Timer

Timers for one-off or periodic tasks.

Note: If moc is invoked with -no-timer, the importing will fail. Note: The resolution of the timers is in the order of the block rate,

  so durations should be chosen well above that. For frequent
  canister wake-ups the heatbeat mechanism should be considered.

type Duration = {#seconds : Nat; #nanoseconds : Nat}

type TimerId = Nat

public func setTimer(d : Duration, job : () -> async ()) : TimerId

Installs a one-off timer that upon expiration after given duration d executes the future job().

motoko no-repl
let now = Time.now();
let thirtyMinutes = 1_000_000_000 * 60 * 30;
func alarmUser() : async () {
  // ...
};
appt.reminder = setTimer(#nanoseconds (Int.abs(appt.when - now - thirtyMinutes)), alarmUser);

public func recurringTimer(d : Duration, job : () -> async ()) : TimerId

Installs a recurring timer that upon expiration after given duration d executes the future job() and reinserts itself for another expiration.

Note: A duration of 0 will only expire once.

motoko no-repl
func checkAndWaterPlants() : async () {
  // ...
};
let daily = recurringTimer(#seconds (24 * 60 * 60), checkAndWaterPlants);

public let cancelTimer : TimerId -> ()

Cancels a still active timer with (id : TimerId). For expired timers and not recognised ids nothing happens.

motoko no-repl
func deleteAppt(appt : Appointment) {
  cancelTimer (appt.reminder);
  // ...
};