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The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
sit-for
pauses and updates the screen, and returns immediately if
input comes in, while sleep-for
pauses without updating the
screen.
This function performs redisplay (provided there is no pending input from the user), then waits seconds seconds, or until input is available. The value is
t
ifsit-for
waited the full time with no input arriving (seeinput-pending-p
in Event Input Misc). Otherwise, the value isnil
.The argument seconds need not be an integer. If it is a floating point number,
sit-for
waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
The expression
(sit-for 0)
is a convenient way to request a redisplay, without any delay. See Forcing Redisplay.If nodisp is non-
nil
, thensit-for
does not redisplay, but it still returns as soon as input is available (or when the timeout elapses).Iconifying or deiconifying a frame makes
sit-for
return, because that generates an event. See Misc Events.The usual purpose of
sit-for
is to give the user time to read text that you display.
This function simply pauses for seconds seconds without updating the display. It pays no attention to available input. It returns
nil
.The argument seconds need not be an integer. If it is a floating point number,
sleep-for
waits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use
sleep-for
when you wish to guarantee a delay.
See Time of Day, for functions to get the current time.