Actor System
Question
An actor is a lightweight execution context. An actor system is a collection of actors that can
execute concurrently in a shared nothing fashion. In an actor system each actor has a mailbox
with an address where it receives messages.
On receiving a message from its mailbox an actor can
● Send messages to other actors in the system
● Create a finite number of new actors in the system
● Change its own state
● Have side effects (print something, log something, change external durable state)...
An actor can process only one message at a time.
The lightweight nature of actors means one can create millions of actors that execute
concurrently even on systems with modest hardware capacity.
Problem
Implement an actor system that contains a set of actors

Actor

• has a unique address in an ActorSystem
• has a finite sized mailbox to receive messages in FIFO order
• can be shut down, after which it doesn't accept/receive any messages in its mailbox
  ActorSystem
• Is initialized with a finite threadpool size.
• Receives messages for actors that it contains.
• Executes actors that have messages to process using fair scheduling (actors don't starve).
• Can be shut down, after which the actor system doesn't accept/relay any new messages.
• Shut down all it's actors once they have processed all their remaining messages.
• Throws appropriate exception if a message cannot be delivered
• All actors should execute concurrently in a thread safe manner.
  Guidelines
• The code should be modular and testable.
• Provide at least one test case and demonstrate the working of your code
• State any assumptions you make.
• Thread Safe code