Question

I would like to drop messages from an actor’s mailbox if it becomes too full. For example, if the queue size reaches 1000 messages, the oldest one should be deleted.

Answer 1

You cannot work with the mailbox directly, but you can implement Message Expiration pattern on top of the existing library.

Send a creation date with every message:

case class ExpirableMessage(msg: String, createdAt: Long) 

Scan the mailbox with reactWithin(0), and filter out expired messages:

react{ 
  case msg: ExpirableMessage => 
    // handle the message
    // clean the mailbox with nested react
    reactWithin(0){
        case ExpirableMessage(_, createdAt) if(currentTimeMillis - createdAt > INTERVAL) =>
        case TIMEOUT =>
    }
}