Some questions about the use of readline()

[Aust zhu]

Hello!
    I am having some problems with readline().  When calling the readline()
function it is blocked. I want to set a timeout for the readline function
to return.
    I tried setting rl_done=1, and fprintf(rl_instream,"\r\n");
fflush(rl_instream); can't make the readline() function return. What should
I do to make the readline() function return?
    I am using libreadline-8.0
    Thank you!