Sleeping actors?

Question

What\'s the best way to have an actor sleep? I have actors set up as agents which want to maintain different parts of a database (including getting data from external sources).

Answer 1

There was a good point to Erlang in the first answer, but it seems disappeared. You can do the same Erlang-like trick with Scala actors easily. E.g. let's create a scheduler that does not use threads:

import actors.{Actor,TIMEOUT}

def scheduler(time: Long)(f: => Unit) = {
  def fixedRateLoop {
    Actor.reactWithin(time) {
      case TIMEOUT => f; fixedRateLoop
      case 'stop => 
    }
  }
  Actor.actor(fixedRateLoop)
}

And let's test it (I did it right in Scala REPL) using a test client actor:

case class Ping(t: Long)

import Actor._
val test = actor { loop {
  receiveWithin(3000) {
    case Ping(t) => println(t/1000)
    case TIMEOUT => println("TIMEOUT")
    case 'stop => exit
  }
} }

Run the scheduler:

import compat.Platform.currentTime
val sched = scheduler(2000) { test ! Ping(currentTime) }

and you will see something like this

scala> 1249383399
1249383401
1249383403
1249383405
1249383407

which means our scheduler sends a message every 2 seconds as expected. Let's stop the scheduler:

sched ! 'stop

the test client will begin to report timeouts:

scala> TIMEOUT
TIMEOUT
TIMEOUT

stop it as well:

test ! 'stop