3.48  timer%

A timer% object encapsulates an event-based alarm. To use a timer, either instantiate it with a timer-callback thunk to perform the alarm-based action, to derive a new class and override the notify method to perform the alarm-based action. Start a timer with start and stop it with stop. Supplying an initial interval (in milliseconds) when creating a timer also starts the timer.

Timers have a relatively high priority in the event queue. Thus, if the timer delay is set low enough, repeated notification for a timer can preempt user activities (which might be directed at stopping the timer). For timers with relatively short delays, call yield within the notify procedure to allow guaranteed event processing.

See Eventspaces for more information about event priorities.

• (new timer% [(notify-callback _)] [(interval _)] [(just-once? _)]) -> timer% object
     notify-callback = void : procedure of no arguments
     interval = #f : exact integer in [0, 1000000000] or #f
   just-once? = #f : boolean

  Creates a timer.

  The notify-callback thunk is called by the default notify method when the timer expires.

  If interval is #f (the default), the timer is not started; in that case, start must be called explicitly. If interval is a number (in milliseconds), then start is called with interval and just-once?.

  
  

Methods
    interval
    notify
    start
    stop