Info Catalog elisp: Special Events elisp: Command Loop elisp: Quitting

elisp: Waiting

 
 20.10 Waiting for Elapsed Time or Input
 =======================================
 
 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.
 
  -- Function: sit-for seconds &optional nodisp
      This function performs redisplay (provided there is no pending
      input from the user), then waits SECONDS seconds, or until input is
      available.  The usual purpose of ‘sit-for’ is to give the user time
      to read text that you display.  The value is ‘t’ if ‘sit-for’
      waited the full time with no input arriving (Event Input
      Misc).  Otherwise, the value is ‘nil’.
 
      The argument SECONDS need not be an integer.  If it is floating
      point, ‘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 expression ‘(sit-for 0)’ is equivalent to ‘(redisplay)’, i.e.,
      it requests a redisplay, without any delay, if there is no pending
      input.  Forcing Redisplay.
 
      If NODISP is non-‘nil’, then ‘sit-for’ does not redisplay, but it
      still returns as soon as input is available (or when the timeout
      elapses).
 
      In batch mode (Batch Mode), ‘sit-for’ cannot be
      interrupted, even by input from the standard input descriptor.  It
      is thus equivalent to ‘sleep-for’, which is described below.
 
      It is also possible to call ‘sit-for’ with three arguments, as
      ‘(sit-for SECONDS MILLISEC NODISP)’, but that is considered
      obsolete.
 
  -- Function: sleep-for seconds &optional millisec
      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 floating
      point, ‘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.
 
    Time of Day, for functions to get the current time.
 

Info Catalog elisp: Special Events elisp: Command Loop elisp: Quitting