU signal. If the
calling process is blocking or ignoring SIGTTOU signals, the process shall be
allowed to perform the operation, and no signal is sent.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html