Concepts: Reminders

Overview

Reminders are low frequency persisted timers. They are called by the framework and may cause the activation of their actor.

The reminders are persisted and usually called as remote messages from the cluster nodes.

Reminders should not be used for high frequency tasks.

Using Reminders

public static interface Match extends Actor, Remindable
{
    // ...
}
public class MatchActor extends AbstractActor implements Match {
    private long lastEvent;
 
    @Override
    public Task startMatch()
    {
        lastEvent = System.currentTimeMillis();
        timer = registerReminder("matchTimeout", 10, 10, TimeUnit.MINUTES);
        return Task.done();
    }
 
    @Override
    public Task processEvent(Match event)
    {
        lastEvent = new Date();
        // ...
        return Task.done();
    }
 
    @Override
    public Task<?> receiveReminder(String reminderName, TickStatus status)
    {
        if(System.currentTimeMillis() - lastEvent > TimeUnit.MINUTES.toMillis(15)) 
        {
            unregisterReminder("matchTimeout");
            return processMathTimeout();
        }
        return Task.done();
    }
}

Reminder/Timer Comparison

Timer	Reminder
Exists only during the activation	Exist until explicitly cancelled by the application
Can be high frequency, seconds and minutes	Should be low frequency, minutes, hours or days
Actor deactivation cancels the timer	Reminder remains after deactivation.
Receive a callback	Call a fixed method
Any actor can use timers	Only actors whose interface implements Remindable can use reminders