I have this code:
(defun do-repeated-work (args)
"some work that need executed repeatedly"
(message nil)
(message "doing some repeated work, arg = %s, current time = %s" args (format-time-string "%H:%M:%S")))
(setq timer (run-with-idle-timer 3 t 'do-repeated-work (list "arg1" "arg2" "arg3")))
The purpose of the code above is: print a line of message in minibuffer repeatedly every three seconds. But I found that, when the function do-repeated-work works again, the old message in emacs minibuffer cannot be cleared, so the new message cannot be displayed. I have already tried the way mentioned in this question: how to empty or clear the emacs minibuffer?, but it doesn't work.
My Emacs version is 25.3
How to cope with this problem?
You've made an incorrect assumption, and consequently your problem isn't what you think it is.
The purpose of the code above is: print a line of message in minibuffer repeatedly every three seconds.
That's not what it does.
You've used run-with-idle-timer which will run one time once Emacs has been idle for 3 (in this case) seconds, and will not repeat until some non-idle activity has taken place -- after which it will again run once Emacs has become idle for 3 seconds.
See C-hf run-with-idle-timer
If you want something which repeats at a consistent interval, use run-with-timer.