Asynchronous service example with signals as promises enabling functional and fluent API interaction.

WhateverService.as

package
{
    public class MyService
    {
        [Inject]
        public var session:ISession;
        private var startedSignal:ISignal;
        
        public function startMyService():ISignal
        {
            // If the started signal is null, initialize the service.
            // 
            // When startedSignal has at least one item in its dispatch history,
            // it will immediately invoke listeners as they're added.
            if(startedSignal == null)
            {
                startedSignal = new ReplaySignal();
                
                // ISession.start() is a potentially asynchronous operation,
                // so it returns an ISignal promise. The ISession implementation
                // is smart and uses a ReplaySignal itself, so it takes advantage
                // of the same caching technique we employ here.
                session.start().addOnce(function(... args):void{
                    //Do miscellaneous service setup, open channels, whatever.
                    //Tell all callers of startMyService() the service is ready.
                    startedSignal.dispatch();
                });
            }
            
            return startedSignal;
        }
    }
}