The tcdrain() function waits 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, will
cause the process group to be sent a SIGTTOU signal. If the calling process is blocking or ignoring SIGTTOU signals,
the process is allowed to perform the operation, and no signal is sent.
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