Question

First off, I am new to Scala:

I am writing a logging facility in Scala that will simply be a class that extends the Actor class. This way a user can just extend this class and the logging features will be available. Basically, I want to write to a log file every time an actor that extends this class sends or receives a message. For clarification every actor will have its own log file which can be collated later. I am taking a Lamport clocks style approach to ordering the events by having each Actor (who extends this class) have their own time variable that gets updated on a message send-receive and the actor will compare the current time variable (simply a positive integer) with the sender’s and update its time variable with the greater of the two.

For now I chose to make it a simple method like

sendMessage(recipient, message)

For sending messages. This will just log to the file that the actor is going to send a message to X.

Now, the part that I am stumped on is doing logging when receiving messages. When an actor gets a message I simply want to log this event in a format like

myLogFile.writeLine(self.ToString+": Got a message from "+X+" at time: "+messageSendTime+", processed the message at" +Math.max(myCurrTime+1, messageSendTime+1))

However I need to know who sent this message, unless I force upon the user to include this info (namely the sender’s name, time variable, etc) in the messages themselves, it gets hard(er). Is there any way to get the reference of the actual sender? I want this to work with remote actors as well. The only way I can think of is if I append to the act method that the user defines in his/her class with some extra case statements like:

def act {
    case => // the user's case statements
    ...

    //somehow I append these statements to the end for the Logger class's use
    case (LoggerClassRegisterInboundMessage, message, timeStamp)
        InboundMessagesMap.put(timeStamp, message)
}

By having this functionality I can do all the logging “behind the scenes” with these hidden messages being sent whenever the user sends a message. However this only works if the sender also uses the Logging facility. So a more general question is: is there a way in Scala to get the name/toString of a sender in Scala regardless of the sender’s class?

I’m actually OK with going with the assumption that every class that sends messages will extend the Logger class. So if anyone knows how to append to the act like or something similar to the above example I will be equally grateful!

Answer 1

As it was said in the comments, Akka is the way to go. It’s so much more powerful than the current Scala Actor API which will become deprecated with 2.10 anyway.

But, to attack your specific problem, you could create a trait for actors which support logging, in a way similar to this (I don’t know if this actually works, but you can try it):

trait LoggingActor extends Actor {
    override def receive[R](pf: PartialFunction[Any, R]): R = {
        //we are appending to the partial function pf a case to handle messages with logging:
        val loggingPf = pf orElse {
            case (LoggerClassRegisterInboundMessage, message, timeStamp) => {
                //do somthing with this log message.
                message //returning the unwrapped result afterwards
            }
        }
        super.receive(loggingPf)
    }

    //overriding the send as well
    override def !(msg: Any): Unit {
        //Wrap it in a logging message
        super ! (LoggerClassRegisterInboundMessage, msg, getTimestamp())
    }
}

And you would create your actors with something like this:

val myActor = new MyActor with LoggingActor

Hope it helps !