Exercises

Working with untyped actors in Akka (a popular toolkit for building concurrent, distributed, and fault-tolerant systems on the JVM) is a great way to understand actor-based concurrency. Below are a few exercises that can help you practice working with untyped actors.

Exercise 1: Simple Ping-Pong

Objective: Implement two actors that send messages to each other.

• Actor 1 (PingActor): Sends a "Ping" message to Actor 2.
• Actor 2 (PongActor): Responds with a "Pong" message when it receives a "Ping".
• PingActor: Upon receiving "Pong", sends another "Ping" after a short delay.

Task:

• Implement the PingActor and PongActor classes.
• Ensure the actors can send messages back and forth indefinitely.

Exercise 2: Counter Actor

Objective: Implement an actor that maintains a state.

• CounterActor: This actor should maintain an integer counter. It should handle the following messages:
  • "Increment": Increments the counter by 1.
  • "Decrement": Decrements the counter by 1.
  • "Get": Replies with the current value of the counter.

Task:

• Implement the CounterActor.
• Create a main method where you create an instance of CounterActor, send several messages to it, and print out the final counter value.

Exercise 3: Actor Hierarchy and Supervision

Objective: Understand actor hierarchy and supervision.

• ParentActor: This actor creates a child actor (ChildActor). It supervises the child and restarts it when it fails.
• ChildActor: This actor might occasionally throw an exception when it receives a "DoWork" message.

Task:

• Implement the ParentActor and ChildActor.
• Set up supervision such that the ParentActor restarts the ChildActor upon failure.
• Create a scenario where the ChildActor occasionally fails, and observe how supervision works.

Exercise 4: Bank Account Actor

Objective: Model a simple bank account system using actors.

• BankAccountActor: This actor should handle the following messages:
  • "Deposit(amount)": Adds the specified amount to the account balance.
  • "Withdraw(amount)": Subtracts the specified amount if there are sufficient funds.
  • "GetBalance": Replies with the current balance.

Task:

• Implement the BankAccountActor.
• Create a main method where you create an instance of BankAccountActor, perform several deposits and withdrawals, and then print the final balance.

Exercise 5: Master-Worker Pattern

Objective: Implement a simple Master-Worker pattern using actors.

• MasterActor: Distributes tasks among several worker actors and collects the results.
• WorkerActor: Performs a computation and returns the result to the master.

Task:

• Implement the MasterActor and WorkerActor.
• The MasterActor should divide a list of integers into sublists and send each sublist to a worker actor to compute the sum.
• Collect and print the final sum of all integers.