tcsetattr problem on Linux with readline

[Anil Tappetla]

Hi, I am using a perl package (IO::Pty) that provides pseudo-terminal
for parent-child processes to communicate. The child is the 'ftp'
client program which uses GNU readline-4.2a. The problem is ftp gets
hung unable to initialize communication when it attempts to set the
attributes of the terminal to which it is writing. The syscall
'tcsetattr(tty, TCADRAIN,..' seems to be causing the problem; however
if I changed this to 'tcsetattr(tty, TCANOW,..' it works fine for
sometime and gets hung again. Next, when I randomnly place puts()
calls and change tcsetattr to 'tcsetattr(tty, TCAFLUSH,..' everything
works fine. The questions are -

1). Why is 'tcsetattr(tty, TCADRAIN,..' not returning ?
2). Why does TCANOW work only for sometime ?
3). How does placing puts() calls and using TCAFLUSH seem to solve the
problem ?

The problem occured on Linux. Thank you for any help.

-Anil.